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+The Project Gutenberg EBook of Astronomical Curiosities, by J. Ellard Gore
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org/license
+
+
+Title: Astronomical Curiosities
+       Facts and Fallacies
+
+Author: J. Ellard Gore
+
+Release Date: March 25, 2012 [EBook #39263]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ASTRONOMICAL CURIOSITIES ***
+
+
+
+
+Produced by The Online Distributed Proofreading Team at
+http://www.pgdp.net (This file was produced from images
+generously made available by The Internet Archive.)
+
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+
+
+
+
+
+
+
+  ASTRONOMICAL CURIOSITIES
+
+  FACTS AND FALLACIES
+
+
+
+
+  ASTRONOMICAL CURIOSITIES
+
+  FACTS AND FALLACIES
+
+
+  BY J. ELLARD GORE
+
+  MEMBER OF THE ROYAL IRISH ACADEMY FELLOW OF THE
+  ROYAL ASTRONOMICAL SOCIETY CORRESPONDING MEMBER
+  OF THE ROYAL ASTRONOMICAL SOCIETY OF CANADA ETC.
+  AUTHOR OF "ASTRONOMICAL ESSAYS," "STUDIES IN
+  ASTRONOMY," "THE VISIBLE UNIVERSE," ETC.
+
+
+  LONDON
+  CHATTO & WINDUS
+  1909
+
+
+
+
+  PRINTED BY
+  WILLIAM CLOWES AND SONS, LIMITED
+  LONDON AND BECCLES
+
+  _All rights reserved_
+
+
+
+
+PREFACE
+
+
+The curious facts, fallacies, and paradoxes contained in the following
+pages have been collected from various sources. Most of the information
+given will not, I think, be found in popular works on astronomy, and will,
+it is hoped, prove of interest to the general reader.
+
+J. E. G.
+
+_September, 1909._
+
+
+
+
+CONTENTS
+
+
+                                                PAGE
+
+  CHAPTER
+
+      I. THE SUN                                   1
+
+     II. MERCURY                                  10
+
+    III. VENUS                                    17
+
+     IV. THE EARTH                                32
+
+      V. THE MOON                                 48
+
+     VI. MARS                                     59
+
+    VII. THE MINOR PLANETS                        68
+
+   VIII. JUPITER                                  74
+
+     IX. SATURN                                   84
+
+      X. URANUS AND NEPTUNE                       91
+
+     XI. COMETS                                   97
+
+    XII. METEORS                                 117
+
+   XIII. THE ZODIACAL LIGHT AND GEGENSCHEIN      127
+
+    XIV. THE STARS                               135
+
+     XV. DOUBLE AND BINARY STARS                 160
+
+    XVI. VARIABLE STARS                          170
+
+   XVII. NEBULÆ AND CLUSTERS                     191
+
+  XVIII. HISTORICAL                              217
+
+    XIX. THE CONSTELLATIONS                      239
+
+     XX. THE VISIBLE UNIVERSE                    313
+
+    XXI. GENERAL                                 329
+
+         INDEX                                   359
+
+
+
+
+ILLUSTRATIONS
+
+
+                                                PAGE
+
+  AL-SUFI'S "EARTHEN JAR"                        247
+
+  AL-SUFI'S "FISHES" IN ANDROMEDA                249
+
+
+
+
+ASTRONOMICAL CURIOSITIES
+
+
+
+
+CHAPTER I
+
+The Sun
+
+
+Some observations recently made by Prof. W. H. Pickering in Jamaica, make
+the value of sunlight 540,000 times that of moonlight. This makes the
+sun's "stellar magnitude" minus 26·83, and that of moonlight minus 12·5.
+Prof. Pickering finds that the light of the full moon is equal to 100,000
+stars of zero magnitude. He finds that the moon's "albedo" is about
+0·0909; or in other words, the moon reflects about one-tenth of the light
+which falls on it from the sun. He also finds that the light of the full
+moon is about twelve times the light of the half moon: a curious and
+rather unexpected result.
+
+M. C. Fabry found that during the total eclipse of the sun on August 30,
+1905, the light of the corona at a distance of five minutes of arc from
+the sun's limit, and in the vicinity of the sun's equator, was about 720
+candle-power. Comparing this with the intrinsic light of the full moon
+(2600 candle-power) we have the ratio of 0·28 to 1. He finds that the
+light of the sun in the zenith, and at its mean distance from the earth,
+is 100,000 times greater than the light of a "decimal candle" placed at a
+distance of one metre from the eye.[1] He also finds that sunlight is
+equal to 60,000 million times the light of Vega. This would make the sun's
+"stellar magnitude" minus 26·7, which does not differ much from Prof.
+Pickering's result, given above, and is probably not far from the truth.
+
+From experiments made in 1906 at Moscow, Prof. Ceraski found that the
+light of the sun's limb is only 31·4 to 38·4 times brighter than the
+illumination of the earth's atmosphere very near the limb. This is a very
+unexpected result; and considering the comparative faintness of the sun's
+corona during a total eclipse, it is not surprising that all attempts to
+photograph it without an eclipse have hitherto failed.[2]
+
+From Paschen's investigations on the heat of the sun's surface, he finds a
+result of 5961° (absolute), "assuming that the sun is a perfectly black
+body."[3] Schuster finds that "There is a stratum near the sun's surface
+having an average temperature of approximately 5500° C., to which about
+0·3 of the sun's radiation is due. The remaining portion of the radiation
+has an intensity equal to that due to a black body having a temperature of
+about 6700° C." The above results agree fairly well with those found by
+the late Dr. W. E. Wilson.[4] The assumption of the sun being "a black
+body" seems a curious paradox; but the simple meaning of the statement is
+that the sun is assumed to act as a radiator as _if it were a perfectly
+black body heated to the high temperature given above_.
+
+According to Prof. Langley, the sun's photosphere is 5000 times brighter
+than the molten metal in a "Bessemer convertor."[5]
+
+Observations of the sun even with small telescopes and protected by dark
+glasses are very dangerous to the eyesight. Galileo blinded himself in
+this way; Sir William Herschel lost one of his eyes; and some modern
+observers have also suffered. The present writer had a narrow escape from
+permanent injury while observing the transit of Venus, in 1874, in India,
+the dark screen before the eyepiece of a 3-inch telescope having
+blistered--that is, partially fused during the observation. Mr. Cooper,
+Markree Castle, Ireland, in observing the sun, used a "drum" of alum water
+and dark spectacles, and found this sufficient protection against the
+glare in using his large refracting telescope of 13·3-inches aperture.
+
+Prof. Mitchell, of Columbia University (U.S.A.), finds that lines due to
+the recently discovered atmospherical gases argon and neon are present in
+the spectrum of the sun's chromosphere. The evidence for the existence of
+krypton and xenon is, however, inconclusive. Prof. Mitchell suggests that
+these gases may possibly have reached the earth's atmosphere from the sun.
+This would agree with the theory advanced by Arrhenius that "ionised
+particles are constantly being repulsed by the pressure of light, and thus
+journey from one sun to another."[6]
+
+Prof. Young in 1870, and Dr. Kreusler in June, 1904, observed the helium
+line D_{3} as a _dark_ line "in the spectrum of the region about a
+sun-spot."[7] This famous line, from which helium was originally
+discovered in the sun, and by which it was long afterwards detected in
+terrestrial minerals, usually appears as a _bright_ line in the spectrum
+of the solar chromosphere and "prominences." It has also been seen _dark_
+by Mr. Buss in sun-spot regions.[8]
+
+The discovery of sun-spots was claimed by Hariotte, in 1610, and by
+Galileo, Fabricius, and Scheiner, in 1611. The latter wrote 800 pages on
+them, and thought they were small planets revolving round the sun! This
+idea was also held by Tardè, who called them _Astra Borbonia_, and by C.
+Malapert, who termed them _Sydera Austricea_. But they seem to have been
+noticed by the ancients.
+
+Although in modern times there has been no extraordinary development of
+sun-spots at the epoch of maximum, it is not altogether impossible that in
+former times these spots may have occasionally increased to such an
+extent, both in number and size, as to have perceptibly darkened the sun's
+light. A more probable explanation of recorded sun-darkenings seems,
+however, to be the passing of a meteoric or nebulous cloud between the sun
+and the earth. A remarkable instance of sun-darkening recorded in Europe
+occurred on May 22, 1870, when the sun's light was observed to be
+considerably reduced in a cloudless sky in the west of Ireland, by the
+late John Birmingham; at Greenwich on the 23rd; and on the same date, but
+at a later hour, in North-Eastern France--"a progressive manifestation,"
+Mr. Birmingham says, "that seems to accord well with the hypothesis of
+moving nebulous matter." A similar phenomenon was observed in New England
+(U.S.A.), on September 6, 1881.
+
+One of the largest spots ever seen on the sun was observed in June, 1843.
+It remained visible for seven or eight days. According to Schwabe--the
+discoverer of the sun-spot period--its diameter was 74,000 miles, so that
+its area was many times that of the earth's surface. The most curious
+thing about this spot was that it appeared near a _minimum_ of the
+sun-spot cycle! and was therefore rather an anomalous phenomenon. It was
+suggested by the late Daniel Kirkwood that this great spot was caused by
+the fall of meteoric matter into the sun; and that it had possibly some
+connection with the great comet of 1843, which approached the sun nearer
+than any other recorded comet, its distance from the sun at perihelion
+being about 65,000 miles, or less than one-third of the moon's distance
+from the earth. This near approach of the comet to the sun occurred about
+three months before the appearance of the great sun-spot; and it seems
+probable that the spot was caused by the downfall of a large meteorite
+travelling in the wake of the comet.[9] The connection between comets and
+meteors is well known.
+
+The so-called blackness of sun-spots is merely relative. They are really
+very bright. The most brilliant light which can be produced artificially
+looks like a black spot when projected on the sun's disc.
+
+According to Sir Robert Ball a pound of coal striking a body with a
+velocity of five miles a second would develop as much heat as it would
+produce by its combustion. A body falling into the sun from infinity would
+have a velocity of 450 miles a second when it reached the sun's surface.
+Now as the momentum varies as the square of the velocity we have a pound
+of coal developing 90{2} (=450/5){2}, or 8,100 times as much heat as would
+be produced by its combustion. If the sun were formed of coal it would be
+consumed in about 3000 years. Hence it follows that the contraction of the
+sun's substance from infinity would produce a supply of heat for 3000 ×
+8100, or 24,300,000 years.
+
+The late Mr. Proctor and Prof. Young believed "that the contraction theory
+of the sun's heat is the true and only available theory." The theory is,
+of course, a sound one; but it may now be supplemented by supposing the
+sun to contain a certain small amount of radium. This would bring physics
+and geology into harmony. Proctor thought the "sun's real globe is very
+much smaller than the globe we see. In other words the process of
+contraction has gone on further than, judging from the sun's apparent
+size, we should suppose it to have done, and therefore represents more sun
+work" done in past ages.
+
+With reference to the suggestion, recently made, that a portion, at least,
+of the sun's heat may be due to radium, and the experiments which have
+been made with negative results, Mr. R. T. Strutt--the eminent
+physicist--has made some calculations on the subject and says, "even if
+all the sun's heat were due to radium, there does not appear to be the
+smallest possibility that the Becquerel radiation from it could ever be
+detected at the earth's surface."[10]
+
+The eminent Swedish physicist Arrhenius, while admitting that a large
+proportion of the sun's heat is due to contraction, considers that it is
+probably the chemical processes going on in the sun, and not the
+contraction which constitute the _chief_ source of the solar heat.[11]
+
+As the centre of gravity of the sun and Jupiter lies at a distance of
+about 460,000 miles from the sun's centre, and the sun's radius is only
+433,000 miles, it follows that the centre of gravity of the sun and planet
+is about 27,000 miles _outside_ the sun's surface. The attractions of the
+other planets perpetually change the position of the centre of gravity of
+the solar system; but in some books on astronomy it is erroneously stated
+that the centre of gravity of the system is _always_ within the sun's
+surface. If _all_ the planets lay on the same side of the sun at the same
+time (as might possibly happen), then the centre of gravity of the whole
+system would lie considerably more than 27,000 miles outside the sun's
+surface.
+
+With reference to the sun's great size, Carl Snyder has well said, "It was
+as if in Vulcan's smithy the gods had moulded one giant ball, and the
+planets were but bits and small shot which had spattered off as the
+glowing ingot was cast and set in space. Little man on a little part of a
+little earth--a minor planet, a million of which might be tumbled into the
+shell of the central sun--was growing very small; his wars, the
+convulsions of a state, were losing consequence. Human endeavour, human
+ambitions could now scarce possess the significance they had when men
+could regard the earth as the central fact of the universe."[12]
+
+With reference to the late Prof. C. A. Young (U.S.A.)--a great authority
+on the sun--an American writer has written the following lines:--
+
+  "The destined course of whirling worlds to trace,
+  To plot the highways of the universe,
+  And hear the morning stars their song rehearse,
+  And find the wandering comet in his place;
+  This is the triumph written in his face,
+  And in the gleaming eye that read the sun
+  Like open book, and from the spectrum won
+  The secrets of immeasurable space."[13]
+
+
+
+
+CHAPTER II
+
+Mercury
+
+
+As the elongation of Mercury from the sun seldom exceeds 18°, it is a
+difficult object, at least in this country, to see without a telescope. As
+the poet says, the planet--
+
+  "Can scarce be caught by philosophic eye
+  Lost in the near effulgence of its blaze."
+
+Tycho Brahé, however, records several observations of Mercury with the
+unaided vision in Denmark.
+
+It can be occasionally caught with the naked eye in this country after
+sunset, when it is favourably placed for observation, and I have so seen
+it several times in Ireland. On February 19, 1888, I found it very visible
+in strong twilight near the western horizon, and apparently brighter than
+an average star of the first magnitude would be in the same position. In
+the clear air of the Punjab sky I observed Mercury on November 24-29,
+1872, near the western horizon after sunset. Its appearance was that of a
+reddish star of the first magnitude. On November 29 I compared its
+brilliancy with that of Saturn, which was some distance above it, and
+making allowance for the glare near the horizon in which Mercury was
+immersed, its brightness appeared to me to be quite equal to that of
+Saturn. In June, 1874, I found it equal to Aldebaran, and of very much the
+same colour. Mr. W. F. Denning, the famous observer of meteors, states
+that he observed Mercury with the naked eye about 150 times during the
+years 1868 to 1905.[14]
+
+He found that the duration of visibility after sunset is about 1{h} 40{m}
+when seen in March, 1{h} 30{m} in April, and 1{h} 20{m} in May. He thinks
+that the planet is, at its brightest, "certainly much brighter than a
+first magnitude star."[15] In February, 1868, he found that its brightness
+rivalled that of Jupiter, then only 2° or 3° distant. In November, 1882,
+it seemed brighter than Sirius. In 1876 it was more striking than Mars,
+but the latter was then "faint and at a considerable distance from the
+earth."
+
+In 1878, when Mercury and Venus were in the same field of view of a
+telescope, Nasmyth found that the surface brightness (or "intrinsic
+brightness," as it is called) of Venus was at least twice as great as that
+of Mercury; and Zöllner found that from a photometric point of view the
+surface of Mercury is comparable with that of the moon.
+
+With reference to the difficulty of seeing Mercury, owing to its proximity
+to the sun, Admiral Smyth says, "Although Mercury is never in _opposition_
+to the earth, he was, when in the house of Mars, always viewed by
+astrologers as a most malignant planet, and one full of evil influences.
+The sages stigmatized him as a false deceitful star (_sidus dolosum_), the
+eternal torment of astronomers, eluding them as much as terrestrial
+mercury did the alchemists; and Goad, who in 1686 published a whole folio
+volume full of astro-meteorological aphorisms, unveiling the choicest
+secrets of nature, contemptuously calls Mercury a 'squinting lacquey of
+the sun, who seldom shows his head in these parts, as if he was in debt.'
+His extreme mobility is so striking that chemists adopted his symbol to
+denote quicksilver."[16]
+
+Prof. W. H. Pickering thinks that the shortness of the cusps (or "horns")
+of Mercury's disc indicates that the planet's atmosphere is of small
+density--even rarer than that of Mars.
+
+The diameter of Mercury is usually stated at about 3000 miles; but a long
+series of measures made by Prof. See in the year 1901 make the real
+diameter about 2702 miles. This would make the planet smaller than some of
+the satellites of the large planets, probably smaller than satellites III.
+and IV. of Jupiter, less than Saturn's satellite Titan, and possibly
+inferior in size to the satellite of Neptune. Prof. Pickering thinks that
+the density of Mercury is about 3 (water = 1). Dr. See's observations show
+"no noticeable falling off in the brightness of Mercury near the limb."
+There is therefore no evidence of any kind of atmospheric absorption in
+Mercury, and the observer "gets the impression that the physical condition
+of the planet is very similar to that of our moon."[17]
+
+Schröter (1780-1815) observed markings on Mercury, from which he inferred
+that the planet's surface was mountainous, and one of these mountains he
+estimated at about 11 miles in height![18] But this seems very doubtful.
+
+To account for the observed irregularities in the motion of Mercury in its
+orbit, Prof. Newcomb thinks it possible that there may exist a ring or
+zone of "asteroids" a little "outside the orbit of Mercury" and having a
+combined mass of "one-fiftieth to one-three-hundredth of the mass of
+Venus, according to its distance from Mercury." Prof. Newcomb, however,
+considers that the existence of such a ring is extremely improbable, and
+regards it "more as a curiosity than a reality."[19]
+
+M. Léo Brenner thinks that he has seen the dark side of Mercury, in the
+same way that the dark side of Venus has been seen by many observers. In
+the case of Mercury the dark side appeared _darker_ than the background of
+the sky. Perhaps this may be due to its being projected on the zodiacal
+light, or outer envelope of the sun.[20]
+
+Mercury is said to have been occulted by Venus in the year 1737.[21] But
+whether this was an actual occultation, or merely a near approach does not
+seem to be certain.
+
+The first transit of Mercury across the sun's disc was observed by
+Gassendi on November 6, 1631, and Halley observed one on November 7, 1677,
+when in the island of St. Helena.
+
+Seen from Mercury, Venus would appear brighter than even we see it, and as
+it would be at its brightest when in opposition to the sun, and seen on a
+dark sky with a full face, it must present a magnificent appearance in the
+midnight sky of Mercury. The earth will also form a brilliant object, and
+the moon would be distinctly visible. The other planets would appear very
+much as they do to us, but with somewhat less brilliancy owing to their
+greater distance.
+
+As the existence of an intra-Mercurial planet (that is a planet revolving
+round the sun within the orbit of Mercury) seems now to be very
+improbable, Prof. Perrine suggests that possibly "the finely divided
+matter which produces the zodiacal light when considered in the aggregate
+may be sufficient to cause the perturbations in the orbit of Mercury."[22]
+Prof. Newcomb, however, questions the exact accuracy of Newton's law, and
+seems to adopt Hall's hypothesis that gravity does not act _exactly_ as
+the inverse square of the distance, and that the exponent of the distance
+is not 2, but 2·0000001574.[23]
+
+Voltaire said, "If Newton had been in Portugal, and any Dominican had
+discovered a heresy in his inverse ratio of the squares of the distances,
+he would without hesitation have been clothed in a _san benito_, and burnt
+as a sacrifice to God at an _auto da fé_."[24]
+
+An occultation of Mercury by Venus was observed with a telescope on May
+17, 1737.[25]
+
+May transits of Mercury across the sun's disc will occur in the years
+1924, 1957, and 1970; and November transits in the years 1914, 1927, and
+1940.[26]
+
+From measurements of the disc of Mercury during the last transit, M. R.
+Jonckheere concludes that the _polar_ diameter of the planet is greater
+than the _equatorial_! His result, which is very curious, if true, seems
+to be supported by the observations of other observers.[27]
+
+The rotation period of Mercury, or the length of its day, seems to be
+still in doubt. From a series of observations made in the years 1896 to
+1909, Mr. John McHarg finds a period of 1·0121162 day, or 1{d} 0{h} 17{m}
+26{s}·8. He thinks that "the planet possesses a considerable atmosphere
+not so clear as that of Mars"; that "its axis is very considerably
+tilted"; and that it "has fairly large sheets of water."[28]
+
+
+
+
+CHAPTER III
+
+Venus
+
+
+Venus was naturally--owing to its brightness--the first of the planets
+known to the ancients. It is mentioned by Hesiod, Homer, Virgil, Martial,
+and Pliny; and Isaiah's remark about "Lucifer, son of the morning" (Isaiah
+xiv. 12) probably refers to Venus as a "morning star." An observation of
+Venus is found on the Nineveh tablets of date B.C. 684. It was observed in
+daylight by Halley in July, 1716.
+
+In _very_ ancient times Venus, when a morning star, was called Phosphorus
+or Lucifer, and when an evening star Hesperus; but, according to Sir G. C.
+Lewis, the identity of the two objects was known so far back as 540 B.C.
+
+When Venus is at its greatest brilliancy, and appears as a morning star
+about Christmas time (which occurred in 1887, and again in 1889), it has
+been mistaken by the public for a return of the "Star of Bethlehem."[29]
+But whatever "the star of the Magi" was it certainly was _not_ Venus. It,
+seems, indeed absurd to suppose that "the wise men" of the East should
+have mistaken a familiar object like Venus for a strange apparition. There
+seems to be nothing whatever in the Bible to lead us to expect that the
+star of Bethlehem will reappear.
+
+Mr. J. H. Stockwell has suggested that the "Star of Bethlehem" may perhaps
+be explained by a conjunction of the planets Venus and Jupiter which
+occurred on May 8, B.C. 6, which was two years before the death of Herod.
+From this it would follow that the Crucifixion took place on April 3, A.D.
+33. But it seems very doubtful that the phenomenon recorded in the Bible
+refers to any conjunction of planets.
+
+Chacornac found the intrinsic brightness of Venus to be ten times greater
+than the most luminous parts of the moon.[30] But this estimate is
+probably too high.
+
+When at its brightest, the planet is visible in broad daylight to good
+eyesight, if its exact position in the sky is known. In the clear air of
+Cambridge (U.S.A.) it is said to be possible to see it in this way in all
+parts of its orbit, except when the planet is within 10° of the sun.[31]
+Mr. A. Cameron, of Yarmouth, Nova Scotia, has, however, seen Venus with
+the naked eye three days before conjunction when the planet was only
+6¼° from the sun.[32] This seems a remarkable observation, and shows
+that the observer's eyesight must have been very keen. In a private letter
+dated October 22, 1888, the late Rev. S. J. Johnson informed the present
+writer that he saw Venus with the naked eye only four days before
+conjunction with the sun in February, 1878, and February, 1886.
+
+The crescent shape of Venus is said to have been seen with the naked eye
+by Theodore Parker in America when he was only 12 years old. Other
+observers have stated the same thing; but the possibility of such an
+observation has been much disputed in recent years.
+
+In the Chinese Annals some records are given of Venus having been seen in
+the Pleiades. On March 16, A.D. 845, it is said that "Venus eclipsed the
+Pleiades." This means, of course, that the cluster was apparently effaced
+by the brilliant light of the planet. Computing backwards for the above
+date, Hind found that on the evening of March 16, 845, Venus was situated
+near the star Electra; and on the following evening the planet passed
+close to Maia; thus showing the accuracy of the Chinese record. Another
+"eclipse" of the Pleiades by Venus is recorded in the same annals as
+having occurred on March 10, A.D. 1002.[33]
+
+When Venus is in the crescent phase, that is near "Inferior conjunction"
+with the sun, it will be noticed, even by a casual observer, that the
+crescent is not of the same shape as that of the crescent moon. The horns
+or "cusps" of the planetary crescent are more prolonged than in the case
+of the moon, and extend beyond the hemisphere. This appearance is caused
+by refraction of the sun's light through the planetary atmosphere, and is,
+in fact, a certain proof that Venus has an atmosphere similar to that of
+the earth. Observations further show that this atmosphere is denser than
+ours.
+
+Seen from Venus, the earth and moon, when in opposition, must present a
+splendid spectacle. I find that the earth would shine as a star about half
+as bright again as Venus at her brightest appears to us, and the moon
+about equal in brightness to Sirius! the two forming a superb "naked eye
+double star"--perhaps the finest sight of its kind in the solar
+system.[34]
+
+Some of the earlier observers, such as La Hire, Fontana, Cassini, and
+Schröter, thought they saw evidence of mountains on Venus. Schröter
+estimated some of these to be 27 or 28 miles in height! but this seems
+very doubtful. Sir William Herschel severely attacked these supposed
+discoveries. Schröter defended himself, and was supported by Beer and
+Mädler, the famous lunar observers. Several modern observers seem to
+confirm Schröter's conclusions; but very little is really known about the
+topography of Venus.
+
+The well-known French astronomer Trouvelot--a most excellent observer--saw
+white spots on Venus similar to those on Mars. These were well seen and
+quite brilliant in July and August, 1876, and in February and November,
+1877. The observations seem to show that these spots do not (unlike Mars)
+increase and decrease with the planet's seasons. These white spots had
+been previously noticed by former observers, including Bianchini, Derham,
+Gruithuisen, and La Hire; but these early observers do not seem to have
+considered them as snow caps, like those of Mars. Trouvelot was led by his
+own observations to conclude that the period of rotation of Venus is
+short, and the best result he obtained was 23{h} 49{m} 28{s}. This does
+not differ much from the results previously found by De Vico, Fritsch, and
+Schröter.[35]
+
+A white spot near the planet's south pole was seen on several occasions by
+H. C. Russell in May and June, 1876.[36]
+
+Photographs of Venus taken on March 18 and April 29, 1908, by M. Quénisset
+at the Observatory of Juvissy, France, show a white polar spot. The spot
+was also seen at the same observatory by M. A. Benoit on May 20, 1903.
+
+The controversy on the period of rotation of Venus, or the length of its
+day, is a very curious one and has not yet been decided. Many good
+observers assert confidently that it is short (about 24 hours); while
+others affirm with equal confidence that it is long (about 225 days, the
+period of the planet's revolution round the sun). Among the observers who
+favour the short period of rotation are: D. Cassini (1667), J. Cassini
+(1730), Schröter (1788-93), Mädler (1836), De Vico (1840?) Trouvelot
+(1871-79), Flammarion, Léo Brenner, Stanley Williams, and J. McHarg; and
+among those who support the long period are: Bianchini (1727),
+Schiaparelli, Cerulli, Tacchini, Mascari, and Lowell. Some recent
+spectroscopic observations seem to favour the short period.
+
+Flammarion thinks that "nothing certain can be descried upon the surface
+of Venus, and that whatever has hitherto been written regarding its period
+of rotation must be considered null and void"; and again he says, "Nothing
+can be affirmed regarding the rotation of Venus, inasmuch as the
+absorption of its immense atmosphere certainly prevents any detail on its
+surface from being perceived."[37]
+
+The eminent Swedish physicist Arrhenius thinks, however, that the dense
+atmosphere and clouds of Venus are in favour of a rapid rotation on its
+axis.[38] He thinks that the mean temperature of Venus may "not differ
+much from the calculated temperature 104° F." "Under these circumstances
+the assumption would appear plausible that a very considerable portion of
+the surface of Venus, and particularly the districts about the poles,
+would be favourable to organic life."[39]
+
+The "secondary light of Venus," or the visibility of the dark side, seems
+to have been first mentioned by Derham in his _Astro Theology_ published
+in 1715. He speaks of the visibility of the dark part of the planet's disc
+"by the aid of a light of a somewhat dull and ruddy colour." The date of
+Derham's observation is not given, but it seems to have been previous to
+the year 1714. The light seems to have been also seen by a friend of
+Derham. We next find observations by Christfried Kirch, assistant
+astronomer to the Berlin Academy of Sciences, on June 7, 1721, and March
+8, 1726. These observations are found in his original papers, and were
+printed in the _Astronomische Nachrichten_, No. 1586. On the first date
+the telescopic image of the planet was "rather tremulous," but in 1726 he
+noticed that the dark part of the circle seemed to belong to a smaller
+circle than the illuminated portion of the disc.[40] The same effect was
+also noted by Webb.[41] A similar illusion is seen in the case of the
+crescent moon, and this has given rise to the saying, "the old moon in the
+new moon's arms."
+
+We next come, in order of date, to an observation made by Andreas Mayer,
+Professor of Mathematics at Griefswald in Prussia. The observation was
+made on October 20, 1759, and the dark part of Venus was seen distinctly
+by Mayer. As the planet's altitude at the time was not more than 14° above
+the horizon, and its apparent distance from the sun only 10°, the
+phenomenon--as Professor Safarik has pointed out--"must have had a most
+unusual intensity."
+
+Sir William Herschel makes no mention of having ever seen the "secondary
+light" of Venus, although he noticed the extension of the horns beyond a
+semicircle.
+
+In the spring and summer of the year 1793, Von Hahn of Remplin in
+Mecklenburg, using excellent telescopes made by Dollond and Herschel, saw
+the dark part of Venus on several occasions, and describes the light as
+"grey verging upon brown."
+
+Schröter of Lilienthal--the famous observer of the moon--saw the horns of
+the crescent of Venus extended many degrees beyond the semicircle on
+several occasions in 1784 and 1795, and the border of the dark part
+faintly lit up by a dusky grey light. On February 14, 1806, at 7 P.M. he
+saw the whole of the dark part visible with an ash-coloured light, and he
+was satisfied that there was no illusion. On January 24 of the same year,
+1806, Harding at Göttingen, using a reflector of 9 inches aperture and
+power 84, saw the dark side of Venus "shining with a pale ash-coloured
+light," and very visible against the dark background of the sky. The
+appearance was seen with various magnifying powers, and he thought that
+there could be no illusion. In fact the phenomenon was as evident as in
+the case of the moon. Harding again saw it on February 28 of the same
+year, the illumination being of a reddish grey colour, "like that of the
+moon in a total eclipse."
+
+The "secondary light" was also seen by Pastorff in 1822, and by
+Gruithuisen in 1825. Since 1824 observations of the "light" were made by
+Berry, Browning, Guthrie, Langdon, Noble, Prince, Webb, and others. Webb
+saw it with powers of 90 and 212 on a 9·38-inch mirror, and found it
+"equally visible when the bright crescent was hidden by a field bar."[42]
+
+Captain Noble's observation was rather unique. He found that the dark side
+was "always distinctly and positively _darker_ than the background upon
+which it is projected."
+
+The "light" was also seen by Lyman in America in 1867, and by Safarik at
+Prague. In 1871 the whole disc of Venus was seen by Professor
+Winnecke.[43] On the other hand, Winnecke stated that he only saw it twice
+in 24 years; and the great observers Dawes and Mädler never saw it at
+all![44]
+
+Various attempts have been made to explain the visibility--at times--of
+the "dark side" of Venus. The following may be mentioned[45]:--(1)
+Reflected earth-light, analogous to the dark side of the crescent moon.
+This explanation was advocated by Harding, Schröter, and others. But,
+although the earth is undoubtedly a bright object in the sky of Venus, the
+explanation is evidently quite inadequate. (2) Phosphorescence of the
+planet's atmosphere. This has been suggested by some observers. (3)
+Visibility by contrast, a theory advanced by the great French astronomer
+Arago. (4) Illumination of the planet's surface by an aurora borealis.
+This also seems rather inadequate, but would account for the light being
+sometimes visible and sometimes not. (5) Luminosity of the oceans--if
+there be any--on Venus. But this also seems inadequate. (6) A planetary
+surface glowing with intense heat. But this seems improbable. (7) The
+Kunstliche Feuer (artificial fire) of Gruithuisen, a very fanciful theory.
+Flammarion thinks that the visibility of the dark side may perhaps be
+explained by its projection on a somewhat lighter background, such as the
+zodiacal light, or an extended solar envelope.[46]
+
+It will be seen that none of these explanations are entirely satisfactory,
+and the phenomenon, if real, remains a sort of astronomical enigma. The
+fact that the "light" is visible on some occasions and not on others would
+render some of the explanations improbable or even inadmissible. But the
+condition of the earth's atmosphere at times might account for its
+invisibility on many occasions.
+
+A curious suggestion was made by Zöllner, namely, that if the secondary
+light of Venus could be observed with the spectroscope it would show
+bright lines! But such an observation would be one of extreme difficulty.
+
+M. Hansky finds that the visibility of the "light" is greater during
+periods of maximum solar activity--that is, at the maxima of sun spots.
+This he explains by the theory of Arrhenius, in which electrified "ions
+emitted by the sun cause the phenomena of terrestrial magnetic storms and
+auroras." "In the same way the dense atmosphere of Venus is rendered more
+phosphorescent, and therefore more easily visible by the increased solar
+activity."[47] This seems a very plausible hypothesis.
+
+On the whole the occasional illumination of the night side of Venus by a
+very brilliant aurora (explanation (4) above) seems to the present writer
+to be the most probable explanation. Gruithuisen's hypothesis (7) seems
+utterly improbable.
+
+There is a curious apparent anomaly about the motion of Venus in the sky.
+Although the planet's period of revolution round the sun is 224·7 days, it
+remains on the same side of the sun, as seen from the earth, for 290 days.
+The reason of this is that the earth is going at the same time round the
+sun in the same direction, though at a slower pace; and Venus must
+continue to appear on the same side of the sun until the excess of her
+daily motion above that of the earth amounts to 179°, and this at the
+daily rate of 37' will be about 290 days.
+
+Several observations have been recorded of a supposed satellite of Venus.
+But the existence of such a body has never been verified. In the year
+1887, M. Stroobant investigated the various accounts, and came to the
+conclusion that in several at least of the recorded observations the
+object seen was certainly a star. Thus, in the observation made by
+Rœdickœr and Boserup on August 4, 1761, a satellite and star are recorded
+as having been seen near the planet. M. Stroobant finds that the supposed
+"satellite" was the star χ_{4} Orionis, and the "star" χ_{3} Orionis. A
+supposed observation of a satellite made by Horrebow on January 3, 1768,
+was undoubtedly θ Libræ. M. Stroobant found that the supposed motion of
+the "satellite" as seen by Horrebow is accurately represented by the
+motion of Venus itself during the time of observation. In most of the
+other supposed observations of a satellite a satisfactory identification
+has also been found. M. Stroobant finds that with a telescope of 6 inches
+aperture, a star of the 8th or even the 9th magnitude can be well seen
+when close to Venus.[49]
+
+On the night of August 13, 1892, Professor Barnard, while examining Venus
+with the great 36-inch telescope of the Lick Observatory, saw a star of
+the 7th magnitude in the same field with the planet. He carefully
+determined the exact position of this star, and found that it is not in
+Argelander's great catalogue, the _Durchmusterung_. Prof. Barnard finds
+that owing to elongation of Venus from the sun at the time of observation
+the star could not possibly be an intra-Mercurial planet (that is, a
+planet revolving round the sun inside the orbit of Mercury); but that
+possibly it might be a planet revolving between the orbits of Venus and
+Mercury. As the brightest of the minor planets--Ceres, Pallas, Juno, and
+Vesta--were not at the time near the position of the observed object, the
+observation remains unexplained. It might possibly have been a _nova_, or
+temporary star.[50]
+
+Scheuten is said to have seen a supposed satellite of Venus following the
+planet across the sun at the end of the transit of June 6, 1761.[51]
+
+Humboldt speaks of the supposed satellite of Venus as among "the
+astronomical myths of an uncritical age."[52]
+
+An occultation of Venus by the moon is mentioned in the Chinese Annals as
+having occurred on March 19, 361 A.D., and Tycho Brahé observed another on
+May 23, 1587.[53]
+
+A close conjunction of Venus and Regulus (α Leonis) is recorded by the
+Arabian astronomer, Ibn Yunis, as having occurred on September 9, 885 A.D.
+Calculations by Hind show that the planet and star were within 2' of arc
+on that night, and consequently would have appeared as a single star to
+the naked eye. The telescope had not then been invented.[54]
+
+Seen from Venus, the maximum apparent distance between the earth and moon
+would vary from about 5' to 31'.[55]
+
+It is related by Arago that Buonaparte, when going to the Luxembourg in
+Paris, where the Directory were giving a fête in his honour, was very
+much surprised to find the crowd assembled in the Rue de Touracour "pay
+more attention to a region of the heavens situated above the palace than
+to his person or the brilliant staff that accompanied him. He inquired the
+cause and learned that these curious persons were observing with
+astonishment, although it was noon, a star, which they supposed to be that
+of the conqueror of Italy--an allusion to which the illustrious general
+did not seem indifferent, when he himself, with his piercing eyes,
+remarked the radiant body." The "star" in question was Venus.[56]
+
+
+
+
+CHAPTER IV
+
+The Earth
+
+
+The earth being our place of abode is, of course, to us the most important
+planet in the solar system. It is a curious paradox that the moon's
+surface (at least the visible portion) is better known to us than the
+surface of the earth. Every spot on the moon's visible surface equal in
+size to say Liverpool or Glasgow is well known to lunar observers, whereas
+there are thousands of square miles on the earth's surface--for example,
+near the poles and in the centre of Australia--which are wholly unknown to
+the earth's inhabitants; and are perhaps likely to remain so.
+
+Many attempts have been made by "paradoxers" to show that the earth is a
+flat plane and not a sphere. But M. Ricco has found by actual experiment
+that the reflected image of the setting sun from a smooth sea is an
+elongated ellipse. This proves mathematically beyond all doubt that the
+surface of the sea is spherical; for the reflection from a plane surface
+would be necessarily _circular_. The theory of a "flat earth" is
+therefore proved to be quite untenable, and all the arguments (?) of the
+"earth flatteners" have now been--like the French Revolution--"blown into
+space."
+
+The pole of minimum temperature in the northern hemisphere, or "the pole
+of cold," as it has been termed, is supposed to lie near Werchojansk in
+Siberia, where a temperature of nearly -70° has been observed.
+
+From a series of observations made at Annapolis (U.S.A.) on the gradual
+disappearance of the blue of the sky after sunset, Dr. See finds that the
+extreme height of the earth's atmosphere is about 130 miles. Prof. Newcomb
+finds that meteors first appear at a mean height of about 74 miles.[57]
+
+An aurora seen in Canada on July 15, 1893, was observed from stations 110
+miles apart, and from these observations the aurora was found to lie at a
+height of 166 miles above the earth's surface. It was computed that if the
+auroral "arch maintained an equal height above the earth its ends were
+1150 miles away, so that the magnificent sight was presented of an auroral
+belt in the sky with 2300 miles between its two extremities."[58]
+
+"Luminous clouds" are bright clouds sometimes seen at night near the end
+of June and beginning of July. They appear above the northern horizon
+over the sun's place about midnight, and evidently lie at a great height
+above the earth's surface. Observations made in Germany by Dr. Jesse, and
+in England by Mr. Backhouse, in the years 1885-91, show that the height of
+these clouds is nearly constant at about 51 miles.[59] The present writer
+has seen these remarkable clouds on one or two occasions in County Sligo,
+Ireland, during the period above mentioned.
+
+M. Montigny has shown that "the approach of violent cyclones or other
+storms is heralded by an increase of scintillation" (or twinkling of the
+stars). The effect is also very evident when such storms pass at a
+considerable distance. He has also made some interesting observations
+(especially on the star Capella), which show that, not only does
+scintillation increase in rainy weather, but that "it is very evident, at
+such times, in stars situated at an altitude at which on other occasions
+it would not be perceptible at all; thus confirming the remark of
+Humboldt's with regard to the advent of the wet season in tropical
+countries."[60]
+
+In a paper on the subject of "Optical Illusions" in _Popular Astronomy_,
+February, 1906, Mr. Arthur K. Bartlett, of Batter Creek, Michigan
+(U.S.A.), makes the following interesting remarks:--
+
+    "The lunar halo which by many persons is regarded as a remarkable and
+    unexplained luminosity associated with the moon, is to meteorological
+    students neither a mysterious nor an anomalous occurrence. It has been
+    frequently observed and for many years thoroughly understood, and at
+    the present time admits of an easy scientific explanation. It is an
+    atmospheric exhibition due to the refraction and dispersion of the
+    moon's light through very minute ice crystals floating at great
+    elevations above the earth, and it is explained by the science of
+    meteorology, to which it properly belongs; for it is not of cosmical
+    origin, and in no way pertains to astronomy, as most persons suppose,
+    except as it depends on the moon, whose light passing through the
+    atmosphere, produces the luminous halo, which as will be seen, is
+    simply an optical illusion, originating, not in the vicinity of the
+    moon--two hundred and forty thousand miles away--but just above the
+    earth's surface, and within the aqueous envelope that surrounds it on
+    all sides.... A halo may form round the sun as well as the moon ...
+    but a halo is more frequently noticed round the moon for the reason
+    that we are too much dazzled by the sun's light to distinguish faint
+    colours surrounding its disc, and to see them it is necessary to look
+    through smoked glass, or view the sun by reflection from the surface
+    of still water, by which its brilliancy is very much reduced."...
+
+"A 'corona' is an appearance of faintly coloured rings often seen around
+the sun and moon when a light fleecy cloud passes over them, and should
+not be mistaken for a halo, which is much larger and more complicated in
+its structure. These two phenomena are frequently confounded by
+inexperienced observers." With these remarks the present writer fully
+concurs.
+
+Mr. Bartlett adds--
+
+    "As a halo is never seen except when the sky is hazy, it indicates
+    that moisture is accumulating in the atmosphere which will form
+    clouds, and usually result in a storm. But the popular notion that the
+    number of bright stars visible within the circle indicates the number
+    of days before the storm will occur, is without any foundation
+    whatever, and the belief is almost too absurd to be refuted. In
+    whatever part of the sky a lunar halo is seen, one or more bright
+    stars are always sure to be noticed inside the luminous ring, and the
+    number visible depends entirely upon the position of the moon.
+    Moreover, when the sky within the circle is examined with even a small
+    telescope, hundreds of stars are visible where only one, or perhaps
+    two or three, are perceived with the naked eye."
+
+It is possible to have five Sundays in February (the year must of course
+be a "leap year"). This occurred in the year 1880, Sunday falling on
+February 1, 8, 15, 22, and 29. But this will not happen again till the
+year 1920. No century year (such as 1900, 2000, etc.) could possibly have
+five Sundays in February, and the Rev. Richard Campbell, who investigated
+this matter, finds the following sequence of years in which five Sundays
+occur in February: 1604, 1632, 1660, 1688, 1728, 1756, 1784, 1824, 1852,
+1880, 1920, 1948, 1976.[61]
+
+In an article on "The Last Day and Year of the Century: Remarks on Time
+Reckoning," in _Nature_, September 10, 1896, Mr. W. T. Lynn, the eminent
+astronomer, says, "The late Astronomer Royal, Sir George Airy, once
+received a letter requesting him to settle a dispute which had arisen in
+some local debating society, as to which would be the first day of the
+next century. His reply was, 'A very little consideration will suffice to
+show that the first day of the twentieth century will be January 1, 1901.'
+Simple as the matter seems, the fact that it is occasionally brought into
+question shows that there is some little difficulty connected with it.
+Probably, however, this is in a great measure due to the circumstance that
+the actual figures are changed on January 1, 1900, the day preceding being
+December 31, 1899. A century is a very definite word for an interval
+respecting which there is no possible room for mistake or difference of
+opinion. But the date of its ending depends upon that of its beginning.
+Our double system of backward and forward reckoning leads to a good deal
+of inconvenience. Our reckoning supposes (what we know was not the case,
+but as an era the date does equally well) that Christ was born at the end
+of B.C. 1. At the end of A.D. 1, therefore, one year had elapsed from the
+event, at the end of A.D. 100, one century, and at the end of 1900,
+nineteen centuries.... It is clear, then, that the year, as we call it, is
+an ordinal number, and that 1900 years from the birth of Christ (reckoning
+as we do from B.C. 1) will not be completed until the end of December 31
+in that year, the twentieth century beginning with January 1, 1901, that
+is (to be exact) at the previous midnight, when the day commences by civil
+reckoning." With these remarks of Mr. Lynn I fully concur, and, so far as
+I know, all astronomers agree with him. As the discussion will probably
+again arise at the end of the twentieth century, I would like to put on
+record here what the scientific opinion was at the close of the nineteenth
+century.
+
+Prof. E. Rutherford, the well-known authority on radium, suggests that
+possibly radium is a source of heat from within the earth. Traces of
+radium have been detected in many rocks and soils, and even in sea water.
+Calculation shows that the total amount distributed through the earth's
+crust is enormously large, although relatively small "compared with the
+annual output of coal for the world." The amount of radium necessary to
+compensate for the present loss of heat from the earth "corresponds to
+only five parts in one hundred million millions per unit mass," and the
+"observations of Elster and Gertel show that the radio-activity observed
+in soils corresponds to the presence of about this proportion of
+radium."[62]
+
+The earth has 12 different motions. These are as follows:--
+
+1. Rotation on its axis, having a period of 24 hours.
+
+2. Revolution round the sun; period 365¼ days.
+
+3. Precession; period of about 25,765 years.
+
+4. Semi-lunar gravitation; period 28 days.
+
+5. Nutation; period 18½ years.
+
+6. Variation in obliquity of the ecliptic; about 47" in 100 years.
+
+7. Variation of eccentricity of orbit.
+
+8. Change of line of apsides; period about 21,000 years.
+
+9. Planetary perturbations.
+
+10. Change of centre of gravity of whole solar system.
+
+11. General motion of solar system in space.
+
+12. Variation of latitude with several degrees of periodicity.[63]
+
+    "An amusing story has been told which affords a good illustration of
+    the ignorance and popular notions regarding the tides prevailing even
+    among persons of average intelligence. 'Tell me,' said a man to an
+    eminent living English astronomer not long ago, 'is it still
+    considered probable that the tides are caused by the moon?' The man of
+    science replied that to the best of his belief it was, and then asked
+    in turn whether the inquirer had any serious reason for questioning
+    the relationship. 'Well, I don't know,' was the answer; 'sometimes
+    when there is no moon there seems to be a tide all the same.'"![64]
+
+With reference to the force of gravitation, on the earth and other bodies
+in the universe, Mr. William B. Taylor has well said, "With each revolving
+year new demonstrations of its absolute precision and of its universal
+domination serves only to fill the mind with added wonder and with added
+confidence in the stability and the supremacy of the power in which has
+been found no variableness neither shadow of turning, but which--the same
+yesterday, to-day and for ever--
+
+  "Lives through all life, extends through all extent,
+  Spreads undivided, operates unspent."[65]
+
+With reference to the habitability of other planets, Tennyson has
+beautifully said--
+
+  "Venus near her! smiling downwards at this earthlier earth of ours,
+  Closer on the sun, perhaps a world of never fading flowers.
+  Hesper, whom the poets call'd the Bringer home of all good things;
+  All good things may move in Hesper; perfect people, perfect kings.
+  Hesper--Venus--were we native to that splendour, or in Mars,
+  We should see the globe we groan in fairest of their evening stars.
+  Could we dream of war and carnage, craft and madness, lust and spite,
+  Roaring London, raving Paris, in that spot of peaceful light?
+  Might we not in glancing heavenward on a star so silver fair,
+  Yearn and clasp the hands, and murmur, 'Would to God that we were
+      there!'"
+
+The ancient Greek writer, Diogenes Laertius, states that Anaximander
+(610-547 B.C.) believed that the earth was a sphere. The Greek words are:
+μισην τε την γην κεισθαι, κεντρυ ταξιν επεχουσαν ουσαν σφαιροειδη.[66]
+
+With reference to the Aurora Borealis, the exact nature of which is not
+accurately known, "a good story used to be told some years ago of a
+candidate who, undergoing the torture of a _vivâ voce_ examination, was
+unable to reply satisfactorily to any of the questions asked. 'Come, sir,'
+said the examiner, with the air of a man asking the simplest question,
+'explain to me the cause of the aurora borealis.' 'Sir,' said the unhappy
+aspirant for physical honours, 'I could have explained it perfectly
+yesterday, but nervousness has, I think, made me lose my memory.' 'This is
+very unfortunate,' said the examiner; 'you are the only man who could have
+explained this mystery, and you have forgotten it.'"[67] This was written
+in the year 1899, and probably the phenomenon of the aurora remains
+nearly as great a mystery to-day. In 1839, MM. Bravais and Lottin made
+observations on the aurora in Norway in about N. latitude 70°. Bravais
+found the height to be between 62 and 93 miles above the earth's surface.
+
+The cause of the so-called Glacial Epoch in the earth's history has been
+much discussed. The Russian physicist, Rogovsky, has advanced the
+following theory--
+
+    "If we suppose that the temperature of the sun at the present time is
+    still increasing, or at least has been increasing until now, the
+    glacial epoch can be easily accounted for. Formerly the earth had a
+    high temperature of its own, but received a lesser quantity of heat
+    from the sun than now; on cooling gradually, the earth's surface
+    attained such a temperature as caused a great part of the surface of
+    the northern and southern hemispheres to be covered with ice; but the
+    sun's radiation increasing, the glaciers melted, and the climatic
+    conditions became as they are now. In a word, the temperature of the
+    earth's surface is a function of two quantities: one decreasing (the
+    earth's own heat), and the other increasing (the sun's radiation), and
+    consequently there may be a minimum, and this minimum was the glacial
+    epoch, which, as shown by recent investigations, those of Luigi de
+    Marchi (Report of _G. Schiaparelli, Meteorolog. Zeitschr._, 30,
+    130-136, 1895), are not local, but general for the whole earth" (see
+    also M. Neumahr, _Erdegeschicht_).[68]
+
+Prof. Percival Lowell thinks that the life of geological palæozoic times
+was supported by the earth's internal heat, which maintained the ocean at
+a comparatively warm temperature.[69]
+
+The following passage in the Book of the Maccabees may possibly refer to
+an aurora--
+
+    "Now about this time Antiochus made his second inroad into Egypt. And
+    it _so_ befell that throughout all the city, for the space of almost
+    forty days, there appeared in the midst of the sky horsemen in swift
+    motion, wearing robes inwrought with gold and _carrying_ spears,
+    equipped in troops for battle; and drawing of swords; and _on the
+    other side_ squadrons of horse in array; and encounters and pursuits
+    of both armies; and shaking of shields, and multitudes of lances, and
+    casting of darts, and flashing of golden trappings, and girding on of
+    all sorts of armour. Wherefore all men besought that the vision might
+    have been given for food."[70]
+
+According to Laplace "the decrease of the mean heat of the earth during a
+period of 2000 years has not, taking the extremist limits, diminished as
+much as 1/300th of a degree Fahrenheit."[71]
+
+From his researches on the cause of the Precession of the Equinoxes,
+Laplace concluded that "the motion of the earth's axis is the same as if
+the whole sea formed a solid mass adhering to its surface."[72]
+
+Laplace found that the major (or longer) axis of the earth's orbit
+coincided with the line of Equinoxes in the year 4107 B.C. The earth's
+perigee then coincided with the autumnal equinox. The epoch at which the
+major axis was perpendicular to the line of equinoxes fell in the year
+1250 A.D.[73]
+
+Leverrier has found the minimum eccentricity of the earth's orbit round
+the sun to be 0·0047; so that the orbit will never become absolutely
+circular, as some have imagined.
+
+Laplace says--
+
+    "Astronomy considered in its entirety is the finest monument of the
+    human mind, the noblest essay of its intelligence. Seduced by the
+    illusions of the senses and of self-pride, for a long time man
+    considered himself as the centre of the movement of the stars; his
+    vain-glory has been punished by the terrors which his own ideas have
+    inspired. At last the efforts of several centuries brushed aside the
+    veil which concealed the system of the world. We discover ourselves
+    upon a planet, itself almost imperceptible in the vast extent of the
+    solar system, which in its turn is only an insensible point in the
+    immensity of space. The sublime results to which this discovery has
+    led should suffice to console us for our extreme littleness, and the
+    rank which it assigns to the earth. Let us treasure with solicitude,
+    let us add to as we may, this store of higher knowledge, the most
+    exquisite treasure of thinking beings."[74]
+
+With reference to probable future changes in climate, the great physicist,
+Arrhenius, says--
+
+    "We often hear lamentation that the coal stored up in the earth is
+    wasted by the present generation without any thought of the future,
+    and we are terrified by the awful destruction of life and property
+    which has followed the volcanic eruptions of our days. We may find a
+    kind of consolation in the consideration that here, as in every other
+    case, there is good mixed with evil. By the influence of the
+    increasing percentage of carbonic acid in the atmosphere, we may hope
+    to enjoy ages with more equable and better climates, especially as
+    regards the colder regions of the earth, ages when the earth will
+    bring forth much more abundant crops than at present, for the benefit
+    of rapidly propagating mankind."[75]
+
+The night of July 1, 1908, was unusually bright. This was noticed in
+various parts of England and Ireland, and by the present writer in Dublin.
+Humboldt states that "at the time of the new moon at midnight in 1743, the
+phosphorescence was so intense that objects could be distinctly recognized
+at a distance of more than 600 feet."[76]
+
+An interesting proof of the earth's rotation on its axis has recently been
+found.
+
+    "In a paper in the _Proceedings_ of the Vienna Academy (June, 1908) by
+    Herr Tumlirz, it is shown mathematically that if a liquid is flowing
+    outwards between two horizontal discs, the lines of flow will be
+    strictly straight only if the discs and vessel be at rest, and will
+    assume certain curves if that vessel and the discs are in rotation,
+    as, for example, due to the earth's rotation. An experimental
+    arrangement was set up with all precautions, and the stream lines were
+    marked with coloured liquids and photographed. These were in general
+    accord with the predictions of theory and the supposition that the
+    earth is rotating about an axis."[77]
+
+In a book published in 1905 entitled _The Rational Almanac_, by Moses B.
+Cotsworth, of York, the author states that (p. 397), "The explanation is
+apparent from the Great Pyramid's Slope, which conclusively proves that
+when it was built the latitude of that region was 7°·1 more than at
+present. Egyptian Memphis now near Cairo was then in latitude 37°·1, where
+Asia Minor now ranges, whilst Syria would then be where the Caucasus
+regions now experience those rigorous winters formerly experienced in
+Syria." But the reality of this comparatively great change of latitude in
+the position of the Great Pyramid can be easily disproved. Pytheas of
+Marseilles--who lived in the time of Alexander the Great, about 330
+B.C.--measured the latitude of Marseilles by means of a gnomon, and found
+it to be about 42° 56'½. As the present latitude of Marseilles is 43° 17'
+50", no great change in the latitude could have taken place in over 2000
+years.[78] From this we may conclude that the latitude of the Great
+Pyramid has _not_ changed by 7°·1 since its construction. There is, it is
+true, a slow diminution going on in the obliquity of the ecliptic (or
+inclination of the earth's axis), but modern observations show that this
+would not amount to as much as one degree in 6000 years. Eudemus of
+Rhodes--a disciple of Aristotle (who died in 322 B.C.)--found the
+obliquity of the ecliptic to be 24°, which differs but little from its
+present value, 23° 27'. Al-Sufi in the tenth century measured the latitude
+of Schiraz in Persia, and found it 29° 36'. Its present latitude is 29°
+36' 30",[79] so that evidently there has been no change in the latitude in
+900 years.
+
+
+
+
+CHAPTER V
+
+The Moon
+
+
+The total area of the moon's surface is about equal to that of North and
+South America. The actual surface visible at any one time is about equal
+to North America.
+
+The famous lunar observer, Schröter, thought that the moon had an
+atmosphere, but estimated its height at only a little over a mile. Its
+density he supposed to be less than that of the vacuum in an air-pump.
+Recent investigations, however, seem to show that owing to its small mass
+and attractive force the moon could not retain an atmosphere like that of
+the earth.
+
+Prof. N. S. Shaler, of Harvard (U.S.A.), finds from a study of the moon
+(from a geological point of view) with the 15-inch refractor of the
+Harvard Observatory, that our satellite has no atmosphere nor any form of
+organic life, and he believes that its surface "was brought to its present
+condition before the earth had even a solid crust."[80]
+
+There is a curious illusion with reference to the moon's apparent
+diameter referred to by Proctor.[81] If, when the moon is absent in the
+winter months, we ask a person whether the moon's diameter is greater or
+less than the distance between the stars δ and ε, and ε and ζ Orionis, the
+three well-known stars in the "belt of Orion," the answer will probably be
+that the moon's apparent diameter is about equal to each of these
+distances. But in reality the apparent distance between δ and ε Orionis
+(or between ε and ζ, which is about the same) is more than double the
+moon's apparent diameter. This seems at first sight a startling statement;
+but its truth is, of course, beyond all doubt and is not open to argument.
+Proctor points out that if a person estimates the moon as a foot in
+diameter, as its apparent diameter is about half a degree, this would
+imply that the observer estimates the circumference of the star sphere as
+about 720 feet (360° × 2), and hence the radius (or the moon's distance
+from the earth) about 115 feet. But in reality all such estimates have no
+scientific (that is, accurate) meaning. Some of the ancients, such as
+Aristotle, Cicero, and Heraclitus, seem to have estimated the moon's
+apparent diameter at about a foot.[82] This shows that even great minds
+may make serious mistakes.
+
+It has been stated by some writer that the moon as seen with the highest
+powers of the great Yerkes telescope (40 inches aperture) appears "just
+as it would be seen with the naked eye if it were suspended 60 miles over
+our heads." But this statement is quite erroneous. The moon as seen with
+the naked eye or with a telescope shows us nearly a whole hemisphere of
+its surface. But if the eye were placed only 60 miles from the moon's
+surface, we should see only a small portion of its surface. In fact, it is
+a curious paradox that the nearer the eye is to a sphere the less we see
+of its surface! The truth of this will be evident from the fact that on a
+level plain an eye placed at a height, say 5 feet, sees a very small
+portion indeed of the earth's surface, and the higher we ascend the more
+of the surface we see. I find that at a distance of 60 miles from the
+moon's surface we should only see a small portion of its visible
+hemisphere (about 1/90th). The lunar features would also appear under a
+different aspect. The view would be more of a landscape than that seen in
+any telescope. This view of the matter is not new. It has been previously
+pointed out, especially by M. Flammarion and Mr. Whitmell, but its truth
+is not, I think, generally recognized. Prof. Newcomb doubts whether with
+any telescope the moon has ever been seen so well as it would be if
+brought within 500 miles of the earth.
+
+A relief map of the moon 19 feet in diameter was added, in 1898, to the
+Field Columbian Museum (U.S.A.). It was prepared with great care from the
+lunar charts of Beer and Mädler, and Dr. Schmidt of the Athens
+Observatory, and it shows the lunar features very accurately. Its
+construction took five years.
+
+On a photograph of a part of the moon's surface near the crater
+Eratosthenes, Prof. William H. Pickering finds markings which very much
+resemble the so-called "canals" of Mars. The photograph was taken in
+Jamaica, and a copy of it is given in Prof. Pickering's book on the Moon,
+and in _Popular Astronomy_, February, 1904.
+
+Experiments made in America by Messrs. Stebbins and F. C. Brown, by means
+of selenium cells, show that the light of the full moon is about nine
+times that of the half moon;[83] and that "the moon is brighter between
+the first quarter and full than in the corresponding phase after full
+moon." They also find that the light of the full moon is equal to "0·23
+candle power,"[83] that is, according to the method of measurement used in
+America, its light is equal to 0·23 of a standard candle placed at a
+distance of one metre (39·37 inches) from the eye.[84]
+
+Mr. H. H. Kimball finds that no less than 52 per cent. of the observed
+changes in intensity of the "earth-shine" visible on the moon when at or
+near the crescent phase is due to the eccentricity of the lunar orbit,
+and "this is probably much greater than could be expected from any
+increase or diminution in the average cloudiness over the hemisphere of
+the earth reflecting light to the moon."[85]
+
+The "moon maiden" is a term applied to a fancied resemblance of a portion
+of the Sinus Iridum to a female head. It forms the "promontory" known as
+Cape Heraclides, and may be looked for when the moon's "age" is about 11
+days. Mr. C. J. Caswell, who observed it on September 29, 1895, describes
+it as resembling "a beautiful silver statuette of a graceful female figure
+with flowing hair."
+
+M. Landerer finds that the angle of polarization of the moon's
+surface--about 33°--agrees well with the polarizing angle for many
+specimens of igneous rocks (30° 51' to 33° 46'). The polarizing angle for
+ice is more than 37°, and this fact is opposed to the theories of lunar
+glaciation advanced by some observers.[86]
+
+Kepler states in his _Somnium_ that he saw the moon in the crescent phase
+on the morning and evening of the _same_ day (that is, before and after
+conjunction with the sun). Kepler could see 14 stars in the Pleiades with
+the naked eye, so his eyesight must have been exceptionally keen.
+
+Investigations on ancient eclipses of the moon show that the eclipse
+mentioned by Josephus as having occurred before the death of Herod is
+probably that which took place on September 15, B.C. 5. This occurred
+about 9.45 p.m.; and probably about six months before the death of Herod
+(St. Matthew ii. 15).
+
+The total lunar eclipse which occurred on October 4, 1884, was remarkable
+for the almost total disappearance of the moon during totality. One
+observer says that "in the open air, if one had not known exactly where to
+look for it, one might have searched for some time without discovering it.
+I speak of course of the naked eye appearance."[87] On the other hand the
+same observer, speaking of the total eclipse of the moon on August 23,
+1877, which was a bright one, says--
+
+    "The moon even in the middle of the total phase was a conspicuous
+    object in the sky, and the ruddy colour was well marked. In the very
+    middle of the eclipse the degree of illumination was as nearly as
+    possible equal all round the edge of the moon, the central parts being
+    darker than those near the edge."
+
+In Roger de Hovedin's _Chronicle_ (A.D. 756) an account is given of the
+occultation of "a bright star," by the moon during a total eclipse. This
+is confirmed by Simeon of Durham, who also dates the eclipse A.D. 756.
+This is, however, a mistake, the eclipse having occurred on the evening of
+November 23, A.D. 755. Calvisius supposed that the occulted "star" might
+have been Aldebaran. Pingré, however, showed that this was impossible, and
+Struyck, in 1740, showed that the planet Jupiter was the "star" referred
+to by the early observer. Further calculations by Hind (1885) show
+conclusively that Struyck was quite correct, and that the phenomenon
+described in the old chronicles was the occultation of Jupiter by a
+totally eclipsed moon--a rather unique phenomenon.[88]
+
+An occultation of Mars by the moon is recorded by the Chinese, on February
+14, B.C. 69, and one of Venus, on March 30, A.D. 361. These have also been
+verified by Hind, and his calculations show the accuracy of these old
+Chinese records.
+
+It has been suggested that the moon may possibly have a satellite
+revolving round it, as the moon itself revolves round the earth. This
+would, of course, form an object of great interest. During the total lunar
+eclipses of March 10 and September 3, 1895, a careful photographic search
+was made by Prof. Barnard for a possible lunar satellite. The eclipse of
+March 10 was not very suitable for the purpose owing to a hazy sky, but
+that of September 3 was "entirely satisfactory," as the sky was very
+clear, and the duration of totality was very long. On the latter occasion
+"six splendid" photographs were obtained of the total phase with a 6-inch
+Willard lens. The result was that none of these photographs "show
+anything which might be taken for a lunar satellite," at least any
+satellite as bright as the 10th or 12th magnitude. It is, of course, just
+possible that the supposed satellite might have been behind the moon
+during the totality.
+
+With reference to the attraction between the earth and moon, Sir Oliver
+Lodge says--
+
+    "The force with which the moon is held in its orbit would be great
+    enough to tear asunder a steel rod 400 miles thick, with a tenacity of
+    30 tons to the square inch, so that if the moon and earth were
+    connected by steel instead of gravity, a forest of pillars would be
+    necessary to whirl the system once a month round their common centre
+    of gravity. Such a force necessarily implies enormous tensure or
+    pressure in the medium. Maxwell calculates that the gravitational
+    stress near the earth, which we must suppose to exist in the invisible
+    medium, is 3000 times greater than what the strongest steel can stand,
+    and near the sun it should be 2500 times as great as that."[89]
+
+With reference to the names given to "craters" on the moon, Prof. W. H.
+Pickering says,[90] "The system of nomenclature is, I think, unfortunate.
+The names of the chief craters are generally those of men who have done
+little or nothing for selenography, or even for astronomy, while the men
+who should be really commemorated are represented in general by small and
+unimportant craters," and again--
+
+    "A serious objection to the whole system of nomenclature lies in the
+    fact that it has apparently been used by some selenographers, from the
+    earliest times up to the present, as a means of satisfying their spite
+    against some of their contemporaries. Under the guise of pretending to
+    honour them by placing their names in perpetuity upon the moon, they
+    have used their names merely to designate the smallest objects that
+    their telescopes were capable of showing. An interesting illustration
+    of this point is found in the craters of Galileo and Riccioli, which
+    lie close together on the moon. It will be remembered that Galileo was
+    the discoverer of the craters on the moon. Both names were given by
+    Riccioli, and the relative size and importance of the craters
+    [Riccioli large, and Galileo very small] probably indicates to us the
+    relative importance that he assigned to the two men themselves. Other
+    examples might be quoted of craters named in the same spirit after men
+    still living.... With the exception of Maedler, one might almost say,
+    the more prominent the selenographer the more insignificant the
+    crater."
+
+The mathematical treatment of the lunar theory is a problem of great
+difficulty. The famous mathematician, Euler, described it as _incredibile
+stadium atque indefessus labor_.[91]
+
+With reference to the "earth-shine" on the moon when in the crescent
+phase, Humboldt says, "Lambert made the remarkable observation (14th of
+February, 1774) of a change of the ash-coloured moonlight into an
+olive-green colour, bordering upon yellow. The moon, which then stood
+vertically over the Atlantic Ocean, received upon its night side the green
+terrestrial light, which is reflected towards her when the sky is clear by
+the forest districts of South America."[92] Arago said, "Il n'est donc pas
+impossible, malgré tout ce qu'un pareil résultat exciterait de surprise au
+premier coup d'œil qu'un jour les météorologistes aillent puiser dans
+l'aspect de la Lune des notions précieuses sur _l'etat moyen_ de
+diaphanité de l'atmosphère terrestre, dans les hemisphères qui
+successivement concurrent à la production de la lumière cendrée."[93]
+
+The "earth-shine" on the new moon was successfully photographed in
+February, 1895, by Prof. Barnard at the Lick Observatory, with a 6-inch
+Willard portrait lens. He says--
+
+    "The earth-lit globe stands out beautifully round, encircled by the
+    slender crescent. All the 'seas' are conspicuously visible, as are
+    also the other prominent features, especially the region about
+    _Tycho_. _Aristarchus_ and _Copernicus_ appear as bright specks, and
+    the light streams from _Tycho_ are very distinct."[94]
+
+Kepler found that the moon completely disappeared during the total eclipse
+of December 9, 1601, and Hevelius observed the same phenomenon during the
+eclipse of April 25, 1642, when "not a vestige of the moon could be
+seen."[95] In the total lunar eclipse of June 10, 1816, the moon during
+totality was not visible in London, even with a telescope![95]
+
+The lunar mountains are _relatively_ much higher than those on the earth.
+Beer and Mädler found the following heights: Dörfel, 23,174 feet; Newton,
+22,141; Casatus, 21,102; Curtius, 20,632; Callippus, 18,946; and Tycho,
+18,748 feet.[96]
+
+Taking the earth's diameter at 7912 miles, the moon's diameter, 2163
+miles, and the height of Mount Everest as 29,000 feet, I find that
+
+      Everest          1            Dörfel        1
+  ---------------- = ----, and --------------- = ---
+  Earth's diameter   1440      moon's diameter   492
+
+From which it follows that the lunar mountains are _proportionately_ about
+three times higher than those on the earth.
+
+According to an hypothesis recently advanced by Dr. See, all the
+satellites of the solar system, including our moon, were "captured" by
+their primaries. He thinks, therefore, that the "moon came to earth from
+heavenly space."[97]
+
+
+
+
+CHAPTER VI
+
+Mars
+
+
+Mars was called by the ancients "the vanishing star," owing to the long
+periods during which it is practically invisible from the earth.[98] It
+was also called πυροεις and Hercules.
+
+I have seen it stated in a book on the "Solar System" by a well-known
+astronomer that the _axis_ of Mars "is inclined to the plane of the orbit"
+at an angle of 24° 50'! But this is quite erroneous. The angle given is
+the angle between _the plane of the planet's equator_ and the plane of its
+orbit, which is quite a different thing. This angle, which may be called
+the obliquity of Mars' ecliptic, does not differ much from that of the
+earth. Lowell finds it 23° 13' from observations in 1907.[99]
+
+The late Mr. Proctor thought that Mars is "far the reddest star in the
+heavens; Aldebaran and Antares are pale beside him."[100] But this does
+not agree with my experience. Antares is to my eye quite as red as Mars.
+Its name is derived from two Greek words implying "redder than Mars." The
+colour of Aldebaran is, I think, quite comparable with that of the "ruddy
+planet." In the telescope the colour of Mars is, I believe, more yellow
+than red, but I have not seen the planet very often in a telescope. Sir
+John Herschel suggested that the reddish colour of Mars may possibly be
+due to red rocks, like those of the Old Red Sandstone, and the red soil
+often associated with such rocks, as I have myself noticed near Torquay
+and other places in Devonshire.
+
+The ruddy colour of Mars was formerly thought to be due to the great
+density of its atmosphere. But modern observations seem to show that the
+planet's atmosphere is, on the contrary, much rarer than that of the
+earth. The persistent visibility of the markings on its surface shows that
+its atmosphere cannot be cloud-laden like ours; and the spectroscope shows
+that the water vapour present is--although perceptible--less than that of
+our terrestrial envelope.
+
+The existence of water vapour is clearly shown by photographs of the
+planet's spectrum taken by Mr. Slipher at the Lowell Observatory in 1908.
+These show that the water vapour bands _a_ and near D are stronger in the
+spectrum of Mars than in that of the moon at the same altitude.[101]
+
+The dark markings on Mars were formerly supposed to represent water and
+the light parts land. But this idea has now been abandoned. Light
+reflected from a water surface is polarized at certain angles. Prof. W. H.
+Pickering, in his observations on Mars, finds no trace of polarization in
+the light reflected from the dark parts of the planet. But under the same
+conditions he finds that the bluish-black ring surrounding the white polar
+cap shows a well-marked polarization of light, thus indicating that this
+dark ring is probably water.[102]
+
+Projections on the limb of the planet have frequently been observed in
+America. These are known _not_ to be mountains, as they do not reappear
+under similar conditions. They are supposed to be clouds, and one seen in
+December, 1900, has been explained as a cloud lying at a height of some 13
+miles above the planet's surface and drifting at the rate of about 27
+miles an hour. If there are any mountains on Mars they have not yet been
+discovered.
+
+The existence of the so-called "canals" of Mars is supposed to be
+confirmed by Lowell's photographs of the planet. But what these "canals"
+really represent, that is the question. They have certainly an artificial
+look about them, and they form one of the most curious and interesting
+problems in the heavens. Prof. Lowell says--
+
+    "Most suggestive of all Martian phenomena are the canals. Were they
+    more generally observable the world would have been spared much
+    scepticism and more theory. They may of course not be artificial, but
+    observations here [Flagstaff] indicate that they are; as will, I
+    think, appear from the drawings. For it is one thing to see two or
+    three canals and quite another to have the planet's disc mapped with
+    them on a most elaborate system of triangulation. In the first place
+    they are this season (August, 1894) bluish-green, of the same colour
+    as the seas into which the longer ones all eventually debouch. In the
+    next place they are almost without exception geodetically straight,
+    supernaturally so, and this in spite of their leading in every
+    possible direction. Then they are of apparently nearly uniform width
+    throughout their length. What they are is another matter. Their mere
+    aspect, however, is enough to cause all theories about glaciation
+    fissures or surface cracks to die an instant and natural death."[103]
+
+Some of the observed colour-changes on Mars are very curious. In April,
+1905, Mr. Lowell observed that the marking known as Mare Erythræum, just
+above Syrtis, had "changed from a blue-green to a chocolate-brown colour."
+The season on Mars corresponded with our February.
+
+Signor V. Cerulli says that, having observed Mars regularly for ten years,
+he has come to the conclusion that the actual existence of the "canals" is
+as much a subject for physiological as for astronomical investigation. He
+states that "the phenomena observed are so near the limit of the range of
+the human eye that in observing them one really experiences an effect
+accompanying the 'birth of vision.' That is to say, the eye sees more and
+more as it becomes accustomed, or strained, to the delicate markings, and
+thus the joining up of spots to form 'canals' and the gemination of the
+latter follow as a physiological effect, and need not necessarily be
+subjective phenomena seen by the unaccustomed eye."[104]
+
+The possibility of life on Mars has been recently much discussed; some
+denying, others asserting. M. E. Rogovsky says--
+
+    "As free oxygen and carbonic dioxide may exist in the atmosphere of
+    _Mars_, vegetable and animal life is quite possible. If the
+    temperature which prevails upon _Mars_ is nearer to -36° C. than to
+    -73° C., the existence of living beings like ourselves is possible. In
+    fact, the ice of some Greenland and Alpine glaciers is covered by red
+    algæ (_Sphærella nivalis_); we find there also different species of
+    rotaloria, variegated spiders, and other animals on the snow fields
+    illuminated by the sun; at the edges of glacier snows in the Tyrol we
+    see violet bells of _Soldanella pusilla_, the stalks of which make
+    their way through the snow by producing heat which melts it round
+    about them. Finally the Siberian town Verkhociansk, near Yakutsk,
+    exists, though the temperature there falls to -69°·8 C. and the mean
+    temperature of January to -51°·2, and the mean pressure of the vapour
+    of water is less than 0·05mm. It is possible, therefore, that living
+    beings have become adapted to the conditions now prevailing upon
+    _Mars_ after the lapse of many ages, and live at an even lower
+    temperature than upon the earth, developing the necessary heat
+    themselves."
+
+M. Rogovsky adds, "Water in organisms is mainly a liquid or solvent, and
+many other liquids may be the same. We have no reason to believe that life
+is possible only under the same conditions and with the same chemical
+composition of organisms as upon the earth, although indeed we cannot
+affirm that they actually exist on Mars."[105] With the above views the
+present writer fully concurs.
+
+Prof. Lowell thinks that the polar regions of Mars, both north and south,
+are actually warmer than the corresponding regions of the earth, although
+the mean temperature of the planet is probably twelve degrees lower than
+the earth's mean temperature.[106]
+
+A writer in _Astronomy and Astrophysics_ (1892, p. 748) says--
+
+    "Whether the planet Mars is inhabited or not seems to be the
+    all-absorbing question with the ordinary reader. With the astronomer
+    this query is almost the last thing about the planet that he would
+    think of when he has an opportunity to study its surface markings ...
+    no astronomer claims to know whether the planet is inhabited or not."
+
+Several suggestions have been made with reference to the possibility of
+signalling to Mars. But, as Mr. Larkin of Mount Lowe (U.S.A.) points out,
+all writers on this subject seem to forget the fact that the night side of
+two planets are never turned towards each other. "When the sun is between
+them it is day on the side of Mars which is towards us, and also day on
+the side of the earth which is towards Mars. When they are on the same
+side of the sun, it is day on Mars when night on the earth, and for this
+reason they could never see our signals. This should make it apparent that
+the task of signalling to Mars is a more difficult one than the most
+hopeful theorist has probably considered. All this is under the
+supposition that the Martians (if there are such) are beings like
+ourselves. If they are not like us, we cannot guess what they are
+like."[107] These views seem to me to be undoubtedly correct, and show the
+futility of visual signals. Electricity might, however, be conceivably
+used for the purpose; but even this seems highly improbable.
+
+Prof. Newcomb, in his work _Astronomy for Everybody_, says with reference
+to this question, "The reader will excuse me from saying nothing in this
+chapter about the possible inhabitants of Mars. He knows just as much
+about the subject as I do, and that is nothing at all."
+
+It is, however, quite possible that life _in some form_ may exist on Mars.
+As Lowell well says, "Life but waits in the wings of existence for its cue
+to enter the scene the moment the stage is set."[108] With reference to
+the "canals" he says--
+
+    "It is certainly no exaggeration to say that they are the most
+    astonishing objects to be viewed in the heavens. There are celestial
+    sights more dazzling, spectacles that inspire more awe, but to the
+    thoughtful observer who is privileged to see them well, there is
+    nothing in the sky so profoundly impressive as these canals of
+    Mars."[109]
+
+The eminent Swedish physicist Arrhenius thinks that the mean annual
+temperature on Mars may possibly be as high as 50° F. He says, "Sometimes
+the snow-caps on the poles of Mars disappear entirely during the Mars
+summer; this never happens on our terrestrial poles. The mean temperature
+of Mars must therefore be above zero, probably about +10° [Centigrade =
+50° Fahrenheit]. Organic life may very probably thrive, therefore, on
+Mars."[110] He thinks that this excess of mean temperature above the
+calculated temperature may be due to an increased amount of carbonic acid
+in the planet's atmosphere, and says "any doubling of the percentage of
+carbon dioxide in the air would raise the temperature of the earth's
+surface by 4°; and if the carbon dioxide were increased fourfold, the
+temperature would rise by 8°."[111]
+
+Denning says,--[112]
+
+    "A few years ago, when christening celestial formations was more in
+    fashion than it is now, a man simply had to use a telescope for an
+    evening or two on Mars or the moon, and spice the relation of his
+    seeings with something in the way of novelty, when his name would be
+    pretty certainly attached to an object and hung in the heavens for all
+    time! A writer in the _Astronomical Register_ for January, 1879,
+    humorously suggested that 'the matter should be put into the hands of
+    an advertising agent,' and 'made the means of raising a revenue for
+    astronomical purposes.' Some men would not object to pay handsomely
+    for the distinction of having their names applied to the seas and
+    continents of Mars or the craters of the moon."
+
+An occultation of Mars by the moon is recorded by Aristotle as having
+occurred on April 4, 357 B.C.[113]
+
+Seen from Mars the maximum apparent distance between the earth and moon
+would vary from 3½' to nearly 17'.[114]
+
+
+
+
+CHAPTER VII
+
+The Minor Planets
+
+
+Up to 1908 the number of minor planets (or asteroids) certainly known
+amounted to over 650.
+
+From an examination of the distribution of the first 512 of these small
+bodies, Dr. P. Stroobant finds that a decided maximum in number occurs
+between the limits of distance of 2·55 and 2·85 (earth's mean distance
+from sun = 1), "199 of the asteroids considered revolving in this
+annulus." He finds that nearly all the asteroidal matter is concentrated
+near to the middle of the ring in the neighbourhood of the mean distance
+of 2·7, and the smallest asteroids are relatively less numerous in the
+richest zones.[115]
+
+There are some "striking similarities" in the orbits of some of the
+asteroids. Thus, in the small planets Sophia (No. 251 in order of
+discovery) and Magdalena (No. 318) we have the mean distance of Sophia
+3·10, and that of Magdalena 3·19 (earth's mean distance = 1). The
+eccentricities of the orbits are 0·09 and 0·07; and the inclinations of
+the orbits to the plane of the ecliptic 10° 29' and 10° 33'
+respectively.[116] This similarity may be--and probably is--merely
+accidental, but it is none the less curious and interesting.
+
+Some very interesting discoveries have recently been made among the minor
+planets. The orbit of Eros intersects the orbit of Mars; and the following
+have nearly the same mean distance from the sun as Jupiter:--
+
+  Achilles (1906 TG), No. 588,
+  Patrocles (1906 XY), No. 617,
+  Hector (1907 XM), No. 624,
+
+and another (No. 659) has been recently found. Each of these small planets
+"moves approximately in a vertex of an equilateral triangle that it forms
+with Jupiter and the sun."[117] The minor planet known provisionally as HN
+is remarkable for the large eccentricity of its orbit (0·38), and its
+small perihelion distance (1·6). When discovered it had a very high South
+Declination (61½°), showing that the inclination of the plane of its
+orbit to the plane of the ecliptic is considerable.[118]
+
+Dr. Bauschinger has made a study of the minor planets discovered up to the
+end of 1900. He finds that the ascending nodes of the orbits show a
+marked tendency to cluster near the ascending node of Jupiter's orbit, a
+fact which agrees well with Prof. Newcomb's theoretical results. There
+seems to be a slight tendency for large inclinations and great
+eccentricities to go together; but there appears to be no connection
+between the eccentricity and the mean distance from the sun. The
+longitudes of the perihelia of these small planets "show a well-marked
+maximum near the longitude of _Jupiter's_ perihelion, and equally
+well-marked minimum near the longitude of his aphelion," which is again in
+good agreement with Newcomb's calculations.[119] Dr. Bauschinger's
+diameter for Eros is 20 miles. He finds that the whole group, including
+those remaining to be discovered, would probably form a sphere of about
+830 miles in diameter.
+
+The total mass of the minor planets has been frequently estimated, but
+generally much too high. Mr. B. M. Roszel of the John Hopkins University
+(U.S.A.) has made a calculation of the probable mass from the known
+diameter of Vesta (319 miles, Pickering), and finds the volume of the
+first 216 asteroids discovered. From this calculation it appears that it
+would take 310 asteroids of the 6th magnitude, or 1200 of the 7th to equal
+the moon in volume. Mr. Roszel concludes that the probable mass of the
+whole asteroidal belt is between 1/50th and 1/100th of that of the
+moon.[120] Subsequently Mr. Roszel extended his study to the mass of 311
+asteroids,[121] and found a combined mass of about 1/40th of the moon's
+mass.
+
+Dr. Palisa finds that the recently discovered minor planet (1905 QY)
+varies in light to a considerable extent.[122] This planet was discovered
+by Dr. Max Wolf on August 23, 1905; but it was subsequently found that it
+is identical with one previously known, (167) Urda.[123] The light
+variation is said to be from the 11th to the 13th magnitude.[124]
+Variation in some of the other minor planets has also been suspected.
+Prof. Wendell found a variation of about half a magnitude in the planet
+Eunomia (No. 15). He also found that Iris (No. 7) varies about a quarter
+of a magnitude in a period of about 6{h} 12{m}.[125] But these variations
+are small, and perhaps doubtful. The variability of Eros is well known.
+
+The planet Eros is a very interesting one. The perihelion portion of its
+orbit lies between the orbits of Mars and the earth, and the aphelion part
+is outside the orbit of Mars. Owing to the great variation in its distance
+from the earth the brightness of Eros varies from the 6th to the 12th
+magnitude. That is, when brightest, it is 250 times brighter than when it
+is faintest.[126] This variation of light, is of course, merely due to the
+variation of distance; but some actual variation in the brightness of the
+planet has been observed.
+
+It has been shown by Oeltzen and Valz that Cacciatore's supposed distant
+comet, mentioned by Admiral Smyth in his _Bedford Catalogue_, must have
+been a minor planet.[127]
+
+Dr. Max Wolf discovered 36 new minor planets by photography in the years
+1892-95. Up to the latter year he had never seen one of these through a
+telescope! His words are, "Ich selsbt habe noch nie einen meinen kleinen
+Planeten am Himmel gesehen."[128]
+
+These small bodies have now become so numerous that it is a matter of much
+difficulty to follow them. At the meeting of the Royal Astronomical
+Society on January 8, 1909, Mr. G. F. Chambers made the following
+facetious remarks--
+
+    "I would like to make a suggestion that has been in my mind for
+    several years past--that it should be made an offence punishable by
+    fine or imprisonment to discover any more minor planets. They seem to
+    be an intolerable nuisance, and are a great burden upon the literary
+    gentlemen who have to keep pace with them and record them. I have
+    never seen, during the last few years at any rate, any good come from
+    them, or likely to come, and I should like to see the supply stopped,
+    and the energies of the German gentlemen who find so many turned into
+    more promising channels."
+
+Among the minor planets numbered 1 to 500, about 40 "have not been seen
+since the year of their discovery, and must be regarded as lost."[129]
+
+
+
+
+CHAPTER VIII
+
+Jupiter
+
+
+This brilliant planet--only inferior to Venus in brightness--was often
+seen by Bond (Jun.) with the naked eye in "high and clear sunshine"; also
+by Denning, who has very keen eyesight. Its brightness on such occasions
+is so great, that--like Venus--it casts a distinct shadow in a dark
+room.[130]
+
+The great "red spot" on Jupiter seems to have been originally discovered
+by Robert Hooke on May 9, 1664, with a telescope of 2 inches aperture and
+12 feet focus. It seems to have existed ever since; at least the evidence
+is, according to Denning, in favour of the identity of Hooke's spot with
+the red spot visible in recent years. The spot was also observed by
+Cassini in the years 1665-72, and is sometimes called "Cassini's spot."
+But the real discoverer was Hooke.[131]
+
+The orbit of Jupiter is so far outside the earth's orbit that there can
+be little visible in the way of "phase"--as in the case of Mars, where the
+"gibbous" phase is sometimes very perceptible. Some books on astronomy
+state that Jupiter shows no phase. But this is incorrect. A distinct,
+although very slight, gibbous appearance is visible when the planet is
+near quadrature. Webb thought it more conspicuous in twilight than in a
+dark sky. With large telescopes, Jupiter's satellites II. and III. have
+been seen--in consequence of Jupiter's phase--to emerge from occultation
+"at a sensible distance from the limb."[132]
+
+According to M. E. Rogovsky, the high "albedo of Jupiter, the appearance
+of the clear (red) and dark spots on its surface and their continual
+variation, the different velocity of rotation of the equatorial and other
+zones of its surface, and particularly its small density (1·33, water as
+unity), all these facts afford irrefragable proofs of the high temperature
+of this planet. The dense and opaque atmosphere hides its glowing surface
+from our view, and we see therefore only the external surface of its
+clouds. The objective existence of this atmosphere is proved by the bands
+and lines of absorption in its spectrum. The interesting photograph
+obtained by Draper, September 27, 1879, in which the blue and green parts
+are more brilliant for the equatorial zone than for the adjacent parts of
+the surface, appears to show that _Jupiter_ emits its proper light. It is
+possible that the constant red spot noticed on its surface by several
+observers, as Gledhill, Lord Rosse, and Copeland (1873), Russel and
+Bredikhin (1876), is the summit of a high glowing mountain. G. W. Hough
+considers Jupiter to be gaseous, and A. Ritter inferred from his formulæ
+that in this case the temperature at the centre would be 600,000° C."[133]
+
+The four brighter satellites of Jupiter are usually known by numbers I.,
+II., III., and IV.; I. being the nearest to the planet, and IV. the
+farthest. III. is usually the brightest, and IV. the faintest, but
+exceptions to this rule have been noticed.
+
+With reference to the recently discovered sixth and seventh satellites of
+Jupiter, Prof. Perrine has suggested that the large inclination of their
+orbits to the plane of the planet's equator seems to indicate that neither
+of these bodies was originally a member of Jupiter's family, but has been
+"captured by the planet." This seems possible as the orbits of some of the
+minor planets lie near the orbit of Jupiter (see "Minor Planets"). A
+similar suggestion has been made by Prof. del Marmol.[134]
+
+Many curious observations have been recorded with reference to Jupiter's
+satellites; some very difficult of explanation. In 1711 Bianchini saw
+satellite IV. so faint for more than an hour that it was hardly visible! A
+similar observation was made by Lassell with a more powerful telescope on
+June 13, 1849. Key, T. T. Smyth, and Denning have also recorded unusual
+faintness.[135] A very remarkable phenomenon was seen by Admiral Smyth,
+Maclear, and Pearson on June 26, 1828. Satellite II., "having fairly
+entered on Jupiter, was found 12 or 13 minutes afterwards _outside the
+limb_, where it remained visible for at least 4 minutes, and then suddenly
+vanished." As Webb says, "Explanation is here set at defiance;
+demonstrably neither in the atmosphere of the earth, nor Jupiter, where
+and what could have been the cause? At present we can get no answer."[136]
+When Jupiter is in opposition to the sun--that is, on the meridian at
+midnight--satellite I. has been seen projected on its own shadow, the
+shadow appearing as a dark ring round the satellite.
+
+On January 28, 1848, at Cambridge (U.S.A.) satellite III. was seen in
+transit lying between the shadows of I. and II. and so black that it could
+not be distinguished from the shadows, "except by the place it occupied."
+This seems to suggest inherent light in the planet's surface, as the
+satellite was at the time illuminated by full sunshine; its apparent
+blackness being due to the effect of contrast. Cassini on one occasion
+failed to find the shadow of satellite I. when it should have been on the
+planet's disc,[137] an observation which again points to the glowing light
+of Jupiter's surface. Sadler and Trouvelot saw the shadow of satellite I.
+double! an observation difficult to explain--but the same phenomenon was
+again seen on the evening of September 19, 1891, by Mr. H. S. Halbert of
+Detroit, Michigan (U.S.A.). He says that the satellite "was in transit
+nearing egress, and it appeared as a white disc against the dark southern
+equatorial belt; following it was the usual shadow, and at an equal
+distance from this was a second shadow, smaller and not so dark as the
+true one, and surrounded by a faint penumbra."[138]
+
+A dark transit of satellite III. was again seen on the evening of December
+19, 1891, by two observers in America. One observer noted that the
+satellite, when on the disc of the planet, was intensely black. To the
+other observer (Willis L. Barnes) it appeared as an ill-defined _dark_
+image.[139] A similar observation was made on October 9 of the same year
+by Messrs. Gale and Innes.[140]
+
+A "black transit" of satellite IV. was seen by several observers in 1873,
+and by Prof. Barnard on May 4, 1886. The same phenomenon was observed on
+October 30, 1903, in America, by Miss Anne S. Young and Willis S. Barnes.
+Miss Young says--
+
+    "The ingress of the satellite took place at 8{h} 50{m} (E. standard
+    time) when it became invisible upon the background of the planet. An
+    hour later it was plainly visible as a dark round spot upon the
+    planet. It was decidedly darker than the equatorial belt."[141]
+
+The rather rare phenomenon of an occultation of one of Jupiter's
+satellites by another was observed by Mr. Apple, director of the Daniel
+Scholl Observatory, Franklin and Marshall College, Lancaster, Pa.
+(U.S.A.), on the evening of March 16, 1908. The satellites in question
+were I. and II., and they were so close that they could not be separated
+with the 11·5-inch telescope of the Observatory.[142] One of the present
+writer's first observations with a telescope is dated May 17, 1873, and is
+as follows: "Observed one of Jupiter's satellites occulted (or very nearly
+so) by another. Appeared as one with power 133" (on 3-inch refractor in
+the Punjab). These satellites were probably I. and II.
+
+Jupiter has been seen on several occasions apparently without his
+satellites; some being behind the disc, some eclipsed in his shadow, and
+some in transit across the disc. This phenomenon was seen by Galileo,
+March 15, 1611; by Molyneux, on November 12, 1681; by Sir William
+Herschel, May 23, 1802; by Wallis, April 15, 1826; by Greisbach, September
+27, 1843; and by several observers on four occasions in the years
+1867-1895.[143] The phenomenon again occurred on October 3, 1907, No. 1
+being eclipsed and occulted, No. 2 in transit, No. 3 eclipsed, and No. 4
+occulted.[144] It was not, however, visible in Europe, but could have been
+seen in Asia and Oceania.[144] The phenomenon will occur again on October
+22, 1913.[145]
+
+On the night of September 19, 1903, a star of magnitude 6½ was occulted by
+the disc of Jupiter. This curious and rare phenomenon was photographed by
+M. Lucien Rudaux at the Observatory of Donville, France.[146] The star was
+Lalande 45698 (= BAC 8129).[147]
+
+Prof. Barnard, using telescopes with apertures from 5 inches up to 36
+inches (Lick), has failed to see a satellite through the planet's limb (an
+observation which has been claimed by other astronomers). He says, "To my
+mind this has been due to either poor seeing, a poor telescope, or an
+excited observer."[148] He adds--
+
+    "I think it is high time that the astronomers reject the idea that the
+    satellites of Jupiter can be seen through his limb at occultation.
+    When the seeing is bad there is a spurious limb to Jupiter that well
+    might give the appearance of transparency at the occultation of a
+    satellite. But under first-class conditions the limb of Jupiter is
+    perfectly opaque. It is quibbling and begging the question altogether
+    to say the phenomenon of transparency may be a rare one and so have
+    escaped my observations. Has any one said that the moon was
+    transparent when a star has been seen projected on it when it ought to
+    have been behind it?"
+
+Prof. Barnard and Mr. Douglass have seen white polar caps on the third and
+fourth satellites of Jupiter. The former says they are "exactly like those
+on Mars." "Both caps of the fourth satellite have been clearly
+distinguished, that at the north being sometimes exceptionally large,
+covering a surface equal to one-quarter or one-third of the diameter of
+the satellite."[149] This was confirmed on November 23, 1906, when Signor
+J. Comas Sola observed a brilliant white spot surrounded by a dark marking
+in the north polar region of the third satellite. There were other dark
+markings visible, and the satellite presented the appearance of a
+miniature of Mars.[150]
+
+An eighth satellite of Jupiter has recently been discovered by Mr. Melotte
+at the Greenwich Observatory by means of photography. It moves in a
+retrograde direction round Jupiter in an orbit inclined about 30° to that
+of the planet. The period of revolution is about two years. The orbit is
+very eccentric, the eccentricity being about one-third, or greater than
+that of any other satellite of the solar system. When nearest to Jupiter
+it is about 9 millions of miles from the planet, and when farthest about
+20 millions.[151] It has been suggested by Mr. George Forbes that this
+satellite may possibly be identical with the lost comet of Lexell which at
+its return in the year 1779 became entangled in Jupiter's system, and has
+not been seen since. If this be the case, we should have the curious
+phenomenon of a comet revolving round a planet!
+
+According to Humboldt the four bright satellites of Jupiter were seen
+almost simultaneously and quite independently by Simon Marius at Ausbach
+on December 29, 1609, and by Galileo at Padua on January 7, 1610.[152] The
+actual priority, therefore, seems to rest with Simon Marius, but the
+publication of the discovery was first made by Galileo in his _Nuncius
+Siderius_ (1610).[153] Grant, however, in his _History of Physical
+Astronomy_, calls Simon Marius an "impudent pretender"! (p. 79).
+
+M. Dupret at Algiers saw Jupiter with the naked eye on September 26, 1890,
+twenty minutes before sunset.[154]
+
+Humboldt states that he saw Jupiter with the naked eye when the sun was
+from 18° to 20° above the horizon.[155] This was in the plains of South
+America near the sea-level.
+
+
+
+
+CHAPTER IX
+
+Saturn
+
+
+To show the advantages of large telescopes over small ones, Mr. C. Roberts
+says that "with the 25-inch refractor of the Cambridge Observatory the
+view of the planet Saturn is indescribably glorious; everything I had ever
+seen before was visible at a glance, and an enormous amount of detail that
+I had never even glimpsed before, after a few minutes' observation."[156]
+
+Chacornac found that the illumination of Saturn's disc is the reverse of
+that of Jupiter, the edges of Saturn being brighter than the centre of the
+disc, while in the case of Jupiter--as in that of the sun--the edges are
+fainter than the centre.[157] According to Mr. Denning, Saturn bears
+satisfactorily "greater magnifying power than either Mars or
+Jupiter."[158]
+
+At an occultation of Saturn by the moon, which occurred on June 13, 1900,
+M. M. Honorat noticed the great contrast between the slightly yellowish
+colour of the moon and the greenish tint of the planet.[159]
+
+In the year 1892, when the rings of Saturn had nearly disappeared, Prof.
+L. W. Underwood, of the Underwood Observatory, Appleton, Wisconsin
+(U.S.A.), saw one of Saturn's satellites (Titan) apparently moving along
+the needlelike appendage to the planet presented by the rings. "The
+apparent diameter of the satellite so far exceeded the apparent thickness
+of the ring that it gave the appearance of a beautiful golden bead moving
+very slowly along a fine golden thread."[160]
+
+In 1907, when the rings of Saturn became invisible in ordinary telescopes,
+Professor Campbell, observing with the great Lick telescope, noticed
+"prominent bright knots, visible ... in Saturn's rings. The knots were
+symmetrically placed, two being to the east and two to the west." This was
+confirmed by Mr. Lowell, who says, "Condensations in Saturn's rings
+confirmed here and measured repeatedly. Symmetric and permanent." This
+phenomenon was previously seen by Bond in the years 1847-56. Measures of
+these light spots made by Prof. Barnard with the 40-inch Yerkes telescope
+show that the outer one corresponded in position with the outer edge of
+the middle ring close to the Cassini division, and the inner condensation,
+curious to say, seemed to coincide in position with the "crape ring."
+Prof. Barnard thinks that the thickness of the rings "must be greatly
+under 100 miles, and probably less than 50 miles," and he says--
+
+    "The important fact clearly brought out at this apparition of _Saturn_
+    is that the bright rings are not opaque to the light of the sun--and
+    this is really what we should expect from the nature of their
+    constitution as shown by the theory of Clerk Maxwell, and the
+    spectroscopic results of Keeler."[161]
+
+Under certain conditions it would be theoretically possible, according to
+Mr. Whitmell, to see the globe of Saturn through the Cassini division in
+the ring. But the observation would be one of great difficulty and
+delicacy. The effect would be that, of the arc of the division which
+crosses the planet's disc, "a small portion will appear bright instead of
+dark, and may almost disappear."[162]
+
+A remarkable white spot was seen on Saturn on June 23, 1903, by Prof.
+Barnard, and afterwards by Mr. Denning.[163] Another white spot was seen
+by Denning on July 9 of the same year.[164] From numerous observations of
+these spots, Denning found a rotation period for the planet of about
+10{h} 39{m} 21{s}.[165] From observations of the same spots Signor Comas
+Sola found a period 10{h} 38{m}·4, a close agreement with Denning's
+result. For Saturn's equator, Prof. Hill found a rotation period of 10{h}
+14{m} 23{s}·8, so that--as in the case of Jupiter--the rotation is faster
+at the equator than in the northern latitudes of the planet. A similar
+phenomenon is observed in the sun. Mr. Denning's results were fully
+confirmed by Herr Leo Brenner, and other German astronomers.[166]
+
+Photographs taken by Prof. V. M. Slipher in America show that the spectrum
+of Saturn is similar to that of Jupiter. None of the bands observed in the
+planet's spectrum are visible in the spectrum of the rings. This shows
+that if the rings possess an atmosphere at all, it must be much rarer than
+that surrounding the ball of the planet. Prof. Slipher says that "none of
+the absorption bands in the spectrum of _Saturn_ can be identified with
+those bands due to absorption in the earth's atmosphere," and there is no
+trace of aqueous vapour.[167]
+
+In September, 1907, M. G. Fournier suspected the existence of a "faint
+transparent and luminous ring" outside the principal rings of Saturn. He
+thinks that it may possibly be subject to periodical fluctuations of
+brightness, sometimes being visible and sometimes not.[168] This dusky
+ring was again suspected at the Geneva Observatory in October, 1908.[169]
+M. Schaer found it a difficult object with a 16-inch Cassegrain reflector.
+Prof. Stromgen at Copenhagen, and Prof. Hartwig at Bamberg, however,
+failed to see any trace of the supposed ring.[170] It was seen at
+Greenwich in October, 1908.
+
+A "dark transit" of Saturn's satellite Titan across the disc of the planet
+has been observed on several occasions. It was seen by Mr. Isaac W. Ward,
+of Belfast, on March 27, 1892, with a 4·3-inch Wray refractor. The
+satellite appeared smaller than its shadow. The phenomenon was also seen
+on March 12 of the same year by the Rev. A. Freeman, Mr. Mee, and M. F.
+Terby; and again on November 6, 1907, by Mr. Paul Chauleur and Mr. A. B.
+Cobham.[171]
+
+The recently discovered tenth satellite of Saturn, Themis, was discovered
+by photography, and has never been seen by the eye even with the largest
+telescopes! But its existence is beyond all doubt, and its orbit round the
+planet has been calculated.
+
+Prof. Hussey of the Lick Observatory finds that Saturn's satellite Mimas
+is probably larger than Hyperion. He also finds from careful measurements
+that the diameter of Titan is certainly overestimated, and that its
+probable diameter is about 2500 miles.[172]
+
+The French astronomer, M. Lucien Rudaux, finds the following variation in
+the light of the satellites of Saturn:--
+
+  Japetus from 9th magnitude to 12th
+  Rhea     "   9       "        10·6
+  Dione    "   9·5     "        10·5
+  Tethys   "   9·8     "        10·5
+  Titan    "   8       "         8·6
+
+The variation of light is, he thinks, due to the fact that the period of
+rotation of each satellite is equal to that of their revolution round the
+planet; as in the case of our moon.[173]
+
+The names of the satellites of Saturn are derived from the ancient heathen
+mythology. They are given in order of distance from the planet, the
+nearest being Mimas and the farthest Themis.
+
+1. Mimas was a Trojan born at the same time as Paris.
+
+2. Enceladus was son of Tartarus and Ge.
+
+3. Tethys was wife of Oceanus, god of ocean currents. She became mother of
+all the chief rivers in the universe, as also the Oceanides or sea nymphs.
+
+4. Dione was one of the wives of Zeus.
+
+5. Rhea was a daughter of Uranus. She married Saturn, and became the
+mother of Vesta, Ceres, Juno, and Pluto.
+
+6. Titan was the eldest son of Uranus.
+
+7. Hyperion was the god of day, and the father of sun and moon.
+
+8. Japetus was the fifth son of Uranus, and father of Atlas and
+Prometheus.[174]
+
+9. Phœbe was daughter of Uranus and Ge.
+
+10. Themis was daughter of Uranus and Ge, and, therefore, sister of
+Phœbe.
+
+In a review of Prof. Comstock's _Text Book of Astronomy_ in _The
+Observatory_, November, 1901, the remark occurs, "We are astonished to see
+that Mr. Comstock alludes with apparent seriousness to the _nine_
+satellites of Saturn. As regards the ninth satellite, we thought that all
+astronomers held with Mrs. Betsy Prig on the subject of this astronomical
+Mrs. Harris." This reads curiously now (1909) when the existence of the
+ninth satellite (Phœbe) has been fully confirmed, and a tenth satellite
+discovered.
+
+
+
+
+CHAPTER X
+
+Uranus and Neptune
+
+
+From observations of Uranus made in 1896, M. Leo Brenner concluded that
+the planet rotates on its axis in about 8½ hours (probably 8{h} 27{m}).
+This is a short period, but considering the short periods of Jupiter and
+Saturn there seems to be nothing improbable about it.
+
+Prof. Barnard finds that the two inner satellites of Uranus are difficult
+objects even with the great 36-inch telescope of the Lick Observatory!
+They have, however, been photographed at Cambridge (U.S.A.) with a 13-inch
+lens, although they are "among the most difficult objects known."[175]
+
+Sir William Huggins in 1871 found strong absorption lines (six strong
+lines) in the spectrum of Uranus. One of these lines indicated the
+presence of hydrogen, a gas which does not exist in our atmosphere. Three
+of the other lines seen were situated near lines in the spectrum of
+atmospheric air. Neither carbonic acid nor sodium showed any indications
+of their presence in the planet's spectrum. A photograph by Prof. Slipher
+of Neptune's spectrum "shows the spectrum of this planet to contain many
+strong absorption bands. These bands are so pronounced in the part of the
+spectrum between the Fraunhofer lines F and D, as to leave the solar
+spectrum unrecognizable.... Neptune's spectrum is strikingly different
+from that of _Uranus_, the bands in the latter planet all being reinforced
+in _Neptune_. In this planet there are also new bands which have not been
+observed in any of the other planets. The F line of hydrogen is remarkably
+dark ... this band is of more than solar strength in the spectrum of
+Uranus also. Thus free hydrogen seems to be present in the atmosphere of
+both these planets. This and the other dark bands in these planets bear
+evidence of an enveloping atmosphere of gases which is quite unlike that
+which surrounds the earth."[176]
+
+With the 18-inch equatorial telescope of the Strasburgh Observatory, M.
+Wirtz measured the diameter of Neptune, and found from forty-nine measures
+made between December 9, 1902, and March 28, 1903, a value of 2"·303 at a
+distance of 30·1093 (earth's distance from sun = 1). This gives a diameter
+of 50,251 kilometres, or about 31,225 miles,[177] and a mean density of
+1·54 (water = 1; earth's mean density = 5·53). Prof. Barnard's measures
+gave a diameter of 32,900 miles, a fairly close agreement, considering the
+difficulty of measuring so small a disc as that shown by Neptune.
+
+The satellite of Neptune was photographed at the Pulkown Observatory in
+the year 1899. The name Triton has been suggested for it. In the old Greek
+mythology Triton was a son of Neptune, so the name would be an appropriate
+one.
+
+The existence of a second satellite of Neptune is suspected by Prof.
+Schaeberle, who thinks he once saw it with the 36-inch telescope of the
+Lick Observatory "on an exceptionally fine night" in 1895.[178] But this
+supposed discovery has not yet been confirmed. Lassell also thought he had
+discovered a second satellite, but this supposed discovery was never
+confirmed.[178]
+
+The ancient Burmese mention eight planets, the sun, the moon, Mercury,
+Venus, Mars, Jupiter, Saturn, and another named Râhu, which is invisible.
+It has been surmised that "Râhu" is Uranus, which is just visible to the
+naked eye, and may possibly have been discovered by keen eyesight in
+ancient times. The present writer has seen it several times without
+optical aid in the West of Ireland, and with a binocular field-glass of 2
+inches aperture he found it quite a conspicuous object.
+
+When Neptune was _visually_ discovered by Galle, at Berlin, he was
+assisted in his observation by Prof. d'Arrest. The incident is thus
+described by Dr. Dreyer, "On the night of June 14, 1874, while observing
+Coggia's comet together, I reminded Prof. d'Arrest how he had once said in
+the course of a lecture, that he had been present at the finding of
+Neptune, and that 'he might say it would not have been found without him.'
+He then told me (and I wrote it down the next day), how he had suggested
+the use of Bremiker's map (as first mentioned by Dr. Galle in 1877) and
+continued, 'We then went back to the dome, where there was a kind of desk,
+at which I placed myself with the map, while Galle, looking through the
+refractor, described the configurations of the stars he saw. I followed
+them on the map one by one, until he said: "And then there is a star of
+the 8th magnitude, in such and such a position," whereupon I immediately
+exclaimed: "That star is not on the map."'"[179] This was the planet. But
+it seems to the present writer that if Galle or d'Arrest had access to
+Harding's Atlas (as they probably had) they might easily have found the
+planet with a good binocular field-glass. As a matter of fact Neptune is
+shown in Harding's Atlas (1822) as a star of the 8th magnitude, having
+been mistaken for a star by Lalande on May 8 and 10, 1795; and the present
+writer has found Harding's 8th magnitude stars quite easy objects with a
+binocular field-glass having object-glasses of two inches diameter, and a
+power of about six diameters.
+
+SUPPOSED PLANET BEYOND NEPTUNE.--The possible existence of a planet beyond
+Neptune has been frequently suggested. From considerations on the aphelia
+of certain comets, Prof. Forbes in 1880 computed the probable position of
+such a body. He thought this hypothetical planet would be considerably
+larger than Jupiter, and probably revolve round the sun at a distance of
+about 100 times the earth's mean distance from the sun. The place
+indicated was between R.A. 11{h} 24{m} and 12{h} 12{m}, and declination 0°
+0' to 6° 0' north. With a view to its discovery, the late Dr. Roberts took
+a series of eighteen photographs covering the region indicated. The result
+of an examination of these photographs showed, Dr. Roberts says, that "no
+planet of greater brightness than a star of the 15th magnitude exists on
+the sky area herein indicated." Prof. W. H. Pickering has recently revived
+the question, and has arrived at the following results: Mean distance of
+the planet from the sun, 51·9 (earth's mean distance = 1); period of
+revolution, 373½ years; mass about twice the earth's mass; probable
+position for 1909 about R.A. 7{h} 47{m}, north declination 21°, or about
+5° south-east of the star κ Geminorum. The supposed planet would be faint,
+its brightness being from 11½ to 13½, according to the "albedo" (or
+reflecting power) it may have.[180]
+
+Prof. Forbes has again attacked the question of a possible ultra-Neptunian
+planet, and from a consideration of the comets of 1556, 1843 I, 1880 I,
+and 1882 II, finds a mean distance of 105·4, with an inclination of the
+orbit of 52° to the plane of the ecliptic. This high inclination implies
+that "during the greatest part of its revolution it is beyond the zodiac,"
+and this, Mr. W. T. Lynn thinks, "may partly account for its not having
+hitherto been found by observation."[181]
+
+From a consideration of the approximately circular shape of the orbits of
+all the large planets of the solar system, Dr. See suggests the existence
+of three planets outside Neptune, with approximate distances from the sun
+of 42, 56, and 72 respectively (earth's distance = 1), and recommends a
+photographic search for them. He says, "To suppose the planetary system to
+terminate with an orbit so round as that of Neptune is as absurd as to
+suppose that Jupiter's system terminates with the orbit of the fourth
+satellite."[182]
+
+According to Grant, even twenty years before the discovery of Neptune the
+error of Prof. Adams' first approximation amounted to little more than
+10°.[183]
+
+
+
+
+CHAPTER XI
+
+Comets
+
+
+We learn from Pliny that comets were classified in ancient times,
+according to their peculiar forms, into twelve classes, of which the
+principal were: _Pogonias_, bearded; _Lampadias_, torch-like; _Xiphias_,
+sword-like; _Pitheus_, tun-like; _Acontias_, javelin-like; _Ceratias_,
+horn-like; _Disceus_, quoit-like; and _Hippias_, horse-mane-like.[184]
+
+Of the numerous comets mentioned in astronomical records, comparatively
+few have been visible to the naked eye. Before the invention of the
+telescope (1610) only those which were so visible _could_, of course, be
+recorded. These number about 400. Of the 400 observed since then, some 70
+or 80 only have been visible by unaided vision; and most of these now
+recorded could never have been seen without a telescope. During the last
+century, out of 300 comets discovered, only 13 were very visible to the
+naked eye. Hence, when we read in the newspapers that a comet has been
+discovered the chances are greatly against it becoming visible to the
+naked eye.[185]
+
+Although comparatively few comets can be seen without a telescope, they
+are sometimes bright enough to be visible in daylight! Such were those of
+B.C. 43, A.D. 1106, 1402, 1532, 1577, 1744, 1843, and the "great September
+comet" of 1882.
+
+If we except the great comet of 1861, through the tail of which the earth
+is supposed to have passed, the comet which came nearest to the earth was
+that of 1770, known as Lexell's, which approached us within two millions
+of miles, moving nearly in the plane of the ecliptic. It produced,
+however, no effect on the tides, nor on the moon's motion, which shows
+that its mass must have been very small. It was computed by Laplace that
+if its mass had equalled that of the earth, the length of our year would
+have been shortened by 2 hours 47 minutes, and as there was no perceptible
+change Laplace concluded that the comet's mass did not exceed 1/5000th of
+the earth's mass. This is the comet which passed so near to Jupiter that
+its period was reduced to 5½ years. Owing to another near approach in
+1779 it became invisible from the earth, and is now lost.[186] Its
+identity with the recently discovered eighth satellite of Jupiter has been
+suggested by Mr. George Forbes (see under "Jupiter"). At the near approach
+of Lexell's comet to the earth in 1770, Messier, "the comet ferret,"
+found that its head had an apparent diameter of 2½°, or nearly five
+times that of the moon!
+
+Another case of near approach to the earth was that of Biela's comet at
+its appearance in 1805. On the evening of December 9 of that year, the
+comet approached the earth within 3,380,000 miles.[187]
+
+The comet of A.D. 1106 is stated to have been seen in daylight close to
+the sun. This was on February 4 of that year. On February 10 it had a tail
+of 60° in length, according to Gaubil.[188]
+
+The comet of 1577 seems to have been one of the brightest on record.
+According to Tycho Brahé, it was visible in broad daylight. He describes
+the head as "round, bright, and of a yellowish light," with a curved tail
+of a reddish colour.[189]
+
+The comet of 1652 was observed for about three weeks only, and Hevelius
+and Comiers state that it was equal to the moon in apparent size! This
+would indicate a near approach to the earth. An orbit computed by Halley
+shows that the least distance was about 12 millions of miles, and the
+diameter of the comet's head rather less than 110,000 miles, or about 14
+times the earth's diameter.
+
+According to Mr. Denning, "most of the periodical comets at perihelion are
+outside the earth's orbit, and hence it follows that they escape
+observation unless the earth is on the same side of the sun as the
+comet."[190]
+
+It was computed by M. Faye that the _volume_ of the famous Donati's comet
+(1858) was about 500 times that of the sun! On the other hand, he
+calculated that its _mass_ (or quantity of matter it contained) was only a
+fraction of the earth's mass. This shows how almost inconceivably tenuous
+the material forming the comet must have been--much more rarefied, indeed,
+than the most perfect vacuum which can be produced in an air-pump. This
+tenuity is shown by the fact that stars were seen through the tail "as if
+the tail did not exist." A mist of a few hundred yards in thickness is
+sufficient to hide the stars from our view, while a thickness of thousands
+of miles of cometary matter does not suffice even to dim their brilliancy!
+
+At the time of the appearance of the great comet of 1843, it was doubtful
+whether the comet had transited the sun's disc. But it is now known, from
+careful calculations by Prof. Hubbard, that a transit really took place
+between 11{h} 28{m} and 12{h} 29{m} on February 27, 1843, and might have
+been observed in the southern hemisphere. The distance of this remarkable
+comet from the sun at its perihelion passage was less than that of any
+known comet. A little before 10 p.m. on February 27, the comet passed
+within 81,500 miles of the sun's surface with the enormous velocity of
+348 miles a second! It remained less than 2¼ hours north of the ecliptic,
+passing from the ascending to the descending node of its orbit in 2{h}
+13{m}·4.[191] The great comet of 1882 transited the sun's disc on Sunday,
+September 17, of that year, the ingress taking place at 4{h} 50{m} 58{s},
+Cape mean time. When on the sun the comet was absolutely invisible,
+showing that there was nothing solid about it. It was visible near the sun
+with the naked eye a little before the transit took place.[192] This great
+comet was found by several computors to have been travelling in an
+elliptic orbit with a period of about eight centuries. Morrison found 712
+years; Frisby, 794; Fabritius, 823; and Kreutz, 843 years.[193]
+
+The great southern comet of 1887 may be described as a comet without a
+head! The popular idea of a comet is a star with a tail. But in this case
+there was no head visible--to the naked eye at least. Dr. Thome of the
+Cordoba Observatory--its discoverer--describes it as "a beautiful
+object--a narrow, straight, sharply defined, graceful tail, over 40° long,
+shining with a soft starry light against a dark sky, beginning apparently
+without a head, and gradually widening and fading as it extended
+upwards."[194]
+
+The great southern comet of 1901 had five tails on May 6 of that year. Two
+were fairly bright, and the remaining three rather faint. Mr. Gale saw a
+number of faint stars through the tails. The light of these seem to have
+been "undimmed." Mr. Cobham noticed that the stars Rigel and β Eridani
+shone through one of the faint tails, and "showed no perceptible
+difference."[195]
+
+Prof. W. H. Pickering says that "the head of a comet, as far as our
+present knowledge is concerned, seems therefore to be merely a meteor
+swarm containing so much gaseous material that when electrified by its
+approach to the sun it will be rendered luminous" (_Harvard Annual_, vol.
+xxxii. part ii. p. 295) "... if the meteors and their atmospheres are
+sufficiently widely separated from one another, the comet may be brilliant
+and yet transparent at the same time."
+
+In the case of Swift's comet of 1892 some periodical differences of
+appearance were due, according to Prof. W. H. Pickering, to a rotation of
+the comet round an axis passing longitudinally through the tail, and he
+estimated the period of rotation at about 94 to 97 hours. He computed that
+in this comet the repulsive force exerted by the sun on the comet's tail
+was "about 39·5 times the gravitational force."[196]
+
+The comet known as 1902_b_ approached the planet Mercury within two
+millions of miles on November 29 of that year. Prof. O. C. Wendell, of
+Harvard Observatory, made some observations on the transparency of this
+comet. He found with the aid of a photometer and the 15-inch telescope of
+the observatory that in the case of two faint stars over which the comet
+passed on October 14, 1902, the absorption of light by the comet was
+insensible, and possibly did not exceed one or two hundredths of a
+magnitude,[197] an amount quite imperceptible to the naked eye, and shows
+conclusively how almost inconceivably rarefied the substance of this comet
+must be.
+
+The comet known as Morehouse (1908_c_) showed some curious and wonderful
+changes. Mr. Borelly found that five tails are visible on a photographic
+plate taken on October 3, 1908, and the trail of an occulted star
+indicates a slight absorption effect. According to M. L. Rabourdin, great
+changes took place from day to day, and even during the course of an hour!
+Similar changes were recorded by G. M. Gauthier; and Prof. Barnard, who
+photographed the comet on 30 nights from September 2 to October 13, states
+that the photographs of September 30 "are unique, whilst the
+transformation which took place between the taking of these and the taking
+of the next one on October 1 was very wonderful."[198] The spectrum
+showed the lines of cyanogen instead of the hydrocarbon spectrum shown by
+most comets.
+
+Prof. Barnard has suggested that all the phenomena of comets' tails cannot
+be explained by a repulsive force from the sun. Short tails issuing from
+the comet's nucleus at considerable angles with the main tail point to
+eruptive action in the comet itself. The rapid changes and distortions
+frequently observed in the tails of some comets suggest motion through a
+resisting medium; and the sudden increase of light also occasionally
+observed points in the same direction.[199]
+
+It was computed by Olbers that if a comet having a mass of 1/2000th of the
+earth's mass--which would form a globe of about 520 miles in diameter and
+of the density of granite--collided with the earth, with a velocity of 40
+miles a second, our globe would be shattered into fragments.[200] But that
+any comet has a solid nucleus of this size seems very doubtful; and we may
+further say that the collision of the earth with _any_ comet is highly
+improbable.
+
+It seems to be a common idea that harvests are affected by comets, and
+even "comet wines" are sometimes spoken of. But we know that the earth
+receives practically no heat from the brightest comet. Even in the case of
+the brilliant comet of 1811, one of the finest on record, it was found
+that "all the efforts to concentrate its rays did not produce the
+slightest effect on the blackened bulb of the most sensitive thermometer."
+Arago found that the year 1808, in which several comets were visible, was
+a cold year, "and 1831, in which there was no comet, enjoyed a much higher
+temperature than 1819, when there were three comets, one of which was very
+brilliant."[201] We may, therefore, safely conclude that even a large
+comet has no effect whatever on the weather.
+
+From calculations on the orbit of Halley's comet, the next return of which
+is due in 1910, Messrs. Cowell and Crommelin find that the identity of the
+comet shown on the Bayeux Tapestry with Halley's comet is now "fully
+established." They find that the date of perihelion passage was March 25,
+1066, which differs by only 4 days from the date found by Hind. The
+imposing aspect of the comet in 1066 described in European chronicles of
+that time is confirmed by the Chinese Annals. In the latter records the
+brightness is compared to that of Venus, and even with that of the moon!
+The comparison with the moon was probably an exaggeration, but the comet
+doubtless made a very brilliant show. In the Bayeux Tapestry the
+inscription on the wall behind the spectators reads: "_isti mirant
+stella_." Now, this is bad Latin, and Mr. W. T. Lynn has made the
+interesting suggestion that some of the letters are hidden by the
+buildings in front and that the real sentence is "_isti mirantur
+stellam_."[202] The present writer has examined the copy of the Bayeux
+Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn's
+suggestion seems very plausible. But the last letter of _stellam_ is
+apparently hidden by the comet's tail, which does not seem very probable!
+
+The conditions under which the comet will appear in 1910 are not unlike
+those of 1066 and 1145. "In each year the comet was discovered as a
+morning star, then lost in the sun's rays; on its emergence it was near
+the earth and moved with great rapidity, finally becoming stationary in
+the neighbourhood of Hydra, where it was lost to view."[203] In 1910 it
+will probably be an evening star before March 17, and after May 11, making
+a near approach to the earth about May 12. About this time its apparent
+motion in the sky will be very rapid. As, however, periodical comets--such
+as Halley's--seem to become fainter at each return, great expectations
+with reference to its appearance in 1910 should not be indulged in.
+
+The appearance of Halley's comet in A.D. 1222 is thus described by
+Pingré--a great authority on comets--(quoting from an ancient writer)--
+
+    "In autumn, that is to say in the months of August and September, a
+    star of the first magnitude was seen, very red, and accompanied by a
+    great tail which extended towards the top of the sky in the form of a
+    cone extremely pointed. It appeared to be very near the earth. It was
+    observed (at first?) near the place of the setting sun in the month of
+    December."
+
+With reference to its appearance in the year 1456, when it was of "vivid
+brightness," and had a tail of 60° in length, Admiral Smyth says,[204] "To
+its malign influence were imputed the rapid successes of Mahomet II.,
+which then threatened all Christendom. The general alarm was greatly
+aggravated by the conduct of Pope Callixtus III., who, though otherwise a
+man of abilities, was a poor astronomer; for that pontiff daily ordered
+the church bells to be rung at noon-tide, extra _Ave-Marias_ to be
+repeated, and a special protest and excommunication was composed,
+exorcising equally the Devil, the Turks, and the comet." With reference to
+this story, Mr. G. F. Chambers points out[205] that it is probably based
+on a passage in Platina's _Vitæ Pontificum_. But in this passage there is
+no mention made of excommunication or exorcism, so that the story, which
+has long been current, is probably mythical. In confirmation of this view,
+the Rev. W. F. Rigge has shown conclusively[206] that no bull was ever
+issued by Pope Callixtus III. containing a reference to _any_ comet. The
+story would therefore seem to be absolutely without foundation, and should
+be consigned to the limbo of all such baseless myths.
+
+With reference to the appearance of Halley's comet, at his last return in
+1835, Sir John Herschel, who observed it at the Cape of Good Hope, says--
+
+    "Among the innumerable stars of all magnitudes, from the ninth
+    downwards, which at various times were seen through it, and some
+    extremely near to the nucleus (though not _exactly on it_) there never
+    appeared the least ground for presuming any extinction of their light
+    in traversing it. Very minute stars indeed, on entering its brightest
+    portions, were obliterated, as they would have been by an equal
+    illumination of the field of view; but stars which before their entry
+    appeared bright enough to bear that degree of illumination, were in no
+    case, so far as I could judge, affected to a greater extent than they
+    would have been by so much lamp-light artificially introduced."[207]
+
+It is computed by Prof. J. Holetschak that, early in October, 1909,
+Halley's comet should have the brightness of a star of about 14½
+magnitude.[208] It should then--if not detected before--be discoverable
+with some of the large telescopes now available.
+
+According to the computations of Messrs. Cowell and Crommelin, the comet
+should enter Pisces from Aries in January, 1910. "Travelling westward
+towards the star γ Piscium until the beginning of May, and then turning
+eastward again, it will travel back through the constellations Cetus,
+Orion, Monoceros, Hydra, and Sextans." From this it seems that observers
+in the southern hemisphere will have a better view of the comet than those
+in northern latitudes. The computed brightness varies from 1 on January 2,
+1910, to 1112 on May 10. But the actual brightness of a comet does not
+always agree with theory. It is sometimes brighter than calculation would
+indicate.
+
+According to Prof. O. C. Wendell, Halley's comet will, on May 12, 1910,
+approach the earth's orbit within 4·6 millions of miles; and he thinks
+that possibly the earth may "encounter some meteors," which are presumably
+connected with the comet. He has computed the "radiant point" of these
+meteors (that is, the point from which they appear to come), and finds its
+position to be R.A. 22{h} 42{m}·9, Decl. N. 1° 18'. This point lies a
+little south-west of the star β Piscium.
+
+According to Dr. Smart, the comet will, on June 2, "cross the Equator
+thirteen degrees south of Regulus, and will then move slowly in the
+direction of φ Leonis. The comet will be at its descending node on the
+ecliptic in the morning of May 16, and the earth will pass through the
+node on the comet's orbit about two and a half days later. The comet's
+orbit at the node is about 13 million miles within that of the earth.
+Matter repelled from the comet's nucleus by the sun with a velocity of
+about 216,000 miles per hour, would just meet the earth when crossing the
+comet's orbit plane. Matter expelled with a velocity of 80,000 miles per
+hour, as in the case of Comet Morehouse, would require seven days for the
+journey. Cometary matter is said to have acquired greater velocities than
+this, for (according to Webb, who quotes Chacornac) Comet II., 1862, shot
+luminous matter towards the sun, with a velocity of nearly 2200 miles per
+second. It is therefore possible that matter thrown off by the comet at
+the node may enter our atmosphere, in which case we must hope that
+cyanogen, which so often appears in cometary spectra, may not be
+inconveniently in evidence."[209]
+
+Cyanogen is, of course, a poisonous gas, but cometary matter is so
+rarefied that injurious effects on the earth need not be feared.
+
+If we can believe the accounts which have been handed down to us, some
+very wonderful comets were visible in ancient times. The following may be
+mentioned:--
+
+B.C. 165. The sun is said to have been "seen for several hours in the
+night." If this was a comet it must have been one of extraordinary
+brilliancy.[210]
+
+B.C. 146. "After the death of Demetrius, king of Syria, the father of
+Demetrius and Antiochus, a little before the war in Achaia, there appeared
+a comet as large as the sun. Its disc was first red, and like fire,
+spreading sufficient light to dissipate the darkness of night; after a
+little while its size diminished, its brilliancy became weakened, and at
+length it entirely disappeared."[211]
+
+B.C. 134. It is recorded that at the birth of Mithridates a great comet
+appeared which "occupied the fourth part of the sky, and its brilliancy
+was superior to that of the sun." (?)[212]
+
+B.C. 75. A comet is described as equal in size to the moon, and giving as
+much light as the sun on a cloudy day. (!)[213]
+
+A.D. 531. In this year a great comet was observed in Europe and China. It
+is described as "a very large and fearful comet," and was visible in the
+west for three weeks. Hind thinks that this was an appearance of Halley's
+comet,[214] and this has been confirmed by Mr. Crommelin.
+
+A.D. 813, August 4. A comet is said to have appeared on this date, of
+which the following curious description is given: "It resembled two moons
+joined together; they separated, and having taken different forms, at
+length appeared like a man without a head." (!)[215]
+
+A.D. 893. A great comet is said to have appeared in this year with a tail
+100° in length, which afterwards increased to 200°![216]
+
+A.D. 1402. A comet appeared in February of this year, which was visible in
+daylight for eight days. "On Palm Sunday, March 19, its size was
+prodigious." Another comet, visible in the daytime, was seen from June to
+September of the same year.
+
+When the orbit of the comet known as 1889 V was computed, it was found
+that it had passed through Jupiter's system in 1886 (July 18-21). The
+calculations show that it must have passed within a distance of 112,300
+miles of the planet itself--or less than half the moon's distance from the
+earth--and "its centre may possibly have grazed the surface of
+Jupiter."[217]
+
+Sir John Herschel thought that the great comet of 1861 was by far the
+brightest comet he had ever seen, those of 1811 and 1858 (Donati's) not
+excepted.[218] Prof. Kreutz found its period of revolution round the sun
+to be about 409 years, with the plane of the orbit nearly at right angles
+to the plane of the ecliptic.
+
+       *       *       *       *       *
+
+On November 9, 1795, Sir William Herschel saw the comet of that year pass
+centrally over a small double star of the 11th and 12th magnitudes, and
+the fainter of the two components remained distinctly visible during the
+comet's transit over the star. This comet was an appearance of the comet
+now known as Encke's.[219] Struve saw a star of the 10th magnitude through
+nearly the brightest part of Encke's comet on November 7, 1828, but the
+star's light was not dimmed by the comet.
+
+Sir John Herschel saw a cluster of stars of the 16th or 17th magnitude
+through Biela's comet, although the interposed cometary matter must have
+been at least 50,000 miles in thickness.[220]
+
+Bessel found that on September 29, 1835, a star of the 10th magnitude
+shone with undimmed lustre through the tail of Halley's comet within 8
+seconds of arc of the central point of the head. At Dorpat (Russia) Struve
+saw the same star "in conjunction only 2"·2 from the brightest point of
+the comet. The star remained continuously visible, and its light was not
+perceptibly diminished whilst the nucleus of the comet seemed to be almost
+extinguished before the radiance of the small star of the 9th or 10th
+magnitude."[221]
+
+Webb says--
+
+    "Donati saw a 7 mg. star enlarged so as to show a sensible disc, when
+    the nucleus of comet III., 1860, passed very near it. Stars are said
+    to have started, or become tremulous, during occultations by comets.
+    Birmingham observed the comet of Encke illuminated by a star over
+    which it passed, August 23, 1868; and Klein, in 1861, remarked an
+    exceptional twinkling in 5 mg. stars involved in the tail."[222]
+
+The comet of 1729 had the greatest perihelion distance of any known
+comet;[223] that is, when nearest to the sun, it did not approach the
+central luminary within four times the earth's distance from the sun!
+
+Barnard's comet, 1889 I., although it never became visible to the naked
+eye, was visible with a telescope from September 2, 1888, to August 18,
+1890, or 715 days--the longest period of visibility of any comet on
+record. When last seen it was 6¼ times the earth's distance from the sun,
+or about 580 millions of miles,[224] or beyond the orbit of Jupiter!
+
+Messier, who was called "the comet ferret," discovered "all his comets
+with a small 2-foot telescope of 2¼ inches aperture, magnifying 5 times,
+and with a field of 4°."[225]
+
+It is a very curious fact that Sir William Herschel, "during all his
+star-gaugings and sweeps for nebulæ, never discovered a comet;"[226] that
+is an object which was afterwards _proved_ to be a comet. Possibly,
+however, some of his nebulæ which are now missing, may have been really
+comets.
+
+Sir William Herschel found the diameter of the head of the great comet of
+1811 to be 127,000 miles. The surrounding envelope he estimated to be at
+least 643,000 miles, or about three-fourths of the sun's diameter.
+
+On a drawing of the tails of the great comet of 1744 given in a little
+book printed in Berlin in that year, no less than 12 tails are shown!
+These vary in length and brightness. A copy of this drawing is given in
+_Copernicus_.[227] The observations were made by "einen geschichten
+Frauenzimmer," who Dr. Dreyer identifies with Christian Kirch, or one of
+her two sisters, daughters of the famous Gottfried and Maria Margaretta
+Kirch (_Idem_, p. 107). Dr. Dreyer thinks that the drawing "seems to have
+been carefully made, and not to be a mere rough sketch as I had at first
+supposed" (_Idem_, p. 185).
+
+The tails of some comets were of immense length. That of the comet of 1769
+had an absolute length of 38 millions of miles. That of 1680, 96 million
+of miles, or more than the sun's distance from the earth. According to Sir
+William Herschel, the tail of the great comet of 1811 was over 100
+millions of miles in length. That of the great comet of 1843--one of the
+finest in history--is supposed to have reached a length of 150 millions of
+miles![228]
+
+In width the tails of comets were in some cases enormous. According to Sir
+William Herschel, the tail of the comet of 1811 had a diameter of 15
+millions of miles! Its volume was, therefore, far greater than that of the
+sun![228]
+
+According to Hevelius the comet of 1652 was of such a magnitude that it
+"resembled the moon when half full; only it shone with a pale and dismal
+light."[229]
+
+Halley's comet at its next appearance will be examined with the
+spectroscope for the first time in its history. At its last return in
+1835, the spectroscope had not been invented.
+
+For the great comet of 1811, Arago computed a period of 3065 years; and
+Encke found a period of 8800 years for the great comet of 1680.[230]
+
+The variation in the orbital velocity of some comets is enormous. The
+velocity of the comet of 1680 when passing round the sun (perihelion) was
+about 212 miles a second! Whereas at its greatest distance from the sun
+(aphelion) the velocity is reduced to about 10 feet a second!
+
+
+
+
+CHAPTER XII
+
+Meteors
+
+
+Mr. Denning thinks that the meteor shower of the month of May, known as
+the Aquarids, is probably connected with Halley's comet. The meteors
+should be looked for after 1 a.m. during the first week in May, and may
+possibly show an enhanced display in May, 1910, when Halley's comet will
+be near the sun and earth.[231]
+
+On November 29, 1905, Sir David Gill observed a fireball with an apparent
+diameter equal to that of the moon, which remained visible for 5 minutes
+and disappeared in a hazy sky. Observed from another place, Mr. Fuller
+found that the meteor was visible 2 hours later! Sir David Gill stated
+that he does not know of any similar phenomenon.[232]
+
+Mr. Denning finds that swiftly moving meteors become visible at a greater
+height above the earth's surface than the slower ones. Thus, for the
+Leonids and Perseids, which are both swift, it has been found that the
+Leonids appear at an average height of 84 miles, and disappear at a height
+of 56 miles; and the Perseids at 80 and 54 miles respectively. "On the
+other hand, the mean height of the very slow meteors average about 65
+miles at the beginning and 38 miles at the end of their appearance."[233]
+
+During the night of July 21-22, 1896, Mr. William Brooks, the well-known
+astronomer, and director of the Smith Observatory at Geneva (New York),
+saw a round dark body pass slowly across the moon's bright disc, the moon
+being nearly full at the time. The apparent diameter of the object was
+about one minute of arc, and the duration of the transit 3 or 4 seconds,
+the direction of motion being from east to west. On August 22 of the same
+year, Mr. Gathman (an American observer) saw a meteor crossing the _sun's_
+disc, the transit lasting about 8 seconds.[234]
+
+A meteor which appeared in Italy on July 7, 1892, was shown by Prof. von
+Niessl to have had an _ascending_ path towards the latter end of its
+course! The length of its path was computed to be 683 miles. When first
+seen, its height above the earth was about 42 miles, and when it
+disappeared its height had increased to about 98 miles, showing that its
+motion was directed upwards![235]
+
+In the case of the fall of meteoric stones, which occasionally occur, it
+has sometimes been noticed that the sound caused by the explosion of the
+meteorite, or its passage through the air, is heard before the meteorite
+is seen to fall. This has been explained by the fact that owing to the
+resistance of the air to a body moving at first with a high velocity its
+speed is so reduced that it strikes the earth with a velocity less than
+that of sound. Hence the sound reaches the earth before the body strikes
+the ground.[236]
+
+The largest meteoric stone preserved in a museum is that known as the
+Anighita, which weighs 36½ tons, and was found at Cape York in
+Greenland. It was brought to the American Museum of Natural History by
+Commander R. E. Peary, the Arctic explorer.
+
+The second largest known is that of Bacubirito in Mexico, the weight of
+which is estimated at 27½ tons.
+
+The third largest is that known as the Williamette, which was found in
+1902 near the town of that name in Western Oregon (U.S.A.). It is composed
+of metallic nickel-iron, and weighs about 13½ tons. It is now in the
+American Museum of Natural History.
+
+A large meteorite was actually seen, from the deck of the steamer _African
+Prince_, to fall into the Atlantic Ocean, on October 7, 1906! The captain
+of the vessel, Captain Anderson, describes it as having a train of light
+resembling "an immense broad electric-coloured band, gradually turning to
+orange, and then to the colour of molten metal. When the meteor came into
+the denser atmosphere close to the earth, it appeared, as nearly as is
+possible to describe it, like a molten mass of metal being poured out. It
+entered the water with a hissing noise close to the ship."[237] This was a
+very curious and perhaps unique phenomenon, and it would seem that the
+vessel had a narrow escape from destruction.
+
+In Central Arizona (U.S.A.) there is a hill called Coon Butte, or Coon
+Mountain. This so-called "mountain" rises to a height of only 130 to 160
+feet above the surrounding plain, and has on its top a crater of 530 to
+560 feet deep; the bottom of the crater--which is dry--being thus 400 feet
+below the level of the surrounding country. This so-called "crater" is
+almost circular and nearly three-quarters of a mile in diameter. It has
+been suggested that this "crater" was formed by the fall of an enormous
+iron meteorite, or small asteroid. The "crater" has been carefully
+examined by a geologist and a physicist. From the evidence and facts
+found, the geologist (Mr. Barringer) states that "they do not leave, in my
+mind, a scintilla of doubt that this mountain and its crater were produced
+by the impact of a huge meteorite or small asteroid." The physicist (Mr.
+Tilghmann) says that he "is justified, under due reserve as to
+subsequently developed facts, in announcing that the formation at this
+locality is due to the impact of a meteor of enormous and unprecedented
+size." There are numerous masses of meteoric iron in the vicinity of the
+"crater." The so-called Canyon Diabolo meteorite was found in a canyon of
+that name about 2½ miles from the Coon Mountain. The investigators
+estimate that the great meteoric fall took place "not more than 5000 years
+ago, perhaps much less." Cedar trees about 700 years old are now growing
+on the rim of the mountain. From the results of artillery experiments, Mr.
+Gilbert finds that "a spherical projectile striking solid limestone with a
+velocity of 1800 feet a second will penetrate to a depth of something less
+than two diameters," and from this Mr. L. Fletcher concludes "that a
+meteorite of large size would not be prevented by the earth's atmosphere
+from having a penetration effect sufficient for the production of such a
+crater."[238]
+
+The meteoric origin of this remarkable "crater" is strongly favoured by
+Mr. G. P. Merrill, Head Curator of Geology, U.S. National Museum.
+
+The Canyon Diabolo meteorite above referred to was found to contain
+diamonds! some black, others transparent. So some have said that "the
+diamond is a gift from Heaven," conveyed to earth in meteoric
+showers.[239] But diamond-bearing meteorites would seem to be rather a
+freak of nature. It does not follow that _all_ diamonds had their origin
+in meteoric stones. The mineral known as periodot is frequently found in
+meteoric stones, but it is also a constituent of terrestrial rocks.
+
+In the year 1882 it was stated by Dr. Halm and Dr. Weinhand that they had
+found fossil sponges, corals, and crinoids in meteoric stones! Dr.
+Weinhand thought he had actually determined three genera![240] But this
+startling result was flatly contradicted by Carl Vogt, who stated that the
+supposed fossils are merely crystalline conformations.[241]
+
+Some meteorites contain a large quantity of occluded gases, hydrogen,
+helium, and carbon oxides. It is stated that Dr. Odling once "lighted up
+the theatre of the Royal Institution with gas brought down from
+interstellar space by meteorites"![242]
+
+On February 10, 1896, a large meteorite burst over Madrid with a loud
+report. The concussion was so great that many windows in the city were
+broken, and some partitions in houses were shaken down![243]
+
+A very brilliant meteor or fireball was seen in daylight on June 9, 1900,
+at 2{h} 55{m} p.m. from various places in Surrey, Sussex, and near London.
+Calculations showed that "the meteor began 59 miles in height over a point
+10 miles east of Valognes, near Cherbourg, France. Meteor ended 23 miles
+in height, over Calais, France. Length of path 175 miles. Radiant point,
+280°, 12°."[244]
+
+It was decided some years ago "in the American Supreme Court that a
+meteorite, though a stone fallen from heaven, belongs to the owner of the
+freehold interest in the land on which it falls, and not to the
+tenant."[245]
+
+With reference to the fall of meteoric matter on the earth, Mr. Proctor
+says, "It is calculated by Dr. Kleiber of St. Petersburgh that 4250 lbs.
+of meteoric dust fall on the earth every hour--that is, 59 tons a day, and
+more than 11,435 tons a year. I believe this to be considerably short of
+the truth. It sounds like a large annual growth, and the downfall of such
+an enormous mass of meteoric matter seems suggestive of some degree of
+danger. But in reality, Dr. Kleiber's estimate gives only about 25
+millions of pounds annually, which is less than 2 ounces annually to each
+square mile of the earth's surface,"[246] a quantity which is, of course,
+quite insignificant.
+
+According to Humboldt, Chladni states that a Franciscan monk was killed by
+the fall of an aërolite at Milan in the year 1660.[247] Humboldt also
+mentions the death by meteoric stones of a monk at Crema on September 4,
+1511, and two Swedish sailors on board ship in 1674.[248]
+
+It is a curious fact that, according to Olbers, "no fossil meteoric
+stones" have ever been discovered.[249] Considering the number which are
+supposed to have fallen to the earth in the course of ages, this fact
+seems a remarkable one.
+
+On May 10, 1879, a shower of meteorites fell at Eitherville, Iowa
+(U.S.A.). Some of the fragments found weighed 437, 170, 92½, 28, 10½, 4
+and 2 lbs. in weight. In the following year (1880) when the prairie grass
+had been consumed by a fire, about "5000 pieces were found from the size
+of a pin to a pound in weight."[250]
+
+According to Prof. Silvestria of Catania, a shower of meteoric dust mixed
+with rain fell on the night of March 29, 1880. The dust contained a large
+proportion of iron in the metallic state. In size the particles varied
+from a tenth to a hundredth of a millimetre.[251]
+
+It is sometimes stated that the average mass of a "shooting star" is only
+a few grains. But from comparisons with an electric arc light, Prof. W.
+H. Pickering concludes that a meteor as bright as a third magnitude star,
+composed of iron or stone, would probably have a diameter of 6 or 7
+inches. An average bright fireball would perhaps measure 5 or 6 feet in
+diameter.[252]
+
+In the Book of Joshua we are told "that the LORD cast down great stones
+from heaven upon them unto Azekah, and they died" (Joshua x. 11). In the
+latter portion of the verse "hailstones" are mentioned, but as the
+original Hebrew word means stones in general (not hailstones), it seems
+very probable that the stones referred to were aërolites.[253]
+
+The stone mentioned in the Acts of the Apostles, from which was found "the
+_image_ which fell down from Jupiter" (Acts xix. 35), was evidently a
+meteoric stone.[253]
+
+The famous stone in the Caaba at Mecca, is probably a stone of meteoric
+origin.[253]
+
+  I
+
+  "Stones from Heaven! Can you wonder,
+    You who scrutinize the Earth,
+  At the love and veneration
+    They received before the birth
+  Of our scientific methods?
+
+
+  II
+
+  "Stones from Heaven! we can handle
+    Fragments fallen from realms of Space;
+  Oh! the marvel and the mystery,
+    Could we understand their place
+  In the scheme of things created!
+
+
+  III
+
+  "Stones from Heaven! With a mighty
+    Comet whirling formed they part?
+  Fell they from their lofty station
+    Like a brilliant fiery dart,
+  Hurl'd from starry fields of Night?"[254]
+
+
+
+
+CHAPTER XIII
+
+The Zodiacal Light and Gegenschein
+
+
+According to Gruson and Brugsch, the Zodiacal Light was known in ancient
+times, and was even worshipped by the Egyptians. Strabo does not mention
+it; but Diodorus Siculus seems to refer to it (B.C. 373), and he probably
+obtained his information from some Greek writers before his time, possibly
+from Zenophon, who lived in the sixth century B.C.[255] Coming to the
+Christian era, it was noticed by Nicephorus, about 410 B.C. In the Koran,
+it is called the "false Aurora"; and it is supposed to be referred to in
+the "Rubáiyát" of Omar Khayyam, the Persian astronomical poet, in the
+second stanza of that poem (Edward Fitzgerald's translation)--
+
+  "Dreaming when Dawn's Left Hand was in the Sky,[256]
+  I heard a voice within the Tavern cry,
+  Awake, my Little ones, and fill the Cup,
+  Before Life's Liquor in its Cup be dry."
+
+It was observed by Cassini in 1668,[257] and by Hooke in 1705. A short
+description of its appearance will be found in Childrey's _Britannia
+Baconica_ (1661), p. 183.
+
+The finest displays of this curious light seem to occur between the middle
+of January and the middle of February. In February, 1856, Secchi found it
+brighter than he had ever seen it before. It was yellowish towards the
+axis of the cone, and it seemed to be brighter than the Milky Way in
+Cygnus. He described it as "un grande spectacle." In the middle of
+February, 1866, Mr. Lassell, during his last residence in Malta, saw a
+remarkable display of the Zodiacal Light. He found it at least twice as
+bright as the brightest part of the Milky Way, and much brighter than he
+had previously seen it. He found that the character of its light differed
+considerably from that of the Milky Way. It was of a much redder hue than
+the Galaxy. In 1874 very remarkable displays were seen in the
+neighbourhood of London in January and February of that year; and in 1875
+on January 24, 25, and 30. On January 24 it was noticed that the "light"
+was distinctly reddish and much excelled in brightness any portion of the
+Milky Way.
+
+Humboldt, who observed it from Andes (at a height of 13,000 to 15,000
+feet), from Venezuela and from Cumana, tells us that he has seen the
+Zodiacal Light equal in brightness to the Milky Way in Sagittarius.
+
+As probably many people have never seen the "light," a caution may be
+given to those who care to look for it. It is defined by the Rev. George
+Jones, Chaplain to the "United States' Japan Expedition" (1853-55), as "a
+brightness that appears in the western sky after sunset, and in the east
+before sunrise; following nearly or quite the line of the ecliptic in the
+heavens, and stretching upwards to various elevations according to the
+season of the year." From the description some might suppose that the
+light is visible _immediately_ after sunset. But this is not so; it never
+appears until twilight is over and "the night has fully set in."
+
+The "light" is usually seen after sunset or before sunrise. But attempts
+have recently been made by Prof. Simon Newcomb to observe it north of the
+sun. To avoid the effects of twilight the sun must be only slightly more
+than 18° below the horizon (that is, a little before or after the longest
+day). This condition limits the place of observation to latitudes not much
+south of 46°; and to reduce atmospheric absorption the observing station
+should be as high as possible above the level of the sea. Prof. Newcomb,
+observing from the Brienzer Rothorn in Switzerland (latitude 46° 47' N.,
+longitude 8° 3' E.), succeeded in tracing the "light" to a distance of 35°
+north of the sun. It would seem, therefore, that the Zodiacal Light
+envelops the sun on all sides, but has a greater extension in the
+direction of the ecliptic.[258] From observations at the Lick Observatory,
+Mr. E. A. Fath found an extension of 46° north of the sun.[259]
+
+From observations of the "light" made by Prof. Barnard at the Yerkes
+Observatory during the summer of 1906, he finds that it extends to at
+least 65° north of the sun, a considerably higher value than that found by
+Prof. Newcomb.[260] The difference may perhaps be explained by actual
+variation of the meteoric matter producing the light. Prof. J. H. Poynting
+thinks that possibly the Zodiacal Light is due to the "dust of long dead
+comets."[261]
+
+From careful observations of the "light," Mr. Gavin J. Burns finds that
+its luminosity is "some 40 or 50 per cent. brighter than the background of
+the sky. Prof. Newcomb has made a precisely similar remark about the
+luminosity of the Milky Way, viz. that it is surprisingly small." This
+agrees with my own observations during many years. It is only on the
+finest and clearest nights that the Milky Way forms a conspicuous object
+in the night sky. And this only in the country. The lights of a city
+almost entirely obliterate it. Mr. Burns finds that the Zodiacal Light
+appears "to be of a yellowish tint; or if we call it white, then the Milky
+Way is comparatively of a bluish tint." During my residence in the Punjab
+the Zodiacal Light seemed to me constantly visible in the evening sky in
+the spring months. In the west of Ireland I have seen it nearly as bright
+as the brightest portions of the Milky Way visible in this country
+(February 20, 1890). The "meteoric theory" of the "light" seems to be the
+one now generally accepted by astronomers, and in this opinion I fully
+concur.
+
+From observations made in Jamaica in the years 1899 and 1901, Mr. Maxwell
+Hall arrived at the conclusion that "the Zodiacal Light is caused by
+reflection of sunlight from masses of meteoric matter still contained in
+the invariable plane, which may be considered the original plane of the
+solar system."[262] According to Humboldt, Cassini believed that the
+Zodiacal Light "consisted of innumerably small planetary bodies revolving
+round the sun."[263]
+
+THE GEGENSCHEIN, or COUNTER-GLOW.--This is a faint patch of light seen
+opposite the sun's place in the sky, that is on the meridian at midnight.
+It is usually elliptical in shape, with its longer axis lying nearly in
+the plane of the ecliptic. It seems to have been first detected by Brorsen
+(the discoverer of the short-period comet of 1846) about the middle of
+the nineteenth century. But it is not easy to see, for the famous Heis of
+Münster, who had very keen eyesight, did not succeed in seeing it for
+several years after Brorsen's announcement.[264] It was afterwards
+independently discovered by Backhouse, and Barnard.
+
+Prof. Barnard's earlier observations seemed to show that the Gegenschein
+does not lie exactly opposite to the sun, but very nearly so. He found its
+longitude is within one degree of 180°, and its latitude about 1°·3 north
+of the ecliptic.[265] But from subsequent observations he came to the
+conclusion that the differences in longitude and apparent latitude are due
+to atmospheric absorption, and that the object really lies in the ecliptic
+and _exactly_ opposite to the sun.[266]
+
+Barnard finds that the Gegenschein is not so faint as is generally
+supposed. He says "it is best seen by averted vision, the face being
+turned 60° or 70° to the right or left, and the eyes alone turned towards
+it." It is invisible in June and December, while in September it is round,
+with a diameter of 20°, and very distinct. No satisfactory theory has yet
+been advanced to account for this curious phenomenon. Prof. Arthur Searle
+of Harvard attributes it to a number of asteroids too small to be seen
+individually. When in "opposition" to the sun these would be fully
+illuminated and nearest to the earth. Its distance from the earth probably
+exceeds that of the moon. Dr. Johnson Stoney thinks that the Gegenschein
+may possibly be due to a "tail" of hydrogen and helium gases repelled from
+the earth by solar action; this "tail" being visible to us by reflected
+sunlight.
+
+It was observed under favourable circumstances in January and February,
+1903, by the French astronomer, M. F. Quénisset. He found that it was
+better seen when the atmosphere was less clear, contrary to his experience
+of the Zodiacal Light. Prof. Barnard's experience confirms this. M.
+Quénisset notes that--as in the case of the Zodiacal Light--the southern
+border of the Gegenschein is sharper than the northern. He found that its
+brightness is less than that of the Milky Way between Betelgeuse and γ
+Geminorum; and thinks that it is merely a strengthening of the Zodiacal
+Light.[267]
+
+A meteoritic theory of the Gegenschein has been advanced by Prof. F. R.
+Moulton, which explains it by light reflected from a swarm of meteorites
+revolving round the sun at a distance of 930,240 miles outside the earth's
+orbit.
+
+Both the Zodiacal Light and Gegenschein were observed by Herr Leo Brenner
+on the evening of March 4, 1896. He found the Zodiacal Light on this
+evening to be "_perhaps eight times brighter_ than the Milky Way in
+Perseus." The "_Gegenschein distinctly visible_ as a round, bright,
+cloud-like nebula below Leo (Virgo), and about twice the brightness of the
+Milky Way in Monoceros between Canis Major and Canis Minor."[268]
+
+Humboldt thought that the fluctuations in the brilliancy of the Zodiacal
+Light were probably due to a real variation in the intensity of the
+phenomenon rather than to the elevated position of the observer.[269] He
+says that he was "astonished in the tropical climates of South America, to
+observe the variable intensity of the light."
+
+
+
+
+CHAPTER XIV
+
+The Stars
+
+
+Pliny says that Hipparchus "ventured to count the stars, a work arduous
+even for the Deity." But this was quite a mistaken idea. Those visible to
+the naked eye are comparatively few in number, and the enumeration of
+those visible in an opera-glass--which of course far exceed those which
+can be seen by unaided vision--is a matter of no great difficulty. Those
+visible in a small telescope of 2¾ inches aperture have all been observed
+and catalogued; and even those shown on photographs taken with large
+telescopes can be easily counted. The present writer has made an attempt
+in this direction, and taking an average of a large number of counts in
+various parts of the sky, as shown on stellar photographs, he finds a
+total of about 64 millions for the whole sky in both hemispheres.[270]
+Probably the total number will not exceed 100 millions. But this is a
+comparatively small number, even when compared with the human population
+of our little globe.
+
+With reference to the charts made by photography in the International
+scheme commenced some years ago, it has now been estimated that the charts
+will probably contain a total of about 9,854,000 stars down to about the
+14th magnitude (13·7). The "catalogue plates" (taken with a shorter
+exposure) will, it is expected, include about 2,676,500 stars down to 11½
+magnitude. These numbers may, however, be somewhat increased when the work
+has been completed.[271] If this estimate proves to be correct, the number
+of stars visible down to the 14th magnitude will be considerably less than
+former estimates have made it.
+
+Prof. E. C. Pickering estimates that the total number of stars visible on
+photographs down to the 16th magnitude (about the faintest visible in the
+great Lick telescope) will be about 50 millions.[272] In the present
+writer's enumeration, above referred to, many stars fainter than the 16th
+magnitude were included.
+
+Admiral Smyth says, with reference to Sir William Herschel--perhaps the
+greatest observer that ever lived--"As to Sir William himself, he could
+unhesitatingly call every star down to the 6th magnitude, by its name,
+letter, or number."[273] This shows great powers of observation, and a
+wonderful memory.
+
+On a photographic plate of the Pleiades taken with the Bruce telescope and
+an exposure of 6 hours, Prof. Bailey of Harvard has counted "3972 stars
+within an area 2° square, having Alcyone at its centre."[274] This would
+give a total of about 41 millions for the whole sky, if of the same
+richness.
+
+With an exposure of 16 hours, Prof. H. C. Wilson finds on an area of less
+that 110' square a total of 4621 stars. He thinks, "That all of these
+stars belong to the Pleiades group is not at all probable. The great
+majority of them probably lie at immense distances beyond the group, and
+simply appear in it by projection."[274] He adds, "It has been found,
+however, by very careful measurements made during the last 75 years at the
+Königsbergh and Yale Observatories, that of the sixty-nine brighter stars,
+including those down to the 9th magnitude, only eight show any certain
+movement with reference to Alcyone. Since Alcyone has a proper motion or
+drift of 6" per century, this means that all the brightest stars except
+the eight mentioned are drifting with Alcyone and so form a true cluster,
+at approximately the same distance from the earth. Six of the eight stars
+which show relative drift are moving in the opposite direction to the
+movement of Alcyone, and at nearly the same rate, so that their motion is
+only apparent. They are really stationary, while Alcyone and the rest of
+the cluster are moving past them."[275] This tends to show that the faint
+stars are really _behind_ the cluster, and are unconnected with it.
+
+It is a popular idea with some people that the Pole Star is the nearest of
+all the stars to the celestial pole. But photographs show that there are
+many faint stars nearer to the pole than the Pole Star. The Pole Star is
+at present at a distance of 1° 13' from the real pole of the heavens, but
+it is slowly approaching it. The minimum distance will be reached in the
+year 2104. From photographs taken by M. Flammarion at the Juvisy
+Observatory, he finds that there are at least 128 stars nearer to the pole
+than the Pole Star! The nearest star to the pole was, in the year 1902, a
+small star of about 12½ magnitude, which was distant about 4 minutes of
+arc from the pole.[276] The estimated magnitude shows that the Pole Star
+is nearly 10,000 times brighter than this faint star!
+
+It has been found that Sirius is bright enough to cast a shadow under
+favourable conditions. On March 22, 1903, the distinguished French
+astronomer Touchet succeeded in photographing the shadow of a brooch cast
+by this brilliant star. The exposure was 1{h} 5{m}.
+
+Martinus Hortensius seems to have been the first to see stars in daylight,
+perhaps early in the seventeenth century. He mentions the fact in a letter
+to Gassendi dated October 12, 1636, but does not give the date of his
+observation. Schickard saw Arcturus in broad daylight early in 1632. Morin
+saw the same bright star half an hour after sunset in March, 1635.
+
+Some interesting observations were made by Professors Payne and H. C.
+Wilson, in the summer of 1904, at Midvale, Montana (U.S.A.), at a height
+of 4790 feet above sea-level. At this height they found the air very clear
+and transparent. "Many more stars were visible at a glance, and the
+familiar stars appeared more brilliant.... In the great bright cloud of
+the Milky Way, between β and γ Cygni, one could count easily sixteen or
+seventeen stars, besides the bright ones η and χ,[277] while at Northfield
+it is difficult to distinctly see eight or nine with the naked eye." Some
+nebulæ and star fields were photographed with good results by the aid of a
+2½-inch Darlot lens and 3 hours' exposure.[278]
+
+Prof. Barnard has taken some good stellar photographs with a lens of only
+1½ inches in diameter, and 4 or 5 inches focus belonging to an
+ordinary "magic lantern"! He says that these "photographs with the small
+lens show us in the most striking manner how the most valuable and
+important information may be obtained with the simplest means."[279]
+
+With reference to the rising and setting of the stars due to the earth's
+rotation on its axis, the late Sir George B. Airy, Astronomer Royal of
+England, once said to a schoolmaster, "I should like to know how far your
+pupils go into the first practical points for which reading is scarcely
+necessary. Do they know that the stars rise and set? Very few people in
+England know it. I once had a correspondence with a literary man of the
+highest rank on a point of Greek astronomy, and found that he did not know
+it!"[280]
+
+Admiral Smyth says, "I have been struck with the beautiful blue tint of
+the smallest stars visible in my telescope. This, however, may be
+attributed to some optical peculiarity." This bluish colour of small stars
+agrees with the conclusion arrived at by Prof. Pickering in recent years,
+that the majority of faint stars in the Milky Way have spectra of the
+Sirian type and, like that brilliant star, are of a bluish white colour.
+Sir William Herschel saw many stars of a redder tinge than other observers
+have noticed. Admiral Smyth says, "This may be owing to the effect of his
+metallic mirror or to some peculiarity of vision, or perhaps both."[281]
+
+The ancient astronomers do not mention any coloured stars except white and
+red. Among the latter they only speak of Arcturus, Aldebaran, Pollux,
+Antares, and Betelgeuse as of a striking red colour. To these Al-Sufi adds
+Alphard (α Hydræ).
+
+Sir William Herschel remarked that no decidedly green or blue star "has
+ever been noticed unassociated with a companion brighter than itself." An
+exception to Herschel's rule seems to be found in the case of the star β
+Libræ, which Admiral Smyth called "pale emerald." Mr. George Knott
+observed it on May 19, 1852, as "beautiful pale green" (3·7 inches
+achromatic, power 80), and on May 9, 1872, as "fine pale green" (5·5
+inches achromatic, power 65).
+
+The motion of stars in the line of sight, as shown by the
+spectroscope--should theoretically alter their brightness in the course of
+time; those approaching the earth becoming gradually brighter, while those
+receding should become fainter. But the distance of the stars is so
+enormous that even with very high velocities the change would not become
+perceptible for ages. Prof. Oudemans found that to change the brightness
+of a star by only one-tenth of a magnitude--a quantity barely perceptible
+to the eye-a number of years would be necessary, which is represented by
+the formula
+
+      5916 years
+  -----------------
+  parallax × motion
+
+for a star approaching the earth, and for a receding star
+
+  6195 years
+  ----------
+    p × m
+
+This is in geographical miles, 1 geographical mile being equal to 4·61
+English miles.
+
+Reducing the above to English miles, and taking an average for both
+approaching and receding stars, we have
+
+  27,660 years
+  ------------
+     p × m
+
+where p = parallax in seconds of arc, and m = radial velocity in English
+miles per second.
+
+Prof. Oudemans found that the only star which could have changed in
+brightness by one-tenth of a magnitude since the time of Hipparchus is
+Aldebaran. This is taking its parallax as 0"·52. But assuming the more
+reliable parallax 0"·12 found by Dr. Elkin, this period is 4⅓ times
+longer. For Procyon, the period would be 5500 years.[282] The above
+calculation shows how absurd it is to suppose that any star could have
+gained or lost in brightness by motion in the line of sight during
+historical times. The "secular variation" of stars is quite another
+thing. This is due to physical changes in the stars themselves.
+
+The famous astronomer Halley, the second Astronomer Royal at Greenwich,
+says (_Phil. Trans._, 1796), "Supposing the number of 1st magnitude stars
+to be 13, at twice the distance from the sun there may be placed four
+times as many, or 52; which with the same allowance would nearly represent
+the star we find to be of the 2nd magnitude. So 9 × 13, or 117, for those
+at three times the distance; and at ten times the distance 100 × 13, or
+1300 stars; of which distance may probably diminish the light of any of
+the stars of the 1st magnitude to that of the 6th, it being but the
+hundredth part of what, at their present distance, they appear with." This
+agrees with the now generally accepted "light ratio" of 2·512 for each
+magnitude, which makes a first magnitude star 100 times the light of a 6th
+magnitude.
+
+On the 4th of March, 1796,[283] the famous French astronomer Lalande
+observed on the meridian a star of small 6th magnitude, the exact position
+of which he determined. On the 15th of the same month he again observed
+the star, and the places found for 1800 refer to numbers 16292-3 of the
+reduced catalogue. In the observation of March 4 he attached the curious
+remark, "Étoile singulière" (the observation of March 15 is without
+note). This remark of Lalande has puzzled observers who failed to find any
+peculiarity about the star. Indeed, "the remark is a strange one for the
+observer of so many thousands of stars to attach unless there was really
+something singular in the star's aspect at the time." On the evening of
+April 18, 1887, the star was examined by the present writer, and the
+following is the record in his observing book, "Lalande's étoile
+singulière (16292-3) about half a magnitude less than η Cancri. With the
+binocular I see two streams of small stars branching out from it, north
+preceding like the tails of comet." This may perhaps have something to do
+with Lalande's curious remark.
+
+The star numbered 1647 in Baily's _Flamsteed Catalogue_ is now known to
+have been an observation of the planet Uranus.[284]
+
+Prof. Pickering states that the fainter stars photographed with the 8-inch
+telescope at Cambridge (U.S.A.) are invisible to the eye in the 15-inch
+telescope.[285]
+
+Sir Norman Lockyer finds that the lines of sulphur are present in the
+spectrum of the bright star Rigel (β Orionis).[286]
+
+About 8½° south of the bright star Regulus (α Leonis) is a faint nebula
+(H I, 4 Sextantis). On or near this spot the Capuchin monk De Rheita
+fancied he saw, in the year 1643, a group of stars representing the
+napkin of S. Veronica--"sudarium Veronicæ sive faciem Domini maxima
+similitudina in astris expressum." And he gave a picture of the napkin and
+star group. But all subsequent observers have failed to find any trace of
+the star group referred to by De Rheita![287]
+
+The Bible story of the star of the Magi is also told in connection with
+the birth of the sun-gods Osiris, Horus, Mithra, Serapis, etc.[288] The
+present writer has also heard it suggested that the phenomenon may have
+been an apparition of Halley's comet! But as this famous comet is known to
+have appeared in the year B.C. 11, and as the date of the Nativity was
+probably not earlier than B.C. 5, the hypothesis seems for this (and other
+reasons) to be inadmissible. It has also been suggested that the
+phenomenon might have been an appearance of Tycho Brahé's temporary star
+of 1572, known as the "Pilgrim star"; but there seems to be no real
+foundation for such an hypothesis. There is no reason to think that
+"temporary" or new stars ever appear a second time.
+
+Admiral Smyth has well said, "It checks one's pride to recollect that if
+our sun with the whole system of planets, asteroids, and moons, and comets
+were to be removed from the spectator to the distance of the nearest
+fixed star, not one of them would be visible, except the sun, which would
+then appear but as a star of perhaps the 2nd magnitude. Nay, more, were
+the whole system of which our globe forms an insignificant member, with
+its central luminary, suddenly annihilated, no effect would be produced on
+those unconnected and remote bodies; and the only annunciation of such a
+catastrophe in the Sidereal "Times" would be that a small star once seen
+in a distant quarter of the sky had ceased to shine."[289]
+
+Prof. George C. Comstock finds that the average parallax of 67 selected
+stars ranging in brightness between the 9th and the 12th magnitude, is of
+the value of 0"·0051.[290] This gives a distance representing a journey
+for light of about 639 years!
+
+Mr. Henry Norris Russell thinks that nearly all the bright stars in the
+constellation of Orion are practically at the same distance from the
+earth. His reasons for this opinion are: (1) the stars are similar in
+their spectra and proper motions, (2) their proper motions are small,
+which suggests a small parallax, and therefore a great distance from the
+earth. Mr. Russell thinks that the average parallax of these stars may
+perhaps be 0"·005, which gives a distance of about 650 "light
+years."[291]
+
+According to Sir Norman Lockyer's classification of the stars, the order
+of _increasing_ temperature is represented by the following, beginning
+with those in the earliest stage of stellar evolution:--Nebulæ, Antares,
+Aldebaran, Polaris, α Cygni, Rigel, ε Tauri, β Crucis. Then we have the
+hottest stars represented by ε Puppis, γ Argus, and Alnitam (ε Orionis).
+_Decreasing_ temperature is represented by (in order), Achernar, Algol,
+Markab, Sirius, Procyon, Arcturus, 19 Piscium, and the "Dark Stars."[292]
+But other astronomers do not agree with this classification. Antares and
+Aldebaran are by some authorities considered to be _cooling_ suns.
+
+According to Ritter's views of the Constitution of the Celestial Bodies,
+if we "divide the stars into three classes according to age corresponding
+to these three stages of development, we shall assign to the first class,
+A, those stars still in the nebular phase of development; to the second
+class, B, those in the transient stage of greatest brilliancy; and to the
+class C, those stars which have already entered into the long period of
+slow extinction. It should be noted in this classification that we refer
+to relative and not absolute age, since a star of slight mass passes
+through the successive phases of its development more rapidly than the
+star of greater mass."[293] Ritter comes to the conclusion that "the
+duration of the period in which the sun as a star had a greater brightness
+than at present was very short in comparison with the period in which it
+had and will continue to have a brightness differing only slightly from
+its present value."[294]
+
+In a valuable and interesting paper on "The Evolution of Solar
+Stars,"[295] Prof. Schuster says that "measurements by E. F. Nichols on
+the heat of Vega and Arcturus indicated a lower temperature for Arcturus,
+and confirms the conclusion arrived at on other grounds, that the hydrogen
+stars have a higher temperature than the solar stars." "An inspection of
+the ultraviolet region of the spectrum gives the same result. These
+different lines of argument, all leading to the same result, justify us in
+saying that the surface temperature of the hydrogen stars is higher than
+that of the solar stars. An extension of the same reasoning leads to the
+belief that the helium stars have a temperature which is higher still."
+Hence we have Schuster, Hale, and Sir William Huggins in agreement that
+the Sirian stars are hotter than the solar stars; and personally I agree
+with these high authorities. The late Dr. W. E. Wilson, however, held the
+opinion that the sun is hotter that Sirius!
+
+Schuster thinks that Lane's law does not apply to the temperature of the
+photosphere and the absorbing layers of the sun and stars, but only to the
+portions between the photosphere and the centre, which probably act like a
+perfect gas. On this view he says the interior might become "hotter and
+hotter until the condensation had reached a point at which the laws of
+gaseous condensation no longer hold."
+
+With reference to the stars having spectra of the 3rd and 4th type
+(usually orange and red in colour), Schuster says--
+
+    "The remaining types of spectra belong to lower temperature still, as
+    in place of metallic lines, or in addition to them, certain bands
+    appear which experiments show us invariably belong to lower
+    temperature than the lines of the same element.
+
+    "If an evolutionary process has been going on, which is similar for
+    all stars, there is little doubt that from the bright-line stars down
+    to the solar stars the order has been (1) helium or _Orion_ stars, (2)
+    hydrogen or Sirian stars, (3) calcium or Procyon stars, (4) solar or
+    Capellan stars."
+
+My investigations on "The Secular Variation of Starlight" (_Studies in
+Astronomy_, chap. 17, and _Astronomical Essays_, chap. 12) based on a
+comparison of Al-Sufi's star magnitudes (tenth century) with modern
+estimates and measures, tend strongly to confirm the above views.
+
+With regard to the 3rd-type stars, such as Betelgeuse and Mira Ceti,
+Schuster says, "It has been already mentioned that observers differ as to
+whether their position is anterior to the hydrogen or posterior to the
+solar stars, and there are valid arguments on both sides."
+
+Scheiner, however, shows, from the behaviour of the lines of magnesium,
+that stars of type I. (Sirian) are the hottest, and type III. the coolest,
+and he says, we have "for the first time a direct proof of the correctness
+of the physical interpretation of Vogel's spectral classes, according to
+which class II. is developed by cooling from I., and III. by a further
+process of cooling from II."[296]
+
+Prof. Hale says that "the resemblance between the spectra of sun-spots and
+of 3rd-type stars is so close as to indicate that the same cause is
+controlling the relative intensities of many lines in both instances. This
+cause, as the laboratory work indicates, is to be regarded as reduced
+temperature."[297]
+
+According to Prof. Schuster, "a spectrum of bright lines may be given by a
+mass of luminous gas, even if the gas is of great thickness. There is,
+therefore, no difficulty in explaining the existence of stars giving
+bright lines." He thinks that the difference between "bright line" stars
+and those showing dark lines depends upon the rate of increase of the
+temperature from the surface towards the centre. If this rate is slow,
+bright lines will be seen. If the rate of increase is rapid, the
+dark-line spectrum shown by the majority of the stars will appear. This
+rate, he thinks, is regulated by the gravitational force. So that in the
+early stages of condensation bright lines are more likely to occur. "If
+the light is not fully absorbed," both bright and dark lines of the same
+element may be visible in the same star. Schuster considers it quite
+possible that if we could remove the outer layers of the Sun's atmosphere,
+we should obtain a spectrum of bright lines.[298]
+
+M. Stratonoff finds that stars having spectra of the Orion and Sirian
+types--supposed to represent an early stage in stellar evolution--tend to
+congregate in or near the Milky Way. Star clusters in general show a
+similar tendency, "but to this law the globular clusters form an
+exception."[299] We may add that the spiral nebulæ--which seem to be
+scattered indifferently over all parts of the sky--also seem to form an
+exception; for the spectra of these wonderful objects seem to show that
+they are really star clusters, in which the components are probably
+relatively small; that is, small in comparison with our sun.
+
+If we accept the hypothesis that suns and systems were evolved from
+nebulæ, and if we consider the comparatively small number of nebulæ
+hitherto discovered in the largest telescopes--about half a million; and
+if we further consider the very small number of red stars, or those having
+spectra of the third and fourth types--usually considered to be dying-out
+suns--we seem led to the conclusion that our sidereal system is now at
+about the zenith of its life-history; comparatively few nebulæ being left
+to consolidate into stars, and comparatively few stars having gone far on
+the road to the final extinction of their light.
+
+Prof. Boss of Albany (U.S.A.) finds that about forty stars of magnitudes
+from 3½ to 7 in the constellation Taurus are apparently drifting
+together towards one point. These stars are included between about R.A.
+3{h} 47{m} to 5{h} 4{m}, and Declination + 5° to + 23° (that is, in the
+region surrounding the Hyades). These motions apparently converge to a
+point near R.A. 6{h}, Declination + 7° (near Betelgeuse). Prof. Boss has
+computed the velocity of the stars in this group to be 45·6 kilometres
+(about 28 miles) a second towards the "vanishing point," and he estimated
+the average parallax of the group to be 0"·025--about 130 years' journey
+for light. Although the motions are apparently converging to a point, it
+does not follow that the stars in question will, in the course of ages,
+meet at the "vanishing point." On the contrary, the observed motions show
+that the stars are moving in parallel lines through space. About 15
+kilometres of the observed speed is due to the sun's motion through space
+in the opposite direction. Prof. Campbell finds from spectroscopic
+measures that of these forty stars, nine are receding from the earth with
+velocities varying from 12 to 60 kilometres a second, and twenty-three
+others with less velocities than 38 kilometres.[300] It will be obvious
+that, as there is a "vanishing point," the motion in the line of sight
+must be one of _recession_ from the earth.
+
+It has been found that on an average the parallax of a star is about
+one-seventh of its "proper motion."[301]
+
+Adopting Prof. Newcomb's parallax of 0"·14 for the famous star 1830
+Groombridge, the velocity perpendicular to the line of sight is about 150
+miles a second. The velocity _in_ the line of sight--as shown by the
+spectroscope--is 59 miles a second approaching the earth. Compounding
+these two velocities we find a velocity through space of about 161 miles a
+second!
+
+An eminent American writer puts into the mouth of one of his characters, a
+young astronomer, the following:--
+
+                          "I read the page
+  Where every letter is a glittering sun."
+
+From an examination of the heat radiated by some bright stars, made by
+Dr. E. F. Nicholls in America with a very sensitive radiometer of his own
+construction, he finds that "we do not receive from Arcturus more heat
+than we should from a candle at a distance of 5 or 6 miles."
+
+With reference to the progressive motion of light, and the different times
+taken by light to reach the earth from different stars, Humboldt says,
+"The aspect of the starry heavens presents to us objects of _unequal
+date_. Much has long ceased to exist before the knowledge of its presence
+reaches us; much has been otherwise arranged."[302]
+
+The photographic method of charting the stars, although a great
+improvement on the old system, seems to have its disadvantages. One of
+these is that the star images are liable to disappear from the plates in
+the course of time. The reduction of stellar photograph plates should,
+therefore, be carried out as soon as possible after they are taken. The
+late Dr. Roberts found that on a plate originally containing 364 stars, no
+less than 130 had completely disappeared in 9¼ years!
+
+It has been assumed by some writers on astronomy that the faint stars
+visible on photographs of the Pleiades are at practically the same
+distance from the earth as the brighter stars of the cluster, and that
+consequently there must be an enormous difference in actual size between
+the brighter and fainter stars. But there is really no warrant for any
+such assumption. Photographs of the vicinity show that the sky all round
+the Pleiades is equally rich in faint stars. It seems, therefore, more
+reasonable to suppose that most of the faint stars visible in the Pleiades
+are really far behind the cluster in space. For if _all_ the faint stars
+visible on photographs belonged to the cluster, then if we imagine the
+cluster removed, a "hole" would be left in the sky, which is of course
+utterly improbable, and indeed absurd. An examination of the proper
+motions tends to confirm this view of the matter, and indicates that the
+Pleiades cluster is a comparatively small one and simply projected on a
+background of fainter stars.
+
+It has long been suspected that the famous star 61 Cygni, which is a
+double star, forms a binary system--that is, that the two stars composing
+it revolve round their common centre of gravity and move together through
+space. But measures of parallax made by Herman S. Davis and Wilsing seem
+to show a difference of parallax between the two components of about 0·08
+of a second of arc. This difference of parallax implies a distance of
+about 2¼ "light years" between the two stars, and "if this is correct,
+the stars are too remote to form a binary system. The proper motions of
+5"·21 and 5"·15 seem to show that they are moving in nearly parallel
+directions; but are probably slowly separating." Mr. Lewis, however,
+thinks that a physical connection probably exists.[303]
+
+Dante speaks of the four bright stars of the Southern Cross as
+emblematical of the four cardinal virtues, Justice, Temperance, Fortitude,
+and Prudence; and he seems to refer to the stars Canopus, Achernar, and
+Foomalhaut under the symbols of Faith, Hope, and Charity. The so-called
+"False Cross" is said to be formed by the stars κ, δ, ε, and ι of the
+constellation Argo Navis. But it seems to me that a better (although
+larger) cross is formed by the stars α Centauri and α, β, and γ of
+Triangulum Australis.
+
+Mr. Monck has pointed out that the names of the brightest stars seem to be
+arranged alphabetically in order of colour, beginning with red and ending
+with blue. Thus we have Aldebaran, Arcturus, Betelgeuse, Capella, Procyon,
+Regulus, Rigel, Sirius, Spica and Vega. But as the origin of these names
+is different, this must be merely a curious coincidence.[304] And, to my
+eye at least, Betelgeuse is redder than Arcturus.
+
+The poet Longfellow speaks of the--
+
+  "Stars, the thoughts of God in the heavens,"[305]
+
+and Drayton says--
+
+  "The stars to me an everlasting book
+  In that eternal register, the sky."[306]
+
+Observing at a height of 12,540 feet on the Andes, the late Dr. Copeland
+saw Sirius with the naked eye less than 10 minutes before sunset.[307] He
+also saw Jupiter 3{m} 47{s} before sunset; and the following bright
+stars--Canopus, 0{m} 52{s} before sunset; Rigel (β Orionis) 16{m} 32{s}
+after sunset; and Procyon 11{m} 28{s} after sunset. From a height of
+12,050 feet at La Paz, Bolivia, he saw with the naked eye in February,
+1883, ten stars in the Pleiades in full moonlight, and seventeen stars in
+the Hyades. He also saw σ Tauri double.[308]
+
+Humboldt says, "In whatever point the vault of heaven has been pierced by
+powerful and far-penetrating telescopic instruments, stars or luminous
+nebulæ are everywhere discoverable, the former in some cases not exceeding
+the 20th or 24th degree of telescopic magnitude."[309] But this is a
+mistake. No star of even the 20th magnitude has ever been seen by any
+telescope. Even on the best photographic plates it is doubtful that any
+stars much below the 18th magnitude are visible. To show a star of the
+20th magnitude--if such stars exist--would require a telescope of 144
+inches or 12 feet in aperture. To show a star of the 24th magnitude--if
+such there be--an aperture of 33 feet would be necessary![310]
+
+It is a popular idea that stars may be seen in the daytime from the bottom
+of a deep pit or high chimney. But this has often been denied. Humboldt
+says, "While practically engaged in mining operations, I was in the habit,
+during many years, of passing a great portion of the day in mines where I
+could see the sky through deep shafts, yet I never was able to observe a
+star."[311]
+
+Stars may, however, be seen in the daytime with even small telescopes. It
+is said that a telescope of 1 inch aperture will show stars of the 2nd
+magnitude; 2 inches, stars of the 3rd magnitude; and 4 inches, stars of
+the 4th magnitude. But I cannot confirm this from personal observation. It
+may be so, but I have not tried the experiment.
+
+Sir George Darwin says--
+
+    "Human life is too short to permit us to watch the leisurely procedure
+    of cosmical evolution, but the celestial museum contains so many
+    exhibits that it may become possible, by the aid of theory, to piece
+    together, bit by bit, the processes through which stars pass in the
+    course of their evolutions."[312]
+
+The so-called "telluric lines" seen in the solar spectrum, are due to
+water vapour in the earth's atmosphere. As the light of the stars also
+passes through the atmosphere, it is evident that these lines should also
+be visible in the spectra of the stars. This is found to be the case by
+Prof. Campbell, Director of the Lick Observatory, who has observed all the
+principal bands in the spectrum of every star he has examined.[313]
+
+The largest "proper motion" now known is that of a star of the 8½
+magnitude in the southern hemisphere, known as Cordoba Zone V. No. 243.
+Its proper motion is 8·07 seconds of arc per annum, thus exceeding that of
+the famous "runaway star," 1830 Groombridge, which has a proper motion of
+7·05 seconds per annum. This greater motion is, however, only apparent.
+Measures of parallax show that the southern "runaway" is much nearer to us
+than its northern rival, its parallax being 0"·32, while that of
+Groombridge 1830 is only 0"·14. With these data the actual velocity across
+the line of sight can be easily computed. That of the southern star comes
+out 80 miles a second, while that of Groombridge 1830 is 148 miles a
+second. The actual velocity of Arcturus is probably still greater.
+
+The poet Barton has well said--
+
+  "The stars! the stars! go forth at night,
+    Lift up thine eyes on high,
+  And view the countless orbs of light,
+    Which gem the midnight sky.
+  Go forth in silence and alone,
+    This glorious sight to scan,
+  And bid the humbled spirit own
+    The littleness of man."
+
+
+
+
+CHAPTER XV
+
+Double and Binary Stars
+
+
+Prof. R. G. Aitken, the eminent American observer of double stars, finds
+that of all the stars down to the 9th magnitude--about the faintest
+visible in a powerful binocular field-glass--1 in 18, or 1 in 20, on the
+average, are double, with the component stars less than 5 seconds of arc
+apart. This proportion of double stars is not, however, the same for all
+parts of the sky; while in some regions double stars are very scarce, in
+other places the proportion rises to 1 in 8.
+
+For the well-known binary star Castor (α Geminorum), several orbits have
+been computed with periods ranging from 232 years (Mädler) to 1001 years
+(Doberck). But Burnham finds that "the orbit is absolutely indeterminate
+at this time, and likely to remain so for another century or longer."[314]
+Both components are spectroscopic binaries, and the system is a most
+interesting one.
+
+The well-known companion of Sirius became invisible in all telescopes in
+the year 1890, owing to its near approach to its brilliant primary. It
+remained invisible until August 20, 1896, when it was again seen by Dr.
+See at the Lowell Observatory.[315] Since then its distance has been
+increasing, and it has been regularly measured. The maximum distance will
+be attained about the year 1922.
+
+The star β Cephei has recently been discovered to be a spectroscopic
+binary with the wonderfully short period of 4{h} 34{m} 11{s}. The orbital
+velocity is about 10½ miles a second, and as this velocity is not very
+great, the distance between the components must be very small, and
+possibly the two component bodies are revolving in actual contact. The
+spectrum is of the "Orion type."[316]
+
+According to Slipher the spectroscopic binary γ Geminorum has the
+comparatively long period (for a spectroscopic binary) of about 3½
+years. This period is comparable with that of the telescopic binary
+system, δ Equulei (period about 5·7 years). The orbit is quite eccentric.
+I have shown elsewhere[317] that γ Geminorum has probably increased in
+brightness since the time of Al-Sufi (tenth century). Possibly its
+spectroscopic duplicity may have something to do with the variation in its
+light.
+
+With reference to the spectra of double stars, Mr. Maunder suggests that
+the fact of the companion of a binary star showing a Sirian spectrum while
+the brighter star has a solar spectrum may be explained by supposing that,
+on the theory of fission, "the smaller body when thrown off consisted of
+the lighter elements, the heavier remaining in the principal star. In
+other words, in these cases spectral type depends upon original chemical
+constitution, and not upon the stage of stellar development
+attained."[318]
+
+A curious paradox with reference to binary stars has recently come to
+light. For many years it was almost taken for granted that the brighter
+star of a pair had a larger mass than the fainter component. This was a
+natural conclusion, as both stars are practically at the same distance
+from the earth. But it has been recently found that in some binary stars
+the fainter component has actually the larger mass! Thus, in the binary
+star ε Hydræ, the "magnitude" of the component stars are 3 and 6,
+indicating that the brighter star is about 16 times brighter than the
+fainter component. Yet calculations by Lewis show that the fainter star
+has 6 times the mass of the brighter, that is, contains 6 times the
+quantity of matter! In the well-known binary 70 Ophiuchi, Prey finds that
+the fainter star has about 4 times the mass of the brighter! In 85
+Pegasi, the brighter star is about 40 times brighter than its companion,
+while Furner finds that the mass of the fainter star is about 4 times that
+of the brighter! And there are other similar cases. In fact, in these
+remarkable combinations of suns the fainter star is really the "primary,"
+and is, so far as mass is concerned, "the predominant partner." This is a
+curious anomaly, and cannot be well explained in the present state of our
+knowledge of stellar systems. In the case of α Centauri the masses of the
+components are about equal, while the primary star is about 3 times
+brighter than the other. But here the discrepancy is satisfactorily
+explained by the difference in character of the spectra, the brighter
+component having a spectrum of the solar type, while the fainter seems
+further advanced on the downward road of evolution, that is, more
+consolidated and having, perhaps, less intrinsic brightness of surface.
+
+In the case of Sirius and its faint attendant, the mass of the bright star
+is about twice the mass of the satellite, while its light is about 40,000
+times greater! Here the satellite is either a cooled-down sun or perhaps a
+gaseous nebula. There seems to be no other explanation of this curious
+paradox. The same remark applies to Procyon, where the bright star is
+about 100,000 times brighter than its faint companion, although its mass
+is only 5 times greater.
+
+The bright star Capella forms a curious anomaly or paradox. Spectroscopic
+observations show that it is a very close binary pair. It has been seen
+"elongated" at the Greenwich Observatory with the great 28-inch
+refractor--the work of Sir Howard Grubb--and the spectroscopic and visual
+measurements agree in indicating that its mass is about 18 times the mass
+of the sun. But its parallax (about 0"·08) shows that it is about 128
+times brighter than the sun! This great brilliancy is inconsistent with
+the star's computed mass, which would indicate a much smaller brightness.
+The sun placed at the distance of Capella would, I find, shine as a star
+of about 5½ magnitude, while Capella is one of the brightest stars in
+the sky. As the spectrum of Capella's light closely resembles the solar
+spectrum, we seem justified in assuming that the two bodies have pretty
+much the same physical composition. The discrepancy between the computed
+and actual brightness of the star cannot be explained satisfactorily, and
+the star remains an astronomical enigma.
+
+Three remarkable double-star systems have been discovered by Dr. See in
+the southern hemisphere. The first of these is the bright star α Phœnicis,
+of which the magnitude is 2·4, or only very slightly fainter than the Pole
+Star. It is attended by a faint star of the 13th magnitude at a distance
+of less than 10 seconds (1897). The bright star is of a deep orange or
+reddish colour, and the great difference in brightness between the
+component stars "renders the system both striking and difficult." The
+second is μ Velorum, a star of the 3rd magnitude, which has a companion of
+the 11th magnitude, and only 2½" from its bright primary (1897). Dr.
+See describes this pair as "one of the most extraordinary in the heavens."
+The third is η Centauri, of 2½ magnitude, with a companion of 13½
+magnitude at a distance of 5"·65 (1897); colours yellow and purple. This
+pair is "extremely difficult, requiring a powerful telescope to see it."
+Dr. See thinks that these three objects "may be regarded as amongst the
+most splendid in the heavens."
+
+The following notes are from Burnham's recently published _General
+Catalogue of Double Stars_.
+
+The Pole Star has a well-known companion of about the 9th magnitude, which
+is a favourite object for small telescopes. Burnham finds that the bright
+star and its faint companion are "relatively fixed," and are probably only
+an "optical pair." Some other companions have been suspected by amateur
+observers, but Burnham finds that "there is nothing nearer" than the known
+companion within the reach of the great 36-inch telescope of the Lick
+Observatory (_Cat._, p. 299).
+
+The well-known companion to the bright star Rigel (β Orionis) has been
+suspected for many years to be a close double star. Burnham concludes that
+it is really a binary star, and its "period may be shorter than that of
+any known pair" (_Cat._, p. 411).
+
+Burnham finds that the four brighter stars in the trapezium in the great
+Orion nebula (in the "sword") are relatively fixed (_Cat._, p. 426).
+
+γ Leonis. This double star was for many years considered to be a binary,
+but Burnham has shown that all the measures may be satisfactorily
+represented by a straight line, and that consequently the pair merely
+forms an "optical double."
+
+42 Comæ Berenices. This is a binary star of which the orbit plane passes
+nearly through the earth. The period is about 25½ years, and Burnham
+says the orbit "is as accurately known as that of any known binary."
+
+σ Coronæ Borealis. Burnham says that the orbits hitherto computed--with
+periods ranging from 195 years (Jacob) to 846 years (Doberck) are "mere
+guess work," and it will require the measures of at least another century,
+and perhaps a much longer time, to give an approximate period (_Cat._, p.
+209). So here is some work left for posterity to do in this field.
+
+70 Ophiuchi. With reference to this well-known binary star, Burnham says,
+"the elements of the orbit are very accurately known." The periods
+computed range from 86·66 years (Doolittle) to 98·15 years (Powell). The
+present writer found a period of 87·84 years, which cannot be far from the
+truth. Burnham found 87·75 years (_Cat._, p. 774). In this case there is
+not much left for posterity to accomplish.
+
+61 Cygni. With reference to this famous star Burnham says, "So far the
+relative motion is practically rectilinear. If the companion is moving in
+a curved path, it will require the measures of at least another
+half-century to make this certain. The deviation of the measured positions
+during the last 70 years from a right line are less than the average
+errors of the observations."
+
+Burnham once saw a faint companion to Sirius of the 16th magnitude, and
+measured its position with reference to the bright star (280°·6: 40"·25:
+1899·86). But he afterwards found that it was "not a real object but a
+reflection from Sirius" (in the eye-piece). Such false images are called
+"ghosts."
+
+With reference to the well-known double (or rather quadruple) star ε Lyræ,
+near Vega, and supposed faint stars near it, Burnham says, "From time to
+time various small stars in the vicinity have been mapped, and much time
+wasted in looking for and speculating about objects which only exist in
+the imagination of the observer." He believes that many of these faint
+stars, supposed to have been seen by various observers, are merely "ghosts
+produced by reflection."
+
+The binary star ζ Boötis, which has long been suspected of small and
+irregular variation of light, showed remarkable spectral changes in the
+year 1905,[319] somewhat similar to those of a _nova_, or temporary star.
+It is curious that such changes should occur in a star having an ordinary
+Sirian type of spectrum!
+
+A curious quadruple system has been discovered by Mr. R. T. A. Innes in
+the southern hemisphere. The star κ Toucani is a binary star with
+components of magnitudes 5 and 7·7, and a period of revolution of perhaps
+about 1000 years. Within 6' of this pair is another star (Lacaille 353),
+which is also a binary, with a period of perhaps 72 years. Both pairs have
+the same proper motion through space, and evidently form a vast quadruple
+system; for which Mr. Innes finds a possible period of 300,000 years.[320]
+
+It is a curious fact that the performance of a really good refracting
+telescope actually exceeds what theory would indicate! at least so far as
+double stars are concerned. For example, the famous double-star observer
+Dawes found that the distance between the components of a double star
+which can just be divided, is found by dividing 4"·56 by the aperture of
+the object-glass in inches. Now theory gives 5"·52 divided by the
+aperture. "The actual telescope--if a really good one--thus exceeds its
+theoretical requirements. The difference between theory and practice in
+this case seems to be due to the fact that in the 'spurious' star disc
+shown by good telescopes, the illumination at the edges of the star disc
+is very feeble, so that its full size is not seen except in the case of a
+very bright star."[321]
+
+
+
+
+CHAPTER XVI
+
+Variable Stars
+
+
+In that interesting work _A Cycle of Celestial Objects_, Admiral Smyth
+says (p. 275), "Geminiano Montanari, as far back as 1670, was so struck
+with the celestial changes, that he projected a work to be intituled the
+_Instabilities of the Firmament_, hoping to show such alterations as would
+be sufficient to make even Aristotle--were he alive--reverse his opinion
+on the incorruptibility of the spangled sky: 'There are now wanting in the
+heavens,' said he, 'two stars of the 2nd magnitude in the stem and yard of
+the ship Argo. I and others observed them in the year 1664, upon occasion
+of the comet that appeared in that year. When they first disappeared I
+know not; only I am sure that on April 10, 1668, there was not the least
+glimpse of them to be seen.'" Smyth adds, "Startling as this account
+is--and I am even disposed to question the fact--it must be recollected
+that Montanari was a man of integrity, and well versed in the theory and
+practice of astronomy; and his account of the wonder will be found--in
+good set Latin--in page 2202 of the _Philosophical Transactions_ for
+1671."
+
+There must be, I think--as Smyth suggests--some mistake in Montanari's
+observations, for it is quite certain that of the stars mentioned by
+Ptolemy (second century A.D.) there is no star of the 2nd magnitude now
+missing. It is true that Al-Sufi (tenth century) mentions a star of the
+_third_ magnitude mentioned by Ptolemy in the constellation of the Centaur
+(about 2° east of the star ε Centauri) which he could not find. But this
+has nothing to do with Montanari's stars. Montanari's words are very
+clear. He says, "_Desunt in Cœlo duæ stellæ_ Secundæ Magnitudinis _in_
+Puppi Navis _ejusve Transtris_ Bayero β et γ, _prope_ Canem Majoris, _à me
+et aliis, occasione præsertim Cometæ_ A. 1664 _observatæ et recognitæ.
+Earum Disparitionem_ cui Anno debeam, non novi; _hoc indubium, quod à die_
+10 April, 1668, _ne_ vestigium quidem _illarum adesse amplius observe;
+cæteris circa eas etium quartæ et quintæ magnitudinis, immotis._" So the
+puzzle remains unsolved.
+
+Sir William Herschel thought that "of all stars which are singly visible,
+about one in thirty are undergoing an observable change."[322] Now taking
+the number of stars visible to the naked eye at 6000, this would give
+about 200 variable stars visible at maximum to the unaided vision. But
+this estimate seems too high. Taking all the stars visible in the largest
+telescopes--possibly about 100 millions--the proportion of variable stars
+will probably be much smaller still.
+
+The theory that the variation of light in the variable stars of the Algol
+type is due to a partial eclipse by a companion star (not necessarily a
+dark body) is now well established by the spectroscope, and is accepted by
+all astronomers. The late Miss Clarke has well said "to argue this point
+would be _enforcer une porte ouverte_."
+
+According to Dr. A. W. Roberts, the components of the following "Algol
+variables" "revolve in contact": V Puppis, X Carinæ, β Lyræ, and υ Pegasi.
+Of those V Puppis and β Lyræ are known spectroscopic binaries. The others
+are beyond the reach of the spectroscope, owing to their faintness.
+
+A very curious variable star of the Algol type is that known as R R
+Draconis. Its normal magnitude is 10, but at minimum it becomes invisible
+in a 7½-inch refracting telescope. The variation must, therefore, be
+over 3 magnitudes, that is, at minimum its light must be reduced to about
+one-sixteenth of its normal brightness. The period of variation from
+maximum to minimum is about 2·83 days. The variation of light near minimum
+is extraordinarily rapid, the light decreasing by about 1 magnitude in
+half an hour.[323]
+
+A very remarkable variable star has been recently discovered in the
+constellation Auriga. Prof. Hartwig found it of the 9th magnitude on March
+6, 1908, the star "having increased four magnitudes in one day, whilst
+within eight days it was less than the 14th magnitude."[324] In other
+words its light increased at least one-hundredfold in eight days!
+
+The period of the well-known variable star β Lyræ seems to be slowly
+increasing. This Dr. Roberts (of South Africa) considers to be due to the
+component stars slowly receding from each other. He finds that "a very
+slight increase of one-thousandth part of the radius of the orbit would
+account for the augmentation in time, 30{m} in a century." According to
+the theory of stellar evolution the lengthening of the period of
+revolution of a binary star would be due to the "drag" caused by the tides
+formed by each component on the other.[325]
+
+M. Sebastian Albrecht finds that in the short-period variable star known
+as T Vulpeculæ (and other variables of this class, such as Y Ophiuchi),
+there can be no eclipse to explain the variation of light (as in the case
+of Algol). The star is a spectroscopic binary, it is true, but the
+maximum of light coincides with the greatest velocity of _approach_ in
+the line of sight, and the minimum with the greatest velocity of
+_recession_. Thus the light curve and the spectroscopic velocity curve are
+very similar in shape, but one is like the other turned upside down. "That
+is, the two curves have a very close correspondence in phase in addition
+to correspondence of shape and period."[326]
+
+The star now known as W Ursæ Majoris (the variability of which was
+discovered by Müller and Kempf in 1902), and which lies between the stars
+θ and υ of that constellation, has the marvellously short period of 4
+hours (from maximum to maximum). Messrs. Jordan and Parkhurst (U.S.A.),
+find from photographic plates that the star varies from 7·24 to 8·17
+magnitude.[327] The light at maximum is, therefore, more than double the
+light at minimum. A sun which loses more than half its light and recovers
+it again in the short period of 4 hours is certainly a curious and
+wonderful object.
+
+In contrast with the above, the same astronomers have discovered a star in
+Perseus which seems to vary from about the 6th to the 7th magnitude in the
+very long period of 7½ years! It is now known as X Persei, and its
+position for 1900 is R.A. 3{h} 49{m} 8{s}, Dec. N. 30° 46', or about one
+degree south-east of the star ζ Persei. It seems to be a variable of the
+Algol type, as the star remained constant in light at about the 6th
+magnitude from 1887 to 1891. It then began to fade, and on December 1,
+1897, it was reduced to about the 7th magnitude.
+
+On the night of August 20, 1886, Prof. Colbert, of Chicago, noticed that
+the star ζ Cassiopeiæ increased in brightness "by quite half a magnitude,
+and about half an hour afterwards began to return to its normal
+magnitude."[328] This curious outburst of light in a star usually constant
+in brightness is (if true) a very unusual phenomenon. But a somewhat
+similar fluctuation of light is recorded by the famous German astronomer
+Heis. On September 26, 1850, he noted that the star "ζ Lyræ became, for a
+moment, _very bright_, and then again faint." (The words in his original
+observing book are: "ζ Lyræ wurde einen _Moment sehr hell_ und hierauf
+wieder dunkel.") As Heis was a remarkably accurate observer of star
+brightness, the above remark deserves the highest confidence.[329]
+
+The variable star known as the V Delphini was found to be invisible in the
+great 40-inch telescope of the Yerkes Observatory on July 20, 1900. Its
+magnitude was, therefore, below the 17th. At its maximum brightness it is
+about 7½, or easily visible in an ordinary opera-glass, so that its
+range of variation is nearly, or quite, ten magnitudes. That is, its light
+at maximum is about 10,000 times its light at minimum. That a sun should
+vary in light to this enormous extent is certainly a wonderful fact. A
+variable discovered by Ceraski (and numbered 7579 in Chandlers' Catalogue)
+"had passed below the limit of the 40-inch in June, 1900, and was,
+therefore, not brighter than 17 mag."[330]
+
+The late Sir C. E. Peck and his assistant, Mr. Grover, made many valuable
+observations of variable stars at the Rousden Observatory during many
+years past. Among other interesting things noted, Peck sometimes saw faint
+stars in the field of view of his telescope which were at other times
+invisible for many months, and he suggested that these are faint variable
+stars with a range of brightness from the 13th to the 20th magnitude. He
+adds, "Here there is a practically unemployed field for the largest
+telescopes." Considering the enormous number of faint stars visible on
+stellar photographs the number of undiscovered variable stars must be very
+large.
+
+Admiral Smyth describes a small star near β Leonis, about 5' distant, of
+about 8th magnitude, and dull red. In 1864 Mr. Knott measured a faint star
+close to Smyth's position, but estimated it only 11·6 magnitude. The
+Admiral's star would thereupon seem to be variable.[331]
+
+The famous variable star η Argus, which Sir John Herschel, when at the
+Cape of Good Hope in 1838, saw involved in dense nebulosity, was in April,
+1869, "seen on the bare sky," with the great Melbourne telescope, "the
+nebula having disappeared for some distance round it." Other changes were
+noticed in this remarkable nebula. The Melbourne observers saw "three
+times as many stars as were seen by Herschel." But of course their
+telescope is much larger--48 inches aperture, compared with Herschel's 20
+inches.
+
+Prof. E. C. Pickering thinks that the fluctuations of light of the
+well-known variable star R Coronæ (in the Northern Crown), "are unlike
+those of any known variable." This very curious object--one of the most
+curious in the heavens--sometimes remains for many months almost constant
+in brightness (just visible to the naked eye), and then rapidly fades in
+light by several magnitudes! Thus its changes of light in April and May,
+1905, were as follows:--
+
+  1905, April 1   6·0 magnitude
+          "  11   7·3     "
+          "  12   8·4     "
+         May  1  11·4     "
+          "   7  12·5     "
+
+Thus between April 1 and May 1, its light was reduced by over 5
+magnitudes. In other words, the light of the star on May 1 was reduced to
+less than one-hundredth of its light on April 1. If our sun were to
+behave in this way nearly all life would soon be destroyed on the face of
+the earth.
+
+M. H. E. Lau finds that the short-period variable star δ Cephei varies
+slightly in colour as well as in light, and that the colour curve is
+parallel to the light curve. Near the minimum of light the colour is
+reddish yellow, almost as red as ζ Cephei; a day later it is pure yellow,
+and of about the same colour as the neighbouring ε Cephei.[332] But it
+would not be easy to fully establish such slight variations of tint.
+
+A remarkably bright maximum of the famous variable Mira Ceti occurred in
+1906. In December of that year it was fully 2nd magnitude. The present
+writer estimated it 1·8, or nearly equal to the brightest on record--1·7
+observed by Sir William Herschel and Wargentin in the year 1779. From
+photographs of the spectrum taken by Mr. Slipher at the Lowell Observatory
+in 1907, he finds strong indications of the presence of the rather rare
+element vanadium in the star's surroundings. Prof. Campbell finds with the
+Mills spectrograph attached to the great 36-inch telescope of the Lick
+Observatory that Mira is receding from the earth at the apparently
+constant velocity of about 38 miles a second.[333] This, of course, has
+nothing to do with the variation in the star's light. Prof. Campbell
+failed to see any trace of the green line of hydrogen in the star's
+spectrum, while two other lines of the hydrogen series "glowed with
+singular intensity."
+
+Mr. Newall has found evidence of the element titanium in the spectrum of
+Betelgeuse (α Orionis); Mr. Goatcher and Mr. Lunt (of the Cape
+Observatory) find tin in Antares (and Scorpii). If the latter observation
+is confirmed it will be the first time this metal has been found in a
+star's atmosphere.[334]
+
+It is a curious fact that Al-Sufi (tenth century) does not mention the
+star ε Aquilæ, which lies closely north-west of ζ Aquilæ, as it is now
+quite conspicuous to the naked eye. It was suspected of variation by Sir
+William Herschel. It was first recorded by Tycho Brahé about 1590, and he
+called it 3rd magnitude. Bayer also rated it 3, and since his time it has
+been variously estimated from 3½ to 4. If it was anything like its
+present brightness (4·21 Harvard) in the tenth century it seems difficult
+to explain how it could have escaped Al-Sufi's careful scrutiny of the
+heavens, unless it is variable. Its colour seems reddish to me.
+
+Mr. W. T. Lynn has shown--and I think conclusively--that the so-called
+"new star" of A.D. 389 (which is said to have appeared near Altair in the
+Eagle) was really a comet.[335]
+
+Near the place of Tycho Brahé's great new star of 1572 (the "Pilgrim
+Star"), Hind and W. E. Plummer observed a small star (No. 129 of
+d'Arrest's catalogue of the region) which seemed to show small
+fluctuations of light, which "scarcely include a whole magnitude." This
+may possibly be identical with Tycho Brahé's wonderful star, and should be
+watched by observers. The place of this small star is (for 1865) R.A. 0{h}
+17{m} 18{s}, N.P.D. 26° 37'·1. The region was examined by Prof. Burnham in
+1890 with the 36-inch telescope of the Lick Observatory. "None of the
+faint stars near the place presented any peculiarity worthy of remark, but
+three double stars were found."[336]
+
+With reference to the famous Nova (T) Coronæ--the "Blaze Star" of
+1866--Prof. Barnard finds from careful comparisons with small stars in its
+vicinity that "the Nova is now essentially of the same brightness it was
+before the outburst of 1866 ... there seems to be no indication of motion
+in the _Nova_."
+
+With reference to the cause of "temporary" stars, or _novæ_, as they are
+now called by astronomers--the late Prof. H. C. Vogel said--
+
+    "A direct collision of two celestial bodies is not regarded by Huggins
+    as an admissible explanation of the Nova; a partial collision has
+    little probability, and the most that can be admitted is perhaps the
+    mutual penetration and admixture of the outer gaseous envelopes of
+    the two bodies at the time of their closest approach. A more probable
+    explanation is given by an hypothesis which we owe to Klinkerfues, and
+    which has more recently been further developed by Wilsing, viz. that
+    by the very close passage of two celestial bodies enormous tidal
+    disturbances are produced and thereby changes in the brightness of the
+    bodies. In the case of the two bodies which form the Nova, it must be
+    assumed that these phenomena are displayed in the highest degree of
+    development, and that changes of pressure have been produced which
+    have caused enormous eruptions from the heated interior of the bodies;
+    the eruptions are perhaps accompanied by electrical actions, and are
+    comparable with the outbursts in our own sun, although they are on a
+    much larger scale."[337]
+
+It will be noticed that this hypothesis agrees with the fundamental
+assumption of the "Planetesimal Hypothesis" advocated by Professors
+Chamberlin and Moulton (see my _Astronomical Essays_, p. 324).
+
+The rush of a comparatively small body through a mass of gaseous matter
+seems also a very plausible hypothesis. This idea was originally advanced
+by Prof. Seeliger, and independently by Mr. Monck.
+
+With reference to the nebula which was observed round the great new star
+of 1901--Nova Persei--Prof. Lewis Bell supports the theory of Seeliger,
+which accounts for the apparent movements of the brightest portions of the
+nebula by supposing that the various parts of the highly tenuous matter
+were successively lighted up by the effects of a travelling
+electro-magnetic wavefront, and he shows that this theory agrees well with
+the observed phenomenon.[338] The "collision theory" which explained the
+sudden outburst of light by the meeting of two dark bodies in space, seems
+to be now abandoned by the best astronomers. The rapid cooling down of the
+supposed bodies indicated by the rapid decrease of light is quite
+inconsistent with this hypothesis.
+
+The rapid diminution in the light of some of these "new stars" is very
+remarkable. Thus the new star which suddenly blazed out near the nucleus
+of the great nebula in Andromeda in August, 1885, faded down in 5 months
+from "the limit of visibility to the naked eye to that of a 26-inch
+telescope"! A _large_ body could not cool in this way.
+
+Mr. Harold K. Palmer thinks that the "complete and astonishingly rapid
+changes of spectral type observed in the case of _Nova Cygni_ and _Nova
+Aurigæ_, and likewise those observed in _Nova Normæ_, _Nova Sagittarii_
+and _Nova Persei_, leave little doubt that the masses of these objects are
+small."[339]
+
+No less than 3748 variable stars had been discovered up to May, 1907. Of
+these 2909 were found at Harvard Observatory (U.S.A.) chiefly by means of
+photography.[340]
+
+The star 14. 1904 Cygni has a period of only 3 hours 14 minutes, which is
+the shortest period known for a variable star.
+
+A very interesting discovery has recently been made with reference to the
+star μ Herculis. It has been long suspected of variable light with a
+period of 35 or 40 days, or perhaps irregular. Frost and Adams now find it
+to be a spectroscopic binary, and further observations at Harvard
+Observatory show that it is a variable of the Algol (or perhaps β Lyræ)
+type. The Algol variation of light was suggested by MM. Baker and
+Schlesinger. The period seems to be about 2·05 days.[341]
+
+The northern of the two "pointers" in the Plough (so called because they
+nearly point to the Pole Star) is about the 2nd magnitude, as Al-Sufi
+rated it. It was thought to be variable in colour by Klein, Konkoly, and
+Weber; and M. Lau has recently found a period of 50 days with a maximum of
+"jaune rougeâtre" on April 2, 1902.
+
+The famous variable star η Argus did "not exceed the 8th magnitude" in
+February, 1907, according to Mr. Tebbutt.[342] This is the faintest ever
+recorded for this wonderful star.
+
+It is stated in _Knowledge_ (vol. 5, p. 3, January 4, 1884) that the
+temporary star of 1876 (in the constellation of Cygnus) "had long been
+known and catalogued as a telescopic star of the 9th magnitude with
+nothing to distinguish it from the common herd." But this is quite
+erroneous. The star was quite unknown before it was discovered by Schmidt
+at Athens on November 24 of that year. The remark apparently refers to the
+"Blaze Star" of 1866 in Corona Borealis, which _was_ known previously as a
+star of about the 9th magnitude before its sudden outburst on May 12 of
+that year.
+
+This "new star" of 1866--T Coronæ, as it is now called--was, with the
+possible exception of Nova Persei (1901), the only example of a _nova_
+which was known to astronomers as a small star previous to the great
+outburst of light. It is the brightest of the _novæ_ still visible. It was
+the first of these interesting objects to be examined with the
+spectroscope. It was observed by Burnham in the years 1904-1906 with the
+great 40-inch telescope of the Yerkes Observatory (U.S.A.). He found its
+colour white, or only slightly tinged with yellow. In August and
+September, 1906, he estimated its magnitude at about 9·3, and "it would
+seem therefore that the Nova is now essentially of the same brightness it
+was before the outburst in 1866." It shows no indication of motion.
+Burnham found no peculiarity about its telescopic image. A small and very
+faint nebula was found by Burnham a little following (that is east of) the
+_nova_.[343]
+
+The following details of the great new star of 1572--the "Pilgrim Star" of
+Tycho Brahé--are given by Delambre.[344] In November, 1572, it was
+brighter than Sirius, Vega, and Jupiter, and almost equal to Venus at its
+brightest. During December it resembled Jupiter in brightness. In January,
+1573, it was fainter and only a little brighter than stars of the 1st
+magnitude. In February and March it was equal to 1st magnitude stars, and
+in April and May was reduced to the 2nd magnitude. In June and July it was
+3rd magnitude; in September of the 4th, and at the end of 1573 it was
+reduced to the 5th magnitude. In February, 1574, it was 6th magnitude, and
+in March of the same year it became invisible to the naked eye.
+
+From this account it will be seen that the decrease in light of this
+curious object was much slower than that of Nova Persei (1901) ("the new
+star of the new century"). This would suggest that it was a much larger
+body.
+
+There were also changes in its colour. When it was of the brightness of
+Venus or Jupiter it shone with a white light. It then became golden, and
+afterwards reddish like Mars, Aldebaran, or Betelgeuse. It afterwards
+became of a livid white colour like Saturn, and this it retained as long
+as it was visible. Tycho Brahé thought that its apparent diameter might
+have been about 3½ minutes of arc, and that it was possibly 361 times
+smaller than the earth(!) But we now know that these estimates were
+probably quite erroneous.
+
+Temporary stars were called by the ancient Chinese "Ke-sing," or guest
+stars.[345]
+
+A temporary star recorded by Ma-tuan-lin (Chinese Annals) in February,
+1578, is described as "a star as large as the sun." But its position is
+not given.[346]
+
+About the middle of September, 1878, Mr. Greely, of Boston (U.S.A.),
+reported to Mr. E. F. Sawyer (the eminent observer of variable stars)
+that, about the middle of August of that year, he had seen the famous
+variable star Mira Ceti of about the 2nd magnitude, although the star did
+not attain its usual maximum until early in October, 1878. Mr. Greely
+stated that several nights after he first saw Mira it had faded to the 4th
+or 5th magnitude. If there was no mistake in this observation (and Sawyer
+could find none) it was quite an unique phenomenon, as nothing of the sort
+has been observed before or since in the history of this famous star. It
+looks as if Mr. Greely had observed a new or "temporary" star near the
+place of Mira Ceti; but as the spot is far from the Milky Way, which is
+the usual seat of such phenomena, this hypothesis seems improbable.
+
+In the so-called Cepheid and Geminid variables of short period, the
+principal characteristics of the light variation are as follows:--
+
+    "1. The light varies without pause.
+
+    "2. The amount of their light variation is usually about 1 magnitude.
+
+    "3. Their periods are short--a few days only.
+
+    "4. They are of a spectral type approximately solar; no Orion, Sirian
+    or Arcturian stars having been found among them.
+
+    "5. They seem to be found in greater numbers in certain parts of the
+    sky, notably in the Milky Way, but exhibit no tendency to form
+    clusters.
+
+    "6. All those stars whose radial velocities have been studied have
+    been found to be binaries whose period of orbital revolution coincides
+    with that of their light change.
+
+    "7. The orbits, so far as determined, are all small, _a_ sin _i_ being
+    2,000,000 kilometres or less.
+
+    "8. Their maximum light synchronizes with their maximum velocity of
+    approach, and minimum light with maximum velocity of recession.
+
+    "9. No case has been found in which the spectrum of more than one
+    component has been bright enough to be recorded in the
+    spectrograms."[347]
+
+It is very difficult to find an hypothesis which will explain
+satisfactorily _all_ these characteristics, and attempts in this direction
+have not proved very successful. Mr. J. C. Duncan suggests the action of
+an absorbing atmosphere surrounding the component stars.
+
+On March 30, 1612, Scheiner saw a star near Jupiter. It was at first equal
+in brightness to Jupiter's satellites. It gradually faded, and on April 8
+of the same year it was only seen with much difficulty in a very clear
+sky. "After that date it was never seen again, although carefully looked
+for under favourable conditions."
+
+An attempted identification of Scheiner's star was made in recent years by
+Winnecke. He found that its position, as indicated by Scheiner, agrees
+with that of the Bonn _Durchmusterung_ star 15°, 2083 (8½ magnitude).
+This star is not a known variable. Winnecke watched it for 17 years, but
+found no variation of light. From Scheiner's recorded observations his
+star seems to have reached the 6th magnitude, which is considerably
+brighter than the _Durchmusterung_ star watched by Winnecke.[348]
+
+With reference to the colours of the stars, the supposed change of colour
+in Sirius from red to white is well known, and will be considered in the
+chapter on the Constellations. The bright star Arcturus has also been
+suspected of variation in colour. About the middle of the nineteenth
+century Dr. Julius Schmidt, of Athens, the well-known observer of variable
+stars, thought it one of the reddest stars in the sky, especially in the
+year 1841, when he found its colour comparable with that of the planet
+Mars.[349] In 1852, however, he was surprised to find it yellow and devoid
+of any reddish tinge; in colour it was lighter than that of Capella. In
+1863, Mr. Jacob Ennis found it "decidedly orange." Ptolemy and Al-Sufi
+called it red.
+
+Mr. Ennis speaks of Capella as "blue" (classing it with Rigel), and
+comparing its colour with that of Vega![350] But the present writer has
+never seen it of this colour. To his eye it seems yellowish or orange. It
+was called red by Ptolemy, El Fergani, and Riccioli; but Al-Sufi says
+nothing about its colour.
+
+Of β Ursæ Minoris, Heis, the eminent German astronomer said, "I have had
+frequent opportunities of convincing myself that the colour of this star
+is not always equally red; at times it is more or less yellow, at others
+most decidedly red."[351]
+
+Among double stars there are many cases in which variation of colour has
+been suspected. In some of these the difference in the recorded colour may
+possibly be due to "colour blindness" in some of the observers; but in
+others there seems to be good evidence in favour of a change. The
+following may be mentioned:--
+
+η Cassiopeiæ. Magnitudes of the components about 4 and 7½. Recorded as
+red and green by Sir John Herschel and South; but yellow and orange by
+Sestini.
+
+ι Trianguli. Magnitudes 5½ and 7. Secchi estimated them as white or
+yellow and blue; but Webb called them yellow and green (1862).
+
+γ Leonis, 2 and 3½. Sir William Herschel noted them white and reddish
+white; but Webb, light orange and greenish yellow.
+
+12 Canum Venaticorum, 2½ and 6½. White and red, Sir William Herschel; but
+Sir John Herschel says in 1830, "With all attention I could perceive no
+contrast of colours in the two stars." Struve found them both white in
+1830, thus agreeing with Sir John Herschel. Sestini saw them yellow and
+blue in 1844; Smyth, in 1855, pale reddish white and lilac; Dembowski, in
+1856, white and pale olive blue; and Webb, in 1862, flushed white and pale
+lilac.
+
+On October 13, 1907, Nova Persei, the great new star of 1901, was
+estimated to be only 11·44 magnitude, or about 11½. When at its
+brightest this famous star was about zero magnitude; so that it has in
+about 6 years faded about 11½ magnitudes in brightness; in other words,
+it has been reduced to 1/40000 of its greatest brilliancy!
+
+
+
+
+CHAPTER XVII
+
+Nebulæ and Clusters
+
+
+In his interesting and valuable work on "The Stars," the late Prof.
+Newcomb said--
+
+    "Great numbers of the nebulæ are therefore thousands of times the
+    dimensions of the earth's orbit, and most of them are thousands of
+    times the dimensions of the whole solar system. That they should be
+    completely transparent through such enormous dimensions shows their
+    extreme tenuity. Were our solar system placed in the midst of one of
+    them it is probable that we should not be able to find any evidence of
+    its existence"!
+
+Prof. Perrine thinks that the total number of the nebulæ will ultimately
+be found to exceed a million.[352]
+
+Dr. Max Wolf has discovered a number of small nebulæ in the regions near
+Algol and Nova Persei (the great "new star" of 1901). He says, "They
+mostly lie in two bands," and are especially numerous where the two bands
+meet, a region of 12 minutes of arc square containing no less than 148 of
+them. They are usually "round with central condensation," and form of
+Andromeda nebula.[353]
+
+Some small nebulæ have been found in the vicinity of the globular
+clusters. They are described by Prof. Perrine as very small and like an
+"out of focus" image of a small star. "They appear to be most numerous
+about clusters which are farthest from the galaxy." Prof. Perrine says,
+"Practically all the small nebulæ about the globular clusters are
+elliptical or circular. Those large enough to show structure are spirals.
+Doubtless the majority of these are spirals."[354] This seems further
+evidence in favour of the "spiral nebular hypothesis" of Chamberlin and
+Moulton.
+
+A great photographic nebula in Orion was discovered by Prof. Barnard in
+1894. In a drawing he gives of the nebula,[355] it forms a long streak
+beginning a little south of γ Orionis (Bellatrix), passing through the
+star 38 Orionis north of 51 and south of 56 and 60 Orionis. Then turning
+south it sweeps round a little north of κ Orionis; then over 29 Orionis,
+and ends a little to the west of η Orionis. There is an outside patch west
+of Rigel. Barnard thinks that the whole forms a vast spiral structure;
+probably connected with the "great nebula" in the "sword of Orion," which
+it surrounds.
+
+From calculations of the brightness of surface ("intrinsic brightness") of
+several "planetary" nebulæ made by the present writer in the year 1905, he
+finds that the luminosity is very small compared with that of the moon.
+The brightest of those examined (_h_ 3365, in the southern hemisphere,
+near the Southern Cross) has a surface luminosity of only 1/400 of that of
+the moon.[356] The great nebulæ in Orion and Andromeda seem to have "still
+smaller intrinsic brightness."
+
+Arago says--
+
+    "The spaces which precede or which follow simple nebulæ, and _a
+    fortiori_ groups of nebulæ, contain generally few stars. Herschel
+    found this rule to be invariable. Thus every time that, during a short
+    interval, no star appeared, in virtue of the diurnal motion, to place
+    itself in the field of his motionless telescope, he was accustomed to
+    say to the secretary who assisted him (Miss Caroline Herschel),
+    'Prepare to write; nebulæ are about to arrive.'"[357]
+
+Commenting on this remark of Arago, the late Herbert Spencer says--
+
+    "How does this fact consist with the hypothesis that nebulæ are remote
+    galaxies? If there were but one nebula, it would be a curious
+    coincidence were this one nebula so placed in the distant regions of
+    space as to agree in direction with a starless spot in our sidereal
+    system! If there were but two nebulæ, and both were so placed, the
+    coincidence would be excessively strange. What shall we say on
+    finding that they are habitually so placed? (the last five words
+    replace some that are possibly a little too strong).... When to the
+    fact that the general mass of nebulæ are antithetical in position to
+    the general mass of the stars, we add the fact that local regions of
+    nebulæ are regions where stars are scarce, and the further fact that
+    single nebulæ are habitually found in comparatively starless spots,
+    does not the proof of a physical connection become overwhelming?"[358]
+
+With reference to the small elongated nebula discovered by Miss Caroline
+Herschel in 1783 near the great nebula in Andromeda, Admiral Smyth says,
+"It lies between two sets of stars, consisting of four each, and each
+disposed like the figure 7, the preceding group being the smallest."[359]
+
+Speaking of the "nebula" Messier 3--a globular cluster in Canes
+Venatici--Admiral Smyth says, "This mass is one of those balls of compact
+and wedged stars whose laws of aggregation it is so impossible to assign;
+but the rotundity of the figure gives full indication of some general
+attractive bond of union."[360] The terms "compact and wedged" are,
+however, too strong, for we know that in the globular clusters the
+component stars must be separated from each other by millions of miles!
+
+Prof. Chamberlin suggests that the secondary nebula (as it is called) in
+the great spiral in Canes Venatici (Messier 51) may possibly represent
+the body which collided with the other (the chief nucleus) in a grazing
+collision, and is now escaping. He considers this secondary body to have
+been "a dead sun"--that is, a dark body.[361] This would be very
+interesting if it could be proved. But it seems to me more probable that
+the secondary nucleus is simply a larger portion of the ejected matter,
+which is now being gradually detached from the parent mass.
+
+Scheiner says "the previous suspicion that the spiral nebulæ are star
+clusters is now raised to a certainty," and that the spectrum of the
+Andromeda nebula is very similar to that of the sun. He says there is "a
+surprising agreement of the two, even in respect to the relative intensity
+of the separate spectral regions."[362]
+
+In the dynamical theory of spiral nebulæ, Dr. E. J. Wilczynski thinks that
+the age of a spiral nebula may be indicated by the number of its coils;
+those having the largest number of coils being the oldest, from the point
+of view of evolution.[363] This seems to be very probable.
+
+In the spectrum of the gaseous nebulæ, the F line of hydrogen (Hβ) is
+visible, but not the C line (Hα). The invisibility of the C line is
+explained by Scheiner as due to a physiological cause, "the eye being
+less sensitive to that part of the spectrum in which the line appears than
+to the part containing the F line."[364]
+
+An apparent paradox is found in the case of the gaseous nebulæ. The
+undefined outlines of these objects render any attempt at measuring their
+parallax very difficult, if not impossible. Their distance from the earth
+is therefore unknown, and perhaps likely to remain so for many years to
+come. It is possible that they may not be farther from us than some of the
+stars visible in their vicinity. On the other hand, they may lie far
+beyond them in space. But whatever their distance from the earth may be,
+it may be easily shown that their attraction on the sun is directly
+proportioned to their distance--that is, the greater their distance, the
+greater the attraction! This is evidently a paradox, and rather a
+startling one too. But it is nevertheless mathematically true, and can be
+easily proved. For, _their distance being unknown_, they may be of any
+dimensions. They might be comparatively small bodies relatively near the
+earth, or they may be immense masses at a vast distance from us. The
+latter is, of course, the more probable. In either case the _apparent_
+size would be the same. Take the case of any round gaseous nebula.
+Assuming it to be of a globular form, its _real_ diameter will depend on
+its distance from the earth--the greater the distance, the greater the
+diameter. Now, as the volumes of spheres vary as the cubes of their
+diameters, it follows that the volume of the nebula will vary as the cube
+of its distance from the earth. As the mass of an attracting body depends
+on its volume and density, its real mass will depend on the cube of its
+distance, the density (although unknown) being a fixed quantity. If at a
+certain distance its mass is _m_, at double the distance (the _apparent_
+diameter being the same) it would have a mass of eight times _m_ (8 being
+the cube of 2), and at treble the distance its mass would be 27 _m_, and
+so on, its _apparent_ size being known, but not its _real_ size. This is
+obvious. Now, the attractive power of a body varies directly as its
+mass--the greater the mass, the greater the attraction. Again, the
+attraction varies _inversely_ as the square of the distance, according to
+the well-known law of Newton. Hence if _d_ be the unknown distance of the
+nebula, we have its attractive power varying as _d_{3} divided by _d_{2},
+or directly as the distance _d_. We have then the curious paradox that for
+a nebula whose distance from the earth is unknown, its attractive power on
+the sun (or earth) will vary directly as the distance--the greater the
+distance the greater the attraction, and, of course, conversely, the
+smaller the distance the less the attractive power. This result seems at
+first sight absurd and incredible, but a little consideration will show
+that it is quite correct. Consider a small wisp of cloud in our
+atmosphere. Its mass is almost infinitesimal and its attractive power on
+the earth practically _nil_. But a gaseous nebula having the same
+_apparent size_ would have an enormous volume, and, although probably
+formed of very tenuous gas, its mass would be very great, and its
+attractive power considerable. The large apparent size of the Orion nebula
+shows that its volume is probably enormous, and as its attraction on the
+sun is not appreciable, its density must be excessively small, less than
+the density of the air remaining in the receiver of the best air-pump
+after the air has been exhausted. How such a tenuous gas can shine as it
+does forms another paradox. Its light is possibly due to some
+phosphorescent or electrical action.
+
+The apparent size of "the great nebula in Andromeda" shows that it must be
+an object of vast dimensions. The nearest star to the earth, Alpha
+Centauri, although probably equal to our sun in volume, certainly does not
+exceed one-hundredth of a second in diameter as seen from the earth. But
+in the case of the Andromeda nebula we have an object of considerable
+apparent size, not measured by seconds of arc, but showing an area about
+three times greater than that of the full moon. The nebula certainly lies
+in the region of the stars--much farther off than Alpha Centauri--and its
+great apparent size shows that it must be of stupendous dimensions. A
+moment's consideration will show that whatever its distance may be, the
+farther it is from the earth the larger it must be in actual size. The sun
+is vastly larger than the moon, but its apparent size is about the same
+owing to its greater distance. Sir William Herschel thought the Andromeda
+nebula to be "undoubtedly the nearest of all the great nebulæ," and he
+estimated its distance at 2000 times the distance of Sirius. This would
+not, however, indicate a relatively near object, as it would imply a
+"light journey" of over 17,000 years! (The distance of Sirius is about 88
+"light years.")
+
+It has been generally supposed that this great nebula lies at a vast
+distance from the earth, possibly far beyond most of the stars seen in the
+same region of the sky; but perhaps not quite so far as Herschel's
+estimate would imply. Recently, however, Prof. Bohlin of Stockholm has
+found from three series of measures made in recent years a parallax of
+0"·17.[365]
+
+This indicates a distance of 1,213,330 times the sun's distance from the
+earth, and a "light journey" of about 19 years. This would make the
+distance of the nebula more than twice the distance of Sirius, about four
+times the distance of α Centauri, but less than that of Capella.
+
+Prof. Bohlin's result is rather unexpected, and will require confirmation
+before it can be accepted. But it will be interesting to inquire what this
+parallax implies as to the real dimensions and probable mass of this vast
+nebula. The extreme length of the nebula may be taken to represent its
+diameter considered as circular. For, although a circle seen obliquely is
+always foreshortened into an ellipse, still the longer axis of the ellipse
+will always represent the real diameter of the circle. This may be seen by
+holding a penny at various angles to the eye. Now, Dr. Roberts found that
+the apparent length of the Andromeda nebula is 2⅓ degrees, or 8400 seconds
+of arc. The diameter in seconds divided by the parallax will give the real
+diameter of the nebula in terms of the sun's distance from the earth taken
+as unity. Now, 8400 divided by 0"·17 gives nearly 50,000, that is, the
+real diameter of the Andromeda nebula would be--on Bohlin's
+parallax--nearly 50,000 times the sun's distance from the earth. As light
+takes about 500 seconds to come from the sun to the earth, the above
+figures imply that light would take about 290 days, or over 9 months to
+cross the diameter of this vast nebula.
+
+Elementary geometrical considerations will show that if the Andromeda
+nebula lies at a greater distance from the earth than that indicated by
+Bohlin's parallax, its real diameter, and therefore its volume and mass,
+will be greater. If, therefore, we assume the parallax found by Bohlin,
+we shall probably find a _minimum_ value for the size and mass of this
+marvellous object.
+
+Among Dr. Roberts' photographs of spiral nebulæ (and the Andromeda nebula
+is undoubtedly a spiral) there are some which are apparently seen nearly
+edgeways, and show that these nebulæ are very thin in proportion to their
+diameter. From a consideration of these photographs we may, I think,
+assume a thickness of about one-hundredth of the diameter. This would give
+a thickness for the Andromeda nebulæ of about 500 times the sun's distance
+from the earth. This great thickness will give some idea of the vast
+proportions of the object we are dealing with. The size of the whole solar
+system--large as it is--is small in comparison. The diameter and thickness
+found above can easily be converted into miles, and from these dimensions
+the actual volume of the nebula can be compared with that of the sun. It
+is merely a question of simple mensuration, and no problem of "high
+mathematics" is involved. Making the necessary calculations, I find that
+the volume of the Andromeda nebula would be about 2·32 trillion times
+(2·32 × 10{18}) the sun's volume! Now, assuming that the nebulous matter
+fills only one-half of the apparent volume of the nebula (allowing for
+spaces between the spiral branches), we have the volume = 1·16 × 10{18}.
+If the nebula had the same density as the sun, this would be its mass in
+terms of the sun's mass taken as unity, a mass probably exceeding the
+combined mass of all the _stars_ visible in the largest telescopes! But
+this assumption is, of course, inadmissible, as the sun is evidently quite
+opaque, whereas the nebula is, partially at least, more or less
+transparent. Let us suppose that the nebula has a _mean_ density equal to
+that of atmospheric air. As water is about 773 times heavier than air, and
+the sun's density is 1·4 (water = 1) we have the mass of the nebula equal
+to 1·16 × 10{18} divided by 773 × 1·4, or about 10{15} times the sun's
+mass, which is still much greater than the probable combined mass of all
+the _visible_ stars. As it seems unreasonable to suppose that the mass of
+an individual member of our sidereal system should exceed the combined
+mass of the remainder of the system, we seem compelled to further reduce
+the density of the Andromeda nebula. Let us assume a mean density of, say,
+a millionth of hydrogen gas (a sufficiently low estimate) which is about
+14·44 times lighter than air, and we obtain a mass of about 8 × 10{7} or
+80 million times the mass of the sun, which is still an enormous mass.
+
+As possibly I may have assumed too great a thickness for the nebula, let
+us take a thickness of one-tenth of that used above, or one thousandth of
+the length of the nebula. This gives a mass of 8 million times the sun's
+mass. This seems a more probable mass if the nebula is--as Bohlin's
+parallax implies--a member of our sidereal system.
+
+If we assume a parallax of say 0"·01--or one-hundredth of a second of
+arc--which would still keep the nebula within the bounds of our sidereal
+system--we have the dimensions of the nebula increased 17 times, and hence
+its mass nearly 5000 times greater (17{3}) than that found above. The mass
+would then be 40,000 million times the sun's mass! This result seems
+highly improbable, for even this small parallax would imply a light
+journey of only 326 years, whereas the distance of the Milky Way has been
+estimated by Prof. Newcomb at about 3000 years' journey for light.
+
+In Dr. Roberts' photograph many small stars are seen scattered over the
+surface of the nebula; but these do not seem to be quite so numerous as in
+the surrounding sky. If the nebula lies nearer to us than the fainter
+stars visible on the photograph, some of them may be obscured by the
+denser portions of the nebula; some may be visible through the openings
+between the spiral branches; while others may be nearer to us and simply
+projected on the nebula.
+
+To add to the difficulty of solving this celestial problem, the
+spectroscope shows that the Andromeda nebula is not gaseous. The spectrum
+is, according to Scheiner, very similar to that of the sun, and "there is
+a surprising agreement of the two, even in respect to the relative
+intensities of the separate spectral regions."[366] He thinks that "the
+greater part of the stars comprising the nucleus of the nebula belong to
+the second spectral class" (solar), and that the nebula "is now in an
+advanced stage of development. No trace of bright nebular lines are
+present, so that the interstellar space in the Andromeda nebula, just as
+in our stellar system, is not appreciably occupied by gaseous
+matter."[366] He suggests that the inner part of the nebula [the
+"nucleus"] "corresponds to the complex of those stars which do not belong
+to the Milky Way, while the latter corresponds to the spirals of the
+Andromeda nebula."[366] On this view of the matter we may suppose that the
+component particles are small bodies widely separated, and in this way the
+_mean_ density of the Andromeda nebula may be very small indeed. They
+cannot be large bodies, as the largest telescopes have failed to resolve
+the nebula into stars, and photographs show no sign of resolution.
+
+It has often been suggested, and sometimes definitely stated, that the
+Andromeda nebula may possibly be an "external" universe, that is an
+universe entirely outside our sidereal system, and comparable with it in
+size. Let us examine the probability of such hypothesis. Assuming that the
+nebula has the same diameter as the Milky Way, or about 6000 "light
+years," as estimated by Prof. Newcomb, I find that its distance from the
+earth would be about 150,000 "light years." As this is about 8000 times
+the distance indicated by Bohlin's parallax, its dimensions would be 8000
+times as great, and hence its volume and mass would be 8000 cubed, or
+512,000,000,000 times greater than that found above. That is, about 4
+trillion (4 × 10{18}) times the sun's mass! As this appears an incredibly
+large mass to be compressed into a volume even so large as that of our
+sidereal system, we seem compelled to reject the hypothesis that the
+nebula represents an external universe. The sun placed at the distance
+corresponding to 150,000 light years would, I find, shine as a star of
+less than the 23rd magnitude, a magnitude which would be invisible in the
+largest telescope that man could ever construct. But the combined light of
+4 trillion of stars of even the 23rd magnitude would be equal to one of
+minus 23·5 magnitude, that is, 23½ magnitude brighter than the zero
+magnitude, or not very much inferior to the sun in brightness. As the
+Andromeda nebula shines only as a star of about the 5th magnitude the
+hypothesis of an external universe seems to be untenable.
+
+It is evident, however, that the mass of the Andromeda nebula must be
+enormous; and if it belongs to our sidereal system, and if the other great
+nebulæ have similar masses, it seems quite possible that the mass of the
+_visible_ universe may much exceed that of the _visible_ stars, and may be
+equal to 1000 million times the sun's mass--as supposed by the late Lord
+Kelvin--or even much more.
+
+With reference to the small star which suddenly blazed out near the
+nucleus of the Andromeda nebula in August, 1885, Prof. Seeliger has
+investigated the decrease in the light of the star on the hypothesis that
+it was a cooling body which had suddenly been raised to an intense heat by
+the shock of a collision, and finds a fair agreement between theory and
+observation. Prof. Auwers points out the similarity between this outburst
+and that of the "temporary star" of 1860, which appeared in the cluster 80
+Messier, and he thinks it very probable that both phenomena were due to
+physical changes in the nebulæ in which they appeared.
+
+The appearance of this temporary star in the Andromeda nebula seems to
+afford further evidence against the hypothesis of the nebula being an
+external universe. For, as I have shown above, our sun, if placed at a
+distance of 150,000 light years, would shine only as a star of the 23rd
+magnitude, or over 15 magnitudes fainter than the temporary star. This
+would imply that the star shone with a brightness of over a million times
+that of the sun, and would therefore indicate a body of enormous size. But
+the rapid fading of its light would, on the contrary, imply a body of
+comparatively small dimensions. We must, therefore, conclude that the
+nebula, whatever it may be, is not an external universe, but forms a
+member of our own sidereal system.
+
+In Sir John Herschel's catalogue of Nebulæ and Clusters of Stars,
+published in 1833, in the _Philosophical Transactions_ of the Royal
+Society, there are many curious objects mentioned. Of these I have
+selected the following:--
+
+No. 496 is described as "a superb cluster which fills the whole field;
+stars 9, 10 ... 13 magnitude and none below, but the whole ground of the
+sky on which it stands is singularly dotted over with infinitely minute
+points." This is No. 22 of Sir William Herschel's 6th class, and will be
+found about 3 degrees south and a little east of the triple star 29
+Monocerotis.
+
+No. 650. This object lies about 3 degrees north of the star μ Leonis, the
+most northern of the bright stars in the well-known "Sickle," and is thus
+described by Sir John Herschel: "A star 12th magnitude with an extremely
+faint nebulous atmosphere about 10" to 12". It is between a star 8-9
+magnitude north preceding, and one 10th magnitude south following, neither
+of which are so affected. A curious object."
+
+No. 1558. Messier 53. A little north-east of the star α Comæ Berenices.
+Described as "a most beautiful highly compressed cluster. Stars very
+small, 12th ... 20th magnitude, with scattered stars to a considerable
+distance; irregularly round, but not globular. Comes up to a blaze in the
+centre; indicating a round mass of pretty equable density. Extremely
+compressed. A most beautiful object. A mass of close-wedged stars 5' in
+diameter; a few 12th magnitude, the rest of the smallest size and
+innumerable." Webb says, "Not very bright with 3-7/10 inches; beautiful
+with 9 inches." This should be a magnificent object with a very large
+telescope, like the Lick or Yerkes.
+
+No. 2018. "A more than usually condensed portion of the enormous cluster
+of the Milky Way. The field has 200 or 300 stars in it at once." This lies
+about 2° south-west of the star 6 Aquilæ, which is near the northern edge
+of the bright spot of Milky Way light in "Sobieski's Shield"--one of the
+brightest spots in the sky.
+
+No. 2093. "A most wonderful phenomenon. A very large space 20' or 30'
+broad in Polar Distance, and 1{m} or 2{m} in Right Ascension, full of
+nebula and stars mixed. The nebula is decidedly attached to the stars, and
+is as decidedly not stellar. It forms irregular lace-work marked out by
+stars, but some parts are decidedly nebulous, wherein no star can be
+seen." Sir John Herschel gives a figure of this curious spot, which he
+says represents its "general character, but not the minute details of
+this object, which would be extremely difficult to give with any degree of
+fidelity." It lies about 3 degrees west of the bright star ζ Cygni.
+
+Among the numerous curious objects observed by Sir John Herschel during
+his visit to the Cape of Good Hope, the following may be mentioned:--
+
+_h_ 2534 (H iv. 77). Near τ{4} Eridani. Sir John Herschel says, "Attached
+cometically to a 9th magnitude star which forms its head. It is an exact
+resemblance to Halley's comet as seen in a night glass."... "A complete
+telescopic comet; a perfect miniature of Halley's comet, only the tail is
+rather broader in proportion."[367]
+
+_h_ 3075. Between γ Monocerotis and γ Canis Majoris. "A very singular
+nebula, and much like the profile of a bust (head, neck, and shoulders) or
+a silhouette portrait, very large, pretty well defined, light nearly
+uniform, about 12' diameter. In a crowded field of Milky Way stars, many
+of which are projected on it."[368]
+
+_h_ 3315 (Dunlop 323). In the Milky Way; about 3° east of the Eta Argûs
+nebula. Sir John Herschel says, "A glorious cluster of immense magnitude,
+being at least 2 fields in extent every way. The stars are 8, 9, 10, and
+11th magnitudes, but chiefly 10th magnitude, of which there must be at
+least 200. It is the most brilliant object of the kind I have ever seen"
+... "has several elegant double stars, and many orange-coloured
+stars."[369] This should form a fine object in even a comparatively small
+telescope, and may be recommended to observers in the southern hemisphere.
+A telescope of 3-inches aperture should show it well.
+
+Among astronomical curiosities may be counted "clusters within clusters."
+A cluster in Gemini (N.G.C. 2331) has a small group of "six or seven stars
+close together and well isolated from the rest."
+
+Lord Rosse describes No. 4511 of Sir John Herschel's General Catalogue of
+Nebulæ and Clusters (_Phil. Trans._, 1864) as "a most gorgeous cluster,
+stars 12-15 magnitude, full of holes."[370] His sketch of this cluster
+shows 3 rings of stars in a line, each ring touching the next on the
+outside. Sir John Herschel described it as "Cluster; very large; very
+rich; stars 11-15 magnitude (Harding, 1827)," but says nothing about the
+rings. This cluster lies about 5 degrees south of δ Cygni.
+
+Dr. See, observing with the large telescope of the Lowell Observatory,
+found that when the sky is clear, the moon absent, and the seeing perfect,
+"the sky appeared in patches to be of a brownish colour," and suggests
+that this colour owes its existence to immense cosmical clouds, which are
+shining by excessively feeble light! Dr. See found that these brown
+patches seem to cluster in certain regions of the Milky Way.[371]
+
+From a comparison of Trouvelot's drawing of the small elongated nebula
+near the great nebula in Andromeda with recent photographs, Mr. Easton
+infers that this small nebula has probably rotated through an angle of
+about 15° in 25 years. An examination I have made of photographs taken in
+different years seems to me to confirm this suspicion, which, if true, is
+evidently a most interesting phenomenon.
+
+Dr. Max Wolf of Heidelberg finds, by spectrum photography, that the
+well-known "ring nebula" in Lyra consists of four rings composed of four
+different gases. Calling the inner ring A, the next B, the next C, and the
+outer D, he finds that A is the smallest ring, and is composed of an
+unknown gas; the next largest, B, is composed of hydrogen gas; the next,
+C, consists of helium gas; and the outer and largest ring, D, is
+composed--like A--of an unknown gas. As the molecular weight of hydrogen
+is 2·016, and that of helium is 3·96, Prof. Bohuslav Brauner suggests that
+the molecular weight of the gas composing the inner ring A is smaller than
+that of hydrogen, and the molecular weight of the gas forming the outer
+ring D is greater than that of helium. He also suggests that the gas of
+ring A may possibly be identical with the "coronium" of the solar corona,
+for which Mendelief found a hypothetical atomic and molecular weight of
+0·4.[372]
+
+With reference to the nebular hypothesis of Laplace, Dr. A. R. Wallace
+argues that "if there exists a sun in a state of expansion in which our
+sun was when it extended to the orbit of Neptune, it would, even with a
+parallax of 1/60th of a second, show a disc of half a second, which could
+be seen with the Lick telescope." My reply to this objection is, that with
+such an expansion there would probably be very little "intrinsic
+brightness," and if luminous enough to be visible the spectrum would be
+that of a gaseous nebula, and no known _star_ gives such a spectrum. But
+some planetary nebulæ look like small stars, and with high powers on large
+telescopes would probably show a disc. On these considerations, Dr.
+Wallace's objection does not seem to be valid.
+
+It is usually stated in popular works on astronomy that the spectra of
+gaseous nebulæ show only three or four bright lines on a faint continuous
+background. But this is quite incorrect. No less than forty bright lines
+have been seen and measured in the spectra of gaseous nebulæ.[373] This
+includes 2 lines of "nebulium," 11 of hydrogen, 5 of helium, 1 of oxygen
+(?), 3 of nitrogen (?), 1 of silicon (?), and 17 of an unknown substance.
+In the great nebulæ in Orion 30 bright lines have been photographed.[374]
+
+D'Arrest found that "gaseous nebulæ are rarely met with outside the Milky
+Way, and never at a considerable distance from it."[375]
+
+Mr. A. E. Fath thinks that "no spiral nebula investigated has a truly
+continuous spectrum." He finds that so feeble is the intensity of the
+light of the spiral nebulæ that, while a spectrogram of Arcturus can be
+secured with the Mills spectrograph "in less than two minutes," "an
+exposure of about 500 hours would be required for the great nebula in
+Andromeda, which is of the same spectral type."[376] Mr. Fath thinks that
+in the case of the Andromeda nebula, the "star cluster" theory "seems to
+be the only one that can at all adequately explain the spectrum
+obtained."[377]
+
+Prof. Barnard finds that the great cluster in Hercules (Messier 13) is
+"composed of stars of different spectral types." This result was confirmed
+by Mr. Fath.[378]
+
+From observations with the great 40-inch telescope of the Yerkes
+Observatory (U.S.A.), Prof. Barnard finds that the nucleus of the
+planetary nebula H. iv. 18 in Andromeda is variable to the extent of at
+least 3 magnitudes. At its brightest it is about the 12th magnitude; and
+the period seems to be about 28 days. Barnard says, "I think this is the
+first case in which the nucleus of a planetary or other nebula has been
+shown to be certainly variable." "The normal condition seems to be
+faint--the nucleus remaining bright for a few days only. In an ordinary
+telescope it looks like a small round disc of a bluish green colour." He
+estimated the brightness of the nebula as that of a star of 8·2
+magnitude.[379] Even in a telescope of 4 inches aperture, this would be a
+fairly bright object. It lies about 3½ degrees south-west of the star ι
+Andromedæ.
+
+The so-called "globular clusters" usually include stars of different
+brightness; comparatively bright telescopic stars of the 10th to 13th
+magnitude with faint stars of the 15th to 17th magnitude. Prof. Perrine of
+the Lick Observatory finds that (_a_) "the division of the stars in
+globular clusters into groups, differing widely in brightness, is
+characteristic of these objects"; (_b_) "the globular clusters are devoid
+of true nebulosity"; and (_c_) "stars fainter than 15th magnitude
+predominate in the Milky Way and globular clusters, but elsewhere are
+relatively scarce." He found that "exposures of one hour or thereabouts
+showed as many stars as exposures four to six times as long; the only
+effect of the longer exposures being in the matter of density." This last
+result confirms the late Dr. Roberts' conclusions. Perrine finds that for
+clusters in the Milky Way, the faint stars (15th to 17th magnitude) "are
+about as numerous in proportion to the bright stars (10th to 13th
+magnitude) as in the globular clusters themselves." This is, however, not
+the case with globular clusters at a distance from the Milky Way. In these
+latter clusters he found that "in the regions outside the limits of the
+cluster there are usually very few faint stars, hardly more than
+one-fourth or one-tenth as many as there are bright stars"; and he thinks
+that "this paucity of faint stars" in the vicinity of these clusters
+"gives rise to the suspicion that all regions at a distance from the
+Galaxy may be almost devoid of these very faint stars." The late Prof.
+Keeler's series of nebular photographs "in or near the Milky Way" tend to
+confirm the above conclusions. Perrine finds the northernmost region of
+the Milky Way "to be almost, if not entirely, devoid of globular
+clusters."[380]
+
+According to Sir John Herschel, "the sublimity of the spectacle afforded"
+by Lord Rosse's great telescope of 6 feet in diameter of some of the
+"larger globular and other clusters" "is declared by all who have
+witnessed it, to be such that no words can express."[381]
+
+In his address to the British Association at Leicester in 1907, Sir David
+Gill said--
+
+    "Evidence upon evidence has accumulated to show that nebulæ consist of
+    the matter out of which stars have been and are being evolved.... The
+    fact of such an evolution with the evidence before us, can hardly be
+    doubted. I most fully believe that, when the modifications of
+    terrestrial spectra under sufficiently varied conditions of
+    temperature, pressure, and environment, have been further studied,
+    this connection will be greatly strengthened."
+
+
+
+
+CHAPTER XVIII
+
+Historical
+
+
+The grouping of the stars into constellations is of great antiquity. The
+exact date of their formation is not exactly known, but an approximate
+result may be arrived at from the following considerations. On the
+celestial spheres, or "globes," used by the ancient astronomers, a portion
+of the southern heavens of a roughly circular form surrounding the South
+Pole was left blank. This space presumably contained the stars in the
+southern hemisphere which they could not see from their northern stations.
+Now, the centre of this circular blank space most probably coincided with
+the South Pole of the heavens at the time when the constellations were
+first formed. Owing to the "Precession of the Equinoxes" this centre has
+now moved away from the South Pole to a considerable distance. It can be
+easily computed at what period this centre coincided with the South Pole,
+and calculations show that this was the case about 2700 B.C. The position
+of this circle also indicates that the constellations were formed at a
+place between 36° and 40° north latitude, and therefore probably somewhere
+in Asia Minor north of Mesopotamia. Again, the most ancient observations
+refer to Taurus as the equinoxial constellation. Virgil says--
+
+  "Candidus auratis aperit cum cornibus annum Taurus."[382]
+
+This would indicate a date about 3000 B.C. There is no tradition, however,
+that the constellation Gemini was ever _seen_ to occupy this position, so
+that 3000 B.C. seems to be the earliest date admissible.[383]
+
+Prof. Sayce thinks that the "signs of the Zodiac" had their origin in the
+plains of Mesopotamia in the twentieth or twenty-third century B.C., and
+Brown gives the probable date as 2084 B.C.[384]
+
+According to Seneca, the study of astronomy among the Greeks dates back to
+about 1400 B.C.; and the ancient constellations were already classical in
+the time of Eudoxus in the fourth century B.C. Eudoxus (408-355 B.C.)
+observed the positions of forty-seven stars visible in Greece, thus
+forming the most ancient star catalogue which has been preserved. He was a
+son of Eschinus, and a pupil of Archytas and probably Plato.
+
+The work of Eudoxus was put into verse by the poet Aratus (third century
+B.C.). This poem describes all the old constellations now known, except
+Libra, the Balance, which was at that time included in the Claws of the
+Scorpion. About B.C. 50, the Romans changed the Claws, or Chelæ, into
+Libra. Curious to say, Aratus states that the constellation Lyra contained
+no bright star![385] Whereas its principal star, Vega, is now one of the
+brightest stars in the heavens!
+
+With reference to the origin of the constellations, Aratus says--
+
+                    "Some men of yore
+  A nomenclature thought of and devised
+  And forms sufficient found."
+
+This shows that even in the time of Aratus the constellations were of
+great antiquity.
+
+Brown says--
+
+    "Writers have often told us, speaking only from the depths of their
+    ignorance, how 'Chaldean' shepherds were wont to gaze at the brilliant
+    nocturnal sky, and to _imagine_ that such and such stars resemble this
+    or that figure. But all this is merely the old effort to make capital
+    out of nescience, and the stars are before our eyes to prove the
+    contrary. Having already certain fixed ideas and figures in his mind,
+    the constellation-former, when he came to his task, applied his
+    figures to the stars and the stars to his figures as harmoniously as
+    possible."[386] "Thus _e.g._ he arranged the stars of _Andromeda_ into
+    the representation of a chained lady, not because they naturally
+    reminded him (or anybody else) of such a figure, but because he
+    desired to express that idea."
+
+A coin of Manius Aquillus, B.C. 94, shows four stars in Aquila, and seems
+to be the oldest representation extant of a star group. On a coin of B.C.
+43, Dr. Vencontre found five stars, one of which was much larger than the
+others, and concludes that it represents the Hyades (in Taurus). He
+attributes the coin to P. Clodius Turrinus, who probably used the
+constellation Taurus or Taurinus as a phonetic reference to his surname. A
+coin struck by L. Lucretius Trio in 74 B.C., shows the seven stars of the
+Plough, or as the ancients called them Septem Triones. Here we have an
+allusion to the name of the magistrate Trio.[387]
+
+In a work published in Berne in 1760, Schmidt contends that the ancient
+Egyptians gave to the constellations of the Zodiac the names of their
+divinities, and expressed them by the signs which were used in their
+hieroglyphics.[388]
+
+Hesiod mentions Orion, the Pleiades, Sirius, Aldebaran, and Arcturus; and
+Homer refers to Orion, Arcturus, the Pleiades, the Hyades, the Great Bear
+(under the name of Amaxa, the Chariot), and the tail of the Little Bear,
+or "Cynosura."
+
+Hipparchus called the constellations Asterisms (αστερισμος), Aristotle and
+Hyginus Σοματα (bodies), and Ptolemy Σχηματα (figures). By some they were
+called Μορφωσεις (configurations), and by others Μετεωρε. Proclus called
+those near the ecliptic Ζωδια (animals). Hence our modern name Zodiac.
+
+Hipparchus, Ptolemy, and Al-Sufi referred the positions of the stars to
+the ecliptic. They are now referred to the equator. Aboul Hassan in the
+thirteenth century (1282) was the first to use Right Ascensions and
+Declinations instead of Longitudes and Latitudes. The ancient writers
+described the stars by their positions in the ancient figures. Thus they
+spoke of "the star in the head of Hercules," "the bright star in the left
+foot of Orion" (Rigel); but Bayer in 1603 introduced the Greek letters to
+designate the brighter stars, and these are now universally used by
+astronomers. These letters being sometimes insufficient, Hevelius added
+numbers, but the numbers in _Flamsteed's Catalogue_ are now generally
+used.
+
+Ptolemy and all the ancient writers described the constellation figures as
+they are seen on globes, that is from the outside. Bayer in his Atlas,
+published in 1603, reversed the figures to show them as they would be seen
+from the _interior_ of a hollow globe and as, of course, they are seen in
+the sky. Hevelius again reversed Bayer's figures to make them correspond
+with those of Ptolemy. According to Bayer's arrangement, Betelgeuse (α
+Orionis) would be on the left shoulder of Orion, instead of the right
+shoulder according to Ptolemy and Al-Sufi, and Rigel (β Orionis) on the
+right foot (Bayer) instead of the left foot (Ptolemy). This change of
+position has led to some confusion; but at present the positions of the
+stars are indicated by their Right Ascensions and Declinations, without
+any reference to their positions in the ancient figures.
+
+The classical constellations of Hipparchus and Ptolemy number forty-eight,
+and this is the number described by Al-Sufi in his "Description of the
+Fixed Stars" written in the tenth century A.D.
+
+Firminicus gives the names of several constellations not mentioned by
+Ptolemy. M. Fréret thought that these were derived from the Egyptian
+sphere of Petosiris. Of these a Fox was placed north of the Scorpion; a
+constellation called Cynocephalus near the southern constellation of the
+Altar (Ara); and to the north of Pisces was placed a Stag. But all these
+have long since been discarded. Curious to say neither the Dragon nor
+Cepheus appears on the old Egyptian sphere.[389]
+
+Other small constellations have also been formed by various astronomers
+from time to time, but these have disappeared from our modern star maps.
+The total number of constellations now recognized in both hemispheres
+amounts to eighty-four.
+
+The first catalogue formed was nominally that of Eudoxus in the fourth
+century B.C. (about 370 B.C.). But this can hardly be dignified by the
+name of catalogue, as it contained only forty-seven stars, and it omits
+several of the brighter stars, notably Sirius! The first complete (or
+nearly complete) catalogue of stars visible to the naked eye was that of
+Hipparchus about 129 B.C. Ptolemy informs us that it was the sudden
+appearance of a bright new or "temporary star" in the year 134 B.C. in the
+constellation Scorpio which led Hipparchus to form his catalogue, and
+there seems to be no reason to doubt the accuracy of this statement, as
+the appearance of this star is recorded in the Chinese Annals. The
+Catalogue of Hipparchus contains only 1080 stars; but as many more are
+visible to the naked eye, Hipparchus must have omitted those which are not
+immediately connected with the old constellation figures of men and
+animals.
+
+Hipparchus' Catalogue was revised by Ptolemy in his famous work the
+_Almagest_. Ptolemy reduced the positions of the stars given by Hipparchus
+to the year 137 A.D.; but used a wrong value of the precession which only
+corresponded to about 50 A.D.; and he probably adopted the star magnitudes
+of Hipparchus without any revision. Indeed, it seems somewhat doubtful
+whether Ptolemy made any observations of the brightness of the stars
+himself. Ptolemy's catalogue contains 1022 stars.
+
+Prof. De Morgan speaks of Ptolemy as "a splendid mathematician and an
+indifferent observer"; and from my own examination of Al-Sufi's work on
+the Fixed Stars, which was based on Ptolemy's work, I think that De
+Morgan's criticism is quite justified.
+
+Al-Sufi's _Description of the Fixed Stars_ was written in the tenth
+century and contains 1018 stars. He seems to have adopted the _positions_
+of the stars given by Ptolemy, merely correcting them for the effects of
+precession; but he made a very careful revision of the star magnitudes of
+Ptolemy (or Hipparchus) from his own observations, and this renders his
+work the most valuable, from this point of view, of all the ancient
+catalogues.
+
+Very little is known about Al-Sufi's life, and the few details we have are
+chiefly derived from the works of the historians Abu'-l-faradji and
+Casiri, and the Oriental writers Hyde, Caussin, Sedillot, etc. Al-Sufi's
+complete name was Abd-al-Rahmän Bin Umar Bin Muhammad Bin Sahl
+Abu'l-husaïn al-Sufi al-Razi. The name Sufi indicates that he belonged to
+the sect of Sufis (Dervishes), and the name Razi that he lived in the town
+of Raï in Persia, to the east of Teheran. He was born on December 7, 903
+A.D., and died on May 25, 986, so that, like many other astronomers, he
+lived to a good old age. According to ancient authorities, Al-Sufi--as he
+is usually called--was a very learned man, who lived at the courts of
+Schiraz and Baghdad under Adhad-al-Davlat--of the dynasty of the
+Buïdes--who was then the ruler of Persia. Al-Sufi was held in high esteem
+and great favour by this prince, who said of him, "Abd-al-Rahmän al-Sufi
+taught me to know the names and positions of the fixed stars, Scharif Ibn
+al-Aalam the use of astronomical tables, and Abu Ali al-Farisi instructed
+me in the principles of grammar." Prince Adhad-al-Davlat died on March 26,
+983. According to Caussin, Al-Sufi also wrote a book on astrology, and a
+work entitled _Al-Ardjouze_, which seems to have been written in verse,
+but its subject is unknown. He also seems to have determined the exact
+length of the year, and to have undertaken geodetic measurements. The
+al-Aalam mentioned above was also an able astronomer, and in addition to
+numerous observations made at Baghdad, he determined with great care the
+precession of the equinoxes. He found the annual constant of precession to
+be 51"·4, a value which differs but little from modern results.
+
+In the year 1874, the late M. Schjellerup, the eminent Danish astronomer,
+published a French translation of two Arabic manuscripts written by
+Al-Sufi and entitled "A Description of the Fixed Stars." One of these
+manuscripts is preserved in the Royal Library at Copenhagen, and the other
+in the Imperial Library at St. Petersburgh.[390]
+
+Al-Sufi seems to have been a most careful and accurate observer, and
+although, as a rule, his estimates of the relative brightness of stars are
+in fairly good agreement with modern estimates and photometric measures,
+there are many remarkable and interesting differences. Al-Sufi's
+observations have an important bearing on the supposed "secular variation"
+of the stars; that is, the slow variation in light which may have occurred
+in the course of ages in certain stars, apart from the periodical
+variation which is known to occur in the so-called variable stars. More
+than 900 years have now elapsed since the date of Al-Sufi's observations
+(about A.D. 964) and over 2000 years in the case of Hipparchus, and
+although these periods are of course very short in the life-history of any
+star, still _some_ changes may possibly have taken place in the brightness
+of some of them. There are several cases in which a star seems to have
+diminished in light since Al-Sufi's time. This change seems to have
+certainly occurred in the case of θ Eridani, β Leonis, ζ Piscis Australis,
+and some others. On the other hand, some stars seem to have certainly
+increased in brightness, and the bearing of these changes on the question
+of "stellar evolution" will be obvious.
+
+In most cases Al-Sufi merely mentions the magnitude which he estimated a
+star to be; such as "third magnitude," "fourth," "small third magnitude,"
+"large fourth," etc. In some cases, however, he directly states that a
+certain star is a little brighter than another star near it. Such
+cases--unfortunately not numerous--are very valuable for comparison with
+modern estimates and measures, when variation is suspected in the light of
+a star. The estimates of Argelander, Heis, and Houzeau are based on the
+same scale as that used by Ptolemy and Al-Sufi. Al-Sufi's estimates are
+given in thirds of a magnitude. Thus, "small third magnitude" means 3⅓, or
+3·33 magnitude in modern measures; "large fourth," 3⅔ or 3·66 magnitude.
+These correspond with the estimates of magnitude given by Argelander,
+Heis, and Houzeau in their catalogues of stars visible to the naked eye,
+and so the estimates can be directly compared.
+
+I have made an independent identification of all the stars mentioned by
+Al-Sufi. In the majority of cases my identifications concur with those of
+Schjellerup; but in some cases I cannot agree with him. In a few cases I
+have found that Al-Sufi himself, although accurately describing the
+position of the stars observed by _him_, has apparently misidentified the
+star observed by Hipparchus and Ptolemy. This becomes evident when we plot
+Ptolemy's positions (as given by Al-Sufi) and compare them with Al-Sufi's
+descriptions of the stars observed by him. This I have done in all cases
+where there seemed to be any doubt; and in this way I have arrived at some
+interesting results which have escaped the notice of Schjellerup. This
+examination shows clearly, I think, that Al-Sufi did not himself measure
+the _positions_ of the stars he observed, but merely adopted those of
+Ptolemy, corrected for the effect of precession. The great value of his
+work, however, consists in his estimates of star magnitudes, which seem to
+have been most carefully made, and from this point of view, his work is
+invaluable. Prof. Pierce says, "The work which the learning of M.
+Schjellerup has brought to light is so important that the smallest errors
+of detail become interesting."[391]
+
+Although Al-Sufi's work is mentioned by the writers referred to above, no
+complete translation of his manuscript was made until the task was
+undertaken by Schjellerup, and even now Al-Sufi's name is not mentioned
+in some popular works on astronomy! But he was certainly the best of all
+the old observers, and his work is deserving of the most careful
+consideration.
+
+Al-Sufi's descriptions of the stars were, it is true, based on Ptolemy's
+catalogue, but his work is not a mere translation of that of his
+predecessor. It is, on the contrary, a careful and independent survey of
+the heavens, made from his own personal observations, each of Ptolemy's
+stars having been carefully examined as to its position and magnitude, and
+Ptolemy's mistakes corrected. In examining his descriptions, Schjellerup
+says, "We soon see the vast extent of his labours, his perseverance, and
+the minute accuracy and almost modern criticism with which he executed his
+work." In fact, Al-Sufi has given us a careful description of the starry
+sky as it appeared in his time, and one which deserves the greatest
+confidence. It far surpasses the work of Ptolemy, which had been without a
+rival for eight centuries previously, and it has only been equalled in
+modern times by the surveys of Argelander, Gould, Heis, and Houzeau. Plato
+remarked with reference to the catalogue of Hipparchus, _Cœlam posteris
+in hereditatem relictum_, and the same may be said of Al-Sufi's work. In
+addition to his own estimates of star magnitudes, Al-Sufi adds the
+magnitudes given by Ptolemy whenever Ptolemy's estimate differs from his
+own; and this makes his work still more valuable, as Ptolemy's magnitudes
+given in all the editions of the _Almagest_ now extant are quite
+untrustworthy.
+
+In the preface to his translation of Al-Sufi's work, Schjellerup mentions
+some remarkable discrepancies between the magnitudes assigned to certain
+stars by Ptolemy and Argelander. This comparison is worthy of confidence
+as it is known that both Al-Sufi and Argelander adopted Ptolemy's (or
+Hipparchus') scale of magnitudes. For example, all these observers agree
+that β Ursæ Minoris (Ptolemy's No. 6 of that constellation) is of the 2nd
+magnitude, while in the case of γ Ursæ Minoris (Ptolemy's No. 7), Ptolemy
+called it 2nd, and Argelander rated it 3rd; Argelander thus making γ one
+magnitude fainter than Ptolemy's estimate. Now, Al-Sufi, observing over
+900 years ago, rated γ of the 3rd magnitude, thus correcting Ptolemy and
+agreeing with Argelander. Modern photometric measures confirm the
+estimates of Al-Sufi and Argelander. But it is, of course, possible that
+one or both stars may be variable in light, and β has actually been
+suspected of variation. Almost all the constellations afford examples of
+this sort. In the majority of cases, however, Al-Sufi agrees well with
+Argelander and Heis, but there are in some cases differences which suggest
+a change in relative brightness.
+
+Among other remarkable things contained in Al-Sufi's most interesting work
+may be mentioned the great nebula in Andromeda, which was first noticed in
+Europe as visible to the naked eye by Simon Marius in 1612. Al-Sufi,
+however, speaks of it as a familiar object in his time.
+
+Schjellerup says--
+
+    "For a long time many of the stars in Ptolemy's catalogue could not be
+    identified in the sky. Most of these discordances were certainly due
+    to mistakes in copying, either in longitude or latitude. Many of these
+    differences were, however, corrected by the help of new manuscripts.
+    For this purpose Al-Sufi's work is of great importance. By a direct
+    examination of the sky he succeeded in finding nearly all the stars
+    reported by Ptolemy (or Hipparchus). And even if his criticism may
+    sometimes seem inconclusive, his descriptions are not subject to
+    similar defects, his positions not depending solely on the places
+    given in Ptolemy's catalogue. For, in addition to the longitudes and
+    latitudes quoted from Ptolemy, he has described by alignment the
+    positions of the stars referred to. In going from the brightest and
+    best known stars of each constellation he indicates the others either
+    by describing some peculiarity in their position, or by giving their
+    mutual distance as so many cubits (_dzirâ_), or a span (_schibr_),
+    units of length which were used at that time to measure apparent
+    celestial distances. The term _dzirâ_ means literally the fore-arm
+    from the bone of the elbow to the tip of the middle finger, or an ell.
+    We should not, however, conclude from this that the Arabians were so
+    unscientific as to measure celestial distances by an ell, as this
+    would be quite in contradiction to their well-known knowledge of
+    Geometry and Trigonometry."
+
+With reference to the arc or angular distance indicated by the "cubit,"
+Al-Sufi states in his description of the constellation Auriga that the
+_dzirâ_ (or cubit) is equal to 2° 20'. Three cubits, therefore, represent
+7°, and 4 cubits 9° 20'.
+
+In Al-Sufi's own preface to his work, after first giving glory to God and
+blessings on "his elected messenger Muhammed and his family," he proceeds
+to state that he had often "met with many persons who wished to know the
+fixed stars, their positions on the celestial vault, and the
+constellations, and had found that these persons may be divided into two
+classes. One followed the method of astronomers and trust to spheres
+designed by artists, who not knowing, the stars themselves, take only the
+longitudes and latitudes which they find in the books, and thus place the
+stars on the sphere, without being able to distinguish truth from error.
+It then follows that those who really know the stars in the sky find on
+examining these spheres that many stars are otherwise than they are in the
+sky. Among these are Al-Battani, Atârid and others."
+
+Al-Sufi seems rather hard on Al-Battani (or Albategnius as he is usually
+called) for he is generally considered to have been the most
+distinguished of the Arabian astronomers. His real name was Mohammed Ibn
+Jaber Ibn Senan Abu Abdallah Al-Harrani. He was born about A.D. 850 at
+Battan, near Harran in Mesopotamia, and died about A.D. 929. He was the
+first to make use of sines instead of chords, and versed sines. The
+_Alphonsine Tables_ of the moon's motions were based on his observations.
+
+After some severe criticisms on the work of Al-Battani and Atârid, Al-Sufi
+goes on to say that the other class of amateurs who desire to know the
+fixed stars follow the method of the Arabians in the science of
+_Anva_[392] and the mansions of the moon and the books written on this
+subject. Al-Sufi found many books on the _anva_, the best being those of
+Abu Hanifa al-Dînavari. This work shows that the author knew the Arabic
+tradition better than any of the other writers on the subject. Al-Sufi,
+however, doubts that he had a good knowledge of the stars themselves, for
+if he had he would not have followed the errors of his predecessors.
+
+According to Al-Sufi, those who know one of these methods do not know the
+other. Among these is Abu-Hanifa, who states in his book that the names of
+the twelve signs (of the Zodiac) did not originate from the arrangement
+or configuration of the stars resembling the figure from which the name
+is derived. The stars, Abu-Hanifa said, "change their places, and although
+the names of the signs do not change, yet the arrangement of the stars
+ceases to be the same. This shows that he was not aware of the fact that
+the arrangement of the stars does not change, and their mutual distances
+and their latitudes, north and south of the ecliptic, are neither
+increased nor diminished." "The stars," Al-Sufi says, "do not change with
+regard to their configurations, because they are carried along together by
+a physical motion and by a motion round the poles of the ecliptic. This is
+why they are called fixed. Abu-Hanifa supposed that they are termed fixed
+because their motion is very slow in comparison with that of the planets."
+"These facts," he says, "can only be known to those who follow the method
+of the astronomers and are skilled in mathematics."
+
+Al-Sufi says that the stars of the Zodiac have a certain movement
+following the order of the signs, which according to Ptolemy and his
+predecessors is a degree in 100 years. But according to the authors of
+_al-mumtahan_ and those who have observed subsequently to Ptolemy, it is a
+degree in 66 years. According to modern measures, the precession is about
+50"·35 per annum, or one degree in 71½ years.
+
+Al-Sufi says that the Arabians did not make use of the figures of the
+Zodiac in their proper signification, because they divided the
+circumference of the sky by the number of days which the moon took to
+describe it--about 28 days--and they looked for conspicuous stars at
+intervals which, to the eye, the moon appeared to describe in a day and a
+night. They began with _al-scharataïn_, "the two marks" (α and β Arietis)
+which were the first striking points following the point of the spring
+equinox. They then sought behind these two marks another point at a
+distance from them, equal to the space described by the moon in a day and
+a night. In this way they found _al-butaïn_ (ε, δ, and ρ Arietis); after
+that _al-tsuraija_, the Pleiades; then _al-dabaran_, the Hyades, and thus
+all the "mansions" of the moon. They paid no attention to the signs of the
+Zodiac, nor to the extent of the figures which composed them. This is why
+they reckoned among the "mansions" _al-haka_ (λ Orionis) which forms no
+part of the signs of the Zodiac, since it belongs to the southern
+constellation of the Giant (Orion). And similarly for other stars near the
+Zodiac, of which Al-Sufi gives some details. He says that Regulus (α
+Leonis) was called by the Arabians _al-maliki_, the Royal Star, and that
+_al-anva_ consists of five stars situated in the two wings of the Virgin.
+These stars seem to be β, η, γ, δ, and ε Virginis, which form with Spica
+(α Virginis) a Y-shaped figure. Spica was called _simak al-azal_, the
+unarmed _simak_; the "armed _simak_" being Arcturus, _simak al-ramih_.
+These old Arabic names seem very fanciful.
+
+Al-Sufi relates that in the year 337 of the Hegira (about A.D. 948) he
+went to Ispahan with Prince Abul-fadhl, who introduced him to an
+inhabitant of that city, named Varvadjah, well known in that country, and
+famous for his astronomical acquirements. Al-Sufi asked him the names of
+the stars on an astrolabe which he had, and he named Aldebaran, the two
+bright stars in the Twins (Castor and Pollux), Regulus, Sirius, and
+Procyon, the two Simaks, etc. Al-Sufi also asked him in what part of the
+sky _Al-fard_ (α Hydræ) was, but he did not know! Afterwards, in the year
+349, this same man was at the court of Prince Adhad-al-Davlat, and in the
+presence of the Prince, Al-Sufi asked him the name of a bright star--it
+was _al-nasr al-vaki_, the falling Vulture (Vega), and he replied, "That
+is _al-aijuk_" (Capella)! thus showing that he only knew the _names_ of
+the stars, but did not know them when he saw them in the sky. Al-Sufi adds
+that all the women "who spin in their houses" knew this star (Vega) by the
+name of _al-atsafi_, the Tripod. But this could not be said even of
+"educated women" at the present day.
+
+With reference to the number of stars which can be seen with the naked
+eye, Al-Sufi says, "Many people believe that the total number of fixed
+stars is 1025, but this is an evident error. The ancients only observed
+this number of stars, which they divided into six classes according to
+magnitude. They placed the brightest in the 1st magnitude; those which are
+a little smaller in the 2nd; those which are a little smaller again in the
+3rd; and so on to the 6th. As to those which are below the 6th magnitude,
+they found that their number was too great to count; and this is why they
+have omitted them. It is easy to convince one's self of this. If we
+attentively fix our gaze on a constellation of which the stars are well
+known and registered, we find in the spaces between them many other stars
+which have not been counted. Take, for example, the Hen [Cygnus]; it is
+composed of seventeen internal stars, the first on the beak, the brightest
+on the tail, the others on the wings, the neck and the breast; and below
+the left wing are two stars which do not come into the figure. Between
+these different stars, if you examine with attention, you will perceive a
+multitude of stars, so small and so crowded that we cannot determine their
+number. It is the same with all the other constellations." These remarks
+are so correct that they might have been written by a modern astronomer.
+It should be added, however, that _all_ the faint stars referred to by
+Al-Sufi--and thousands of others still fainter--have now been mapped down
+and their positions accurately determined.
+
+About the year 1437, Ulugh Beigh, son of Shah Rokh, and grandson of the
+Mogul Emperor Tamerlane, published a catalogue of stars in which he
+corrected Ptolemy's positions. But he seems to have accepted Al-Sufi's
+star magnitudes without any attempt at revision. This is unfortunate, for
+an _independent_ estimate of star magnitudes made in the fifteenth century
+would now be very valuable for comparison with Al-Sufi's work and with
+modern measures. Ulugh Beigh's catalogue contains 1018 stars, nearly the
+same number as given by Ali-Sufi.[393]
+
+
+
+
+CHAPTER XIX
+
+The Constellations[394]
+
+
+Curious to say, Al-Sufi rated the Pole Star as 3rd magnitude; for it is
+now only slightly less than the 2nd. At present it is about the same
+brightness as β of the same constellation (Ursa Minor) which Al-Sufi rated
+2nd magnitude. It was, however, also rated 3rd magnitude by Ptolemy (or
+Hipparchus), and it may possibly have varied in brightness since ancient
+times. Admiral Smyth says that in his time (1830) it was "not even a very
+bright third size" (!)[395] Spectroscopic measures show that it is
+approaching the earth at the rate of 16 miles a second; but this would
+have no perceptible effect on its brightness in historical times. This may
+seem difficult to understand, and to some perhaps incredible; but the
+simple explanation is that its distance from the earth is so great that a
+journey of even 2000 years with the above velocity would make no
+_appreciable_ difference in its distance! This is undoubtedly true, as a
+simple calculation will show, and the fact will give some idea of the vast
+distance of the stars. The well-known 9th magnitude companion to the Pole
+Star was seen _by day_ in the Dorpat telescope by Struve and Wrangel; and
+"on one occasion by Encke and Argelander."[396]
+
+The star β Ursæ Minoris was called by the Arabians _Kaukab al-shamáli_,
+the North Star, as it was--owing to the precession of the
+Equinoxes--nearer to the Pole in ancient times than our present Pole Star
+was _then_.
+
+The "Plough" (or Great Bear) is supposed to represent a waggon and horses.
+"Charles' Wain" is a corruption of "churl's wain," or peasant's cart. The
+Arabians thought that the four stars in the quadrilateral represented a
+bier, and the three in the "tail" the children of the deceased following
+as mourners! In the Greek mythology, Ursa Major represented the nymph
+Callisto, a daughter of Lycaon, who was loved by Jupiter, and turned into
+a bear by the jealous Juno. Among the old Hindoos the seven stars
+represented the seven Rishis. It is the Otawa of the great Finnish epic,
+the "Kalevala." It was also called "David's Chariot," and in America it
+is known as "The Dipper."
+
+Closely north of the star θ in Ursa Major is a small star known as
+Flamsteed 26. This is not mentioned by Al-Sufi, but is now, I find from
+personal observation, very visible, and indeed conspicuous, to the naked
+eye. I find, however, that owing to the large "proper motion" of the
+bright star (1"·1 per annum) the two stars were much closer together in
+Al-Sufi's time than they are at present, and this probably accounts for
+Al-Sufi's omission. This is an interesting and curious fact, and shows the
+small changes which occur in the heavens during the course of ages.
+
+Close to the star ζ, the middle star of the "tail" of Ursa Major (or
+handle of the "Plough"), is a small star known as Alcor, which is easily
+visible to good eyesight without optical aid. It is mentioned by Al-Sufi,
+who says the Arabians called it _al-suha_, "the little unnoticed one." He
+says that "Ptolemy does not mention it, and it is a star which seems to
+test the powers of the eyesight." He adds, however, an Arabian proverb, "I
+show him _al-suha_, and he shows me the moon," which seems to suggest that
+to some eyes, at least, it was no test of sight at all. It has, however,
+been suspected of variation in light. It was rated 5th magnitude by
+Argelander, Heis, and Houzeau, but was measured 4·02 at Harvard
+Observatory. It has recently been found to be a spectroscopic binary.
+
+The constellation of the Dragon (Draco) is probably referred to in Job
+(chap. xxvi. v. 13), where it is called "the crooked serpent." In the
+Greek mythology it is supposed to represent the dragon which guarded the
+golden apples in the Garden of the Hesperides. Some have suggested that it
+represented the serpent which tempted Eve. Dryden says, in his translation
+of Virgil--
+
+  "Around our Pole the spiry Dragon glides,
+  And like a wand'ring stream the Bears divides."
+
+The fact that the constellation Boötis rises quickly and sets slowly,
+owing to its lying horizontally when rising and vertically when setting,
+was noted by Aratus, who says--
+
+  "The Bearward now, past seen,
+  But more obscured, near the horizon lies;
+  For with the four Signs the Ploughman, as he sinks,
+  The deep receives; and when tired of day
+  At even lingers more than half the night,
+  When with the sinking sun he likewise sets
+  These nights from his late setting bear their name."[397]
+
+The cosmical setting of Boötis--that is, when he sets at sunset--is stated
+by Ovid to occur on March 5 of each year.
+
+With reference to the constellation Hercules, Admiral Smyth says--
+
+    "The kneeling posture has given rise to momentous discussion; and
+    whether it represents Lycaon lamenting his daughter's transformation,
+    or Prometheus sentenced, or Ixion ditto, or Thamyrus mourning his
+    broken fiddle, remains still uncertain. But in process of time, this
+    figure became a lion, and Hyginus mentions both the lion's skin and
+    the club; while the right foot's being just over the head of the
+    Dragon, satisfied the mythologists that he was crushing the Lernæan
+    hydra.... Some have considered the emblem as typifying the serpent
+    which infested the vicinity of Cape Tænarus, whence a sub-genus of
+    Ophidians still derives its name. At all events a poet, indignant at
+    the heathen exaltation of Hevelius, has said--
+
+        "'To Cerberus, too, a place is given--
+        His home of old was far from heaven.'"[398]
+
+Aratus speaks of Hercules as "the Phantom whose name none can tell."
+
+There were several heroes of the name of Hercules, but the most famous was
+Hercules the Theban, son of Jupiter and Alcmene wife of Amphitryon, King
+of Thebes, who is said to have lived some years before the siege of Troy,
+and went on the voyage of the Argonauts about 1300 B.C. According to some
+ancient writers, another Hercules lived about 2400 B.C., and was a
+contemporary of Atlas and Theseus. But according to Pétau, Atlas lived
+about 1638 B.C., and Lalande thought that this chronology is the more
+probable.
+
+The small constellation Lyra, which contains the bright star Vega, is
+called by Al-Sufi the Lyre, the Goose, the Persian harp, and the Tortoise.
+In his translation of Al-Sufi's work, Schjellerup suggests that the name
+"Goose" may perhaps mean a plucked goose, which somewhat resembles a Greek
+lyre, and also a tortoise. The name of the bright star Vega is a
+corruption of the Arabic _vâki_. Ptolemy and Al-Sufi included all the very
+brightest stars in the "first magnitude," making no distinction between
+them, but it is evident at a glance that several of them, such as Arcturus
+and Vega, are brighter than an average star of the first magnitude, like
+Aldebaran.
+
+The constellation Perseus, which lies south-east of "Cassiopeia's Chair,"
+may be recognized by the festoon formed by some of its stars, the bright
+star α Persei being among them. It is called by Al-Sufi "_barschânsch_,
+Περσευς, Perseus, who is _hamil râs al-gul_, the Bearer of the head of
+_al-gul_." According to Kazimirski, "_Gul_ was a kind of demon or ogre who
+bewilders travellers and devours them, beginning at the feet. In general
+any mischievous demon capable of taking all sorts of forms." In the Greek
+mythology Perseus was supposed to be the son of Jupiter and Danæ. He is
+said to have been cast into the sea with his mother and saved by King
+Polydectus. He afterwards cut off the head of Medusa, one of the Gorgons,
+while she slept, and armed with this he delivered Andromeda from the
+sea-monster.
+
+The constellation Auriga lies east of Perseus and contains the bright star
+Capella, one of the three brightest stars in the northern hemisphere (the
+others being Arcturus and Vega). Theon, in his commentary on Aratus, says
+that Bellerophon invented the chariot, and that it is represented in the
+heavens by Auriga, the celestial coachman. According to Dupuis, Auriga
+represents Phæton, who tried to drive the chariot of the sun, and losing
+his head fell into the river Eridanus. The setting of Eridanus precedes by
+a few minutes that of Auriga, which was called by some of the ancient
+writers Amnis Phaï-tontis.[399] Auriga is called by Al-Sufi _numsick
+al-ainna_--He who holds the reins, the Coachman; also _al-inâz_, the
+She-goat. M. Dorn found in Ptolemy's work, the Greek name Ἡνιοχοι, Auriga,
+written in Arabic characters. Al-Sufi says, "This constellation is
+represented by the figure of a standing man behind 'He who holds the head
+of _al-gûl_' [Perseus], and between the Pleiades and the Great Bear."
+
+Capella is, Al-Sufi says, "the bright and great star of the first
+magnitude which is on the left shoulder [of the ancient figure] on the
+eastern edge of the Milky Way. It is that which is marked on the astrolabe
+as _al-aijûk_." The real meaning of this name is unknown. Schjellerup
+thought, contrary to what Ideler says, that the name is identical with
+the Greek word Αιξ (a goat). Capella was observed at Babylon about 2000
+B.C., and was then known as Dilgan. The Assyrian name was _Icu_, and the
+Persian name _colca_. It was also called Capra Hircus, Cabrilla, Amalthea,
+and Olenia. In ancient times the rising of Capella was supposed to presage
+the approach of storms. Ovid says, "Olenia sidus pluviale Capellæ."
+
+The constellation Aquila is called by Al-Sufi _al-ukab_, the Eagle, or
+_al-nasr al-tâïr_, the flying vulture. According to the ancient poets the
+eagle carried nectar to Jupiter when he was hidden in a cave in Crete.
+This eagle also assisted Jupiter in his victory over the Giants and
+contributed to his other pleasures. For these reasons the eagle was
+consecrated to Jupiter, and was placed in the sky. Al-Sufi says, "There
+are in this figure three famous stars [γ, α, and β Aquilæ], which are
+called _al-nasr al-tâïr_." Hence is derived the modern name Altair for the
+bright star α Aquilæ. Al-Sufi says that the "common people" call "the
+three famous stars" _al-mîzân_, the Balance, on account of the equality of
+the stars." This probably refers to the approximately equal distances
+between γ and α, and α and β, and not to their relative brightness. He
+says "Between the bright one of the tail [ξ Aquilæ] and the star in the
+beak of the Hen [β Cygni] in the thinnest part of the Milky Way, we see
+the figure of a little earthen jar, of which the stars begin at the
+bright one in the tail, and extend towards the north-west. [This seems to
+refer to ε Aquilæ and the small stars near it.] They then turn towards the
+east in the base of the jar, and then towards the south-east to a little
+cloud [4, 5, etc. Vulpeculæ, a well-known group of small stars] which is
+found to the north of the two stars in the shaft of the Arrow [α and β
+Sagittæ]. The cloud is on the eastern edge of the jar, and the bright one
+on the tail on the western edge; the orifice is turned towards the flying
+Vulture [Aquila], and the base towards the north. Among these are
+distinguished some of the fourth, fifth, and sixth magnitudes [including,
+probably, 110, 111, 112, 113 Hercules, and 1 Vulpeculæ] and Ptolemy says
+nothing of this figure, except the bright star in the tail of the Eagle"
+(see figure). The above is a good example of the minute accuracy of detail
+in Al-Sufi's description.
+
+[Illustration: AL-SUFI'S "EARTHEN JAR."]
+
+The southern portion of Aquila was formerly called Antinous, who was said
+to have been a young man of great beauty born at Claudiopolis in Bithynia,
+and drowned in the Nile. Others say that he sacrificed his life to save
+that of the Emperor Hadrian, who afterwards raised altars in his honour
+and placed his image on coins.[400]
+
+The constellation Pegasus, Al-Sufi says, "is represented by the figure of
+a horse, which has the head, legs, and forepart of the body to the end of
+the back, but it has neither hind quarters nor hind legs." According to
+Brown, Pegasus was the horse of Poseidon, the sea god. Half of it was
+supposed to be hidden in the sea, into which the river Eridanus
+flowed.[401] In the Greek mythology it was supposed to represent the
+winged horse produced by the blood which fell from the head of Medusa when
+she was killed by Perseus! Some think that it represents Bellerophon's
+horse, and others the horse of Nimrod. It was also called Sagmaria and
+Ephippiatus, and was sometimes represented with a saddle instead of wings.
+
+In describing the constellation Andromeda, Al-Sufi speaks of two series of
+stars which start from the great nebula in Andromeda; one series going
+through 32 Andromedæ, π, δ and ε to ζ and η; and the other through ν, μ, β
+Andromedæ into the constellation Pisces. He says they enclose a
+fish-shaped figure called by the Arabians _al-hût_, the Fish, _par
+excellence_. He speaks of two other series of stars which begin at τ and
+υ, and diverging meet again at χ Persei, forming another "fish-like
+figure." The eastern stream starts from τ and passes through 55, γ, 60,
+62, 64, and 65 Andromedæ; and the western stream from υ through χ 51, 54,
+and _g_ Persei up to χ Persei. The head of the first "fish," _al-hût_, is
+turned towards the north, and that of the second towards the south (see
+figure).
+
+[Illustration: AL-SUFI'S "FISHES" IN ANDROMEDA.]
+
+Al-Sufi says that the stars α Persei, γ, β, δ, and α Andromedæ, and β
+Pegasi form a curved line. This is quite correct, and this fine curve of
+bright stars may be seen at a glance on a clear night in September, when
+all the stars are high in the sky.
+
+The first constellation of the Zodiac, Aries, the Ram, was called,
+according to Aratus and Eratosthenes, κριος. It is mentioned by Ovid under
+the name of Hellas. It was also called by the ancients the Ram with the
+golden horns. Manilius (fourth century B.C.) called it "The Prince." It is
+supposed to have represented the god Bel. Among the Accadians the sign
+meant "He who dwells on the altar of uprightness." It first appears on the
+Egyptian Zodiac; and it was sacred to Jupiter Ammon. In the Greek
+mythology it was supposed to represent the ram, the loss of whose fleece
+led to the voyage of the Argonauts. In the time of Hipparchus, about 2000
+years ago, it was the first sign of the Zodiac, or that in which the sun
+is situated at the Vernal Equinox (about March 21 in each year). But owing
+to the precession of the equinoxes, this point has now moved back into
+Pisces.
+
+The brightest star of Aries (α) is sometimes called Hamal, derived from
+the Arabic _al-hamal_, a name given to the constellation itself by
+Al-Sufi. In the Accadian language it was called _Dilkur_, "the dawn
+proclaimer." Ali-Sufi says that close to α, "as if it were attached to
+it," is a small star of the 6th magnitude, not mentioned by Ptolemy. This
+is clearly κ Arietis. The fact of Al-Sufi having seen and noticed this
+small star, which modern measures show to be below the 5th magnitude, is
+good evidence of his keen eyesight and accuracy of observation.
+
+According to Al-Sufi, the stars β and γ Arietis were called by the
+Arabians _al-scharatain_, "the two marks." They marked the "first mansion
+of the moon," and ε, δ, and ρ the second mansion. With reference to these
+so-called "mansions of the moon," Admiral Smyth says--
+
+    "The famous _Manazil al-kamar_, i.e. Lunar mansions, constituted a
+    supposed broad circle in Oriental astronomy divided into twenty-eight
+    unequal parts, corresponding with the moon's course, and therefore
+    called the abodes of the moon. This was not a bad arrangement for a
+    certain class of gazers, since the luminary was observed to be in or
+    near one or other of these parts, or constellations every night.
+    Though tampered with by astrologers, these Lunar mansions are probably
+    the earliest step in ancient astronomy."[402]
+
+Taurus, the second constellation of the Zodiac, was in ancient times
+represented by the figure of a bull, the hinder part of which is turned
+towards the south-west, and the fore part towards the east. It had no hind
+legs, and the head was turned to one side, with the horns extended towards
+the east. Its most ancient name was _Te_, possibly a corruption of the
+Accadian _dimmena_, "a foundation-stone." The Greek name is αθωρ (θωωρ,
+Eusebius). In the old Egyptian mythology Taurus represented the god Apis.
+According to Dupuis it also represented the 10th "labour of Hercules,"
+namely, his victory over the cows of Geryon, King of Spain.[403] It was
+also supposed to represent the bull under the form of which Jupiter
+carried off Europa, daughter of Agenor, King of the Phœnicians. It may
+also refer to Io or Isis, who is supposed to have taught the ancient
+Egyptians the art of agriculture.
+
+Aldebaran is the well-known bright red star in the Hyades. It was called
+by Ptolemy _Fulgur succularum_. Ali-Sufi says it was marked on the old
+astrolabes as _al-dabaran_, "the Follower" (because it follows the Hyades
+in the diurnal motion), and also _ain al-tsaur_, the eye of the bull. It
+may be considered as a standard star of the 1st magnitude. Modern
+observations show that it has a parallax of 0"·107. It is receding from
+the earth, according to Vogel, at the rate of about 30 miles a second;
+but even with this high velocity it will take thousands of years before
+its brightness is perceptibly diminished. It has a faint companion of
+about the 10th magnitude at the distance of 118", which forms a good
+"light test" for telescopes of 3 or 4 inches aperture. I saw it well with
+a 4-inch Wray in the Punjab sky. The Hyades were called _Succulæ_ by the
+Romans, and in the Greek mythology were said to be children of Atlas.
+
+The star β Tauri, sometimes called Nath, from the Arabic _al-nátih_, the
+butting, is a bright star between Capella and γ Orionis (Bellatrix). It is
+on the tip of the horn in the ancient figure of Taurus, and "therefore"
+(says Admiral Smyth) "at the greatest distance from the hoof; can this
+have given rise to the otherwise pointless sarcasm of not knowing B from a
+bull's foot?"[404] Al-Sufi says that an imaginary line drawn from the star
+now known as A Tauri to τ Tauri would pass between υ and κ Tauri, which is
+quite correct, another proof of the accuracy of his observations. He also
+says that the star ω Tauri is exactly midway between A and ε, which is
+again correct. He points out that Ptolemy's position of ω is incorrect.
+This is often the case with Ptolemy's positions, and tends to show that
+Ptolemy adopted the position given by Hipparchus without attempting to
+verify their position in the sky. Al-Sufi himself adopts the longitudes
+and latitudes of the stars as given by Ptolemy in the _Almagest_, but
+corrects the positions in his _descriptions_, when he found Ptolemy's
+places erroneous.
+
+The famous group of the Pleiades is well known; but there is great
+difficulty in understanding Al-Sufi's description of the cluster. He says,
+"The 29th star (of Taurus) is the more northern of the anterior side of
+the Pleiades themselves, and the 30th is the southern of the same side;
+the 31st is the following vertex of the Pleiades, and is in the more
+narrow part. The 32nd is situated outside the northern side. Among these
+stars, the 32nd is of the 4th magnitude, the others of the 5th." Now, it
+is very difficult or impossible to identify these stars with the stars in
+the Pleiades as they are at present. The brightest of all, Alcyone (η
+Tauri), now about 3rd magnitude, does not seem to be mentioned at all by
+Al-Sufi! as he says distinctly that "the brightest star" (No 32 of Taurus)
+is "outside" the Pleiades "on the northern side." It seems impossible to
+suppose that Al-Sufi could have overlooked Alcyone had it the same
+brightness it has now. The 32nd star seems to have disappeared, or at
+least diminished greatly in brightness, since the days of Al-Sufi. More
+than four stars were, however, seen by Al-Sufi, for he adds, "It is true
+that the stars of the Pleiades must exceed the four mentioned above, but
+I limit myself to these four because they are very near each other and the
+largest [that is, the brightest]; this is why I have mentioned them,
+neglecting the others." A full examination of the whole question is given
+by Flammarion in his interesting work _Les Étoiles_ (pp. 289-307), and I
+must refer my readers to this investigation for further details.
+
+According to Brown, Simonides of Keos (B.C. 556-467) says, "Atlas was the
+sire of seven daughters with violet locks, who are called the heavenly
+_Peleiades_."[405] The name is by some supposed to be derived from the
+Greek πλειων, full. The Old Testament word _Kimah_ (Job ix. 9 and xxviii.
+31) and Amos (v. 8) is derived from the Assyrian _Kimta_, a "family."
+Aratus describes the Pleiades in the following lines:--
+
+  "Near his[406] left thigh together sweep along
+  The flock of Clusterers. Not a mighty span
+  Holds all, and they themselves are dim to see,
+  And seven paths aloft men say they take,
+  Yet six alone are viewed by mortal eye.
+  These seven are called by name Alkyonî
+  Kelainî, Meropî and Steropî
+  Taygetî, Elecktrî, Maia queen.
+  They thus together small and faint roll on
+  Yet notable at morn and eve through Zeus."[407]
+
+The Pleiades are mentioned by Ovid. According to the ancient poets they
+were supposed to represent the children of Atlas and Hesperus, and on
+this account they were called Atlantids or Hesperides. From the
+resemblance in sound to the word πλειας, a pigeon, they were sometimes
+called "the doves," and for the same reason the word πλειν, to navigate,
+led to their being called the "shipping stars." The word πλειας was also
+applied to the priestesses of the god Zeus (Jupiter) at Dordona, in the
+groves of which temple there were a number of pigeons. This is, perhaps,
+what Aratus refers to in the last line of the extract quoted above.
+According to Neapolitan legends, the name of Virgil's mother was Maia. The
+mother of Buddha, the Hindoo _avatar_, was also named Maia. In Italy the
+Pleiades were called _Gallinata_, and in France _poussinière_, both of
+which mean the hen and chickens, a term also given to them by Al-Sufi. The
+old Blackfoot Indians called them "The Seven Perfect Ones." The Crees and
+Ojibway Indians called them the "Fisher Stars." The Adipones of Brazil and
+some other nations claimed that they sprang from the Pleiades! The Wyandot
+Indians called them "The Singing Maidens."
+
+Photographs show that the brighter stars of the Pleiades are involved in
+nebulosity. That surrounding Maia seems to be of a spiral form. Now, there
+is a Sanscrit myth which represents Maia as "weaving the palpable
+universe," for which reason she was "typified as a spider." This seems
+very appropriate, considering the web of nebulous light which surrounds
+the stars of the group. Maia was also considered as a type of the
+universe, which again seems appropriate, as probably most of the stars
+were evolved from spiral nebulæ.
+
+The name Hyades is supposed to be derived from the Greek word ὑειν, to
+rain, because in ancient times they rose at the rainy season.
+
+In ancient Egypt, Aldebaran was called _ary_; and the Pleiades _chooa_, a
+word which means "thousands." The name Aldebaran seems to have been
+originally applied to the whole of the Hyades group. Aldebaran was also
+called by the Arabians _al-fanik_, the great Camel, and the Hyades
+_al-kilas_, the young Camels. The two close stars υ and κ Tauri were
+called _al-kalbaïn_, the dogs of Aldebaran. La Condamine states that the
+Indians of the Amazon saw in the Hyades the head of a bull.
+
+Gemini, the Twins, is the third constellation of the Zodiac. It was also
+called Gemelli, etc. According to Dupuis it represents the 11th "labour of
+Hercules"--his triumph over the dog Cerberus.[408] But some of Dupuis'
+ideas seem very fanciful. The Twins are usually called Castor and Pollux,
+but they were also called by the ancient writers Apollo and Hercules;
+Jason and Triptolemus; Amphion and Zethus; and Theseus and Peritheus. In
+Egypt they represented the deities Horus and Hippocrates. Brown thinks
+that the "Great Twins" were originally the sun and moon, "who live
+alternately. As one is born the other dies; as one rises the other
+sets."[409] This applies to the full moon, but does not seem applicable to
+the other lunar phases.
+
+Gemini was the constellation to which Dante supposed himself transported
+when he visited the stellar heavens.[410] He says he was born under the
+influence of this "sign."
+
+Cancer, the Crab, is the next sign of the Zodiac. In the Greek mythology
+it was supposed to have been placed in the sky by Juno to commemorate the
+crab which pinched the toes of Hercules in the Lernæan marsh. The Greek
+name was τυβι. According to Dupuis it represents the 12th "labour of
+Hercules"--his capture of the golden apples in the Garden of the
+Hesperides, which were guarded by a Dragon. This Dragon is Draco, which
+was also called Custos Hesperidum.[411] But the connection between a crab
+and the myth of the golden apples is not obvious--unless some reference to
+"crab apples" is intended! Among the Romans, Cancer was consecrated to
+Mercury, and by the ancient Egyptians to their god Anubis.
+
+The well-known cluster in Cancer called the Præsape, Al-Sufi says, is "a
+little spot which resembles a cloud, and is surrounded by four stars, two
+to the west [η and θ Cancri] and two to the east" [γ and δ]. This cluster
+is mentioned by Aratus, who calls it the "Manger." The word Præsape is
+often translated "Beehive," but there can be no doubt that it really means
+"Manger," referring to the stars γ and δ Cancri, which the ancients called
+Aselli, the ass's colts. These were supposed to represent the asses which
+in the war of Jupiter against the Giants helped his victory by their
+braying!
+
+Admiral Smyth says in his _Bedford Catalogue_ (p. 202) that he found γ and
+δ Cancri both of 4th magnitude; but the photometric measures show that δ
+is now distinctly brighter than γ. An occultation of δ Cancri by the moon
+is recorded as having occurred on September 3, B.C. 240.
+
+The fine constellation Leo, the Lion, is the next "sign" of the Zodiac,
+and is marked by the well-known "Sickle." According to Dupuis, it
+represents the first "labour of Hercules"--the killing of the Nemælian
+lion. Manilius called it Nemæus. It was also called Janonus sidus, Bacchi
+sidus, etc. The Greek name was μεχιρ, μεχειρ, or μεχος. In ancient Egypt,
+Leo was sacred to Osiris, and many of the Egyptian monuments are
+ornamented with lions' heads. It is stated in the Horapolla that its
+appearance was supposed to announce the annual rising of the Nile.
+
+Regulus (α Leonis) is the brightest and most southern of the stars in the
+"Sickle." Al-Sufi says "it is situated in the heart and is of the 1st
+magnitude. It is that which is called _al-maliki_, the royal star. It is
+marked on the astrolabe as _kalb al-asad_, the Heart of the Lion" (whence
+the name Cor Leonis). Modern photometric measures make it about 1·3
+magnitude. It has an 8½ magnitude companion at about 177" distance
+(Burnham) which is moving through space with the bright star, and is
+therefore at probably the same distance from the earth as its brilliant
+primary. This companion is double (8·5, 12·5: 3"·05, Burnham). The
+spectroscope shows that Regulus is approaching the earth at the rate of
+5½ miles a second. Its parallax is very small--about 0"·022, according
+to Dr. Elkin--which indicates that it is at a vast distance from the
+earth; and its brightness shows that it must be a sun of enormous size.
+Ptolemy called it βασιλισκος, whence its Latin name Regulus, first used by
+Copernicus as the diminutive of _rex_.[412]
+
+The next constellation of the Zodiac is Virgo, the Virgin. It was also
+called by the ancients Ceres, Isis, Erigone, Fortuna, Concorda, Astræa,
+and Themis. The Greek name was φαμενωθ. Ceres was the goddess of the
+harvest. Brown thinks that it probably represents the ancient goddess
+Istar, and also Ashtoreth. According to Prof. Sayce it is the same as the
+Accadian sign of "the errand of Istar, a name due to the belief that it
+was in August that the goddess Astarte descended into Hades in search of
+her betrothed, the sun god Tammuz, or Adonis, who had been slain by the
+boar's tusk."[413] The ear of corn (Spica) is found on the ancient
+Egyptian monuments, and is supposed to represent the fertility caused by
+the annual rising of the Nile. According to Aratus, the Virgin lived on
+earth during the golden age under the name of Justice, but that in the
+bronze age she left the earth and took up her abode in the heavens.
+
+  "Justice, loathing that race of men,
+  Winged her flight to heaven."
+
+The Sphinx near the Great Pyramid has the head of a virgin on the body of
+a lion, representing the goddess Isis (Virgo) and her husband Osiris
+(Leo).
+
+Al-Sufi's 5th star of Virgo is Flamsteed 63 Virginis. Al-Sufi says it is a
+double star of the 5th magnitude. In Al-Sufi's time it formed a "naked-eye
+double" with 61 Virginis, but owing to large proper motion, 61 has now
+moved about 26 minutes of arc towards the south, and no longer forms a
+double with 63. This interesting fact was first pointed out by Flammarion
+in his work _Les Étoiles_ (p. 373).
+
+Libra, the Balance, is one of the "signs" of the Zodiac, but originally
+formed the claws of the Scorpion. It was called Juguna by Cicero, and
+Mochos by Ampelius. The Greek name was φαρμουθε. Virgil suggests that it
+represented the justice of the emperor Augustus, honoured by the name of a
+constellation; but probably this refers to the birth of Augustus under the
+sign of Libra, as Scaliger has pointed out. According to Brown, "the daily
+seizing of the dying western sun by the claws of the Scorpion of darkness
+is reduplicated annually at the Autumnal Equinox, when the feeble waning
+sun of shortening days falls ever earlier into his enemy's grasp;"[414]
+and he says, "The Balance or Scales (Libra), which it will be observed is
+in itself neither diurnal nor nocturnal, is the only one of the zodiacal
+signs not Euphratean in origin, having been imported from Egypt and
+representing originally the balance of the sun at the horizon between the
+upper and under worlds; and secondarily the equality of the days and
+nights at the equinox."[415]
+
+According to Houzeau, Libra was formed at the beginning of the second
+century B.C., and it does not appear in any writings before those of
+Geminus and Varron.[416]
+
+Milton says in _Paradise Lost_:--
+
+  "The Eternal to prevent such horrid fray,
+  Hung forth in heaven his golden scales, yet seen
+  Betwixt Astræa and the Scorpion's sign."
+
+(Here Astræa is Virgo.)
+
+It is worth noticing that both Ptolemy and Al-Sufi rated the star κ Libræ
+as two magnitudes brighter than λ Libræ. The two stars are now practically
+of equal brightness (5th magnitude), and it seems impossible to believe
+that this could have been the case in Al-Sufi's time. Surely a careful
+observer like Al-Sufi, who estimated the relative brightness of stars to a
+third of a magnitude, could not possibly have made an error of two
+magnitudes in the brightness of two stars near each other! It should be
+stated, however, that κ Libræ was rated 5th magnitude by Argelander and
+Heis, and λ, 6th magnitude by the same excellent observers.
+
+The next "sign" of the Zodiac, Scorpion, was consecrated by the Romans to
+Mars, and by the Egyptians to Typhon.[417] It was called _Nepa_ by Cicero,
+_Martis sidus_ by Manilius, and _Fera magna_ by Aratus. The Greek name was
+παχων.
+
+Mr. E. B. Knobel has called attention to a curious remark of Ptolemy with
+reference to the bright star Antares (α Scorpii), "Media earum quæ _tendit
+ad rapinam_ quæ dicitur Cor Scorpionis"; and he made a similar remark
+with reference to Betelgeuse (α Orionis) and others. But Mr. Robert
+Brown[418] explains the remark by the fact that in ancient times these
+stars rose in the morning at a time when caravans were exposed to dangers
+from robbers. Thus the term had nothing to do with the aspect or colour of
+these stars, but was merely a reference to their supposed astrological
+influence on human affairs.
+
+In the Egyptian _Book of the Dead_, Silkit was a goddess who assumed the
+form of a scorpion in the sky. She was supposed to be the daughter of
+_Ra_.
+
+With reference to stars "outside" the ancient figure of Scorpio, the
+first, Al-Sufi says, "is a star which immediately follows _al-schaulat_"
+[λ] and κ, "it is of small 4th magnitude; Ptolemy calls it νεφελοειδης"
+[nebulous]. Schjelerup, in his translation of Al-Sufi's work, does not
+identify this object; but it is very evidently γ Telescopii, which lies
+exactly in the position described by Al-Sufi. Now, it is a very
+interesting and curious fact that Ptolemy called it nebulous, for in the
+same telescopic field with it is the nebula _h_ 3705 (= Dunlop 557).
+Dunlop describes it as a "small well-defined rather bright nebula, about
+20" in diameter; a very small star precedes it, but is not involved;
+following γ Telescopii." Sir John Herschel at the Cape found it fairly
+resolved into very faint stars, and adds, "The whole _ground_ of the
+heavens, for an immense extent is thickly sown with such stars. A
+beautiful object."[419] This perhaps accounts for the nebulous appearance
+of the star as seen by Ptolemy.
+
+Several _novæ_ or temporary stars are recorded as having appeared in
+Scorpio. One in the year B.C. 134 is stated by Pliny to have induced
+Hipparchus to form his catalogue of stars. This star was also observed in
+China. Its exact position is unknown, but Flammarion thinks it may
+possibly have appeared about 4° north of the star β Scorpii.
+Another new star is said to have appeared in A.D. 393, somewhere in the
+Scorpion's tail. One in A.D. 1203 and another in 1584 are also mentioned,
+the latter near π Scorpii.
+
+The constellation Scorpio seems to be referred to by Dante in his
+_Purgatorio_ (ix. 4-6) in the lines--
+
+  "De gemma la sua fronte era lucenta
+  Poste in figura del fredda animale
+  Che con la coda percota la genta,"
+
+perhaps suggested by Ovid's remark--
+
+  "Scorpius exhibit caudaque menabitur unca."[420]
+
+Next to Scorpio comes Sagittarius, the Archer. It is said to have been
+placed in the sky as a symbol of Hercules, a hero who was held in the
+greatest veneration by the ancient Egyptians. The horse, usually
+associated with this constellation, was a symbol of war. It was also
+called by the ancients Chiron, Arcitenens, Minotaurus, Croton, etc. The
+Greek name was παυνι, or παωνι. Chiron was supposed to be the son of
+Saturn and Phillyra, and first taught men to ride on horses. The name is
+derived from the Greek χειρ, a hand. Some writers, however, think that
+Chiron is represented by the constellation of the Centaur, and others say
+that Sagittarius represents the Minotaur loved by Persephone. According to
+Dupuis, Sagittarius represents the 5th "labour of Hercules," which
+consisted in hunting the birds of the lake Stymphalus, which ravaged the
+neighbouring countries. These birds are perhaps represented by Cygnus,
+Altair, and the Vulture (Lyra). The Lyre probably represents the musical
+instrument which Hercules used to frighten the birds.[421]
+
+According to Al-Sufi, the Arabians called the stars γ, δ, ε, and η
+Sagittarii which form a quadrilateral figure, "the Ostrich which goes to
+the watering place," because they compared the Milky Way to a river. They
+compared the stars σ, φ, τ, and ζ Sagittarii, which form another
+quadrilateral, to an ostrich which has drunk and returns from the
+"watering place." He says that the star λ Sagittarii forms with these two
+"ostriches" a tent, and certainly the figure formed by λ, φ, ζ, ε, and δ
+is not unlike a tent. Al-Sufi says more about these "ostriches"; but the
+ideas of the old Arabians about the stars seem very fanciful.
+
+A "temporary star" is recorded in the Chinese Annals of Ma-touan-lin as
+having appeared in May, B.C. 48, about 4° distant from μ Sagittarii.
+Another in the year 1011 A.D. appeared near the quadrilateral figure
+formed by the stars σ, τ, ζ, and φ Sagittarii. This may perhaps be
+identified with the object referred to by Hepidannus in the year 1012,
+which was of extraordinary brilliancy, and remained visible "in the
+southern part of the heavens during three months." Another is mentioned
+near the same place in A.D. 386 (April to July).[422] The number of
+"temporary stars" recorded in this part of the heavens is very remarkable.
+
+According to Brown, Sagittarius is depicted on a stone, cir. B.C. 1100,
+found at Bâbilu, and now in the British Museum.[423]
+
+       *       *       *       *       *
+
+The next of the "signs of the Zodiac" is Capricornus, the Goat. In the
+Arabo-Latin edition of Ptolemy's _Almagest_ it is called Alcaucurus. It is
+supposed to represent Amalthea, the goat which nursed Jupiter. According
+to Dupuis it represented the 6th "labour of Hercules," which was the
+cleaning out of the Augean stables.[424]
+
+α_{2} Capricorni is the northern of two stars of the 4th magnitude (α and
+β Capricorni). It really consists of two stars visible to the naked eye.
+The second of these two stars (α_{1}) is not mentioned by Al-Sufi, but I
+find that, owing to proper motion, they were nearer together in his time
+(tenth century), and were evidently seen by him as one star. β Capricorni
+(about 3rd magnitude) is a very wide double star (3½, 6; 205"), which may
+be seen with any small telescope. The fainter star was found to be a close
+double by Burnham. At present β is brighter than α, although rated of the
+same brightness by Al-Sufi.
+
+Aquarius is the next "sign of the Zodiac." It is supposed to represent a
+man pouring water out of an urn or bucket. Other names given to this
+constellation were Aristæus, Ganymede, Cecrops, Amphora, Urna, and Aqua
+tyrannus. According to Dupuis it represents the 7th "labour of Hercules,"
+which was his victory over the famous bull which ravaged Crete.[425] But
+the connection between a bull and a bucket is not obvious. Aquarius is
+represented in several places on the Egyptian monuments. Some of the
+ancient poets supposed that it represented Deucalion (the Noah of the
+Greek story of the Deluge); others thought that it represented Cecrops,
+who came to Greece from Egypt, built Athens, and was also called Bifornis.
+Others say that he was Ganymede, the cup-bearer of the gods.
+
+There is some difficulty about the identification of some of Al-Sufi's
+stars in Aquarius. His sixth star (Fl. 7) is nearly 10° south-west of β
+Aquarii, and is, Al-Sufi says, "the following of three stars in the left
+hand, and precedes the fourth [β] ... it is of the 6th magnitude. Ptolemy
+calls it third, but in reality it is very faint" [now about 6th
+magnitude]. The seventh [μ] is the middle one of the three and about 4½
+magnitude, although Al-Sufi calls it "small fifth" [Ptolemy rated it 4].
+The eighth star, ε, is the preceding of the three and about 3·8, agreeing
+closely with Al-Sufi's 4·3. Ptolemy rated it 3. This star is mentioned
+under the name _nou_ in the time of _Tcheou-Kong_ in the twelfth century
+B.C. Al-Sufi says, "These three stars are followed by a star of the 5th
+magnitude which Ptolemy has not mentioned. It is brighter than the sixth
+star" [Fl. 7]. This is evidently ν Aquarii. If, however, we plot Ptolemy's
+positions as given by Al-Sufi, it seems probable that _Ptolemy's_ sixth
+star was really ν, and that either μ or Fl. 7 was not seen by him. As
+Ptolemy called his seventh star 4th magnitude, and his sixth and eighth
+stars 3rd magnitude, some considerable change of brightness seems to have
+taken place in these stars; as ν is now only 4½ and Fl. 7 only a bright
+sixth. Variation was suspected in Fl. 7[426] by Gould. I found it very
+reddish with binocular in October, 1892. Burnham found it to be a close
+double star, the companion being about 12th magnitude at a distance of
+only 2". It is probably a binary.
+
+According to Al-Sufi, the Arabians called the second and third stars of
+the figure (α and ο Aquarii) _sad al-malik_ (_malk_ or _mulk_), "the Good
+Fortune of the king." They called the fourth and fifth stars (β and ξ
+Aquarii) with the twenty-eighth star of Capricornus (_c_) _sad al-sund_,
+"the Good Fortune of the Happy Events." "This is the 24th mansion of the
+moon." These stars rose at the time of year when the cold ends, and they
+set at the time the heat ends. Hence, Al-Sufi says, "when they rise the
+rains begin, and when they set the unhealthy winds cease, fertility
+abounds, and the dew falls." Hence probably the Arabic names. This, of
+course, applies to the climate of Persia and Arabia, and not to the
+British Isles. Al-Sufi says, "They call the 6th, 7th, and 8th stars _sad
+bula_, 'The Good Fortune which swallows up!' This is the 23rd mansion of
+the moon. They say that it is so called because that at the time of the
+Deluge it rose at the moment when God said, 'O earth! absorb the waters'
+(Koran, chap, xi., v. 46). They called the stars γ, π, ζ and η Aquarii
+_sad al-achbija_, 'the the Good Fortune of the tents'; this is the 25th
+mansion of the moon, and they give them this name because of these four
+stars, three form a triangle, the fourth [ζ] being in the middle." The
+three were considered to form a tent.
+
+The Arabians called the bright star Fomalhaut "in the mouth of the
+southern fish _al-dhifda al-auval_, 'the first Frog,' as the bright one on
+the southern point of the tail of Kîtus [Cetus] is called _al-dhifda
+al-tsani_ [β Ceti], 'the second Frog.'" Fomalhaut was also called
+_al-zhalim_, "the male ostrich."
+
+Al-Sufi says, "Some of the Arabians state that a ship is situated to the
+south of Aquarius." The stars in the Southern Fish (Piscis Australis) seem
+to be here referred to.
+
+The constellation Pisces, the Fishes, is the last of the "signs of the
+Zodiac." The Fishes appear on an ancient Greek obelisk described by
+Pococke. Among the Greeks this sign was consecrated to Venus; and in Egypt
+to Nepthys, wife of Typhon and goddess of the sea. Pisces is said to end
+the Zodiac as the Mediterranean Sea terminated Egypt. This idea was
+suggested by Schmidt, who also conjectured that the Ram (Aries) was placed
+at the beginning of the Zodiac because Thebes, a town sacred to Jupiter
+Ammon, was at the beginning of Egypt in ancient times; and he thought that
+the constellation Triangulum, the Triangle, represented the Nile Delta,
+Eridanus being the Nile.[427] The constellation was represented in ancient
+times by two fishes connected by a cord tied to their tails. The southern
+of these "fishes" lies south of the "Square of Pegasus," and the northern
+between Andromeda and Aries. According to Manilius, the origin of these
+fishes is as follows: Venus, seeing Typhon on the banks of the river
+Euphrates, cast herself with her son into the river and they were
+transformed into fishes!
+
+Some of the Arabians substituted a swallow for the northern of the two
+fishes--the one below Andromeda. The swallow was a symbol of Spring.
+According to Dupuis, Pisces represents the 8th "labour of Hercules," his
+triumph over the mares of Diomed which emitted fire from their
+nostrils.[428] But the connection between fishes and mares is not obvious,
+and some of Dupuis' ideas seem very fanciful. Here he seems to have found
+a "mare's nest."
+
+The constellation Cetus, the Whale, represents, according to ancient
+writers, the sea monster sent by Neptune to devour Andromeda when she was
+chained to the rock. Aratus calls Cetus the "dusky monster," and Brown
+remarks that "the 'Dusky Star' would be peculiarly appropriate to Mira
+(the wondrous ο Ceti)."[429] Cetus was also called Canis Tritonis, or Dog
+of the Sea, Bayer in his Atlas (1603) shows a dragon instead of a whale,
+finding it so represented on some ancient spheres. Al-Sufi calls it Kîtus
+or κητος, the whale. He says, "it is represented by the figure of a
+marine animal, of which the fore part is turned towards the east, to the
+south of the Ram, and the hinder part towards the west behind the three
+'extern' stars of Aquarius."
+
+Al-Sufi does not mention the variable star ο Ceti, now called Mira, or the
+"wonderful," nor does he refer to any star in its immediate vicinity. We
+may, therefore, conclude that it was near a minimum of light at the time
+of his observation of the stars of Cetus.
+
+The constellation of Orion, one of the finest in the heavens, was called
+by Al-Sufi _al-djabbar_, "the Giant," and also _al-djauza_, "the Spouse."
+The poet Longfellow says--
+
+  "Sirius was rising in the east
+  And, slow ascending one by one,
+  The kindling constellations shone
+  Begirt with many a blazing star
+  Stood the great giant Al-gebar
+  Orion, hunter of the beast!
+  His sword hung gleaming at his side
+  And on his arm, the lion's hide--
+  Scattered across the midnight air
+  The golden radiance of its hair."
+
+Al-Sufi says it "is represented by the figure of a standing man, to the
+south of the sun's path. This constellation very much resembles a human
+figure with a head and two shoulders. It is called _al-djabbar_, 'the
+Giant,' because it has two thrones, holds a club in his hand, and is
+girded with a sword." Orion is supposed to have been a son of Neptune;
+but there are many stories of the origin of the name. It is also said to
+be derived from the Greek word ωρα, because the constellation was used to
+mark the different times of the year. According to the ancient fable,
+Orion was killed by a scorpion, and was placed in the sky at the request
+of Diana. According to Houzeau, the name comes from _oriri_, to be born.
+Scorpio rises when Orion sets, and he thinks that the idea of the ancients
+was that the Scorpion in this way kills the giant Orion.
+
+In ancient Egypt Orion was called _Sahu_. This name occurs on the
+monuments of the Ptolemies, and also on those of the Pharaohs. It is also
+mentioned in the _Book of the Dead_. It seems to have been considered of
+great importance in ancient Egypt, as its heliacal rising announced that
+of Sirius, which heralded the annual rising of the Nile.
+
+The constellation Eridanus lies south of Taurus, east of Cetus, and west
+of Lepus. In ancient times it was supposed to represent the Nile or the
+Po. Ptolemy merely calls it Ποταμου αστερισμος, or asterism of the river.
+It was called Eridanus by the Greeks, and Fluvius by the Romans. It
+appears to correspond with the Hebrew Shicor. Al-Sufi calls it _al-nahr_,
+"the River."
+
+One of the most interesting points in Al-Sufi's most interesting work is
+the identity of the bright star known to the ancient astronomers as
+_achir al-nahr_, "the End of the River," and called by Ptolemy Εσχατος του
+ποταμου, "the Last in the River." Some astronomers have identified this
+star with α Eridani (Achernar), a bright southern star of the 1st
+magnitude, south of Eridanus. But Al-Sufi's description shows clearly that
+the star he refers to is really θ Eridani; and the reader will find it
+interesting to follow his description with a star map before him.
+Describing Ptolemy's 34th star of Eridanus (the star in question), he
+says, "the 34th star is found before [that is west of] these three stars
+[the 31st, 32nd, and 33rd, which are υ{2}, Du, and υ' in Proctor's Atlas],
+the distance between it and that of the three which is nearest being about
+4 cubits [9° 20']. It is of the first magnitude; it is that which is
+marked on the southern astrolabe, and called _achir al-nahr_, 'the End of
+the River.' There are before this bright one two stars, one to the south,
+[σ Eridani, not shown in Proctor's small Atlas], the other to the north [ι
+Eridani]; Ptolemy does not mention these. One of these stars is of the 4th
+magnitude, the other of the 5th. There is behind the same [that is, east
+of it] a star of the 4th magnitude distant from it two cubits [ε Eridani].
+To the south of the three stars which follow the bright one there are some
+stars of the 4th and 5th magnitudes, which he [Ptolemy] has not
+mentioned."
+
+Now, a glance at a star map of this region will show clearly that the
+bright star referred to by Al-Sufi is undoubtedly θ Eridani, which is
+therefore the star known to the ancients as the "End of the River," or the
+"Last in the River."
+
+The position given by Ptolemy agrees fairly well with Al-Sufi's
+description, although the place is slightly erroneous, as is also the case
+with Fomalhaut and β Centauri. It is impossible to suppose that either
+Ptolemy or Al-Sufi could have seen α Eridani, as it is too far south to be
+visible from their stations, and, owing to the precession of the
+equinoxes, the star was still further south in ancient times. Al-Sufi says
+distinctly that the distance between Ptolemy's 33rd star (which is
+undoubtedly _h_ Eridani, or Proctor's υ') and the 34th star was "4
+cubits," or 9° 20'. The actual distance is about 9° 11', so that Al-Sufi's
+estimate was practically correct. Halley, in his _Catalogus Stellarium
+Australium_, identifies Ptolemy's star with θ Eridani, and Baily agreed
+with him.[430] Ulugh Beigh also identifies the "Last in the River" with θ
+Eridani. The Arabic observer Mohammed Ali Achsasi, who observed in the
+seventeenth century, called θ Eridani _Achr al-nahr_, and rated it first
+magnitude.[431] To argue, as Bode and Flammarion have done, that Ptolemy
+and Al-Sufi may have heard of α Eridani from travellers in the southern
+hemisphere, is to beg the whole question at issue. This is especially true
+with reference to Al-Sufi, who says, in the preface to his work, that he
+has described the stars "as seen with my own eyes." α Eridani is over 11
+"cubits" from _h_ Eridani instead of "4 cubits" as Al-Sufi says. This
+shows conclusively that the star seen by Al-Sufi was certainly _not_ α
+Eridani. The interest of the identification is that Al-Sufi rated θ
+Eridani of the _first_ magnitude, whereas it is now only 3rd magnitude! It
+was measured 3·06 at Harvard and estimated 3·4 by Stanley Williams, so
+that it has evidently diminished greatly in brightness since Al-Sufi's
+time. There is an interesting paper on this subject by Dr. Anderson (the
+discoverer of Nova Aurigæ and Nova Persei) in _Knowledge_ for July, 1893,
+in which he states that the "Last in the River," according to the
+statements of Hipparchus and Ptolemy, _did_ rise above their horizon at a
+certain time of the year, which α Eridani could not possibly have done.
+This seems sufficient to settle the question in favour of θ Eridani. Dr.
+Anderson says, "It is much to be regretted that Professor Schjellerup, the
+able and industrious translator of Sufi, has allowed this to escape his
+notice, and helped in the preface and note to his work to propagate the
+delusion that α Eridani is Ptolemy's 'Last in the River'"; and in this
+opinion I fully concur. Al-Sufi's clear account places it beyond a doubt
+that the star known to Hipparchus, Ptolemy, Al-Sufi, and Ulugh Beigh as
+the "Last in the River" was θ Eridani. θ must have diminished greatly in
+brightness since Al-Sufi's time, for in ranking it as 1st magnitude he
+placed it in a very select list. He only rated thirteen stars in the whole
+heavens as being of the 1st magnitude. These are: Arcturus, Vega, Capella,
+Aldebaran, Regulus, β Leonis, Fomalhaut, Rigel, θ Eridani, Sirius,
+Procyon, Canopus, and α Centauri. _All_ these stars were actually _seen_
+by Al-Sufi, _and described from his own observations_. He does not mention
+α Eridani, as it was not visible from his station in Persia.
+
+θ Eridani is a splendid double star (3·40, 4·49: 8"·38, 1902, Tebbutt). I
+found the components white and light yellow with 3-inch refractor in the
+Punjab. Dr. Gould thinks that one of the components is variable to some
+extent. This is interesting, considering the brilliancy of the star in
+Al-Sufi's time. The brighter component was found to be a spectroscopic
+binary by Wright, so that on the whole the star is a most interesting
+object.
+
+The small constellation Lepus, the Hare, lies south of Orion. Pliny calls
+it Dasypus, and Virgil Auritus. In ancient Egypt it was the symbol of
+vigilance, prudence, fear, solitude, and speed.[432] It may perhaps
+represent the hare hunted by Orion; but some say it was placed in the sky
+to commemorate a terrible plague of hares which occurred in Sicily in
+ancient times.
+
+A little north-west of the star μ Leporis is Hind's "crimson star" (R.A.
+4{h} 53{m}, S. 14° 57', 1900) described by him as "of the most intense
+crimson, resembling a blood drop on the background of the sky; as regards
+depth of colour, no other star visible in these latitudes could be
+compared with it." It is variable from about the 6th to the 8th magnitude,
+with a period of about 436 days from maximum to maximum.
+
+The constellation Canis Major, the Great Dog, is remarkable for containing
+Sirius, the brightest star in the heavens. In the Greek mythology it was
+supposed to represent a dog given by Aurora to Cephalus as the swiftest of
+all dogs. Cephalus wished to match it against a fox which he thought
+surpassed all animals for speed. They both ran for so long a time, so the
+story goes, that Jupiter rewarded the dog by placing it among the stars.
+But probably the dog comes from Anubis, the dog-headed god of the ancient
+Egyptians. According to Brown, Theogirius (B.C. 544) refers to the
+constellation of the Dog.[433] He thinks that Canis Major is probably "a
+reduplication" of Orion; Sirius and β Canis Majoris corresponding to α and
+γ Orionis; δ, 22, and ε Canis Majoris to the stars in Orion's belt (δ, ε,
+and ζ Orionis); and η; and κ Canis Majoris with κ and β Orionis.[434]
+
+The Arabic name of Sirius was _al-schira_, which might easily be corrupted
+into Sirius. The Hebrew name was Sihor. According to Plutarch, the
+Ethiopians paid regal honours to the Celestial Dog. The Romans used to
+sacrifice a dog in its honour at the fetes called Robigalia, which were
+held on the seventh day before the Calends of May, and nine days after the
+entry of the sun into Taurus. Pliny says, "Hoc tempus Varro determinat
+sole decimam partem Tauri obtinenti quod canis occidit, sidus per se
+vehemens," etc.[435]
+
+Owing to some remarks of Cicero, Horace, and Seneca, it has been supposed
+that in ancient times Sirius was of red colour. Seneca says, "Nec mirum
+est, si terra omnis generis et varia evaporatio est; quam in cœlo
+quoque non unus appareat color rerum, sed acrior sit Caniculæ rubor,
+Nartis remissior, Jovis nullus, in lucem puram nitore perducto."[436] It
+is now brilliantly white with a bluish tinge. But this change of colour is
+somewhat doubtful. The remarks of the ancient writers may possibly refer
+to its great brilliancy rather than its colour. Al-Sufi says nothing about
+its colour, and it was probably a white star in his time. If it were red
+in his day he would most probably have mentioned the fact, as he does in
+the case of several red stars. Brown, however, quotes the following from
+Ibn Alraqqa, an Arabian observer:--
+
+  "I recognize Sirius _shining red_, whilst the morning is becoming white.
+  The night fading away, has risen and left him,
+  The night is not afraid to lose him, since he follows her."
+
+Schjellerup thinks that it is very doubtful that Sirius was really red as
+seen by Hipparchus and Ptolemy. But in an exhaustive inquiry made by Dr.
+See on the supposed change of colour,[437] he comes to the conclusion that
+Sirius was really red in ancient times. Seneca states distinctly that it
+was redder than Mars (see extract above), and other ancient writers refer
+to its red colour. It has been generally supposed that the Arabian
+astronomer Alfraganus, in his translation of Ptolemy's _Almagest_, refers
+to only five red stars observed by Ptolemy, namely, Arcturus, Aldebaran,
+Betelgeuse, Antares, and Pollux. But Dr. See shows that this idea is due
+to a mistranslation of Alfraganus by Plato Tibertinus in 1537, and that
+Ptolemy did not speak of "five red stars," but five _nebulous_ stars, as
+stated by Christmann and Golius. Ptolemy described Sirius as υποκιρρος,
+"fiery red," the same word used with reference to the other stars
+mentioned above. The change of colour, if any, probably took place before
+Al-Sufi's time.
+
+Dr. See says--
+
+    "Prof. Newcomb rejects the former well-authenticated redness of
+    Sirius, because he cannot explain the fact. But the ink was scarcely
+    dry on his new book on the stars, in which he takes this position,
+    when Nova Persei blazed forth in 1901; and observers saw it change
+    colour from day to day and week to week. Could any one explain the
+    cause of these numerous and conspicuous changes of colour? Shall we,
+    then, deny the changes of colour in Nova Persei, some of which were
+    noticed when it was nearly as bright as Sirius?"[438]
+
+On the ceiling of the Memnonium at Thebes the heliacal rising of Sirius is
+represented under the form and name of Isis. The coincidence of this
+rising with the annual rising of the Nile is mentioned by Tibullus and
+Aclian. About 4000 B.C. the heliacal rising of Sirius coincided with the
+summer solstice (about June 21) and the beginning of the rising of the
+Nile. The festival in honour of this event was held by the Egyptians about
+July 20, and this marked the beginning of the sacred Egyptian year. On the
+summit of Mount Pelion in Thessaly there was a temple dedicated to Zeus,
+where sacrifices were offered at the rising of Sirius by men of rank who
+were chosen for the purpose by the priests and wore fresh sheepskins.
+
+Sirius seems to have been worshipped by the ancient Egyptians under the
+name of Sothis, and it was regarded as the star of Isis and Osiris. The
+last name without the initial O very much resembles our modern name.
+
+According to Al-Sufi, the Arabians called Sirius _al-schira al-abûr_,
+"Sirius which has passed across," also _al-schira al Jamânija_, "the
+Sirius of Yémen." He says it is called _al-abûr_, "because it has passed
+across the Milky Way into the southern region." He relates a mythological
+story why Sirius "fled towards the south" and passed across the Milky Way
+towards Suhail (Canopus). The same story is told by Albufaragius[439]
+(thirteenth century). (The story was probably derived from Al-Sufi.) Now,
+it seems to me a curious and interesting fact that the large proper motion
+of Sirius would have carried it across the Milky Way from the eastern to
+the western border in a period of 60,000 years. Possibly the Arabian story
+may be based on a tradition of Sirius having been seen on the opposite, or
+eastern, side of the Milky Way by the men of the early Stone Age. However
+this may be, we know from the amount and direction of the star's proper
+motion that it must have passed across the Milky Way from east to west
+within the period above stated. The Arabic name _al-abûr_ is not,
+therefore, a merely fanciful one, but denotes an _actual fact_. The
+proper motion of Sirius could not possibly have been known to the
+ancients, as it was only revealed by accurate modern observations.
+
+The little constellation Canis Minor, the Little Dog, lies south of Gemini
+and Cancer. Small as it is, it was one of the original forty-eight
+constellations of Ptolemy. In the Greek mythology it was supposed to
+represent either one of Diana's hunting dogs, or one of Orion's hounds.
+Ovid calls it the dog of Icarus. Others say it was the dog of Helen, who
+was carried off by Paris. According to the old poets, Orion's dog, or the
+dog of Icarus, threw himself into a well after seeing his master perish.
+The name Fovea, given to the constellation by Bayer, signifies a pit where
+corn was deposited. This comes from the fact that the rising of the star
+Procyon (α Canis Minoris) indicated the season of abundance. But Lalande
+thought it more probable that the idea of a pit came from the Greek
+σειρος, which means a corn store, and that it was confounded with Sirius.
+
+The name of the bright star Procyon (α Canis Minoris) is derived from the
+Greek προκυων, "the advanced day," because it appeared in the morning sky
+before Sirius. Procyon was called by the Hindoos Hanouman after their
+famous monkey god, from whose tail a bridge is said to have been formed to
+enable the army of Rama to pass from India to Ceylon. Al-Sufi says that
+the star was marked on the old astrolabes as _al-schira al-schamia_, "the
+Syrian Sirius." It was also called, he says, _al-schira al-gumaisa_, "the
+Sirius with blear eyes" (!) from weeping because Sirius had passed across
+the Milky Way, Procyon remaining on the eastern side. Here we have the
+same legend again. The proper motion of Procyon (about the same in amount
+and direction as that of Sirius) shows that the star has been on the
+eastern side of the Milky Way for many ages past. About 60,000 years
+hence, Procyon will be near the star θ Canis Majoris, and will then--like
+Sirius--have passed across the Milky Way.
+
+Argo, the Ship, is a large constellation south of Hydra, Monoceros, and
+Canis Major. It is called by Al-Sufi _al-safîna_, "the Ship." It is
+supposed to represent the first ship ever built. The name is derived from
+the builder Argo, or from the Greek word Αργος. This ship is said to have
+been built in Thessaly by order of Minerva and Neptune, to go on the
+expedition for the conquest of the golden fleece. The date of this
+expedition, commanded by Jason, is usually fixed at 1300 or 1400 B.C. With
+reference to the position of this supposed ship in the sky, Proctor says,
+"It is noteworthy that when we make due correction for the effects of
+precession during the past 4000 years, the old constellation Argo is set
+on an even keel, instead of being tilted some 45° to the horizon, as at
+present when due south." He connects Argo with Noah's Ark.
+
+The brightest star of Argo is Canopus, called Suhaïl by Al-Sufi. It is the
+second brightest star in the heavens; but it is not visible in northern
+latitudes. The Harvard photometric measures make it nearly one magnitude
+brighter than the zero magnitude, about two magnitudes brighter than
+Aldebaran, and about half the brightness of Sirius. This fine star has
+been suspected of variable light. Webb says, "It was thought (1861) in
+Chili brighter than Sirius." Observing it in the Punjab, the present
+writer found it on several occasions but little inferior to Sirius,
+although very low on the southern horizon. From recent observations by Mr.
+H. C. McKay in Australia, he believes that it is variable to the extent of
+at least half a magnitude.[440] But it is difficult to establish
+variations of light in very bright stars. The parallax of Canopus is
+_very_ small, so its distance from the earth is very great, and it must be
+a sun of gigantic size. According to Al-Fargani, Canopus was called the
+star of St. Catherine by the Christian pilgrims in the tenth century.[441]
+It was called Suhaïl by the old Arabians, a name apparently derived from
+the root _sahl_, "a plain"; and Schjellerup suggests that the name was
+probably applied to this and some other southern stars because they seem
+to move along a plain near the southern horizon. Al-Sufi says that he
+measured the latitude of Schiraz in Persia, where he observed, and found
+it to be 29° 36'; and hence for that place Canopus, when on the meridian,
+had an altitude of about 9°. Canopus was the ancient name of Aboukir in
+Egypt, and is said to have derived its name from the pilot of Menelaus,
+whose name was Kanobus, and who died there from the bite of a snake. The
+star is supposed to have been named after him, and it was worshipped by
+the ancient Egyptians.
+
+Al-Sufi does not mention the famous variable star η Argûs, which, owing to
+the precession of the equinoxes, he might possibly have seen _close to the
+horizon_, if it had been a bright star in his day. It lies between φ
+Velorum and α Crucis. Both of these stars are mentioned by Al-Sufi, but he
+says nothing of any bright star (or indeed any star) between them. This
+negative evidence tends to show that η Argûs was not visible to the naked
+eye in Al-Sufi's time. This extraordinary star has in modern times varied
+through all degrees of brightness from Sirius down to the 8th magnitude!
+Schönfeld thought that a regular period is very improbable. It seems to be
+a sort of connecting link between the long period variables and the _novæ_
+or temporary stars. It is reddish in colour, and the spectrum of its light
+is very similar to that of the temporary stars. Whether it will ever
+become a brilliant object again, time alone can tell; but from the fact
+that it was presumably faint in Al-Sufi's time, and afterwards increased
+to the brightness of Sirius, it seems possible that its light may again
+revive.
+
+The long constellation Hydra lies south of Cancer, Leo, Crater, Corvus,
+Virgo, and Libra. It was also called Asina, Coluber, Anguis, Sublimatus,
+etc. In the Greek mythology it was supposed to represent the Lernæan
+serpent killed by Hercules. According to Ovid, who fixed its acronycal
+rising for February 14, it had a common origin with Corvus and Crater.
+Apollo, wishing to sacrifice to Jupiter, sent the Crow with a cup to fetch
+water. On his way to the well the Crow stopped at a fig tree and waited
+for the fruit to ripen! Afterwards, to excuse his delay, he said that a
+serpent had prevented him from drawing the water. But Apollo, to punish
+the Crow for his deception, changed his plumage from white to black, and
+ordered the serpent to prevent the Crow from drinking.[442] Hydra was
+called by Al-Sufi _al-schudja_, "the Serpent, or Hydra." He says that "it
+contains twenty-five stars in the figure and two 'outside', and its head
+is to the south of the southern scale of the Balance" (α Libræ). But this
+is clearly a mistake (one of the very few errors to be found in Al-Sufi's
+work), for he goes on to say that the head is composed of four stars
+forming a figure like the head of a horse, and he adds, "This head is in
+the middle between _al-shira al-gumaisa_ [Procyon] and _Kalb al-asad_
+[Regulus] the Heart, inclining from these two stars a little to the
+south." This clearly indicates the stars δ, ε, η, and σ Hydræ which, with
+ζ Hydræ, have always been considered as forming the Hydra's head. These
+stars lie south of α and β Cancri, not south of Libra as Al-Sufi says
+(doubtless by a slip of the pen).
+
+Ptolemy's 12th star of Hydra (α Hydræ) is, Al-Sufi says, "the bright red
+star which is found at the end of the neck where the back begins; it is of
+the 2nd magnitude. It is that which is marked on the astrolabe as _unk
+al-schudja_, 'the neck of the serpent,' also _al-fard_, 'the solitary
+one.'" Al-Sufi's estimate of its brightness agrees well with modern
+measures; but it has been suspected of variable light. Sir John Herschel's
+estimates at the Cape of Good Hope varied from 1·75 to 2·58 magnitude. He
+thought that its apparent variation might be due to its reddish colour,
+and compares it to the case of α Cassiopeiæ. But as this latter star is
+now _known_ to be irregularly variable it seems probable that α Hydræ may
+be variable also. Gemmill found it remarkably bright on May 9, 1883, when
+he thought it nearly equal to Pollux (1·2 magnitude). On the other hand,
+Franks thought it nearer the 3rd than the 2nd magnitude on March 2, 1878.
+On April 9, 1884, the present writer found it only slightly less than
+Regulus (1·3 magnitude). On April 6, 1886, how-ever, it was considerably
+less than Regulus, but half a magnitude brighter than β Canis Minoris, or
+about 2½ magnitude. In the Chinese Annals it is called the "Red Bird."
+In a list of thirty stars found on a tablet at Birs-Nimroud, it is called
+"The son of the supreme temple." Although to the naked eye deserving the
+name of Alphard or "the solitary one," it is by no means an isolated star
+when examined with a telescope. It has a faint and distant companion,
+observed by Admiral Smyth; and about 25' to the west of it Ward saw a
+small double star (8, 13: 90°: 50"). With a 3-inch refractor in the
+Punjab, I saw a small star of about 8½ magnitude to the south and a
+little east of the bright star, probably identical with Smyth's companion.
+Farther off in the same direction I saw a fainter star, and others at
+greater distances in the field. There is also a faint star a little to the
+north. I also saw Ward's double with the 3-inch telescope.
+
+There is some difficulty in identifying the stars numbered by Ptolemy 13,
+14, and 15 in Hydra. Having plotted a map from Ptolemy's positions (as
+given by Al-Sufi), I have come to the conclusion that Ptolemy's stars are
+13 = κ Hydræ; 14 = υ; and 15 = λ Hydræ, probably. From the clear
+description given by Al-Sufi of the stars observed by _him_, I find that
+_his_ stars are 13 = υ_{1}; 14 = υ_{2}; and 15 = λ Hydræ. We must,
+therefore, conclude that Ptolemy and Al-Sufi saw only three stars where
+now there are four,[443] and that κ Hydræ was not seen, or at least is not
+mentioned by Al-Sufi. κ is, therefore, probably variable. It was rated 4
+by Tycho Brahé, Bayer, and Hevelius; it is at present about 5th magnitude.
+If Ptolemy did not see υ_{2} it is probably variable also, and, indeed, it
+has been suspected of variable light.[444]
+
+The small constellation of Crater, the Cup, lies north of Hydra, and south
+of Leo and Virgo. Al-Sufi calls it _al-batija_, "the Jar, or Cup." He says
+the Arabians called it _al-malif_, "the Crib, or Manger." According to
+Brown, the stars of Crater exactly form a Bakhian κανθαρος, with its two
+handles rising above the two extremities of the circumference.[445] An
+Asia Minor legend "connected Crater with the mixing of human blood with
+wine in a bowl." Crater is referred to by Ovid in the lines--
+
+  "Dixit et antiqui monumenta perennia facti
+  Anguis, Avis, Crater sidera, juncta micunt."
+
+The star α Crateris was rated 4th magnitude by Al-Sufi and all other
+observers, and the Harvard measures make it 4·20, a satisfactory
+agreement. It has three companions noted by Admiral Smyth. One of these he
+called "intense blood colour." This is R Crateris, now known to be
+variable from above the 8th magnitude to below the 9th. Sir John Herschel
+called it an "intense scarlet star, a curious colour." With 3-inch
+refractor in the Punjab I found it "full scarlet." It is one of an open
+pair, the further of the two from α. There is a third star about 9th
+magnitude a little south of it. Ward saw a 13th magnitude star between α
+and R with a 2⅞-inch (Wray) refractor. This I saw "readily" with my
+3-inch. Smyth does not mention this faint star, although he used a much
+larger telescope.
+
+Corvus, the Crow, is a small constellation, north of Hydra. Aratus says
+"the Crow form seems to peck the fold of the water snake" (Hydra). The
+victory which Valerius Corvinus is said to have owed to a crow has given
+it the name of Pomptina, because the victory took place near the Pontine
+marshes.[446] A quadrilateral figure is formed by its four brightest
+stars, γ, δ, β, and ε Corvi. This figure has sometimes been mistaken for
+the Southern Cross by those who are not familiar with the heavens. But the
+stars of the Southern Cross are much brighter.
+
+The constellation Centaurus, the Centaur, lies south of Hydra and Libra,
+and north of the Southern Cross. According to Dupuis, Centaurus represents
+the 3rd "labour of Hercules," his triumph over the Centaurs.[447] The
+Centaurs were supposed to be a people living in the vicinity of Mount
+Ossa, who first rode on horses. The constellation was also called Semivir,
+Chiron, Phobos, Minotaurus, etc. Al-Sufi says it "is represented by the
+figure of an animal, of which the forepart is the upper part of a man from
+the head to end of the back, and its hinder part is the hinder part of a
+horse, from the beginning of the back to the tail. It is to the south of
+the Balance [Libra] turning its face towards the east, and the hinder part
+of the beast towards the west."
+
+Al-Sufi describes very clearly the four bright stars of the famous
+"Southern Cross." Owing to precession these stars were some 7° further
+north in the tenth century than they are at present, and they could have
+been all seen by Al-Sufi, when on the meridian. In the time of Ptolemy and
+Hipparchus, they were still further north, and about 5000 years ago they
+were visible in the latitude of London. Dante speaks of these four stars
+as emblematical of the four cardinal virtues, Justice, Temperance,
+Fortitude, and Prudence.
+
+Closely south-east of α and β Crucis is the dark spot in the Milky Way
+known as the "Coal Sack," which forms such a conspicuous object near the
+Southern Cross. It was first described by Pinzon in 1499; and afterwards
+by Lacaille in 1755. Although to the naked eye apparently black,
+photographs show that it contains many faint stars, but, of course, much
+less numerous than in the surrounding regions. The dark effect is chiefly
+caused by contrast with the brilliancy of the Milky Way surrounding it.
+
+Al-Sufi also mentions the bright stars α and β Centauri which follow the
+Southern Cross. He says that the distance between them "is four cubits,"
+that is about 9° 20', but it is less than this now. α has a large "proper
+motion" of 3"·67 per annum, and was farther from β in Al-Sufi's time than
+it is at present. This, however, would not _wholly_ account for the
+difference, and Al-Sufi's over-estimate is probably due to the well-known
+effect by which the distance between two stars is _apparently_ increased
+when they are near the horizon. Several of Al-Sufi's distances between
+southern stars are over-estimated, probably for the same reason.
+
+The constellation Lupus, the Wolf, is south of Libra and Scorpio. It lies
+along the western border of the Milky Way. According to ancient writers it
+represents Lycaon, King of Arcadia, a contemporary of Cecrops, who is said
+to have sacrificed human victims, and on account of his cruelty was
+changed into a wolf. Another fable is that it represents a wolf
+sacrificed by the Centaur Chiron. According to Brown, Lupus appears on the
+Euphratian planisphere discovered by George Smyth in the palace of
+Sennacherib. Al-Sufi called it _al-sabu_, "the Wild Beast." It was also
+called _al-fand_, "the Leopard," and _al-asada_, "the Lioness."
+
+Ara, the Altar, lies south of Scorpio. According to ancient writers it
+represents an altar built by Vulcan, when the gods made war against the
+Titans. It is called by Al-Sufi _al-midjman_, "the Scent Box," or "the
+Altar."
+
+The little constellation Corona Australis, the Southern Crown, lies south
+and west of Sagittarius, east of Scorpio, and west of Telescopium. Aratus
+refers to the stars in Corona Australis as--
+
+                          "Other few
+  Before the Archer under his forefeet
+  Led round in circle roll without a name."[449]
+
+But the constellation was known by the names Caduceus, Orbiculus, Corona
+Sagittarii, etc. The ancient poets relate that Bacchus placed this crown
+in the sky in honour of his mother Semele.[450] Others say that it
+represents the crown conferred on Corinne of Thebes, famous as a poet.
+
+The small constellation Piscis Australis, or the Southern Fish, lies
+south of Capricornus and Aquarius. In the most ancient maps it is
+represented as a fish drinking the water which flows from the urn of
+Aquarius.
+
+       *       *       *       *       *
+
+A good many constellations have been added to the heavens since the days
+of Al-Sufi, and notes on some of these may be of interest.
+
+CAMELOPARDALIS.--This constellation first appears on a celestial
+planisphere published by Bartschius in the year 1624. It was not formed by
+Bartschius himself, but by the navigators of the sixteenth century. It
+lies south of Ursa Minor, north of Perseus and Auriga, east of Draco, and
+west of Cassiopeia. It contains no star brighter than the 4th magnitude.
+
+LYNX.--This constellation is south of Camelopardalis and Ursa Major, and
+north of Gemini and Cancer. It was formed by Hevelius in 1660, and he
+called it the Lynx, because, he said, it contained only faint stars and
+"it was necessary to have the eyes of a lynx" to see them! Some of them
+were, however, observed by Ptolemy and Al-Sufi, and are mentioned by the
+latter under Ursa Major.
+
+CANES VENATICI, or the Hunting Dogs.--This was formed by Hevelius in 1660.
+It lies south of the Great Bear's tail, north of Coma Berenices, east of
+Ursa Major, and west of Boötis. Its brightest stars α (12) and β (8) were
+observed by Al-Sufi, and included by him in the "extern" stars of Ursa
+Major.
+
+COMA BERENICES.--This constellation lies between Canes Venatici and Virgo.
+Although it was not included among the old forty-eight constellations of
+Ptolemy, it is referred to by Al-Sufi as the Plat, or Tress of Hair, and
+he included its stars Flamsteed 12, 15, and 21 in the "extern" stars of
+Leo. It was originally formed by the poet Callimachus in the third century
+B.C., but was not generally accepted until reformed by Hevelius.
+Callimachus lived at Alexandria in the reigns of Ptolemy Philadelphus and
+Ptolemy Euergetes, and was chief librarian of the famous library of
+Alexandria from about B.C. 260 until his death in B.C. 240. Eratosthenes
+was one of his pupils. The history of the constellation is as follows:
+Berenice, wife of Ptolemy Euergetes, made a vow, when her husband was
+leaving her on a military expedition, that if he returned in safety she
+would cut off her hair and consecrate it in the temple of Mars. Her
+husband returned, and she fulfilled her vow. But on the next day the hair
+had disappeared--stolen from the temple--and Conon the mathematician
+showed Ptolemy seven stars near the constellation of the Lion which did
+not belong to any constellation. These were formed into a constellation
+and called Berenice's Hair. Conon is referred to by Catullus in the
+lines--
+
+  "Idem me ille Conon cœleste numine vidit
+  E. Berenico vertice Cæsariem."
+
+Coma Berenices first occurs as a distinct constellation in the catalogue
+contained in the Rudolphine Tables formed by Kepler (epoch 1600) from the
+observations of Tycho Brahé.[451] Bayer substituted a sheaf of corn, an
+idea derived from an ancient manuscript.
+
+LEO MINOR.--This small constellation lies between Ursa Major and Leo, and
+east of the Lynx. It was formed by Halley about the year 1660; but is
+referred to by Al-Sufi, who includes one of its stars (Fl. 41) in the
+"extern" stars of Leo. There are, however, several brighter stars in the
+group. The brightest, Fl. 46, was measured 3·92 at Harvard. The star Fl.
+37 was called _præcipua_ (or brightest) by Tycho Brahé, and rated 3, but
+as it was measured only 4·77 at Harvard it may possibly have diminished in
+brightness.
+
+SEXTANS.--This constellation lies south of Leo, and north and east of
+Hydra. It was formed by Hevelius about the year 1680. According to the
+Harvard photometric measures its brightest star is Fl. 15 (4·50).
+
+MONOCEROS, or the Unicorn, lies south of Gemini and Canis Minor, north of
+Canis Major and Argo, east of Orion, and west of Hydra. It appears on the
+planisphere of Bartschius, published in 1624. According to Scaliger it is
+shown on an old Persian sphere. One of its stars, Fl. 22, is mentioned by
+Al-Sufi among the "extern" stars of Canis Major (No. 1). Another, Fl. 30,
+is given under Hydra ("Extern" No. 1) and Fl. 8, 13, and 15 are apparently
+referred to in Gemini. The star 15 Monocerotis is a little south of ξ
+Geminorum, and was measured 4·59 magnitude at Harvard. It was at one time
+supposed to be variable with a short period (about 3½ days), but this
+variation has not been confirmed. The spectrum is of the fifth type--with
+bright lines--a very rare type among naked-eye stars. It is a triple star
+(5, 8·8, 11·2: 2"·9, 16"·3) and should be seen with a 4-inch telescope. It
+has several other small companions, one of which (139°·2: 75"·7) has been
+suspected of variation in light. It was estimated 8½ by Main in 1863,
+but only 12 by Sadler in 1875. Observing it on March 28, 1889, with 3-inch
+refractor, I found it about one magnitude brighter than a star closely
+preceding, and estimated it 8 or 8½ magnitude. It is probably variable
+and should be watched.
+
+SCUTUM SOBIESKI.--This is, or was, a small constellation in the southern
+portion of Aquila, which was formed by Hevelius in 1660 in honour of the
+Polish hero Sobieski. Its principal stars, which lie south-west of λ
+Aquilæ, were mentioned by Al-Sufi and are referred to by him under that
+constellation. It contains a very bright spot of Milky Way light, which
+may be well seen in the month of July just below the star λ Aquilæ.
+Closely south of the star 6 Aquilæ is a remarkable variable star R Scuti
+(R.A. 18{h} 42{m}·2, S. 5° 49'). It varies from 4·8 to 7·8 with an
+irregular period. All the light changes can be observed with a good
+opera-glass.
+
+VULPECULA, the Fox.--This modern constellation lies south of Cygnus, north
+of Sagitta and Delphinus, east of Hercules, and west of Pegasus. It was
+formed by Hevelius in 1660. One of its stars, 6 Vulpeculæ, is mentioned by
+Al-Sufi in describing the constellation Cygnus. Closely north-west of 32
+Vulpeculæ is the short-period variable T Vulpeculæ. It varies from 5·5 to
+6·2 magnitude, and its period is 4·436 days. This is an interesting
+object, and all the changes of light can be observed with an opera-glass.
+
+LACERTA.--This little constellation lies south of Cepheus and north of
+Pegasus. Its formation was first suggested by Roger and Anthelm in 1679,
+and it was called by them "The Sceptre and the Hand of Justice." It was
+named Lacerta by Hevelius in 1690, and this name it still retains. Al-Sufi
+seems to refer to its stars in his description of Andromeda, but does not
+mention any star in particular. It brightest star Fl. 7 (α Lacertæ) is
+about the 4th magnitude. About one degree south-west of 7 is 5 Lacertæ, a
+deep orange star with a blue companion in a fine field.
+
+There are some constellations south of the Equator which, although above
+Al-Sufi's horizon when on the meridian, are not described by him, as they
+were formed since his time. These are as follows:--
+
+SCULPTOR.--This constellation lies south of Aquarius and Cetus, and north
+of Phœnix. Some of its stars are referred to by Al-Sufi under Eridanus as
+lying within the large triangle formed by β Ceti, Fomalhaut, and α
+Phœnicis. The brightest star is α, about 12° south of β Ceti (4·39
+magnitude Harvard). About 7° south-east of α is the red and variable star
+R Sculptoris; variable from 6·2 to 8·8 magnitude, with a period of about
+376 days. Gould describes it as "intense scarlet." It has a spectrum of
+the fourth type.
+
+PHŒNIX.--This constellation lies south of Sculptor. Some of its stars are
+referred to by Al-Sufi, under Eridanus, as forming a boat-shaped figure.
+These are evidently α, κ, μ, β, ν, and γ. α is at the south-eastern angle
+of Al-Sufi's triangle referred to above (under "Sculptor"). (See Proctor's
+Atlas, No. 3.)
+
+FORNAX, the Furnace, lies south of Cetus, west of Eridanus, and east of
+Sculptor and Phœnix. It was formed by Lacaille, and is supposed to
+represent a chemical furnace with an alembic and receiver! Its brightest
+star, α Fornacis, is identical with 12 Eridani.
+
+CÆLUM, the Sculptor's Tools, is a small constellation east of Columba, and
+west of Eridanus. It was formed by Lacaille. The brightest stars are α and
+γ, which are about 4½ magnitude. α has a faint companion; and γ is a wide
+double star to the naked eye.
+
+ANTLIA, the Air Pump, lies south of Hydra, east and north of Argo, and
+west of Centaurus. It was formed by Lacaille. It contains no star brighter
+than 4th magnitude. The brightest, α, has been variously rated from 4 to
+5, and Stanley Williams thinks its variability "highly probable."
+
+NORMA, the Rule, lies south of Scorpio. It contains no star brighter than
+the 4th magnitude.
+
+TELESCOPIUM.--This modern constellation lies south of Corona Australis,
+and north of Pavo. Its stars α, δ, and ζ, which lie near the northern
+boundary of the constellation, are referred to by Al-Sufi in his
+description of Ara.
+
+MICROSCOPIUM.--This small constellation is south of Capricornus, and west
+of Piscis Australis. Its stars seem to be referred to by Al-Sufi as having
+been seen by Ptolemy, but he does not specify their exact positions. It
+contains no star brighter than 4½ magnitude.
+
+       *       *       *       *       *
+
+South of Al-Sufi's horizon are a number of constellations surrounding the
+south pole, which, of course, he could not see. Most of these have been
+formed since his time, and these will now be considered; beginning with
+that immediately surrounding the South Pole (Octans), and then following
+the others as nearly as possible in order of Right Ascension.
+
+OCTANS.--This is the constellation surrounding the South Pole of the
+heavens. There is no bright star near the Pole, the nearest visible to the
+naked eye being σ Octantis, which is within one degree of the pole. It was
+estimated 5·8 at Cordoba. The brightest star in the constellation is ν
+Octantis (α, Proctor), which lies about 12 degrees from the pole in the
+direction of Indus and Microscopium. The Harvard measure is 3·74
+magnitude.
+
+HYDRUS, the Water-Snake, is north of Octans in the direction of Achernar
+(α Eridani). The brightest star is β, which lies close to θ Octantis. The
+Harvard measure is 2·90. Gould says its colour is "clear yellow." It has a
+large proper motion of 2"·28 per annum. Sir David Gill found a parallax of
+0"·134, and this combined with the proper motion gives a velocity of 50
+miles a second at right angles to the line of sight. γ Hydri is a
+comparatively bright star of about the 3rd magnitude, about 15½ degrees
+from the South Pole. It is reddish, with a spectrum of the third type.
+
+HOROLOGIUM, the Clock, is north of Hydra, and south of Eridanus. Three of
+its stars, α, δ, and ψ, at the extreme northern end of the constellation,
+seem to be referred to by Al-Sufi in his description of Eridanus, but he
+does not give their exact positions. Most of the stars forming this
+constellation were below Al-Sufi's horizon.
+
+RETICULUM, the Net, is a small constellation to the east of Hydrus and
+Horologium. The brightest star of the constellation is α (3·36 Harvard,
+3·3 Cordoba, and "coloured").
+
+DORADO, the Sword Fish, lies east of Reticulum and west of Pictor. It
+contains only two stars brighter than the 4th magnitude. These are α (3·47
+Harvard) and β (3·81 Harvard, but suspected of variation). About 3° east
+of α Reticuli is the variable star R Doradus. It varies from 4·8 to 6·8,
+and its period is about 345 days. Gould calls it "excessively red." It may
+be followed through all its fluctuations of light with an opera-glass.
+
+MENSA, or Mons Mensa, the Table Mountain, lies between Dorado and the
+South Pole, and represents the Table Mountain of the Cape of Good Hope. It
+contains no star brighter than the 5th magnitude.
+
+PICTOR, the Painter's Easel, lies north of Doradus, and south of Columba.
+It contains no very bright stars, the brightest being α (3·30 Harvard).
+
+VOLANS, the Flying Fish, is north of Mensa, and south and west of Argo.
+Its brighter stars, with the exception of α and β, form an irregular
+six-sided figure. Its brightest star is β (3·65) according to the Harvard
+measures. The Cordoba estimates, however, range from 3·6 to 4·4, and Gould
+says its colour is "bright yellow." Williams rated it 3·8.
+
+CHAMÆLION.--This small constellation lies south of Volans, and north of
+Mensa and Octans. None of its stars are brighter than the 4th magnitude,
+its brightest being α (4·08 Harvard) and γ (4·10).
+
+ARGO.--This large constellation extends much further south than Al-Sufi
+could follow it. The most southern star he mentions is ε Carinæ, but south
+of this are several bright stars. β Carinæ is 1·80 according to the
+Harvard measures; υ Carinæ, 3·08; θ, 3·03; ω, 3·56; and others. A little
+north-west of ι is the long-period variable R Carinæ (9{h} 29{m}·7, S. 62°
+21', 1900). It varies from 4·5 at maximum to 10 at minimum, and the period
+is about 309·7 days. A little east of R Carinæ is another remarkable
+variable star, _l_ Carinæ (R.A. 9{h} 42{m}·5, S. 62° 3'). It varies from
+3·6 to 5·0 magnitude, with a period of 35½ days from maximum to
+maximum. All the light changes can be observed with an opera-glass, or
+even with the naked eye. It was discovered at Cordoba. The spectrum is of
+the solar type (G).
+
+MUSCA, the Bee, is a small constellation south of the Southern Cross and
+Centaurus. Its brightest stars are α (2·84 Harvard) and β (3·26). These
+two stars form a fine pair south of α Crucis. Closely south-east of α is
+the short-period variable R Muscæ. It varies from 6·5 to 7·6 magnitude,
+and its period is about 19 hours. All its changes of light may be observed
+with a good opera-glass.
+
+APUS, the Bird of Paradise, lies south-east of Musca, and north of Octans.
+Its brightest star is α, about the 4th magnitude. Williams calls it "deep
+yellow." About 3° north-west of α, in the direction of the Southern Cross,
+is θ Apodis, which was found to be variable at Cordoba from 5½ to 6½. The
+spectrum is of the third type, which includes so many variable stars.
+
+TRIANGULUM AUSTRALIS, the Southern Triangle, is a small constellation
+north of Apus, and south of Norma. A fine triangle, nearly isosceles, is
+formed by its three bright stars, α, β, γ, the brightest α being at the
+vertex. These three stars form with α Centauri an elongated cross. The
+stars β and γ are about 3rd magnitude. β is reddish. ε (4·11, Harvard) is
+also reddish, and is nearly midway between β and γ, and near the centre of
+the cross above referred to. α is a fine star (1·88 Harvard) and is one of
+the brightest stars in the sky--No. 33 in a list of 1500 highest stars
+given by Pickering. About 1° 40' west of ε is the short-period variable R
+Trianguli Australis (R.A. 15{h} 10{m}·8, S. 66° 8') discovered at Cordoba
+in 1871. It varies from 6·7 to 7·4, and the period is about 3{d} 7{h}·2.
+Although not visible to ordinary eyesight it is given here, as it is an
+interesting object and all its light changes may be well seen with an
+opera-glass. A little south-east of β is another short-period variable, S
+Trianguli Australis (R.A. 15{h} 52{m}·2, S. 63° 30'), which varies from
+6·4 to 7·4, with a period of 6·3 days; and all its fluctuations of light
+may also be observed with a good opera-glass.
+
+CIRCINUS, the Compass, is a very small constellation lying between
+Triangulum and Centaurus. Its brightest star, α, is about 3½ magnitude,
+about 4° south of α Centauri.
+
+PAVO, the Peacock, lies north of Octans and Apus, and south of
+Telescopium. Its brightest star is α, which is a fine bright star (2·12
+Harvard). κ is a short-period variable. It varies from 3·8 to 5·2, and the
+period is about 9 days. This is an interesting object, as all the
+fluctations of light can be observed by the naked eye or an opera-glass. ε
+Pavonis was measured 4·10 at Harvard, but the Cordoba estimates vary from
+3·6 to 4·2. Gould says "it is of a remarkably blue colour."
+
+INDUS.--This constellation lies north of Octans, and south of Sagittarius,
+Microscopium, and Grus. One of its stars, α, is probably referred to by
+Al-Sufi in his description of Sagittarius; it lies nearly midway between β
+Sagittarii and α Gruis, and is the brightest star of the constellation.
+The star ε Indi (4·74 Harvard) has a remarkably large proper motion of
+4"·68 per annum. Its parallax is about 0"·28, and the proper motion
+indicates a velocity of about 49 miles a second at right angles to the
+line of sight.
+
+TOUCAN.--This constellation lies north of Octans, and south of Phœnix and
+Grus, east of Indus, and west of Hydrus. Its brightest star is α, of about
+the 3rd magnitude.
+
+       *       *       *       *       *
+
+There are seven "celestial rivers" alluded to by the ancient
+astronomers:--
+
+1. The Fish River, which flows from the urn of Aquarius.
+
+2. The "River of the Bird," or the Milky Way in Cygnus.
+
+3. The River of the Birds--2, including Aquila.
+
+4. The River of Orion--Eridanus.
+
+5. The River of the god Marduk--perhaps the Milky Way in Perseus.
+
+6. The River of Serpents (Serpens, or Hydra).
+
+7. The River of Gan-gal (The High Cloud)--probably the Milky Way as a
+whole.
+
+There are four serpents represented among the constellations. These are
+Hydra, Hydrus, Serpens, and Draco.
+
+According to the late Mr. Proctor the date of the building of the Great
+Pyramid was about 3400 B.C.[452] At this time the Spring Equinox was in
+Taurus, and this is referred to by Virgil. But this was not so in Virgil's
+time, when--on account of the precession of the equinoxes--the equinoctial
+point had already entered Pisces, in which constellation it still remains.
+At the date 3400 B.C. the celestial equator ran along the whole length of
+the constellation Hydra, nearly through Procyon, and a little north of the
+bright red star Antares.
+
+The star Fomalhaut (α Piscis Australis) is interesting as being the most
+southern 1st magnitude star visible in England, its meridian altitude at
+Greenwich being little more than eight degrees.[453]
+
+With reference to the Greek letters given to the brighter stars by Bayer
+(in his Atlas published in 1603), and now generally used by astronomers,
+Mr. Lynn has shown that although "Bayer did uniformly designate the
+brightest stars in each constellation by the letter α,"[454] it is a
+mistake to suppose--as has often been stated in popular books on
+astronomy--that he added the other Greek letters _in order of brightness_.
+That this is an error clearly appears from Bayer's own "Explicatio" to his
+Atlas, and was long since pointed out by Argelander (1832), and by Dr.
+Gould in his _Uranometria Argentina_. Gould says, "For the stars of each
+order, the sequence of the letters in no manner represents that of their
+brightness, but depended upon the positions of the stars in the figure,
+beginning usually at the head, and following its course until all the
+stars of that order of magnitude were exhausted." Mr. Lynn says, "Perhaps
+one of the most remarkable instances in which the lettering is seen at a
+glance not to follow the order of the letters is that of the three
+brightest stars in Aquila [Al-Sufi's 'three famous stars'], γ being
+evidently brighter than β. But there is no occasion to conjecture from
+this that any change of relative brightness has taken place. Bayer
+reckoned both of these two of the third magnitude, and appears to have
+arranged β before γ, according to his usual custom, simply because β is in
+the neck of the supposed eagle, and γ at the root of one of the
+wings."[455] Another good example is found in the stars of the "Plough,"
+in which the stars are evidently arranged in the order of the figure and
+not in the order of relative brightness. In fact, Bayer is no guide at all
+with reference to star magnitudes. How different Al-Sufi was in this
+respect!
+
+The stars Aldebaran, Regulus, Antares, and Fomalhaut were called royal
+stars by the ancients. The reason of this was that they lie roughly about
+90° apart, that is 6 hours of Right Ascension. So, if through the north
+and south poles of the heavens and each of these stars we draw great
+circles of the sphere, these circles will divide the sphere into four
+nearly equal parts, and the ancients supposed that each of these stars
+ruled over a quarter of the sphere, an idea probably connected with
+astrology. As the position of Aldebaran is R.A. 4{h} 30{m}, Declination
+North 16° 19', and that of Antares is R.A. 16{h} 15{m}, Declination South
+25° 2', these two stars lie at nearly opposite points of the celestial
+sphere. From this it follows that our sun seen from Aldebaran would lie
+not very far from Antares, and seen from Antares it would appear not far
+from Aldebaran.
+
+The following may be considered as representative stars of different
+magnitudes. For those of first magnitude and fainter I have only given
+those for which all the best observers in ancient and modern times agree,
+and which have been confirmed by modern photometric measures. The Harvard
+measures are given:--
+
+  Brighter than "zero magnitude"    Sirius (-1·58); Canopus (-0·86)
+
+  Zero magnitude                    α Centauri (0·06)
+
+  0 to 0·4 magnitude                Vega (0·14); Capella (0·21);
+                                    Arcturus (0·24); Rigel (0·34)
+
+  0·5 magnitude                     Procyon (0·48)
+
+  1st     "                         Aldebaran (1·06)
+
+  2nd     "                         α Persei (1·90);
+                                    β Aurigæ (2·07)
+
+  3rd     "                         η Boötis (3·08);
+                                    ζ Capricorni (2·98)
+
+  4th     "                         ρ Leonis (3·85);
+                                    λ Scorpii (4·16);
+                                    γ Crateris(4·14);
+                                    ρ Herculis (4·14)
+
+  5th     "                         ο Pegasi (4·85);
+                                    μ Capricorni (5·10)
+
+
+
+
+CHAPTER XX
+
+The Visible Universe
+
+
+Some researches on the distribution of stars in the sky have recently been
+made at the Harvard Observatory (U.S.A.). The principal results are:--(1)
+The number of stars on any "given area of the Milky Way is about twice as
+great as in an equal area of any other region." (2) This ratio does not
+increase for faint stars down to the 12th magnitude. (3) "The Milky Way
+covers about one-third of the sky and contains about half of the stars."
+(4) There are about 10,000 stars of magnitude 6·6 or brighter, 100,000
+down to magnitude 8·7, one million to magnitude 11, and two millions to
+magnitude 11·9. It is estimated that there are about 18 millions of stars
+down to the 15th magnitude visible in a telescope of 15 inches
+aperture.[456]
+
+According to Prof. Kapteyn's researches on stellar distribution, he finds
+that going out from the earth into space, the "star density"--that is,
+the number of stars per unit volume of space--is fairly constant until we
+reach a distance of about 200 "light years." From this point the density
+gradually diminishes out to a distance of 2500 "light years," at which
+distance it is reduced to about one-fifth of the density in the sun's
+vicinity.[457]
+
+In a letter to the late Mr. Proctor (_Knowledge_, November, 1885, p. 21),
+Sir John Herschel suggested that our Galaxy (or stellar system) "contained
+within itself miniatures of itself." This beautiful idea is probably true.
+In his account of the greater "Magellanic cloud," Sir John Herschel
+describes one of the numerous objects it contains as follows:--
+
+    "Very bright, very large; oval; very gradually pretty, much brighter
+    in the middle; a beautiful nebula; it has very much the resemblance to
+    the Nubecula Major itself as seen with the naked eye, but it is far
+    brighter and more impressive in its general aspect as if it were
+    doubled in intensity. Note--July 29, 1837. I well remember this
+    observation, it was the result of repeated comparisons between the
+    object seen in the telescope and the actual nubecula as seen high in
+    the sky on the meridian, and no vague estimate carelessly set down.
+    And who can say whether in this object, magnified and analysed by
+    telescopes infinitely superior to what we now possess, there may not
+    exist all the complexity of detail that the nubecula itself presents
+    to our examination?"[458]
+
+The late Lord Kelvin, in a remarkable address delivered before the
+Physical Science Section of the British Association at its meeting at
+Glasgow in 1901, considered the probable quantity of matter contained in
+our Visible Universe. He takes a sphere of radius represented by the
+distance of a star having a parallax of one-thousandth of a second (or
+about 3000 years' journey for light), and he supposes that uniformly
+distributed within this sphere there exists a mass of matter equal to 1000
+million times the sun's mass. With these data he finds that a body placed
+originally at the surface of the sphere would in 5 million years acquire
+by gravitational force a velocity of about 12½ miles a second, and
+after 25 million of years a velocity of about 67 miles a second. As these
+velocities are of the same order as the observed velocities among the
+stars, Lord Kelvin concludes that there _is_ probably as much matter in
+our universe as would be represented by a thousand million suns. If we
+assumed a mass of ten thousand suns the velocities would be much too high.
+The most probable estimate of the total number of the visible stars is
+about 100 millions; so that if Lord Kelvin's calculations are correct we
+seem bound to assume that space contains a number of dark bodies. The
+nebulæ, however, probably contain vast masses of matter, and this may
+perhaps account--partially, at least--for the large amount of matter
+estimated by Lord Kelvin. (See Chapter on "Nebulæ.")
+
+In some notes on photographs of the Milky Way, Prof. Barnard says with
+reference to the great nebula near ρ Ophiuchi, "The peculiarity of this
+region has suggested to me the idea that the apparently small stars
+forming the ground work of the Milky Way here, are really very small
+bodies compared with our own sun"; and again, referring to the region near
+β Cygni, "One is specially struck with the apparent extreme smallness of
+the general mass of the stars in this region." Again, with reference to χ
+Cygni, he says, "The stars here also are remarkably uniform in size."[459]
+
+Eastman's results for parallax seem to show that "the fainter rather than
+the brighter stars are nearest to our system." But this apparent paradox
+is considered by Mr. Monck to be very misleading;[460] and the present
+writer holds the same opinion.
+
+Prof. Kapteyn finds "that stars whose proper motions exceed 0"·05 are not
+more numerous in the Milky Way than in other parts of the sky; or, in
+other words, if only the stars having proper motions of 0"·05 or upwards
+were mapped, there would be no aggregation of stars showing the existence
+of the Milky Way."[461]
+
+With reference to the number of stars visible on photographs, the late Dr.
+Isaac Roberts says--
+
+    "So far as I am able at present to judge, under the atmospheric
+    conditions prevalent in this country, the limit of the photographic
+    method of delineation will be reached at stellar, or nebular, light of
+    the feebleness of about 18th-magnitude stars. The reason for this
+    inference is that the general illumination of the atmosphere by
+    starlight concentrated upon a film by the instrument will mask the
+    light of objects that are fainter than about 18th-magnitude
+    stars."[462]
+
+With reference to blank spaces in the sky, the late Mr. Norman Pogson
+remarked--
+
+    "Near S Ophiuchi we find one of the most remarkable vacuities in this
+    hemisphere--an elliptic space of about 65' in length in the direction
+    of R.A., and 40' in width, in which there exists _no_ star larger than
+    the 13th magnitude ... it is impossible to turn a large telescope in
+    that direction and, if I may so express it, view such black darkness,
+    without a feeling that we are here searching into the remote regions
+    of space, far beyond the limits of our own sidereal system."[463]
+
+Prof. Barnard describes some regions in the constellation Taurus
+containing "dark lanes" in a groundwork of faint nebulosity. He gives two
+beautiful photographs of the regions referred to, and says that the dark
+holes and lanes are apparently darker than the sky in the immediate
+vicinity. He says, "A very singular feature in this connection is that the
+stars also are absent in general from the lanes." A close examination of
+these photographs has given the present writer the impression that the
+dark lanes and spots are _in_ the nebulosity, and that the nebulosity is
+mixed up with the stars. This would account for the fact that the stars
+are in general absent from the dark lanes. For if there is an intimate
+relation between the stars and the nebulosity, it would follow that where
+there is no nebulosity in this particular region there would be no stars.
+Prof. Barnard adds that the nebulosity is easily visible in a 12-inch
+telescope.[464]
+
+With reference to the life of the universe, Prof. F. R. Moulton well
+says--
+
+    "The lifetime of a man seems fairly long, and the epoch when Troy was
+    besieged, or when the Pharaohs piled up the pyramids in the valley of
+    the Nile, or when our ancestors separated on the high plateaux of
+    Asia, seems extremely remote, but these intervals are only moments
+    compared to the immense periods required for geological evolutions and
+    the enormously greater ones consumed in the developement of worlds
+    from widely extended nebulous masses. We recognize the existence of
+    only those forces whose immediate consequences are appreciable, and it
+    may be that those whose effects are yet unseen are really of the
+    highest importance. A little creature whose life extended over only
+    two or three hours of a summer's day might be led, if he were
+    sufficiently endowed with intelligence, to infer that passing clouds
+    were the chief influence at work in changing the climate instead of
+    perceiving that the sun's slow motion across the sky would bring on
+    the night and its southward motion the winter."[465]
+
+In a review of my book _Astronomical Essays_ in _The Observatory_,
+September, 1907, the following words occur. They seem to form a good and
+sufficient answer to people who ask, What is there beyond our visible
+universe? "If the stellar universe is contained in a sphere of say 1000
+stellar units radius, what is there beyond? To this the astronomer will
+reply that theories and hypotheses are put forward for the purpose of
+explaining observed facts; when there are no facts to be explained, no
+theory is required. As there are no observed facts as to what exists
+beyond the farthest stars, the mind of the astronomer is a complete blank
+on the subject. Popular imagination can fill up the blank as it pleases."
+With these remarks I fully concur.
+
+In his address to the British Association, Prof. G. H. Darwin (now Sir
+George Darwin) said--
+
+    "Man is but a microscopic being relatively to astronomical space, and
+    he lives on a puny planet circling round a star of inferior rank. Does
+    it not, then, seem futile to imagine that he can discover the origin
+    and tendency of the Universe as to expect a housefly to instruct us as
+    to the theory of the motions of the planets? And yet, so long as he
+    shall last, he will pursue his search, and will no doubt discover many
+    wonderful things which are still hidden. We may indeed be amazed at
+    all that man has been able to find out, but the immeasurable magnitude
+    of the undiscovered will throughout all time remain to humble his
+    pride. Our children's children will still be gazing and marvelling at
+    the starry heavens, but the riddle will never be read."
+
+The ancient philosopher Lucretius said--
+
+  "Globed from the atoms falling slow or swift
+  I see the suns, I see the systems lift
+  Their forms; and even the system and the suns
+  Shall go back slowly to the eternal drift."[466]
+
+But it has been well said that the structure of the universe "has a
+fascination of its own for most readers quite apart from any real progress
+which may be made towards its solution."[467]
+
+The Milky Way itself, Mr. Stratonoff considers to be an agglomeration of
+immense condensations, or stellar clouds, which are scattered round the
+region of the galactic equator. These clouds, or masses of stars,
+sometimes leave spaces between them, and sometimes they overlap, and in
+this way he accounts for the great rifts, like the Coal Sack, which allow
+us to see through this great circle of light. He finds other
+condensations of stars; the nearest is one of which our sun is a member,
+chiefly composed of stars of the higher magnitudes which "thin out rapidly
+as the Milky Way is approached." There are other condensations: one in
+stars of magnitudes 6·5 to 8·5; and a third, farther off, in stars of
+magnitudes 7·6 to 8. These may be called opera-glass, or field-glass
+stars.
+
+Stratonoff finds that stars with spectra of the first type (class A, B, C,
+and D of Harvard) which include the Sirian and Orion stars, are
+principally situated near the Milky Way, while those of type II. (which
+includes the solar stars) "are principally condensed in a region
+coinciding roughly with the terrestrial pole, and only show a slight
+increase, as compared with other stars, as the galaxy is approached."[468]
+
+Prof. Kapteyn thinks that "undoubtedly one of the greatest difficulties,
+if not the greatest of all, in the way of obtaining an understanding of
+the real distribution of the stars in space, lies in our uncertainty about
+the amount of loss suffered by the light of the stars on its way to the
+observer."[469] He says, "There can be little doubt in my opinion, about
+the existence of absorption in space, and I think that even a good guess
+as to the order of its amount can be made. For, first we know that space
+contains an enormous mass of meteoric matter. This matter must necessarily
+intercept some part of the star-light."
+
+This absorption, however, seems to be comparatively small. Kapteyn finds a
+value of 0·016 (about 1/60th) of a magnitude for a star at a distance
+corresponding to a parallax of one-tenth of a second (about 33 "light
+years"). This is a quantity almost imperceptible in the most delicate
+photometer. But for very great distances--such as 3000 "light years"--the
+absorption would evidently become very considerable, and would account
+satisfactorily for the gradual "thinning out" of the fainter stars. If
+this were fully proved, we should have to consider the fainter stars of
+the Milky Way to be in all probability fairly large suns, the light of
+which is reduced by absorption.
+
+That some of the ancients knew that the Milky Way is composed of stars is
+shown by the following lines translated from Ovid:--
+
+  "A way there is in heaven's extended plain
+  Which when the skies are clear is seen below
+  And mortals, by the name of Milky, know;
+  The groundwork is of stars, through which the road
+  Lies open to great Jupiter's abode."[470]
+
+From an examination of the distribution of the faint stars composing the
+Milky Way, and those shown in Argelander's charts of stars down to the
+9½ magnitude, Easton finds that there is "a real connection between the
+distribution of 9th and 10th magnitude stars, and that of the faint stars
+of the Milky Way, and that consequently the faint or very faint stars of
+the galactic zone are at a distance which does not greatly exceed that of
+the 9th and 10th magnitude stars."[471] A similar conclusion was, I think,
+arrived at by Proctor many years ago. Now let us consider the meaning of
+this result. Taking stars of the 15th magnitude, if their faintness were
+merely due to greater distance, their actual brightness--if of the same
+size--would imply that they are at 10 times the distance of stars of the
+10th magnitude. But if at the same distance from us, a 10th magnitude star
+would be 100 times brighter than a 15th magnitude star, and if of the same
+density and "intrinsic brightness" (or luminosity of surface) the 10th
+magnitude would have 10 times the diameter of the fainter star, and hence
+its volume would be 1000 times greater (10{3}), and this great difference
+is not perhaps improbable.
+
+The constitution of the Milky Way is not the same in all its parts. The
+bright spot between β and γ Cygni is due to relatively bright stars.
+Others equally dense but fainter regions in Auriga and Monoceros are only
+evident in stars of the 8th and 9th magnitude, and the light of the
+well-known luminous spot in "Sobieski's Shield," closely south of λ
+Aquilæ, is due to stars below magnitude 9½.
+
+The correspondence in distribution between the stars of Argelander's
+charts and the fainter stars of the Milky Way shows, as Easton points out,
+that Herschel's hypothesis of a uniform distribution of stars of
+approximately equal size is quite untenable.
+
+It has been suggested that the Milky Way may perhaps form a ring of stars
+with the sun placed nearly, but not exactly, in the centre of the ring.
+But were it really a ring of uniform width with the sun eccentrically
+placed within it, we should expect to find the Milky Way wider at its
+nearest part, and gradually narrowing towards the opposite point. Now,
+Herschel's "gages" and Celoria's counts show that the Galaxy is wider in
+Aquila than in Monoceros. This is confirmed by Easton, who says, "_for the
+faint stars taken as a whole, the Milky Way is widest in its brightest
+part_" (the italics are Easton's). From this we should conclude that the
+Milky Way is nearer to us in the direction of Aquila than in that of
+Monoceros. Sir John Herschel suggested that the southern parts of the
+galactic zone are nearer to us on account of their greater _brightness_ in
+those regions.[472] But greater width is a safer test of distance than
+relative brightness. For it may be easily shown than the _intrinsic_
+brightness of an area containing a large number of stars would be the
+same for _all_ distances (neglecting the supposed absorption of light in
+space). For suppose any given area crowded with stars to be removed to a
+greater distance. The light of each star would be diminished inversely as
+the square of the distance. But the given area would also be diminished
+_directly_ as the square of the distance, so we should have a diminished
+amount of light on an equally diminished area, and hence the intrinsic
+brightness, or luminosity of the area per unit of surface, would remain
+unaltered. The increased brightness of the Milky Way in Aquila is
+accounted for by the fact that Herschel's "gages" show an increased number
+of stars, and hence the brightness in Aquila and Sagittarius does not
+necessarily imply that the Milky Way is nearer to us in those parts, but
+that it is richer in small stars than in other regions.
+
+Easton is of opinion that the annular hypothesis of the Milky Way is
+inconsistent with our present knowledge of the galactic phenomena, and he
+suggests that its actual constitution resembles more that of a spiral
+nebula.[473] On this hypothesis the increase in the number of stars in the
+regions above referred to may be due to our seeing one branch of the
+supposed "two-branched spiral" projected on another branch of the same
+spiral. This seems supported by Sir John Herschel's observations in the
+southern hemisphere, where he found in some places "a tissue as it were of
+large stars spread over another of very small ones, the immediate
+magnitudes being wanting." Again, portions of the spiral branches may be
+richer than others, as photographs of spiral nebulæ seem to indicate.
+Celoria, rejecting the hypothesis of a single ring, suggests the existence
+of _two_ galactic rings inclined to each other at an angle of about 20°,
+one of these including the brighter stars, and the other the fainter. But
+this seems to be a more artificial arrangement then the hypothesis of a
+spiral. Further, the complicated structure of the Milky Way cannot be well
+explained by Celoria's hypothesis of two distinct rings one inside the
+other. From analogy the spiral hypothesis seems much more probable.
+
+Considering the Milky Way to represent a colossal spiral nebula viewed
+from a point not far removed from the centre of the spiral branches,
+Easton suggests that the bright region between β and γ Cygni, which is
+very rich in comparatively bright stars, may possibly represent the
+"_central accumulations of the Milky Way_," that is, the portion
+corresponding to the nucleus of a spiral nebula. If this be so, this
+portion of the Milky Way should be nearer to us than others. Easton also
+thinks that the so-called "solar cluster" of Gould, Kapteyn, and
+Schiaparelli may perhaps be "the expression of the central condensation
+of the galactic system itself, composed of the most part of suns
+comparable with our own, and which would thus embrace most of the bright
+stars to the 9th or 10th magnitude. The distance of the galactic streams
+and convolutions would thus be comparable with the distances of these
+stars." He thinks that the sun lies within a gigantic spiral, "in a
+comparatively sparse region between the central nucleus and Orion."
+
+Scheiner thinks that "the irregularities of the Milky Way, especially in
+streams, can be quite well accounted for, as Easton has attempted to do,
+if they are regarded as a system of spirals, and not as a ring system."
+
+Evidence in favour of the spiral hypothesis of the Milky Way, as advocated
+by Easton and Scheiner, may be found in Kapteyn's researches on the proper
+motions of the stars. This eminent astronomer finds that stars with
+measurable proper motions--and therefore in all probability relatively
+near the earth--have mostly spectra of the solar type, and seem to cluster
+round "a point adjacent to the sun, in total disregard to the position of
+the Milky Way," and that stars with little or no proper motion collect
+round the galactic plain. He is also of opinion that the Milky Way
+resembles the Andromeda nebula, "the globular nucleus representing the
+solar cluster, and the far spreading wings or whorls the compressed layer
+of stars enclosed by the rings of the remote Galaxy."
+
+With reference to the plurality of inhabited worlds, it has been well said
+by the ancient writer Metrodorus (third century B.C.), "The idea that
+there is but a single world in all infinitude would be as absurd as to
+suppose that a vast field had been formed to produce a single blade of
+wheat."[474] With this opinion the present writer fully concurs.
+
+
+
+
+CHAPTER XXI
+
+General
+
+
+The achievements of Hipparchus in astronomy were very remarkable,
+considering the age in which he lived. He found the amount of the apparent
+motion of the stars due to the precession of the equinoxes (of which he
+was the discoverer) to be 59" per annum. The correct amount is about 50".
+He measured the length of the year to within 9 minutes of its true value.
+He found the inclination of the ecliptic to the plane of the equator to be
+23° 51'. It was then 23° 46'--as we now know by modern calculations--so
+that Hipparchus' estimation was a wonderfully close approximation to the
+truth. He computed the moon's parallax to be 57', which is about its
+correct value. He found the eccentricity of the sun's apparent orbit round
+the earth to be one twenty-fourth, the real value being then about
+one-thirteenth. He determined other motions connected with the earth and
+moon; and formed a catalogue of 1080 stars. All this work has earned for
+him the well-merited title of "The Father of Astronomy."[475]
+
+The following is a translation of a Greek passage ascribed to Ptolemy: "I
+know that I am mortal and the creature of a day, but when I search out the
+many rolling circles of the stars, my feet touch the earth no longer, but
+with Zeus himself I take my fill of ambrosia, the food of the gods."[476]
+This was inscribed (in Greek) on a silver loving cup presented to the late
+Professor C. A. Young, the famous American astronomer.[477]
+
+Some curious and interesting phenomena are recorded in the old Chinese
+Annals, which go back to a great antiquity. In 687 B.C. "a night" is
+mentioned "without clouds and without stars" (!) This may perhaps refer to
+a total eclipse of the sun; but if so, the eclipse is not mentioned in the
+Chinese list of eclipses. In the year 141 B.C., it is stated that the sun
+and moon appeared of a deep red colour during 5 days, a phenomenon which
+caused great terror among the people. In 74 B.C., it is related that a
+star as large as the moon appeared, and was followed in its motion by
+several stars of ordinary size. This probably refers to an unusually large
+"bolide" or "fireball." In 38 B.C., a fall of meteoric stones is recorded
+"of the size of a walnut." In A.D. 88, another fall of stones is
+mentioned. In A.D. 321, sun-spots were visible to the naked eye.
+
+Homer speaks of a curious darkness which occurred during one of the great
+battles in the last year of the Trojan war. Mr. Stockwell identifies this
+with an eclipse of the sun which took place on August 28, 1184 B.C. An
+eclipse referred to by Thucydides as having occurred during the first year
+of the Peloponnesian War, when the darkness was so great that some stars
+were seen, is identified by Stockwell with a total eclipse of the sun,
+which took place on August 2, 430 B.C.
+
+A great eclipse of the sun is supposed to have occurred in the year 43 or
+44 B.C., soon after the death of Julius Cæsar. Baron de Zach and Arago
+mention it as the first annular eclipse on record. But calculations show
+that no solar eclipse whatever, visible in Italy, occurred in either of
+these years. The phenomenon referred to must therefore have been of
+atmospherical origin, and indeed this is suggested by a passage in
+Suetonius, one of the authors quoted on the subject.
+
+M. Guillaume thinks that the ninth Egyptian plague, the thick "darkness"
+(Exodus x. 21-23), may perhaps be explained by a total eclipse of the sun
+which occurred in 1332 B.C. It is true that the account states that the
+darkness lasted "three days," but this, M. Guillaume thinks, may be due to
+an error in the translation.[478] This explanation, however, seems very
+improbable.
+
+According to Hind, the moon was eclipsed on the generally received date
+of the Crucifixion, A.D. 33, April 3. He says, "I find she had emerged
+from the earth's dark shadow a quarter of an hour before she rose at
+Jerusalem (6{h} 36{m} p.m.); but the penumbra continued upon her disc for
+an hour afterwards." An eclipse could not have had anything to do with the
+"darkness over all the land" during the Crucifixion. For this lasted for
+three hours, and the totality of a solar eclipse can only last a few
+minutes at the most. As a matter of fact the "eclipse of Phlegon," a
+partial one (A.D. 29, November 24) was "the only solar eclipse that could
+have been visible in Jerusalem during the period usually fixed for the
+ministry of Christ."
+
+It is mentioned in the Anglo-Saxon Chronicle that a total eclipse of the
+sun took place in the year after King Alfred's great battle with the
+Danes. Now, calculation shows that this eclipse occurred on October 29,
+878 A.D. King Alfred's victory over the Danes must, therefore, have taken
+place in 877 A.D., and his death probably occurred in 899 A.D. This solar
+eclipse is also mentioned in the Annals of Ulster. From this it will be
+seen that in some cases the dates of historical events can be accurately
+fixed by astronomical phenomena.
+
+It is stated by some historians that an eclipse of the sun took place on
+the morning of the battle of Crecy, August 26, 1346. But calculation
+shows that there was no eclipse of the sun visible in England in that
+year. At the time of the famous battle the moon had just entered on her
+first quarter, and she was partially eclipsed six days afterwards--that is
+on the 1st of September. The mistake seems to have arisen from a
+mistranslation of the old French word _esclistre_, which means lightning.
+This was mistaken for _esclipse_. The account seems to indicate that there
+was a heavy thunderstorm on the morning of the battle.
+
+A dark shade was seen on the waning moon by Messrs. Hirst and J. C.
+Russell on October 21, 1878, "as dark as the shadow during an eclipse of
+the moon."[479] If this observation is correct, it is certainly most
+difficult to explain. Another curious observation is recorded by Mr. E.
+Stone Wiggins, who says that a partial eclipse of the sun by a dark body
+was observed in the State of Michigan (U.S.A.) on May 16, 1884, at 7 p.m.
+The "moon at that moment was 12 degrees south of the equator and the sun
+as many degrees north of it." The existence of a dark satellite of the
+earth has been suggested, but this seems highly improbable.
+
+The sun's corona seems to have been first noticed in the total eclipse of
+the sun which occurred at the death of the Roman emperor Domitian, A.D.
+95. Philostratus in his _Life of Apollonius_ says, with reference to this
+eclipse, "In the heavens there appeared a prodigy of this nature: a
+certain _corona_ resembling the Iris surrounded the orb of the sun, and
+obscured its light."[480] In more modern times the corona seems to have
+been first noticed by Clavius during the total eclipse of April 9,
+1567.[481] Kepler proved that this eclipse was total, not annular, so that
+the ring seen by Clavius must have been the corona.
+
+With reference to the visibility of planets and stars during total
+eclipses of the sun; in the eclipse of May 12, 1706, Venus, Mercury, and
+Aldebaran, and several other stars were seen. During the totality of the
+eclipse of May 3, 1715, about twenty stars were seen with the naked
+eye.[482] At the eclipse of May 22, 1724, Venus and Mercury, and a few
+fixed stars were seen.[483] The corona was also noticed. At the eclipse of
+May 2, 1733, Jupiter, the stars of the "Plough," Capella, and other stars
+were visible to the naked eye; and the corona was again seen.[483]
+
+During the total eclipses of February 9, 1766, June 24, 1778, and June 16,
+1806, the corona was again noticed. But its true character was then
+unknown.
+
+At the eclipse of July 8, 1842, it was noticed by observers at Lipesk
+that the stars Aldebaran and Betelgeuse (α Orionis), which are usually
+red, "appeared quite white."[484]
+
+There will be seven eclipses in the years 1917, 1935, and 1985. In the
+year 1935 there will be five eclipses of the sun, a rare event; and in
+1985 there will be three total eclipses of the moon, a most unusual
+occurrence.[485]
+
+Among the ancient Hindoos, the common people believed that eclipses were
+caused by the interposition of a monstrous demon called Raha. This absurd
+idea, and others equally ridiculous, were based on declarations in their
+sacred books, and no pious Hindoo would think of denying it.
+
+The following cases of darkenings of the sun are given by Humboldt:--
+
+According to Plutarch the sun remained pale for a whole year at the death
+of Julius Cæsar, and gave less than its usual heat.[486]
+
+A sun-darkening lasting for two hours is recorded on August 22, 358 A.D.,
+before the great earthquake of Nicomedia.
+
+In 360 A.D. there was a sun-darkening from early morn till noon. The
+description given by the historians of the time corresponds to an eclipse
+of the sun, but the duration of the obscurity is inexplicable.
+
+In 409 A.D., when Alaric lay siege to Rome, "there was so great a
+darkness that the stars were seen by day."
+
+In 536 A.D. the sun is said to have been darkened for a year and two
+months!
+
+In 626 A.D., according to Abul Farag, half the sun's disc was darkened for
+eight months!
+
+In 934 A.D. the sun lost its brightness for two months in Portugal.
+
+In 1090 A.D. the sun was darkened for three hours.
+
+In 1096, sun-spots were seen with the naked eye on March 3.
+
+In 1206 A.D. on the last day of February, "there was complete darkness for
+six hours, turning the day into night." This seems to have occurred in
+Spain.
+
+In 1241 the sun was so darkened that stars could be seen at 3 p.m. on
+Michaelmas day. This happened in Vienna.[487]
+
+The sun is said to have been so darkened in the year 1547 A.D. for three
+days that stars were visible at midday. This occurred about the time of
+the battle of Mühlbergh.[488]
+
+Some of these darkenings may possibly have been due to an enormous
+development of sun-spots; but in some cases the darkness is supposed by
+Chladni and Schnurrer to have been caused by "the passage of meteoric
+masses before the sun's disc."
+
+The first observer of a transit of Venus was Jeremiah Horrocks, who
+observed the transit of November 24 (O.S.), 1639. He had previously
+corrected Kepler's predicted time of the transit from 8{h} 8{m} a.m. at
+Manchester to 5{h} 57{m} p.m. At the end of 1875 a marble scroll was
+placed on the pedestal of the monument of John Conduitt (nephew of Sir
+Isaac Newton, and who adopted Horrocks' theory of lunar motions) at the
+west end of the nave of Westminster Abbey, bearing this inscription from
+the pen of Dean Stanley--
+
+  "Ad majora avocatus
+  quæ ob hæc parerga negligi non decuit"
+  IN MEMORY OF
+  JEREMIAH HORROCKS
+  Curate of Hoole in Lancashire
+  Who died on the 3{d} of January, 1641, in or near his
+  22{d} year
+  Having in so short a life
+  Detected the long inequality in the mean motion of
+  Jupiter and Saturn
+  Discovered the orbit of the Moon to be an ellipse;
+  Determined the motion of the lunar aspe,
+  Suggested the physical cause of its revolution;
+  And predicted from his own observations, the
+  Transit of Venus
+  Which was seen by himself and his friend
+  WILLIAM CRABTREE
+  On Sunday, the 24th November (O.S.) 1639;
+  This Tablet, facing the Monument of Newton
+  Was raised after the lapse of more than two centuries
+  December 9, 1874.[489]
+
+The transit of Venus which occurred in 1761 was observed on board ship(!)
+by the famous but unfortunate French astronomer Le Gentil. The ship was
+the frigate _Sylphide_, sent to the help of Pondicherry (India) which was
+then being besieged by the English. Owing to unfavourable winds the
+_Sylphide_ was tossed about from March 25, 1761, to May 24 of the same
+year. When, on the later date, off the coast of Malabar, the captain of
+the frigate learned that Pondicherry had been captured by the English, the
+vessel returned to the Isle of France, where it arrived on June 23, after
+touching at Point de Galle on May 30. It was between these two places that
+Le Gentil made his observations of the transit of Venus under such
+unfavourable conditions. He had an object-glass of 15 feet (French) focus,
+and this he mounted in a tube formed of "four pine planks." This rough
+instrument was fixed to a small mast set up on the quarter-deck and worked
+by ropes. The observations made under such curious conditions, were not,
+as may be imagined, very satisfactory. As another transit was to take
+place on June 3, 1769, Le Gentil made the heroic resolution of remaining
+in the southern hemisphere to observe it! This determination was duly
+carried out, but his devotion to astronomy was not rewarded; for on the
+day of the long waited for transit the sky at Pondicherry (where he had
+gone to observe it) was clouded over during the whole phenomenon,
+"although for many days previous the sky had been cloudless." To add to
+his feeling of disappointment he heard that at Manilla, where he had been
+staying some time previously, the sky was quite clear, and two of his
+friends there had seen the transit without any difficulty.[490] Truly the
+unfortunate Le Gentil was a martyr to science.
+
+The famous German astronomer Bessel once said "that a practical astronomer
+could make observations of value if he had only a cart-wheel and a gun
+barrel"; and Watson said that "the most important part of the instrument
+is the person at the small end."[491]
+
+With reference to Father Hell's supposed forgery of his observations of
+the transit of Venus in 1769, and Littrow's criticism of some of the
+entries in Hell's manuscript being corrected with a different coloured
+ink, Professor Newcomb ascertained from Weiss that Littrow was colour
+blind, and could not distinguish between the colour of Aldebaran and the
+whitest star. Newcomb adds, "For half a century the astronomical world had
+based an impression on the innocent but mistaken evidence of a
+colour-blind man respecting the tint of ink in a manuscript."
+
+It is recorded that on February 26, B.C. 2012, the moon, Mercury, Venus,
+Jupiter, and Saturn, were in the same constellation, and within 14
+degrees of each other. On September 14, 1186 A.D., the sun, moon, and all
+the planets then known, are said to have been situated in Libra.[492]
+
+In the Sanscrit epic poem, "The Ramaya," it is stated that at the birth of
+Rama, the moon was in Cancer, the sun in Aries, Mercury in Taurus, Venus
+in Pisces, Mars in Capricornus, Jupiter in Cancer, and Saturn in Libra.
+From these data, Mr. Walter R. Old has computed that Rama was born on
+February 10, 1761 B.C.[493]
+
+A close conjunction of Mars and Saturn was observed by Denning on
+September 29, 1889, the bright star Regulus (α Leonis) being at the time
+only 47' distant from the planets.[494]
+
+An occultation of the Pleiades by the moon was observed by Timocharis at
+Alexandria on January 29, 282 B.C. Calculations by Schjellerup show that
+Alcyone (η Tauri) was occulted; but the exact time of the day recorded by
+Timocharis differs very considerably from that computed by
+Schjellerup.[495] Another occultation of the Pleiades is recorded by
+Agrippa in the reign of Domitian. According to Schjellerup the phenomenon
+occurred on November 29, A.D. 92.
+
+"Kepler states that on the 9th of January, 1591, Mæstlin and himself
+witnessed an occultation of Jupiter by Mars. The red colour of the latter
+on that occasion plainly indicated that it was the inferior planet."[496]
+That is, that Mars was nearer to the sun than Jupiter. But as the
+telescope had not then been invented, this may have been merely a near
+approach of the two planets.
+
+According to Kepler, Mæstlin saw an occultation of Mars by Venus on
+October 3, 1590. But this may also have been merely a near approach.[496]
+
+A curious paradox is that one can discover an object without seeing it,
+and see an object without discovering it! The planet Neptune was
+discovered by Adams and Leverrier by calculation before it was seen in the
+telescope by Galle; and it was actually seen by Lalande on May 8 and 10,
+1795, but he took it for a _star_ and thus missed the discovery. In fact,
+he _saw_ the planet, but did not _discover_ it. It actually appears as a
+star of the 8th magnitude in Harding's Atlas (1822). The great "new star"
+of February, 1901, known as Nova Persei, was probably seen by some people
+before its discovery was announced; and it was actually noticed by a
+well-known American astronomer, who thought it was some bright star with
+which he was not familiar! But this did not amount to a discovery. Any one
+absolutely ignorant of astronomy might have made the same observation. An
+object must be _identified_ as a _new_ object before a discovery can be
+claimed. Some years ago a well-known Irish naturalist discovered a spider
+new to science, and after its discovery he found that it was common in
+nearly every house in Dublin! But this fact did not detract in the least
+from the merit of its scientific discovery.
+
+There is a story of an eminent astronomer who had been on several eclipse
+expeditions, and yet was heard to remark that he had never seen a total
+eclipse of the sun. "But your observations of several eclipses are on
+record," it was objected. "Certainly, I have on several occasions made
+observations, but I have always been too busy to look at the eclipse." He
+was probably in a dark tent taking photographs or using a spectroscope
+during the totality. This was observing an eclipse without seeing it!
+
+Humboldt gives the credit of the invention of the telescope to Hans
+Lippershey, a native of Wesel and a spectacle-maker at Middleburgh; to
+Jacob Adreaansz, surnamed Metius, who is also said to have made
+burning-glasses of ice; and to Zachariah Jansen.[497]
+
+With reference to the parabolic figure of the large mirrors of reflecting
+telescopes, Dr. Robinson remarked at the meeting of the British
+Association at Cork in 1843, "between the spherical and parabolic figures
+the extreme difference is so slight, even in the telescope of 6-feet
+aperture [Lord Rosse's] that if the two surfaces touched at their vertex,
+the distance at the edge would not amount to the 1/10000th of an inch, a
+space which few can measure, and none without a microscope."[498]
+
+In the year 1758, Roger Long, Lowndean Professor of Astronomy at
+Cambridge, constructed an "orrery" on a novel principle. It was a hollow
+metal sphere of about 18 feet in diameter with its fixed axis parallel to
+the earth's axis. It was rotated, by means of a winch and rackwork. It
+held about thirty persons in its interior, where astronomical lectures
+were delivered. The constellations were painted on the interior surface;
+and holes pierced through the shell and illuminated from the outside
+represented the stars according to their different magnitudes. This
+ingenious machine was much neglected for many years, but was still in
+existence in Admiral Smyth's time, 1844.[499]
+
+A "temporary star" is said to have been seen by Hepidanus in the
+constellation Aries in either 1006 or 1012 A.D. The late M. Schönfeld, a
+great authority on variable stars, found from an Arabic and Syrian
+chronicle that 1012 is the correct year (396 of the Hegira), but that the
+word translated Aries would by a probable emendation mean Scorpio. The
+word in the Syrian record is not the word for Aries.[500]
+
+Mr. Heber D. Curtis finds that the faintest stars mentioned in Ptolemy's
+Catalogue are about 5·38 magnitude on the scale of the Harvard
+_Photometric Durchmustering_.[501] Heis and Houzeau saw stars of 6-7
+magnitude (about 6·4 on Harvard scale). The present writer found that he
+could see most of Heis' faintest stars in the west of Ireland (Co. Sligo)
+without optical aid (except short-sighted spectacles).
+
+With reference to the apparent changes in the stellar heavens produced by
+the precession of the equinoxes, Humboldt says--
+
+    "Canopus was fully 1° 20' below the horizon of Toledo (39° 54' north
+    latitude) in the time of Columbus; and now the same star is almost as
+    much above the horizon of Cadiz. While at Berlin, and in northern
+    latitudes, the stars of the Southern Cross, as well as α and β
+    Centauri, are receding more and more from view, the Magellanic Clouds
+    are slowly approaching our latitudes. Canopus was at its greatest
+    northern approximation during last century [eighteenth], and is now
+    moving nearer and nearer to the south, although very slowly, owing to
+    its vicinity to the south pole of the ecliptic. The Southern Cross
+    began to become invisible in 52° 30' north latitude 2900 years before
+    our era, since, according to Galle, this constellation might
+    previously have reached an altitude of more than 10°. When it had
+    disappeared from the horizon of the countries of the Baltic, the great
+    pyramid of Cheops had already been erected more than five hundred
+    years. The pastoral tribe of the Hyksos made their incursion seven
+    hundred years earlier. The past seems to be visibly nearer to us when
+    we connect its measurement with great and memorable events."[502]
+
+With reference to the great Grecian philosopher and scientist Eratosthenes
+of Cyrene, keeper of the Alexandrian Library under Ptolemy Euergetes, Carl
+Snyder says, "Above all the Alexanders, Cæsars, Tadema-Napoleons, I set
+the brain which first spanned the earth, over whose little patches these
+fought through their empty bootless lives. Why should we have no poet to
+celebrate so great a deed?"[503] And with reference to Aristarchus he
+says, "If grandeur of conceptions be a measure of the brain, or ingenuity
+of its powers, then we must rank Aristarchus as one of the three or four
+most acute intellects of the ancient world."[504]
+
+Lagrange, who often asserted Newton to be the greatest genius that ever
+existed, used to remark also--"and the most fortunate; we do not find more
+than once a system of the world to establish."[505]
+
+Grant says--
+
+    "Lagrange deserves to be ranked among the greatest mathematical
+    geniuses of ancient or modern times. In this respect he is worthy of a
+    place with Archimedes or Newton, although he was far from possessing
+    the sagacity in physical enquiries which distinguished these
+    illustrious sages. From the very outset of his career he assumed a
+    commanding position among the mathematicians of the age, and during
+    the course of nearly half a century previous to his death, he
+    continued to divide with Laplace the homage due to pre-eminence in the
+    exact sciences. His great rival survived him fourteen years, during
+    which he reigned alone as the prince of mathematicians and theoretical
+    astronomers."[506]
+
+A writer in _Nature_ (May 25, 1871) relates the following anecdote with
+reference to Sir John Herschel: "Some time after the death of Laplace, the
+writer of this notice, while travelling on the continent in company with
+the celebrated French _savant_ Biot, ventured to put to him the question,
+not altogether a wise one, 'And whom of all the philosophers of Europe do
+you regard as the most worthy successor of Laplace?' Probably no man was
+better able than Biot to form a correct conclusion, and the reply was more
+judicious than the question. It was this, 'If I did not love him so much I
+should unhesitatingly say, Sir John Herschel.'" Dr. Gill (now Sir David
+Gill), in an address at the Cape of Good Hope in June, 1898, spoke of Sir
+John Herschel as "the prose poet of science; his popular scientific works
+are models of clearness, and his presidential addresses teem with
+passages of surpassing beauty. His life was a pure and blameless one from
+first to last, full of the noblest effort and the noblest aim from the
+time when as a young Cambridge graduate he registered a vow 'to try to
+leave the world wiser than he found it'--a vow that his life amply
+fulfilled."[507]
+
+Prof. Newcomb said of Adams, the co-discoverer of Neptune with Leverrier,
+"Adams' intellect was one of the keenest I ever knew. The most difficult
+problem of mathematical astronomy and the most recondite principles that
+underlie the theory of the celestial motions were to him but child's
+play." Airy he regarded as "the most commanding figure in the astronomy of
+our time."[508] He spoke of Delaunay, the great French astronomer, as a
+most kindly and attractive man, and says, "His investigations of the
+moon's motion is one of the most extraordinary pieces of mathematical work
+ever turned out by a single person. It fills two quarto volumes, and the
+reader who attempts to go through any part of the calculations will wonder
+how one man could do the work in a lifetime."[509]
+
+Sir George B. Airy and Prof. J. C. Adams died in the same month. The
+former on January 2, 1892, and the latter on January 22 of the same year.
+
+It is known from the parish register of Burstow in Surrey that Flamsteed
+(Rev. John Flamsteed), the first Astronomer Royal at Greenwich, was buried
+in the church at that place on January 12, 1720; but a search for his
+grave made by Mr. J. Carpenter in 1866 and by Mr. Lynn in 1880 led to no
+result. In Mrs. Flamsteed's will a sum of twenty-five pounds was left for
+the purpose of erecting a monument to the memory of the great astronomer
+in Burstow Church; but it does not appear that any monument was ever
+erected. Flamsteed was Rector of the Parish of Burstow.[510] He was
+succeeded in 1720 by the Rev. James Pound, another well-known astronomer.
+Pound died in 1724.[511]
+
+Evelyn says in his Diary, 1676, September 10, "Dined with Mr. Flamsteed,
+the learned astrologer and mathematician, whom his Majesty had established
+in the new Observatory in Greenwich Park furnished with the choicest
+instruments. An honest sincere man."[512] This shows that in those days
+the term "astrologer" was synonymous with "astronomer."
+
+In an article on "Our Debt to Astronomy," by Prof. Russell Tracy Crawford
+(Berkeley Astronomical Department, California, U.S.A.), the following
+remarks occur:--
+
+    "Behind the artisan is a chemist, behind the chemist is a physicist,
+    behind the physicist is a mathematician, and behind the mathematician
+    is an astronomer." "Were it not for the data furnished by astronomers,
+    commerce by sea would practically stop. The sailing-master on the high
+    seas could not determine his position, nor in what direction to head
+    his ship in order to reach a desired harbour. Think what this means in
+    dollars and cents, and estimate it if you can. For this one service
+    alone the science of astronomy is worth more in dollars and cents to
+    the world in one week than has been expended upon it since the
+    beginning of civilization. Do you think that Great Britain, for
+    instance, would take in exchange an amount equal to its national debt
+    for what astronomy gives it? I answer for you most emphatically,
+    'No.'"
+
+In his interesting book, _Reminiscences of an Astronomer_, Prof. Simon
+Newcomb says with reference to the calculations for the _Nautical Almanac_
+(referred to in the above extract)--
+
+    "A more hopeless problem than this could not be presented to the
+    ordinary human intellect. There are tens of thousands of men who could
+    be successful in all the ordinary walks of life, hundreds who could
+    wield empires, thousands who could gain wealth, for one who could take
+    up this astronomical problem with any hope of success. The men who
+    have done it are, therefore, in intellect the select few of the human
+    race--an aristocracy ranking above all others in the scale of being.
+    The astronomical ephemeris is the last outcome of their productive
+    genius."
+
+In a paper on the "Aspects of American Astronomy," Prof. Newcomb says, "A
+great telescope is of no use without a man at the end of it, and what the
+telescope may do depends more upon this appendage than upon the instrument
+itself. The place which telescopes and observatories have taken in
+astronomical history are by no means proportional to their dimensions.
+Many a great instrument has been a mere toy in the hands of its owner.
+Many a small one has become famous. Twenty years ago there was here in
+your city [Chicago] a modest little instrument which, judged by its size,
+could not hold up its head with the great ones even of that day. It was
+the private property of a young man holding no scientific position and
+scarcely known to the public. And yet that little telescope is to-day
+among the famous ones of the world, having made memorable advances in the
+astronomy of double stars, and shown its owner to be a worthy successor of
+the Herschels and Struves in that line of work."[513] Here Prof. Newcomb
+evidently refers to Prof. Burnham, and the 6-inch telescope with which he
+made many of his remarkable discoveries of double stars. With reference to
+Burnham's work, Prof. Barnard says--
+
+    "It represents the labour of a struggling amateur, who during the day
+    led the drudging life of a stenographer in the United States court in
+    Chicago, and at night worked among the stars for the pure love of it.
+    Such work deserves an everlasting fame, and surely this has fallen to
+    Mr. Burnham."
+
+Admiral Smyth says--
+
+    "A man may prove a good astronomer without possessing a spacious
+    observatory: thus Kepler was wont to observe on the bridge at Prague;
+    Schröter studied the moon, and Harding found a planet from a
+    _gloriette_; while Olbers discovered two new planets from an attic of
+    his house."[514]
+
+It is probably not generally known that "some of the greatest astronomers
+of modern times, such as Kepler, Newton, Hansen, Laplace, and Leverrier,
+scarcely ever looked through a telescope."[515]
+
+Kepler, who always signed himself Keppler in German, is usually supposed
+to have been born on December 21, 1571, in the imperial town of Weil, but
+according to Baron von Breitschwert,[516] he was really born on December
+27, 1571, in the village of Magstadt in Wurtemberg.
+
+According to Lieut. Winterhalter, M. Perrotin of the Nice Observatory
+declared "that two hours' work with a large instrument is as fatiguing as
+eight with a small one, the labour involved increasing in proportion to
+the cube of the aperture, the chances of seeing decreasing in the same
+ratio, while it can hardly be said that the advantages increase in like
+proportion."[517]
+
+The late Mr. Proctor has well said--
+
+    "It is well to remember that the hatred which many entertain against
+    the doctrine of development as applied to solar systems and stellar
+    galaxies is not in reality a sign, as they imagine, of humility, but
+    is an effort to avoid the recognition of the nothingness of man in the
+    presence of the infinities of space and time and vitality presented
+    within the universe of God."[518]
+
+Humboldt says--
+
+    "That arrogant spirit of incredulity, which rejects facts without
+    attempting to investigate them, is in some cases almost more injurious
+    than an unquestioning credulity. Both are alike detrimental to the
+    force of investigations."[519]
+
+With reference to the precession of the equinoxes and the changes it
+produces in the position of the Pole Star, it is stated in a recent book
+on science that the entrance passage of the Great Pyramid of Ghizeh is
+inclined at an angle of 30° to the horizon, and therefore points to the
+celestial pole. But this is quite incorrect. The Great Pyramid, it is
+true, is situated close to the latitude of 30°. But the entrance passage
+does not point exactly to the pole. The inclination was measured by Col.
+Vyse, and found to be 26° 45'. For six out of the nine pyramids of
+Ghizeh, Col. Vyse found an _average_ inclination of 26° 47', these
+inclinations ranging from 25° 55' (2nd, or pyramid of Mycerinus) to 28° 0'
+(9th pyramid).[520] Sir John Herschel gives 3970 B.C. as the probable date
+of the erection of the Great Pyramid.[520] At that time the distance of α
+Draconis (the Pole Star of that day) from the pole was 3° 44' 25", so that
+when on the meridian _below_ the pole (its lower culmination as it is
+termed) its altitude was 30° - 3° 44' 25" = 26° 15' 35", which agrees
+fairly well with the inclination of the entrance passage. Letronne found a
+date of 3430 B.C.; but the earlier date agrees better with the evidence
+derived from Egyptology.
+
+Emerson says--
+
+  "I am brother to him who squared the pyramids
+  By the same stars I watch."
+
+From February 6 to 15, 1908, all the bright planets were visible together
+at the same time. Mercury was visible above the western horizon after
+sunset, Venus very brilliant with Saturn a little above it, Mars higher
+still, all ranged along the ecliptic, and lastly Jupiter rising in the
+east.[521] This simultaneous visibility of all the bright planets is
+rather a rare occurrence.
+
+With reference to the great improbability of Laplace's original Nebular
+Hypothesis being true, Dr. See says, "We may calculate from the
+preponderance of small bodies actually found in the solar system--eight
+principal planets, twenty-five satellites (besides our moon), and 625
+asteroids--that the chances of a nebula devoid of hydrostatic pressure
+producing small bodies is about 2{658} to 1, or a decillion decillion
+(10{66}){6} to the sixth power, to unity. This figure is so very large
+that we shall content ourselves with illustrating a decillion decillion,
+and for this purpose we avail ourselves of a method employed by ARCHIMEDES
+to illustrate his system of enumeration. Imagine sand so fine that 10,000
+grains will be contained in the space occupied by a poppy seed, itself
+about the size of a pin's head; and then conceive a sphere described about
+our sun with a radius of 200,000 astronomical units[522] (α Centauri being
+at a distance of 275,000) entirely filled with this fine sand. The number
+of grains of sand in this sphere of the fixed stars would be a decillion
+decillion[523] (10{66}){6}. All these grains of sand against one is the
+probability that a nebula devoid of hydrostatical pressure, such as that
+which formed the planets and satellites, will lead to the genesis of such
+small bodies revolving about a greatly predominant central mass."[524] In
+other words, it is practically certain that the solar system was _not_
+formed from a gaseous nebula in the manner originally proposed by Laplace.
+On the other hand, the evolution of the solar system from a rotating
+spiral nebula seems very probable.
+
+       *       *       *       *       *
+
+Some one has said that "the world knows nothing of its greatest men." The
+name of Mr. George W. Hill will probably be unknown to many of my readers.
+But the late Prof. Simon Newcomb said of him that he "will easily rank as
+the greatest master of mathematical astronomy during the last quarter of
+the nineteenth century."[525] Of Prof. Newcomb himself--also a great
+master in the same subject--Sir Robert Ball says he was "the most
+conspicuous figure among the brilliant band of contemporary American
+astronomers."[526]
+
+An astronomer is supposed to say, with reference to unwelcome visitors to
+his observatory, "Who steals my purse steals trash; but he that filches
+from me my clear nights, robs me of that which not enriches him, and makes
+me poor indeed."[527]
+
+Cicero said, "In the heavens there is nothing fortuitous, unadvised,
+inconstant, or variable; all there is order, truth, reason, and
+constancy"; and he adds, "The creation is as plain a signal of the being
+of a God, as a globe, a clock, or other artificial machine, is of a
+man."[528]
+
+"Of all the epigrams attributed rightly or wrongly to Plato, the most
+famous has been expanded by Shelley into the four glorious lines--
+
+  "'Thou wert the morning star among the living
+    Ere thy pure light had fled,
+  Now having died, thou art as Hesperus, giving
+    New splendour to the dead.'"[529]
+
+Sir David Brewster has well said,[530] "Isaiah furnishes us with a
+striking passage, in which the occupants of the earth and the heavens are
+separately described, 'I have made the earth, and created man upon it: I,
+even My hands, have stretched out the heavens, and all _their_ host have I
+commanded' (Isaiah xlv. 12). But in addition to these obvious references
+to life and things pertaining to life, we find in Isaiah the following
+remarkable passage: 'For thus saith the Lord that created the heavens; God
+Himself that formed the earth and made it; He hath established it, _He
+created it not_ IN VAIN, He formed _it to be inhabited_' (Isaiah xlv. 18).
+Here we have a distinct declaration from the inspired prophet that the
+_earth would have been created_ IN VAIN _if it had not been formed to be
+inhabited_; and hence we draw the conclusion that as the Creator cannot be
+supposed to have made the worlds of our system and those in the sidereal
+system in vain, they must have been formed to be inhabited." This seems to
+the present writer to be a good and sufficient reply to Dr. Wallace's
+theory that our earth is the only inhabited world in the Universe![531]
+Such a theory seems incredible.
+
+The recent discovery made by Prof. Kapteyn, and confirmed by Mr.
+Eddington, of two drifts of stars, indicating the existence of _two_
+universes, seems to render untenable Dr. Wallace's hypothesis of the
+earth's central position in a single universe.[531]
+
+
+NOTE ADDED IN THE PRESS.
+
+While these pages were in the Press, it was announced, by Dr. Max Wolf of
+Heidelberg, that he found Halley's comet on a photograph taken on the
+early morning of September 12, 1909. The discovery has been confirmed at
+Greenwich Observatory. The comet was close to the position predicted by
+the calculations of Messrs. Cowell and Crommelin of Greenwich Observatory
+(_Nature_, September 16, 1908).
+
+
+
+
+INDEX
+
+
+  A
+
+  Aboukir, 287
+
+  Aboul Hassan, 221
+
+  Abu Ali al Farisi, 225
+
+  Abu-Hanifa, 233, 234
+
+  Abul-fadl, 236
+
+  Accadians, 250, 252
+
+  Achernar, 275
+
+  Aclian, 282
+
+  Adam, 96, 347
+
+  Adhad-al-Davlat, 225, 236
+
+  Adonis, 261
+
+  Adreaansz, 342
+
+  Airy, Sir G. B., 87, 140, 347, 357
+
+  Aitken, 160
+
+  Al-Battani, 232, 233
+
+  Albrecht, 173
+
+  Albufaragius, 283
+
+  Alcor, 241
+
+  Alcyone, 137
+
+  Aldebaran, 60, 156, 236, 252, 257, 310, 311
+
+  Alfard, 236, 289
+
+  Alfargani, 286
+
+  Alfraganus, 281
+
+  Almagest, 281
+
+  Al-Sufi, 47, 149, 179, 189, 221, 224, 225-238, 244, 246, 250, 251, 253,
+      254, 261, 263, 264, 266-270, 272, 274-278, 285, 287, 289, 290, 293,
+      298, 300-302, 304, 307
+
+  Altair, 246
+
+  Ampelius, 262
+
+  Amphion, 257
+
+  Ancient eclipses, 52, 53
+
+  Anderson, 120, 277
+
+  Andromeda nebula, 198-206, 231
+
+  Annals of Ulster, 332
+
+  Antares, 60, 179, 310, 311
+
+  Anthelm, 300
+
+  Antinous, 248
+
+  Antlia, 302
+
+  Apollo, 257
+
+  Apparent diameter of moon, 49
+
+  Apple, 79
+
+  "Apples, golden," 258
+
+  Apus, 306
+
+  Aquarius, 268
+
+  Aquila, 246
+
+  Aquillus, 220
+
+  Ara 295
+
+  Arago, 26, 30, 57, 116, 193, 331
+
+  Aratus, 219, 242, 245, 250, 255, 256, 261, 263, 272
+
+  Archimedes, 346, 354
+
+  Arcturus, 148, 188, 244
+
+  Argelander, 29, 227, 229, 230, 240
+
+  Argo, 285-288, 305
+
+  Argon in sun, 4
+
+  Argonauts, 243, 250
+
+  Aries, 250
+
+  Aristotle, 49, 67
+
+  Arrhenius, 4, 8, 22, 45, 66
+
+  Ashtoreth, 260
+
+  _Astra Borbonia_, 4
+
+  Astræa, 263
+
+  Astronomy, Laplace on, 44
+
+  _Astro Theology_, 23
+
+  Atarid, 232, 233
+
+  Atmosphere, height of, 33
+
+  Augean stables, 269
+
+  Augustus, 262
+
+  Auriga, 245
+
+  Aurora, 33, 41, 42
+
+  Auwers, 206
+
+  Axis of Mars, 59
+
+
+  B
+
+  Babilu, 267
+
+  Baily, 137, 144
+
+  Baker, 183
+
+  Ball, Sir Robert, 6, 355
+
+  Barnard, Prof., 29, 54, 57, 79, 80, 81, 85, 86, 91, 93, 103, 104, 114,
+      130, 132, 139, 192, 213, 316, 317, 350
+
+  Barnes, 78, 79
+
+  Bartlett, 35, 36
+
+  Bartschius, 296, 298
+
+  Bauschingen, 69, 70
+
+  Bayer, 179, 221, 272, 284, 309, 310
+
+  Bayeux Tapestry, 105
+
+  Becquerel, 8
+
+  "Beehive," 259
+
+  Beer, 20
+
+  Bel, 250
+
+  Bellatrix, 253
+
+  Benoit, 22
+
+  Berenice, 297
+
+  Berry, 25
+
+  Bessel, 339
+
+  Betelgeuse, 179, 222, 264
+
+  Bianchini, 21, 22, 77
+
+  Biela's comet, 99
+
+  Bifornis, 268
+
+  Binary stars, 162
+
+  Birmingham, 5, 114
+
+  "Black body," 3
+
+  "Blackness" of sun-spots, 6
+
+  "Blaze star," 180, 184
+
+  Bode, 276
+
+  Bohlin, 199, 200
+
+  Bond, 85
+
+  Bond (Jun.), 74
+
+  _Book of the Dead_, 264, 274
+
+  Borelly, 103
+
+  Boserup, 28
+
+  Boss, 152
+
+  Brahé, Tycho. _See_ Tycho Brahé
+
+  Brauner, 211
+
+  Bravais, 42
+
+  Bredikhin, 76
+
+  Bremiker, 94
+
+  Brenner, Léo, 13, 22, 87, 91, 133
+
+  Brewster, 356
+
+  Brightness of Mercury, 10-12
+
+      "      of nebulæ, 193
+
+      "      of sun, 1, 2, 3
+
+      "      of Venus, 14, 17, 19, 31
+
+  Bright clouds, 33, 34
+
+    "    night, 45
+
+    "    stars, 278
+
+  Brooks, 118
+
+  Brown, 218, 219, 248, 255, 260, 267, 272, 279, 281, 291, 295
+
+  Browning, 25
+
+  Brugsch, 127
+
+  Buddha, 256
+
+  Bull, Pope's, 107
+
+  "Bull's foot," 253
+
+  Buonaparte, 30
+
+  Burnham, 160, 165-167, 180, 184, 260, 350, 351
+
+  Burns, 130
+
+  Buss, 4
+
+
+  C
+
+  Caaba, 125
+
+  Cacciatore, 72
+
+  Cælum, 302
+
+  Callimachus, 297
+
+  Callixtus III., 107
+
+  Calvisius, 53
+
+  Camelopardalis, 296
+
+  Cameron, 18
+
+  Campbell, 85, 153, 159, 178
+
+  "Canals" on Mars, 61-63
+
+  Cancer, 258, 259
+
+  Canes Venatici, 296
+
+  Canicula, 280
+
+  Canis Major, 279
+
+    "   Minor, 284
+
+  Canopus, 157, 286, 344
+
+  Capella, 156, 164, 189, 236, 245, 246
+
+  Capricornus, 267, 268
+
+  "Capture" of satellites, 58
+
+  Carbonic acid, 66
+
+  Cassini, 20, 22, 74, 78, 358
+
+  Cassiopeia's Chair, 244
+
+  Castor, 160, 257
+
+  Caswell, 52
+
+  Catullus, 297
+
+  Caussin, 225
+
+  Cecrops, 268
+
+  "Celestial Rivers," 308
+
+  Celoria, 324, 326
+
+  Centaurus, 292, 293
+
+  Centre of gravity, 8
+
+  Cephalus, 279
+
+  Cepheid variables, 187
+
+  Ceraski, 2, 176
+
+  Cerberus, 243, 257
+
+  Ceres, 260
+
+  Cerulli, 22, 62
+
+  Cetus, 272
+
+  Chacornac, 18, 84
+
+  Chamælion, 305
+
+  Chamberlin, 194
+
+  Chambers, 72
+
+  "Charles' Wain," 240
+
+  Chinese Annals, 19, 30, 105, 186, 223, 267, 330
+
+  Childrey, 128
+
+  Chiron, 295
+
+  Christmann, 281
+
+  Chromosphere, sun's, 4
+
+  Cicero, 49, 262, 280, 355
+
+  Circinus, 307
+
+  Clavius, 334
+
+  Climate, 45
+
+  "Coal Sack," 293, 320
+
+  Cobham, 88, 102
+
+  Colbert, 175
+
+  Colours of stars, 140, 141, 188-190
+
+  Coma Berenices, 297, 298
+
+  Comets, number of, 98
+
+    "     tails of, 115, 116
+
+  Comet years, 104
+
+  Comiers, 99
+
+  Comstock, 90, 146
+
+  Condamine, 257
+
+  Conon, 297
+
+  Coon Butte mountain, 120, 121
+
+  Cooper, 3
+
+  Copeland, 76, 157
+
+  Corona, sun's, 1, 334
+
+    "     round moon, 35, 36
+
+  Corona Australis, 295
+
+  Corvinus, 292
+
+  Corvus, 292
+
+  Cotsworth, 46
+
+  Cowell, 105
+
+  Crabtree, 337
+
+  Crater, 291
+
+  Craters on moon, 55, 56
+
+  Crawford, 348
+
+  Crecy, Battle of, 333
+
+  Crescent of Venus, 19, 20
+
+  Crommelin, 105, 111
+
+  Crucifixion, 18
+
+  Curtis, 344
+
+  Cusps of Venus, 20
+
+  Cygnus, (61), 155
+
+  Cynocephalus, 222
+
+
+  D
+
+  Dante, 156, 258, 265
+
+  Dark shade on moon, 333
+
+  D'Arrest, 94
+
+  Darwin, Sir George, 158, 319
+
+  "David's Chariot," 241
+
+  Davis, 155
+
+  Dawes, 168
+
+  "Dawn proclaimer," 251
+
+  Delambre, 185
+
+  Delauney, 347
+
+  Dembowski, 190
+
+  Demetrius, 111
+
+  Denning, 11, 74, 77, 84, 86, 87, 89, 99, 118, 340
+
+  Derham, 21, 23
+
+  Deucalion, 268
+
+  De Vico, 21, 22
+
+  Diamonds in meteorites, 127
+
+  Dilkur, 251
+
+  Diodorus Siculus, 127
+
+  Diogenes Laertius, 41
+
+  Diomed, 272
+
+  Dione, 89
+
+  "Dipper," 241
+
+  Doberck, 160
+
+  Dollond, 24
+
+  Domitian, 334
+
+  Donati's comet, 100
+
+  Dorado, 304
+
+  Dordona, 256
+
+  Dorn, 245
+
+  Douglass, 81
+
+  Dragon, 242
+
+  Draper, 75
+
+  Drayton, 156
+
+  Dreyer, 115
+
+  Drifting stars, 152
+
+  Dryden, 242
+
+  Duncan, 187
+
+  Dunlop, 264
+
+  Dupret, 83
+
+  Dupuis, 245, 252, 257, 258, 259, 266, 267, 268
+
+  "Dusky star," 272
+
+
+  E
+
+  "Earthen jar," 247
+
+  Earth's attraction on moon, 55
+
+  Earth's motions, 39
+
+    "     rotation, 46
+
+    "     surface, 32
+
+  "Earthshine" on moon, 51, 52, 56, 57
+
+  Eastmann, 316
+
+  Easton, 323, 324, 325
+
+  Eclipses, ancient, 52, 53, 57, 58
+
+     "      dark, of moon, 53, 57, 58
+
+  Ecliptic, obliquity of, 47
+
+  Eddington, 357
+
+  Electra, 19
+
+  Elster, 39
+
+  Emerson, 353
+
+  Enceladus, 89
+
+  Encke, 113, 116, 240
+
+  Ennis, 189
+
+  Eratosthenes, 250, 297, 345
+
+  Eridanus, 274-278
+
+  Eros, 69, 70, 71
+
+  Eta Argus, 177, 287
+
+  Eudemus, 47
+
+  Eudoxus, 218, 219, 223
+
+  Euler, 56
+
+  Eunomia, 71
+
+  Europa, 252
+
+
+  F
+
+  Fabritius, 4, 101
+
+  Fabry, 1
+
+  Faint stars in telescope, 176
+
+  "False Cross," 156
+
+  "Famous stars," 246
+
+  Fath, 130, 213
+
+  Faye, 100
+
+  February, Five Sundays in, 36
+
+  Fergani, 189
+
+  "Fisher Stars," 256
+
+  "Fishes in Andromeda," 249
+
+  Fitzgerald, 127
+
+  Flammarion, 22, 26, 50, 138, 255, 265, 276
+
+  Flamsteed, 348
+
+  "Flat earth" theory, 32
+
+  Fomalhaut, 271, 309, 310
+
+  Fontana, 20
+
+  Fontenelle, 357
+
+  Forbes, 82, 95, 96
+
+  Fornax, 301
+
+  Fournier, 87
+
+  Fovea, 284
+
+  Freeman, 88
+
+  Fréret, 222
+
+  Frisby, 101
+
+  Fritsch, 21
+
+  Furner, 163
+
+
+  G
+
+  Gale, 78
+
+  Galileo, 3, 4, 80, 82
+
+  Galle, 94, 341
+
+  Ganymede, 268
+
+  Gaseous nebula, spectra of, 195-198, 212
+
+  Gassendi, 14, 139
+
+  Gathman, 118
+
+  Gaubil, 99
+
+  Gauthier, 103
+
+  Gegenschein, 131
+
+  Gemini, 257, 258
+
+  Geminid variables, 187
+
+  Gentil, Le, 338, 339
+
+  Gertel, 39
+
+  Ghizeh, Pyramids of, 353
+
+  Gibbous phase of Jupiter, 75
+
+  Gill, Sir David, 118, 215, 216, 346
+
+  Glacial epoch, 42
+
+  Gledhill, 76
+
+  Globular clusters, 214, 215
+
+  Goad, 12
+
+  Goatcher, 179
+
+  "Golden apples," 258
+
+  Golius, 281
+
+  Gould, 229, 278, 301, 304, 309, 310, 326
+
+  Grant, 82, 96, 345
+
+  Gravitation, Law of, 15, 40
+
+  Greely, 186
+
+  Greisbach, 80
+
+  Groombridge 1830, 159
+
+  Grubb, Sir Howard, 164
+
+  Gruithuisen, 21, 25, 26, 28
+
+  Gruson, 127
+
+  Guillaume, 331
+
+  Guthrie, 25
+
+
+  H
+
+  Habitability of Mars, 63-66
+
+       "       of planets, 40
+
+  Hadrian, 248
+
+  Halbert, 78
+
+  Hale, 148, 150
+
+  Hall, 15, 131
+
+  Halley, 14, 17, 99, 105, 106, 108, 109, 116, 143, 145, 276
+
+  Halm, 122
+
+  Halo, 35, 36
+
+  Hanouman, 284
+
+  Hansen, 351
+
+  Hansky, 27
+
+  Harding, 25, 26, 94
+
+  "Harris, Mrs.," 90
+
+  Hartwig, 88, 173
+
+  Harvests, 104
+
+  Heat of sun, 2, 3, 7
+
+  Height of atmosphere, 33
+
+  Heis, 132, 175, 189, 227, 229, 344
+
+  Helium, 4
+
+  Hepidanus, 267, 348
+
+  Hercules, 243, 259, 268
+
+  Herod, 18, 53
+
+  Herschel, Miss Caroline, 193, 194, 324, 357
+
+  Herschel, Sir John, 112, 177, 190, 207, 209, 210, 215, 289, 314, 346,
+      353
+
+  Herschel, Sir Wm., 3, 24, 80, 112, 114, 115, 116, 171, 178, 179, 190,
+      324, 325
+
+  Hesiod, 17, 220
+
+  Hesperus, 256
+
+  Hevelius, 99, 116, 221, 296, 299, 300
+
+  Hill, 87, 355
+
+  Hind, 19, 30, 54, 105, 111, 180
+
+  Hipparchus, 135, 221-223, 226, 250, 278, 281, 293, 329
+
+  Hippocrates, 258
+
+  Hirst, 333
+
+  Holetschak, 108
+
+  Homer, 17
+
+  Honorat, 84
+
+  Hooke, 74, 128
+
+  Horace, 280
+
+  Horologium, 303
+
+  Horus, 145, 258
+
+  Horrebow, 29
+
+  Horrocks, 337
+
+  Hortensus, Martinus, 139
+
+  Hough, 76
+
+  Houzeau, 227, 229, 262, 274, 344
+
+  Hovedin, Roger de, 53
+
+  Hubbard, 100
+
+  Huggins, Sir Wm., 91, 148, 180
+
+  Humboldt, 30, 82, 83, 124, 128, 134, 154, 157, 342, 352, 357
+
+  Hussey, 88
+
+  Hyades, 157, 252, 253, 257
+
+  Hydra, 288
+
+  Hydrus, 303
+
+  Hyperion, 88, 90
+
+
+  I
+
+  Ibn al-Aalam, 225
+
+  Ibn Alraqqa, 281
+
+  Icarus, 284
+
+  Indus, 307
+
+  Inhabited worlds, 328, 357
+
+  Innes, 78, 168
+
+  Intra-Mercurial planet, 14, 15, 29
+
+  Invention of telescope, 342
+
+  Io, 252
+
+  Ions, 27
+
+  Iris, 71
+
+  Isaiah, 17, 356
+
+  Isis, 252, 261, 282, 283
+
+  Istar, 260
+
+
+  J
+
+  Jansen, 342
+
+  Japetus, 89, 90
+
+  Jason, 257, 285
+
+  Johnson, Rev. S. J., 19
+
+  Jonckheere, 15
+
+  Jones, 129
+
+  Jordan, 174
+
+  Jupiter, chap. viii.
+
+     "     gibbous form of, 75
+
+     "     and sun, 8
+
+
+  K
+
+  Kalevala, 240
+
+  Kapteyn, 314, 316, 321, 322, 326, 357
+
+  Kazemerski, 244
+
+  Keeler, 86, 215
+
+  Kelvin, Lord, 206, 315, 316
+
+  Kempf, 174
+
+  Kepler, 52, 57, 298, 340, 341, 351
+
+  Khayyam, Omar, 127
+
+  Kimah, 255
+
+  Kimball, 51
+
+  Kimta, 255
+
+  Kirch, 23, 115
+
+  Kirkwood, 6
+
+  Kleiber, 123
+
+  Klein, 114, 183
+
+  Knobel, 238, 263
+
+  Konkoly, 183
+
+  Koran, 127, 270
+
+  Kreusler, 4
+
+  Kreutz, 101, 112
+
+
+  L
+
+  Lacaille, 294, 301, 302
+
+  Lacerta, 300
+
+  Lagrange, 345
+
+  La Hire, 20, 21
+
+  Lalande, 143, 144, 284
+
+  Landerer, 52
+
+  Langdon, 25
+
+  Langley, Prof., 3
+
+  Laplace, 43, 44, 98, 346, 351, 354
+
+  Larkin, 65
+
+  Lassell, 77, 128
+
+  "Last in the River," 275-298
+
+  Last year of century, 37
+
+  Lau, 178, 183
+
+  Leo, 259
+
+  Leo Minor, 298
+
+  Lepus, 278, 279
+
+  Lernæan marsh, 258
+
+  Leverrier, 44, 347, 351
+
+  Lewis, 156, 162
+
+  Lewis, Sir G. C., 17
+
+  Lexell's comet, 98
+
+  Libra, 262
+
+  Life, possible, in Mars, 63-65
+
+  Light of full moon, 1, 51
+
+  Lippershey, 342
+
+  Littrow, 339
+
+  Lockyer, Sir Norman, 144, 147
+
+  Lodge, Sir Oliver, 55
+
+  Long, 343, 357
+
+  Longfellow, 156, 273
+
+  Lottin, 42
+
+  Lowell, 22, 43, 59, 61, 64, 88
+
+  Lucifer, 17
+
+  Lucretius, 320
+
+  "Luminous clouds," 33, 34
+
+  Lunar craters, 55, 56
+
+    "   "mansions," 251
+
+    "   mountains, 58
+
+    "   theory, 56
+
+  Lunt, 179
+
+  Lupus, 294
+
+  Lyman, 25
+
+  Lynn, 37, 38, 96, 106, 179, 243, 244, 310
+
+  Lynx, 296
+
+  Lyra, 243, 244, 266
+
+
+  M
+
+  Maclear, 77
+
+  Mädler, 20, 22
+
+  Mæstlin, 341
+
+  Magi, star of, 1, 18, 145
+
+  Magnitudes, star, 311
+
+  Maia, 19, 256
+
+  Mairan, 357
+
+  "Manger," 259
+
+  Manilius, 250, 259, 272
+
+  Marius, Simon, 82, 83, 231
+
+  Markree Castle, 3
+
+  Marmol, 76
+
+  Mars, chap. vi.;
+    axis of 59;
+    red colour of, 60;
+    water vapour in, 60;
+    clouds in, 61;
+    "canals" in, 61
+
+  Martial, 17
+
+  Mascari, 22
+
+  Ma-tuan-lin, 186, 267
+
+  Mayer, 24
+
+  May transits of Mercury, 15
+
+  Maxwell, Clerk, 86
+
+  McHarg, 16
+
+  McKay, 286
+
+  Medusa, 244
+
+  Mee, 88
+
+  Melotte, 82
+
+  Mendelief, 212
+
+  Mensa, 304
+
+  Mercury, chap, ii., 258
+
+  Merrill, 121
+
+  Messier, 114
+
+  Meteoric stones, 119
+
+  Meteors, 33
+
+  Metius, 342
+
+  Microscopium, 302
+
+  Milky Way, 320, 323, 325, 326, 328
+
+  Milton, 263
+
+  Mimas, 88, 89
+
+  Minor planets, chap. vii.
+
+  Mira Ceti, 178, 186, 272, 273
+
+  Mitchell, 4
+
+  Mithridates, 111
+
+  Mitra, 145
+
+  Molyneux, 80
+
+  Monck, 156, 181
+
+  Monoceros, 298
+
+  Montanari, 170, 171
+
+  Montigny, 34
+
+  Moon, light of, 1, 51
+
+    "   as seen through a telescope, 50
+
+  "Moon maiden," 52
+
+  Moon mountains, 58
+
+  Morehouse, 103, 110
+
+  Motions of stars in line of sight, 141, 142
+
+  Moulton, 133, 318
+
+  Mountains, lunar, 58
+
+  Müller, 174
+
+  Musca, 305
+
+  Mycerinus, Pyramid of, 353
+
+
+  N
+
+  Nasmyth, 11
+
+  Nath, 253
+
+  Nautical Almanac, 349
+
+  Nebula in Andromeda, 198-206, 231
+
+  Nebulæ, gaseous, 195-198, 212, 213
+
+  Nebulæ, spiral, 213
+
+  Nebular hypothesis, 354
+
+  Nemælian lion, 259
+
+  Nemæus, 259
+
+  Neon in sun, 4
+
+  Nepthys, 271
+
+  Neptune, 341
+
+  Newcomb, 13, 15, 33, 50, 65, 70, 129, 130, 153, 191, 203, 282, 339, 347,
+      349, 350, 355
+
+  Newton, 15, 351
+
+  Nicephorus, 127
+
+  Nicholls, 148, 154
+
+  Nineveh tablets, 17
+
+  Noble, 25
+
+  Norma, 302
+
+  Novæ, 180-182, 265, 267, 343
+
+  Nova Persei, 190
+
+  November transits of Mercury, 15
+
+  Number of nebulæ, 191
+
+    "    of stars, 135, 136, 236, 237
+
+    "    of variable stars, 182, 183
+
+
+  O
+
+  Obliquity of ecliptic, 47
+
+  Occupations, 14, 15, 54, 67, 80, 84, 85, 259, 340, 341
+
+  Octans, 303
+
+  Odling, 122
+
+  Oeltzen, 72
+
+  Olbers, 104, 124
+
+  Old, 340
+
+  Orion, 49, 146, 273, 274
+
+  Osiris, 145, 259, 261, 283
+
+  "Ostriches," 266
+
+  Otawa, 240
+
+  Ovid, 242, 250, 255, 265, 288, 291, 322
+
+
+  P
+
+  Palisa, 71
+
+  Palmer, 182
+
+  Parker, 19
+
+  Parkhurst, 174
+
+  Paschen, 2
+
+  Pastorff, 25
+
+  Pavo, 307
+
+  Payne, 139
+
+  Pearson, 77
+
+  Peary, 119
+
+  Peck, 176
+
+  Pegasus, 248
+
+  Pelion, 282
+
+  Peritheus, 258
+
+  Perrine, 15, 76, 191, 192, 214
+
+  Perrotin, 351
+
+  Perseus, 244
+
+  Petosiris, 222
+
+  Philostratus, 334
+
+  Phlegon, 332
+
+  Phœbe, 90
+
+  Phœnix, 301
+
+  Phosphorus, 17
+
+  Photographic nebula, 192
+
+  Pickering, E. C., 125, 140, 144, 177
+
+  Pickering, W. H., 1, 12, 51, 61, 95, 102
+
+  Pictor, 304
+
+  Pierce, 228
+
+  "Pilgrim Star," 180, 185, 186
+
+  Pingré, 54
+
+  Pinzon, 294
+
+  Pisces, 271
+
+  Piscis Australis, 295, 296
+
+  Planetary nebulæ, 213
+
+  Platina, 107
+
+  Pleiades, 19, 52, 137, 154, 157, 235, 254-257
+
+  Pliny, 17, 265, 280
+
+  Plummer, W. E., 180
+
+  Plurality of worlds, 328, 356, 357
+
+  Pococke, 271
+
+  Pogson, 317
+
+  Polarization of moon's surface, 52
+
+  Polarization on Mars, 61
+
+  Pole of cold, 33
+
+    "  star, 138, 239, 240
+
+  Pollux, 257
+
+  Polydectus, 244
+
+  Poor, 15 (footnote)
+
+  Poynting, 130
+
+  Præsape, 259
+
+  Prince, 25
+
+  Proclus, 221
+
+  Proctor, 7, 49, 59, 123, 285, 308, 323, 352
+
+  Procyon, 156, 157, 236, 284
+
+  Ptolemy, 189, 221-223, 224, 227, 230, 231, 234, 238, 244, 252, 253, 260,
+      263, 264, 267, 269, 275, 278, 281, 284, 293, 302, 330
+
+  Pyramid, Great, 46, 47, 308, 353
+
+  Pytheas, 46
+
+
+  Q
+
+  Quadruple system, 168
+
+  Quénisset, 21, 133
+
+
+  R
+
+  Rabourdin, 103
+
+  Radium, 7, 8, 38
+
+  Râhu, 93
+
+  Rama, 284, 340
+
+  _Rational Almanac_, 46
+
+  "Red Bird," 290
+
+  Red star, 279, 292
+
+  Regulus, 30, 156, 235, 236, 260, 310, 340
+
+  Remote galaxies, 193, 204, 205
+
+  Reticulum, 304
+
+  Rhea, 89
+
+  Rheita, De, 144
+
+  Riccioli, 189
+
+  Ricco, 32
+
+  Rigel, 156, 157, 222
+
+  Rigge, 107
+
+  Ring nebula in Lyra, 211
+
+  Rings of Saturn, 85
+
+  Rishis, 240
+
+  Ritter, 76, 147
+
+  "Rivers, celestial," 308
+
+  Roberts, Dr. A. W., 172, 173
+
+  Roberts, Dr. I., 95, 154, 200, 201, 203, 317
+
+  Roberts, C., 84
+
+  Robigalia, 280
+
+  Robinson, 342, 357
+
+  Rœdeckœr, 28
+
+  Rogovsky, 42, 43, 44, 75
+
+  Rosse, Lord, 76
+
+  Roszel, 70
+
+  Rotation of Mercury, 16
+
+     "     of Uranus, 91
+
+     "     of Venus, 22
+
+  Rubáiyát, 127
+
+  Rudaux, 80, 89
+
+  Russell, H. C., 21
+
+  Russell, H. N., 146
+
+  Russell, J. C., 333
+
+  Rutherford, 38
+
+
+  S
+
+  Sadler, 78, 299
+
+  Safarik, 24, 25
+
+  Sagittarius, 265-267
+
+  _Sahu_, 274
+
+  Santini, 357
+
+  Satellite, eighth, of Jupiter, 82
+
+      "      possible lunar, 54
+
+      "      of Venus, 28, 29
+
+  Sawyer, 186
+
+  Sayce, 218, 261
+
+  Scaliger, 299
+
+  Schaeberle, 93
+
+  Schaer, 88
+
+  Scheiner, 4, 150, 188, 195
+
+  Scheuter, 30
+
+  Schiaparelli, 22, 326
+
+  Schjellerup, 226, 228, 230, 231, 264, 277, 281, 340
+
+  Schlesinger, 183
+
+  Schönfeld, 287
+
+  Schiraz, 47
+
+  Schmidt, 51, 188, 220, 271
+
+  Scholl, 79
+
+  Schröter, 13, 20, 21, 22, 24, 26, 48
+
+  Schuster, 2, 148, 149, 150
+
+  Schwabe, 5
+
+  Scorpio, 263-265
+
+  Sculptor, 301
+
+  Scutum, 299
+
+  Searle, 132
+
+  "Secondary light" of Venus, 23-28
+
+  See, Dr., 12, 13, 33, 58, 96, 161, 164, 165, 210, 211, 281, 282, 354
+
+  Seeliger, 181, 206
+
+  Seneca, 218, 220
+
+  Serapis, 145
+
+  Sestini, 190
+
+  "Seven Perfect Ones," 256
+
+  Sextans, 298
+
+  Shaler, 48
+
+  Sharpe, 357
+
+  Shelley, 356
+
+  Shicor, 274
+
+  "Ship," 285
+
+  "Sickle," 259
+
+  Signalling to Mars, 65
+
+  Sihor, 280
+
+  Silkit, 264
+
+  Silvestria, 124
+
+  Simeon of Durham, 53
+
+  Simonides, 255
+
+  "Singing Maidens," 256
+
+  Sirius, 138, 156, 157, 160, 163, 236, 274, 280, 282, 283
+
+  Slipher, 60, 87, 161, 178
+
+  Smart, 109
+
+  Smyth, Admiral, 12, 72, 77, 107, 136, 140, 145, 170, 176, 190, 194, 253,
+      259, 351
+
+  Snyder, Carl, 8, 345
+
+  Sobieski, 299
+
+  Sola, Comas, 81, 87
+
+  Somerville, Mrs., 357
+
+  Sothis, 286
+
+  Southern Cross, 293, 344
+
+  Spectra of double stars, 162
+
+  Spectrum of gaseous nebulæ, 195-198, 212
+
+  Spectrum of sun's chromosphere, 4
+
+  Spencer, Herbert, 193
+
+  Sphinx, 261
+
+  Spica, 156, 236
+
+  Spiral nebulæ, 213
+
+  Star magnitudes, 311
+
+  "Star of Bethlehem," 17, 18
+
+  Stars in daytime, 158
+
+  Stebbins, 51
+
+  Stockwell, 18, 331
+
+  "Stones from heaven," 125, 126
+
+  Stoney, 133
+
+  Strabo, 127
+
+  Stratonoff, 151, 320, 321
+
+  Stromgen, 88
+
+  Strutt, 7
+
+  Struve, 113, 240
+
+  Struyck, 54
+
+  Succulæ, 253
+
+  Suhail, 283, 286
+
+  Sun darkenings, 5, 335, 336
+
+  Sun's heat, 7
+
+  Sunlight, 1, 2
+
+  Sun-spots, 5, 6
+
+  Swift, 102
+
+  _Sydera Austricea_, 5
+
+
+  T
+
+  Tacchini, 22
+
+  Tamerlane, 238
+
+  Tammuz, 261
+
+  Tardé, 4
+
+  Taurus, 251
+
+  Taylor, 40
+
+  T Coronæ, 184
+
+  Tebbutt, 183, 278
+
+  Telescopium, 302
+
+  Temporary stars, 180-182, 265, 267, 343
+
+  Tennyson, 40
+
+  Terby, 88
+
+  Tethys, 89
+
+  Thales, 357
+
+  Thebes, 271
+
+  Themis, 88-90
+
+  Theogirus, 279
+
+  Theon, 245
+
+  Theseus, 257
+
+  Thome, 101
+
+  Thucydides, 331
+
+  Tibertinus, 281
+
+  Tibullus, 282
+
+  Tides, 40
+
+  Timocharis, 340
+
+  Tin, 179
+
+  Titan, 85, 88, 89
+
+  Titanium, 179
+
+  Toucan, 308
+
+  Transits of Mercury, 14, 15
+
+     "     of Venus, 337, 338, 339
+
+  Triangulum, 271
+
+       "      Australis, 306
+
+  Trio, 220
+
+  Triptolemus, 257
+
+  Triton, 93
+
+  Trouvelot, 21, 22, 78, 211
+
+  Tumlirz, 46
+
+  Turrinus, 220
+
+  Tycho Brahé, 10, 30, 99, 145, 179, 298
+
+  Typhon, 263, 272
+
+
+  U
+
+  Ulugh Beigh, 238, 276, 278
+
+  Underwood, 85
+
+  Uranus, chap. x.;
+    spectrum of, 91, 92
+
+  Urda, 71
+
+
+  V
+
+  Valz 72
+
+  "Vanishing star," 59
+
+  Varvadjah, 236
+
+  Vega, 148, 156, 244
+
+  Vencontre, 220
+
+  Venus, chap. iii.;
+    apparent motion of, 28;
+    supposed satellite of, 28, 29;
+    transit of, 337-339
+
+  Veronica, S, 145
+
+  Vesta, 70
+
+  Virgil, 17, 218, 242, 262, 309
+
+  Virgo, 260
+
+  Vogel, 180
+
+  Vogt, 122
+
+  Volans, 304
+
+  Voltaire, 15
+
+  Von Hahn, 24
+
+  Vulpecula, 300
+
+
+  W
+
+  Wallace, Dr., 212, 357
+
+  Wallis, 80
+
+  Ward, 88
+
+  Wargentin, 178
+
+  Watson, 339
+
+  Webb, 24, 25, 77, 190, 286
+
+  Weber, 183
+
+  Weinhand, 122
+
+  Wendell, 71, 103, 109
+
+  Werchojansk, 33
+
+  White spots on Jupiter's satellites, 81
+
+  White spots on Venus, 21
+
+  Whitmell, 50, 86
+
+  Wiggins, 333
+
+  Wilczyniski, 195
+
+  Williams, Stanley, 22, 277, 302
+
+  Wilsing, 155
+
+  Wilson, H. C., 137, 139
+
+  Wilson, Dr. W. E., 3, 148
+
+  Winnecke, 26, 188
+
+  Winterhalter, 351
+
+  Wolf, Dr. Max, 71, 72, 191, 211, Note p. 537
+
+  Wrangel, 240
+
+
+  Y
+
+  Young, Prof., 4, 7, 9
+
+  Young, Miss Anne S., 79
+
+  Yunis, Ibn, 30
+
+
+  Z
+
+  Zach, 331
+
+  Zenophon, 127
+
+  Zethas, 257
+
+  Zöllner, 27
+
+
+THE END
+
+
+PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLES.
+
+
+[Illustration]
+
+
+
+
+FOOTNOTES:
+
+[1] _Comptes Rendus_, 1903, December 7.
+
+[2] _Nature_, April 11, 1907.
+
+[3] _Astrophysical Journal_, vol. 19 (1904), p. 39.
+
+[4] _Astrophysical Journal_, vol. 21 (1905), p. 260.
+
+[5] _Knowledge_, July, 1902, p. 132.
+
+[6] _Nature_, April 30, 1903.
+
+[7] _Ibid._, May 18, 1905.
+
+[8] _Ibid._, May 18, 1905.
+
+[9] _Nature_, June 29, 1871.
+
+[10] _Nature_, October 15, 1903.
+
+[11] _The Life of the Universe_ (1909), vol. ii. p. 209.
+
+[12] _The World Machine_, p. 234.
+
+[13] Quoted in _The Observatory_, March 1908, p. 125.
+
+[14] _The Observatory_, September, 1906.
+
+[15] _Nature_, March 1, 1900.
+
+[16] _Cycle of Celestial Objects_, p. 96.
+
+[17] _Ast. Nach._ No. 3737.
+
+[18] _Observatory_, September, 1906.
+
+[19] _Nature_, November 29 and December 20, 1894.
+
+[20] _Bulletin, Ast. Soc. de France_, July, 1898.
+
+[21] _Observatory_, vol. 8 (1885), pp. 306-7.
+
+[22] _Nature_, October 30, 1902.
+
+[23] Charles Lane Poor, _The Solar System_, p. 170.
+
+[24] Smyth, _Celestial Cycle_, p. 60.
+
+[25] Denning, _Telescopic Work for Starlight Evenings_, p. 225.
+
+[26] _The Observatory_, 1894, p. 395.
+
+[27] _Ast. Nach._ 4333, quoted in _Nature_, July 1, 1909, p. 20.
+
+[28] _English Mechanic_, July 23, 1909.
+
+[29] _Nature_, December 22, 1892.
+
+[30] _Celestial Objects_, vol. i. p. 52, footnote.
+
+[31] _Ibid._, p. 54.
+
+[32] _Astronomy and Astrophysics_, 1892, p. 618.
+
+[33] _Nature_, August 7, 1879.
+
+[34] _The World of Space_, p. 56.
+
+[35] _Nature_, September 15, 1892.
+
+[36] _Observatory_, 1880, p. 574.
+
+[37] _Knowledge_, November 1, 1897, pp. 260, 261.
+
+[38] _Worlds in the Making_, p. 61.
+
+[39] _Ibid._, p. 48.
+
+[40] _Nature_, June 1, 1876.
+
+[41] _Cel. Objects_, vol. i. p. 66 (5th Edition).
+
+[42] _Celestial Objects_, vol. i. p. 65 (5th Edition).
+
+[43] _Ast. Nach._ No. 1863.
+
+[44] _Nature_, June 1, 1876.
+
+[45] _Ibid._, June 8, 1876.
+
+[46] _Nature_, October 17, 1895.
+
+[47] _Ibid._, July 27, 1905.
+
+[48] _Celestial Cycle_, p. 107.
+
+[49] _Nature_, October 6, 1887.
+
+[50] _Ast. Nach._, No. 4106.
+
+[51] _Copernicus_, vol. ii. p. 168.
+
+[52] _Cosmos_, vol. iv. p. 476, footnote.
+
+[53] Denning, _Telescopic Work for Starlight Evenings_, p. 153.
+
+[54] _Ibid._, p. 154.
+
+[55] _Nature_, July 13, 1876.
+
+[56] P. M. Ryves in _Knowledge_, June 1, 1897, p. 144.
+
+[57] _Bulletin, Ast. Soc. de France_, August, 1905.
+
+[58] _Nature_, April 5, 1894.
+
+[59] _Nature_, May 14, 1896. Some have attributed these "luminous clouds"
+to light reflected from the dust of the Krakatoa eruption (1883).
+
+[60] _The Observatory_, 1877, p. 90.
+
+[61] _Popular Astronomy_, vol. 11 (1903), p. 293.
+
+[62] _Popular Astronomy_, vol. 13 (1905), p. 226.
+
+[63] _Nature_, July 25, 1901 (from Flammarion).
+
+[64] _Popular Astronomy_, vol. 11 (1903), p. 496.
+
+[65] _Kinetic Theories of Gravitation_, Washington, 1877.
+
+[66] _The Observatory_, June, 1894, p. 208.
+
+[67] _Nature_, June 8, 1899.
+
+[68] _Astrophysical Journal_, vol. 14 (1901), p. 238, footnote.
+
+[69] _Mars as the Abode of Life_, p. 52.
+
+[70] Second Book of the Maccabees v. 1-4 (Revised Edition).
+
+[71] Humboldt's _Cosmos_, vol. i. p. 169 (Otté's translation).
+
+[72] Quoted by Grant in _History of Physical Astronomy_, p. 71.
+
+[73] _Ibid._, pp. 100, 101.
+
+[74] _Exposition du Système du Monde_, quoted by Carl Snyder in _The World
+Machine_, p. 226.
+
+[75] _Worlds in the Making_, p. 63.
+
+[76] _Cosmos_, vol. i. p. 131.
+
+[77] _The Observatory_, June, 1909, p. 261.
+
+[78] _Astronomical Essays_, pp. 61, 62.
+
+[79] _Encyclopædia Britannica_ (_Schiraz_).
+
+[80] _Monthly Notices_, R.A.S., February, 1905.
+
+[81] _Nature_, March 3, 1870.
+
+[82] _Ibid._, March 31, 1870, p. 557.
+
+[83] Prof. W. H. Pickering found 12 times (see p. 1).
+
+[84] _Nature_, January 30, 1908.
+
+[85] _Nature_, September 5, 1901.
+
+[86] _Ibid._, July 31, 1890.
+
+[87] _Nature_, October 16, 1884.
+
+[88] _Nature_, February 19, 1885.
+
+[89] _Nature_, January 14, 1909, p. 323.
+
+[90] _Photographic Atlas of the Moon, Annals of Harvard Observatory_, vol.
+li. pp. 14, 15.
+
+[91] _Nature_, January 18, 1906.
+
+[92] Humboldt's _Cosmos_, vol. iv. p. 481.
+
+[93] _Ibid._, p. 482.
+
+[94] _Monthly Notices_, R.A.S., June, 1895.
+
+[95] Humboldt's _Cosmos_, vol. iv. p. 483 (Otté's translation).
+
+[96] Grant, _History of Physical Astronomy_, p. 229.
+
+[97] _Popular Astronomy_, vol. xvii. No. 6, p. 387 (June-July, 1909).
+
+[98] _Nature_, October 7, 1875.
+
+[99] _Mars as an Abode of Life_ (1908), p. 281.
+
+[100] _Knowledge_, May 2, 1886.
+
+[101] _Nature_, March 12, 1908.
+
+[102] _Bulletin, Ast. Soc. de France_, April, 1899.
+
+[103] _Astronomy and Astrophysics_ (1894), p. 649.
+
+[104] _Nature_, April 20, 1905.
+
+[105] _Astrophysical Journal_, vol. 14 (1901), p. 258.
+
+[106] _Nature_, August 22, 1907.
+
+[107] _Popular Astronomy_, vol. 12 (1904), p. 679.
+
+[108] _Mars as an Abode of Life_, p. 69.
+
+[109] _Ibid._, p. 146.
+
+[110] _Worlds in the Making_, p. 49.
+
+[111] _Worlds in the Making_, p. 53.
+
+[112] Denning, _Telescopic Work for Starlight Evenings_, p. 158.
+
+[113] _Ibid._, p. 166.
+
+[114] _Nature_, July 13, 1876.
+
+[115] _Nature_, May 2, 1907.
+
+[116] _Nature_, May 30, 1907.
+
+[117] _Publications of the Astronomical Society of the Pacific_, August,
+1908.
+
+[118] _Monthly Notices_, R.A.S., 1902, p. 291.
+
+[119] _Monthly Notices_, R.A.S., February, 1902, p. 291.
+
+[120] _Nature_, May 24, 1894.
+
+[121] _Ibid._, February 14, 1895.
+
+[122] _Ibid._, September 14, 1905.
+
+[123] _Ibid._, September 21, 1905.
+
+[124] _Ibid._, September 28, 1905.
+
+[125] _Ibid._, July 13, 1905.
+
+[126] _Nature_, November 3, 1898.
+
+[127] _Ibid._, July 14, 1881, p. 235.
+
+[128] Quoted in _The Observatory_, February, 1896, p. 104, from _Ast.
+Nach._, No. 3319.
+
+[129] _Monthly Notices_, R.A.S., February, 1909.
+
+[130] _Celestial Objects_, vol. i. p. 163.
+
+[131] _Nature_, December 29, 1898.
+
+[132] _Celestial Objects_, vol. i. p. 166.
+
+[133] _Astrophysical Journal_, vol. 14 (1901), pp. 248-9.
+
+[134] _Nature_, August 27, 1908.
+
+[135] Webb's _Celestial Objects_, vol. i. p. 177.
+
+[136] _Ibid._, vol. i. p. 187.
+
+[137] _Celestial Objects_, vol. i. p. 186.
+
+[138] _Astronomy and Astrophysics_, 1892, p. 87.
+
+[139] _Ibid._, 1892, pp. 94-5.
+
+[140] _Observatory_, December, 1891.
+
+[141] _Popular Astronomy_, vol. 11 (1903), p. 574.
+
+[142] _Ibid._, October, 1908.
+
+[143] _Bulletin, Ast. Soc. de France_, August, 1907.
+
+[144] _Nature_, August, 29 1907.
+
+[145] _Ibid._, March 7, 1907.
+
+[146] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[147] _The Observatory_, October, 1903, p. 392.
+
+[148] _Astronomy and Astrophysics_, 1894, p. 277.
+
+[149] _Nature_, November 18, 1897.
+
+[150] _Journal_, B.A.A., January, 1907.
+
+[151] _Journal_, B.A.A., February, 1909, p. 161.
+
+[152] _Cosmos_, vol. ii. p. 703.
+
+[153] _Ibid._
+
+[154] Denning, _Telescopic Work for Starlight Evenings_, p. 349.
+
+[155] _Cosmos_, vol. iii. p. 75.
+
+[156] _Journal_, B.A.A., June, 1896.
+
+[157] _Celestial Objects_, vol. i. p. 191.
+
+[158] _Nature_, May 30, 1901.
+
+[159] _Bulletin, Ast. Soc. de France_, August, 1900.
+
+[160] _Astronomy and Astrophysics_, 1892.
+
+[161] _Astrophysical Journal_, January, 1908, p. 35.
+
+[162] _Nature_, May 22, 1902.
+
+[163] _Ibid._, July 9, 1903.
+
+[164] _Ibid._, July 16, 1903.
+
+[165] _Nature_, September 24, 1903.
+
+[166] _Ibid._, October 8, 1903.
+
+[167] _Astrophysical Journal_, vol. 26 (1907), p. 60.
+
+[168] _Nature_, January 30, 1908.
+
+[169] _Ibid._, October 15, 1908.
+
+[170] _Ibid._, October 29, 1908.
+
+[171] _Journal_, B.A.A., March, 1908, and June 22, 1908.
+
+[172] _Nature_, June 25, 1903.
+
+[173] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[174] _Pop. Ast._, vol. 12, pp. 408-9.
+
+[175] _Nature_, August 29, 1889.
+
+[176] _Astrophysical Journal_, vol. 26 (1907), p. 62.
+
+[177] _Bulletin, Ast. Soc. de France_, January, 1904.
+
+[178] Humboldt's _Cosmos_, vol. iv. p. 532.
+
+[179] _Copernicus_, vol. ii. p. 64.
+
+[180] _Knowledge_, May, 1909.
+
+[181] _Journal_, British Astronomical Association, January, 1909, p. 132.
+
+[182] _Ast. Nach._, No. 4308.
+
+[183] _History of Physical Astronomy_, p. 204.
+
+[184] Smyth's _Celestial Cycle_, pp. 210, 211.
+
+[185] Poor, _The Solar System_, p. 274.
+
+[186] _Celestial Cycle_, p. 246.
+
+[187] _Nature_, October 2, 1879.
+
+[188] _Ibid._, May 6, 1880.
+
+[189] _Ibid._, February 19, 1880.
+
+[190] _Nature_, September 30, 1897.
+
+[191] _Nature_, August 5, 1875.
+
+[192] _Ibid._, October 12, 1882, and _Copernicus_, vol. iii. p. 85.
+
+[193] _Nature_, May 8, 1884.
+
+[194] _Ibid._, June 16, 1887.
+
+[195] _Journal_, B.A.A., December 13, 1901.
+
+[196] _Nature_, September 20, 1900.
+
+[197] _Ast. Nach._, No. 3868, and _Nature_, March 12, 1903.
+
+[198] _Nature_, November 13, 1908.
+
+[199] _Nature_, December 7, 1905.
+
+[200] _Celestial Cycle_, p. 259.
+
+[201] _Celestial Cycle_, p. 260.
+
+[202] _Journal_, B.A.A., April, 1907.
+
+[203] _Monthly Notices_, R.A.S., March, 1908.
+
+[204] _Celestial Cycle_, p. 231.
+
+[205] _Journal_, B.A.A., July, 1908.
+
+[206] _Popular Astronomy_, October, 1908.
+
+[207] _Cape Obs._, p. 401.
+
+[208] _Nature_, July 2, 1908.
+
+[209] _Journal_, B.A.A., January 20, 1909, pp. 123-4.
+
+[210] Chambers' _Handbook of Astronomy_, Catalogue of Comets.
+
+[211] Seneca, quoted by Chambers, _Handbook_, vol. i. p. 554 (Fourth
+Edition).
+
+[212] _Ibid._
+
+[213] _Ibid._
+
+[214] _Ibid._, p. 534.
+
+[215] _Ibid._
+
+[216] Ma-tuoan-lin, quoted by Chambers, _Handbook_, p. 570.
+
+[217] _Astronomy and Astrophysics_, 1893, p. 798.
+
+[218] _The Observatory_, October, 1898.
+
+[219] Grant's _History of Physical Astronomy_, p. 293.
+
+[220] _Ibid._, p. 294.
+
+[221] Humboldt's _Cosmos_, vol. i. pp. 89, 90 (Otté's translation).
+
+[222] _Celestial Objects_, vol. i. p. 211, footnote.
+
+[223] Denning, _Telescopic Work for Starlight Evenings_, p. 248.
+
+[224] _Ibid._, p. 248.
+
+[225] _Ibid._, p. 250.
+
+[226] _Ibid._, p. 231.
+
+[227] Vol. iii. p. 106.
+
+[228] Grant's _History of Physical Astronomy_, p. 298.
+
+[229] _Ibid._, p. 305.
+
+[230] Humboldt's _Cosmos_, vol. i. p. 95.
+
+[231] _Nature_, April 30, 1908.
+
+[232] _Bulletin, Ast. Soc. de France_, May, 1906.
+
+[233] _Nature_, November 24, 1904.
+
+[234] _Ibid._, September 10, 1896.
+
+[235] _Ibid._, June 29, 1893.
+
+[236] _Journal_, B.A.A., May 22, 1903.
+
+[237] _Nature_, December 13, 1906, p. 159.
+
+[238] _Nature_, September 13, 1906.
+
+[239] _Nature_, October 12, 1905, p. 596.
+
+[240] _Knowledge_, January 13, 1882.
+
+[241] _Ibid._, January 20, 1882.
+
+[242] _Popular Astronomy_, June-July, 1908, p. 345.
+
+[243] _The Observatory_, March, 1896, p. 135.
+
+[244] _The Observatory_, February, 1900, pp. 106-7.
+
+[245] _Knowledge_, March, 1893, p. 51.
+
+[246] _Ibid._, July 3, 1885, p. 11.
+
+[247] _Cosmos_, vol. i. p. 108 (Otté's translation).
+
+[248] _Ibid._, vol. i. p. 124.
+
+[249] _Ibid._, vol. i. p. 119, footnote.
+
+[250] _Copernicus_, vol. i. p. 72.
+
+[251] _Ibid._
+
+[252] _Astrophysical Journal_, June, 1909, pp. 378-9.
+
+[253] _Knowledge_, July, 1909, p. 264.
+
+[254] Quoted by Miss Irene E. T. Warner in _Knowledge_, July, 1909, p.
+264.
+
+[255] _The Observatory_, November, 1900.
+
+[256] Or, "Before the phantom of false morning died" (4th edition); _The
+Observatory_, September, 1905, p. 356.
+
+[257] _The Observatory_, July, 1896, p. 274.
+
+[258] _Journal_, B.A.A., January 24, 1906.
+
+[259] _Ast. Soc. of the Pacific_, December, 1908, p. 280.
+
+[260] _Nature_, November 1, 1906.
+
+[261] _Ibid._, November 22, 1906, p. 93.
+
+[262] _Nature_, August 30, 1906.
+
+[263] _Cosmos_, vol. i. p. 131, footnote.
+
+[264] _Nature_, December 16, 1875.
+
+[265] _Ibid._, July 23, 1891.
+
+[266] _Bulletin, Ast. Soc. de France_, April, 1903.
+
+[267] _Bulletin, Ast. Soc. de France_, April, 1903.
+
+[268] _The Observatory_, May, 1896. The italics are Brenner's.
+
+[269] _Cosmos_, vol. iv. p. 563.
+
+[270] For details of this enumeration, see _Astronomical Essays_, p. 222.
+
+[271] _Nature_, June 11, 1908.
+
+[272] _Popular Astronomy_, vol. 14 (1906), p. 510.
+
+[273] _Bedford Catalogue_, p. 532.
+
+[274] _Popular Astronomy_, vol. 15 (1907), p. 194.
+
+[275] _Popular Astronomy_, vol. 15 (1907), p. 195.
+
+[276] _Bulletin, Ast. Soc. de France_, February, 1903.
+
+[277] Here χ is probably 17 Cygni, χ being the famous variable near it.
+
+[278] _Popular Astronomy_, vol. 13 (1904), p. 509.
+
+[279] _Astrophysical Journal_, December, 1895.
+
+[280] _The Observatory_, July, 1895, p. 290.
+
+[281] _Celestial Cycle_, p. 302.
+
+[282] _Nature_, December 13, 1894.
+
+[283] _Histoire Celeste_, p. 211.
+
+[284] _Nature_, October, 1887.
+
+[285] _Ibid._, August 29, 1889.
+
+[286] _Science Abstracts_, February 25, 1908, pp. 82, 83.
+
+[287] _Bedford Catalogue_, pp. 227-8.
+
+[288] _Knowledge_, February 1, 1888.
+
+[289] _Celestial Cycle_, p. 280.
+
+[290] _Popular Astronomy_, February, 1904.
+
+[291] _Ibid._, vol. 15 (1907), p. 444.
+
+[292] _Journal_, B.A.A., June, 1899.
+
+[293] _Astrophysical Journal_, vol. 8 (1898), p. 314.
+
+[294] _Astrophysical Journal_, vol. 8, p. 213.
+
+[295] _Ibid._, vol. 17, January to June, 1902.
+
+[296] _Astronomy and Astrophysics_, 1894, pp. 569-70.
+
+[297] _The Study of Stellar Evolution_ (1908), p. 171.
+
+[298] _Astrophysical Journal_, January, 1905.
+
+[299] _Journal_, B.A.A., June, 1901.
+
+[300] _Ast. Soc. of the Pacific_, December, 1908.
+
+[301] _The Observatory_, November, 1902, p. 391.
+
+[302] _Cosmos_, vol. iv. p. 567 (Otté's translation).
+
+[303] _Journal_, B.A.A., February, 1898.
+
+[304] _The Observatory_, April, 1887.
+
+[305] _Evangeline_, Part the Second, III.
+
+[306] _Legend of Robert, Duke of Normandy._
+
+[307] _Copernicus_, vol. iii. p. 231.
+
+[308] _Ibid._, p. 61.
+
+[309] _Cosmos_, vol. i. p. 142.
+
+[310] These apertures are computed from the formula, minimum visible = 9 +
+5 log. aperture.
+
+[311] _Cosmos_, vol. iii. p. 73.
+
+[312] _Darwin and Modern Science_, p. 563.
+
+[313] _Journal_, B.A.A., October, 1895.
+
+[314] Burnham's _General Catalogue of Double Stars_, p. 494.
+
+[315] _Journal_, B.A.A., November 18, 1896.
+
+[316] _Ibid._, B.A.A., January, 1907.
+
+[317] _Studies in Astronomy_, p. 185.
+
+[318] _Knowledge_, June, 1891.
+
+[319] Seen by Drs. Ludendorff and Eberhard, _The Observatory_, April,
+1906, p. 166, quoted from _Ast. Nach._, No. 4067.
+
+[320] _The Observatory_, January, 1907, p. 61.
+
+[321] _Astronomy and Astrophysics_, 1894.
+
+[322] Smyth's _Celestial Cycle_, p. 223.
+
+[323] _Nature_, February 7, 1907.
+
+[324] _Ibid._, March 19, 1908.
+
+[325] _Popular Astronomy_, vol. 15 (1907), p. 9.
+
+[326] _Astrophysical Journal_, June, 1907, p. 330.
+
+[327] _Ibid._, vol. 22, p. 172.
+
+[328] _Nature_, November 18, 1886.
+
+[329] _Astrophysical Journal_, vol. 17 (1903), p. 282.
+
+[330] _Astrophysical Journal_, vol. 12 (1900), p. 54.
+
+[331] _Nature_, March 21, 1878.
+
+[332] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[333] _Journal_, B.A.A., vol. 17 (1903), p. 282.
+
+[334] _Nature_, June 20, 1909.
+
+[335] _The Observatory_, vol. 7 (1884), p. 17.
+
+[336] _The Observatory_, vol. 14 (1891), p. 69.
+
+[337] _Astronomy and Astrophysics_, 1896, p. 54
+
+[338] _Nature_, August 28, 1902.
+
+[339] _Astrophysical Journal_, October, 1903.
+
+[340] _Nature_, May 30, 1907.
+
+[341] _Popular Astronomy_, February, 1909, p. 125.
+
+[342] _The Observatory_, May, 1907, p. 216.
+
+[343] _Astrophysical Journal_, May, 1907.
+
+[344] _Histoire de l'Astronomie Moderne_, vol. i. pp. 185-6.
+
+[345] Humboldt's _Cosmos_, vol. iii. p. 210 (Otté's translation).
+
+[346] _Ibid._, vol. iii. pp. 213-14.
+
+[347] J. C. Duncan, _Lick Observatory Bulletin_, No. 151.
+
+[348] _Astrophysical Journal_, vol. 17, p. 283.
+
+[349] _The Origin of the Stars_, p. 143.
+
+[350] _Ibid._, p. 135.
+
+[351] Quoted by Ennis in _The Origin of the Stars_, p. 133.
+
+[352] _Astrophysical Journal_, vol. 20 (1904), p. 357.
+
+[353] _Nature_, March 8, 1906.
+
+[354] _Astronomical Society of the Pacific_, August, 1908.
+
+[355] _Astronomy and Astrophysics_, 1894, p. 812.
+
+[356] _The Observatory_, May, 1905.
+
+[357] This is a misquotation. See my _Astronomical Essays_, p. 135.
+
+[358] _Nature_, February 3, 1870.
+
+[359] _Bedford Catalogue_, p. 14.
+
+[360] _Ibid._, p. 307.
+
+[361] _Astrophysical Journal_, vol. 14, p. 37.
+
+[362] _Ibid._, vol. 9, p. 149.
+
+[363] _Nature_, July 20, 1899.
+
+[364] _Ast. Nach._, No. 3476.
+
+[365] _Astronomische Nachrichten_, No. 4213.
+
+[366] _Astrophysical Journal_, vol. 9, p. 149.
+
+[367] _Cape Observations_, p. 61.
+
+[368] _Ibid._, p. 85.
+
+[369] _Cape Observations_, p. 98.
+
+[370] _Transactions_, Royal Dublin Society, vol. 2.
+
+[371] _Ast. Nach._, 3628, quoted in _The Observatory_, April, 1900.
+
+[372] _Nature_, April 8, 1909.
+
+[373] _Problems in Astrophysics_, p. 477.
+
+[374] _Ibid._, p. 499.
+
+[375] _Copernicus_, vol. iii. p. 55.
+
+[376] _Lick Observatory Bulletin_, No. 149.
+
+[377] _Ibid._
+
+[378] _Ibid._
+
+[379] _Monthly Notices_, R.A.S., April, 1908, pp. 465-481.
+
+[380] _Lick Observatory Bulletin_, No. 155 (February, 1909).
+
+[381] _Outlines of Astronomy_, par. 870 (Edition of 1875).
+
+[382] _Georgics_, i. II. 217-18.
+
+[383] See paper by Mr. and Mrs. Maunder in _Monthly Notices_, R.A.S.,
+March, 1904, p. 506.
+
+[384] _Primitive Constellations_, vol. ii. p. 143.
+
+[385] _Recherches sur l'Histoire de l'Astronomie Ancienne_, by Paul
+Tannery (1893), p. 298.
+
+[386] _Primitive Constellations_, vol. ii. p. 225.
+
+[387] _Nature_, October 2, 1890.
+
+[388] Lalande's _Astronomie_, vol. i. pp. 243-4.
+
+[389] Lalande's _Astronomie_, vol. i. pp. 242-3.
+
+[390] There are three copies of Al-Sufi's work in the Imperial Library at
+Paris, but these are inaccurate. There is also one in the British Museum
+Library, and another in the India Office Library; but these are imperfect,
+considerable portions of the original work being missing.
+
+[391] _Harvard Annals_, vol. ix. p. 51.
+
+[392] The science of the risings and settings of the stars was called _ilm
+el-anwa_ (Caussin, _Notices et Extraits des Manuscrits de la Bibliothèque
+due Roi_, tome xii. p. 237).
+
+[393] See Mr. E. B. Knobel's papers on this subject in the _Monthly
+Notices_, R.A.S., for 1879 and 1884.
+
+[394] In reading this chapter the reader is recommended to have a Star
+Atlas beside him for reference; Proctor's smaller Star Atlas will be found
+very convenient for this purpose. On the title-page of this useful work
+the author quotes Carlyle's words, "Why did not somebody teach me the
+constellations and make me at home in the starry heavens which are always
+overhead, and which I don't half know to this day?"
+
+[395] _Bedford Catalogue_, p. 29.
+
+[396] _Cosmos_, vol. iii. p. 87.
+
+[397] _Heavenly Display_, 579-85.
+
+[398] _Bedford Catalogue_, p. 385.
+
+[399] Lalande's _Astronomie_, vol. iv. p. 529.
+
+[400] Lalande's _Astronomie_, vol. i. pp. 268-9.
+
+[401] _Primitive Constellations_, vol. i. p. 48.
+
+[402] _Bedford Catalogue_, pp. 27, 28.
+
+[403] Lalande's _Astronomie_, vol. iv. p. 492.
+
+[404] _Bedford Catalogue_, p. 120.
+
+[405] _Primitive Constellations_, vol. i. p. 143.
+
+[406] Perseus.
+
+[407] _Heavenly Display_, 254-8, 261-5, quoted by Brown in _Primitive
+Constellations_, vol. i. p. 274.
+
+[408] Lalande's _Astronomie_, vol. iv. p. 493.
+
+[409] _Primitive Constellations_, vol. i. p. 292.
+
+[410] _Paradiso_, xxii. 111.
+
+[411] Lalande's _Astronomie_, vol. iv. p. 493.
+
+[412] _Bedford Catalogue_, p. 225.
+
+[413] _Nature_, April 6, 1882.
+
+[414] _Primitive Constellations_, vol. i. p. 68.
+
+[415] _Ibid._, vol. i. p. 71.
+
+[416] _Bibliographie Gènèrale de l'Astronomie_, vol. i. Introduction, pp.
+131, 132.
+
+[417] Lalande's _Astronomie_, vol. i. p. 296.
+
+[418] _Primitive Constellations_, vol. i. p. 74.
+
+[419] _Cape Observations_, p. 116.
+
+[420] _Metamorphoses_, xv. 371.
+
+[421] Lalande's _Astronomie_, vol. iv. p. 487.
+
+[422] _Monthly Notices_, R.A.S., April 14, 1848.
+
+[423] _Prim. Const._, vol. ii. p. 45.
+
+[424] Lalande's _Astronomie_, pp. 472-3.
+
+[425] Lalande's _Astronomie_, vol. iv. p. 485.
+
+[426] This star is not shown in Proctor's small Atlas, but it lies between
+μ and ν, nearer to μ.
+
+[427] Lalande's _Astronomie_, vol. i. p. 247.
+
+[428] Lalande's _Astronomie_, vol. iv. p. 489.
+
+[429] _Primitive Constellations_, vol. i. p. 91.
+
+[430] _Memoirs_, R.A.S., vol. xiii. 61.
+
+[431] _Monthly Notices_, R.A.S., June, 1895.
+
+[432] Lalande's _Astronomie_, vol. i. p. 274.
+
+[433] _Primitive Constellations_, vol. i. p. 143.
+
+[434] _Primitive Constellations_, vol. i. p. 278.
+
+[435] Lalande's _Astronomie_, vol. iv. p. 468.
+
+[436] _Quæst. Nat._, Lib. 1, Cap. I. § 6; quoted by Dr. See. "Canicula" is
+Sirius, and "Nartis," Mars.
+
+[437] _Astronomy and Astrophysics_, vol. 11, 1892.
+
+[438] _The Observatory_, April, 1906, p. 175.
+
+[439] Houzeau, _Bibliographie Gènèrale de l'Astronomie_, vol. i.,
+Introduction, p. 129.
+
+[440] _English Mechanic_, March 25, 1904, p. 145.
+
+[441] Humboldt's _Cosmos_, vol. iii. p. 185, footnote (Otté's
+translation).
+
+[442] Lalande's _Astronomie_, vol, i. p. 277.
+
+[443] This was pointed out by Flammarion in his work _Les Étoiles_, page
+532; but his identifications do not agree exactly with mine.
+
+[444] See Proctor's Map 7, now x.
+
+[445] _Primitive Constellations_, vol. i. p. 106.
+
+[446] Lalande's _Astronomie_, vol. i. p. 278.
+
+[447] Lalande's _Astronomie_, vol. iv.
+
+[448] _Primitive Constellations_, vol. i. p. 112.
+
+[449] _Ibid._, vol. i. p. 113.
+
+[450] Lalande's _Astronomie_, vol. i.
+
+[451] W. T. Lynn in _The Observatory_, vol. 22, p. 236.
+
+[452] _Knowledge_, May 1, 1889. Sir John Herschel, however, gives 3970
+B.C.
+
+[453] _The Observatory_, November 1907, p. 412.
+
+[454] This is not, however, _invariably_ the case, as pointed out by Mr.
+Denning in _The Observatory_, 1885, p. 340.
+
+[455] _The Observatory_, vol. 8 (1885), pp. 246-7.
+
+[456] _Harvard College Observatory Annals_, vol. xlviii. No. 5.
+
+[457] _Popular Astronomy_, vol. 15 (1907), p. 529.
+
+[458] _Cape Observations_, p. 77.
+
+[459] _Monthly Notices_, R.A.S., March, 1899.
+
+[460] _Nature_, February 13, 1890.
+
+[461] _Popular Astronomy_, vol. 15 (1907), p. 530.
+
+[462] _Photographs of Star-Clusters and Nebulæ_, vol. ii. p. 17.
+
+[463] _Monthly Notices_, R.A.S., May 9, 1856.
+
+[464] _Astrophysical Journal_, vol. 25 (1907), p. 219.
+
+[465] _Popular Astronomy_, vol. 11 (1903), p. 293.
+
+[466] Translated by W. H. Mallock, _Nature_, February 8, 1900, p. 352.
+
+[467] Howard Payn, _Nature_, May 16, 1901, p. 56.
+
+[468] Howard Payn, _Nature_, May 16, 1901, p. 56.
+
+[469] _Contributions from the Mount Wilson Solar Observatory_, No. 31.
+
+[470] Quoted by Denning in _Telescopic Work for Starlight Evenings_, p.
+297.
+
+[471] _Astrophysical Journal_, March, 1895.
+
+[472] _Outlines of Astronomy_, Tenth Edition, p. 571.
+
+[473] _Astrophysical Journal_, vol. 12, p. 136.
+
+[474] _De Placitis._ Quoted by Carl Snyder in _The World Machine_ p. 354.
+
+[475] _Popular Astronomy_, vol. 14 (1906), p. 638.
+
+[476] Article on "The Greek Anthology," _Nineteenth Century_, April, 1907,
+quoted in _The Observatory_, May, 1907.
+
+[477] _Popular Astronomy_, vol. 13 (1905), p. 346.
+
+[478] _Bulletin de la Soc. Ast. de France_, April, 1908.
+
+[479] _The Observatory_, vol. 11, p. 375.
+
+[480] Grant, _History of Physical Astronomy_, p. 364.
+
+[481] _Ibid._, p. 377.
+
+[482] _Ibid._, p. 366.
+
+[483] _Ibid._, p. 367.
+
+[484] Grant, _History of Physical Astronomy_, p. 370.
+
+[485] _Nature_, July 25, 1889.
+
+[486] _Cosmos_, vol. iv. p. 381.
+
+[487] _Cosmos_, vol. iv. pp. 381-6.
+
+[488] _Ibid._, vol. i. p. 121.
+
+[489] _The Observatory_, vol. 6 (1883), pp. 327-8.
+
+[490] _Nature_, June 25, 1874.
+
+[491] _Popular Astronomy_, May, 1895, "Reflectors or Refractors."
+
+[492] Denning, _Telescopic Work for Starlight Evenings_, p. 225.
+
+[493] _Nature_, November 2, 1893.
+
+[494] _Telescopic Work_, p. 226.
+
+[495] _Copernicus_, vol. i. p. 229.
+
+[496] Grant, _History of Physical Astronomy_, p. 433.
+
+[497] _Cosmos_, vol. ii. p. 699.
+
+[498] Grant, _History of Physical Astronomy_, p. 536, footnote.
+
+[499] _Bedford Catalogue_, p. 179.
+
+[500] _The Observatory_, July, 1891.
+
+[501] _Nature_, September 3, 1903.
+
+[502] _Cosmos_, vol. ii. p. 669.
+
+[503] _The World Machine_, p. 80.
+
+[504] _Ibid._, p. 89.
+
+[505] Grant, _History of Physical Astronomy_, p. 107.
+
+[506] Grant, _History of Physical Astronomy_, p. 113.
+
+[507] _Nature_, August 11, 1898.
+
+[508] _Ibid._, August 18, 1898.
+
+[509] _Ibid._, October 20, 1898.
+
+[510] _The Observatory_, vol. iv. (1881), p. 234.
+
+[511] W. T. Lynn, _The Observatory_, July, 1909, p. 291.
+
+[512] Quoted in _The Observatory_, July, 1902, p. 281.
+
+[513] _Astrophysical Journal_, vol. 6, 1897, p. 304.
+
+[514] _Celestial Cycle_, p. 367.
+
+[515] _The Observatory_, vol. 5 (1882), p. 251.
+
+[516] Quoted by Humboldt in _Cosmos_, vol. ii. p. 696, footnote.
+
+[517] Quoted by Denning in _Telescopic Work_, p. 347.
+
+[518] _Knowledge_, February 20, 1885, p. 149.
+
+[519] Humboldt's _Cosmos_, vol. i. p. 123.
+
+[520] _Outlines of Astronomy_, par. 319; edition of 1875.
+
+[521] _Bulletin de la Soc. Ast. de France_, March, 1908, p. 146.
+
+[522] An "astronomical unit" is the sun's mean distance from the earth.
+
+[523] This is on the American and French system of notation, but on the
+English system, 10{66} = 10{60} × 10{6} would be a million decillion.
+
+[524] _Astronomical Society of the Pacific_, April, 1909 (No. 125), and
+_Popular Astronomy_, May, 1909.
+
+[525] _Nature_, July 22, 1909.
+
+[526] _Ibid._
+
+[527] _The Observatory_, vol. 9 (December, 1886), p. 389.
+
+[528] _De Nat. Deorum_, quoted in Smyth's _Cycle_, p. 19.
+
+[529] _The Observatory_, May, 1907.
+
+[530] _More Worlds than Ours_, p. 17.
+
+[531] _Man's Place in Nature._
+
+
+
+
+Transcriber's Notes:
+
+Passages in italics are indicated by _italics_.
+
+Superscripted characters are indicated by {superscript}.
+
+Subscripted characters are indicated by _{subscript}.
+
+Foonote 48 appears on page 28 of the text, but there is no corresponding
+marker on the page.
+
+Foonote 448 appears on page 295 of the text, but there is no corresponding
+marker on the page.
+
+
+
+
+
+
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+The Project Gutenberg EBook of Astronomical Curiosities, by J. Ellard Gore
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org/license
+
+
+Title: Astronomical Curiosities
+       Facts and Fallacies
+
+Author: J. Ellard Gore
+
+Release Date: March 25, 2012 [EBook #39263]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ASTRONOMICAL CURIOSITIES ***
+
+
+
+
+Produced by The Online Distributed Proofreading Team at
+http://www.pgdp.net (This file was produced from images
+generously made available by The Internet Archive.)
+
+
+
+
+
+
+
+
+
+  ASTRONOMICAL CURIOSITIES
+
+  FACTS AND FALLACIES
+
+
+
+
+  ASTRONOMICAL CURIOSITIES
+
+  FACTS AND FALLACIES
+
+
+  BY J. ELLARD GORE
+
+  MEMBER OF THE ROYAL IRISH ACADEMY FELLOW OF THE
+  ROYAL ASTRONOMICAL SOCIETY CORRESPONDING MEMBER
+  OF THE ROYAL ASTRONOMICAL SOCIETY OF CANADA ETC.
+  AUTHOR OF "ASTRONOMICAL ESSAYS," "STUDIES IN
+  ASTRONOMY," "THE VISIBLE UNIVERSE," ETC.
+
+
+  LONDON
+  CHATTO & WINDUS
+  1909
+
+
+
+
+  PRINTED BY
+  WILLIAM CLOWES AND SONS, LIMITED
+  LONDON AND BECCLES
+
+  _All rights reserved_
+
+
+
+
+PREFACE
+
+
+The curious facts, fallacies, and paradoxes contained in the following
+pages have been collected from various sources. Most of the information
+given will not, I think, be found in popular works on astronomy, and will,
+it is hoped, prove of interest to the general reader.
+
+J. E. G.
+
+_September, 1909._
+
+
+
+
+CONTENTS
+
+
+                                                PAGE
+
+  CHAPTER
+
+      I. THE SUN                                   1
+
+     II. MERCURY                                  10
+
+    III. VENUS                                    17
+
+     IV. THE EARTH                                32
+
+      V. THE MOON                                 48
+
+     VI. MARS                                     59
+
+    VII. THE MINOR PLANETS                        68
+
+   VIII. JUPITER                                  74
+
+     IX. SATURN                                   84
+
+      X. URANUS AND NEPTUNE                       91
+
+     XI. COMETS                                   97
+
+    XII. METEORS                                 117
+
+   XIII. THE ZODIACAL LIGHT AND GEGENSCHEIN      127
+
+    XIV. THE STARS                               135
+
+     XV. DOUBLE AND BINARY STARS                 160
+
+    XVI. VARIABLE STARS                          170
+
+   XVII. NEBUL� AND CLUSTERS                     191
+
+  XVIII. HISTORICAL                              217
+
+    XIX. THE CONSTELLATIONS                      239
+
+     XX. THE VISIBLE UNIVERSE                    313
+
+    XXI. GENERAL                                 329
+
+         INDEX                                   359
+
+
+
+
+ILLUSTRATIONS
+
+
+                                                PAGE
+
+  AL-SUFI'S "EARTHEN JAR"                        247
+
+  AL-SUFI'S "FISHES" IN ANDROMEDA                249
+
+
+
+
+ASTRONOMICAL CURIOSITIES
+
+
+
+
+CHAPTER I
+
+The Sun
+
+
+Some observations recently made by Prof. W. H. Pickering in Jamaica, make
+the value of sunlight 540,000 times that of moonlight. This makes the
+sun's "stellar magnitude" minus 26�83, and that of moonlight minus 12�5.
+Prof. Pickering finds that the light of the full moon is equal to 100,000
+stars of zero magnitude. He finds that the moon's "albedo" is about
+0�0909; or in other words, the moon reflects about one-tenth of the light
+which falls on it from the sun. He also finds that the light of the full
+moon is about twelve times the light of the half moon: a curious and
+rather unexpected result.
+
+M. C. Fabry found that during the total eclipse of the sun on August 30,
+1905, the light of the corona at a distance of five minutes of arc from
+the sun's limit, and in the vicinity of the sun's equator, was about 720
+candle-power. Comparing this with the intrinsic light of the full moon
+(2600 candle-power) we have the ratio of 0�28 to 1. He finds that the
+light of the sun in the zenith, and at its mean distance from the earth,
+is 100,000 times greater than the light of a "decimal candle" placed at a
+distance of one metre from the eye.[1] He also finds that sunlight is
+equal to 60,000 million times the light of Vega. This would make the sun's
+"stellar magnitude" minus 26�7, which does not differ much from Prof.
+Pickering's result, given above, and is probably not far from the truth.
+
+From experiments made in 1906 at Moscow, Prof. Ceraski found that the
+light of the sun's limb is only 31�4 to 38�4 times brighter than the
+illumination of the earth's atmosphere very near the limb. This is a very
+unexpected result; and considering the comparative faintness of the sun's
+corona during a total eclipse, it is not surprising that all attempts to
+photograph it without an eclipse have hitherto failed.[2]
+
+From Paschen's investigations on the heat of the sun's surface, he finds a
+result of 5961� (absolute), "assuming that the sun is a perfectly black
+body."[3] Schuster finds that "There is a stratum near the sun's surface
+having an average temperature of approximately 5500� C., to which about
+0�3 of the sun's radiation is due. The remaining portion of the radiation
+has an intensity equal to that due to a black body having a temperature of
+about 6700� C." The above results agree fairly well with those found by
+the late Dr. W. E. Wilson.[4] The assumption of the sun being "a black
+body" seems a curious paradox; but the simple meaning of the statement is
+that the sun is assumed to act as a radiator as _if it were a perfectly
+black body heated to the high temperature given above_.
+
+According to Prof. Langley, the sun's photosphere is 5000 times brighter
+than the molten metal in a "Bessemer convertor."[5]
+
+Observations of the sun even with small telescopes and protected by dark
+glasses are very dangerous to the eyesight. Galileo blinded himself in
+this way; Sir William Herschel lost one of his eyes; and some modern
+observers have also suffered. The present writer had a narrow escape from
+permanent injury while observing the transit of Venus, in 1874, in India,
+the dark screen before the eyepiece of a 3-inch telescope having
+blistered--that is, partially fused during the observation. Mr. Cooper,
+Markree Castle, Ireland, in observing the sun, used a "drum" of alum water
+and dark spectacles, and found this sufficient protection against the
+glare in using his large refracting telescope of 13�3-inches aperture.
+
+Prof. Mitchell, of Columbia University (U.S.A.), finds that lines due to
+the recently discovered atmospherical gases argon and neon are present in
+the spectrum of the sun's chromosphere. The evidence for the existence of
+krypton and xenon is, however, inconclusive. Prof. Mitchell suggests that
+these gases may possibly have reached the earth's atmosphere from the sun.
+This would agree with the theory advanced by Arrhenius that "ionised
+particles are constantly being repulsed by the pressure of light, and thus
+journey from one sun to another."[6]
+
+Prof. Young in 1870, and Dr. Kreusler in June, 1904, observed the helium
+line D_{3} as a _dark_ line "in the spectrum of the region about a
+sun-spot."[7] This famous line, from which helium was originally
+discovered in the sun, and by which it was long afterwards detected in
+terrestrial minerals, usually appears as a _bright_ line in the spectrum
+of the solar chromosphere and "prominences." It has also been seen _dark_
+by Mr. Buss in sun-spot regions.[8]
+
+The discovery of sun-spots was claimed by Hariotte, in 1610, and by
+Galileo, Fabricius, and Scheiner, in 1611. The latter wrote 800 pages on
+them, and thought they were small planets revolving round the sun! This
+idea was also held by Tard�, who called them _Astra Borbonia_, and by C.
+Malapert, who termed them _Sydera Austricea_. But they seem to have been
+noticed by the ancients.
+
+Although in modern times there has been no extraordinary development of
+sun-spots at the epoch of maximum, it is not altogether impossible that in
+former times these spots may have occasionally increased to such an
+extent, both in number and size, as to have perceptibly darkened the sun's
+light. A more probable explanation of recorded sun-darkenings seems,
+however, to be the passing of a meteoric or nebulous cloud between the sun
+and the earth. A remarkable instance of sun-darkening recorded in Europe
+occurred on May 22, 1870, when the sun's light was observed to be
+considerably reduced in a cloudless sky in the west of Ireland, by the
+late John Birmingham; at Greenwich on the 23rd; and on the same date, but
+at a later hour, in North-Eastern France--"a progressive manifestation,"
+Mr. Birmingham says, "that seems to accord well with the hypothesis of
+moving nebulous matter." A similar phenomenon was observed in New England
+(U.S.A.), on September 6, 1881.
+
+One of the largest spots ever seen on the sun was observed in June, 1843.
+It remained visible for seven or eight days. According to Schwabe--the
+discoverer of the sun-spot period--its diameter was 74,000 miles, so that
+its area was many times that of the earth's surface. The most curious
+thing about this spot was that it appeared near a _minimum_ of the
+sun-spot cycle! and was therefore rather an anomalous phenomenon. It was
+suggested by the late Daniel Kirkwood that this great spot was caused by
+the fall of meteoric matter into the sun; and that it had possibly some
+connection with the great comet of 1843, which approached the sun nearer
+than any other recorded comet, its distance from the sun at perihelion
+being about 65,000 miles, or less than one-third of the moon's distance
+from the earth. This near approach of the comet to the sun occurred about
+three months before the appearance of the great sun-spot; and it seems
+probable that the spot was caused by the downfall of a large meteorite
+travelling in the wake of the comet.[9] The connection between comets and
+meteors is well known.
+
+The so-called blackness of sun-spots is merely relative. They are really
+very bright. The most brilliant light which can be produced artificially
+looks like a black spot when projected on the sun's disc.
+
+According to Sir Robert Ball a pound of coal striking a body with a
+velocity of five miles a second would develop as much heat as it would
+produce by its combustion. A body falling into the sun from infinity would
+have a velocity of 450 miles a second when it reached the sun's surface.
+Now as the momentum varies as the square of the velocity we have a pound
+of coal developing 90{2} (=450/5){2}, or 8,100 times as much heat as would
+be produced by its combustion. If the sun were formed of coal it would be
+consumed in about 3000 years. Hence it follows that the contraction of the
+sun's substance from infinity would produce a supply of heat for 3000 �
+8100, or 24,300,000 years.
+
+The late Mr. Proctor and Prof. Young believed "that the contraction theory
+of the sun's heat is the true and only available theory." The theory is,
+of course, a sound one; but it may now be supplemented by supposing the
+sun to contain a certain small amount of radium. This would bring physics
+and geology into harmony. Proctor thought the "sun's real globe is very
+much smaller than the globe we see. In other words the process of
+contraction has gone on further than, judging from the sun's apparent
+size, we should suppose it to have done, and therefore represents more sun
+work" done in past ages.
+
+With reference to the suggestion, recently made, that a portion, at least,
+of the sun's heat may be due to radium, and the experiments which have
+been made with negative results, Mr. R. T. Strutt--the eminent
+physicist--has made some calculations on the subject and says, "even if
+all the sun's heat were due to radium, there does not appear to be the
+smallest possibility that the Becquerel radiation from it could ever be
+detected at the earth's surface."[10]
+
+The eminent Swedish physicist Arrhenius, while admitting that a large
+proportion of the sun's heat is due to contraction, considers that it is
+probably the chemical processes going on in the sun, and not the
+contraction which constitute the _chief_ source of the solar heat.[11]
+
+As the centre of gravity of the sun and Jupiter lies at a distance of
+about 460,000 miles from the sun's centre, and the sun's radius is only
+433,000 miles, it follows that the centre of gravity of the sun and planet
+is about 27,000 miles _outside_ the sun's surface. The attractions of the
+other planets perpetually change the position of the centre of gravity of
+the solar system; but in some books on astronomy it is erroneously stated
+that the centre of gravity of the system is _always_ within the sun's
+surface. If _all_ the planets lay on the same side of the sun at the same
+time (as might possibly happen), then the centre of gravity of the whole
+system would lie considerably more than 27,000 miles outside the sun's
+surface.
+
+With reference to the sun's great size, Carl Snyder has well said, "It was
+as if in Vulcan's smithy the gods had moulded one giant ball, and the
+planets were but bits and small shot which had spattered off as the
+glowing ingot was cast and set in space. Little man on a little part of a
+little earth--a minor planet, a million of which might be tumbled into the
+shell of the central sun--was growing very small; his wars, the
+convulsions of a state, were losing consequence. Human endeavour, human
+ambitions could now scarce possess the significance they had when men
+could regard the earth as the central fact of the universe."[12]
+
+With reference to the late Prof. C. A. Young (U.S.A.)--a great authority
+on the sun--an American writer has written the following lines:--
+
+  "The destined course of whirling worlds to trace,
+  To plot the highways of the universe,
+  And hear the morning stars their song rehearse,
+  And find the wandering comet in his place;
+  This is the triumph written in his face,
+  And in the gleaming eye that read the sun
+  Like open book, and from the spectrum won
+  The secrets of immeasurable space."[13]
+
+
+
+
+CHAPTER II
+
+Mercury
+
+
+As the elongation of Mercury from the sun seldom exceeds 18�, it is a
+difficult object, at least in this country, to see without a telescope. As
+the poet says, the planet--
+
+  "Can scarce be caught by philosophic eye
+  Lost in the near effulgence of its blaze."
+
+Tycho Brah�, however, records several observations of Mercury with the
+unaided vision in Denmark.
+
+It can be occasionally caught with the naked eye in this country after
+sunset, when it is favourably placed for observation, and I have so seen
+it several times in Ireland. On February 19, 1888, I found it very visible
+in strong twilight near the western horizon, and apparently brighter than
+an average star of the first magnitude would be in the same position. In
+the clear air of the Punjab sky I observed Mercury on November 24-29,
+1872, near the western horizon after sunset. Its appearance was that of a
+reddish star of the first magnitude. On November 29 I compared its
+brilliancy with that of Saturn, which was some distance above it, and
+making allowance for the glare near the horizon in which Mercury was
+immersed, its brightness appeared to me to be quite equal to that of
+Saturn. In June, 1874, I found it equal to Aldebaran, and of very much the
+same colour. Mr. W. F. Denning, the famous observer of meteors, states
+that he observed Mercury with the naked eye about 150 times during the
+years 1868 to 1905.[14]
+
+He found that the duration of visibility after sunset is about 1{h} 40{m}
+when seen in March, 1{h} 30{m} in April, and 1{h} 20{m} in May. He thinks
+that the planet is, at its brightest, "certainly much brighter than a
+first magnitude star."[15] In February, 1868, he found that its brightness
+rivalled that of Jupiter, then only 2� or 3� distant. In November, 1882,
+it seemed brighter than Sirius. In 1876 it was more striking than Mars,
+but the latter was then "faint and at a considerable distance from the
+earth."
+
+In 1878, when Mercury and Venus were in the same field of view of a
+telescope, Nasmyth found that the surface brightness (or "intrinsic
+brightness," as it is called) of Venus was at least twice as great as that
+of Mercury; and Z�llner found that from a photometric point of view the
+surface of Mercury is comparable with that of the moon.
+
+With reference to the difficulty of seeing Mercury, owing to its proximity
+to the sun, Admiral Smyth says, "Although Mercury is never in _opposition_
+to the earth, he was, when in the house of Mars, always viewed by
+astrologers as a most malignant planet, and one full of evil influences.
+The sages stigmatized him as a false deceitful star (_sidus dolosum_), the
+eternal torment of astronomers, eluding them as much as terrestrial
+mercury did the alchemists; and Goad, who in 1686 published a whole folio
+volume full of astro-meteorological aphorisms, unveiling the choicest
+secrets of nature, contemptuously calls Mercury a 'squinting lacquey of
+the sun, who seldom shows his head in these parts, as if he was in debt.'
+His extreme mobility is so striking that chemists adopted his symbol to
+denote quicksilver."[16]
+
+Prof. W. H. Pickering thinks that the shortness of the cusps (or "horns")
+of Mercury's disc indicates that the planet's atmosphere is of small
+density--even rarer than that of Mars.
+
+The diameter of Mercury is usually stated at about 3000 miles; but a long
+series of measures made by Prof. See in the year 1901 make the real
+diameter about 2702 miles. This would make the planet smaller than some of
+the satellites of the large planets, probably smaller than satellites III.
+and IV. of Jupiter, less than Saturn's satellite Titan, and possibly
+inferior in size to the satellite of Neptune. Prof. Pickering thinks that
+the density of Mercury is about 3 (water = 1). Dr. See's observations show
+"no noticeable falling off in the brightness of Mercury near the limb."
+There is therefore no evidence of any kind of atmospheric absorption in
+Mercury, and the observer "gets the impression that the physical condition
+of the planet is very similar to that of our moon."[17]
+
+Schr�ter (1780-1815) observed markings on Mercury, from which he inferred
+that the planet's surface was mountainous, and one of these mountains he
+estimated at about 11 miles in height![18] But this seems very doubtful.
+
+To account for the observed irregularities in the motion of Mercury in its
+orbit, Prof. Newcomb thinks it possible that there may exist a ring or
+zone of "asteroids" a little "outside the orbit of Mercury" and having a
+combined mass of "one-fiftieth to one-three-hundredth of the mass of
+Venus, according to its distance from Mercury." Prof. Newcomb, however,
+considers that the existence of such a ring is extremely improbable, and
+regards it "more as a curiosity than a reality."[19]
+
+M. L�o Brenner thinks that he has seen the dark side of Mercury, in the
+same way that the dark side of Venus has been seen by many observers. In
+the case of Mercury the dark side appeared _darker_ than the background of
+the sky. Perhaps this may be due to its being projected on the zodiacal
+light, or outer envelope of the sun.[20]
+
+Mercury is said to have been occulted by Venus in the year 1737.[21] But
+whether this was an actual occultation, or merely a near approach does not
+seem to be certain.
+
+The first transit of Mercury across the sun's disc was observed by
+Gassendi on November 6, 1631, and Halley observed one on November 7, 1677,
+when in the island of St. Helena.
+
+Seen from Mercury, Venus would appear brighter than even we see it, and as
+it would be at its brightest when in opposition to the sun, and seen on a
+dark sky with a full face, it must present a magnificent appearance in the
+midnight sky of Mercury. The earth will also form a brilliant object, and
+the moon would be distinctly visible. The other planets would appear very
+much as they do to us, but with somewhat less brilliancy owing to their
+greater distance.
+
+As the existence of an intra-Mercurial planet (that is a planet revolving
+round the sun within the orbit of Mercury) seems now to be very
+improbable, Prof. Perrine suggests that possibly "the finely divided
+matter which produces the zodiacal light when considered in the aggregate
+may be sufficient to cause the perturbations in the orbit of Mercury."[22]
+Prof. Newcomb, however, questions the exact accuracy of Newton's law, and
+seems to adopt Hall's hypothesis that gravity does not act _exactly_ as
+the inverse square of the distance, and that the exponent of the distance
+is not 2, but 2�0000001574.[23]
+
+Voltaire said, "If Newton had been in Portugal, and any Dominican had
+discovered a heresy in his inverse ratio of the squares of the distances,
+he would without hesitation have been clothed in a _san benito_, and burnt
+as a sacrifice to God at an _auto da f�_."[24]
+
+An occultation of Mercury by Venus was observed with a telescope on May
+17, 1737.[25]
+
+May transits of Mercury across the sun's disc will occur in the years
+1924, 1957, and 1970; and November transits in the years 1914, 1927, and
+1940.[26]
+
+From measurements of the disc of Mercury during the last transit, M. R.
+Jonckheere concludes that the _polar_ diameter of the planet is greater
+than the _equatorial_! His result, which is very curious, if true, seems
+to be supported by the observations of other observers.[27]
+
+The rotation period of Mercury, or the length of its day, seems to be
+still in doubt. From a series of observations made in the years 1896 to
+1909, Mr. John McHarg finds a period of 1�0121162 day, or 1{d} 0{h} 17{m}
+26{s}�8. He thinks that "the planet possesses a considerable atmosphere
+not so clear as that of Mars"; that "its axis is very considerably
+tilted"; and that it "has fairly large sheets of water."[28]
+
+
+
+
+CHAPTER III
+
+Venus
+
+
+Venus was naturally--owing to its brightness--the first of the planets
+known to the ancients. It is mentioned by Hesiod, Homer, Virgil, Martial,
+and Pliny; and Isaiah's remark about "Lucifer, son of the morning" (Isaiah
+xiv. 12) probably refers to Venus as a "morning star." An observation of
+Venus is found on the Nineveh tablets of date B.C. 684. It was observed in
+daylight by Halley in July, 1716.
+
+In _very_ ancient times Venus, when a morning star, was called Phosphorus
+or Lucifer, and when an evening star Hesperus; but, according to Sir G. C.
+Lewis, the identity of the two objects was known so far back as 540 B.C.
+
+When Venus is at its greatest brilliancy, and appears as a morning star
+about Christmas time (which occurred in 1887, and again in 1889), it has
+been mistaken by the public for a return of the "Star of Bethlehem."[29]
+But whatever "the star of the Magi" was it certainly was _not_ Venus. It,
+seems, indeed absurd to suppose that "the wise men" of the East should
+have mistaken a familiar object like Venus for a strange apparition. There
+seems to be nothing whatever in the Bible to lead us to expect that the
+star of Bethlehem will reappear.
+
+Mr. J. H. Stockwell has suggested that the "Star of Bethlehem" may perhaps
+be explained by a conjunction of the planets Venus and Jupiter which
+occurred on May 8, B.C. 6, which was two years before the death of Herod.
+From this it would follow that the Crucifixion took place on April 3, A.D.
+33. But it seems very doubtful that the phenomenon recorded in the Bible
+refers to any conjunction of planets.
+
+Chacornac found the intrinsic brightness of Venus to be ten times greater
+than the most luminous parts of the moon.[30] But this estimate is
+probably too high.
+
+When at its brightest, the planet is visible in broad daylight to good
+eyesight, if its exact position in the sky is known. In the clear air of
+Cambridge (U.S.A.) it is said to be possible to see it in this way in all
+parts of its orbit, except when the planet is within 10� of the sun.[31]
+Mr. A. Cameron, of Yarmouth, Nova Scotia, has, however, seen Venus with
+the naked eye three days before conjunction when the planet was only
+6-1/4� from the sun.[32] This seems a remarkable observation, and shows
+that the observer's eyesight must have been very keen. In a private letter
+dated October 22, 1888, the late Rev. S. J. Johnson informed the present
+writer that he saw Venus with the naked eye only four days before
+conjunction with the sun in February, 1878, and February, 1886.
+
+The crescent shape of Venus is said to have been seen with the naked eye
+by Theodore Parker in America when he was only 12 years old. Other
+observers have stated the same thing; but the possibility of such an
+observation has been much disputed in recent years.
+
+In the Chinese Annals some records are given of Venus having been seen in
+the Pleiades. On March 16, A.D. 845, it is said that "Venus eclipsed the
+Pleiades." This means, of course, that the cluster was apparently effaced
+by the brilliant light of the planet. Computing backwards for the above
+date, Hind found that on the evening of March 16, 845, Venus was situated
+near the star Electra; and on the following evening the planet passed
+close to Maia; thus showing the accuracy of the Chinese record. Another
+"eclipse" of the Pleiades by Venus is recorded in the same annals as
+having occurred on March 10, A.D. 1002.[33]
+
+When Venus is in the crescent phase, that is near "Inferior conjunction"
+with the sun, it will be noticed, even by a casual observer, that the
+crescent is not of the same shape as that of the crescent moon. The horns
+or "cusps" of the planetary crescent are more prolonged than in the case
+of the moon, and extend beyond the hemisphere. This appearance is caused
+by refraction of the sun's light through the planetary atmosphere, and is,
+in fact, a certain proof that Venus has an atmosphere similar to that of
+the earth. Observations further show that this atmosphere is denser than
+ours.
+
+Seen from Venus, the earth and moon, when in opposition, must present a
+splendid spectacle. I find that the earth would shine as a star about half
+as bright again as Venus at her brightest appears to us, and the moon
+about equal in brightness to Sirius! the two forming a superb "naked eye
+double star"--perhaps the finest sight of its kind in the solar
+system.[34]
+
+Some of the earlier observers, such as La Hire, Fontana, Cassini, and
+Schr�ter, thought they saw evidence of mountains on Venus. Schr�ter
+estimated some of these to be 27 or 28 miles in height! but this seems
+very doubtful. Sir William Herschel severely attacked these supposed
+discoveries. Schr�ter defended himself, and was supported by Beer and
+M�dler, the famous lunar observers. Several modern observers seem to
+confirm Schr�ter's conclusions; but very little is really known about the
+topography of Venus.
+
+The well-known French astronomer Trouvelot--a most excellent observer--saw
+white spots on Venus similar to those on Mars. These were well seen and
+quite brilliant in July and August, 1876, and in February and November,
+1877. The observations seem to show that these spots do not (unlike Mars)
+increase and decrease with the planet's seasons. These white spots had
+been previously noticed by former observers, including Bianchini, Derham,
+Gruithuisen, and La Hire; but these early observers do not seem to have
+considered them as snow caps, like those of Mars. Trouvelot was led by his
+own observations to conclude that the period of rotation of Venus is
+short, and the best result he obtained was 23{h} 49{m} 28{s}. This does
+not differ much from the results previously found by De Vico, Fritsch, and
+Schr�ter.[35]
+
+A white spot near the planet's south pole was seen on several occasions by
+H. C. Russell in May and June, 1876.[36]
+
+Photographs of Venus taken on March 18 and April 29, 1908, by M. Qu�nisset
+at the Observatory of Juvissy, France, show a white polar spot. The spot
+was also seen at the same observatory by M. A. Benoit on May 20, 1903.
+
+The controversy on the period of rotation of Venus, or the length of its
+day, is a very curious one and has not yet been decided. Many good
+observers assert confidently that it is short (about 24 hours); while
+others affirm with equal confidence that it is long (about 225 days, the
+period of the planet's revolution round the sun). Among the observers who
+favour the short period of rotation are: D. Cassini (1667), J. Cassini
+(1730), Schr�ter (1788-93), M�dler (1836), De Vico (1840?) Trouvelot
+(1871-79), Flammarion, L�o Brenner, Stanley Williams, and J. McHarg; and
+among those who support the long period are: Bianchini (1727),
+Schiaparelli, Cerulli, Tacchini, Mascari, and Lowell. Some recent
+spectroscopic observations seem to favour the short period.
+
+Flammarion thinks that "nothing certain can be descried upon the surface
+of Venus, and that whatever has hitherto been written regarding its period
+of rotation must be considered null and void"; and again he says, "Nothing
+can be affirmed regarding the rotation of Venus, inasmuch as the
+absorption of its immense atmosphere certainly prevents any detail on its
+surface from being perceived."[37]
+
+The eminent Swedish physicist Arrhenius thinks, however, that the dense
+atmosphere and clouds of Venus are in favour of a rapid rotation on its
+axis.[38] He thinks that the mean temperature of Venus may "not differ
+much from the calculated temperature 104� F." "Under these circumstances
+the assumption would appear plausible that a very considerable portion of
+the surface of Venus, and particularly the districts about the poles,
+would be favourable to organic life."[39]
+
+The "secondary light of Venus," or the visibility of the dark side, seems
+to have been first mentioned by Derham in his _Astro Theology_ published
+in 1715. He speaks of the visibility of the dark part of the planet's disc
+"by the aid of a light of a somewhat dull and ruddy colour." The date of
+Derham's observation is not given, but it seems to have been previous to
+the year 1714. The light seems to have been also seen by a friend of
+Derham. We next find observations by Christfried Kirch, assistant
+astronomer to the Berlin Academy of Sciences, on June 7, 1721, and March
+8, 1726. These observations are found in his original papers, and were
+printed in the _Astronomische Nachrichten_, No. 1586. On the first date
+the telescopic image of the planet was "rather tremulous," but in 1726 he
+noticed that the dark part of the circle seemed to belong to a smaller
+circle than the illuminated portion of the disc.[40] The same effect was
+also noted by Webb.[41] A similar illusion is seen in the case of the
+crescent moon, and this has given rise to the saying, "the old moon in the
+new moon's arms."
+
+We next come, in order of date, to an observation made by Andreas Mayer,
+Professor of Mathematics at Griefswald in Prussia. The observation was
+made on October 20, 1759, and the dark part of Venus was seen distinctly
+by Mayer. As the planet's altitude at the time was not more than 14� above
+the horizon, and its apparent distance from the sun only 10�, the
+phenomenon--as Professor Safarik has pointed out--"must have had a most
+unusual intensity."
+
+Sir William Herschel makes no mention of having ever seen the "secondary
+light" of Venus, although he noticed the extension of the horns beyond a
+semicircle.
+
+In the spring and summer of the year 1793, Von Hahn of Remplin in
+Mecklenburg, using excellent telescopes made by Dollond and Herschel, saw
+the dark part of Venus on several occasions, and describes the light as
+"grey verging upon brown."
+
+Schr�ter of Lilienthal--the famous observer of the moon--saw the horns of
+the crescent of Venus extended many degrees beyond the semicircle on
+several occasions in 1784 and 1795, and the border of the dark part
+faintly lit up by a dusky grey light. On February 14, 1806, at 7 P.M. he
+saw the whole of the dark part visible with an ash-coloured light, and he
+was satisfied that there was no illusion. On January 24 of the same year,
+1806, Harding at G�ttingen, using a reflector of 9 inches aperture and
+power 84, saw the dark side of Venus "shining with a pale ash-coloured
+light," and very visible against the dark background of the sky. The
+appearance was seen with various magnifying powers, and he thought that
+there could be no illusion. In fact the phenomenon was as evident as in
+the case of the moon. Harding again saw it on February 28 of the same
+year, the illumination being of a reddish grey colour, "like that of the
+moon in a total eclipse."
+
+The "secondary light" was also seen by Pastorff in 1822, and by
+Gruithuisen in 1825. Since 1824 observations of the "light" were made by
+Berry, Browning, Guthrie, Langdon, Noble, Prince, Webb, and others. Webb
+saw it with powers of 90 and 212 on a 9�38-inch mirror, and found it
+"equally visible when the bright crescent was hidden by a field bar."[42]
+
+Captain Noble's observation was rather unique. He found that the dark side
+was "always distinctly and positively _darker_ than the background upon
+which it is projected."
+
+The "light" was also seen by Lyman in America in 1867, and by Safarik at
+Prague. In 1871 the whole disc of Venus was seen by Professor
+Winnecke.[43] On the other hand, Winnecke stated that he only saw it twice
+in 24 years; and the great observers Dawes and M�dler never saw it at
+all![44]
+
+Various attempts have been made to explain the visibility--at times--of
+the "dark side" of Venus. The following may be mentioned[45]:--(1)
+Reflected earth-light, analogous to the dark side of the crescent moon.
+This explanation was advocated by Harding, Schr�ter, and others. But,
+although the earth is undoubtedly a bright object in the sky of Venus, the
+explanation is evidently quite inadequate. (2) Phosphorescence of the
+planet's atmosphere. This has been suggested by some observers. (3)
+Visibility by contrast, a theory advanced by the great French astronomer
+Arago. (4) Illumination of the planet's surface by an aurora borealis.
+This also seems rather inadequate, but would account for the light being
+sometimes visible and sometimes not. (5) Luminosity of the oceans--if
+there be any--on Venus. But this also seems inadequate. (6) A planetary
+surface glowing with intense heat. But this seems improbable. (7) The
+Kunstliche Feuer (artificial fire) of Gruithuisen, a very fanciful theory.
+Flammarion thinks that the visibility of the dark side may perhaps be
+explained by its projection on a somewhat lighter background, such as the
+zodiacal light, or an extended solar envelope.[46]
+
+It will be seen that none of these explanations are entirely satisfactory,
+and the phenomenon, if real, remains a sort of astronomical enigma. The
+fact that the "light" is visible on some occasions and not on others would
+render some of the explanations improbable or even inadmissible. But the
+condition of the earth's atmosphere at times might account for its
+invisibility on many occasions.
+
+A curious suggestion was made by Z�llner, namely, that if the secondary
+light of Venus could be observed with the spectroscope it would show
+bright lines! But such an observation would be one of extreme difficulty.
+
+M. Hansky finds that the visibility of the "light" is greater during
+periods of maximum solar activity--that is, at the maxima of sun spots.
+This he explains by the theory of Arrhenius, in which electrified "ions
+emitted by the sun cause the phenomena of terrestrial magnetic storms and
+auroras." "In the same way the dense atmosphere of Venus is rendered more
+phosphorescent, and therefore more easily visible by the increased solar
+activity."[47] This seems a very plausible hypothesis.
+
+On the whole the occasional illumination of the night side of Venus by a
+very brilliant aurora (explanation (4) above) seems to the present writer
+to be the most probable explanation. Gruithuisen's hypothesis (7) seems
+utterly improbable.
+
+There is a curious apparent anomaly about the motion of Venus in the sky.
+Although the planet's period of revolution round the sun is 224�7 days, it
+remains on the same side of the sun, as seen from the earth, for 290 days.
+The reason of this is that the earth is going at the same time round the
+sun in the same direction, though at a slower pace; and Venus must
+continue to appear on the same side of the sun until the excess of her
+daily motion above that of the earth amounts to 179�, and this at the
+daily rate of 37' will be about 290 days.
+
+Several observations have been recorded of a supposed satellite of Venus.
+But the existence of such a body has never been verified. In the year
+1887, M. Stroobant investigated the various accounts, and came to the
+conclusion that in several at least of the recorded observations the
+object seen was certainly a star. Thus, in the observation made by
+Roedickoer and Boserup on August 4, 1761, a satellite and star are
+recorded as having been seen near the planet. M. Stroobant finds that the
+supposed "satellite" was the star [Greek: ch]_{4} Orionis, and the "star"
+[Greek: ch]_{3} Orionis. A supposed observation of a satellite made by
+Horrebow on January 3, 1768, was undoubtedly [Greek: th] Libr�. M.
+Stroobant found that the supposed motion of the "satellite" as seen by
+Horrebow is accurately represented by the motion of Venus itself during
+the time of observation. In most of the other supposed observations of a
+satellite a satisfactory identification has also been found. M. Stroobant
+finds that with a telescope of 6 inches aperture, a star of the 8th or
+even the 9th magnitude can be well seen when close to Venus.[49]
+
+On the night of August 13, 1892, Professor Barnard, while examining Venus
+with the great 36-inch telescope of the Lick Observatory, saw a star of
+the 7th magnitude in the same field with the planet. He carefully
+determined the exact position of this star, and found that it is not in
+Argelander's great catalogue, the _Durchmusterung_. Prof. Barnard finds
+that owing to elongation of Venus from the sun at the time of observation
+the star could not possibly be an intra-Mercurial planet (that is, a
+planet revolving round the sun inside the orbit of Mercury); but that
+possibly it might be a planet revolving between the orbits of Venus and
+Mercury. As the brightest of the minor planets--Ceres, Pallas, Juno, and
+Vesta--were not at the time near the position of the observed object, the
+observation remains unexplained. It might possibly have been a _nova_, or
+temporary star.[50]
+
+Scheuten is said to have seen a supposed satellite of Venus following the
+planet across the sun at the end of the transit of June 6, 1761.[51]
+
+Humboldt speaks of the supposed satellite of Venus as among "the
+astronomical myths of an uncritical age."[52]
+
+An occultation of Venus by the moon is mentioned in the Chinese Annals as
+having occurred on March 19, 361 A.D., and Tycho Brah� observed another on
+May 23, 1587.[53]
+
+A close conjunction of Venus and Regulus ([Greek: a] Leonis) is recorded
+by the Arabian astronomer, Ibn Yunis, as having occurred on September 9,
+885 A.D. Calculations by Hind show that the planet and star were within 2'
+of arc on that night, and consequently would have appeared as a single
+star to the naked eye. The telescope had not then been invented.[54]
+
+Seen from Venus, the maximum apparent distance between the earth and moon
+would vary from about 5' to 31'.[55]
+
+It is related by Arago that Buonaparte, when going to the Luxembourg in
+Paris, where the Directory were giving a f�te in his honour, was very
+much surprised to find the crowd assembled in the Rue de Touracour "pay
+more attention to a region of the heavens situated above the palace than
+to his person or the brilliant staff that accompanied him. He inquired the
+cause and learned that these curious persons were observing with
+astonishment, although it was noon, a star, which they supposed to be that
+of the conqueror of Italy--an allusion to which the illustrious general
+did not seem indifferent, when he himself, with his piercing eyes,
+remarked the radiant body." The "star" in question was Venus.[56]
+
+
+
+
+CHAPTER IV
+
+The Earth
+
+
+The earth being our place of abode is, of course, to us the most important
+planet in the solar system. It is a curious paradox that the moon's
+surface (at least the visible portion) is better known to us than the
+surface of the earth. Every spot on the moon's visible surface equal in
+size to say Liverpool or Glasgow is well known to lunar observers, whereas
+there are thousands of square miles on the earth's surface--for example,
+near the poles and in the centre of Australia--which are wholly unknown to
+the earth's inhabitants; and are perhaps likely to remain so.
+
+Many attempts have been made by "paradoxers" to show that the earth is a
+flat plane and not a sphere. But M. Ricco has found by actual experiment
+that the reflected image of the setting sun from a smooth sea is an
+elongated ellipse. This proves mathematically beyond all doubt that the
+surface of the sea is spherical; for the reflection from a plane surface
+would be necessarily _circular_. The theory of a "flat earth" is
+therefore proved to be quite untenable, and all the arguments (?) of the
+"earth flatteners" have now been--like the French Revolution--"blown into
+space."
+
+The pole of minimum temperature in the northern hemisphere, or "the pole
+of cold," as it has been termed, is supposed to lie near Werchojansk in
+Siberia, where a temperature of nearly -70� has been observed.
+
+From a series of observations made at Annapolis (U.S.A.) on the gradual
+disappearance of the blue of the sky after sunset, Dr. See finds that the
+extreme height of the earth's atmosphere is about 130 miles. Prof. Newcomb
+finds that meteors first appear at a mean height of about 74 miles.[57]
+
+An aurora seen in Canada on July 15, 1893, was observed from stations 110
+miles apart, and from these observations the aurora was found to lie at a
+height of 166 miles above the earth's surface. It was computed that if the
+auroral "arch maintained an equal height above the earth its ends were
+1150 miles away, so that the magnificent sight was presented of an auroral
+belt in the sky with 2300 miles between its two extremities."[58]
+
+"Luminous clouds" are bright clouds sometimes seen at night near the end
+of June and beginning of July. They appear above the northern horizon
+over the sun's place about midnight, and evidently lie at a great height
+above the earth's surface. Observations made in Germany by Dr. Jesse, and
+in England by Mr. Backhouse, in the years 1885-91, show that the height of
+these clouds is nearly constant at about 51 miles.[59] The present writer
+has seen these remarkable clouds on one or two occasions in County Sligo,
+Ireland, during the period above mentioned.
+
+M. Montigny has shown that "the approach of violent cyclones or other
+storms is heralded by an increase of scintillation" (or twinkling of the
+stars). The effect is also very evident when such storms pass at a
+considerable distance. He has also made some interesting observations
+(especially on the star Capella), which show that, not only does
+scintillation increase in rainy weather, but that "it is very evident, at
+such times, in stars situated at an altitude at which on other occasions
+it would not be perceptible at all; thus confirming the remark of
+Humboldt's with regard to the advent of the wet season in tropical
+countries."[60]
+
+In a paper on the subject of "Optical Illusions" in _Popular Astronomy_,
+February, 1906, Mr. Arthur K. Bartlett, of Batter Creek, Michigan
+(U.S.A.), makes the following interesting remarks:--
+
+    "The lunar halo which by many persons is regarded as a remarkable and
+    unexplained luminosity associated with the moon, is to meteorological
+    students neither a mysterious nor an anomalous occurrence. It has been
+    frequently observed and for many years thoroughly understood, and at
+    the present time admits of an easy scientific explanation. It is an
+    atmospheric exhibition due to the refraction and dispersion of the
+    moon's light through very minute ice crystals floating at great
+    elevations above the earth, and it is explained by the science of
+    meteorology, to which it properly belongs; for it is not of cosmical
+    origin, and in no way pertains to astronomy, as most persons suppose,
+    except as it depends on the moon, whose light passing through the
+    atmosphere, produces the luminous halo, which as will be seen, is
+    simply an optical illusion, originating, not in the vicinity of the
+    moon--two hundred and forty thousand miles away--but just above the
+    earth's surface, and within the aqueous envelope that surrounds it on
+    all sides.... A halo may form round the sun as well as the moon ...
+    but a halo is more frequently noticed round the moon for the reason
+    that we are too much dazzled by the sun's light to distinguish faint
+    colours surrounding its disc, and to see them it is necessary to look
+    through smoked glass, or view the sun by reflection from the surface
+    of still water, by which its brilliancy is very much reduced."...
+
+"A 'corona' is an appearance of faintly coloured rings often seen around
+the sun and moon when a light fleecy cloud passes over them, and should
+not be mistaken for a halo, which is much larger and more complicated in
+its structure. These two phenomena are frequently confounded by
+inexperienced observers." With these remarks the present writer fully
+concurs.
+
+Mr. Bartlett adds--
+
+    "As a halo is never seen except when the sky is hazy, it indicates
+    that moisture is accumulating in the atmosphere which will form
+    clouds, and usually result in a storm. But the popular notion that the
+    number of bright stars visible within the circle indicates the number
+    of days before the storm will occur, is without any foundation
+    whatever, and the belief is almost too absurd to be refuted. In
+    whatever part of the sky a lunar halo is seen, one or more bright
+    stars are always sure to be noticed inside the luminous ring, and the
+    number visible depends entirely upon the position of the moon.
+    Moreover, when the sky within the circle is examined with even a small
+    telescope, hundreds of stars are visible where only one, or perhaps
+    two or three, are perceived with the naked eye."
+
+It is possible to have five Sundays in February (the year must of course
+be a "leap year"). This occurred in the year 1880, Sunday falling on
+February 1, 8, 15, 22, and 29. But this will not happen again till the
+year 1920. No century year (such as 1900, 2000, etc.) could possibly have
+five Sundays in February, and the Rev. Richard Campbell, who investigated
+this matter, finds the following sequence of years in which five Sundays
+occur in February: 1604, 1632, 1660, 1688, 1728, 1756, 1784, 1824, 1852,
+1880, 1920, 1948, 1976.[61]
+
+In an article on "The Last Day and Year of the Century: Remarks on Time
+Reckoning," in _Nature_, September 10, 1896, Mr. W. T. Lynn, the eminent
+astronomer, says, "The late Astronomer Royal, Sir George Airy, once
+received a letter requesting him to settle a dispute which had arisen in
+some local debating society, as to which would be the first day of the
+next century. His reply was, 'A very little consideration will suffice to
+show that the first day of the twentieth century will be January 1, 1901.'
+Simple as the matter seems, the fact that it is occasionally brought into
+question shows that there is some little difficulty connected with it.
+Probably, however, this is in a great measure due to the circumstance that
+the actual figures are changed on January 1, 1900, the day preceding being
+December 31, 1899. A century is a very definite word for an interval
+respecting which there is no possible room for mistake or difference of
+opinion. But the date of its ending depends upon that of its beginning.
+Our double system of backward and forward reckoning leads to a good deal
+of inconvenience. Our reckoning supposes (what we know was not the case,
+but as an era the date does equally well) that Christ was born at the end
+of B.C. 1. At the end of A.D. 1, therefore, one year had elapsed from the
+event, at the end of A.D. 100, one century, and at the end of 1900,
+nineteen centuries.... It is clear, then, that the year, as we call it, is
+an ordinal number, and that 1900 years from the birth of Christ (reckoning
+as we do from B.C. 1) will not be completed until the end of December 31
+in that year, the twentieth century beginning with January 1, 1901, that
+is (to be exact) at the previous midnight, when the day commences by civil
+reckoning." With these remarks of Mr. Lynn I fully concur, and, so far as
+I know, all astronomers agree with him. As the discussion will probably
+again arise at the end of the twentieth century, I would like to put on
+record here what the scientific opinion was at the close of the nineteenth
+century.
+
+Prof. E. Rutherford, the well-known authority on radium, suggests that
+possibly radium is a source of heat from within the earth. Traces of
+radium have been detected in many rocks and soils, and even in sea water.
+Calculation shows that the total amount distributed through the earth's
+crust is enormously large, although relatively small "compared with the
+annual output of coal for the world." The amount of radium necessary to
+compensate for the present loss of heat from the earth "corresponds to
+only five parts in one hundred million millions per unit mass," and the
+"observations of Elster and Gertel show that the radio-activity observed
+in soils corresponds to the presence of about this proportion of
+radium."[62]
+
+The earth has 12 different motions. These are as follows:--
+
+1. Rotation on its axis, having a period of 24 hours.
+
+2. Revolution round the sun; period 365-1/4 days.
+
+3. Precession; period of about 25,765 years.
+
+4. Semi-lunar gravitation; period 28 days.
+
+5. Nutation; period 18-1/2 years.
+
+6. Variation in obliquity of the ecliptic; about 47" in 100 years.
+
+7. Variation of eccentricity of orbit.
+
+8. Change of line of apsides; period about 21,000 years.
+
+9. Planetary perturbations.
+
+10. Change of centre of gravity of whole solar system.
+
+11. General motion of solar system in space.
+
+12. Variation of latitude with several degrees of periodicity.[63]
+
+    "An amusing story has been told which affords a good illustration of
+    the ignorance and popular notions regarding the tides prevailing even
+    among persons of average intelligence. 'Tell me,' said a man to an
+    eminent living English astronomer not long ago, 'is it still
+    considered probable that the tides are caused by the moon?' The man of
+    science replied that to the best of his belief it was, and then asked
+    in turn whether the inquirer had any serious reason for questioning
+    the relationship. 'Well, I don't know,' was the answer; 'sometimes
+    when there is no moon there seems to be a tide all the same.'"![64]
+
+With reference to the force of gravitation, on the earth and other bodies
+in the universe, Mr. William B. Taylor has well said, "With each revolving
+year new demonstrations of its absolute precision and of its universal
+domination serves only to fill the mind with added wonder and with added
+confidence in the stability and the supremacy of the power in which has
+been found no variableness neither shadow of turning, but which--the same
+yesterday, to-day and for ever--
+
+  "Lives through all life, extends through all extent,
+  Spreads undivided, operates unspent."[65]
+
+With reference to the habitability of other planets, Tennyson has
+beautifully said--
+
+  "Venus near her! smiling downwards at this earthlier earth of ours,
+  Closer on the sun, perhaps a world of never fading flowers.
+  Hesper, whom the poets call'd the Bringer home of all good things;
+  All good things may move in Hesper; perfect people, perfect kings.
+  Hesper--Venus--were we native to that splendour, or in Mars,
+  We should see the globe we groan in fairest of their evening stars.
+  Could we dream of war and carnage, craft and madness, lust and spite,
+  Roaring London, raving Paris, in that spot of peaceful light?
+  Might we not in glancing heavenward on a star so silver fair,
+  Yearn and clasp the hands, and murmur, 'Would to God that we were
+      there!'"
+
+The ancient Greek writer, Diogenes Laertius, states that Anaximander
+(610-547 B.C.) believed that the earth was a sphere. The Greek words are:
+[Greek: mis�n te t�n g�n keisthai, kentry taxin epechousan ousan
+sphairoeid�].[66]
+
+With reference to the Aurora Borealis, the exact nature of which is not
+accurately known, "a good story used to be told some years ago of a
+candidate who, undergoing the torture of a _viv� voce_ examination, was
+unable to reply satisfactorily to any of the questions asked. 'Come, sir,'
+said the examiner, with the air of a man asking the simplest question,
+'explain to me the cause of the aurora borealis.' 'Sir,' said the unhappy
+aspirant for physical honours, 'I could have explained it perfectly
+yesterday, but nervousness has, I think, made me lose my memory.' 'This is
+very unfortunate,' said the examiner; 'you are the only man who could have
+explained this mystery, and you have forgotten it.'"[67] This was written
+in the year 1899, and probably the phenomenon of the aurora remains
+nearly as great a mystery to-day. In 1839, MM. Bravais and Lottin made
+observations on the aurora in Norway in about N. latitude 70�. Bravais
+found the height to be between 62 and 93 miles above the earth's surface.
+
+The cause of the so-called Glacial Epoch in the earth's history has been
+much discussed. The Russian physicist, Rogovsky, has advanced the
+following theory--
+
+    "If we suppose that the temperature of the sun at the present time is
+    still increasing, or at least has been increasing until now, the
+    glacial epoch can be easily accounted for. Formerly the earth had a
+    high temperature of its own, but received a lesser quantity of heat
+    from the sun than now; on cooling gradually, the earth's surface
+    attained such a temperature as caused a great part of the surface of
+    the northern and southern hemispheres to be covered with ice; but the
+    sun's radiation increasing, the glaciers melted, and the climatic
+    conditions became as they are now. In a word, the temperature of the
+    earth's surface is a function of two quantities: one decreasing (the
+    earth's own heat), and the other increasing (the sun's radiation), and
+    consequently there may be a minimum, and this minimum was the glacial
+    epoch, which, as shown by recent investigations, those of Luigi de
+    Marchi (Report of _G. Schiaparelli, Meteorolog. Zeitschr._, 30,
+    130-136, 1895), are not local, but general for the whole earth" (see
+    also M. Neumahr, _Erdegeschicht_).[68]
+
+Prof. Percival Lowell thinks that the life of geological pal�ozoic times
+was supported by the earth's internal heat, which maintained the ocean at
+a comparatively warm temperature.[69]
+
+The following passage in the Book of the Maccabees may possibly refer to
+an aurora--
+
+    "Now about this time Antiochus made his second inroad into Egypt. And
+    it _so_ befell that throughout all the city, for the space of almost
+    forty days, there appeared in the midst of the sky horsemen in swift
+    motion, wearing robes inwrought with gold and _carrying_ spears,
+    equipped in troops for battle; and drawing of swords; and _on the
+    other side_ squadrons of horse in array; and encounters and pursuits
+    of both armies; and shaking of shields, and multitudes of lances, and
+    casting of darts, and flashing of golden trappings, and girding on of
+    all sorts of armour. Wherefore all men besought that the vision might
+    have been given for food."[70]
+
+According to Laplace "the decrease of the mean heat of the earth during a
+period of 2000 years has not, taking the extremist limits, diminished as
+much as 1/300th of a degree Fahrenheit."[71]
+
+From his researches on the cause of the Precession of the Equinoxes,
+Laplace concluded that "the motion of the earth's axis is the same as if
+the whole sea formed a solid mass adhering to its surface."[72]
+
+Laplace found that the major (or longer) axis of the earth's orbit
+coincided with the line of Equinoxes in the year 4107 B.C. The earth's
+perigee then coincided with the autumnal equinox. The epoch at which the
+major axis was perpendicular to the line of equinoxes fell in the year
+1250 A.D.[73]
+
+Leverrier has found the minimum eccentricity of the earth's orbit round
+the sun to be 0�0047; so that the orbit will never become absolutely
+circular, as some have imagined.
+
+Laplace says--
+
+    "Astronomy considered in its entirety is the finest monument of the
+    human mind, the noblest essay of its intelligence. Seduced by the
+    illusions of the senses and of self-pride, for a long time man
+    considered himself as the centre of the movement of the stars; his
+    vain-glory has been punished by the terrors which his own ideas have
+    inspired. At last the efforts of several centuries brushed aside the
+    veil which concealed the system of the world. We discover ourselves
+    upon a planet, itself almost imperceptible in the vast extent of the
+    solar system, which in its turn is only an insensible point in the
+    immensity of space. The sublime results to which this discovery has
+    led should suffice to console us for our extreme littleness, and the
+    rank which it assigns to the earth. Let us treasure with solicitude,
+    let us add to as we may, this store of higher knowledge, the most
+    exquisite treasure of thinking beings."[74]
+
+With reference to probable future changes in climate, the great physicist,
+Arrhenius, says--
+
+    "We often hear lamentation that the coal stored up in the earth is
+    wasted by the present generation without any thought of the future,
+    and we are terrified by the awful destruction of life and property
+    which has followed the volcanic eruptions of our days. We may find a
+    kind of consolation in the consideration that here, as in every other
+    case, there is good mixed with evil. By the influence of the
+    increasing percentage of carbonic acid in the atmosphere, we may hope
+    to enjoy ages with more equable and better climates, especially as
+    regards the colder regions of the earth, ages when the earth will
+    bring forth much more abundant crops than at present, for the benefit
+    of rapidly propagating mankind."[75]
+
+The night of July 1, 1908, was unusually bright. This was noticed in
+various parts of England and Ireland, and by the present writer in Dublin.
+Humboldt states that "at the time of the new moon at midnight in 1743, the
+phosphorescence was so intense that objects could be distinctly recognized
+at a distance of more than 600 feet."[76]
+
+An interesting proof of the earth's rotation on its axis has recently been
+found.
+
+    "In a paper in the _Proceedings_ of the Vienna Academy (June, 1908) by
+    Herr Tumlirz, it is shown mathematically that if a liquid is flowing
+    outwards between two horizontal discs, the lines of flow will be
+    strictly straight only if the discs and vessel be at rest, and will
+    assume certain curves if that vessel and the discs are in rotation,
+    as, for example, due to the earth's rotation. An experimental
+    arrangement was set up with all precautions, and the stream lines were
+    marked with coloured liquids and photographed. These were in general
+    accord with the predictions of theory and the supposition that the
+    earth is rotating about an axis."[77]
+
+In a book published in 1905 entitled _The Rational Almanac_, by Moses B.
+Cotsworth, of York, the author states that (p. 397), "The explanation is
+apparent from the Great Pyramid's Slope, which conclusively proves that
+when it was built the latitude of that region was 7��1 more than at
+present. Egyptian Memphis now near Cairo was then in latitude 37��1, where
+Asia Minor now ranges, whilst Syria would then be where the Caucasus
+regions now experience those rigorous winters formerly experienced in
+Syria." But the reality of this comparatively great change of latitude in
+the position of the Great Pyramid can be easily disproved. Pytheas of
+Marseilles--who lived in the time of Alexander the Great, about 330
+B.C.--measured the latitude of Marseilles by means of a gnomon, and found
+it to be about 42� 56'-1/2. As the present latitude of Marseilles is 43�
+17' 50", no great change in the latitude could have taken place in over
+2000 years.[78] From this we may conclude that the latitude of the Great
+Pyramid has _not_ changed by 7��1 since its construction. There is, it is
+true, a slow diminution going on in the obliquity of the ecliptic (or
+inclination of the earth's axis), but modern observations show that this
+would not amount to as much as one degree in 6000 years. Eudemus of
+Rhodes--a disciple of Aristotle (who died in 322 B.C.)--found the
+obliquity of the ecliptic to be 24�, which differs but little from its
+present value, 23� 27'. Al-Sufi in the tenth century measured the latitude
+of Schiraz in Persia, and found it 29� 36'. Its present latitude is 29�
+36' 30",[79] so that evidently there has been no change in the latitude in
+900 years.
+
+
+
+
+CHAPTER V
+
+The Moon
+
+
+The total area of the moon's surface is about equal to that of North and
+South America. The actual surface visible at any one time is about equal
+to North America.
+
+The famous lunar observer, Schr�ter, thought that the moon had an
+atmosphere, but estimated its height at only a little over a mile. Its
+density he supposed to be less than that of the vacuum in an air-pump.
+Recent investigations, however, seem to show that owing to its small mass
+and attractive force the moon could not retain an atmosphere like that of
+the earth.
+
+Prof. N. S. Shaler, of Harvard (U.S.A.), finds from a study of the moon
+(from a geological point of view) with the 15-inch refractor of the
+Harvard Observatory, that our satellite has no atmosphere nor any form of
+organic life, and he believes that its surface "was brought to its present
+condition before the earth had even a solid crust."[80]
+
+There is a curious illusion with reference to the moon's apparent
+diameter referred to by Proctor.[81] If, when the moon is absent in the
+winter months, we ask a person whether the moon's diameter is greater or
+less than the distance between the stars [Greek: d] and [Greek: e], and
+[Greek: e] and [Greek: z] Orionis, the three well-known stars in the "belt
+of Orion," the answer will probably be that the moon's apparent diameter
+is about equal to each of these distances. But in reality the apparent
+distance between [Greek: d] and [Greek: e] Orionis (or between [Greek: e]
+and [Greek: z], which is about the same) is more than double the moon's
+apparent diameter. This seems at first sight a startling statement; but
+its truth is, of course, beyond all doubt and is not open to argument.
+Proctor points out that if a person estimates the moon as a foot in
+diameter, as its apparent diameter is about half a degree, this would
+imply that the observer estimates the circumference of the star sphere as
+about 720 feet (360� � 2), and hence the radius (or the moon's distance
+from the earth) about 115 feet. But in reality all such estimates have no
+scientific (that is, accurate) meaning. Some of the ancients, such as
+Aristotle, Cicero, and Heraclitus, seem to have estimated the moon's
+apparent diameter at about a foot.[82] This shows that even great minds
+may make serious mistakes.
+
+It has been stated by some writer that the moon as seen with the highest
+powers of the great Yerkes telescope (40 inches aperture) appears "just
+as it would be seen with the naked eye if it were suspended 60 miles over
+our heads." But this statement is quite erroneous. The moon as seen with
+the naked eye or with a telescope shows us nearly a whole hemisphere of
+its surface. But if the eye were placed only 60 miles from the moon's
+surface, we should see only a small portion of its surface. In fact, it is
+a curious paradox that the nearer the eye is to a sphere the less we see
+of its surface! The truth of this will be evident from the fact that on a
+level plain an eye placed at a height, say 5 feet, sees a very small
+portion indeed of the earth's surface, and the higher we ascend the more
+of the surface we see. I find that at a distance of 60 miles from the
+moon's surface we should only see a small portion of its visible
+hemisphere (about 1/90th). The lunar features would also appear under a
+different aspect. The view would be more of a landscape than that seen in
+any telescope. This view of the matter is not new. It has been previously
+pointed out, especially by M. Flammarion and Mr. Whitmell, but its truth
+is not, I think, generally recognized. Prof. Newcomb doubts whether with
+any telescope the moon has ever been seen so well as it would be if
+brought within 500 miles of the earth.
+
+A relief map of the moon 19 feet in diameter was added, in 1898, to the
+Field Columbian Museum (U.S.A.). It was prepared with great care from the
+lunar charts of Beer and M�dler, and Dr. Schmidt of the Athens
+Observatory, and it shows the lunar features very accurately. Its
+construction took five years.
+
+On a photograph of a part of the moon's surface near the crater
+Eratosthenes, Prof. William H. Pickering finds markings which very much
+resemble the so-called "canals" of Mars. The photograph was taken in
+Jamaica, and a copy of it is given in Prof. Pickering's book on the Moon,
+and in _Popular Astronomy_, February, 1904.
+
+Experiments made in America by Messrs. Stebbins and F. C. Brown, by means
+of selenium cells, show that the light of the full moon is about nine
+times that of the half moon;[83] and that "the moon is brighter between
+the first quarter and full than in the corresponding phase after full
+moon." They also find that the light of the full moon is equal to "0�23
+candle power,"[83] that is, according to the method of measurement used in
+America, its light is equal to 0�23 of a standard candle placed at a
+distance of one metre (39�37 inches) from the eye.[84]
+
+Mr. H. H. Kimball finds that no less than 52 per cent. of the observed
+changes in intensity of the "earth-shine" visible on the moon when at or
+near the crescent phase is due to the eccentricity of the lunar orbit,
+and "this is probably much greater than could be expected from any
+increase or diminution in the average cloudiness over the hemisphere of
+the earth reflecting light to the moon."[85]
+
+The "moon maiden" is a term applied to a fancied resemblance of a portion
+of the Sinus Iridum to a female head. It forms the "promontory" known as
+Cape Heraclides, and may be looked for when the moon's "age" is about 11
+days. Mr. C. J. Caswell, who observed it on September 29, 1895, describes
+it as resembling "a beautiful silver statuette of a graceful female figure
+with flowing hair."
+
+M. Landerer finds that the angle of polarization of the moon's
+surface--about 33�--agrees well with the polarizing angle for many
+specimens of igneous rocks (30� 51' to 33� 46'). The polarizing angle for
+ice is more than 37�, and this fact is opposed to the theories of lunar
+glaciation advanced by some observers.[86]
+
+Kepler states in his _Somnium_ that he saw the moon in the crescent phase
+on the morning and evening of the _same_ day (that is, before and after
+conjunction with the sun). Kepler could see 14 stars in the Pleiades with
+the naked eye, so his eyesight must have been exceptionally keen.
+
+Investigations on ancient eclipses of the moon show that the eclipse
+mentioned by Josephus as having occurred before the death of Herod is
+probably that which took place on September 15, B.C. 5. This occurred
+about 9.45 p.m.; and probably about six months before the death of Herod
+(St. Matthew ii. 15).
+
+The total lunar eclipse which occurred on October 4, 1884, was remarkable
+for the almost total disappearance of the moon during totality. One
+observer says that "in the open air, if one had not known exactly where to
+look for it, one might have searched for some time without discovering it.
+I speak of course of the naked eye appearance."[87] On the other hand the
+same observer, speaking of the total eclipse of the moon on August 23,
+1877, which was a bright one, says--
+
+    "The moon even in the middle of the total phase was a conspicuous
+    object in the sky, and the ruddy colour was well marked. In the very
+    middle of the eclipse the degree of illumination was as nearly as
+    possible equal all round the edge of the moon, the central parts being
+    darker than those near the edge."
+
+In Roger de Hovedin's _Chronicle_ (A.D. 756) an account is given of the
+occultation of "a bright star," by the moon during a total eclipse. This
+is confirmed by Simeon of Durham, who also dates the eclipse A.D. 756.
+This is, however, a mistake, the eclipse having occurred on the evening of
+November 23, A.D. 755. Calvisius supposed that the occulted "star" might
+have been Aldebaran. Pingr�, however, showed that this was impossible, and
+Struyck, in 1740, showed that the planet Jupiter was the "star" referred
+to by the early observer. Further calculations by Hind (1885) show
+conclusively that Struyck was quite correct, and that the phenomenon
+described in the old chronicles was the occultation of Jupiter by a
+totally eclipsed moon--a rather unique phenomenon.[88]
+
+An occultation of Mars by the moon is recorded by the Chinese, on February
+14, B.C. 69, and one of Venus, on March 30, A.D. 361. These have also been
+verified by Hind, and his calculations show the accuracy of these old
+Chinese records.
+
+It has been suggested that the moon may possibly have a satellite
+revolving round it, as the moon itself revolves round the earth. This
+would, of course, form an object of great interest. During the total lunar
+eclipses of March 10 and September 3, 1895, a careful photographic search
+was made by Prof. Barnard for a possible lunar satellite. The eclipse of
+March 10 was not very suitable for the purpose owing to a hazy sky, but
+that of September 3 was "entirely satisfactory," as the sky was very
+clear, and the duration of totality was very long. On the latter occasion
+"six splendid" photographs were obtained of the total phase with a 6-inch
+Willard lens. The result was that none of these photographs "show
+anything which might be taken for a lunar satellite," at least any
+satellite as bright as the 10th or 12th magnitude. It is, of course, just
+possible that the supposed satellite might have been behind the moon
+during the totality.
+
+With reference to the attraction between the earth and moon, Sir Oliver
+Lodge says--
+
+    "The force with which the moon is held in its orbit would be great
+    enough to tear asunder a steel rod 400 miles thick, with a tenacity of
+    30 tons to the square inch, so that if the moon and earth were
+    connected by steel instead of gravity, a forest of pillars would be
+    necessary to whirl the system once a month round their common centre
+    of gravity. Such a force necessarily implies enormous tensure or
+    pressure in the medium. Maxwell calculates that the gravitational
+    stress near the earth, which we must suppose to exist in the invisible
+    medium, is 3000 times greater than what the strongest steel can stand,
+    and near the sun it should be 2500 times as great as that."[89]
+
+With reference to the names given to "craters" on the moon, Prof. W. H.
+Pickering says,[90] "The system of nomenclature is, I think, unfortunate.
+The names of the chief craters are generally those of men who have done
+little or nothing for selenography, or even for astronomy, while the men
+who should be really commemorated are represented in general by small and
+unimportant craters," and again--
+
+    "A serious objection to the whole system of nomenclature lies in the
+    fact that it has apparently been used by some selenographers, from the
+    earliest times up to the present, as a means of satisfying their spite
+    against some of their contemporaries. Under the guise of pretending to
+    honour them by placing their names in perpetuity upon the moon, they
+    have used their names merely to designate the smallest objects that
+    their telescopes were capable of showing. An interesting illustration
+    of this point is found in the craters of Galileo and Riccioli, which
+    lie close together on the moon. It will be remembered that Galileo was
+    the discoverer of the craters on the moon. Both names were given by
+    Riccioli, and the relative size and importance of the craters
+    [Riccioli large, and Galileo very small] probably indicates to us the
+    relative importance that he assigned to the two men themselves. Other
+    examples might be quoted of craters named in the same spirit after men
+    still living.... With the exception of Maedler, one might almost say,
+    the more prominent the selenographer the more insignificant the
+    crater."
+
+The mathematical treatment of the lunar theory is a problem of great
+difficulty. The famous mathematician, Euler, described it as _incredibile
+stadium atque indefessus labor_.[91]
+
+With reference to the "earth-shine" on the moon when in the crescent
+phase, Humboldt says, "Lambert made the remarkable observation (14th of
+February, 1774) of a change of the ash-coloured moonlight into an
+olive-green colour, bordering upon yellow. The moon, which then stood
+vertically over the Atlantic Ocean, received upon its night side the green
+terrestrial light, which is reflected towards her when the sky is clear by
+the forest districts of South America."[92] Arago said, "Il n'est donc pas
+impossible, malgr� tout ce qu'un pareil r�sultat exciterait de surprise au
+premier coup d'oeil qu'un jour les m�t�orologistes aillent puiser dans
+l'aspect de la Lune des notions pr�cieuses sur _l'etat moyen_ de
+diaphanit� de l'atmosph�re terrestre, dans les hemisph�res qui
+successivement concurrent � la production de la lumi�re cendr�e."[93]
+
+The "earth-shine" on the new moon was successfully photographed in
+February, 1895, by Prof. Barnard at the Lick Observatory, with a 6-inch
+Willard portrait lens. He says--
+
+    "The earth-lit globe stands out beautifully round, encircled by the
+    slender crescent. All the 'seas' are conspicuously visible, as are
+    also the other prominent features, especially the region about
+    _Tycho_. _Aristarchus_ and _Copernicus_ appear as bright specks, and
+    the light streams from _Tycho_ are very distinct."[94]
+
+Kepler found that the moon completely disappeared during the total eclipse
+of December 9, 1601, and Hevelius observed the same phenomenon during the
+eclipse of April 25, 1642, when "not a vestige of the moon could be
+seen."[95] In the total lunar eclipse of June 10, 1816, the moon during
+totality was not visible in London, even with a telescope![95]
+
+The lunar mountains are _relatively_ much higher than those on the earth.
+Beer and M�dler found the following heights: D�rfel, 23,174 feet; Newton,
+22,141; Casatus, 21,102; Curtius, 20,632; Callippus, 18,946; and Tycho,
+18,748 feet.[96]
+
+Taking the earth's diameter at 7912 miles, the moon's diameter, 2163
+miles, and the height of Mount Everest as 29,000 feet, I find that
+
+      Everest          1            D�rfel        1
+  ---------------- = ----, and --------------- = ---
+  Earth's diameter   1440      moon's diameter   492
+
+From which it follows that the lunar mountains are _proportionately_ about
+three times higher than those on the earth.
+
+According to an hypothesis recently advanced by Dr. See, all the
+satellites of the solar system, including our moon, were "captured" by
+their primaries. He thinks, therefore, that the "moon came to earth from
+heavenly space."[97]
+
+
+
+
+CHAPTER VI
+
+Mars
+
+
+Mars was called by the ancients "the vanishing star," owing to the long
+periods during which it is practically invisible from the earth.[98] It
+was also called [Greek: puroeis] and Hercules.
+
+I have seen it stated in a book on the "Solar System" by a well-known
+astronomer that the _axis_ of Mars "is inclined to the plane of the orbit"
+at an angle of 24� 50'! But this is quite erroneous. The angle given is
+the angle between _the plane of the planet's equator_ and the plane of its
+orbit, which is quite a different thing. This angle, which may be called
+the obliquity of Mars' ecliptic, does not differ much from that of the
+earth. Lowell finds it 23� 13' from observations in 1907.[99]
+
+The late Mr. Proctor thought that Mars is "far the reddest star in the
+heavens; Aldebaran and Antares are pale beside him."[100] But this does
+not agree with my experience. Antares is to my eye quite as red as Mars.
+Its name is derived from two Greek words implying "redder than Mars." The
+colour of Aldebaran is, I think, quite comparable with that of the "ruddy
+planet." In the telescope the colour of Mars is, I believe, more yellow
+than red, but I have not seen the planet very often in a telescope. Sir
+John Herschel suggested that the reddish colour of Mars may possibly be
+due to red rocks, like those of the Old Red Sandstone, and the red soil
+often associated with such rocks, as I have myself noticed near Torquay
+and other places in Devonshire.
+
+The ruddy colour of Mars was formerly thought to be due to the great
+density of its atmosphere. But modern observations seem to show that the
+planet's atmosphere is, on the contrary, much rarer than that of the
+earth. The persistent visibility of the markings on its surface shows that
+its atmosphere cannot be cloud-laden like ours; and the spectroscope shows
+that the water vapour present is--although perceptible--less than that of
+our terrestrial envelope.
+
+The existence of water vapour is clearly shown by photographs of the
+planet's spectrum taken by Mr. Slipher at the Lowell Observatory in 1908.
+These show that the water vapour bands _a_ and near D are stronger in the
+spectrum of Mars than in that of the moon at the same altitude.[101]
+
+The dark markings on Mars were formerly supposed to represent water and
+the light parts land. But this idea has now been abandoned. Light
+reflected from a water surface is polarized at certain angles. Prof. W. H.
+Pickering, in his observations on Mars, finds no trace of polarization in
+the light reflected from the dark parts of the planet. But under the same
+conditions he finds that the bluish-black ring surrounding the white polar
+cap shows a well-marked polarization of light, thus indicating that this
+dark ring is probably water.[102]
+
+Projections on the limb of the planet have frequently been observed in
+America. These are known _not_ to be mountains, as they do not reappear
+under similar conditions. They are supposed to be clouds, and one seen in
+December, 1900, has been explained as a cloud lying at a height of some 13
+miles above the planet's surface and drifting at the rate of about 27
+miles an hour. If there are any mountains on Mars they have not yet been
+discovered.
+
+The existence of the so-called "canals" of Mars is supposed to be
+confirmed by Lowell's photographs of the planet. But what these "canals"
+really represent, that is the question. They have certainly an artificial
+look about them, and they form one of the most curious and interesting
+problems in the heavens. Prof. Lowell says--
+
+    "Most suggestive of all Martian phenomena are the canals. Were they
+    more generally observable the world would have been spared much
+    scepticism and more theory. They may of course not be artificial, but
+    observations here [Flagstaff] indicate that they are; as will, I
+    think, appear from the drawings. For it is one thing to see two or
+    three canals and quite another to have the planet's disc mapped with
+    them on a most elaborate system of triangulation. In the first place
+    they are this season (August, 1894) bluish-green, of the same colour
+    as the seas into which the longer ones all eventually debouch. In the
+    next place they are almost without exception geodetically straight,
+    supernaturally so, and this in spite of their leading in every
+    possible direction. Then they are of apparently nearly uniform width
+    throughout their length. What they are is another matter. Their mere
+    aspect, however, is enough to cause all theories about glaciation
+    fissures or surface cracks to die an instant and natural death."[103]
+
+Some of the observed colour-changes on Mars are very curious. In April,
+1905, Mr. Lowell observed that the marking known as Mare Erythr�um, just
+above Syrtis, had "changed from a blue-green to a chocolate-brown colour."
+The season on Mars corresponded with our February.
+
+Signor V. Cerulli says that, having observed Mars regularly for ten years,
+he has come to the conclusion that the actual existence of the "canals" is
+as much a subject for physiological as for astronomical investigation. He
+states that "the phenomena observed are so near the limit of the range of
+the human eye that in observing them one really experiences an effect
+accompanying the 'birth of vision.' That is to say, the eye sees more and
+more as it becomes accustomed, or strained, to the delicate markings, and
+thus the joining up of spots to form 'canals' and the gemination of the
+latter follow as a physiological effect, and need not necessarily be
+subjective phenomena seen by the unaccustomed eye."[104]
+
+The possibility of life on Mars has been recently much discussed; some
+denying, others asserting. M. E. Rogovsky says--
+
+    "As free oxygen and carbonic dioxide may exist in the atmosphere of
+    _Mars_, vegetable and animal life is quite possible. If the
+    temperature which prevails upon _Mars_ is nearer to -36� C. than to
+    -73� C., the existence of living beings like ourselves is possible. In
+    fact, the ice of some Greenland and Alpine glaciers is covered by red
+    alg� (_Sph�rella nivalis_); we find there also different species of
+    rotaloria, variegated spiders, and other animals on the snow fields
+    illuminated by the sun; at the edges of glacier snows in the Tyrol we
+    see violet bells of _Soldanella pusilla_, the stalks of which make
+    their way through the snow by producing heat which melts it round
+    about them. Finally the Siberian town Verkhociansk, near Yakutsk,
+    exists, though the temperature there falls to -69��8 C. and the mean
+    temperature of January to -51��2, and the mean pressure of the vapour
+    of water is less than 0�05mm. It is possible, therefore, that living
+    beings have become adapted to the conditions now prevailing upon
+    _Mars_ after the lapse of many ages, and live at an even lower
+    temperature than upon the earth, developing the necessary heat
+    themselves."
+
+M. Rogovsky adds, "Water in organisms is mainly a liquid or solvent, and
+many other liquids may be the same. We have no reason to believe that life
+is possible only under the same conditions and with the same chemical
+composition of organisms as upon the earth, although indeed we cannot
+affirm that they actually exist on Mars."[105] With the above views the
+present writer fully concurs.
+
+Prof. Lowell thinks that the polar regions of Mars, both north and south,
+are actually warmer than the corresponding regions of the earth, although
+the mean temperature of the planet is probably twelve degrees lower than
+the earth's mean temperature.[106]
+
+A writer in _Astronomy and Astrophysics_ (1892, p. 748) says--
+
+    "Whether the planet Mars is inhabited or not seems to be the
+    all-absorbing question with the ordinary reader. With the astronomer
+    this query is almost the last thing about the planet that he would
+    think of when he has an opportunity to study its surface markings ...
+    no astronomer claims to know whether the planet is inhabited or not."
+
+Several suggestions have been made with reference to the possibility of
+signalling to Mars. But, as Mr. Larkin of Mount Lowe (U.S.A.) points out,
+all writers on this subject seem to forget the fact that the night side of
+two planets are never turned towards each other. "When the sun is between
+them it is day on the side of Mars which is towards us, and also day on
+the side of the earth which is towards Mars. When they are on the same
+side of the sun, it is day on Mars when night on the earth, and for this
+reason they could never see our signals. This should make it apparent that
+the task of signalling to Mars is a more difficult one than the most
+hopeful theorist has probably considered. All this is under the
+supposition that the Martians (if there are such) are beings like
+ourselves. If they are not like us, we cannot guess what they are
+like."[107] These views seem to me to be undoubtedly correct, and show the
+futility of visual signals. Electricity might, however, be conceivably
+used for the purpose; but even this seems highly improbable.
+
+Prof. Newcomb, in his work _Astronomy for Everybody_, says with reference
+to this question, "The reader will excuse me from saying nothing in this
+chapter about the possible inhabitants of Mars. He knows just as much
+about the subject as I do, and that is nothing at all."
+
+It is, however, quite possible that life _in some form_ may exist on Mars.
+As Lowell well says, "Life but waits in the wings of existence for its cue
+to enter the scene the moment the stage is set."[108] With reference to
+the "canals" he says--
+
+    "It is certainly no exaggeration to say that they are the most
+    astonishing objects to be viewed in the heavens. There are celestial
+    sights more dazzling, spectacles that inspire more awe, but to the
+    thoughtful observer who is privileged to see them well, there is
+    nothing in the sky so profoundly impressive as these canals of
+    Mars."[109]
+
+The eminent Swedish physicist Arrhenius thinks that the mean annual
+temperature on Mars may possibly be as high as 50� F. He says, "Sometimes
+the snow-caps on the poles of Mars disappear entirely during the Mars
+summer; this never happens on our terrestrial poles. The mean temperature
+of Mars must therefore be above zero, probably about +10� [Centigrade =
+50� Fahrenheit]. Organic life may very probably thrive, therefore, on
+Mars."[110] He thinks that this excess of mean temperature above the
+calculated temperature may be due to an increased amount of carbonic acid
+in the planet's atmosphere, and says "any doubling of the percentage of
+carbon dioxide in the air would raise the temperature of the earth's
+surface by 4�; and if the carbon dioxide were increased fourfold, the
+temperature would rise by 8�."[111]
+
+Denning says,--[112]
+
+    "A few years ago, when christening celestial formations was more in
+    fashion than it is now, a man simply had to use a telescope for an
+    evening or two on Mars or the moon, and spice the relation of his
+    seeings with something in the way of novelty, when his name would be
+    pretty certainly attached to an object and hung in the heavens for all
+    time! A writer in the _Astronomical Register_ for January, 1879,
+    humorously suggested that 'the matter should be put into the hands of
+    an advertising agent,' and 'made the means of raising a revenue for
+    astronomical purposes.' Some men would not object to pay handsomely
+    for the distinction of having their names applied to the seas and
+    continents of Mars or the craters of the moon."
+
+An occultation of Mars by the moon is recorded by Aristotle as having
+occurred on April 4, 357 B.C.[113]
+
+Seen from Mars the maximum apparent distance between the earth and moon
+would vary from 3-1/2' to nearly 17'.[114]
+
+
+
+
+CHAPTER VII
+
+The Minor Planets
+
+
+Up to 1908 the number of minor planets (or asteroids) certainly known
+amounted to over 650.
+
+From an examination of the distribution of the first 512 of these small
+bodies, Dr. P. Stroobant finds that a decided maximum in number occurs
+between the limits of distance of 2�55 and 2�85 (earth's mean distance
+from sun = 1), "199 of the asteroids considered revolving in this
+annulus." He finds that nearly all the asteroidal matter is concentrated
+near to the middle of the ring in the neighbourhood of the mean distance
+of 2�7, and the smallest asteroids are relatively less numerous in the
+richest zones.[115]
+
+There are some "striking similarities" in the orbits of some of the
+asteroids. Thus, in the small planets Sophia (No. 251 in order of
+discovery) and Magdalena (No. 318) we have the mean distance of Sophia
+3�10, and that of Magdalena 3�19 (earth's mean distance = 1). The
+eccentricities of the orbits are 0�09 and 0�07; and the inclinations of
+the orbits to the plane of the ecliptic 10� 29' and 10� 33'
+respectively.[116] This similarity may be--and probably is--merely
+accidental, but it is none the less curious and interesting.
+
+Some very interesting discoveries have recently been made among the minor
+planets. The orbit of Eros intersects the orbit of Mars; and the following
+have nearly the same mean distance from the sun as Jupiter:--
+
+  Achilles (1906 TG), No. 588,
+  Patrocles (1906 XY), No. 617,
+  Hector (1907 XM), No. 624,
+
+and another (No. 659) has been recently found. Each of these small planets
+"moves approximately in a vertex of an equilateral triangle that it forms
+with Jupiter and the sun."[117] The minor planet known provisionally as HN
+is remarkable for the large eccentricity of its orbit (0�38), and its
+small perihelion distance (1�6). When discovered it had a very high South
+Declination (61-1/2�), showing that the inclination of the plane of its
+orbit to the plane of the ecliptic is considerable.[118]
+
+Dr. Bauschinger has made a study of the minor planets discovered up to the
+end of 1900. He finds that the ascending nodes of the orbits show a
+marked tendency to cluster near the ascending node of Jupiter's orbit, a
+fact which agrees well with Prof. Newcomb's theoretical results. There
+seems to be a slight tendency for large inclinations and great
+eccentricities to go together; but there appears to be no connection
+between the eccentricity and the mean distance from the sun. The
+longitudes of the perihelia of these small planets "show a well-marked
+maximum near the longitude of _Jupiter's_ perihelion, and equally
+well-marked minimum near the longitude of his aphelion," which is again in
+good agreement with Newcomb's calculations.[119] Dr. Bauschinger's
+diameter for Eros is 20 miles. He finds that the whole group, including
+those remaining to be discovered, would probably form a sphere of about
+830 miles in diameter.
+
+The total mass of the minor planets has been frequently estimated, but
+generally much too high. Mr. B. M. Roszel of the John Hopkins University
+(U.S.A.) has made a calculation of the probable mass from the known
+diameter of Vesta (319 miles, Pickering), and finds the volume of the
+first 216 asteroids discovered. From this calculation it appears that it
+would take 310 asteroids of the 6th magnitude, or 1200 of the 7th to equal
+the moon in volume. Mr. Roszel concludes that the probable mass of the
+whole asteroidal belt is between 1/50th and 1/100th of that of the
+moon.[120] Subsequently Mr. Roszel extended his study to the mass of 311
+asteroids,[121] and found a combined mass of about 1/40th of the moon's
+mass.
+
+Dr. Palisa finds that the recently discovered minor planet (1905 QY)
+varies in light to a considerable extent.[122] This planet was discovered
+by Dr. Max Wolf on August 23, 1905; but it was subsequently found that it
+is identical with one previously known, (167) Urda.[123] The light
+variation is said to be from the 11th to the 13th magnitude.[124]
+Variation in some of the other minor planets has also been suspected.
+Prof. Wendell found a variation of about half a magnitude in the planet
+Eunomia (No. 15). He also found that Iris (No. 7) varies about a quarter
+of a magnitude in a period of about 6{h} 12{m}.[125] But these variations
+are small, and perhaps doubtful. The variability of Eros is well known.
+
+The planet Eros is a very interesting one. The perihelion portion of its
+orbit lies between the orbits of Mars and the earth, and the aphelion part
+is outside the orbit of Mars. Owing to the great variation in its distance
+from the earth the brightness of Eros varies from the 6th to the 12th
+magnitude. That is, when brightest, it is 250 times brighter than when it
+is faintest.[126] This variation of light, is of course, merely due to the
+variation of distance; but some actual variation in the brightness of the
+planet has been observed.
+
+It has been shown by Oeltzen and Valz that Cacciatore's supposed distant
+comet, mentioned by Admiral Smyth in his _Bedford Catalogue_, must have
+been a minor planet.[127]
+
+Dr. Max Wolf discovered 36 new minor planets by photography in the years
+1892-95. Up to the latter year he had never seen one of these through a
+telescope! His words are, "Ich selsbt habe noch nie einen meinen kleinen
+Planeten am Himmel gesehen."[128]
+
+These small bodies have now become so numerous that it is a matter of much
+difficulty to follow them. At the meeting of the Royal Astronomical
+Society on January 8, 1909, Mr. G. F. Chambers made the following
+facetious remarks--
+
+    "I would like to make a suggestion that has been in my mind for
+    several years past--that it should be made an offence punishable by
+    fine or imprisonment to discover any more minor planets. They seem to
+    be an intolerable nuisance, and are a great burden upon the literary
+    gentlemen who have to keep pace with them and record them. I have
+    never seen, during the last few years at any rate, any good come from
+    them, or likely to come, and I should like to see the supply stopped,
+    and the energies of the German gentlemen who find so many turned into
+    more promising channels."
+
+Among the minor planets numbered 1 to 500, about 40 "have not been seen
+since the year of their discovery, and must be regarded as lost."[129]
+
+
+
+
+CHAPTER VIII
+
+Jupiter
+
+
+This brilliant planet--only inferior to Venus in brightness--was often
+seen by Bond (Jun.) with the naked eye in "high and clear sunshine"; also
+by Denning, who has very keen eyesight. Its brightness on such occasions
+is so great, that--like Venus--it casts a distinct shadow in a dark
+room.[130]
+
+The great "red spot" on Jupiter seems to have been originally discovered
+by Robert Hooke on May 9, 1664, with a telescope of 2 inches aperture and
+12 feet focus. It seems to have existed ever since; at least the evidence
+is, according to Denning, in favour of the identity of Hooke's spot with
+the red spot visible in recent years. The spot was also observed by
+Cassini in the years 1665-72, and is sometimes called "Cassini's spot."
+But the real discoverer was Hooke.[131]
+
+The orbit of Jupiter is so far outside the earth's orbit that there can
+be little visible in the way of "phase"--as in the case of Mars, where the
+"gibbous" phase is sometimes very perceptible. Some books on astronomy
+state that Jupiter shows no phase. But this is incorrect. A distinct,
+although very slight, gibbous appearance is visible when the planet is
+near quadrature. Webb thought it more conspicuous in twilight than in a
+dark sky. With large telescopes, Jupiter's satellites II. and III. have
+been seen--in consequence of Jupiter's phase--to emerge from occultation
+"at a sensible distance from the limb."[132]
+
+According to M. E. Rogovsky, the high "albedo of Jupiter, the appearance
+of the clear (red) and dark spots on its surface and their continual
+variation, the different velocity of rotation of the equatorial and other
+zones of its surface, and particularly its small density (1�33, water as
+unity), all these facts afford irrefragable proofs of the high temperature
+of this planet. The dense and opaque atmosphere hides its glowing surface
+from our view, and we see therefore only the external surface of its
+clouds. The objective existence of this atmosphere is proved by the bands
+and lines of absorption in its spectrum. The interesting photograph
+obtained by Draper, September 27, 1879, in which the blue and green parts
+are more brilliant for the equatorial zone than for the adjacent parts of
+the surface, appears to show that _Jupiter_ emits its proper light. It is
+possible that the constant red spot noticed on its surface by several
+observers, as Gledhill, Lord Rosse, and Copeland (1873), Russel and
+Bredikhin (1876), is the summit of a high glowing mountain. G. W. Hough
+considers Jupiter to be gaseous, and A. Ritter inferred from his formul�
+that in this case the temperature at the centre would be 600,000� C."[133]
+
+The four brighter satellites of Jupiter are usually known by numbers I.,
+II., III., and IV.; I. being the nearest to the planet, and IV. the
+farthest. III. is usually the brightest, and IV. the faintest, but
+exceptions to this rule have been noticed.
+
+With reference to the recently discovered sixth and seventh satellites of
+Jupiter, Prof. Perrine has suggested that the large inclination of their
+orbits to the plane of the planet's equator seems to indicate that neither
+of these bodies was originally a member of Jupiter's family, but has been
+"captured by the planet." This seems possible as the orbits of some of the
+minor planets lie near the orbit of Jupiter (see "Minor Planets"). A
+similar suggestion has been made by Prof. del Marmol.[134]
+
+Many curious observations have been recorded with reference to Jupiter's
+satellites; some very difficult of explanation. In 1711 Bianchini saw
+satellite IV. so faint for more than an hour that it was hardly visible! A
+similar observation was made by Lassell with a more powerful telescope on
+June 13, 1849. Key, T. T. Smyth, and Denning have also recorded unusual
+faintness.[135] A very remarkable phenomenon was seen by Admiral Smyth,
+Maclear, and Pearson on June 26, 1828. Satellite II., "having fairly
+entered on Jupiter, was found 12 or 13 minutes afterwards _outside the
+limb_, where it remained visible for at least 4 minutes, and then suddenly
+vanished." As Webb says, "Explanation is here set at defiance;
+demonstrably neither in the atmosphere of the earth, nor Jupiter, where
+and what could have been the cause? At present we can get no answer."[136]
+When Jupiter is in opposition to the sun--that is, on the meridian at
+midnight--satellite I. has been seen projected on its own shadow, the
+shadow appearing as a dark ring round the satellite.
+
+On January 28, 1848, at Cambridge (U.S.A.) satellite III. was seen in
+transit lying between the shadows of I. and II. and so black that it could
+not be distinguished from the shadows, "except by the place it occupied."
+This seems to suggest inherent light in the planet's surface, as the
+satellite was at the time illuminated by full sunshine; its apparent
+blackness being due to the effect of contrast. Cassini on one occasion
+failed to find the shadow of satellite I. when it should have been on the
+planet's disc,[137] an observation which again points to the glowing light
+of Jupiter's surface. Sadler and Trouvelot saw the shadow of satellite I.
+double! an observation difficult to explain--but the same phenomenon was
+again seen on the evening of September 19, 1891, by Mr. H. S. Halbert of
+Detroit, Michigan (U.S.A.). He says that the satellite "was in transit
+nearing egress, and it appeared as a white disc against the dark southern
+equatorial belt; following it was the usual shadow, and at an equal
+distance from this was a second shadow, smaller and not so dark as the
+true one, and surrounded by a faint penumbra."[138]
+
+A dark transit of satellite III. was again seen on the evening of December
+19, 1891, by two observers in America. One observer noted that the
+satellite, when on the disc of the planet, was intensely black. To the
+other observer (Willis L. Barnes) it appeared as an ill-defined _dark_
+image.[139] A similar observation was made on October 9 of the same year
+by Messrs. Gale and Innes.[140]
+
+A "black transit" of satellite IV. was seen by several observers in 1873,
+and by Prof. Barnard on May 4, 1886. The same phenomenon was observed on
+October 30, 1903, in America, by Miss Anne S. Young and Willis S. Barnes.
+Miss Young says--
+
+    "The ingress of the satellite took place at 8{h} 50{m} (E. standard
+    time) when it became invisible upon the background of the planet. An
+    hour later it was plainly visible as a dark round spot upon the
+    planet. It was decidedly darker than the equatorial belt."[141]
+
+The rather rare phenomenon of an occultation of one of Jupiter's
+satellites by another was observed by Mr. Apple, director of the Daniel
+Scholl Observatory, Franklin and Marshall College, Lancaster, Pa.
+(U.S.A.), on the evening of March 16, 1908. The satellites in question
+were I. and II., and they were so close that they could not be separated
+with the 11�5-inch telescope of the Observatory.[142] One of the present
+writer's first observations with a telescope is dated May 17, 1873, and is
+as follows: "Observed one of Jupiter's satellites occulted (or very nearly
+so) by another. Appeared as one with power 133" (on 3-inch refractor in
+the Punjab). These satellites were probably I. and II.
+
+Jupiter has been seen on several occasions apparently without his
+satellites; some being behind the disc, some eclipsed in his shadow, and
+some in transit across the disc. This phenomenon was seen by Galileo,
+March 15, 1611; by Molyneux, on November 12, 1681; by Sir William
+Herschel, May 23, 1802; by Wallis, April 15, 1826; by Greisbach, September
+27, 1843; and by several observers on four occasions in the years
+1867-1895.[143] The phenomenon again occurred on October 3, 1907, No. 1
+being eclipsed and occulted, No. 2 in transit, No. 3 eclipsed, and No. 4
+occulted.[144] It was not, however, visible in Europe, but could have been
+seen in Asia and Oceania.[144] The phenomenon will occur again on October
+22, 1913.[145]
+
+On the night of September 19, 1903, a star of magnitude 6-1/2 was occulted
+by the disc of Jupiter. This curious and rare phenomenon was photographed
+by M. Lucien Rudaux at the Observatory of Donville, France.[146] The star
+was Lalande 45698 (= BAC 8129).[147]
+
+Prof. Barnard, using telescopes with apertures from 5 inches up to 36
+inches (Lick), has failed to see a satellite through the planet's limb (an
+observation which has been claimed by other astronomers). He says, "To my
+mind this has been due to either poor seeing, a poor telescope, or an
+excited observer."[148] He adds--
+
+    "I think it is high time that the astronomers reject the idea that the
+    satellites of Jupiter can be seen through his limb at occultation.
+    When the seeing is bad there is a spurious limb to Jupiter that well
+    might give the appearance of transparency at the occultation of a
+    satellite. But under first-class conditions the limb of Jupiter is
+    perfectly opaque. It is quibbling and begging the question altogether
+    to say the phenomenon of transparency may be a rare one and so have
+    escaped my observations. Has any one said that the moon was
+    transparent when a star has been seen projected on it when it ought to
+    have been behind it?"
+
+Prof. Barnard and Mr. Douglass have seen white polar caps on the third and
+fourth satellites of Jupiter. The former says they are "exactly like those
+on Mars." "Both caps of the fourth satellite have been clearly
+distinguished, that at the north being sometimes exceptionally large,
+covering a surface equal to one-quarter or one-third of the diameter of
+the satellite."[149] This was confirmed on November 23, 1906, when Signor
+J. Comas Sola observed a brilliant white spot surrounded by a dark marking
+in the north polar region of the third satellite. There were other dark
+markings visible, and the satellite presented the appearance of a
+miniature of Mars.[150]
+
+An eighth satellite of Jupiter has recently been discovered by Mr. Melotte
+at the Greenwich Observatory by means of photography. It moves in a
+retrograde direction round Jupiter in an orbit inclined about 30� to that
+of the planet. The period of revolution is about two years. The orbit is
+very eccentric, the eccentricity being about one-third, or greater than
+that of any other satellite of the solar system. When nearest to Jupiter
+it is about 9 millions of miles from the planet, and when farthest about
+20 millions.[151] It has been suggested by Mr. George Forbes that this
+satellite may possibly be identical with the lost comet of Lexell which at
+its return in the year 1779 became entangled in Jupiter's system, and has
+not been seen since. If this be the case, we should have the curious
+phenomenon of a comet revolving round a planet!
+
+According to Humboldt the four bright satellites of Jupiter were seen
+almost simultaneously and quite independently by Simon Marius at Ausbach
+on December 29, 1609, and by Galileo at Padua on January 7, 1610.[152] The
+actual priority, therefore, seems to rest with Simon Marius, but the
+publication of the discovery was first made by Galileo in his _Nuncius
+Siderius_ (1610).[153] Grant, however, in his _History of Physical
+Astronomy_, calls Simon Marius an "impudent pretender"! (p. 79).
+
+M. Dupret at Algiers saw Jupiter with the naked eye on September 26, 1890,
+twenty minutes before sunset.[154]
+
+Humboldt states that he saw Jupiter with the naked eye when the sun was
+from 18� to 20� above the horizon.[155] This was in the plains of South
+America near the sea-level.
+
+
+
+
+CHAPTER IX
+
+Saturn
+
+
+To show the advantages of large telescopes over small ones, Mr. C. Roberts
+says that "with the 25-inch refractor of the Cambridge Observatory the
+view of the planet Saturn is indescribably glorious; everything I had ever
+seen before was visible at a glance, and an enormous amount of detail that
+I had never even glimpsed before, after a few minutes' observation."[156]
+
+Chacornac found that the illumination of Saturn's disc is the reverse of
+that of Jupiter, the edges of Saturn being brighter than the centre of the
+disc, while in the case of Jupiter--as in that of the sun--the edges are
+fainter than the centre.[157] According to Mr. Denning, Saturn bears
+satisfactorily "greater magnifying power than either Mars or
+Jupiter."[158]
+
+At an occultation of Saturn by the moon, which occurred on June 13, 1900,
+M. M. Honorat noticed the great contrast between the slightly yellowish
+colour of the moon and the greenish tint of the planet.[159]
+
+In the year 1892, when the rings of Saturn had nearly disappeared, Prof.
+L. W. Underwood, of the Underwood Observatory, Appleton, Wisconsin
+(U.S.A.), saw one of Saturn's satellites (Titan) apparently moving along
+the needlelike appendage to the planet presented by the rings. "The
+apparent diameter of the satellite so far exceeded the apparent thickness
+of the ring that it gave the appearance of a beautiful golden bead moving
+very slowly along a fine golden thread."[160]
+
+In 1907, when the rings of Saturn became invisible in ordinary telescopes,
+Professor Campbell, observing with the great Lick telescope, noticed
+"prominent bright knots, visible ... in Saturn's rings. The knots were
+symmetrically placed, two being to the east and two to the west." This was
+confirmed by Mr. Lowell, who says, "Condensations in Saturn's rings
+confirmed here and measured repeatedly. Symmetric and permanent." This
+phenomenon was previously seen by Bond in the years 1847-56. Measures of
+these light spots made by Prof. Barnard with the 40-inch Yerkes telescope
+show that the outer one corresponded in position with the outer edge of
+the middle ring close to the Cassini division, and the inner condensation,
+curious to say, seemed to coincide in position with the "crape ring."
+Prof. Barnard thinks that the thickness of the rings "must be greatly
+under 100 miles, and probably less than 50 miles," and he says--
+
+    "The important fact clearly brought out at this apparition of _Saturn_
+    is that the bright rings are not opaque to the light of the sun--and
+    this is really what we should expect from the nature of their
+    constitution as shown by the theory of Clerk Maxwell, and the
+    spectroscopic results of Keeler."[161]
+
+Under certain conditions it would be theoretically possible, according to
+Mr. Whitmell, to see the globe of Saturn through the Cassini division in
+the ring. But the observation would be one of great difficulty and
+delicacy. The effect would be that, of the arc of the division which
+crosses the planet's disc, "a small portion will appear bright instead of
+dark, and may almost disappear."[162]
+
+A remarkable white spot was seen on Saturn on June 23, 1903, by Prof.
+Barnard, and afterwards by Mr. Denning.[163] Another white spot was seen
+by Denning on July 9 of the same year.[164] From numerous observations of
+these spots, Denning found a rotation period for the planet of about
+10{h} 39{m} 21{s}.[165] From observations of the same spots Signor Comas
+Sola found a period 10{h} 38{m}�4, a close agreement with Denning's
+result. For Saturn's equator, Prof. Hill found a rotation period of 10{h}
+14{m} 23{s}�8, so that--as in the case of Jupiter--the rotation is faster
+at the equator than in the northern latitudes of the planet. A similar
+phenomenon is observed in the sun. Mr. Denning's results were fully
+confirmed by Herr Leo Brenner, and other German astronomers.[166]
+
+Photographs taken by Prof. V. M. Slipher in America show that the spectrum
+of Saturn is similar to that of Jupiter. None of the bands observed in the
+planet's spectrum are visible in the spectrum of the rings. This shows
+that if the rings possess an atmosphere at all, it must be much rarer than
+that surrounding the ball of the planet. Prof. Slipher says that "none of
+the absorption bands in the spectrum of _Saturn_ can be identified with
+those bands due to absorption in the earth's atmosphere," and there is no
+trace of aqueous vapour.[167]
+
+In September, 1907, M. G. Fournier suspected the existence of a "faint
+transparent and luminous ring" outside the principal rings of Saturn. He
+thinks that it may possibly be subject to periodical fluctuations of
+brightness, sometimes being visible and sometimes not.[168] This dusky
+ring was again suspected at the Geneva Observatory in October, 1908.[169]
+M. Schaer found it a difficult object with a 16-inch Cassegrain reflector.
+Prof. Stromgen at Copenhagen, and Prof. Hartwig at Bamberg, however,
+failed to see any trace of the supposed ring.[170] It was seen at
+Greenwich in October, 1908.
+
+A "dark transit" of Saturn's satellite Titan across the disc of the planet
+has been observed on several occasions. It was seen by Mr. Isaac W. Ward,
+of Belfast, on March 27, 1892, with a 4�3-inch Wray refractor. The
+satellite appeared smaller than its shadow. The phenomenon was also seen
+on March 12 of the same year by the Rev. A. Freeman, Mr. Mee, and M. F.
+Terby; and again on November 6, 1907, by Mr. Paul Chauleur and Mr. A. B.
+Cobham.[171]
+
+The recently discovered tenth satellite of Saturn, Themis, was discovered
+by photography, and has never been seen by the eye even with the largest
+telescopes! But its existence is beyond all doubt, and its orbit round the
+planet has been calculated.
+
+Prof. Hussey of the Lick Observatory finds that Saturn's satellite Mimas
+is probably larger than Hyperion. He also finds from careful measurements
+that the diameter of Titan is certainly overestimated, and that its
+probable diameter is about 2500 miles.[172]
+
+The French astronomer, M. Lucien Rudaux, finds the following variation in
+the light of the satellites of Saturn:--
+
+  Japetus from 9th magnitude to 12th
+  Rhea     "   9       "        10�6
+  Dione    "   9�5     "        10�5
+  Tethys   "   9�8     "        10�5
+  Titan    "   8       "         8�6
+
+The variation of light is, he thinks, due to the fact that the period of
+rotation of each satellite is equal to that of their revolution round the
+planet; as in the case of our moon.[173]
+
+The names of the satellites of Saturn are derived from the ancient heathen
+mythology. They are given in order of distance from the planet, the
+nearest being Mimas and the farthest Themis.
+
+1. Mimas was a Trojan born at the same time as Paris.
+
+2. Enceladus was son of Tartarus and Ge.
+
+3. Tethys was wife of Oceanus, god of ocean currents. She became mother of
+all the chief rivers in the universe, as also the Oceanides or sea nymphs.
+
+4. Dione was one of the wives of Zeus.
+
+5. Rhea was a daughter of Uranus. She married Saturn, and became the
+mother of Vesta, Ceres, Juno, and Pluto.
+
+6. Titan was the eldest son of Uranus.
+
+7. Hyperion was the god of day, and the father of sun and moon.
+
+8. Japetus was the fifth son of Uranus, and father of Atlas and
+Prometheus.[174]
+
+9. Phoebe was daughter of Uranus and Ge.
+
+10. Themis was daughter of Uranus and Ge, and, therefore, sister of
+Phoebe.
+
+In a review of Prof. Comstock's _Text Book of Astronomy_ in _The
+Observatory_, November, 1901, the remark occurs, "We are astonished to see
+that Mr. Comstock alludes with apparent seriousness to the _nine_
+satellites of Saturn. As regards the ninth satellite, we thought that all
+astronomers held with Mrs. Betsy Prig on the subject of this astronomical
+Mrs. Harris." This reads curiously now (1909) when the existence of the
+ninth satellite (Phoebe) has been fully confirmed, and a tenth satellite
+discovered.
+
+
+
+
+CHAPTER X
+
+Uranus and Neptune
+
+
+From observations of Uranus made in 1896, M. Leo Brenner concluded that
+the planet rotates on its axis in about 8-1/2 hours (probably 8{h} 27{m}).
+This is a short period, but considering the short periods of Jupiter and
+Saturn there seems to be nothing improbable about it.
+
+Prof. Barnard finds that the two inner satellites of Uranus are difficult
+objects even with the great 36-inch telescope of the Lick Observatory!
+They have, however, been photographed at Cambridge (U.S.A.) with a 13-inch
+lens, although they are "among the most difficult objects known."[175]
+
+Sir William Huggins in 1871 found strong absorption lines (six strong
+lines) in the spectrum of Uranus. One of these lines indicated the
+presence of hydrogen, a gas which does not exist in our atmosphere. Three
+of the other lines seen were situated near lines in the spectrum of
+atmospheric air. Neither carbonic acid nor sodium showed any indications
+of their presence in the planet's spectrum. A photograph by Prof. Slipher
+of Neptune's spectrum "shows the spectrum of this planet to contain many
+strong absorption bands. These bands are so pronounced in the part of the
+spectrum between the Fraunhofer lines F and D, as to leave the solar
+spectrum unrecognizable.... Neptune's spectrum is strikingly different
+from that of _Uranus_, the bands in the latter planet all being reinforced
+in _Neptune_. In this planet there are also new bands which have not been
+observed in any of the other planets. The F line of hydrogen is remarkably
+dark ... this band is of more than solar strength in the spectrum of
+Uranus also. Thus free hydrogen seems to be present in the atmosphere of
+both these planets. This and the other dark bands in these planets bear
+evidence of an enveloping atmosphere of gases which is quite unlike that
+which surrounds the earth."[176]
+
+With the 18-inch equatorial telescope of the Strasburgh Observatory, M.
+Wirtz measured the diameter of Neptune, and found from forty-nine measures
+made between December 9, 1902, and March 28, 1903, a value of 2"�303 at a
+distance of 30�1093 (earth's distance from sun = 1). This gives a diameter
+of 50,251 kilometres, or about 31,225 miles,[177] and a mean density of
+1�54 (water = 1; earth's mean density = 5�53). Prof. Barnard's measures
+gave a diameter of 32,900 miles, a fairly close agreement, considering the
+difficulty of measuring so small a disc as that shown by Neptune.
+
+The satellite of Neptune was photographed at the Pulkown Observatory in
+the year 1899. The name Triton has been suggested for it. In the old Greek
+mythology Triton was a son of Neptune, so the name would be an appropriate
+one.
+
+The existence of a second satellite of Neptune is suspected by Prof.
+Schaeberle, who thinks he once saw it with the 36-inch telescope of the
+Lick Observatory "on an exceptionally fine night" in 1895.[178] But this
+supposed discovery has not yet been confirmed. Lassell also thought he had
+discovered a second satellite, but this supposed discovery was never
+confirmed.[178]
+
+The ancient Burmese mention eight planets, the sun, the moon, Mercury,
+Venus, Mars, Jupiter, Saturn, and another named R�hu, which is invisible.
+It has been surmised that "R�hu" is Uranus, which is just visible to the
+naked eye, and may possibly have been discovered by keen eyesight in
+ancient times. The present writer has seen it several times without
+optical aid in the West of Ireland, and with a binocular field-glass of 2
+inches aperture he found it quite a conspicuous object.
+
+When Neptune was _visually_ discovered by Galle, at Berlin, he was
+assisted in his observation by Prof. d'Arrest. The incident is thus
+described by Dr. Dreyer, "On the night of June 14, 1874, while observing
+Coggia's comet together, I reminded Prof. d'Arrest how he had once said in
+the course of a lecture, that he had been present at the finding of
+Neptune, and that 'he might say it would not have been found without him.'
+He then told me (and I wrote it down the next day), how he had suggested
+the use of Bremiker's map (as first mentioned by Dr. Galle in 1877) and
+continued, 'We then went back to the dome, where there was a kind of desk,
+at which I placed myself with the map, while Galle, looking through the
+refractor, described the configurations of the stars he saw. I followed
+them on the map one by one, until he said: "And then there is a star of
+the 8th magnitude, in such and such a position," whereupon I immediately
+exclaimed: "That star is not on the map."'"[179] This was the planet. But
+it seems to the present writer that if Galle or d'Arrest had access to
+Harding's Atlas (as they probably had) they might easily have found the
+planet with a good binocular field-glass. As a matter of fact Neptune is
+shown in Harding's Atlas (1822) as a star of the 8th magnitude, having
+been mistaken for a star by Lalande on May 8 and 10, 1795; and the present
+writer has found Harding's 8th magnitude stars quite easy objects with a
+binocular field-glass having object-glasses of two inches diameter, and a
+power of about six diameters.
+
+SUPPOSED PLANET BEYOND NEPTUNE.--The possible existence of a planet beyond
+Neptune has been frequently suggested. From considerations on the aphelia
+of certain comets, Prof. Forbes in 1880 computed the probable position of
+such a body. He thought this hypothetical planet would be considerably
+larger than Jupiter, and probably revolve round the sun at a distance of
+about 100 times the earth's mean distance from the sun. The place
+indicated was between R.A. 11{h} 24{m} and 12{h} 12{m}, and declination 0�
+0' to 6� 0' north. With a view to its discovery, the late Dr. Roberts took
+a series of eighteen photographs covering the region indicated. The result
+of an examination of these photographs showed, Dr. Roberts says, that "no
+planet of greater brightness than a star of the 15th magnitude exists on
+the sky area herein indicated." Prof. W. H. Pickering has recently revived
+the question, and has arrived at the following results: Mean distance of
+the planet from the sun, 51�9 (earth's mean distance = 1); period of
+revolution, 373-1/2 years; mass about twice the earth's mass; probable
+position for 1909 about R.A. 7{h} 47{m}, north declination 21�, or about
+5� south-east of the star [Greek: k] Geminorum. The supposed planet would
+be faint, its brightness being from 11-1/2 to 13-1/2, according to the
+"albedo" (or reflecting power) it may have.[180]
+
+Prof. Forbes has again attacked the question of a possible ultra-Neptunian
+planet, and from a consideration of the comets of 1556, 1843 I, 1880 I,
+and 1882 II, finds a mean distance of 105�4, with an inclination of the
+orbit of 52� to the plane of the ecliptic. This high inclination implies
+that "during the greatest part of its revolution it is beyond the zodiac,"
+and this, Mr. W. T. Lynn thinks, "may partly account for its not having
+hitherto been found by observation."[181]
+
+From a consideration of the approximately circular shape of the orbits of
+all the large planets of the solar system, Dr. See suggests the existence
+of three planets outside Neptune, with approximate distances from the sun
+of 42, 56, and 72 respectively (earth's distance = 1), and recommends a
+photographic search for them. He says, "To suppose the planetary system to
+terminate with an orbit so round as that of Neptune is as absurd as to
+suppose that Jupiter's system terminates with the orbit of the fourth
+satellite."[182]
+
+According to Grant, even twenty years before the discovery of Neptune the
+error of Prof. Adams' first approximation amounted to little more than
+10�.[183]
+
+
+
+
+CHAPTER XI
+
+Comets
+
+
+We learn from Pliny that comets were classified in ancient times,
+according to their peculiar forms, into twelve classes, of which the
+principal were: _Pogonias_, bearded; _Lampadias_, torch-like; _Xiphias_,
+sword-like; _Pitheus_, tun-like; _Acontias_, javelin-like; _Ceratias_,
+horn-like; _Disceus_, quoit-like; and _Hippias_, horse-mane-like.[184]
+
+Of the numerous comets mentioned in astronomical records, comparatively
+few have been visible to the naked eye. Before the invention of the
+telescope (1610) only those which were so visible _could_, of course, be
+recorded. These number about 400. Of the 400 observed since then, some 70
+or 80 only have been visible by unaided vision; and most of these now
+recorded could never have been seen without a telescope. During the last
+century, out of 300 comets discovered, only 13 were very visible to the
+naked eye. Hence, when we read in the newspapers that a comet has been
+discovered the chances are greatly against it becoming visible to the
+naked eye.[185]
+
+Although comparatively few comets can be seen without a telescope, they
+are sometimes bright enough to be visible in daylight! Such were those of
+B.C. 43, A.D. 1106, 1402, 1532, 1577, 1744, 1843, and the "great September
+comet" of 1882.
+
+If we except the great comet of 1861, through the tail of which the earth
+is supposed to have passed, the comet which came nearest to the earth was
+that of 1770, known as Lexell's, which approached us within two millions
+of miles, moving nearly in the plane of the ecliptic. It produced,
+however, no effect on the tides, nor on the moon's motion, which shows
+that its mass must have been very small. It was computed by Laplace that
+if its mass had equalled that of the earth, the length of our year would
+have been shortened by 2 hours 47 minutes, and as there was no perceptible
+change Laplace concluded that the comet's mass did not exceed 1/5000th of
+the earth's mass. This is the comet which passed so near to Jupiter that
+its period was reduced to 5-1/2 years. Owing to another near approach in
+1779 it became invisible from the earth, and is now lost.[186] Its
+identity with the recently discovered eighth satellite of Jupiter has been
+suggested by Mr. George Forbes (see under "Jupiter"). At the near approach
+of Lexell's comet to the earth in 1770, Messier, "the comet ferret,"
+found that its head had an apparent diameter of 2-1/2�, or nearly five
+times that of the moon!
+
+Another case of near approach to the earth was that of Biela's comet at
+its appearance in 1805. On the evening of December 9 of that year, the
+comet approached the earth within 3,380,000 miles.[187]
+
+The comet of A.D. 1106 is stated to have been seen in daylight close to
+the sun. This was on February 4 of that year. On February 10 it had a tail
+of 60� in length, according to Gaubil.[188]
+
+The comet of 1577 seems to have been one of the brightest on record.
+According to Tycho Brah�, it was visible in broad daylight. He describes
+the head as "round, bright, and of a yellowish light," with a curved tail
+of a reddish colour.[189]
+
+The comet of 1652 was observed for about three weeks only, and Hevelius
+and Comiers state that it was equal to the moon in apparent size! This
+would indicate a near approach to the earth. An orbit computed by Halley
+shows that the least distance was about 12 millions of miles, and the
+diameter of the comet's head rather less than 110,000 miles, or about 14
+times the earth's diameter.
+
+According to Mr. Denning, "most of the periodical comets at perihelion are
+outside the earth's orbit, and hence it follows that they escape
+observation unless the earth is on the same side of the sun as the
+comet."[190]
+
+It was computed by M. Faye that the _volume_ of the famous Donati's comet
+(1858) was about 500 times that of the sun! On the other hand, he
+calculated that its _mass_ (or quantity of matter it contained) was only a
+fraction of the earth's mass. This shows how almost inconceivably tenuous
+the material forming the comet must have been--much more rarefied, indeed,
+than the most perfect vacuum which can be produced in an air-pump. This
+tenuity is shown by the fact that stars were seen through the tail "as if
+the tail did not exist." A mist of a few hundred yards in thickness is
+sufficient to hide the stars from our view, while a thickness of thousands
+of miles of cometary matter does not suffice even to dim their brilliancy!
+
+At the time of the appearance of the great comet of 1843, it was doubtful
+whether the comet had transited the sun's disc. But it is now known, from
+careful calculations by Prof. Hubbard, that a transit really took place
+between 11{h} 28{m} and 12{h} 29{m} on February 27, 1843, and might have
+been observed in the southern hemisphere. The distance of this remarkable
+comet from the sun at its perihelion passage was less than that of any
+known comet. A little before 10 p.m. on February 27, the comet passed
+within 81,500 miles of the sun's surface with the enormous velocity of
+348 miles a second! It remained less than 2-1/4 hours north of the
+ecliptic, passing from the ascending to the descending node of its orbit
+in 2{h} 13{m}�4.[191] The great comet of 1882 transited the sun's disc on
+Sunday, September 17, of that year, the ingress taking place at 4{h} 50{m}
+58{s}, Cape mean time. When on the sun the comet was absolutely invisible,
+showing that there was nothing solid about it. It was visible near the sun
+with the naked eye a little before the transit took place.[192] This great
+comet was found by several computors to have been travelling in an
+elliptic orbit with a period of about eight centuries. Morrison found 712
+years; Frisby, 794; Fabritius, 823; and Kreutz, 843 years.[193]
+
+The great southern comet of 1887 may be described as a comet without a
+head! The popular idea of a comet is a star with a tail. But in this case
+there was no head visible--to the naked eye at least. Dr. Thome of the
+Cordoba Observatory--its discoverer--describes it as "a beautiful
+object--a narrow, straight, sharply defined, graceful tail, over 40� long,
+shining with a soft starry light against a dark sky, beginning apparently
+without a head, and gradually widening and fading as it extended
+upwards."[194]
+
+The great southern comet of 1901 had five tails on May 6 of that year. Two
+were fairly bright, and the remaining three rather faint. Mr. Gale saw a
+number of faint stars through the tails. The light of these seem to have
+been "undimmed." Mr. Cobham noticed that the stars Rigel and [Greek: b]
+Eridani shone through one of the faint tails, and "showed no perceptible
+difference."[195]
+
+Prof. W. H. Pickering says that "the head of a comet, as far as our
+present knowledge is concerned, seems therefore to be merely a meteor
+swarm containing so much gaseous material that when electrified by its
+approach to the sun it will be rendered luminous" (_Harvard Annual_, vol.
+xxxii. part ii. p. 295) "... if the meteors and their atmospheres are
+sufficiently widely separated from one another, the comet may be brilliant
+and yet transparent at the same time."
+
+In the case of Swift's comet of 1892 some periodical differences of
+appearance were due, according to Prof. W. H. Pickering, to a rotation of
+the comet round an axis passing longitudinally through the tail, and he
+estimated the period of rotation at about 94 to 97 hours. He computed that
+in this comet the repulsive force exerted by the sun on the comet's tail
+was "about 39�5 times the gravitational force."[196]
+
+The comet known as 1902_b_ approached the planet Mercury within two
+millions of miles on November 29 of that year. Prof. O. C. Wendell, of
+Harvard Observatory, made some observations on the transparency of this
+comet. He found with the aid of a photometer and the 15-inch telescope of
+the observatory that in the case of two faint stars over which the comet
+passed on October 14, 1902, the absorption of light by the comet was
+insensible, and possibly did not exceed one or two hundredths of a
+magnitude,[197] an amount quite imperceptible to the naked eye, and shows
+conclusively how almost inconceivably rarefied the substance of this comet
+must be.
+
+The comet known as Morehouse (1908_c_) showed some curious and wonderful
+changes. Mr. Borelly found that five tails are visible on a photographic
+plate taken on October 3, 1908, and the trail of an occulted star
+indicates a slight absorption effect. According to M. L. Rabourdin, great
+changes took place from day to day, and even during the course of an hour!
+Similar changes were recorded by G. M. Gauthier; and Prof. Barnard, who
+photographed the comet on 30 nights from September 2 to October 13, states
+that the photographs of September 30 "are unique, whilst the
+transformation which took place between the taking of these and the taking
+of the next one on October 1 was very wonderful."[198] The spectrum
+showed the lines of cyanogen instead of the hydrocarbon spectrum shown by
+most comets.
+
+Prof. Barnard has suggested that all the phenomena of comets' tails cannot
+be explained by a repulsive force from the sun. Short tails issuing from
+the comet's nucleus at considerable angles with the main tail point to
+eruptive action in the comet itself. The rapid changes and distortions
+frequently observed in the tails of some comets suggest motion through a
+resisting medium; and the sudden increase of light also occasionally
+observed points in the same direction.[199]
+
+It was computed by Olbers that if a comet having a mass of 1/2000th of the
+earth's mass--which would form a globe of about 520 miles in diameter and
+of the density of granite--collided with the earth, with a velocity of 40
+miles a second, our globe would be shattered into fragments.[200] But that
+any comet has a solid nucleus of this size seems very doubtful; and we may
+further say that the collision of the earth with _any_ comet is highly
+improbable.
+
+It seems to be a common idea that harvests are affected by comets, and
+even "comet wines" are sometimes spoken of. But we know that the earth
+receives practically no heat from the brightest comet. Even in the case of
+the brilliant comet of 1811, one of the finest on record, it was found
+that "all the efforts to concentrate its rays did not produce the
+slightest effect on the blackened bulb of the most sensitive thermometer."
+Arago found that the year 1808, in which several comets were visible, was
+a cold year, "and 1831, in which there was no comet, enjoyed a much higher
+temperature than 1819, when there were three comets, one of which was very
+brilliant."[201] We may, therefore, safely conclude that even a large
+comet has no effect whatever on the weather.
+
+From calculations on the orbit of Halley's comet, the next return of which
+is due in 1910, Messrs. Cowell and Crommelin find that the identity of the
+comet shown on the Bayeux Tapestry with Halley's comet is now "fully
+established." They find that the date of perihelion passage was March 25,
+1066, which differs by only 4 days from the date found by Hind. The
+imposing aspect of the comet in 1066 described in European chronicles of
+that time is confirmed by the Chinese Annals. In the latter records the
+brightness is compared to that of Venus, and even with that of the moon!
+The comparison with the moon was probably an exaggeration, but the comet
+doubtless made a very brilliant show. In the Bayeux Tapestry the
+inscription on the wall behind the spectators reads: "_isti mirant
+stella_." Now, this is bad Latin, and Mr. W. T. Lynn has made the
+interesting suggestion that some of the letters are hidden by the
+buildings in front and that the real sentence is "_isti mirantur
+stellam_."[202] The present writer has examined the copy of the Bayeux
+Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn's
+suggestion seems very plausible. But the last letter of _stellam_ is
+apparently hidden by the comet's tail, which does not seem very probable!
+
+The conditions under which the comet will appear in 1910 are not unlike
+those of 1066 and 1145. "In each year the comet was discovered as a
+morning star, then lost in the sun's rays; on its emergence it was near
+the earth and moved with great rapidity, finally becoming stationary in
+the neighbourhood of Hydra, where it was lost to view."[203] In 1910 it
+will probably be an evening star before March 17, and after May 11, making
+a near approach to the earth about May 12. About this time its apparent
+motion in the sky will be very rapid. As, however, periodical comets--such
+as Halley's--seem to become fainter at each return, great expectations
+with reference to its appearance in 1910 should not be indulged in.
+
+The appearance of Halley's comet in A.D. 1222 is thus described by
+Pingr�--a great authority on comets--(quoting from an ancient writer)--
+
+    "In autumn, that is to say in the months of August and September, a
+    star of the first magnitude was seen, very red, and accompanied by a
+    great tail which extended towards the top of the sky in the form of a
+    cone extremely pointed. It appeared to be very near the earth. It was
+    observed (at first?) near the place of the setting sun in the month of
+    December."
+
+With reference to its appearance in the year 1456, when it was of "vivid
+brightness," and had a tail of 60� in length, Admiral Smyth says,[204] "To
+its malign influence were imputed the rapid successes of Mahomet II.,
+which then threatened all Christendom. The general alarm was greatly
+aggravated by the conduct of Pope Callixtus III., who, though otherwise a
+man of abilities, was a poor astronomer; for that pontiff daily ordered
+the church bells to be rung at noon-tide, extra _Ave-Marias_ to be
+repeated, and a special protest and excommunication was composed,
+exorcising equally the Devil, the Turks, and the comet." With reference to
+this story, Mr. G. F. Chambers points out[205] that it is probably based
+on a passage in Platina's _Vit� Pontificum_. But in this passage there is
+no mention made of excommunication or exorcism, so that the story, which
+has long been current, is probably mythical. In confirmation of this view,
+the Rev. W. F. Rigge has shown conclusively[206] that no bull was ever
+issued by Pope Callixtus III. containing a reference to _any_ comet. The
+story would therefore seem to be absolutely without foundation, and should
+be consigned to the limbo of all such baseless myths.
+
+With reference to the appearance of Halley's comet, at his last return in
+1835, Sir John Herschel, who observed it at the Cape of Good Hope, says--
+
+    "Among the innumerable stars of all magnitudes, from the ninth
+    downwards, which at various times were seen through it, and some
+    extremely near to the nucleus (though not _exactly on it_) there never
+    appeared the least ground for presuming any extinction of their light
+    in traversing it. Very minute stars indeed, on entering its brightest
+    portions, were obliterated, as they would have been by an equal
+    illumination of the field of view; but stars which before their entry
+    appeared bright enough to bear that degree of illumination, were in no
+    case, so far as I could judge, affected to a greater extent than they
+    would have been by so much lamp-light artificially introduced."[207]
+
+It is computed by Prof. J. Holetschak that, early in October, 1909,
+Halley's comet should have the brightness of a star of about 14-1/2
+magnitude.[208] It should then--if not detected before--be discoverable
+with some of the large telescopes now available.
+
+According to the computations of Messrs. Cowell and Crommelin, the comet
+should enter Pisces from Aries in January, 1910. "Travelling westward
+towards the star [Greek: g] Piscium until the beginning of May, and then
+turning eastward again, it will travel back through the constellations
+Cetus, Orion, Monoceros, Hydra, and Sextans." From this it seems that
+observers in the southern hemisphere will have a better view of the comet
+than those in northern latitudes. The computed brightness varies from 1 on
+January 2, 1910, to 1112 on May 10. But the actual brightness of a comet
+does not always agree with theory. It is sometimes brighter than
+calculation would indicate.
+
+According to Prof. O. C. Wendell, Halley's comet will, on May 12, 1910,
+approach the earth's orbit within 4�6 millions of miles; and he thinks
+that possibly the earth may "encounter some meteors," which are presumably
+connected with the comet. He has computed the "radiant point" of these
+meteors (that is, the point from which they appear to come), and finds its
+position to be R.A. 22{h} 42{m}�9, Decl. N. 1� 18'. This point lies a
+little south-west of the star [Greek: b] Piscium.
+
+According to Dr. Smart, the comet will, on June 2, "cross the Equator
+thirteen degrees south of Regulus, and will then move slowly in the
+direction of [Greek: ph] Leonis. The comet will be at its descending node
+on the ecliptic in the morning of May 16, and the earth will pass through
+the node on the comet's orbit about two and a half days later. The
+comet's orbit at the node is about 13 million miles within that of the
+earth. Matter repelled from the comet's nucleus by the sun with a velocity
+of about 216,000 miles per hour, would just meet the earth when crossing
+the comet's orbit plane. Matter expelled with a velocity of 80,000 miles
+per hour, as in the case of Comet Morehouse, would require seven days for
+the journey. Cometary matter is said to have acquired greater velocities
+than this, for (according to Webb, who quotes Chacornac) Comet II., 1862,
+shot luminous matter towards the sun, with a velocity of nearly 2200 miles
+per second. It is therefore possible that matter thrown off by the comet
+at the node may enter our atmosphere, in which case we must hope that
+cyanogen, which so often appears in cometary spectra, may not be
+inconveniently in evidence."[209]
+
+Cyanogen is, of course, a poisonous gas, but cometary matter is so
+rarefied that injurious effects on the earth need not be feared.
+
+If we can believe the accounts which have been handed down to us, some
+very wonderful comets were visible in ancient times. The following may be
+mentioned:--
+
+B.C. 165. The sun is said to have been "seen for several hours in the
+night." If this was a comet it must have been one of extraordinary
+brilliancy.[210]
+
+B.C. 146. "After the death of Demetrius, king of Syria, the father of
+Demetrius and Antiochus, a little before the war in Achaia, there appeared
+a comet as large as the sun. Its disc was first red, and like fire,
+spreading sufficient light to dissipate the darkness of night; after a
+little while its size diminished, its brilliancy became weakened, and at
+length it entirely disappeared."[211]
+
+B.C. 134. It is recorded that at the birth of Mithridates a great comet
+appeared which "occupied the fourth part of the sky, and its brilliancy
+was superior to that of the sun." (?)[212]
+
+B.C. 75. A comet is described as equal in size to the moon, and giving as
+much light as the sun on a cloudy day. (!)[213]
+
+A.D. 531. In this year a great comet was observed in Europe and China. It
+is described as "a very large and fearful comet," and was visible in the
+west for three weeks. Hind thinks that this was an appearance of Halley's
+comet,[214] and this has been confirmed by Mr. Crommelin.
+
+A.D. 813, August 4. A comet is said to have appeared on this date, of
+which the following curious description is given: "It resembled two moons
+joined together; they separated, and having taken different forms, at
+length appeared like a man without a head." (!)[215]
+
+A.D. 893. A great comet is said to have appeared in this year with a tail
+100� in length, which afterwards increased to 200�![216]
+
+A.D. 1402. A comet appeared in February of this year, which was visible in
+daylight for eight days. "On Palm Sunday, March 19, its size was
+prodigious." Another comet, visible in the daytime, was seen from June to
+September of the same year.
+
+When the orbit of the comet known as 1889 V was computed, it was found
+that it had passed through Jupiter's system in 1886 (July 18-21). The
+calculations show that it must have passed within a distance of 112,300
+miles of the planet itself--or less than half the moon's distance from the
+earth--and "its centre may possibly have grazed the surface of
+Jupiter."[217]
+
+Sir John Herschel thought that the great comet of 1861 was by far the
+brightest comet he had ever seen, those of 1811 and 1858 (Donati's) not
+excepted.[218] Prof. Kreutz found its period of revolution round the sun
+to be about 409 years, with the plane of the orbit nearly at right angles
+to the plane of the ecliptic.
+
+       *       *       *       *       *
+
+On November 9, 1795, Sir William Herschel saw the comet of that year pass
+centrally over a small double star of the 11th and 12th magnitudes, and
+the fainter of the two components remained distinctly visible during the
+comet's transit over the star. This comet was an appearance of the comet
+now known as Encke's.[219] Struve saw a star of the 10th magnitude through
+nearly the brightest part of Encke's comet on November 7, 1828, but the
+star's light was not dimmed by the comet.
+
+Sir John Herschel saw a cluster of stars of the 16th or 17th magnitude
+through Biela's comet, although the interposed cometary matter must have
+been at least 50,000 miles in thickness.[220]
+
+Bessel found that on September 29, 1835, a star of the 10th magnitude
+shone with undimmed lustre through the tail of Halley's comet within 8
+seconds of arc of the central point of the head. At Dorpat (Russia) Struve
+saw the same star "in conjunction only 2"�2 from the brightest point of
+the comet. The star remained continuously visible, and its light was not
+perceptibly diminished whilst the nucleus of the comet seemed to be almost
+extinguished before the radiance of the small star of the 9th or 10th
+magnitude."[221]
+
+Webb says--
+
+    "Donati saw a 7 mg. star enlarged so as to show a sensible disc, when
+    the nucleus of comet III., 1860, passed very near it. Stars are said
+    to have started, or become tremulous, during occultations by comets.
+    Birmingham observed the comet of Encke illuminated by a star over
+    which it passed, August 23, 1868; and Klein, in 1861, remarked an
+    exceptional twinkling in 5 mg. stars involved in the tail."[222]
+
+The comet of 1729 had the greatest perihelion distance of any known
+comet;[223] that is, when nearest to the sun, it did not approach the
+central luminary within four times the earth's distance from the sun!
+
+Barnard's comet, 1889 I., although it never became visible to the naked
+eye, was visible with a telescope from September 2, 1888, to August 18,
+1890, or 715 days--the longest period of visibility of any comet on
+record. When last seen it was 6-1/4 times the earth's distance from the
+sun, or about 580 millions of miles,[224] or beyond the orbit of Jupiter!
+
+Messier, who was called "the comet ferret," discovered "all his comets
+with a small 2-foot telescope of 2-1/4 inches aperture, magnifying 5
+times, and with a field of 4�."[225]
+
+It is a very curious fact that Sir William Herschel, "during all his
+star-gaugings and sweeps for nebul�, never discovered a comet;"[226] that
+is an object which was afterwards _proved_ to be a comet. Possibly,
+however, some of his nebul� which are now missing, may have been really
+comets.
+
+Sir William Herschel found the diameter of the head of the great comet of
+1811 to be 127,000 miles. The surrounding envelope he estimated to be at
+least 643,000 miles, or about three-fourths of the sun's diameter.
+
+On a drawing of the tails of the great comet of 1744 given in a little
+book printed in Berlin in that year, no less than 12 tails are shown!
+These vary in length and brightness. A copy of this drawing is given in
+_Copernicus_.[227] The observations were made by "einen geschichten
+Frauenzimmer," who Dr. Dreyer identifies with Christian Kirch, or one of
+her two sisters, daughters of the famous Gottfried and Maria Margaretta
+Kirch (_Idem_, p. 107). Dr. Dreyer thinks that the drawing "seems to have
+been carefully made, and not to be a mere rough sketch as I had at first
+supposed" (_Idem_, p. 185).
+
+The tails of some comets were of immense length. That of the comet of 1769
+had an absolute length of 38 millions of miles. That of 1680, 96 million
+of miles, or more than the sun's distance from the earth. According to Sir
+William Herschel, the tail of the great comet of 1811 was over 100
+millions of miles in length. That of the great comet of 1843--one of the
+finest in history--is supposed to have reached a length of 150 millions of
+miles![228]
+
+In width the tails of comets were in some cases enormous. According to Sir
+William Herschel, the tail of the comet of 1811 had a diameter of 15
+millions of miles! Its volume was, therefore, far greater than that of the
+sun![228]
+
+According to Hevelius the comet of 1652 was of such a magnitude that it
+"resembled the moon when half full; only it shone with a pale and dismal
+light."[229]
+
+Halley's comet at its next appearance will be examined with the
+spectroscope for the first time in its history. At its last return in
+1835, the spectroscope had not been invented.
+
+For the great comet of 1811, Arago computed a period of 3065 years; and
+Encke found a period of 8800 years for the great comet of 1680.[230]
+
+The variation in the orbital velocity of some comets is enormous. The
+velocity of the comet of 1680 when passing round the sun (perihelion) was
+about 212 miles a second! Whereas at its greatest distance from the sun
+(aphelion) the velocity is reduced to about 10 feet a second!
+
+
+
+
+CHAPTER XII
+
+Meteors
+
+
+Mr. Denning thinks that the meteor shower of the month of May, known as
+the Aquarids, is probably connected with Halley's comet. The meteors
+should be looked for after 1 a.m. during the first week in May, and may
+possibly show an enhanced display in May, 1910, when Halley's comet will
+be near the sun and earth.[231]
+
+On November 29, 1905, Sir David Gill observed a fireball with an apparent
+diameter equal to that of the moon, which remained visible for 5 minutes
+and disappeared in a hazy sky. Observed from another place, Mr. Fuller
+found that the meteor was visible 2 hours later! Sir David Gill stated
+that he does not know of any similar phenomenon.[232]
+
+Mr. Denning finds that swiftly moving meteors become visible at a greater
+height above the earth's surface than the slower ones. Thus, for the
+Leonids and Perseids, which are both swift, it has been found that the
+Leonids appear at an average height of 84 miles, and disappear at a height
+of 56 miles; and the Perseids at 80 and 54 miles respectively. "On the
+other hand, the mean height of the very slow meteors average about 65
+miles at the beginning and 38 miles at the end of their appearance."[233]
+
+During the night of July 21-22, 1896, Mr. William Brooks, the well-known
+astronomer, and director of the Smith Observatory at Geneva (New York),
+saw a round dark body pass slowly across the moon's bright disc, the moon
+being nearly full at the time. The apparent diameter of the object was
+about one minute of arc, and the duration of the transit 3 or 4 seconds,
+the direction of motion being from east to west. On August 22 of the same
+year, Mr. Gathman (an American observer) saw a meteor crossing the _sun's_
+disc, the transit lasting about 8 seconds.[234]
+
+A meteor which appeared in Italy on July 7, 1892, was shown by Prof. von
+Niessl to have had an _ascending_ path towards the latter end of its
+course! The length of its path was computed to be 683 miles. When first
+seen, its height above the earth was about 42 miles, and when it
+disappeared its height had increased to about 98 miles, showing that its
+motion was directed upwards![235]
+
+In the case of the fall of meteoric stones, which occasionally occur, it
+has sometimes been noticed that the sound caused by the explosion of the
+meteorite, or its passage through the air, is heard before the meteorite
+is seen to fall. This has been explained by the fact that owing to the
+resistance of the air to a body moving at first with a high velocity its
+speed is so reduced that it strikes the earth with a velocity less than
+that of sound. Hence the sound reaches the earth before the body strikes
+the ground.[236]
+
+The largest meteoric stone preserved in a museum is that known as the
+Anighita, which weighs 36-1/2 tons, and was found at Cape York in
+Greenland. It was brought to the American Museum of Natural History by
+Commander R. E. Peary, the Arctic explorer.
+
+The second largest known is that of Bacubirito in Mexico, the weight of
+which is estimated at 27-1/2 tons.
+
+The third largest is that known as the Williamette, which was found in
+1902 near the town of that name in Western Oregon (U.S.A.). It is composed
+of metallic nickel-iron, and weighs about 13-1/2 tons. It is now in the
+American Museum of Natural History.
+
+A large meteorite was actually seen, from the deck of the steamer _African
+Prince_, to fall into the Atlantic Ocean, on October 7, 1906! The captain
+of the vessel, Captain Anderson, describes it as having a train of light
+resembling "an immense broad electric-coloured band, gradually turning to
+orange, and then to the colour of molten metal. When the meteor came into
+the denser atmosphere close to the earth, it appeared, as nearly as is
+possible to describe it, like a molten mass of metal being poured out. It
+entered the water with a hissing noise close to the ship."[237] This was a
+very curious and perhaps unique phenomenon, and it would seem that the
+vessel had a narrow escape from destruction.
+
+In Central Arizona (U.S.A.) there is a hill called Coon Butte, or Coon
+Mountain. This so-called "mountain" rises to a height of only 130 to 160
+feet above the surrounding plain, and has on its top a crater of 530 to
+560 feet deep; the bottom of the crater--which is dry--being thus 400 feet
+below the level of the surrounding country. This so-called "crater" is
+almost circular and nearly three-quarters of a mile in diameter. It has
+been suggested that this "crater" was formed by the fall of an enormous
+iron meteorite, or small asteroid. The "crater" has been carefully
+examined by a geologist and a physicist. From the evidence and facts
+found, the geologist (Mr. Barringer) states that "they do not leave, in my
+mind, a scintilla of doubt that this mountain and its crater were produced
+by the impact of a huge meteorite or small asteroid." The physicist (Mr.
+Tilghmann) says that he "is justified, under due reserve as to
+subsequently developed facts, in announcing that the formation at this
+locality is due to the impact of a meteor of enormous and unprecedented
+size." There are numerous masses of meteoric iron in the vicinity of the
+"crater." The so-called Canyon Diabolo meteorite was found in a canyon of
+that name about 2-1/2 miles from the Coon Mountain. The investigators
+estimate that the great meteoric fall took place "not more than 5000 years
+ago, perhaps much less." Cedar trees about 700 years old are now growing
+on the rim of the mountain. From the results of artillery experiments, Mr.
+Gilbert finds that "a spherical projectile striking solid limestone with a
+velocity of 1800 feet a second will penetrate to a depth of something less
+than two diameters," and from this Mr. L. Fletcher concludes "that a
+meteorite of large size would not be prevented by the earth's atmosphere
+from having a penetration effect sufficient for the production of such a
+crater."[238]
+
+The meteoric origin of this remarkable "crater" is strongly favoured by
+Mr. G. P. Merrill, Head Curator of Geology, U.S. National Museum.
+
+The Canyon Diabolo meteorite above referred to was found to contain
+diamonds! some black, others transparent. So some have said that "the
+diamond is a gift from Heaven," conveyed to earth in meteoric
+showers.[239] But diamond-bearing meteorites would seem to be rather a
+freak of nature. It does not follow that _all_ diamonds had their origin
+in meteoric stones. The mineral known as periodot is frequently found in
+meteoric stones, but it is also a constituent of terrestrial rocks.
+
+In the year 1882 it was stated by Dr. Halm and Dr. Weinhand that they had
+found fossil sponges, corals, and crinoids in meteoric stones! Dr.
+Weinhand thought he had actually determined three genera![240] But this
+startling result was flatly contradicted by Carl Vogt, who stated that the
+supposed fossils are merely crystalline conformations.[241]
+
+Some meteorites contain a large quantity of occluded gases, hydrogen,
+helium, and carbon oxides. It is stated that Dr. Odling once "lighted up
+the theatre of the Royal Institution with gas brought down from
+interstellar space by meteorites"![242]
+
+On February 10, 1896, a large meteorite burst over Madrid with a loud
+report. The concussion was so great that many windows in the city were
+broken, and some partitions in houses were shaken down![243]
+
+A very brilliant meteor or fireball was seen in daylight on June 9, 1900,
+at 2{h} 55{m} p.m. from various places in Surrey, Sussex, and near London.
+Calculations showed that "the meteor began 59 miles in height over a point
+10 miles east of Valognes, near Cherbourg, France. Meteor ended 23 miles
+in height, over Calais, France. Length of path 175 miles. Radiant point,
+280�, 12�."[244]
+
+It was decided some years ago "in the American Supreme Court that a
+meteorite, though a stone fallen from heaven, belongs to the owner of the
+freehold interest in the land on which it falls, and not to the
+tenant."[245]
+
+With reference to the fall of meteoric matter on the earth, Mr. Proctor
+says, "It is calculated by Dr. Kleiber of St. Petersburgh that 4250 lbs.
+of meteoric dust fall on the earth every hour--that is, 59 tons a day, and
+more than 11,435 tons a year. I believe this to be considerably short of
+the truth. It sounds like a large annual growth, and the downfall of such
+an enormous mass of meteoric matter seems suggestive of some degree of
+danger. But in reality, Dr. Kleiber's estimate gives only about 25
+millions of pounds annually, which is less than 2 ounces annually to each
+square mile of the earth's surface,"[246] a quantity which is, of course,
+quite insignificant.
+
+According to Humboldt, Chladni states that a Franciscan monk was killed by
+the fall of an a�rolite at Milan in the year 1660.[247] Humboldt also
+mentions the death by meteoric stones of a monk at Crema on September 4,
+1511, and two Swedish sailors on board ship in 1674.[248]
+
+It is a curious fact that, according to Olbers, "no fossil meteoric
+stones" have ever been discovered.[249] Considering the number which are
+supposed to have fallen to the earth in the course of ages, this fact
+seems a remarkable one.
+
+On May 10, 1879, a shower of meteorites fell at Eitherville, Iowa
+(U.S.A.). Some of the fragments found weighed 437, 170, 92-1/2, 28,
+10-1/2, 4 and 2 lbs. in weight. In the following year (1880) when the
+prairie grass had been consumed by a fire, about "5000 pieces were found
+from the size of a pin to a pound in weight."[250]
+
+According to Prof. Silvestria of Catania, a shower of meteoric dust mixed
+with rain fell on the night of March 29, 1880. The dust contained a large
+proportion of iron in the metallic state. In size the particles varied
+from a tenth to a hundredth of a millimetre.[251]
+
+It is sometimes stated that the average mass of a "shooting star" is only
+a few grains. But from comparisons with an electric arc light, Prof. W.
+H. Pickering concludes that a meteor as bright as a third magnitude star,
+composed of iron or stone, would probably have a diameter of 6 or 7
+inches. An average bright fireball would perhaps measure 5 or 6 feet in
+diameter.[252]
+
+In the Book of Joshua we are told "that the LORD cast down great stones
+from heaven upon them unto Azekah, and they died" (Joshua x. 11). In the
+latter portion of the verse "hailstones" are mentioned, but as the
+original Hebrew word means stones in general (not hailstones), it seems
+very probable that the stones referred to were a�rolites.[253]
+
+The stone mentioned in the Acts of the Apostles, from which was found "the
+_image_ which fell down from Jupiter" (Acts xix. 35), was evidently a
+meteoric stone.[253]
+
+The famous stone in the Caaba at Mecca, is probably a stone of meteoric
+origin.[253]
+
+  I
+
+  "Stones from Heaven! Can you wonder,
+    You who scrutinize the Earth,
+  At the love and veneration
+    They received before the birth
+  Of our scientific methods?
+
+
+  II
+
+  "Stones from Heaven! we can handle
+    Fragments fallen from realms of Space;
+  Oh! the marvel and the mystery,
+    Could we understand their place
+  In the scheme of things created!
+
+
+  III
+
+  "Stones from Heaven! With a mighty
+    Comet whirling formed they part?
+  Fell they from their lofty station
+    Like a brilliant fiery dart,
+  Hurl'd from starry fields of Night?"[254]
+
+
+
+
+CHAPTER XIII
+
+The Zodiacal Light and Gegenschein
+
+
+According to Gruson and Brugsch, the Zodiacal Light was known in ancient
+times, and was even worshipped by the Egyptians. Strabo does not mention
+it; but Diodorus Siculus seems to refer to it (B.C. 373), and he probably
+obtained his information from some Greek writers before his time, possibly
+from Zenophon, who lived in the sixth century B.C.[255] Coming to the
+Christian era, it was noticed by Nicephorus, about 410 B.C. In the Koran,
+it is called the "false Aurora"; and it is supposed to be referred to in
+the "Rub�iy�t" of Omar Khayyam, the Persian astronomical poet, in the
+second stanza of that poem (Edward Fitzgerald's translation)--
+
+  "Dreaming when Dawn's Left Hand was in the Sky,[256]
+  I heard a voice within the Tavern cry,
+  Awake, my Little ones, and fill the Cup,
+  Before Life's Liquor in its Cup be dry."
+
+It was observed by Cassini in 1668,[257] and by Hooke in 1705. A short
+description of its appearance will be found in Childrey's _Britannia
+Baconica_ (1661), p. 183.
+
+The finest displays of this curious light seem to occur between the middle
+of January and the middle of February. In February, 1856, Secchi found it
+brighter than he had ever seen it before. It was yellowish towards the
+axis of the cone, and it seemed to be brighter than the Milky Way in
+Cygnus. He described it as "un grande spectacle." In the middle of
+February, 1866, Mr. Lassell, during his last residence in Malta, saw a
+remarkable display of the Zodiacal Light. He found it at least twice as
+bright as the brightest part of the Milky Way, and much brighter than he
+had previously seen it. He found that the character of its light differed
+considerably from that of the Milky Way. It was of a much redder hue than
+the Galaxy. In 1874 very remarkable displays were seen in the
+neighbourhood of London in January and February of that year; and in 1875
+on January 24, 25, and 30. On January 24 it was noticed that the "light"
+was distinctly reddish and much excelled in brightness any portion of the
+Milky Way.
+
+Humboldt, who observed it from Andes (at a height of 13,000 to 15,000
+feet), from Venezuela and from Cumana, tells us that he has seen the
+Zodiacal Light equal in brightness to the Milky Way in Sagittarius.
+
+As probably many people have never seen the "light," a caution may be
+given to those who care to look for it. It is defined by the Rev. George
+Jones, Chaplain to the "United States' Japan Expedition" (1853-55), as "a
+brightness that appears in the western sky after sunset, and in the east
+before sunrise; following nearly or quite the line of the ecliptic in the
+heavens, and stretching upwards to various elevations according to the
+season of the year." From the description some might suppose that the
+light is visible _immediately_ after sunset. But this is not so; it never
+appears until twilight is over and "the night has fully set in."
+
+The "light" is usually seen after sunset or before sunrise. But attempts
+have recently been made by Prof. Simon Newcomb to observe it north of the
+sun. To avoid the effects of twilight the sun must be only slightly more
+than 18� below the horizon (that is, a little before or after the longest
+day). This condition limits the place of observation to latitudes not much
+south of 46�; and to reduce atmospheric absorption the observing station
+should be as high as possible above the level of the sea. Prof. Newcomb,
+observing from the Brienzer Rothorn in Switzerland (latitude 46� 47' N.,
+longitude 8� 3' E.), succeeded in tracing the "light" to a distance of 35�
+north of the sun. It would seem, therefore, that the Zodiacal Light
+envelops the sun on all sides, but has a greater extension in the
+direction of the ecliptic.[258] From observations at the Lick Observatory,
+Mr. E. A. Fath found an extension of 46� north of the sun.[259]
+
+From observations of the "light" made by Prof. Barnard at the Yerkes
+Observatory during the summer of 1906, he finds that it extends to at
+least 65� north of the sun, a considerably higher value than that found by
+Prof. Newcomb.[260] The difference may perhaps be explained by actual
+variation of the meteoric matter producing the light. Prof. J. H. Poynting
+thinks that possibly the Zodiacal Light is due to the "dust of long dead
+comets."[261]
+
+From careful observations of the "light," Mr. Gavin J. Burns finds that
+its luminosity is "some 40 or 50 per cent. brighter than the background of
+the sky. Prof. Newcomb has made a precisely similar remark about the
+luminosity of the Milky Way, viz. that it is surprisingly small." This
+agrees with my own observations during many years. It is only on the
+finest and clearest nights that the Milky Way forms a conspicuous object
+in the night sky. And this only in the country. The lights of a city
+almost entirely obliterate it. Mr. Burns finds that the Zodiacal Light
+appears "to be of a yellowish tint; or if we call it white, then the Milky
+Way is comparatively of a bluish tint." During my residence in the Punjab
+the Zodiacal Light seemed to me constantly visible in the evening sky in
+the spring months. In the west of Ireland I have seen it nearly as bright
+as the brightest portions of the Milky Way visible in this country
+(February 20, 1890). The "meteoric theory" of the "light" seems to be the
+one now generally accepted by astronomers, and in this opinion I fully
+concur.
+
+From observations made in Jamaica in the years 1899 and 1901, Mr. Maxwell
+Hall arrived at the conclusion that "the Zodiacal Light is caused by
+reflection of sunlight from masses of meteoric matter still contained in
+the invariable plane, which may be considered the original plane of the
+solar system."[262] According to Humboldt, Cassini believed that the
+Zodiacal Light "consisted of innumerably small planetary bodies revolving
+round the sun."[263]
+
+THE GEGENSCHEIN, or COUNTER-GLOW.--This is a faint patch of light seen
+opposite the sun's place in the sky, that is on the meridian at midnight.
+It is usually elliptical in shape, with its longer axis lying nearly in
+the plane of the ecliptic. It seems to have been first detected by Brorsen
+(the discoverer of the short-period comet of 1846) about the middle of
+the nineteenth century. But it is not easy to see, for the famous Heis of
+M�nster, who had very keen eyesight, did not succeed in seeing it for
+several years after Brorsen's announcement.[264] It was afterwards
+independently discovered by Backhouse, and Barnard.
+
+Prof. Barnard's earlier observations seemed to show that the Gegenschein
+does not lie exactly opposite to the sun, but very nearly so. He found its
+longitude is within one degree of 180�, and its latitude about 1��3 north
+of the ecliptic.[265] But from subsequent observations he came to the
+conclusion that the differences in longitude and apparent latitude are due
+to atmospheric absorption, and that the object really lies in the ecliptic
+and _exactly_ opposite to the sun.[266]
+
+Barnard finds that the Gegenschein is not so faint as is generally
+supposed. He says "it is best seen by averted vision, the face being
+turned 60� or 70� to the right or left, and the eyes alone turned towards
+it." It is invisible in June and December, while in September it is round,
+with a diameter of 20�, and very distinct. No satisfactory theory has yet
+been advanced to account for this curious phenomenon. Prof. Arthur Searle
+of Harvard attributes it to a number of asteroids too small to be seen
+individually. When in "opposition" to the sun these would be fully
+illuminated and nearest to the earth. Its distance from the earth probably
+exceeds that of the moon. Dr. Johnson Stoney thinks that the Gegenschein
+may possibly be due to a "tail" of hydrogen and helium gases repelled from
+the earth by solar action; this "tail" being visible to us by reflected
+sunlight.
+
+It was observed under favourable circumstances in January and February,
+1903, by the French astronomer, M. F. Qu�nisset. He found that it was
+better seen when the atmosphere was less clear, contrary to his experience
+of the Zodiacal Light. Prof. Barnard's experience confirms this. M.
+Qu�nisset notes that--as in the case of the Zodiacal Light--the southern
+border of the Gegenschein is sharper than the northern. He found that its
+brightness is less than that of the Milky Way between Betelgeuse and
+[Greek: g] Geminorum; and thinks that it is merely a strengthening of the
+Zodiacal Light.[267]
+
+A meteoritic theory of the Gegenschein has been advanced by Prof. F. R.
+Moulton, which explains it by light reflected from a swarm of meteorites
+revolving round the sun at a distance of 930,240 miles outside the earth's
+orbit.
+
+Both the Zodiacal Light and Gegenschein were observed by Herr Leo Brenner
+on the evening of March 4, 1896. He found the Zodiacal Light on this
+evening to be "_perhaps eight times brighter_ than the Milky Way in
+Perseus." The "_Gegenschein distinctly visible_ as a round, bright,
+cloud-like nebula below Leo (Virgo), and about twice the brightness of the
+Milky Way in Monoceros between Canis Major and Canis Minor."[268]
+
+Humboldt thought that the fluctuations in the brilliancy of the Zodiacal
+Light were probably due to a real variation in the intensity of the
+phenomenon rather than to the elevated position of the observer.[269] He
+says that he was "astonished in the tropical climates of South America, to
+observe the variable intensity of the light."
+
+
+
+
+CHAPTER XIV
+
+The Stars
+
+
+Pliny says that Hipparchus "ventured to count the stars, a work arduous
+even for the Deity." But this was quite a mistaken idea. Those visible to
+the naked eye are comparatively few in number, and the enumeration of
+those visible in an opera-glass--which of course far exceed those which
+can be seen by unaided vision--is a matter of no great difficulty. Those
+visible in a small telescope of 2-3/4 inches aperture have all been
+observed and catalogued; and even those shown on photographs taken with
+large telescopes can be easily counted. The present writer has made an
+attempt in this direction, and taking an average of a large number of
+counts in various parts of the sky, as shown on stellar photographs, he
+finds a total of about 64 millions for the whole sky in both
+hemispheres.[270] Probably the total number will not exceed 100 millions.
+But this is a comparatively small number, even when compared with the
+human population of our little globe.
+
+With reference to the charts made by photography in the International
+scheme commenced some years ago, it has now been estimated that the charts
+will probably contain a total of about 9,854,000 stars down to about the
+14th magnitude (13�7). The "catalogue plates" (taken with a shorter
+exposure) will, it is expected, include about 2,676,500 stars down to
+11-1/2 magnitude. These numbers may, however, be somewhat increased when
+the work has been completed.[271] If this estimate proves to be correct,
+the number of stars visible down to the 14th magnitude will be
+considerably less than former estimates have made it.
+
+Prof. E. C. Pickering estimates that the total number of stars visible on
+photographs down to the 16th magnitude (about the faintest visible in the
+great Lick telescope) will be about 50 millions.[272] In the present
+writer's enumeration, above referred to, many stars fainter than the 16th
+magnitude were included.
+
+Admiral Smyth says, with reference to Sir William Herschel--perhaps the
+greatest observer that ever lived--"As to Sir William himself, he could
+unhesitatingly call every star down to the 6th magnitude, by its name,
+letter, or number."[273] This shows great powers of observation, and a
+wonderful memory.
+
+On a photographic plate of the Pleiades taken with the Bruce telescope and
+an exposure of 6 hours, Prof. Bailey of Harvard has counted "3972 stars
+within an area 2� square, having Alcyone at its centre."[274] This would
+give a total of about 41 millions for the whole sky, if of the same
+richness.
+
+With an exposure of 16 hours, Prof. H. C. Wilson finds on an area of less
+that 110' square a total of 4621 stars. He thinks, "That all of these
+stars belong to the Pleiades group is not at all probable. The great
+majority of them probably lie at immense distances beyond the group, and
+simply appear in it by projection."[274] He adds, "It has been found,
+however, by very careful measurements made during the last 75 years at the
+K�nigsbergh and Yale Observatories, that of the sixty-nine brighter stars,
+including those down to the 9th magnitude, only eight show any certain
+movement with reference to Alcyone. Since Alcyone has a proper motion or
+drift of 6" per century, this means that all the brightest stars except
+the eight mentioned are drifting with Alcyone and so form a true cluster,
+at approximately the same distance from the earth. Six of the eight stars
+which show relative drift are moving in the opposite direction to the
+movement of Alcyone, and at nearly the same rate, so that their motion is
+only apparent. They are really stationary, while Alcyone and the rest of
+the cluster are moving past them."[275] This tends to show that the faint
+stars are really _behind_ the cluster, and are unconnected with it.
+
+It is a popular idea with some people that the Pole Star is the nearest of
+all the stars to the celestial pole. But photographs show that there are
+many faint stars nearer to the pole than the Pole Star. The Pole Star is
+at present at a distance of 1� 13' from the real pole of the heavens, but
+it is slowly approaching it. The minimum distance will be reached in the
+year 2104. From photographs taken by M. Flammarion at the Juvisy
+Observatory, he finds that there are at least 128 stars nearer to the pole
+than the Pole Star! The nearest star to the pole was, in the year 1902, a
+small star of about 12-1/2 magnitude, which was distant about 4 minutes of
+arc from the pole.[276] The estimated magnitude shows that the Pole Star
+is nearly 10,000 times brighter than this faint star!
+
+It has been found that Sirius is bright enough to cast a shadow under
+favourable conditions. On March 22, 1903, the distinguished French
+astronomer Touchet succeeded in photographing the shadow of a brooch cast
+by this brilliant star. The exposure was 1{h} 5{m}.
+
+Martinus Hortensius seems to have been the first to see stars in daylight,
+perhaps early in the seventeenth century. He mentions the fact in a letter
+to Gassendi dated October 12, 1636, but does not give the date of his
+observation. Schickard saw Arcturus in broad daylight early in 1632. Morin
+saw the same bright star half an hour after sunset in March, 1635.
+
+Some interesting observations were made by Professors Payne and H. C.
+Wilson, in the summer of 1904, at Midvale, Montana (U.S.A.), at a height
+of 4790 feet above sea-level. At this height they found the air very clear
+and transparent. "Many more stars were visible at a glance, and the
+familiar stars appeared more brilliant.... In the great bright cloud of
+the Milky Way, between [Greek: b] and [Greek: g] Cygni, one could count
+easily sixteen or seventeen stars, besides the bright ones [Greek: �] and
+[Greek: ch],[277] while at Northfield it is difficult to distinctly see
+eight or nine with the naked eye." Some nebul� and star fields were
+photographed with good results by the aid of a 2-1/2-inch Darlot lens and
+3 hours' exposure.[278]
+
+Prof. Barnard has taken some good stellar photographs with a lens of only
+1-1/2 inches in diameter, and 4 or 5 inches focus belonging to an
+ordinary "magic lantern"! He says that these "photographs with the small
+lens show us in the most striking manner how the most valuable and
+important information may be obtained with the simplest means."[279]
+
+With reference to the rising and setting of the stars due to the earth's
+rotation on its axis, the late Sir George B. Airy, Astronomer Royal of
+England, once said to a schoolmaster, "I should like to know how far your
+pupils go into the first practical points for which reading is scarcely
+necessary. Do they know that the stars rise and set? Very few people in
+England know it. I once had a correspondence with a literary man of the
+highest rank on a point of Greek astronomy, and found that he did not know
+it!"[280]
+
+Admiral Smyth says, "I have been struck with the beautiful blue tint of
+the smallest stars visible in my telescope. This, however, may be
+attributed to some optical peculiarity." This bluish colour of small stars
+agrees with the conclusion arrived at by Prof. Pickering in recent years,
+that the majority of faint stars in the Milky Way have spectra of the
+Sirian type and, like that brilliant star, are of a bluish white colour.
+Sir William Herschel saw many stars of a redder tinge than other observers
+have noticed. Admiral Smyth says, "This may be owing to the effect of his
+metallic mirror or to some peculiarity of vision, or perhaps both."[281]
+
+The ancient astronomers do not mention any coloured stars except white and
+red. Among the latter they only speak of Arcturus, Aldebaran, Pollux,
+Antares, and Betelgeuse as of a striking red colour. To these Al-Sufi adds
+Alphard ([Greek: a] Hydr�).
+
+Sir William Herschel remarked that no decidedly green or blue star "has
+ever been noticed unassociated with a companion brighter than itself." An
+exception to Herschel's rule seems to be found in the case of the star
+[Greek: b] Libr�, which Admiral Smyth called "pale emerald." Mr. George
+Knott observed it on May 19, 1852, as "beautiful pale green" (3�7 inches
+achromatic, power 80), and on May 9, 1872, as "fine pale green" (5�5
+inches achromatic, power 65).
+
+The motion of stars in the line of sight, as shown by the
+spectroscope--should theoretically alter their brightness in the course of
+time; those approaching the earth becoming gradually brighter, while those
+receding should become fainter. But the distance of the stars is so
+enormous that even with very high velocities the change would not become
+perceptible for ages. Prof. Oudemans found that to change the brightness
+of a star by only one-tenth of a magnitude--a quantity barely perceptible
+to the eye-a number of years would be necessary, which is represented by
+the formula
+
+      5916 years
+  -----------------
+  parallax � motion
+
+for a star approaching the earth, and for a receding star
+
+  6195 years
+  ----------
+    p � m
+
+This is in geographical miles, 1 geographical mile being equal to 4�61
+English miles.
+
+Reducing the above to English miles, and taking an average for both
+approaching and receding stars, we have
+
+  27,660 years
+  ------------
+     p � m
+
+where p = parallax in seconds of arc, and m = radial velocity in English
+miles per second.
+
+Prof. Oudemans found that the only star which could have changed in
+brightness by one-tenth of a magnitude since the time of Hipparchus is
+Aldebaran. This is taking its parallax as 0"�52. But assuming the more
+reliable parallax 0"�12 found by Dr. Elkin, this period is 4-1/3 times
+longer. For Procyon, the period would be 5500 years.[282] The above
+calculation shows how absurd it is to suppose that any star could have
+gained or lost in brightness by motion in the line of sight during
+historical times. The "secular variation" of stars is quite another
+thing. This is due to physical changes in the stars themselves.
+
+The famous astronomer Halley, the second Astronomer Royal at Greenwich,
+says (_Phil. Trans._, 1796), "Supposing the number of 1st magnitude stars
+to be 13, at twice the distance from the sun there may be placed four
+times as many, or 52; which with the same allowance would nearly represent
+the star we find to be of the 2nd magnitude. So 9 � 13, or 117, for those
+at three times the distance; and at ten times the distance 100 � 13, or
+1300 stars; of which distance may probably diminish the light of any of
+the stars of the 1st magnitude to that of the 6th, it being but the
+hundredth part of what, at their present distance, they appear with." This
+agrees with the now generally accepted "light ratio" of 2�512 for each
+magnitude, which makes a first magnitude star 100 times the light of a 6th
+magnitude.
+
+On the 4th of March, 1796,[283] the famous French astronomer Lalande
+observed on the meridian a star of small 6th magnitude, the exact position
+of which he determined. On the 15th of the same month he again observed
+the star, and the places found for 1800 refer to numbers 16292-3 of the
+reduced catalogue. In the observation of March 4 he attached the curious
+remark, "�toile singuli�re" (the observation of March 15 is without
+note). This remark of Lalande has puzzled observers who failed to find any
+peculiarity about the star. Indeed, "the remark is a strange one for the
+observer of so many thousands of stars to attach unless there was really
+something singular in the star's aspect at the time." On the evening of
+April 18, 1887, the star was examined by the present writer, and the
+following is the record in his observing book, "Lalande's �toile
+singuli�re (16292-3) about half a magnitude less than [Greek: �] Cancri.
+With the binocular I see two streams of small stars branching out from it,
+north preceding like the tails of comet." This may perhaps have something
+to do with Lalande's curious remark.
+
+The star numbered 1647 in Baily's _Flamsteed Catalogue_ is now known to
+have been an observation of the planet Uranus.[284]
+
+Prof. Pickering states that the fainter stars photographed with the 8-inch
+telescope at Cambridge (U.S.A.) are invisible to the eye in the 15-inch
+telescope.[285]
+
+Sir Norman Lockyer finds that the lines of sulphur are present in the
+spectrum of the bright star Rigel ([Greek: b] Orionis).[286]
+
+About 8-1/2� south of the bright star Regulus ([Greek: a] Leonis) is a
+faint nebula (H I, 4 Sextantis). On or near this spot the Capuchin monk De
+Rheita fancied he saw, in the year 1643, a group of stars representing
+the napkin of S. Veronica--"sudarium Veronic� sive faciem Domini maxima
+similitudina in astris expressum." And he gave a picture of the napkin and
+star group. But all subsequent observers have failed to find any trace of
+the star group referred to by De Rheita![287]
+
+The Bible story of the star of the Magi is also told in connection with
+the birth of the sun-gods Osiris, Horus, Mithra, Serapis, etc.[288] The
+present writer has also heard it suggested that the phenomenon may have
+been an apparition of Halley's comet! But as this famous comet is known to
+have appeared in the year B.C. 11, and as the date of the Nativity was
+probably not earlier than B.C. 5, the hypothesis seems for this (and other
+reasons) to be inadmissible. It has also been suggested that the
+phenomenon might have been an appearance of Tycho Brah�'s temporary star
+of 1572, known as the "Pilgrim star"; but there seems to be no real
+foundation for such an hypothesis. There is no reason to think that
+"temporary" or new stars ever appear a second time.
+
+Admiral Smyth has well said, "It checks one's pride to recollect that if
+our sun with the whole system of planets, asteroids, and moons, and comets
+were to be removed from the spectator to the distance of the nearest
+fixed star, not one of them would be visible, except the sun, which would
+then appear but as a star of perhaps the 2nd magnitude. Nay, more, were
+the whole system of which our globe forms an insignificant member, with
+its central luminary, suddenly annihilated, no effect would be produced on
+those unconnected and remote bodies; and the only annunciation of such a
+catastrophe in the Sidereal "Times" would be that a small star once seen
+in a distant quarter of the sky had ceased to shine."[289]
+
+Prof. George C. Comstock finds that the average parallax of 67 selected
+stars ranging in brightness between the 9th and the 12th magnitude, is of
+the value of 0"�0051.[290] This gives a distance representing a journey
+for light of about 639 years!
+
+Mr. Henry Norris Russell thinks that nearly all the bright stars in the
+constellation of Orion are practically at the same distance from the
+earth. His reasons for this opinion are: (1) the stars are similar in
+their spectra and proper motions, (2) their proper motions are small,
+which suggests a small parallax, and therefore a great distance from the
+earth. Mr. Russell thinks that the average parallax of these stars may
+perhaps be 0"�005, which gives a distance of about 650 "light
+years."[291]
+
+According to Sir Norman Lockyer's classification of the stars, the order
+of _increasing_ temperature is represented by the following, beginning
+with those in the earliest stage of stellar evolution:--Nebul�, Antares,
+Aldebaran, Polaris, [Greek: a] Cygni, Rigel, [Greek: e] Tauri, [Greek: b]
+Crucis. Then we have the hottest stars represented by [Greek: e] Puppis,
+[Greek: g] Argus, and Alnitam ([Greek: e] Orionis). _Decreasing_
+temperature is represented by (in order), Achernar, Algol, Markab, Sirius,
+Procyon, Arcturus, 19 Piscium, and the "Dark Stars."[292] But other
+astronomers do not agree with this classification. Antares and Aldebaran
+are by some authorities considered to be _cooling_ suns.
+
+According to Ritter's views of the Constitution of the Celestial Bodies,
+if we "divide the stars into three classes according to age corresponding
+to these three stages of development, we shall assign to the first class,
+A, those stars still in the nebular phase of development; to the second
+class, B, those in the transient stage of greatest brilliancy; and to the
+class C, those stars which have already entered into the long period of
+slow extinction. It should be noted in this classification that we refer
+to relative and not absolute age, since a star of slight mass passes
+through the successive phases of its development more rapidly than the
+star of greater mass."[293] Ritter comes to the conclusion that "the
+duration of the period in which the sun as a star had a greater brightness
+than at present was very short in comparison with the period in which it
+had and will continue to have a brightness differing only slightly from
+its present value."[294]
+
+In a valuable and interesting paper on "The Evolution of Solar
+Stars,"[295] Prof. Schuster says that "measurements by E. F. Nichols on
+the heat of Vega and Arcturus indicated a lower temperature for Arcturus,
+and confirms the conclusion arrived at on other grounds, that the hydrogen
+stars have a higher temperature than the solar stars." "An inspection of
+the ultraviolet region of the spectrum gives the same result. These
+different lines of argument, all leading to the same result, justify us in
+saying that the surface temperature of the hydrogen stars is higher than
+that of the solar stars. An extension of the same reasoning leads to the
+belief that the helium stars have a temperature which is higher still."
+Hence we have Schuster, Hale, and Sir William Huggins in agreement that
+the Sirian stars are hotter than the solar stars; and personally I agree
+with these high authorities. The late Dr. W. E. Wilson, however, held the
+opinion that the sun is hotter that Sirius!
+
+Schuster thinks that Lane's law does not apply to the temperature of the
+photosphere and the absorbing layers of the sun and stars, but only to the
+portions between the photosphere and the centre, which probably act like a
+perfect gas. On this view he says the interior might become "hotter and
+hotter until the condensation had reached a point at which the laws of
+gaseous condensation no longer hold."
+
+With reference to the stars having spectra of the 3rd and 4th type
+(usually orange and red in colour), Schuster says--
+
+    "The remaining types of spectra belong to lower temperature still, as
+    in place of metallic lines, or in addition to them, certain bands
+    appear which experiments show us invariably belong to lower
+    temperature than the lines of the same element.
+
+    "If an evolutionary process has been going on, which is similar for
+    all stars, there is little doubt that from the bright-line stars down
+    to the solar stars the order has been (1) helium or _Orion_ stars, (2)
+    hydrogen or Sirian stars, (3) calcium or Procyon stars, (4) solar or
+    Capellan stars."
+
+My investigations on "The Secular Variation of Starlight" (_Studies in
+Astronomy_, chap. 17, and _Astronomical Essays_, chap. 12) based on a
+comparison of Al-Sufi's star magnitudes (tenth century) with modern
+estimates and measures, tend strongly to confirm the above views.
+
+With regard to the 3rd-type stars, such as Betelgeuse and Mira Ceti,
+Schuster says, "It has been already mentioned that observers differ as to
+whether their position is anterior to the hydrogen or posterior to the
+solar stars, and there are valid arguments on both sides."
+
+Scheiner, however, shows, from the behaviour of the lines of magnesium,
+that stars of type I. (Sirian) are the hottest, and type III. the coolest,
+and he says, we have "for the first time a direct proof of the correctness
+of the physical interpretation of Vogel's spectral classes, according to
+which class II. is developed by cooling from I., and III. by a further
+process of cooling from II."[296]
+
+Prof. Hale says that "the resemblance between the spectra of sun-spots and
+of 3rd-type stars is so close as to indicate that the same cause is
+controlling the relative intensities of many lines in both instances. This
+cause, as the laboratory work indicates, is to be regarded as reduced
+temperature."[297]
+
+According to Prof. Schuster, "a spectrum of bright lines may be given by a
+mass of luminous gas, even if the gas is of great thickness. There is,
+therefore, no difficulty in explaining the existence of stars giving
+bright lines." He thinks that the difference between "bright line" stars
+and those showing dark lines depends upon the rate of increase of the
+temperature from the surface towards the centre. If this rate is slow,
+bright lines will be seen. If the rate of increase is rapid, the
+dark-line spectrum shown by the majority of the stars will appear. This
+rate, he thinks, is regulated by the gravitational force. So that in the
+early stages of condensation bright lines are more likely to occur. "If
+the light is not fully absorbed," both bright and dark lines of the same
+element may be visible in the same star. Schuster considers it quite
+possible that if we could remove the outer layers of the Sun's atmosphere,
+we should obtain a spectrum of bright lines.[298]
+
+M. Stratonoff finds that stars having spectra of the Orion and Sirian
+types--supposed to represent an early stage in stellar evolution--tend to
+congregate in or near the Milky Way. Star clusters in general show a
+similar tendency, "but to this law the globular clusters form an
+exception."[299] We may add that the spiral nebul�--which seem to be
+scattered indifferently over all parts of the sky--also seem to form an
+exception; for the spectra of these wonderful objects seem to show that
+they are really star clusters, in which the components are probably
+relatively small; that is, small in comparison with our sun.
+
+If we accept the hypothesis that suns and systems were evolved from
+nebul�, and if we consider the comparatively small number of nebul�
+hitherto discovered in the largest telescopes--about half a million; and
+if we further consider the very small number of red stars, or those having
+spectra of the third and fourth types--usually considered to be dying-out
+suns--we seem led to the conclusion that our sidereal system is now at
+about the zenith of its life-history; comparatively few nebul� being left
+to consolidate into stars, and comparatively few stars having gone far on
+the road to the final extinction of their light.
+
+Prof. Boss of Albany (U.S.A.) finds that about forty stars of magnitudes
+from 3-1/2 to 7 in the constellation Taurus are apparently drifting
+together towards one point. These stars are included between about R.A.
+3{h} 47{m} to 5{h} 4{m}, and Declination + 5� to + 23� (that is, in the
+region surrounding the Hyades). These motions apparently converge to a
+point near R.A. 6{h}, Declination + 7� (near Betelgeuse). Prof. Boss has
+computed the velocity of the stars in this group to be 45�6 kilometres
+(about 28 miles) a second towards the "vanishing point," and he estimated
+the average parallax of the group to be 0"�025--about 130 years' journey
+for light. Although the motions are apparently converging to a point, it
+does not follow that the stars in question will, in the course of ages,
+meet at the "vanishing point." On the contrary, the observed motions show
+that the stars are moving in parallel lines through space. About 15
+kilometres of the observed speed is due to the sun's motion through space
+in the opposite direction. Prof. Campbell finds from spectroscopic
+measures that of these forty stars, nine are receding from the earth with
+velocities varying from 12 to 60 kilometres a second, and twenty-three
+others with less velocities than 38 kilometres.[300] It will be obvious
+that, as there is a "vanishing point," the motion in the line of sight
+must be one of _recession_ from the earth.
+
+It has been found that on an average the parallax of a star is about
+one-seventh of its "proper motion."[301]
+
+Adopting Prof. Newcomb's parallax of 0"�14 for the famous star 1830
+Groombridge, the velocity perpendicular to the line of sight is about 150
+miles a second. The velocity _in_ the line of sight--as shown by the
+spectroscope--is 59 miles a second approaching the earth. Compounding
+these two velocities we find a velocity through space of about 161 miles a
+second!
+
+An eminent American writer puts into the mouth of one of his characters, a
+young astronomer, the following:--
+
+                          "I read the page
+  Where every letter is a glittering sun."
+
+From an examination of the heat radiated by some bright stars, made by
+Dr. E. F. Nicholls in America with a very sensitive radiometer of his own
+construction, he finds that "we do not receive from Arcturus more heat
+than we should from a candle at a distance of 5 or 6 miles."
+
+With reference to the progressive motion of light, and the different times
+taken by light to reach the earth from different stars, Humboldt says,
+"The aspect of the starry heavens presents to us objects of _unequal
+date_. Much has long ceased to exist before the knowledge of its presence
+reaches us; much has been otherwise arranged."[302]
+
+The photographic method of charting the stars, although a great
+improvement on the old system, seems to have its disadvantages. One of
+these is that the star images are liable to disappear from the plates in
+the course of time. The reduction of stellar photograph plates should,
+therefore, be carried out as soon as possible after they are taken. The
+late Dr. Roberts found that on a plate originally containing 364 stars, no
+less than 130 had completely disappeared in 9-1/4 years!
+
+It has been assumed by some writers on astronomy that the faint stars
+visible on photographs of the Pleiades are at practically the same
+distance from the earth as the brighter stars of the cluster, and that
+consequently there must be an enormous difference in actual size between
+the brighter and fainter stars. But there is really no warrant for any
+such assumption. Photographs of the vicinity show that the sky all round
+the Pleiades is equally rich in faint stars. It seems, therefore, more
+reasonable to suppose that most of the faint stars visible in the Pleiades
+are really far behind the cluster in space. For if _all_ the faint stars
+visible on photographs belonged to the cluster, then if we imagine the
+cluster removed, a "hole" would be left in the sky, which is of course
+utterly improbable, and indeed absurd. An examination of the proper
+motions tends to confirm this view of the matter, and indicates that the
+Pleiades cluster is a comparatively small one and simply projected on a
+background of fainter stars.
+
+It has long been suspected that the famous star 61 Cygni, which is a
+double star, forms a binary system--that is, that the two stars composing
+it revolve round their common centre of gravity and move together through
+space. But measures of parallax made by Herman S. Davis and Wilsing seem
+to show a difference of parallax between the two components of about 0�08
+of a second of arc. This difference of parallax implies a distance of
+about 2-1/4 "light years" between the two stars, and "if this is correct,
+the stars are too remote to form a binary system. The proper motions of
+5"�21 and 5"�15 seem to show that they are moving in nearly parallel
+directions; but are probably slowly separating." Mr. Lewis, however,
+thinks that a physical connection probably exists.[303]
+
+Dante speaks of the four bright stars of the Southern Cross as
+emblematical of the four cardinal virtues, Justice, Temperance, Fortitude,
+and Prudence; and he seems to refer to the stars Canopus, Achernar, and
+Foomalhaut under the symbols of Faith, Hope, and Charity. The so-called
+"False Cross" is said to be formed by the stars [Greek: k], [Greek: d],
+[Greek: e], and [Greek: i] of the constellation Argo Navis. But it seems
+to me that a better (although larger) cross is formed by the stars [Greek:
+a] Centauri and [Greek: a], [Greek: b], and [Greek: g] of Triangulum
+Australis.
+
+Mr. Monck has pointed out that the names of the brightest stars seem to be
+arranged alphabetically in order of colour, beginning with red and ending
+with blue. Thus we have Aldebaran, Arcturus, Betelgeuse, Capella, Procyon,
+Regulus, Rigel, Sirius, Spica and Vega. But as the origin of these names
+is different, this must be merely a curious coincidence.[304] And, to my
+eye at least, Betelgeuse is redder than Arcturus.
+
+The poet Longfellow speaks of the--
+
+  "Stars, the thoughts of God in the heavens,"[305]
+
+and Drayton says--
+
+  "The stars to me an everlasting book
+  In that eternal register, the sky."[306]
+
+Observing at a height of 12,540 feet on the Andes, the late Dr. Copeland
+saw Sirius with the naked eye less than 10 minutes before sunset.[307] He
+also saw Jupiter 3{m} 47{s} before sunset; and the following bright
+stars--Canopus, 0{m} 52{s} before sunset; Rigel ([Greek: b] Orionis) 16{m}
+32{s} after sunset; and Procyon 11{m} 28{s} after sunset. From a height of
+12,050 feet at La Paz, Bolivia, he saw with the naked eye in February,
+1883, ten stars in the Pleiades in full moonlight, and seventeen stars in
+the Hyades. He also saw [Greek: s] Tauri double.[308]
+
+Humboldt says, "In whatever point the vault of heaven has been pierced by
+powerful and far-penetrating telescopic instruments, stars or luminous
+nebul� are everywhere discoverable, the former in some cases not exceeding
+the 20th or 24th degree of telescopic magnitude."[309] But this is a
+mistake. No star of even the 20th magnitude has ever been seen by any
+telescope. Even on the best photographic plates it is doubtful that any
+stars much below the 18th magnitude are visible. To show a star of the
+20th magnitude--if such stars exist--would require a telescope of 144
+inches or 12 feet in aperture. To show a star of the 24th magnitude--if
+such there be--an aperture of 33 feet would be necessary![310]
+
+It is a popular idea that stars may be seen in the daytime from the bottom
+of a deep pit or high chimney. But this has often been denied. Humboldt
+says, "While practically engaged in mining operations, I was in the habit,
+during many years, of passing a great portion of the day in mines where I
+could see the sky through deep shafts, yet I never was able to observe a
+star."[311]
+
+Stars may, however, be seen in the daytime with even small telescopes. It
+is said that a telescope of 1 inch aperture will show stars of the 2nd
+magnitude; 2 inches, stars of the 3rd magnitude; and 4 inches, stars of
+the 4th magnitude. But I cannot confirm this from personal observation. It
+may be so, but I have not tried the experiment.
+
+Sir George Darwin says--
+
+    "Human life is too short to permit us to watch the leisurely procedure
+    of cosmical evolution, but the celestial museum contains so many
+    exhibits that it may become possible, by the aid of theory, to piece
+    together, bit by bit, the processes through which stars pass in the
+    course of their evolutions."[312]
+
+The so-called "telluric lines" seen in the solar spectrum, are due to
+water vapour in the earth's atmosphere. As the light of the stars also
+passes through the atmosphere, it is evident that these lines should also
+be visible in the spectra of the stars. This is found to be the case by
+Prof. Campbell, Director of the Lick Observatory, who has observed all the
+principal bands in the spectrum of every star he has examined.[313]
+
+The largest "proper motion" now known is that of a star of the 8-1/2
+magnitude in the southern hemisphere, known as Cordoba Zone V. No. 243.
+Its proper motion is 8�07 seconds of arc per annum, thus exceeding that of
+the famous "runaway star," 1830 Groombridge, which has a proper motion of
+7�05 seconds per annum. This greater motion is, however, only apparent.
+Measures of parallax show that the southern "runaway" is much nearer to us
+than its northern rival, its parallax being 0"�32, while that of
+Groombridge 1830 is only 0"�14. With these data the actual velocity across
+the line of sight can be easily computed. That of the southern star comes
+out 80 miles a second, while that of Groombridge 1830 is 148 miles a
+second. The actual velocity of Arcturus is probably still greater.
+
+The poet Barton has well said--
+
+  "The stars! the stars! go forth at night,
+    Lift up thine eyes on high,
+  And view the countless orbs of light,
+    Which gem the midnight sky.
+  Go forth in silence and alone,
+    This glorious sight to scan,
+  And bid the humbled spirit own
+    The littleness of man."
+
+
+
+
+CHAPTER XV
+
+Double and Binary Stars
+
+
+Prof. R. G. Aitken, the eminent American observer of double stars, finds
+that of all the stars down to the 9th magnitude--about the faintest
+visible in a powerful binocular field-glass--1 in 18, or 1 in 20, on the
+average, are double, with the component stars less than 5 seconds of arc
+apart. This proportion of double stars is not, however, the same for all
+parts of the sky; while in some regions double stars are very scarce, in
+other places the proportion rises to 1 in 8.
+
+For the well-known binary star Castor ([Greek: a] Geminorum), several
+orbits have been computed with periods ranging from 232 years (M�dler) to
+1001 years (Doberck). But Burnham finds that "the orbit is absolutely
+indeterminate at this time, and likely to remain so for another century or
+longer."[314] Both components are spectroscopic binaries, and the system
+is a most interesting one.
+
+The well-known companion of Sirius became invisible in all telescopes in
+the year 1890, owing to its near approach to its brilliant primary. It
+remained invisible until August 20, 1896, when it was again seen by Dr.
+See at the Lowell Observatory.[315] Since then its distance has been
+increasing, and it has been regularly measured. The maximum distance will
+be attained about the year 1922.
+
+The star [Greek: b] Cephei has recently been discovered to be a
+spectroscopic binary with the wonderfully short period of 4{h} 34{m}
+11{s}. The orbital velocity is about 10-1/2 miles a second, and as this
+velocity is not very great, the distance between the components must be
+very small, and possibly the two component bodies are revolving in actual
+contact. The spectrum is of the "Orion type."[316]
+
+According to Slipher the spectroscopic binary [Greek: g] Geminorum has the
+comparatively long period (for a spectroscopic binary) of about 3-1/2
+years. This period is comparable with that of the telescopic binary
+system, [Greek: d] Equulei (period about 5�7 years). The orbit is quite
+eccentric. I have shown elsewhere[317] that [Greek: g] Geminorum has
+probably increased in brightness since the time of Al-Sufi (tenth
+century). Possibly its spectroscopic duplicity may have something to do
+with the variation in its light.
+
+With reference to the spectra of double stars, Mr. Maunder suggests that
+the fact of the companion of a binary star showing a Sirian spectrum while
+the brighter star has a solar spectrum may be explained by supposing that,
+on the theory of fission, "the smaller body when thrown off consisted of
+the lighter elements, the heavier remaining in the principal star. In
+other words, in these cases spectral type depends upon original chemical
+constitution, and not upon the stage of stellar development
+attained."[318]
+
+A curious paradox with reference to binary stars has recently come to
+light. For many years it was almost taken for granted that the brighter
+star of a pair had a larger mass than the fainter component. This was a
+natural conclusion, as both stars are practically at the same distance
+from the earth. But it has been recently found that in some binary stars
+the fainter component has actually the larger mass! Thus, in the binary
+star [Greek: e] Hydr�, the "magnitude" of the component stars are 3 and 6,
+indicating that the brighter star is about 16 times brighter than the
+fainter component. Yet calculations by Lewis show that the fainter star
+has 6 times the mass of the brighter, that is, contains 6 times the
+quantity of matter! In the well-known binary 70 Ophiuchi, Prey finds that
+the fainter star has about 4 times the mass of the brighter! In 85
+Pegasi, the brighter star is about 40 times brighter than its companion,
+while Furner finds that the mass of the fainter star is about 4 times that
+of the brighter! And there are other similar cases. In fact, in these
+remarkable combinations of suns the fainter star is really the "primary,"
+and is, so far as mass is concerned, "the predominant partner." This is a
+curious anomaly, and cannot be well explained in the present state of our
+knowledge of stellar systems. In the case of [Greek: a] Centauri the
+masses of the components are about equal, while the primary star is about
+3 times brighter than the other. But here the discrepancy is
+satisfactorily explained by the difference in character of the spectra,
+the brighter component having a spectrum of the solar type, while the
+fainter seems further advanced on the downward road of evolution, that is,
+more consolidated and having, perhaps, less intrinsic brightness of
+surface.
+
+In the case of Sirius and its faint attendant, the mass of the bright star
+is about twice the mass of the satellite, while its light is about 40,000
+times greater! Here the satellite is either a cooled-down sun or perhaps a
+gaseous nebula. There seems to be no other explanation of this curious
+paradox. The same remark applies to Procyon, where the bright star is
+about 100,000 times brighter than its faint companion, although its mass
+is only 5 times greater.
+
+The bright star Capella forms a curious anomaly or paradox. Spectroscopic
+observations show that it is a very close binary pair. It has been seen
+"elongated" at the Greenwich Observatory with the great 28-inch
+refractor--the work of Sir Howard Grubb--and the spectroscopic and visual
+measurements agree in indicating that its mass is about 18 times the mass
+of the sun. But its parallax (about 0"�08) shows that it is about 128
+times brighter than the sun! This great brilliancy is inconsistent with
+the star's computed mass, which would indicate a much smaller brightness.
+The sun placed at the distance of Capella would, I find, shine as a star
+of about 5-1/2 magnitude, while Capella is one of the brightest stars in
+the sky. As the spectrum of Capella's light closely resembles the solar
+spectrum, we seem justified in assuming that the two bodies have pretty
+much the same physical composition. The discrepancy between the computed
+and actual brightness of the star cannot be explained satisfactorily, and
+the star remains an astronomical enigma.
+
+Three remarkable double-star systems have been discovered by Dr. See in
+the southern hemisphere. The first of these is the bright star [Greek: a]
+Phoenicis, of which the magnitude is 2�4, or only very slightly fainter
+than the Pole Star. It is attended by a faint star of the 13th magnitude
+at a distance of less than 10 seconds (1897). The bright star is of a
+deep orange or reddish colour, and the great difference in brightness
+between the component stars "renders the system both striking and
+difficult." The second is [Greek: m] Velorum, a star of the 3rd magnitude,
+which has a companion of the 11th magnitude, and only 2-1/2" from its
+bright primary (1897). Dr. See describes this pair as "one of the most
+extraordinary in the heavens." The third is [Greek: �] Centauri, of 2-1/2
+magnitude, with a companion of 13-1/2 magnitude at a distance of 5"�65
+(1897); colours yellow and purple. This pair is "extremely difficult,
+requiring a powerful telescope to see it." Dr. See thinks that these three
+objects "may be regarded as amongst the most splendid in the heavens."
+
+The following notes are from Burnham's recently published _General
+Catalogue of Double Stars_.
+
+The Pole Star has a well-known companion of about the 9th magnitude, which
+is a favourite object for small telescopes. Burnham finds that the bright
+star and its faint companion are "relatively fixed," and are probably only
+an "optical pair." Some other companions have been suspected by amateur
+observers, but Burnham finds that "there is nothing nearer" than the known
+companion within the reach of the great 36-inch telescope of the Lick
+Observatory (_Cat._, p. 299).
+
+The well-known companion to the bright star Rigel ([Greek: b] Orionis)
+has been suspected for many years to be a close double star. Burnham
+concludes that it is really a binary star, and its "period may be shorter
+than that of any known pair" (_Cat._, p. 411).
+
+Burnham finds that the four brighter stars in the trapezium in the great
+Orion nebula (in the "sword") are relatively fixed (_Cat._, p. 426).
+
+[Greek: g] Leonis. This double star was for many years considered to be a
+binary, but Burnham has shown that all the measures may be satisfactorily
+represented by a straight line, and that consequently the pair merely
+forms an "optical double."
+
+42 Com� Berenices. This is a binary star of which the orbit plane passes
+nearly through the earth. The period is about 25-1/2 years, and Burnham
+says the orbit "is as accurately known as that of any known binary."
+
+[Greek: s] Coron� Borealis. Burnham says that the orbits hitherto
+computed--with periods ranging from 195 years (Jacob) to 846 years
+(Doberck) are "mere guess work," and it will require the measures of at
+least another century, and perhaps a much longer time, to give an
+approximate period (_Cat._, p. 209). So here is some work left for
+posterity to do in this field.
+
+70 Ophiuchi. With reference to this well-known binary star, Burnham says,
+"the elements of the orbit are very accurately known." The periods
+computed range from 86�66 years (Doolittle) to 98�15 years (Powell). The
+present writer found a period of 87�84 years, which cannot be far from the
+truth. Burnham found 87�75 years (_Cat._, p. 774). In this case there is
+not much left for posterity to accomplish.
+
+61 Cygni. With reference to this famous star Burnham says, "So far the
+relative motion is practically rectilinear. If the companion is moving in
+a curved path, it will require the measures of at least another
+half-century to make this certain. The deviation of the measured positions
+during the last 70 years from a right line are less than the average
+errors of the observations."
+
+Burnham once saw a faint companion to Sirius of the 16th magnitude, and
+measured its position with reference to the bright star (280��6: 40"�25:
+1899�86). But he afterwards found that it was "not a real object but a
+reflection from Sirius" (in the eye-piece). Such false images are called
+"ghosts."
+
+With reference to the well-known double (or rather quadruple) star [Greek:
+e] Lyr�, near Vega, and supposed faint stars near it, Burnham says, "From
+time to time various small stars in the vicinity have been mapped, and
+much time wasted in looking for and speculating about objects which only
+exist in the imagination of the observer." He believes that many of these
+faint stars, supposed to have been seen by various observers, are merely
+"ghosts produced by reflection."
+
+The binary star [Greek: z] Bo�tis, which has long been suspected of small
+and irregular variation of light, showed remarkable spectral changes in
+the year 1905,[319] somewhat similar to those of a _nova_, or temporary
+star. It is curious that such changes should occur in a star having an
+ordinary Sirian type of spectrum!
+
+A curious quadruple system has been discovered by Mr. R. T. A. Innes in
+the southern hemisphere. The star [Greek: k] Toucani is a binary star with
+components of magnitudes 5 and 7�7, and a period of revolution of perhaps
+about 1000 years. Within 6' of this pair is another star (Lacaille 353),
+which is also a binary, with a period of perhaps 72 years. Both pairs have
+the same proper motion through space, and evidently form a vast quadruple
+system; for which Mr. Innes finds a possible period of 300,000 years.[320]
+
+It is a curious fact that the performance of a really good refracting
+telescope actually exceeds what theory would indicate! at least so far as
+double stars are concerned. For example, the famous double-star observer
+Dawes found that the distance between the components of a double star
+which can just be divided, is found by dividing 4"�56 by the aperture of
+the object-glass in inches. Now theory gives 5"�52 divided by the
+aperture. "The actual telescope--if a really good one--thus exceeds its
+theoretical requirements. The difference between theory and practice in
+this case seems to be due to the fact that in the 'spurious' star disc
+shown by good telescopes, the illumination at the edges of the star disc
+is very feeble, so that its full size is not seen except in the case of a
+very bright star."[321]
+
+
+
+
+CHAPTER XVI
+
+Variable Stars
+
+
+In that interesting work _A Cycle of Celestial Objects_, Admiral Smyth
+says (p. 275), "Geminiano Montanari, as far back as 1670, was so struck
+with the celestial changes, that he projected a work to be intituled the
+_Instabilities of the Firmament_, hoping to show such alterations as would
+be sufficient to make even Aristotle--were he alive--reverse his opinion
+on the incorruptibility of the spangled sky: 'There are now wanting in the
+heavens,' said he, 'two stars of the 2nd magnitude in the stem and yard of
+the ship Argo. I and others observed them in the year 1664, upon occasion
+of the comet that appeared in that year. When they first disappeared I
+know not; only I am sure that on April 10, 1668, there was not the least
+glimpse of them to be seen.'" Smyth adds, "Startling as this account
+is--and I am even disposed to question the fact--it must be recollected
+that Montanari was a man of integrity, and well versed in the theory and
+practice of astronomy; and his account of the wonder will be found--in
+good set Latin--in page 2202 of the _Philosophical Transactions_ for
+1671."
+
+There must be, I think--as Smyth suggests--some mistake in Montanari's
+observations, for it is quite certain that of the stars mentioned by
+Ptolemy (second century A.D.) there is no star of the 2nd magnitude now
+missing. It is true that Al-Sufi (tenth century) mentions a star of the
+_third_ magnitude mentioned by Ptolemy in the constellation of the Centaur
+(about 2� east of the star [Greek: e] Centauri) which he could not find.
+But this has nothing to do with Montanari's stars. Montanari's words are
+very clear. He says, "_Desunt in Coelo du� stell�_ Secund� Magnitudinis
+_in_ Puppi Navis _ejusve Transtris_ Bayero [Greek: b] et [Greek: g],
+_prope_ Canem Majoris, _� me et aliis, occasione pr�sertim Comet�_ A. 1664
+_observat� et recognit�. Earum Disparitionem_ cui Anno debeam, non novi;
+_hoc indubium, quod � die_ 10 April, 1668, _ne_ vestigium quidem _illarum
+adesse amplius observe; c�teris circa eas etium quart� et quint�
+magnitudinis, immotis._" So the puzzle remains unsolved.
+
+Sir William Herschel thought that "of all stars which are singly visible,
+about one in thirty are undergoing an observable change."[322] Now taking
+the number of stars visible to the naked eye at 6000, this would give
+about 200 variable stars visible at maximum to the unaided vision. But
+this estimate seems too high. Taking all the stars visible in the largest
+telescopes--possibly about 100 millions--the proportion of variable stars
+will probably be much smaller still.
+
+The theory that the variation of light in the variable stars of the Algol
+type is due to a partial eclipse by a companion star (not necessarily a
+dark body) is now well established by the spectroscope, and is accepted by
+all astronomers. The late Miss Clarke has well said "to argue this point
+would be _enforcer une porte ouverte_."
+
+According to Dr. A. W. Roberts, the components of the following "Algol
+variables" "revolve in contact": V Puppis, X Carin�, [Greek: b] Lyr�, and
+[Greek: u] Pegasi. Of those V Puppis and [Greek: b] Lyr� are known
+spectroscopic binaries. The others are beyond the reach of the
+spectroscope, owing to their faintness.
+
+A very curious variable star of the Algol type is that known as R R
+Draconis. Its normal magnitude is 10, but at minimum it becomes invisible
+in a 7-1/2-inch refracting telescope. The variation must, therefore, be
+over 3 magnitudes, that is, at minimum its light must be reduced to about
+one-sixteenth of its normal brightness. The period of variation from
+maximum to minimum is about 2�83 days. The variation of light near minimum
+is extraordinarily rapid, the light decreasing by about 1 magnitude in
+half an hour.[323]
+
+A very remarkable variable star has been recently discovered in the
+constellation Auriga. Prof. Hartwig found it of the 9th magnitude on March
+6, 1908, the star "having increased four magnitudes in one day, whilst
+within eight days it was less than the 14th magnitude."[324] In other
+words its light increased at least one-hundredfold in eight days!
+
+The period of the well-known variable star [Greek: b] Lyr� seems to be
+slowly increasing. This Dr. Roberts (of South Africa) considers to be due
+to the component stars slowly receding from each other. He finds that "a
+very slight increase of one-thousandth part of the radius of the orbit
+would account for the augmentation in time, 30{m} in a century." According
+to the theory of stellar evolution the lengthening of the period of
+revolution of a binary star would be due to the "drag" caused by the tides
+formed by each component on the other.[325]
+
+M. Sebastian Albrecht finds that in the short-period variable star known
+as T Vulpecul� (and other variables of this class, such as Y Ophiuchi),
+there can be no eclipse to explain the variation of light (as in the case
+of Algol). The star is a spectroscopic binary, it is true, but the
+maximum of light coincides with the greatest velocity of _approach_ in
+the line of sight, and the minimum with the greatest velocity of
+_recession_. Thus the light curve and the spectroscopic velocity curve are
+very similar in shape, but one is like the other turned upside down. "That
+is, the two curves have a very close correspondence in phase in addition
+to correspondence of shape and period."[326]
+
+The star now known as W Urs� Majoris (the variability of which was
+discovered by M�ller and Kempf in 1902), and which lies between the stars
+[Greek: th] and [Greek: u] of that constellation, has the marvellously
+short period of 4 hours (from maximum to maximum). Messrs. Jordan and
+Parkhurst (U.S.A.), find from photographic plates that the star varies
+from 7�24 to 8�17 magnitude.[327] The light at maximum is, therefore, more
+than double the light at minimum. A sun which loses more than half its
+light and recovers it again in the short period of 4 hours is certainly a
+curious and wonderful object.
+
+In contrast with the above, the same astronomers have discovered a star in
+Perseus which seems to vary from about the 6th to the 7th magnitude in the
+very long period of 7-1/2 years! It is now known as X Persei, and its
+position for 1900 is R.A. 3{h} 49{m} 8{s}, Dec. N. 30� 46', or about one
+degree south-east of the star [Greek: z] Persei. It seems to be a
+variable of the Algol type, as the star remained constant in light at
+about the 6th magnitude from 1887 to 1891. It then began to fade, and on
+December 1, 1897, it was reduced to about the 7th magnitude.
+
+On the night of August 20, 1886, Prof. Colbert, of Chicago, noticed that
+the star [Greek: z] Cassiopei� increased in brightness "by quite half a
+magnitude, and about half an hour afterwards began to return to its normal
+magnitude."[328] This curious outburst of light in a star usually constant
+in brightness is (if true) a very unusual phenomenon. But a somewhat
+similar fluctuation of light is recorded by the famous German astronomer
+Heis. On September 26, 1850, he noted that the star "[Greek: z] Lyr�
+became, for a moment, _very bright_, and then again faint." (The words in
+his original observing book are: "[Greek: z] Lyr� wurde einen _Moment sehr
+hell_ und hierauf wieder dunkel.") As Heis was a remarkably accurate
+observer of star brightness, the above remark deserves the highest
+confidence.[329]
+
+The variable star known as the V Delphini was found to be invisible in the
+great 40-inch telescope of the Yerkes Observatory on July 20, 1900. Its
+magnitude was, therefore, below the 17th. At its maximum brightness it is
+about 7-1/2, or easily visible in an ordinary opera-glass, so that its
+range of variation is nearly, or quite, ten magnitudes. That is, its light
+at maximum is about 10,000 times its light at minimum. That a sun should
+vary in light to this enormous extent is certainly a wonderful fact. A
+variable discovered by Ceraski (and numbered 7579 in Chandlers' Catalogue)
+"had passed below the limit of the 40-inch in June, 1900, and was,
+therefore, not brighter than 17 mag."[330]
+
+The late Sir C. E. Peck and his assistant, Mr. Grover, made many valuable
+observations of variable stars at the Rousden Observatory during many
+years past. Among other interesting things noted, Peck sometimes saw faint
+stars in the field of view of his telescope which were at other times
+invisible for many months, and he suggested that these are faint variable
+stars with a range of brightness from the 13th to the 20th magnitude. He
+adds, "Here there is a practically unemployed field for the largest
+telescopes." Considering the enormous number of faint stars visible on
+stellar photographs the number of undiscovered variable stars must be very
+large.
+
+Admiral Smyth describes a small star near [Greek: b] Leonis, about 5'
+distant, of about 8th magnitude, and dull red. In 1864 Mr. Knott measured
+a faint star close to Smyth's position, but estimated it only 11�6
+magnitude. The Admiral's star would thereupon seem to be variable.[331]
+
+The famous variable star [Greek: �] Argus, which Sir John Herschel, when
+at the Cape of Good Hope in 1838, saw involved in dense nebulosity, was in
+April, 1869, "seen on the bare sky," with the great Melbourne telescope,
+"the nebula having disappeared for some distance round it." Other changes
+were noticed in this remarkable nebula. The Melbourne observers saw "three
+times as many stars as were seen by Herschel." But of course their
+telescope is much larger--48 inches aperture, compared with Herschel's 20
+inches.
+
+Prof. E. C. Pickering thinks that the fluctuations of light of the
+well-known variable star R Coron� (in the Northern Crown), "are unlike
+those of any known variable." This very curious object--one of the most
+curious in the heavens--sometimes remains for many months almost constant
+in brightness (just visible to the naked eye), and then rapidly fades in
+light by several magnitudes! Thus its changes of light in April and May,
+1905, were as follows:--
+
+  1905, April 1   6�0 magnitude
+          "  11   7�3     "
+          "  12   8�4     "
+         May  1  11�4     "
+          "   7  12�5     "
+
+Thus between April 1 and May 1, its light was reduced by over 5
+magnitudes. In other words, the light of the star on May 1 was reduced to
+less than one-hundredth of its light on April 1. If our sun were to
+behave in this way nearly all life would soon be destroyed on the face of
+the earth.
+
+M. H. E. Lau finds that the short-period variable star [Greek: d] Cephei
+varies slightly in colour as well as in light, and that the colour curve
+is parallel to the light curve. Near the minimum of light the colour is
+reddish yellow, almost as red as [Greek: z] Cephei; a day later it is pure
+yellow, and of about the same colour as the neighbouring [Greek: e]
+Cephei.[332] But it would not be easy to fully establish such slight
+variations of tint.
+
+A remarkably bright maximum of the famous variable Mira Ceti occurred in
+1906. In December of that year it was fully 2nd magnitude. The present
+writer estimated it 1�8, or nearly equal to the brightest on record--1�7
+observed by Sir William Herschel and Wargentin in the year 1779. From
+photographs of the spectrum taken by Mr. Slipher at the Lowell Observatory
+in 1907, he finds strong indications of the presence of the rather rare
+element vanadium in the star's surroundings. Prof. Campbell finds with the
+Mills spectrograph attached to the great 36-inch telescope of the Lick
+Observatory that Mira is receding from the earth at the apparently
+constant velocity of about 38 miles a second.[333] This, of course, has
+nothing to do with the variation in the star's light. Prof. Campbell
+failed to see any trace of the green line of hydrogen in the star's
+spectrum, while two other lines of the hydrogen series "glowed with
+singular intensity."
+
+Mr. Newall has found evidence of the element titanium in the spectrum of
+Betelgeuse ([Greek: a] Orionis); Mr. Goatcher and Mr. Lunt (of the Cape
+Observatory) find tin in Antares (and Scorpii). If the latter observation
+is confirmed it will be the first time this metal has been found in a
+star's atmosphere.[334]
+
+It is a curious fact that Al-Sufi (tenth century) does not mention the
+star [Greek: e] Aquil�, which lies closely north-west of [Greek: z]
+Aquil�, as it is now quite conspicuous to the naked eye. It was suspected
+of variation by Sir William Herschel. It was first recorded by Tycho Brah�
+about 1590, and he called it 3rd magnitude. Bayer also rated it 3, and
+since his time it has been variously estimated from 3-1/2 to 4. If it was
+anything like its present brightness (4�21 Harvard) in the tenth century
+it seems difficult to explain how it could have escaped Al-Sufi's careful
+scrutiny of the heavens, unless it is variable. Its colour seems reddish
+to me.
+
+Mr. W. T. Lynn has shown--and I think conclusively--that the so-called
+"new star" of A.D. 389 (which is said to have appeared near Altair in the
+Eagle) was really a comet.[335]
+
+Near the place of Tycho Brah�'s great new star of 1572 (the "Pilgrim
+Star"), Hind and W. E. Plummer observed a small star (No. 129 of
+d'Arrest's catalogue of the region) which seemed to show small
+fluctuations of light, which "scarcely include a whole magnitude." This
+may possibly be identical with Tycho Brah�'s wonderful star, and should be
+watched by observers. The place of this small star is (for 1865) R.A. 0{h}
+17{m} 18{s}, N.P.D. 26� 37'�1. The region was examined by Prof. Burnham in
+1890 with the 36-inch telescope of the Lick Observatory. "None of the
+faint stars near the place presented any peculiarity worthy of remark, but
+three double stars were found."[336]
+
+With reference to the famous Nova (T) Coron�--the "Blaze Star" of
+1866--Prof. Barnard finds from careful comparisons with small stars in its
+vicinity that "the Nova is now essentially of the same brightness it was
+before the outburst of 1866 ... there seems to be no indication of motion
+in the _Nova_."
+
+With reference to the cause of "temporary" stars, or _nov�_, as they are
+now called by astronomers--the late Prof. H. C. Vogel said--
+
+    "A direct collision of two celestial bodies is not regarded by Huggins
+    as an admissible explanation of the Nova; a partial collision has
+    little probability, and the most that can be admitted is perhaps the
+    mutual penetration and admixture of the outer gaseous envelopes of
+    the two bodies at the time of their closest approach. A more probable
+    explanation is given by an hypothesis which we owe to Klinkerfues, and
+    which has more recently been further developed by Wilsing, viz. that
+    by the very close passage of two celestial bodies enormous tidal
+    disturbances are produced and thereby changes in the brightness of the
+    bodies. In the case of the two bodies which form the Nova, it must be
+    assumed that these phenomena are displayed in the highest degree of
+    development, and that changes of pressure have been produced which
+    have caused enormous eruptions from the heated interior of the bodies;
+    the eruptions are perhaps accompanied by electrical actions, and are
+    comparable with the outbursts in our own sun, although they are on a
+    much larger scale."[337]
+
+It will be noticed that this hypothesis agrees with the fundamental
+assumption of the "Planetesimal Hypothesis" advocated by Professors
+Chamberlin and Moulton (see my _Astronomical Essays_, p. 324).
+
+The rush of a comparatively small body through a mass of gaseous matter
+seems also a very plausible hypothesis. This idea was originally advanced
+by Prof. Seeliger, and independently by Mr. Monck.
+
+With reference to the nebula which was observed round the great new star
+of 1901--Nova Persei--Prof. Lewis Bell supports the theory of Seeliger,
+which accounts for the apparent movements of the brightest portions of the
+nebula by supposing that the various parts of the highly tenuous matter
+were successively lighted up by the effects of a travelling
+electro-magnetic wavefront, and he shows that this theory agrees well with
+the observed phenomenon.[338] The "collision theory" which explained the
+sudden outburst of light by the meeting of two dark bodies in space, seems
+to be now abandoned by the best astronomers. The rapid cooling down of the
+supposed bodies indicated by the rapid decrease of light is quite
+inconsistent with this hypothesis.
+
+The rapid diminution in the light of some of these "new stars" is very
+remarkable. Thus the new star which suddenly blazed out near the nucleus
+of the great nebula in Andromeda in August, 1885, faded down in 5 months
+from "the limit of visibility to the naked eye to that of a 26-inch
+telescope"! A _large_ body could not cool in this way.
+
+Mr. Harold K. Palmer thinks that the "complete and astonishingly rapid
+changes of spectral type observed in the case of _Nova Cygni_ and _Nova
+Aurig�_, and likewise those observed in _Nova Norm�_, _Nova Sagittarii_
+and _Nova Persei_, leave little doubt that the masses of these objects are
+small."[339]
+
+No less than 3748 variable stars had been discovered up to May, 1907. Of
+these 2909 were found at Harvard Observatory (U.S.A.) chiefly by means of
+photography.[340]
+
+The star 14. 1904 Cygni has a period of only 3 hours 14 minutes, which is
+the shortest period known for a variable star.
+
+A very interesting discovery has recently been made with reference to the
+star [Greek: m] Herculis. It has been long suspected of variable light
+with a period of 35 or 40 days, or perhaps irregular. Frost and Adams now
+find it to be a spectroscopic binary, and further observations at Harvard
+Observatory show that it is a variable of the Algol (or perhaps [Greek: b]
+Lyr�) type. The Algol variation of light was suggested by MM. Baker and
+Schlesinger. The period seems to be about 2�05 days.[341]
+
+The northern of the two "pointers" in the Plough (so called because they
+nearly point to the Pole Star) is about the 2nd magnitude, as Al-Sufi
+rated it. It was thought to be variable in colour by Klein, Konkoly, and
+Weber; and M. Lau has recently found a period of 50 days with a maximum of
+"jaune rouge�tre" on April 2, 1902.
+
+The famous variable star [Greek: �] Argus did "not exceed the 8th
+magnitude" in February, 1907, according to Mr. Tebbutt.[342] This is the
+faintest ever recorded for this wonderful star.
+
+It is stated in _Knowledge_ (vol. 5, p. 3, January 4, 1884) that the
+temporary star of 1876 (in the constellation of Cygnus) "had long been
+known and catalogued as a telescopic star of the 9th magnitude with
+nothing to distinguish it from the common herd." But this is quite
+erroneous. The star was quite unknown before it was discovered by Schmidt
+at Athens on November 24 of that year. The remark apparently refers to the
+"Blaze Star" of 1866 in Corona Borealis, which _was_ known previously as a
+star of about the 9th magnitude before its sudden outburst on May 12 of
+that year.
+
+This "new star" of 1866--T Coron�, as it is now called--was, with the
+possible exception of Nova Persei (1901), the only example of a _nova_
+which was known to astronomers as a small star previous to the great
+outburst of light. It is the brightest of the _nov�_ still visible. It was
+the first of these interesting objects to be examined with the
+spectroscope. It was observed by Burnham in the years 1904-1906 with the
+great 40-inch telescope of the Yerkes Observatory (U.S.A.). He found its
+colour white, or only slightly tinged with yellow. In August and
+September, 1906, he estimated its magnitude at about 9�3, and "it would
+seem therefore that the Nova is now essentially of the same brightness it
+was before the outburst in 1866." It shows no indication of motion.
+Burnham found no peculiarity about its telescopic image. A small and very
+faint nebula was found by Burnham a little following (that is east of) the
+_nova_.[343]
+
+The following details of the great new star of 1572--the "Pilgrim Star" of
+Tycho Brah�--are given by Delambre.[344] In November, 1572, it was
+brighter than Sirius, Vega, and Jupiter, and almost equal to Venus at its
+brightest. During December it resembled Jupiter in brightness. In January,
+1573, it was fainter and only a little brighter than stars of the 1st
+magnitude. In February and March it was equal to 1st magnitude stars, and
+in April and May was reduced to the 2nd magnitude. In June and July it was
+3rd magnitude; in September of the 4th, and at the end of 1573 it was
+reduced to the 5th magnitude. In February, 1574, it was 6th magnitude, and
+in March of the same year it became invisible to the naked eye.
+
+From this account it will be seen that the decrease in light of this
+curious object was much slower than that of Nova Persei (1901) ("the new
+star of the new century"). This would suggest that it was a much larger
+body.
+
+There were also changes in its colour. When it was of the brightness of
+Venus or Jupiter it shone with a white light. It then became golden, and
+afterwards reddish like Mars, Aldebaran, or Betelgeuse. It afterwards
+became of a livid white colour like Saturn, and this it retained as long
+as it was visible. Tycho Brah� thought that its apparent diameter might
+have been about 3-1/2 minutes of arc, and that it was possibly 361 times
+smaller than the earth(!) But we now know that these estimates were
+probably quite erroneous.
+
+Temporary stars were called by the ancient Chinese "Ke-sing," or guest
+stars.[345]
+
+A temporary star recorded by Ma-tuan-lin (Chinese Annals) in February,
+1578, is described as "a star as large as the sun." But its position is
+not given.[346]
+
+About the middle of September, 1878, Mr. Greely, of Boston (U.S.A.),
+reported to Mr. E. F. Sawyer (the eminent observer of variable stars)
+that, about the middle of August of that year, he had seen the famous
+variable star Mira Ceti of about the 2nd magnitude, although the star did
+not attain its usual maximum until early in October, 1878. Mr. Greely
+stated that several nights after he first saw Mira it had faded to the 4th
+or 5th magnitude. If there was no mistake in this observation (and Sawyer
+could find none) it was quite an unique phenomenon, as nothing of the sort
+has been observed before or since in the history of this famous star. It
+looks as if Mr. Greely had observed a new or "temporary" star near the
+place of Mira Ceti; but as the spot is far from the Milky Way, which is
+the usual seat of such phenomena, this hypothesis seems improbable.
+
+In the so-called Cepheid and Geminid variables of short period, the
+principal characteristics of the light variation are as follows:--
+
+    "1. The light varies without pause.
+
+    "2. The amount of their light variation is usually about 1 magnitude.
+
+    "3. Their periods are short--a few days only.
+
+    "4. They are of a spectral type approximately solar; no Orion, Sirian
+    or Arcturian stars having been found among them.
+
+    "5. They seem to be found in greater numbers in certain parts of the
+    sky, notably in the Milky Way, but exhibit no tendency to form
+    clusters.
+
+    "6. All those stars whose radial velocities have been studied have
+    been found to be binaries whose period of orbital revolution coincides
+    with that of their light change.
+
+    "7. The orbits, so far as determined, are all small, _a_ sin _i_ being
+    2,000,000 kilometres or less.
+
+    "8. Their maximum light synchronizes with their maximum velocity of
+    approach, and minimum light with maximum velocity of recession.
+
+    "9. No case has been found in which the spectrum of more than one
+    component has been bright enough to be recorded in the
+    spectrograms."[347]
+
+It is very difficult to find an hypothesis which will explain
+satisfactorily _all_ these characteristics, and attempts in this direction
+have not proved very successful. Mr. J. C. Duncan suggests the action of
+an absorbing atmosphere surrounding the component stars.
+
+On March 30, 1612, Scheiner saw a star near Jupiter. It was at first equal
+in brightness to Jupiter's satellites. It gradually faded, and on April 8
+of the same year it was only seen with much difficulty in a very clear
+sky. "After that date it was never seen again, although carefully looked
+for under favourable conditions."
+
+An attempted identification of Scheiner's star was made in recent years by
+Winnecke. He found that its position, as indicated by Scheiner, agrees
+with that of the Bonn _Durchmusterung_ star 15�, 2083 (8-1/2 magnitude).
+This star is not a known variable. Winnecke watched it for 17 years, but
+found no variation of light. From Scheiner's recorded observations his
+star seems to have reached the 6th magnitude, which is considerably
+brighter than the _Durchmusterung_ star watched by Winnecke.[348]
+
+With reference to the colours of the stars, the supposed change of colour
+in Sirius from red to white is well known, and will be considered in the
+chapter on the Constellations. The bright star Arcturus has also been
+suspected of variation in colour. About the middle of the nineteenth
+century Dr. Julius Schmidt, of Athens, the well-known observer of variable
+stars, thought it one of the reddest stars in the sky, especially in the
+year 1841, when he found its colour comparable with that of the planet
+Mars.[349] In 1852, however, he was surprised to find it yellow and devoid
+of any reddish tinge; in colour it was lighter than that of Capella. In
+1863, Mr. Jacob Ennis found it "decidedly orange." Ptolemy and Al-Sufi
+called it red.
+
+Mr. Ennis speaks of Capella as "blue" (classing it with Rigel), and
+comparing its colour with that of Vega![350] But the present writer has
+never seen it of this colour. To his eye it seems yellowish or orange. It
+was called red by Ptolemy, El Fergani, and Riccioli; but Al-Sufi says
+nothing about its colour.
+
+Of [Greek: b] Urs� Minoris, Heis, the eminent German astronomer said, "I
+have had frequent opportunities of convincing myself that the colour of
+this star is not always equally red; at times it is more or less yellow,
+at others most decidedly red."[351]
+
+Among double stars there are many cases in which variation of colour has
+been suspected. In some of these the difference in the recorded colour may
+possibly be due to "colour blindness" in some of the observers; but in
+others there seems to be good evidence in favour of a change. The
+following may be mentioned:--
+
+[Greek: �] Cassiopei�. Magnitudes of the components about 4 and 7-1/2.
+Recorded as red and green by Sir John Herschel and South; but yellow and
+orange by Sestini.
+
+[Greek: i] Trianguli. Magnitudes 5-1/2 and 7. Secchi estimated them as
+white or yellow and blue; but Webb called them yellow and green (1862).
+
+[Greek: g] Leonis, 2 and 3-1/2. Sir William Herschel noted them white and
+reddish white; but Webb, light orange and greenish yellow.
+
+12 Canum Venaticorum, 2-1/2 and 6-1/2. White and red, Sir William
+Herschel; but Sir John Herschel says in 1830, "With all attention I could
+perceive no contrast of colours in the two stars." Struve found them both
+white in 1830, thus agreeing with Sir John Herschel. Sestini saw them
+yellow and blue in 1844; Smyth, in 1855, pale reddish white and lilac;
+Dembowski, in 1856, white and pale olive blue; and Webb, in 1862, flushed
+white and pale lilac.
+
+On October 13, 1907, Nova Persei, the great new star of 1901, was
+estimated to be only 11�44 magnitude, or about 11-1/2. When at its
+brightest this famous star was about zero magnitude; so that it has in
+about 6 years faded about 11-1/2 magnitudes in brightness; in other words,
+it has been reduced to 1/40000 of its greatest brilliancy!
+
+
+
+
+CHAPTER XVII
+
+Nebul� and Clusters
+
+
+In his interesting and valuable work on "The Stars," the late Prof.
+Newcomb said--
+
+    "Great numbers of the nebul� are therefore thousands of times the
+    dimensions of the earth's orbit, and most of them are thousands of
+    times the dimensions of the whole solar system. That they should be
+    completely transparent through such enormous dimensions shows their
+    extreme tenuity. Were our solar system placed in the midst of one of
+    them it is probable that we should not be able to find any evidence of
+    its existence"!
+
+Prof. Perrine thinks that the total number of the nebul� will ultimately
+be found to exceed a million.[352]
+
+Dr. Max Wolf has discovered a number of small nebul� in the regions near
+Algol and Nova Persei (the great "new star" of 1901). He says, "They
+mostly lie in two bands," and are especially numerous where the two bands
+meet, a region of 12 minutes of arc square containing no less than 148 of
+them. They are usually "round with central condensation," and form of
+Andromeda nebula.[353]
+
+Some small nebul� have been found in the vicinity of the globular
+clusters. They are described by Prof. Perrine as very small and like an
+"out of focus" image of a small star. "They appear to be most numerous
+about clusters which are farthest from the galaxy." Prof. Perrine says,
+"Practically all the small nebul� about the globular clusters are
+elliptical or circular. Those large enough to show structure are spirals.
+Doubtless the majority of these are spirals."[354] This seems further
+evidence in favour of the "spiral nebular hypothesis" of Chamberlin and
+Moulton.
+
+A great photographic nebula in Orion was discovered by Prof. Barnard in
+1894. In a drawing he gives of the nebula,[355] it forms a long streak
+beginning a little south of [Greek: g] Orionis (Bellatrix), passing
+through the star 38 Orionis north of 51 and south of 56 and 60 Orionis.
+Then turning south it sweeps round a little north of [Greek: k] Orionis;
+then over 29 Orionis, and ends a little to the west of [Greek: �] Orionis.
+There is an outside patch west of Rigel. Barnard thinks that the whole
+forms a vast spiral structure; probably connected with the "great nebula"
+in the "sword of Orion," which it surrounds.
+
+From calculations of the brightness of surface ("intrinsic brightness") of
+several "planetary" nebul� made by the present writer in the year 1905, he
+finds that the luminosity is very small compared with that of the moon.
+The brightest of those examined (_h_ 3365, in the southern hemisphere,
+near the Southern Cross) has a surface luminosity of only 1/400 of that of
+the moon.[356] The great nebul� in Orion and Andromeda seem to have "still
+smaller intrinsic brightness."
+
+Arago says--
+
+    "The spaces which precede or which follow simple nebul�, and _a
+    fortiori_ groups of nebul�, contain generally few stars. Herschel
+    found this rule to be invariable. Thus every time that, during a short
+    interval, no star appeared, in virtue of the diurnal motion, to place
+    itself in the field of his motionless telescope, he was accustomed to
+    say to the secretary who assisted him (Miss Caroline Herschel),
+    'Prepare to write; nebul� are about to arrive.'"[357]
+
+Commenting on this remark of Arago, the late Herbert Spencer says--
+
+    "How does this fact consist with the hypothesis that nebul� are remote
+    galaxies? If there were but one nebula, it would be a curious
+    coincidence were this one nebula so placed in the distant regions of
+    space as to agree in direction with a starless spot in our sidereal
+    system! If there were but two nebul�, and both were so placed, the
+    coincidence would be excessively strange. What shall we say on
+    finding that they are habitually so placed? (the last five words
+    replace some that are possibly a little too strong).... When to the
+    fact that the general mass of nebul� are antithetical in position to
+    the general mass of the stars, we add the fact that local regions of
+    nebul� are regions where stars are scarce, and the further fact that
+    single nebul� are habitually found in comparatively starless spots,
+    does not the proof of a physical connection become overwhelming?"[358]
+
+With reference to the small elongated nebula discovered by Miss Caroline
+Herschel in 1783 near the great nebula in Andromeda, Admiral Smyth says,
+"It lies between two sets of stars, consisting of four each, and each
+disposed like the figure 7, the preceding group being the smallest."[359]
+
+Speaking of the "nebula" Messier 3--a globular cluster in Canes
+Venatici--Admiral Smyth says, "This mass is one of those balls of compact
+and wedged stars whose laws of aggregation it is so impossible to assign;
+but the rotundity of the figure gives full indication of some general
+attractive bond of union."[360] The terms "compact and wedged" are,
+however, too strong, for we know that in the globular clusters the
+component stars must be separated from each other by millions of miles!
+
+Prof. Chamberlin suggests that the secondary nebula (as it is called) in
+the great spiral in Canes Venatici (Messier 51) may possibly represent
+the body which collided with the other (the chief nucleus) in a grazing
+collision, and is now escaping. He considers this secondary body to have
+been "a dead sun"--that is, a dark body.[361] This would be very
+interesting if it could be proved. But it seems to me more probable that
+the secondary nucleus is simply a larger portion of the ejected matter,
+which is now being gradually detached from the parent mass.
+
+Scheiner says "the previous suspicion that the spiral nebul� are star
+clusters is now raised to a certainty," and that the spectrum of the
+Andromeda nebula is very similar to that of the sun. He says there is "a
+surprising agreement of the two, even in respect to the relative intensity
+of the separate spectral regions."[362]
+
+In the dynamical theory of spiral nebul�, Dr. E. J. Wilczynski thinks that
+the age of a spiral nebula may be indicated by the number of its coils;
+those having the largest number of coils being the oldest, from the point
+of view of evolution.[363] This seems to be very probable.
+
+In the spectrum of the gaseous nebul�, the F line of hydrogen (H[Greek:
+b]) is visible, but not the C line (H[Greek: a]). The invisibility of the
+C line is explained by Scheiner as due to a physiological cause, "the eye
+being less sensitive to that part of the spectrum in which the line
+appears than to the part containing the F line."[364]
+
+An apparent paradox is found in the case of the gaseous nebul�. The
+undefined outlines of these objects render any attempt at measuring their
+parallax very difficult, if not impossible. Their distance from the earth
+is therefore unknown, and perhaps likely to remain so for many years to
+come. It is possible that they may not be farther from us than some of the
+stars visible in their vicinity. On the other hand, they may lie far
+beyond them in space. But whatever their distance from the earth may be,
+it may be easily shown that their attraction on the sun is directly
+proportioned to their distance--that is, the greater their distance, the
+greater the attraction! This is evidently a paradox, and rather a
+startling one too. But it is nevertheless mathematically true, and can be
+easily proved. For, _their distance being unknown_, they may be of any
+dimensions. They might be comparatively small bodies relatively near the
+earth, or they may be immense masses at a vast distance from us. The
+latter is, of course, the more probable. In either case the _apparent_
+size would be the same. Take the case of any round gaseous nebula.
+Assuming it to be of a globular form, its _real_ diameter will depend on
+its distance from the earth--the greater the distance, the greater the
+diameter. Now, as the volumes of spheres vary as the cubes of their
+diameters, it follows that the volume of the nebula will vary as the cube
+of its distance from the earth. As the mass of an attracting body depends
+on its volume and density, its real mass will depend on the cube of its
+distance, the density (although unknown) being a fixed quantity. If at a
+certain distance its mass is _m_, at double the distance (the _apparent_
+diameter being the same) it would have a mass of eight times _m_ (8 being
+the cube of 2), and at treble the distance its mass would be 27 _m_, and
+so on, its _apparent_ size being known, but not its _real_ size. This is
+obvious. Now, the attractive power of a body varies directly as its
+mass--the greater the mass, the greater the attraction. Again, the
+attraction varies _inversely_ as the square of the distance, according to
+the well-known law of Newton. Hence if _d_ be the unknown distance of the
+nebula, we have its attractive power varying as _d_{3} divided by _d_{2},
+or directly as the distance _d_. We have then the curious paradox that for
+a nebula whose distance from the earth is unknown, its attractive power on
+the sun (or earth) will vary directly as the distance--the greater the
+distance the greater the attraction, and, of course, conversely, the
+smaller the distance the less the attractive power. This result seems at
+first sight absurd and incredible, but a little consideration will show
+that it is quite correct. Consider a small wisp of cloud in our
+atmosphere. Its mass is almost infinitesimal and its attractive power on
+the earth practically _nil_. But a gaseous nebula having the same
+_apparent size_ would have an enormous volume, and, although probably
+formed of very tenuous gas, its mass would be very great, and its
+attractive power considerable. The large apparent size of the Orion nebula
+shows that its volume is probably enormous, and as its attraction on the
+sun is not appreciable, its density must be excessively small, less than
+the density of the air remaining in the receiver of the best air-pump
+after the air has been exhausted. How such a tenuous gas can shine as it
+does forms another paradox. Its light is possibly due to some
+phosphorescent or electrical action.
+
+The apparent size of "the great nebula in Andromeda" shows that it must be
+an object of vast dimensions. The nearest star to the earth, Alpha
+Centauri, although probably equal to our sun in volume, certainly does not
+exceed one-hundredth of a second in diameter as seen from the earth. But
+in the case of the Andromeda nebula we have an object of considerable
+apparent size, not measured by seconds of arc, but showing an area about
+three times greater than that of the full moon. The nebula certainly lies
+in the region of the stars--much farther off than Alpha Centauri--and its
+great apparent size shows that it must be of stupendous dimensions. A
+moment's consideration will show that whatever its distance may be, the
+farther it is from the earth the larger it must be in actual size. The sun
+is vastly larger than the moon, but its apparent size is about the same
+owing to its greater distance. Sir William Herschel thought the Andromeda
+nebula to be "undoubtedly the nearest of all the great nebul�," and he
+estimated its distance at 2000 times the distance of Sirius. This would
+not, however, indicate a relatively near object, as it would imply a
+"light journey" of over 17,000 years! (The distance of Sirius is about 88
+"light years.")
+
+It has been generally supposed that this great nebula lies at a vast
+distance from the earth, possibly far beyond most of the stars seen in the
+same region of the sky; but perhaps not quite so far as Herschel's
+estimate would imply. Recently, however, Prof. Bohlin of Stockholm has
+found from three series of measures made in recent years a parallax of
+0"�17.[365]
+
+This indicates a distance of 1,213,330 times the sun's distance from the
+earth, and a "light journey" of about 19 years. This would make the
+distance of the nebula more than twice the distance of Sirius, about four
+times the distance of [Greek: a] Centauri, but less than that of Capella.
+
+Prof. Bohlin's result is rather unexpected, and will require confirmation
+before it can be accepted. But it will be interesting to inquire what this
+parallax implies as to the real dimensions and probable mass of this vast
+nebula. The extreme length of the nebula may be taken to represent its
+diameter considered as circular. For, although a circle seen obliquely is
+always foreshortened into an ellipse, still the longer axis of the ellipse
+will always represent the real diameter of the circle. This may be seen by
+holding a penny at various angles to the eye. Now, Dr. Roberts found that
+the apparent length of the Andromeda nebula is 2-1/3 degrees, or 8400
+seconds of arc. The diameter in seconds divided by the parallax will give
+the real diameter of the nebula in terms of the sun's distance from the
+earth taken as unity. Now, 8400 divided by 0"�17 gives nearly 50,000, that
+is, the real diameter of the Andromeda nebula would be--on Bohlin's
+parallax--nearly 50,000 times the sun's distance from the earth. As light
+takes about 500 seconds to come from the sun to the earth, the above
+figures imply that light would take about 290 days, or over 9 months to
+cross the diameter of this vast nebula.
+
+Elementary geometrical considerations will show that if the Andromeda
+nebula lies at a greater distance from the earth than that indicated by
+Bohlin's parallax, its real diameter, and therefore its volume and mass,
+will be greater. If, therefore, we assume the parallax found by Bohlin,
+we shall probably find a _minimum_ value for the size and mass of this
+marvellous object.
+
+Among Dr. Roberts' photographs of spiral nebul� (and the Andromeda nebula
+is undoubtedly a spiral) there are some which are apparently seen nearly
+edgeways, and show that these nebul� are very thin in proportion to their
+diameter. From a consideration of these photographs we may, I think,
+assume a thickness of about one-hundredth of the diameter. This would give
+a thickness for the Andromeda nebul� of about 500 times the sun's distance
+from the earth. This great thickness will give some idea of the vast
+proportions of the object we are dealing with. The size of the whole solar
+system--large as it is--is small in comparison. The diameter and thickness
+found above can easily be converted into miles, and from these dimensions
+the actual volume of the nebula can be compared with that of the sun. It
+is merely a question of simple mensuration, and no problem of "high
+mathematics" is involved. Making the necessary calculations, I find that
+the volume of the Andromeda nebula would be about 2�32 trillion times
+(2�32 � 10{18}) the sun's volume! Now, assuming that the nebulous matter
+fills only one-half of the apparent volume of the nebula (allowing for
+spaces between the spiral branches), we have the volume = 1�16 � 10{18}.
+If the nebula had the same density as the sun, this would be its mass in
+terms of the sun's mass taken as unity, a mass probably exceeding the
+combined mass of all the _stars_ visible in the largest telescopes! But
+this assumption is, of course, inadmissible, as the sun is evidently quite
+opaque, whereas the nebula is, partially at least, more or less
+transparent. Let us suppose that the nebula has a _mean_ density equal to
+that of atmospheric air. As water is about 773 times heavier than air, and
+the sun's density is 1�4 (water = 1) we have the mass of the nebula equal
+to 1�16 � 10{18} divided by 773 � 1�4, or about 10{15} times the sun's
+mass, which is still much greater than the probable combined mass of all
+the _visible_ stars. As it seems unreasonable to suppose that the mass of
+an individual member of our sidereal system should exceed the combined
+mass of the remainder of the system, we seem compelled to further reduce
+the density of the Andromeda nebula. Let us assume a mean density of, say,
+a millionth of hydrogen gas (a sufficiently low estimate) which is about
+14�44 times lighter than air, and we obtain a mass of about 8 � 10{7} or
+80 million times the mass of the sun, which is still an enormous mass.
+
+As possibly I may have assumed too great a thickness for the nebula, let
+us take a thickness of one-tenth of that used above, or one thousandth of
+the length of the nebula. This gives a mass of 8 million times the sun's
+mass. This seems a more probable mass if the nebula is--as Bohlin's
+parallax implies--a member of our sidereal system.
+
+If we assume a parallax of say 0"�01--or one-hundredth of a second of
+arc--which would still keep the nebula within the bounds of our sidereal
+system--we have the dimensions of the nebula increased 17 times, and hence
+its mass nearly 5000 times greater (17{3}) than that found above. The mass
+would then be 40,000 million times the sun's mass! This result seems
+highly improbable, for even this small parallax would imply a light
+journey of only 326 years, whereas the distance of the Milky Way has been
+estimated by Prof. Newcomb at about 3000 years' journey for light.
+
+In Dr. Roberts' photograph many small stars are seen scattered over the
+surface of the nebula; but these do not seem to be quite so numerous as in
+the surrounding sky. If the nebula lies nearer to us than the fainter
+stars visible on the photograph, some of them may be obscured by the
+denser portions of the nebula; some may be visible through the openings
+between the spiral branches; while others may be nearer to us and simply
+projected on the nebula.
+
+To add to the difficulty of solving this celestial problem, the
+spectroscope shows that the Andromeda nebula is not gaseous. The spectrum
+is, according to Scheiner, very similar to that of the sun, and "there is
+a surprising agreement of the two, even in respect to the relative
+intensities of the separate spectral regions."[366] He thinks that "the
+greater part of the stars comprising the nucleus of the nebula belong to
+the second spectral class" (solar), and that the nebula "is now in an
+advanced stage of development. No trace of bright nebular lines are
+present, so that the interstellar space in the Andromeda nebula, just as
+in our stellar system, is not appreciably occupied by gaseous
+matter."[366] He suggests that the inner part of the nebula [the
+"nucleus"] "corresponds to the complex of those stars which do not belong
+to the Milky Way, while the latter corresponds to the spirals of the
+Andromeda nebula."[366] On this view of the matter we may suppose that the
+component particles are small bodies widely separated, and in this way the
+_mean_ density of the Andromeda nebula may be very small indeed. They
+cannot be large bodies, as the largest telescopes have failed to resolve
+the nebula into stars, and photographs show no sign of resolution.
+
+It has often been suggested, and sometimes definitely stated, that the
+Andromeda nebula may possibly be an "external" universe, that is an
+universe entirely outside our sidereal system, and comparable with it in
+size. Let us examine the probability of such hypothesis. Assuming that the
+nebula has the same diameter as the Milky Way, or about 6000 "light
+years," as estimated by Prof. Newcomb, I find that its distance from the
+earth would be about 150,000 "light years." As this is about 8000 times
+the distance indicated by Bohlin's parallax, its dimensions would be 8000
+times as great, and hence its volume and mass would be 8000 cubed, or
+512,000,000,000 times greater than that found above. That is, about 4
+trillion (4 � 10{18}) times the sun's mass! As this appears an incredibly
+large mass to be compressed into a volume even so large as that of our
+sidereal system, we seem compelled to reject the hypothesis that the
+nebula represents an external universe. The sun placed at the distance
+corresponding to 150,000 light years would, I find, shine as a star of
+less than the 23rd magnitude, a magnitude which would be invisible in the
+largest telescope that man could ever construct. But the combined light of
+4 trillion of stars of even the 23rd magnitude would be equal to one of
+minus 23�5 magnitude, that is, 23-1/2 magnitude brighter than the zero
+magnitude, or not very much inferior to the sun in brightness. As the
+Andromeda nebula shines only as a star of about the 5th magnitude the
+hypothesis of an external universe seems to be untenable.
+
+It is evident, however, that the mass of the Andromeda nebula must be
+enormous; and if it belongs to our sidereal system, and if the other great
+nebul� have similar masses, it seems quite possible that the mass of the
+_visible_ universe may much exceed that of the _visible_ stars, and may be
+equal to 1000 million times the sun's mass--as supposed by the late Lord
+Kelvin--or even much more.
+
+With reference to the small star which suddenly blazed out near the
+nucleus of the Andromeda nebula in August, 1885, Prof. Seeliger has
+investigated the decrease in the light of the star on the hypothesis that
+it was a cooling body which had suddenly been raised to an intense heat by
+the shock of a collision, and finds a fair agreement between theory and
+observation. Prof. Auwers points out the similarity between this outburst
+and that of the "temporary star" of 1860, which appeared in the cluster 80
+Messier, and he thinks it very probable that both phenomena were due to
+physical changes in the nebul� in which they appeared.
+
+The appearance of this temporary star in the Andromeda nebula seems to
+afford further evidence against the hypothesis of the nebula being an
+external universe. For, as I have shown above, our sun, if placed at a
+distance of 150,000 light years, would shine only as a star of the 23rd
+magnitude, or over 15 magnitudes fainter than the temporary star. This
+would imply that the star shone with a brightness of over a million times
+that of the sun, and would therefore indicate a body of enormous size. But
+the rapid fading of its light would, on the contrary, imply a body of
+comparatively small dimensions. We must, therefore, conclude that the
+nebula, whatever it may be, is not an external universe, but forms a
+member of our own sidereal system.
+
+In Sir John Herschel's catalogue of Nebul� and Clusters of Stars,
+published in 1833, in the _Philosophical Transactions_ of the Royal
+Society, there are many curious objects mentioned. Of these I have
+selected the following:--
+
+No. 496 is described as "a superb cluster which fills the whole field;
+stars 9, 10 ... 13 magnitude and none below, but the whole ground of the
+sky on which it stands is singularly dotted over with infinitely minute
+points." This is No. 22 of Sir William Herschel's 6th class, and will be
+found about 3 degrees south and a little east of the triple star 29
+Monocerotis.
+
+No. 650. This object lies about 3 degrees north of the star [Greek: m]
+Leonis, the most northern of the bright stars in the well-known "Sickle,"
+and is thus described by Sir John Herschel: "A star 12th magnitude with an
+extremely faint nebulous atmosphere about 10" to 12". It is between a star
+8-9 magnitude north preceding, and one 10th magnitude south following,
+neither of which are so affected. A curious object."
+
+No. 1558. Messier 53. A little north-east of the star [Greek: a] Com�
+Berenices. Described as "a most beautiful highly compressed cluster.
+Stars very small, 12th ... 20th magnitude, with scattered stars to a
+considerable distance; irregularly round, but not globular. Comes up to a
+blaze in the centre; indicating a round mass of pretty equable density.
+Extremely compressed. A most beautiful object. A mass of close-wedged
+stars 5' in diameter; a few 12th magnitude, the rest of the smallest size
+and innumerable." Webb says, "Not very bright with 3-7/10 inches;
+beautiful with 9 inches." This should be a magnificent object with a very
+large telescope, like the Lick or Yerkes.
+
+No. 2018. "A more than usually condensed portion of the enormous cluster
+of the Milky Way. The field has 200 or 300 stars in it at once." This lies
+about 2� south-west of the star 6 Aquil�, which is near the northern edge
+of the bright spot of Milky Way light in "Sobieski's Shield"--one of the
+brightest spots in the sky.
+
+No. 2093. "A most wonderful phenomenon. A very large space 20' or 30'
+broad in Polar Distance, and 1{m} or 2{m} in Right Ascension, full of
+nebula and stars mixed. The nebula is decidedly attached to the stars, and
+is as decidedly not stellar. It forms irregular lace-work marked out by
+stars, but some parts are decidedly nebulous, wherein no star can be
+seen." Sir John Herschel gives a figure of this curious spot, which he
+says represents its "general character, but not the minute details of
+this object, which would be extremely difficult to give with any degree of
+fidelity." It lies about 3 degrees west of the bright star [Greek: z]
+Cygni.
+
+Among the numerous curious objects observed by Sir John Herschel during
+his visit to the Cape of Good Hope, the following may be mentioned:--
+
+_h_ 2534 (H iv. 77). Near [Greek: t]{4} Eridani. Sir John Herschel says,
+"Attached cometically to a 9th magnitude star which forms its head. It is
+an exact resemblance to Halley's comet as seen in a night glass."... "A
+complete telescopic comet; a perfect miniature of Halley's comet, only the
+tail is rather broader in proportion."[367]
+
+_h_ 3075. Between [Greek: g] Monocerotis and [Greek: g] Canis Majoris. "A
+very singular nebula, and much like the profile of a bust (head, neck, and
+shoulders) or a silhouette portrait, very large, pretty well defined,
+light nearly uniform, about 12' diameter. In a crowded field of Milky Way
+stars, many of which are projected on it."[368]
+
+_h_ 3315 (Dunlop 323). In the Milky Way; about 3� east of the Eta Arg�s
+nebula. Sir John Herschel says, "A glorious cluster of immense magnitude,
+being at least 2 fields in extent every way. The stars are 8, 9, 10, and
+11th magnitudes, but chiefly 10th magnitude, of which there must be at
+least 200. It is the most brilliant object of the kind I have ever seen"
+... "has several elegant double stars, and many orange-coloured
+stars."[369] This should form a fine object in even a comparatively small
+telescope, and may be recommended to observers in the southern hemisphere.
+A telescope of 3-inches aperture should show it well.
+
+Among astronomical curiosities may be counted "clusters within clusters."
+A cluster in Gemini (N.G.C. 2331) has a small group of "six or seven stars
+close together and well isolated from the rest."
+
+Lord Rosse describes No. 4511 of Sir John Herschel's General Catalogue of
+Nebul� and Clusters (_Phil. Trans._, 1864) as "a most gorgeous cluster,
+stars 12-15 magnitude, full of holes."[370] His sketch of this cluster
+shows 3 rings of stars in a line, each ring touching the next on the
+outside. Sir John Herschel described it as "Cluster; very large; very
+rich; stars 11-15 magnitude (Harding, 1827)," but says nothing about the
+rings. This cluster lies about 5 degrees south of [Greek: d] Cygni.
+
+Dr. See, observing with the large telescope of the Lowell Observatory,
+found that when the sky is clear, the moon absent, and the seeing perfect,
+"the sky appeared in patches to be of a brownish colour," and suggests
+that this colour owes its existence to immense cosmical clouds, which are
+shining by excessively feeble light! Dr. See found that these brown
+patches seem to cluster in certain regions of the Milky Way.[371]
+
+From a comparison of Trouvelot's drawing of the small elongated nebula
+near the great nebula in Andromeda with recent photographs, Mr. Easton
+infers that this small nebula has probably rotated through an angle of
+about 15� in 25 years. An examination I have made of photographs taken in
+different years seems to me to confirm this suspicion, which, if true, is
+evidently a most interesting phenomenon.
+
+Dr. Max Wolf of Heidelberg finds, by spectrum photography, that the
+well-known "ring nebula" in Lyra consists of four rings composed of four
+different gases. Calling the inner ring A, the next B, the next C, and the
+outer D, he finds that A is the smallest ring, and is composed of an
+unknown gas; the next largest, B, is composed of hydrogen gas; the next,
+C, consists of helium gas; and the outer and largest ring, D, is
+composed--like A--of an unknown gas. As the molecular weight of hydrogen
+is 2�016, and that of helium is 3�96, Prof. Bohuslav Brauner suggests that
+the molecular weight of the gas composing the inner ring A is smaller than
+that of hydrogen, and the molecular weight of the gas forming the outer
+ring D is greater than that of helium. He also suggests that the gas of
+ring A may possibly be identical with the "coronium" of the solar corona,
+for which Mendelief found a hypothetical atomic and molecular weight of
+0�4.[372]
+
+With reference to the nebular hypothesis of Laplace, Dr. A. R. Wallace
+argues that "if there exists a sun in a state of expansion in which our
+sun was when it extended to the orbit of Neptune, it would, even with a
+parallax of 1/60th of a second, show a disc of half a second, which could
+be seen with the Lick telescope." My reply to this objection is, that with
+such an expansion there would probably be very little "intrinsic
+brightness," and if luminous enough to be visible the spectrum would be
+that of a gaseous nebula, and no known _star_ gives such a spectrum. But
+some planetary nebul� look like small stars, and with high powers on large
+telescopes would probably show a disc. On these considerations, Dr.
+Wallace's objection does not seem to be valid.
+
+It is usually stated in popular works on astronomy that the spectra of
+gaseous nebul� show only three or four bright lines on a faint continuous
+background. But this is quite incorrect. No less than forty bright lines
+have been seen and measured in the spectra of gaseous nebul�.[373] This
+includes 2 lines of "nebulium," 11 of hydrogen, 5 of helium, 1 of oxygen
+(?), 3 of nitrogen (?), 1 of silicon (?), and 17 of an unknown substance.
+In the great nebul� in Orion 30 bright lines have been photographed.[374]
+
+D'Arrest found that "gaseous nebul� are rarely met with outside the Milky
+Way, and never at a considerable distance from it."[375]
+
+Mr. A. E. Fath thinks that "no spiral nebula investigated has a truly
+continuous spectrum." He finds that so feeble is the intensity of the
+light of the spiral nebul� that, while a spectrogram of Arcturus can be
+secured with the Mills spectrograph "in less than two minutes," "an
+exposure of about 500 hours would be required for the great nebula in
+Andromeda, which is of the same spectral type."[376] Mr. Fath thinks that
+in the case of the Andromeda nebula, the "star cluster" theory "seems to
+be the only one that can at all adequately explain the spectrum
+obtained."[377]
+
+Prof. Barnard finds that the great cluster in Hercules (Messier 13) is
+"composed of stars of different spectral types." This result was confirmed
+by Mr. Fath.[378]
+
+From observations with the great 40-inch telescope of the Yerkes
+Observatory (U.S.A.), Prof. Barnard finds that the nucleus of the
+planetary nebula H. iv. 18 in Andromeda is variable to the extent of at
+least 3 magnitudes. At its brightest it is about the 12th magnitude; and
+the period seems to be about 28 days. Barnard says, "I think this is the
+first case in which the nucleus of a planetary or other nebula has been
+shown to be certainly variable." "The normal condition seems to be
+faint--the nucleus remaining bright for a few days only. In an ordinary
+telescope it looks like a small round disc of a bluish green colour." He
+estimated the brightness of the nebula as that of a star of 8�2
+magnitude.[379] Even in a telescope of 4 inches aperture, this would be a
+fairly bright object. It lies about 3-1/2 degrees south-west of the star
+[Greek: i] Andromed�.
+
+The so-called "globular clusters" usually include stars of different
+brightness; comparatively bright telescopic stars of the 10th to 13th
+magnitude with faint stars of the 15th to 17th magnitude. Prof. Perrine of
+the Lick Observatory finds that (_a_) "the division of the stars in
+globular clusters into groups, differing widely in brightness, is
+characteristic of these objects"; (_b_) "the globular clusters are devoid
+of true nebulosity"; and (_c_) "stars fainter than 15th magnitude
+predominate in the Milky Way and globular clusters, but elsewhere are
+relatively scarce." He found that "exposures of one hour or thereabouts
+showed as many stars as exposures four to six times as long; the only
+effect of the longer exposures being in the matter of density." This last
+result confirms the late Dr. Roberts' conclusions. Perrine finds that for
+clusters in the Milky Way, the faint stars (15th to 17th magnitude) "are
+about as numerous in proportion to the bright stars (10th to 13th
+magnitude) as in the globular clusters themselves." This is, however, not
+the case with globular clusters at a distance from the Milky Way. In these
+latter clusters he found that "in the regions outside the limits of the
+cluster there are usually very few faint stars, hardly more than
+one-fourth or one-tenth as many as there are bright stars"; and he thinks
+that "this paucity of faint stars" in the vicinity of these clusters
+"gives rise to the suspicion that all regions at a distance from the
+Galaxy may be almost devoid of these very faint stars." The late Prof.
+Keeler's series of nebular photographs "in or near the Milky Way" tend to
+confirm the above conclusions. Perrine finds the northernmost region of
+the Milky Way "to be almost, if not entirely, devoid of globular
+clusters."[380]
+
+According to Sir John Herschel, "the sublimity of the spectacle afforded"
+by Lord Rosse's great telescope of 6 feet in diameter of some of the
+"larger globular and other clusters" "is declared by all who have
+witnessed it, to be such that no words can express."[381]
+
+In his address to the British Association at Leicester in 1907, Sir David
+Gill said--
+
+    "Evidence upon evidence has accumulated to show that nebul� consist of
+    the matter out of which stars have been and are being evolved.... The
+    fact of such an evolution with the evidence before us, can hardly be
+    doubted. I most fully believe that, when the modifications of
+    terrestrial spectra under sufficiently varied conditions of
+    temperature, pressure, and environment, have been further studied,
+    this connection will be greatly strengthened."
+
+
+
+
+CHAPTER XVIII
+
+Historical
+
+
+The grouping of the stars into constellations is of great antiquity. The
+exact date of their formation is not exactly known, but an approximate
+result may be arrived at from the following considerations. On the
+celestial spheres, or "globes," used by the ancient astronomers, a portion
+of the southern heavens of a roughly circular form surrounding the South
+Pole was left blank. This space presumably contained the stars in the
+southern hemisphere which they could not see from their northern stations.
+Now, the centre of this circular blank space most probably coincided with
+the South Pole of the heavens at the time when the constellations were
+first formed. Owing to the "Precession of the Equinoxes" this centre has
+now moved away from the South Pole to a considerable distance. It can be
+easily computed at what period this centre coincided with the South Pole,
+and calculations show that this was the case about 2700 B.C. The position
+of this circle also indicates that the constellations were formed at a
+place between 36� and 40� north latitude, and therefore probably somewhere
+in Asia Minor north of Mesopotamia. Again, the most ancient observations
+refer to Taurus as the equinoxial constellation. Virgil says--
+
+  "Candidus auratis aperit cum cornibus annum Taurus."[382]
+
+This would indicate a date about 3000 B.C. There is no tradition, however,
+that the constellation Gemini was ever _seen_ to occupy this position, so
+that 3000 B.C. seems to be the earliest date admissible.[383]
+
+Prof. Sayce thinks that the "signs of the Zodiac" had their origin in the
+plains of Mesopotamia in the twentieth or twenty-third century B.C., and
+Brown gives the probable date as 2084 B.C.[384]
+
+According to Seneca, the study of astronomy among the Greeks dates back to
+about 1400 B.C.; and the ancient constellations were already classical in
+the time of Eudoxus in the fourth century B.C. Eudoxus (408-355 B.C.)
+observed the positions of forty-seven stars visible in Greece, thus
+forming the most ancient star catalogue which has been preserved. He was a
+son of Eschinus, and a pupil of Archytas and probably Plato.
+
+The work of Eudoxus was put into verse by the poet Aratus (third century
+B.C.). This poem describes all the old constellations now known, except
+Libra, the Balance, which was at that time included in the Claws of the
+Scorpion. About B.C. 50, the Romans changed the Claws, or Chel�, into
+Libra. Curious to say, Aratus states that the constellation Lyra contained
+no bright star![385] Whereas its principal star, Vega, is now one of the
+brightest stars in the heavens!
+
+With reference to the origin of the constellations, Aratus says--
+
+                    "Some men of yore
+  A nomenclature thought of and devised
+  And forms sufficient found."
+
+This shows that even in the time of Aratus the constellations were of
+great antiquity.
+
+Brown says--
+
+    "Writers have often told us, speaking only from the depths of their
+    ignorance, how 'Chaldean' shepherds were wont to gaze at the brilliant
+    nocturnal sky, and to _imagine_ that such and such stars resemble this
+    or that figure. But all this is merely the old effort to make capital
+    out of nescience, and the stars are before our eyes to prove the
+    contrary. Having already certain fixed ideas and figures in his mind,
+    the constellation-former, when he came to his task, applied his
+    figures to the stars and the stars to his figures as harmoniously as
+    possible."[386] "Thus _e.g._ he arranged the stars of _Andromeda_ into
+    the representation of a chained lady, not because they naturally
+    reminded him (or anybody else) of such a figure, but because he
+    desired to express that idea."
+
+A coin of Manius Aquillus, B.C. 94, shows four stars in Aquila, and seems
+to be the oldest representation extant of a star group. On a coin of B.C.
+43, Dr. Vencontre found five stars, one of which was much larger than the
+others, and concludes that it represents the Hyades (in Taurus). He
+attributes the coin to P. Clodius Turrinus, who probably used the
+constellation Taurus or Taurinus as a phonetic reference to his surname. A
+coin struck by L. Lucretius Trio in 74 B.C., shows the seven stars of the
+Plough, or as the ancients called them Septem Triones. Here we have an
+allusion to the name of the magistrate Trio.[387]
+
+In a work published in Berne in 1760, Schmidt contends that the ancient
+Egyptians gave to the constellations of the Zodiac the names of their
+divinities, and expressed them by the signs which were used in their
+hieroglyphics.[388]
+
+Hesiod mentions Orion, the Pleiades, Sirius, Aldebaran, and Arcturus; and
+Homer refers to Orion, Arcturus, the Pleiades, the Hyades, the Great Bear
+(under the name of Amaxa, the Chariot), and the tail of the Little Bear,
+or "Cynosura."
+
+Hipparchus called the constellations Asterisms ([Greek: asterismos]),
+Aristotle and Hyginus [Greek: Somata] (bodies), and Ptolemy [Greek:
+Sch�mata] (figures). By some they were called [Greek: Morph�seis]
+(configurations), and by others [Greek: Mete�re]. Proclus called those
+near the ecliptic [Greek: Z�dia] (animals). Hence our modern name Zodiac.
+
+Hipparchus, Ptolemy, and Al-Sufi referred the positions of the stars to
+the ecliptic. They are now referred to the equator. Aboul Hassan in the
+thirteenth century (1282) was the first to use Right Ascensions and
+Declinations instead of Longitudes and Latitudes. The ancient writers
+described the stars by their positions in the ancient figures. Thus they
+spoke of "the star in the head of Hercules," "the bright star in the left
+foot of Orion" (Rigel); but Bayer in 1603 introduced the Greek letters to
+designate the brighter stars, and these are now universally used by
+astronomers. These letters being sometimes insufficient, Hevelius added
+numbers, but the numbers in _Flamsteed's Catalogue_ are now generally
+used.
+
+Ptolemy and all the ancient writers described the constellation figures as
+they are seen on globes, that is from the outside. Bayer in his Atlas,
+published in 1603, reversed the figures to show them as they would be seen
+from the _interior_ of a hollow globe and as, of course, they are seen in
+the sky. Hevelius again reversed Bayer's figures to make them correspond
+with those of Ptolemy. According to Bayer's arrangement, Betelgeuse
+([Greek: a] Orionis) would be on the left shoulder of Orion, instead of
+the right shoulder according to Ptolemy and Al-Sufi, and Rigel ([Greek: b]
+Orionis) on the right foot (Bayer) instead of the left foot (Ptolemy).
+This change of position has led to some confusion; but at present the
+positions of the stars are indicated by their Right Ascensions and
+Declinations, without any reference to their positions in the ancient
+figures.
+
+The classical constellations of Hipparchus and Ptolemy number forty-eight,
+and this is the number described by Al-Sufi in his "Description of the
+Fixed Stars" written in the tenth century A.D.
+
+Firminicus gives the names of several constellations not mentioned by
+Ptolemy. M. Fr�ret thought that these were derived from the Egyptian
+sphere of Petosiris. Of these a Fox was placed north of the Scorpion; a
+constellation called Cynocephalus near the southern constellation of the
+Altar (Ara); and to the north of Pisces was placed a Stag. But all these
+have long since been discarded. Curious to say neither the Dragon nor
+Cepheus appears on the old Egyptian sphere.[389]
+
+Other small constellations have also been formed by various astronomers
+from time to time, but these have disappeared from our modern star maps.
+The total number of constellations now recognized in both hemispheres
+amounts to eighty-four.
+
+The first catalogue formed was nominally that of Eudoxus in the fourth
+century B.C. (about 370 B.C.). But this can hardly be dignified by the
+name of catalogue, as it contained only forty-seven stars, and it omits
+several of the brighter stars, notably Sirius! The first complete (or
+nearly complete) catalogue of stars visible to the naked eye was that of
+Hipparchus about 129 B.C. Ptolemy informs us that it was the sudden
+appearance of a bright new or "temporary star" in the year 134 B.C. in the
+constellation Scorpio which led Hipparchus to form his catalogue, and
+there seems to be no reason to doubt the accuracy of this statement, as
+the appearance of this star is recorded in the Chinese Annals. The
+Catalogue of Hipparchus contains only 1080 stars; but as many more are
+visible to the naked eye, Hipparchus must have omitted those which are not
+immediately connected with the old constellation figures of men and
+animals.
+
+Hipparchus' Catalogue was revised by Ptolemy in his famous work the
+_Almagest_. Ptolemy reduced the positions of the stars given by Hipparchus
+to the year 137 A.D.; but used a wrong value of the precession which only
+corresponded to about 50 A.D.; and he probably adopted the star magnitudes
+of Hipparchus without any revision. Indeed, it seems somewhat doubtful
+whether Ptolemy made any observations of the brightness of the stars
+himself. Ptolemy's catalogue contains 1022 stars.
+
+Prof. De Morgan speaks of Ptolemy as "a splendid mathematician and an
+indifferent observer"; and from my own examination of Al-Sufi's work on
+the Fixed Stars, which was based on Ptolemy's work, I think that De
+Morgan's criticism is quite justified.
+
+Al-Sufi's _Description of the Fixed Stars_ was written in the tenth
+century and contains 1018 stars. He seems to have adopted the _positions_
+of the stars given by Ptolemy, merely correcting them for the effects of
+precession; but he made a very careful revision of the star magnitudes of
+Ptolemy (or Hipparchus) from his own observations, and this renders his
+work the most valuable, from this point of view, of all the ancient
+catalogues.
+
+Very little is known about Al-Sufi's life, and the few details we have are
+chiefly derived from the works of the historians Abu'-l-faradji and
+Casiri, and the Oriental writers Hyde, Caussin, Sedillot, etc. Al-Sufi's
+complete name was Abd-al-Rahm�n Bin Umar Bin Muhammad Bin Sahl
+Abu'l-husa�n al-Sufi al-Razi. The name Sufi indicates that he belonged to
+the sect of Sufis (Dervishes), and the name Razi that he lived in the town
+of Ra� in Persia, to the east of Teheran. He was born on December 7, 903
+A.D., and died on May 25, 986, so that, like many other astronomers, he
+lived to a good old age. According to ancient authorities, Al-Sufi--as he
+is usually called--was a very learned man, who lived at the courts of
+Schiraz and Baghdad under Adhad-al-Davlat--of the dynasty of the
+Bu�des--who was then the ruler of Persia. Al-Sufi was held in high esteem
+and great favour by this prince, who said of him, "Abd-al-Rahm�n al-Sufi
+taught me to know the names and positions of the fixed stars, Scharif Ibn
+al-Aalam the use of astronomical tables, and Abu Ali al-Farisi instructed
+me in the principles of grammar." Prince Adhad-al-Davlat died on March 26,
+983. According to Caussin, Al-Sufi also wrote a book on astrology, and a
+work entitled _Al-Ardjouze_, which seems to have been written in verse,
+but its subject is unknown. He also seems to have determined the exact
+length of the year, and to have undertaken geodetic measurements. The
+al-Aalam mentioned above was also an able astronomer, and in addition to
+numerous observations made at Baghdad, he determined with great care the
+precession of the equinoxes. He found the annual constant of precession to
+be 51"�4, a value which differs but little from modern results.
+
+In the year 1874, the late M. Schjellerup, the eminent Danish astronomer,
+published a French translation of two Arabic manuscripts written by
+Al-Sufi and entitled "A Description of the Fixed Stars." One of these
+manuscripts is preserved in the Royal Library at Copenhagen, and the other
+in the Imperial Library at St. Petersburgh.[390]
+
+Al-Sufi seems to have been a most careful and accurate observer, and
+although, as a rule, his estimates of the relative brightness of stars are
+in fairly good agreement with modern estimates and photometric measures,
+there are many remarkable and interesting differences. Al-Sufi's
+observations have an important bearing on the supposed "secular variation"
+of the stars; that is, the slow variation in light which may have occurred
+in the course of ages in certain stars, apart from the periodical
+variation which is known to occur in the so-called variable stars. More
+than 900 years have now elapsed since the date of Al-Sufi's observations
+(about A.D. 964) and over 2000 years in the case of Hipparchus, and
+although these periods are of course very short in the life-history of any
+star, still _some_ changes may possibly have taken place in the brightness
+of some of them. There are several cases in which a star seems to have
+diminished in light since Al-Sufi's time. This change seems to have
+certainly occurred in the case of [Greek: th] Eridani, [Greek: b] Leonis,
+[Greek: z] Piscis Australis, and some others. On the other hand, some
+stars seem to have certainly increased in brightness, and the bearing of
+these changes on the question of "stellar evolution" will be obvious.
+
+In most cases Al-Sufi merely mentions the magnitude which he estimated a
+star to be; such as "third magnitude," "fourth," "small third magnitude,"
+"large fourth," etc. In some cases, however, he directly states that a
+certain star is a little brighter than another star near it. Such
+cases--unfortunately not numerous--are very valuable for comparison with
+modern estimates and measures, when variation is suspected in the light of
+a star. The estimates of Argelander, Heis, and Houzeau are based on the
+same scale as that used by Ptolemy and Al-Sufi. Al-Sufi's estimates are
+given in thirds of a magnitude. Thus, "small third magnitude" means 3-1/3,
+or 3�33 magnitude in modern measures; "large fourth," 3-2/3 or 3�66
+magnitude. These correspond with the estimates of magnitude given by
+Argelander, Heis, and Houzeau in their catalogues of stars visible to the
+naked eye, and so the estimates can be directly compared.
+
+I have made an independent identification of all the stars mentioned by
+Al-Sufi. In the majority of cases my identifications concur with those of
+Schjellerup; but in some cases I cannot agree with him. In a few cases I
+have found that Al-Sufi himself, although accurately describing the
+position of the stars observed by _him_, has apparently misidentified the
+star observed by Hipparchus and Ptolemy. This becomes evident when we plot
+Ptolemy's positions (as given by Al-Sufi) and compare them with Al-Sufi's
+descriptions of the stars observed by him. This I have done in all cases
+where there seemed to be any doubt; and in this way I have arrived at some
+interesting results which have escaped the notice of Schjellerup. This
+examination shows clearly, I think, that Al-Sufi did not himself measure
+the _positions_ of the stars he observed, but merely adopted those of
+Ptolemy, corrected for the effect of precession. The great value of his
+work, however, consists in his estimates of star magnitudes, which seem to
+have been most carefully made, and from this point of view, his work is
+invaluable. Prof. Pierce says, "The work which the learning of M.
+Schjellerup has brought to light is so important that the smallest errors
+of detail become interesting."[391]
+
+Although Al-Sufi's work is mentioned by the writers referred to above, no
+complete translation of his manuscript was made until the task was
+undertaken by Schjellerup, and even now Al-Sufi's name is not mentioned
+in some popular works on astronomy! But he was certainly the best of all
+the old observers, and his work is deserving of the most careful
+consideration.
+
+Al-Sufi's descriptions of the stars were, it is true, based on Ptolemy's
+catalogue, but his work is not a mere translation of that of his
+predecessor. It is, on the contrary, a careful and independent survey of
+the heavens, made from his own personal observations, each of Ptolemy's
+stars having been carefully examined as to its position and magnitude, and
+Ptolemy's mistakes corrected. In examining his descriptions, Schjellerup
+says, "We soon see the vast extent of his labours, his perseverance, and
+the minute accuracy and almost modern criticism with which he executed his
+work." In fact, Al-Sufi has given us a careful description of the starry
+sky as it appeared in his time, and one which deserves the greatest
+confidence. It far surpasses the work of Ptolemy, which had been without a
+rival for eight centuries previously, and it has only been equalled in
+modern times by the surveys of Argelander, Gould, Heis, and Houzeau. Plato
+remarked with reference to the catalogue of Hipparchus, _Coelam posteris
+in hereditatem relictum_, and the same may be said of Al-Sufi's work. In
+addition to his own estimates of star magnitudes, Al-Sufi adds the
+magnitudes given by Ptolemy whenever Ptolemy's estimate differs from his
+own; and this makes his work still more valuable, as Ptolemy's magnitudes
+given in all the editions of the _Almagest_ now extant are quite
+untrustworthy.
+
+In the preface to his translation of Al-Sufi's work, Schjellerup mentions
+some remarkable discrepancies between the magnitudes assigned to certain
+stars by Ptolemy and Argelander. This comparison is worthy of confidence
+as it is known that both Al-Sufi and Argelander adopted Ptolemy's (or
+Hipparchus') scale of magnitudes. For example, all these observers agree
+that [Greek: b] Urs� Minoris (Ptolemy's No. 6 of that constellation) is of
+the 2nd magnitude, while in the case of [Greek: g] Urs� Minoris (Ptolemy's
+No. 7), Ptolemy called it 2nd, and Argelander rated it 3rd; Argelander
+thus making [Greek: g] one magnitude fainter than Ptolemy's estimate. Now,
+Al-Sufi, observing over 900 years ago, rated [Greek: g] of the 3rd
+magnitude, thus correcting Ptolemy and agreeing with Argelander. Modern
+photometric measures confirm the estimates of Al-Sufi and Argelander. But
+it is, of course, possible that one or both stars may be variable in
+light, and [Greek: b] has actually been suspected of variation. Almost all
+the constellations afford examples of this sort. In the majority of cases,
+however, Al-Sufi agrees well with Argelander and Heis, but there are in
+some cases differences which suggest a change in relative brightness.
+
+Among other remarkable things contained in Al-Sufi's most interesting work
+may be mentioned the great nebula in Andromeda, which was first noticed in
+Europe as visible to the naked eye by Simon Marius in 1612. Al-Sufi,
+however, speaks of it as a familiar object in his time.
+
+Schjellerup says--
+
+    "For a long time many of the stars in Ptolemy's catalogue could not be
+    identified in the sky. Most of these discordances were certainly due
+    to mistakes in copying, either in longitude or latitude. Many of these
+    differences were, however, corrected by the help of new manuscripts.
+    For this purpose Al-Sufi's work is of great importance. By a direct
+    examination of the sky he succeeded in finding nearly all the stars
+    reported by Ptolemy (or Hipparchus). And even if his criticism may
+    sometimes seem inconclusive, his descriptions are not subject to
+    similar defects, his positions not depending solely on the places
+    given in Ptolemy's catalogue. For, in addition to the longitudes and
+    latitudes quoted from Ptolemy, he has described by alignment the
+    positions of the stars referred to. In going from the brightest and
+    best known stars of each constellation he indicates the others either
+    by describing some peculiarity in their position, or by giving their
+    mutual distance as so many cubits (_dzir�_), or a span (_schibr_),
+    units of length which were used at that time to measure apparent
+    celestial distances. The term _dzir�_ means literally the fore-arm
+    from the bone of the elbow to the tip of the middle finger, or an ell.
+    We should not, however, conclude from this that the Arabians were so
+    unscientific as to measure celestial distances by an ell, as this
+    would be quite in contradiction to their well-known knowledge of
+    Geometry and Trigonometry."
+
+With reference to the arc or angular distance indicated by the "cubit,"
+Al-Sufi states in his description of the constellation Auriga that the
+_dzir�_ (or cubit) is equal to 2� 20'. Three cubits, therefore, represent
+7�, and 4 cubits 9� 20'.
+
+In Al-Sufi's own preface to his work, after first giving glory to God and
+blessings on "his elected messenger Muhammed and his family," he proceeds
+to state that he had often "met with many persons who wished to know the
+fixed stars, their positions on the celestial vault, and the
+constellations, and had found that these persons may be divided into two
+classes. One followed the method of astronomers and trust to spheres
+designed by artists, who not knowing, the stars themselves, take only the
+longitudes and latitudes which they find in the books, and thus place the
+stars on the sphere, without being able to distinguish truth from error.
+It then follows that those who really know the stars in the sky find on
+examining these spheres that many stars are otherwise than they are in the
+sky. Among these are Al-Battani, At�rid and others."
+
+Al-Sufi seems rather hard on Al-Battani (or Albategnius as he is usually
+called) for he is generally considered to have been the most
+distinguished of the Arabian astronomers. His real name was Mohammed Ibn
+Jaber Ibn Senan Abu Abdallah Al-Harrani. He was born about A.D. 850 at
+Battan, near Harran in Mesopotamia, and died about A.D. 929. He was the
+first to make use of sines instead of chords, and versed sines. The
+_Alphonsine Tables_ of the moon's motions were based on his observations.
+
+After some severe criticisms on the work of Al-Battani and At�rid, Al-Sufi
+goes on to say that the other class of amateurs who desire to know the
+fixed stars follow the method of the Arabians in the science of
+_Anva_[392] and the mansions of the moon and the books written on this
+subject. Al-Sufi found many books on the _anva_, the best being those of
+Abu Hanifa al-D�navari. This work shows that the author knew the Arabic
+tradition better than any of the other writers on the subject. Al-Sufi,
+however, doubts that he had a good knowledge of the stars themselves, for
+if he had he would not have followed the errors of his predecessors.
+
+According to Al-Sufi, those who know one of these methods do not know the
+other. Among these is Abu-Hanifa, who states in his book that the names of
+the twelve signs (of the Zodiac) did not originate from the arrangement
+or configuration of the stars resembling the figure from which the name
+is derived. The stars, Abu-Hanifa said, "change their places, and although
+the names of the signs do not change, yet the arrangement of the stars
+ceases to be the same. This shows that he was not aware of the fact that
+the arrangement of the stars does not change, and their mutual distances
+and their latitudes, north and south of the ecliptic, are neither
+increased nor diminished." "The stars," Al-Sufi says, "do not change with
+regard to their configurations, because they are carried along together by
+a physical motion and by a motion round the poles of the ecliptic. This is
+why they are called fixed. Abu-Hanifa supposed that they are termed fixed
+because their motion is very slow in comparison with that of the planets."
+"These facts," he says, "can only be known to those who follow the method
+of the astronomers and are skilled in mathematics."
+
+Al-Sufi says that the stars of the Zodiac have a certain movement
+following the order of the signs, which according to Ptolemy and his
+predecessors is a degree in 100 years. But according to the authors of
+_al-mumtahan_ and those who have observed subsequently to Ptolemy, it is a
+degree in 66 years. According to modern measures, the precession is about
+50"�35 per annum, or one degree in 71-1/2 years.
+
+Al-Sufi says that the Arabians did not make use of the figures of the
+Zodiac in their proper signification, because they divided the
+circumference of the sky by the number of days which the moon took to
+describe it--about 28 days--and they looked for conspicuous stars at
+intervals which, to the eye, the moon appeared to describe in a day and a
+night. They began with _al-scharata�n_, "the two marks" ([Greek: a] and
+[Greek: b] Arietis) which were the first striking points following the
+point of the spring equinox. They then sought behind these two marks
+another point at a distance from them, equal to the space described by the
+moon in a day and a night. In this way they found _al-buta�n_ ([Greek: e],
+[Greek: d], and [Greek: r] Arietis); after that _al-tsuraija_, the
+Pleiades; then _al-dabaran_, the Hyades, and thus all the "mansions" of
+the moon. They paid no attention to the signs of the Zodiac, nor to the
+extent of the figures which composed them. This is why they reckoned among
+the "mansions" _al-haka_ ([Greek: l] Orionis) which forms no part of the
+signs of the Zodiac, since it belongs to the southern constellation of the
+Giant (Orion). And similarly for other stars near the Zodiac, of which
+Al-Sufi gives some details. He says that Regulus ([Greek: a] Leonis) was
+called by the Arabians _al-maliki_, the Royal Star, and that _al-anva_
+consists of five stars situated in the two wings of the Virgin. These
+stars seem to be [Greek: b], [Greek: �], [Greek: g], [Greek: d], and
+[Greek: e] Virginis, which form with Spica ([Greek: a] Virginis) a
+Y-shaped figure. Spica was called _simak al-azal_, the unarmed _simak_;
+the "armed _simak_" being Arcturus, _simak al-ramih_. These old Arabic
+names seem very fanciful.
+
+Al-Sufi relates that in the year 337 of the Hegira (about A.D. 948) he
+went to Ispahan with Prince Abul-fadhl, who introduced him to an
+inhabitant of that city, named Varvadjah, well known in that country, and
+famous for his astronomical acquirements. Al-Sufi asked him the names of
+the stars on an astrolabe which he had, and he named Aldebaran, the two
+bright stars in the Twins (Castor and Pollux), Regulus, Sirius, and
+Procyon, the two Simaks, etc. Al-Sufi also asked him in what part of the
+sky _Al-fard_ ([Greek: a] Hydr�) was, but he did not know! Afterwards, in
+the year 349, this same man was at the court of Prince Adhad-al-Davlat,
+and in the presence of the Prince, Al-Sufi asked him the name of a bright
+star--it was _al-nasr al-vaki_, the falling Vulture (Vega), and he
+replied, "That is _al-aijuk_" (Capella)! thus showing that he only knew
+the _names_ of the stars, but did not know them when he saw them in the
+sky. Al-Sufi adds that all the women "who spin in their houses" knew this
+star (Vega) by the name of _al-atsafi_, the Tripod. But this could not be
+said even of "educated women" at the present day.
+
+With reference to the number of stars which can be seen with the naked
+eye, Al-Sufi says, "Many people believe that the total number of fixed
+stars is 1025, but this is an evident error. The ancients only observed
+this number of stars, which they divided into six classes according to
+magnitude. They placed the brightest in the 1st magnitude; those which are
+a little smaller in the 2nd; those which are a little smaller again in the
+3rd; and so on to the 6th. As to those which are below the 6th magnitude,
+they found that their number was too great to count; and this is why they
+have omitted them. It is easy to convince one's self of this. If we
+attentively fix our gaze on a constellation of which the stars are well
+known and registered, we find in the spaces between them many other stars
+which have not been counted. Take, for example, the Hen [Cygnus]; it is
+composed of seventeen internal stars, the first on the beak, the brightest
+on the tail, the others on the wings, the neck and the breast; and below
+the left wing are two stars which do not come into the figure. Between
+these different stars, if you examine with attention, you will perceive a
+multitude of stars, so small and so crowded that we cannot determine their
+number. It is the same with all the other constellations." These remarks
+are so correct that they might have been written by a modern astronomer.
+It should be added, however, that _all_ the faint stars referred to by
+Al-Sufi--and thousands of others still fainter--have now been mapped down
+and their positions accurately determined.
+
+About the year 1437, Ulugh Beigh, son of Shah Rokh, and grandson of the
+Mogul Emperor Tamerlane, published a catalogue of stars in which he
+corrected Ptolemy's positions. But he seems to have accepted Al-Sufi's
+star magnitudes without any attempt at revision. This is unfortunate, for
+an _independent_ estimate of star magnitudes made in the fifteenth century
+would now be very valuable for comparison with Al-Sufi's work and with
+modern measures. Ulugh Beigh's catalogue contains 1018 stars, nearly the
+same number as given by Ali-Sufi.[393]
+
+
+
+
+CHAPTER XIX
+
+The Constellations[394]
+
+
+Curious to say, Al-Sufi rated the Pole Star as 3rd magnitude; for it is
+now only slightly less than the 2nd. At present it is about the same
+brightness as [Greek: b] of the same constellation (Ursa Minor) which
+Al-Sufi rated 2nd magnitude. It was, however, also rated 3rd magnitude by
+Ptolemy (or Hipparchus), and it may possibly have varied in brightness
+since ancient times. Admiral Smyth says that in his time (1830) it was
+"not even a very bright third size" (!)[395] Spectroscopic measures show
+that it is approaching the earth at the rate of 16 miles a second; but
+this would have no perceptible effect on its brightness in historical
+times. This may seem difficult to understand, and to some perhaps
+incredible; but the simple explanation is that its distance from the earth
+is so great that a journey of even 2000 years with the above velocity
+would make no _appreciable_ difference in its distance! This is
+undoubtedly true, as a simple calculation will show, and the fact will
+give some idea of the vast distance of the stars. The well-known 9th
+magnitude companion to the Pole Star was seen _by day_ in the Dorpat
+telescope by Struve and Wrangel; and "on one occasion by Encke and
+Argelander."[396]
+
+The star [Greek: b] Urs� Minoris was called by the Arabians _Kaukab
+al-sham�li_, the North Star, as it was--owing to the precession of the
+Equinoxes--nearer to the Pole in ancient times than our present Pole Star
+was _then_.
+
+The "Plough" (or Great Bear) is supposed to represent a waggon and horses.
+"Charles' Wain" is a corruption of "churl's wain," or peasant's cart. The
+Arabians thought that the four stars in the quadrilateral represented a
+bier, and the three in the "tail" the children of the deceased following
+as mourners! In the Greek mythology, Ursa Major represented the nymph
+Callisto, a daughter of Lycaon, who was loved by Jupiter, and turned into
+a bear by the jealous Juno. Among the old Hindoos the seven stars
+represented the seven Rishis. It is the Otawa of the great Finnish epic,
+the "Kalevala." It was also called "David's Chariot," and in America it
+is known as "The Dipper."
+
+Closely north of the star [Greek: th] in Ursa Major is a small star known
+as Flamsteed 26. This is not mentioned by Al-Sufi, but is now, I find from
+personal observation, very visible, and indeed conspicuous, to the naked
+eye. I find, however, that owing to the large "proper motion" of the
+bright star (1"�1 per annum) the two stars were much closer together in
+Al-Sufi's time than they are at present, and this probably accounts for
+Al-Sufi's omission. This is an interesting and curious fact, and shows the
+small changes which occur in the heavens during the course of ages.
+
+Close to the star [Greek: z], the middle star of the "tail" of Ursa Major
+(or handle of the "Plough"), is a small star known as Alcor, which is
+easily visible to good eyesight without optical aid. It is mentioned by
+Al-Sufi, who says the Arabians called it _al-suha_, "the little unnoticed
+one." He says that "Ptolemy does not mention it, and it is a star which
+seems to test the powers of the eyesight." He adds, however, an Arabian
+proverb, "I show him _al-suha_, and he shows me the moon," which seems to
+suggest that to some eyes, at least, it was no test of sight at all. It
+has, however, been suspected of variation in light. It was rated 5th
+magnitude by Argelander, Heis, and Houzeau, but was measured 4�02 at
+Harvard Observatory. It has recently been found to be a spectroscopic
+binary.
+
+The constellation of the Dragon (Draco) is probably referred to in Job
+(chap. xxvi. v. 13), where it is called "the crooked serpent." In the
+Greek mythology it is supposed to represent the dragon which guarded the
+golden apples in the Garden of the Hesperides. Some have suggested that it
+represented the serpent which tempted Eve. Dryden says, in his translation
+of Virgil--
+
+  "Around our Pole the spiry Dragon glides,
+  And like a wand'ring stream the Bears divides."
+
+The fact that the constellation Bo�tis rises quickly and sets slowly,
+owing to its lying horizontally when rising and vertically when setting,
+was noted by Aratus, who says--
+
+  "The Bearward now, past seen,
+  But more obscured, near the horizon lies;
+  For with the four Signs the Ploughman, as he sinks,
+  The deep receives; and when tired of day
+  At even lingers more than half the night,
+  When with the sinking sun he likewise sets
+  These nights from his late setting bear their name."[397]
+
+The cosmical setting of Bo�tis--that is, when he sets at sunset--is stated
+by Ovid to occur on March 5 of each year.
+
+With reference to the constellation Hercules, Admiral Smyth says--
+
+    "The kneeling posture has given rise to momentous discussion; and
+    whether it represents Lycaon lamenting his daughter's transformation,
+    or Prometheus sentenced, or Ixion ditto, or Thamyrus mourning his
+    broken fiddle, remains still uncertain. But in process of time, this
+    figure became a lion, and Hyginus mentions both the lion's skin and
+    the club; while the right foot's being just over the head of the
+    Dragon, satisfied the mythologists that he was crushing the Lern�an
+    hydra.... Some have considered the emblem as typifying the serpent
+    which infested the vicinity of Cape T�narus, whence a sub-genus of
+    Ophidians still derives its name. At all events a poet, indignant at
+    the heathen exaltation of Hevelius, has said--
+
+        "'To Cerberus, too, a place is given--
+        His home of old was far from heaven.'"[398]
+
+Aratus speaks of Hercules as "the Phantom whose name none can tell."
+
+There were several heroes of the name of Hercules, but the most famous was
+Hercules the Theban, son of Jupiter and Alcmene wife of Amphitryon, King
+of Thebes, who is said to have lived some years before the siege of Troy,
+and went on the voyage of the Argonauts about 1300 B.C. According to some
+ancient writers, another Hercules lived about 2400 B.C., and was a
+contemporary of Atlas and Theseus. But according to P�tau, Atlas lived
+about 1638 B.C., and Lalande thought that this chronology is the more
+probable.
+
+The small constellation Lyra, which contains the bright star Vega, is
+called by Al-Sufi the Lyre, the Goose, the Persian harp, and the Tortoise.
+In his translation of Al-Sufi's work, Schjellerup suggests that the name
+"Goose" may perhaps mean a plucked goose, which somewhat resembles a Greek
+lyre, and also a tortoise. The name of the bright star Vega is a
+corruption of the Arabic _v�ki_. Ptolemy and Al-Sufi included all the very
+brightest stars in the "first magnitude," making no distinction between
+them, but it is evident at a glance that several of them, such as Arcturus
+and Vega, are brighter than an average star of the first magnitude, like
+Aldebaran.
+
+The constellation Perseus, which lies south-east of "Cassiopeia's Chair,"
+may be recognized by the festoon formed by some of its stars, the bright
+star [Greek: a] Persei being among them. It is called by Al-Sufi
+"_barsch�nsch_, [Greek: Perseus], Perseus, who is _hamil r�s al-gul_, the
+Bearer of the head of _al-gul_." According to Kazimirski, "_Gul_ was a
+kind of demon or ogre who bewilders travellers and devours them, beginning
+at the feet. In general any mischievous demon capable of taking all sorts
+of forms." In the Greek mythology Perseus was supposed to be the son of
+Jupiter and Dan�. He is said to have been cast into the sea with his
+mother and saved by King Polydectus. He afterwards cut off the head of
+Medusa, one of the Gorgons, while she slept, and armed with this he
+delivered Andromeda from the sea-monster.
+
+The constellation Auriga lies east of Perseus and contains the bright star
+Capella, one of the three brightest stars in the northern hemisphere (the
+others being Arcturus and Vega). Theon, in his commentary on Aratus, says
+that Bellerophon invented the chariot, and that it is represented in the
+heavens by Auriga, the celestial coachman. According to Dupuis, Auriga
+represents Ph�ton, who tried to drive the chariot of the sun, and losing
+his head fell into the river Eridanus. The setting of Eridanus precedes by
+a few minutes that of Auriga, which was called by some of the ancient
+writers Amnis Pha�-tontis.[399] Auriga is called by Al-Sufi _numsick
+al-ainna_--He who holds the reins, the Coachman; also _al-in�z_, the
+She-goat. M. Dorn found in Ptolemy's work, the Greek name [Greek:
+H�niochoi], Auriga, written in Arabic characters. Al-Sufi says, "This
+constellation is represented by the figure of a standing man behind 'He
+who holds the head of _al-g�l_' [Perseus], and between the Pleiades and
+the Great Bear."
+
+Capella is, Al-Sufi says, "the bright and great star of the first
+magnitude which is on the left shoulder [of the ancient figure] on the
+eastern edge of the Milky Way. It is that which is marked on the astrolabe
+as _al-aij�k_." The real meaning of this name is unknown. Schjellerup
+thought, contrary to what Ideler says, that the name is identical with
+the Greek word [Greek: Aix] (a goat). Capella was observed at Babylon
+about 2000 B.C., and was then known as Dilgan. The Assyrian name was
+_Icu_, and the Persian name _colca_. It was also called Capra Hircus,
+Cabrilla, Amalthea, and Olenia. In ancient times the rising of Capella was
+supposed to presage the approach of storms. Ovid says, "Olenia sidus
+pluviale Capell�."
+
+The constellation Aquila is called by Al-Sufi _al-ukab_, the Eagle, or
+_al-nasr al-t��r_, the flying vulture. According to the ancient poets the
+eagle carried nectar to Jupiter when he was hidden in a cave in Crete.
+This eagle also assisted Jupiter in his victory over the Giants and
+contributed to his other pleasures. For these reasons the eagle was
+consecrated to Jupiter, and was placed in the sky. Al-Sufi says, "There
+are in this figure three famous stars [[Greek: g], [Greek: a], and [Greek:
+b] Aquil�], which are called _al-nasr al-t��r_." Hence is derived the
+modern name Altair for the bright star [Greek: a] Aquil�. Al-Sufi says
+that the "common people" call "the three famous stars" _al-m�z�n_, the
+Balance, on account of the equality of the stars." This probably refers to
+the approximately equal distances between [Greek: g] and [Greek: a], and
+[Greek: a] and [Greek: b], and not to their relative brightness. He says
+"Between the bright one of the tail [[Greek: x] Aquil�] and the star in
+the beak of the Hen [[Greek: b] Cygni] in the thinnest part of the Milky
+Way, we see the figure of a little earthen jar, of which the stars begin
+at the bright one in the tail, and extend towards the north-west. [This
+seems to refer to [Greek: e] Aquil� and the small stars near it.] They
+then turn towards the east in the base of the jar, and then towards the
+south-east to a little cloud [4, 5, etc. Vulpecul�, a well-known group of
+small stars] which is found to the north of the two stars in the shaft of
+the Arrow [[Greek: a] and [Greek: b] Sagitt�]. The cloud is on the eastern
+edge of the jar, and the bright one on the tail on the western edge; the
+orifice is turned towards the flying Vulture [Aquila], and the base
+towards the north. Among these are distinguished some of the fourth,
+fifth, and sixth magnitudes [including, probably, 110, 111, 112, 113
+Hercules, and 1 Vulpecul�] and Ptolemy says nothing of this figure, except
+the bright star in the tail of the Eagle" (see figure). The above is a
+good example of the minute accuracy of detail in Al-Sufi's description.
+
+[Illustration: AL-SUFI'S "EARTHEN JAR."]
+
+The southern portion of Aquila was formerly called Antinous, who was said
+to have been a young man of great beauty born at Claudiopolis in Bithynia,
+and drowned in the Nile. Others say that he sacrificed his life to save
+that of the Emperor Hadrian, who afterwards raised altars in his honour
+and placed his image on coins.[400]
+
+The constellation Pegasus, Al-Sufi says, "is represented by the figure of
+a horse, which has the head, legs, and forepart of the body to the end of
+the back, but it has neither hind quarters nor hind legs." According to
+Brown, Pegasus was the horse of Poseidon, the sea god. Half of it was
+supposed to be hidden in the sea, into which the river Eridanus
+flowed.[401] In the Greek mythology it was supposed to represent the
+winged horse produced by the blood which fell from the head of Medusa when
+she was killed by Perseus! Some think that it represents Bellerophon's
+horse, and others the horse of Nimrod. It was also called Sagmaria and
+Ephippiatus, and was sometimes represented with a saddle instead of wings.
+
+In describing the constellation Andromeda, Al-Sufi speaks of two series of
+stars which start from the great nebula in Andromeda; one series going
+through 32 Andromed�, [Greek: p, d], and [Greek: e] to [Greek: z] and
+[Greek: �]; and the other through [Greek: n, m, b] Andromed� into the
+constellation Pisces. He says they enclose a fish-shaped figure called by
+the Arabians _al-h�t_, the Fish, _par excellence_. He speaks of two other
+series of stars which begin at [Greek: t] and [Greek: u], and diverging
+meet again at [Greek: ch] Persei, forming another "fish-like figure." The
+eastern stream starts from [Greek: t] and passes through 55, [Greek: g],
+60, 62, 64, and 65 Andromed�; and the western stream from [Greek: u]
+through [Greek: ch] 51, 54, and _g_ Persei up to [Greek: ch] Persei. The
+head of the first "fish," _al-h�t_, is turned towards the north, and that
+of the second towards the south (see figure).
+
+[Illustration: AL-SUFI'S "FISHES" IN ANDROMEDA.]
+
+Al-Sufi says that the stars [Greek: a] Persei, [Greek: g, b, d], and
+[Greek: a] Andromed�, and [Greek: b] Pegasi form a curved line. This is
+quite correct, and this fine curve of bright stars may be seen at a glance
+on a clear night in September, when all the stars are high in the sky.
+
+The first constellation of the Zodiac, Aries, the Ram, was called,
+according to Aratus and Eratosthenes, [Greek: krios]. It is mentioned by
+Ovid under the name of Hellas. It was also called by the ancients the Ram
+with the golden horns. Manilius (fourth century B.C.) called it "The
+Prince." It is supposed to have represented the god Bel. Among the
+Accadians the sign meant "He who dwells on the altar of uprightness." It
+first appears on the Egyptian Zodiac; and it was sacred to Jupiter Ammon.
+In the Greek mythology it was supposed to represent the ram, the loss of
+whose fleece led to the voyage of the Argonauts. In the time of
+Hipparchus, about 2000 years ago, it was the first sign of the Zodiac, or
+that in which the sun is situated at the Vernal Equinox (about March 21 in
+each year). But owing to the precession of the equinoxes, this point has
+now moved back into Pisces.
+
+The brightest star of Aries ([Greek: a]) is sometimes called Hamal,
+derived from the Arabic _al-hamal_, a name given to the constellation
+itself by Al-Sufi. In the Accadian language it was called _Dilkur_, "the
+dawn proclaimer." Ali-Sufi says that close to [Greek: a], "as if it were
+attached to it," is a small star of the 6th magnitude, not mentioned by
+Ptolemy. This is clearly [Greek: k] Arietis. The fact of Al-Sufi having
+seen and noticed this small star, which modern measures show to be below
+the 5th magnitude, is good evidence of his keen eyesight and accuracy of
+observation.
+
+According to Al-Sufi, the stars [Greek: b] and [Greek: g] Arietis were
+called by the Arabians _al-scharatain_, "the two marks." They marked the
+"first mansion of the moon," and [Greek: e, d], and [Greek: r] the second
+mansion. With reference to these so-called "mansions of the moon," Admiral
+Smyth says--
+
+    "The famous _Manazil al-kamar_, i.e. Lunar mansions, constituted a
+    supposed broad circle in Oriental astronomy divided into twenty-eight
+    unequal parts, corresponding with the moon's course, and therefore
+    called the abodes of the moon. This was not a bad arrangement for a
+    certain class of gazers, since the luminary was observed to be in or
+    near one or other of these parts, or constellations every night.
+    Though tampered with by astrologers, these Lunar mansions are probably
+    the earliest step in ancient astronomy."[402]
+
+Taurus, the second constellation of the Zodiac, was in ancient times
+represented by the figure of a bull, the hinder part of which is turned
+towards the south-west, and the fore part towards the east. It had no hind
+legs, and the head was turned to one side, with the horns extended towards
+the east. Its most ancient name was _Te_, possibly a corruption of the
+Accadian _dimmena_, "a foundation-stone." The Greek name is [Greek: ath�r]
+([Greek: th��r], Eusebius). In the old Egyptian mythology Taurus
+represented the god Apis. According to Dupuis it also represented the 10th
+"labour of Hercules," namely, his victory over the cows of Geryon, King of
+Spain.[403] It was also supposed to represent the bull under the form of
+which Jupiter carried off Europa, daughter of Agenor, King of the
+Phoenicians. It may also refer to Io or Isis, who is supposed to have
+taught the ancient Egyptians the art of agriculture.
+
+Aldebaran is the well-known bright red star in the Hyades. It was called
+by Ptolemy _Fulgur succularum_. Ali-Sufi says it was marked on the old
+astrolabes as _al-dabaran_, "the Follower" (because it follows the Hyades
+in the diurnal motion), and also _ain al-tsaur_, the eye of the bull. It
+may be considered as a standard star of the 1st magnitude. Modern
+observations show that it has a parallax of 0"�107. It is receding from
+the earth, according to Vogel, at the rate of about 30 miles a second;
+but even with this high velocity it will take thousands of years before
+its brightness is perceptibly diminished. It has a faint companion of
+about the 10th magnitude at the distance of 118", which forms a good
+"light test" for telescopes of 3 or 4 inches aperture. I saw it well with
+a 4-inch Wray in the Punjab sky. The Hyades were called _Succul�_ by the
+Romans, and in the Greek mythology were said to be children of Atlas.
+
+The star [Greek: b] Tauri, sometimes called Nath, from the Arabic
+_al-n�tih_, the butting, is a bright star between Capella and [Greek: g]
+Orionis (Bellatrix). It is on the tip of the horn in the ancient figure of
+Taurus, and "therefore" (says Admiral Smyth) "at the greatest distance
+from the hoof; can this have given rise to the otherwise pointless sarcasm
+of not knowing B from a bull's foot?"[404] Al-Sufi says that an imaginary
+line drawn from the star now known as A Tauri to [Greek: t] Tauri would
+pass between [Greek: u] and [Greek: k] Tauri, which is quite correct,
+another proof of the accuracy of his observations. He also says that the
+star [Greek: �] Tauri is exactly midway between A and [Greek: e], which is
+again correct. He points out that Ptolemy's position of [Greek: �] is
+incorrect. This is often the case with Ptolemy's positions, and tends to
+show that Ptolemy adopted the position given by Hipparchus without
+attempting to verify their position in the sky. Al-Sufi himself adopts
+the longitudes and latitudes of the stars as given by Ptolemy in the
+_Almagest_, but corrects the positions in his _descriptions_, when he
+found Ptolemy's places erroneous.
+
+The famous group of the Pleiades is well known; but there is great
+difficulty in understanding Al-Sufi's description of the cluster. He says,
+"The 29th star (of Taurus) is the more northern of the anterior side of
+the Pleiades themselves, and the 30th is the southern of the same side;
+the 31st is the following vertex of the Pleiades, and is in the more
+narrow part. The 32nd is situated outside the northern side. Among these
+stars, the 32nd is of the 4th magnitude, the others of the 5th." Now, it
+is very difficult or impossible to identify these stars with the stars in
+the Pleiades as they are at present. The brightest of all, Alcyone
+([Greek: �] Tauri), now about 3rd magnitude, does not seem to be mentioned
+at all by Al-Sufi! as he says distinctly that "the brightest star" (No 32
+of Taurus) is "outside" the Pleiades "on the northern side." It seems
+impossible to suppose that Al-Sufi could have overlooked Alcyone had it
+the same brightness it has now. The 32nd star seems to have disappeared,
+or at least diminished greatly in brightness, since the days of Al-Sufi.
+More than four stars were, however, seen by Al-Sufi, for he adds, "It is
+true that the stars of the Pleiades must exceed the four mentioned above,
+but I limit myself to these four because they are very near each other and
+the largest [that is, the brightest]; this is why I have mentioned them,
+neglecting the others." A full examination of the whole question is given
+by Flammarion in his interesting work _Les �toiles_ (pp. 289-307), and I
+must refer my readers to this investigation for further details.
+
+According to Brown, Simonides of Keos (B.C. 556-467) says, "Atlas was the
+sire of seven daughters with violet locks, who are called the heavenly
+_Peleiades_."[405] The name is by some supposed to be derived from the
+Greek [Greek: plei�n], full. The Old Testament word _Kimah_ (Job ix. 9 and
+xxviii. 31) and Amos (v. 8) is derived from the Assyrian _Kimta_, a
+"family." Aratus describes the Pleiades in the following lines:--
+
+  "Near his[406] left thigh together sweep along
+  The flock of Clusterers. Not a mighty span
+  Holds all, and they themselves are dim to see,
+  And seven paths aloft men say they take,
+  Yet six alone are viewed by mortal eye.
+  These seven are called by name Alkyon�
+  Kelain�, Merop� and Sterop�
+  Tayget�, Elecktr�, Maia queen.
+  They thus together small and faint roll on
+  Yet notable at morn and eve through Zeus."[407]
+
+The Pleiades are mentioned by Ovid. According to the ancient poets they
+were supposed to represent the children of Atlas and Hesperus, and on
+this account they were called Atlantids or Hesperides. From the
+resemblance in sound to the word [Greek: pleias], a pigeon, they were
+sometimes called "the doves," and for the same reason the word [Greek:
+plein], to navigate, led to their being called the "shipping stars." The
+word [Greek: pleias] was also applied to the priestesses of the god Zeus
+(Jupiter) at Dordona, in the groves of which temple there were a number of
+pigeons. This is, perhaps, what Aratus refers to in the last line of the
+extract quoted above. According to Neapolitan legends, the name of
+Virgil's mother was Maia. The mother of Buddha, the Hindoo _avatar_, was
+also named Maia. In Italy the Pleiades were called _Gallinata_, and in
+France _poussini�re_, both of which mean the hen and chickens, a term also
+given to them by Al-Sufi. The old Blackfoot Indians called them "The Seven
+Perfect Ones." The Crees and Ojibway Indians called them the "Fisher
+Stars." The Adipones of Brazil and some other nations claimed that they
+sprang from the Pleiades! The Wyandot Indians called them "The Singing
+Maidens."
+
+Photographs show that the brighter stars of the Pleiades are involved in
+nebulosity. That surrounding Maia seems to be of a spiral form. Now, there
+is a Sanscrit myth which represents Maia as "weaving the palpable
+universe," for which reason she was "typified as a spider." This seems
+very appropriate, considering the web of nebulous light which surrounds
+the stars of the group. Maia was also considered as a type of the
+universe, which again seems appropriate, as probably most of the stars
+were evolved from spiral nebul�.
+
+The name Hyades is supposed to be derived from the Greek word [Greek:
+hyein], to rain, because in ancient times they rose at the rainy season.
+
+In ancient Egypt, Aldebaran was called _ary_; and the Pleiades _chooa_, a
+word which means "thousands." The name Aldebaran seems to have been
+originally applied to the whole of the Hyades group. Aldebaran was also
+called by the Arabians _al-fanik_, the great Camel, and the Hyades
+_al-kilas_, the young Camels. The two close stars [Greek: u] and [Greek:
+k] Tauri were called _al-kalba�n_, the dogs of Aldebaran. La Condamine
+states that the Indians of the Amazon saw in the Hyades the head of a
+bull.
+
+Gemini, the Twins, is the third constellation of the Zodiac. It was also
+called Gemelli, etc. According to Dupuis it represents the 11th "labour of
+Hercules"--his triumph over the dog Cerberus.[408] But some of Dupuis'
+ideas seem very fanciful. The Twins are usually called Castor and Pollux,
+but they were also called by the ancient writers Apollo and Hercules;
+Jason and Triptolemus; Amphion and Zethus; and Theseus and Peritheus. In
+Egypt they represented the deities Horus and Hippocrates. Brown thinks
+that the "Great Twins" were originally the sun and moon, "who live
+alternately. As one is born the other dies; as one rises the other
+sets."[409] This applies to the full moon, but does not seem applicable to
+the other lunar phases.
+
+Gemini was the constellation to which Dante supposed himself transported
+when he visited the stellar heavens.[410] He says he was born under the
+influence of this "sign."
+
+Cancer, the Crab, is the next sign of the Zodiac. In the Greek mythology
+it was supposed to have been placed in the sky by Juno to commemorate the
+crab which pinched the toes of Hercules in the Lern�an marsh. The Greek
+name was [Greek: tybi]. According to Dupuis it represents the 12th "labour
+of Hercules"--his capture of the golden apples in the Garden of the
+Hesperides, which were guarded by a Dragon. This Dragon is Draco, which
+was also called Custos Hesperidum.[411] But the connection between a crab
+and the myth of the golden apples is not obvious--unless some reference to
+"crab apples" is intended! Among the Romans, Cancer was consecrated to
+Mercury, and by the ancient Egyptians to their god Anubis.
+
+The well-known cluster in Cancer called the Pr�sape, Al-Sufi says, is "a
+little spot which resembles a cloud, and is surrounded by four stars, two
+to the west [[Greek: �] and [Greek: th] Cancri] and two to the east"
+[[Greek: g] and [Greek: d]]. This cluster is mentioned by Aratus, who
+calls it the "Manger." The word Pr�sape is often translated "Beehive," but
+there can be no doubt that it really means "Manger," referring to the
+stars [Greek: g] and [Greek: d] Cancri, which the ancients called Aselli,
+the ass's colts. These were supposed to represent the asses which in the
+war of Jupiter against the Giants helped his victory by their braying!
+
+Admiral Smyth says in his _Bedford Catalogue_ (p. 202) that he found
+[Greek: g] and [Greek: d] Cancri both of 4th magnitude; but the
+photometric measures show that [Greek: d] is now distinctly brighter than
+[Greek: g]. An occultation of [Greek: d] Cancri by the moon is recorded as
+having occurred on September 3, B.C. 240.
+
+The fine constellation Leo, the Lion, is the next "sign" of the Zodiac,
+and is marked by the well-known "Sickle." According to Dupuis, it
+represents the first "labour of Hercules"--the killing of the Nem�lian
+lion. Manilius called it Nem�us. It was also called Janonus sidus, Bacchi
+sidus, etc. The Greek name was [Greek: mechir], [Greek: mecheir], or
+[Greek: mechos]. In ancient Egypt, Leo was sacred to Osiris, and many of
+the Egyptian monuments are ornamented with lions' heads. It is stated in
+the Horapolla that its appearance was supposed to announce the annual
+rising of the Nile.
+
+Regulus ([Greek: a] Leonis) is the brightest and most southern of the
+stars in the "Sickle." Al-Sufi says "it is situated in the heart and is of
+the 1st magnitude. It is that which is called _al-maliki_, the royal star.
+It is marked on the astrolabe as _kalb al-asad_, the Heart of the Lion"
+(whence the name Cor Leonis). Modern photometric measures make it about
+1�3 magnitude. It has an 8-1/2 magnitude companion at about 177" distance
+(Burnham) which is moving through space with the bright star, and is
+therefore at probably the same distance from the earth as its brilliant
+primary. This companion is double (8�5, 12�5: 3"�05, Burnham). The
+spectroscope shows that Regulus is approaching the earth at the rate of
+5-1/2 miles a second. Its parallax is very small--about 0"�022, according
+to Dr. Elkin--which indicates that it is at a vast distance from the
+earth; and its brightness shows that it must be a sun of enormous size.
+Ptolemy called it [Greek: basiliskos], whence its Latin name Regulus,
+first used by Copernicus as the diminutive of _rex_.[412]
+
+The next constellation of the Zodiac is Virgo, the Virgin. It was also
+called by the ancients Ceres, Isis, Erigone, Fortuna, Concorda, Astr�a,
+and Themis. The Greek name was [Greek: phamen�th]. Ceres was the goddess
+of the harvest. Brown thinks that it probably represents the ancient
+goddess Istar, and also Ashtoreth. According to Prof. Sayce it is the
+same as the Accadian sign of "the errand of Istar, a name due to the
+belief that it was in August that the goddess Astarte descended into Hades
+in search of her betrothed, the sun god Tammuz, or Adonis, who had been
+slain by the boar's tusk."[413] The ear of corn (Spica) is found on the
+ancient Egyptian monuments, and is supposed to represent the fertility
+caused by the annual rising of the Nile. According to Aratus, the Virgin
+lived on earth during the golden age under the name of Justice, but that
+in the bronze age she left the earth and took up her abode in the heavens.
+
+  "Justice, loathing that race of men,
+  Winged her flight to heaven."
+
+The Sphinx near the Great Pyramid has the head of a virgin on the body of
+a lion, representing the goddess Isis (Virgo) and her husband Osiris
+(Leo).
+
+Al-Sufi's 5th star of Virgo is Flamsteed 63 Virginis. Al-Sufi says it is a
+double star of the 5th magnitude. In Al-Sufi's time it formed a "naked-eye
+double" with 61 Virginis, but owing to large proper motion, 61 has now
+moved about 26 minutes of arc towards the south, and no longer forms a
+double with 63. This interesting fact was first pointed out by Flammarion
+in his work _Les �toiles_ (p. 373).
+
+Libra, the Balance, is one of the "signs" of the Zodiac, but originally
+formed the claws of the Scorpion. It was called Juguna by Cicero, and
+Mochos by Ampelius. The Greek name was [Greek: pharmouthe]. Virgil
+suggests that it represented the justice of the emperor Augustus, honoured
+by the name of a constellation; but probably this refers to the birth of
+Augustus under the sign of Libra, as Scaliger has pointed out. According
+to Brown, "the daily seizing of the dying western sun by the claws of the
+Scorpion of darkness is reduplicated annually at the Autumnal Equinox,
+when the feeble waning sun of shortening days falls ever earlier into his
+enemy's grasp;"[414] and he says, "The Balance or Scales (Libra), which it
+will be observed is in itself neither diurnal nor nocturnal, is the only
+one of the zodiacal signs not Euphratean in origin, having been imported
+from Egypt and representing originally the balance of the sun at the
+horizon between the upper and under worlds; and secondarily the equality
+of the days and nights at the equinox."[415]
+
+According to Houzeau, Libra was formed at the beginning of the second
+century B.C., and it does not appear in any writings before those of
+Geminus and Varron.[416]
+
+Milton says in _Paradise Lost_:--
+
+  "The Eternal to prevent such horrid fray,
+  Hung forth in heaven his golden scales, yet seen
+  Betwixt Astr�a and the Scorpion's sign."
+
+(Here Astr�a is Virgo.)
+
+It is worth noticing that both Ptolemy and Al-Sufi rated the star [Greek:
+k] Libr� as two magnitudes brighter than [Greek: l] Libr�. The two stars
+are now practically of equal brightness (5th magnitude), and it seems
+impossible to believe that this could have been the case in Al-Sufi's
+time. Surely a careful observer like Al-Sufi, who estimated the relative
+brightness of stars to a third of a magnitude, could not possibly have
+made an error of two magnitudes in the brightness of two stars near each
+other! It should be stated, however, that [Greek: k] Libr� was rated 5th
+magnitude by Argelander and Heis, and [Greek: l], 6th magnitude by the
+same excellent observers.
+
+The next "sign" of the Zodiac, Scorpion, was consecrated by the Romans to
+Mars, and by the Egyptians to Typhon.[417] It was called _Nepa_ by Cicero,
+_Martis sidus_ by Manilius, and _Fera magna_ by Aratus. The Greek name was
+[Greek: pach�n].
+
+Mr. E. B. Knobel has called attention to a curious remark of Ptolemy with
+reference to the bright star Antares ([Greek: a] Scorpii), "Media earum
+qu� _tendit ad rapinam_ qu� dicitur Cor Scorpionis"; and he made a similar
+remark with reference to Betelgeuse ([Greek: a] Orionis) and others. But
+Mr. Robert Brown[418] explains the remark by the fact that in ancient
+times these stars rose in the morning at a time when caravans were exposed
+to dangers from robbers. Thus the term had nothing to do with the aspect
+or colour of these stars, but was merely a reference to their supposed
+astrological influence on human affairs.
+
+In the Egyptian _Book of the Dead_, Silkit was a goddess who assumed the
+form of a scorpion in the sky. She was supposed to be the daughter of
+_Ra_.
+
+With reference to stars "outside" the ancient figure of Scorpio, the
+first, Al-Sufi says, "is a star which immediately follows _al-schaulat_"
+[[Greek: l]] and [Greek: k], "it is of small 4th magnitude; Ptolemy calls
+it [Greek: nepheloeid�s]" [nebulous]. Schjelerup, in his translation of
+Al-Sufi's work, does not identify this object; but it is very evidently
+[Greek: g] Telescopii, which lies exactly in the position described by
+Al-Sufi. Now, it is a very interesting and curious fact that Ptolemy
+called it nebulous, for in the same telescopic field with it is the nebula
+_h_ 3705 (= Dunlop 557). Dunlop describes it as a "small well-defined
+rather bright nebula, about 20" in diameter; a very small star precedes
+it, but is not involved; following [Greek: g] Telescopii." Sir John
+Herschel at the Cape found it fairly resolved into very faint stars, and
+adds, "The whole _ground_ of the heavens, for an immense extent is
+thickly sown with such stars. A beautiful object."[419] This perhaps
+accounts for the nebulous appearance of the star as seen by Ptolemy.
+
+Several _nov�_ or temporary stars are recorded as having appeared in
+Scorpio. One in the year B.C. 134 is stated by Pliny to have induced
+Hipparchus to form his catalogue of stars. This star was also observed in
+China. Its exact position is unknown, but Flammarion thinks it may
+possibly have appeared about 4� north of the star [Greek: b] Scorpii.
+Another new star is said to have appeared in A.D. 393, somewhere in the
+Scorpion's tail. One in A.D. 1203 and another in 1584 are also mentioned,
+the latter near [Greek: p] Scorpii.
+
+The constellation Scorpio seems to be referred to by Dante in his
+_Purgatorio_ (ix. 4-6) in the lines--
+
+  "De gemma la sua fronte era lucenta
+  Poste in figura del fredda animale
+  Che con la coda percota la genta,"
+
+perhaps suggested by Ovid's remark--
+
+  "Scorpius exhibit caudaque menabitur unca."[420]
+
+Next to Scorpio comes Sagittarius, the Archer. It is said to have been
+placed in the sky as a symbol of Hercules, a hero who was held in the
+greatest veneration by the ancient Egyptians. The horse, usually
+associated with this constellation, was a symbol of war. It was also
+called by the ancients Chiron, Arcitenens, Minotaurus, Croton, etc. The
+Greek name was [Greek: pauni], or [Greek: pa�ni]. Chiron was supposed to
+be the son of Saturn and Phillyra, and first taught men to ride on horses.
+The name is derived from the Greek [Greek: cheir], a hand. Some writers,
+however, think that Chiron is represented by the constellation of the
+Centaur, and others say that Sagittarius represents the Minotaur loved by
+Persephone. According to Dupuis, Sagittarius represents the 5th "labour of
+Hercules," which consisted in hunting the birds of the lake Stymphalus,
+which ravaged the neighbouring countries. These birds are perhaps
+represented by Cygnus, Altair, and the Vulture (Lyra). The Lyre probably
+represents the musical instrument which Hercules used to frighten the
+birds.[421]
+
+According to Al-Sufi, the Arabians called the stars [Greek: g, d, e], and
+[Greek: �] Sagittarii which form a quadrilateral figure, "the Ostrich
+which goes to the watering place," because they compared the Milky Way to
+a river. They compared the stars [Greek: s, ph, t], and [Greek: z]
+Sagittarii, which form another quadrilateral, to an ostrich which has
+drunk and returns from the "watering place." He says that the star [Greek:
+l] Sagittarii forms with these two "ostriches" a tent, and certainly the
+figure formed by [Greek: l, ph, z, e], and [Greek: d] is not unlike a
+tent. Al-Sufi says more about these "ostriches"; but the ideas of the old
+Arabians about the stars seem very fanciful.
+
+A "temporary star" is recorded in the Chinese Annals of Ma-touan-lin as
+having appeared in May, B.C. 48, about 4� distant from [Greek: m]
+Sagittarii. Another in the year 1011 A.D. appeared near the quadrilateral
+figure formed by the stars [Greek: s, t, z], and [Greek: ph] Sagittarii.
+This may perhaps be identified with the object referred to by Hepidannus
+in the year 1012, which was of extraordinary brilliancy, and remained
+visible "in the southern part of the heavens during three months." Another
+is mentioned near the same place in A.D. 386 (April to July).[422] The
+number of "temporary stars" recorded in this part of the heavens is very
+remarkable.
+
+According to Brown, Sagittarius is depicted on a stone, cir. B.C. 1100,
+found at B�bilu, and now in the British Museum.[423]
+
+       *       *       *       *       *
+
+The next of the "signs of the Zodiac" is Capricornus, the Goat. In the
+Arabo-Latin edition of Ptolemy's _Almagest_ it is called Alcaucurus. It is
+supposed to represent Amalthea, the goat which nursed Jupiter. According
+to Dupuis it represented the 6th "labour of Hercules," which was the
+cleaning out of the Augean stables.[424]
+
+[Greek: a]_{2} Capricorni is the northern of two stars of the 4th
+magnitude ([Greek: a] and [Greek: b] Capricorni). It really consists of
+two stars visible to the naked eye. The second of these two stars ([Greek:
+a]_{1}) is not mentioned by Al-Sufi, but I find that, owing to proper
+motion, they were nearer together in his time (tenth century), and were
+evidently seen by him as one star. [Greek: b] Capricorni (about 3rd
+magnitude) is a very wide double star (3-1/2, 6; 205"), which may be seen
+with any small telescope. The fainter star was found to be a close double
+by Burnham. At present [Greek: b] is brighter than [Greek: a], although
+rated of the same brightness by Al-Sufi.
+
+Aquarius is the next "sign of the Zodiac." It is supposed to represent a
+man pouring water out of an urn or bucket. Other names given to this
+constellation were Arist�us, Ganymede, Cecrops, Amphora, Urna, and Aqua
+tyrannus. According to Dupuis it represents the 7th "labour of Hercules,"
+which was his victory over the famous bull which ravaged Crete.[425] But
+the connection between a bull and a bucket is not obvious. Aquarius is
+represented in several places on the Egyptian monuments. Some of the
+ancient poets supposed that it represented Deucalion (the Noah of the
+Greek story of the Deluge); others thought that it represented Cecrops,
+who came to Greece from Egypt, built Athens, and was also called Bifornis.
+Others say that he was Ganymede, the cup-bearer of the gods.
+
+There is some difficulty about the identification of some of Al-Sufi's
+stars in Aquarius. His sixth star (Fl. 7) is nearly 10� south-west of
+[Greek: b] Aquarii, and is, Al-Sufi says, "the following of three stars in
+the left hand, and precedes the fourth [[Greek: b]] ... it is of the 6th
+magnitude. Ptolemy calls it third, but in reality it is very faint" [now
+about 6th magnitude]. The seventh [[Greek: m]] is the middle one of the
+three and about 4-1/2 magnitude, although Al-Sufi calls it "small fifth"
+[Ptolemy rated it 4]. The eighth star, [Greek: e], is the preceding of the
+three and about 3�8, agreeing closely with Al-Sufi's 4�3. Ptolemy rated it
+3. This star is mentioned under the name _nou_ in the time of
+_Tcheou-Kong_ in the twelfth century B.C. Al-Sufi says, "These three stars
+are followed by a star of the 5th magnitude which Ptolemy has not
+mentioned. It is brighter than the sixth star" [Fl. 7]. This is evidently
+[Greek: n] Aquarii. If, however, we plot Ptolemy's positions as given by
+Al-Sufi, it seems probable that _Ptolemy's_ sixth star was really [Greek:
+n], and that either [Greek: m] or Fl. 7 was not seen by him. As Ptolemy
+called his seventh star 4th magnitude, and his sixth and eighth stars 3rd
+magnitude, some considerable change of brightness seems to have taken
+place in these stars; as [Greek: n] is now only 4-1/2 and Fl. 7 only a
+bright sixth. Variation was suspected in Fl. 7[426] by Gould. I found it
+very reddish with binocular in October, 1892. Burnham found it to be a
+close double star, the companion being about 12th magnitude at a distance
+of only 2". It is probably a binary.
+
+According to Al-Sufi, the Arabians called the second and third stars of
+the figure ([Greek: a] and [Greek: o] Aquarii) _sad al-malik_ (_malk_ or
+_mulk_), "the Good Fortune of the king." They called the fourth and fifth
+stars ([Greek: b] and [Greek: x] Aquarii) with the twenty-eighth star of
+Capricornus (_c_) _sad al-sund_, "the Good Fortune of the Happy Events."
+"This is the 24th mansion of the moon." These stars rose at the time of
+year when the cold ends, and they set at the time the heat ends. Hence,
+Al-Sufi says, "when they rise the rains begin, and when they set the
+unhealthy winds cease, fertility abounds, and the dew falls." Hence
+probably the Arabic names. This, of course, applies to the climate of
+Persia and Arabia, and not to the British Isles. Al-Sufi says, "They call
+the 6th, 7th, and 8th stars _sad bula_, 'The Good Fortune which swallows
+up!' This is the 23rd mansion of the moon. They say that it is so called
+because that at the time of the Deluge it rose at the moment when God
+said, 'O earth! absorb the waters' (Koran, chap, xi., v. 46). They called
+the stars [Greek: g, p, z] and [Greek: �] Aquarii _sad al-achbija_, 'the
+the Good Fortune of the tents'; this is the 25th mansion of the moon, and
+they give them this name because of these four stars, three form a
+triangle, the fourth [[Greek: z]] being in the middle." The three were
+considered to form a tent.
+
+The Arabians called the bright star Fomalhaut "in the mouth of the
+southern fish _al-dhifda al-auval_, 'the first Frog,' as the bright one on
+the southern point of the tail of K�tus [Cetus] is called _al-dhifda
+al-tsani_ [[Greek: b] Ceti], 'the second Frog.'" Fomalhaut was also called
+_al-zhalim_, "the male ostrich."
+
+Al-Sufi says, "Some of the Arabians state that a ship is situated to the
+south of Aquarius." The stars in the Southern Fish (Piscis Australis) seem
+to be here referred to.
+
+The constellation Pisces, the Fishes, is the last of the "signs of the
+Zodiac." The Fishes appear on an ancient Greek obelisk described by
+Pococke. Among the Greeks this sign was consecrated to Venus; and in Egypt
+to Nepthys, wife of Typhon and goddess of the sea. Pisces is said to end
+the Zodiac as the Mediterranean Sea terminated Egypt. This idea was
+suggested by Schmidt, who also conjectured that the Ram (Aries) was placed
+at the beginning of the Zodiac because Thebes, a town sacred to Jupiter
+Ammon, was at the beginning of Egypt in ancient times; and he thought that
+the constellation Triangulum, the Triangle, represented the Nile Delta,
+Eridanus being the Nile.[427] The constellation was represented in ancient
+times by two fishes connected by a cord tied to their tails. The southern
+of these "fishes" lies south of the "Square of Pegasus," and the northern
+between Andromeda and Aries. According to Manilius, the origin of these
+fishes is as follows: Venus, seeing Typhon on the banks of the river
+Euphrates, cast herself with her son into the river and they were
+transformed into fishes!
+
+Some of the Arabians substituted a swallow for the northern of the two
+fishes--the one below Andromeda. The swallow was a symbol of Spring.
+According to Dupuis, Pisces represents the 8th "labour of Hercules," his
+triumph over the mares of Diomed which emitted fire from their
+nostrils.[428] But the connection between fishes and mares is not obvious,
+and some of Dupuis' ideas seem very fanciful. Here he seems to have found
+a "mare's nest."
+
+The constellation Cetus, the Whale, represents, according to ancient
+writers, the sea monster sent by Neptune to devour Andromeda when she was
+chained to the rock. Aratus calls Cetus the "dusky monster," and Brown
+remarks that "the 'Dusky Star' would be peculiarly appropriate to Mira
+(the wondrous [Greek: o] Ceti)."[429] Cetus was also called Canis
+Tritonis, or Dog of the Sea, Bayer in his Atlas (1603) shows a dragon
+instead of a whale, finding it so represented on some ancient spheres.
+Al-Sufi calls it K�tus or [Greek: k�tos], the whale. He says, "it is
+represented by the figure of a marine animal, of which the fore part is
+turned towards the east, to the south of the Ram, and the hinder part
+towards the west behind the three 'extern' stars of Aquarius."
+
+Al-Sufi does not mention the variable star [Greek: o] Ceti, now called
+Mira, or the "wonderful," nor does he refer to any star in its immediate
+vicinity. We may, therefore, conclude that it was near a minimum of light
+at the time of his observation of the stars of Cetus.
+
+The constellation of Orion, one of the finest in the heavens, was called
+by Al-Sufi _al-djabbar_, "the Giant," and also _al-djauza_, "the Spouse."
+The poet Longfellow says--
+
+  "Sirius was rising in the east
+  And, slow ascending one by one,
+  The kindling constellations shone
+  Begirt with many a blazing star
+  Stood the great giant Al-gebar
+  Orion, hunter of the beast!
+  His sword hung gleaming at his side
+  And on his arm, the lion's hide--
+  Scattered across the midnight air
+  The golden radiance of its hair."
+
+Al-Sufi says it "is represented by the figure of a standing man, to the
+south of the sun's path. This constellation very much resembles a human
+figure with a head and two shoulders. It is called _al-djabbar_, 'the
+Giant,' because it has two thrones, holds a club in his hand, and is
+girded with a sword." Orion is supposed to have been a son of Neptune;
+but there are many stories of the origin of the name. It is also said to
+be derived from the Greek word [Greek: �ra], because the constellation was
+used to mark the different times of the year. According to the ancient
+fable, Orion was killed by a scorpion, and was placed in the sky at the
+request of Diana. According to Houzeau, the name comes from _oriri_, to be
+born. Scorpio rises when Orion sets, and he thinks that the idea of the
+ancients was that the Scorpion in this way kills the giant Orion.
+
+In ancient Egypt Orion was called _Sahu_. This name occurs on the
+monuments of the Ptolemies, and also on those of the Pharaohs. It is also
+mentioned in the _Book of the Dead_. It seems to have been considered of
+great importance in ancient Egypt, as its heliacal rising announced that
+of Sirius, which heralded the annual rising of the Nile.
+
+The constellation Eridanus lies south of Taurus, east of Cetus, and west
+of Lepus. In ancient times it was supposed to represent the Nile or the
+Po. Ptolemy merely calls it [Greek: Potamou asterismos], or asterism of
+the river. It was called Eridanus by the Greeks, and Fluvius by the
+Romans. It appears to correspond with the Hebrew Shicor. Al-Sufi calls it
+_al-nahr_, "the River."
+
+One of the most interesting points in Al-Sufi's most interesting work is
+the identity of the bright star known to the ancient astronomers as
+_achir al-nahr_, "the End of the River," and called by Ptolemy [Greek:
+Eschatos tou potamou], "the Last in the River." Some astronomers have
+identified this star with [Greek: a] Eridani (Achernar), a bright southern
+star of the 1st magnitude, south of Eridanus. But Al-Sufi's description
+shows clearly that the star he refers to is really [Greek: th] Eridani;
+and the reader will find it interesting to follow his description with a
+star map before him. Describing Ptolemy's 34th star of Eridanus (the star
+in question), he says, "the 34th star is found before [that is west of]
+these three stars [the 31st, 32nd, and 33rd, which are [Greek: u]{2}, Du,
+and [Greek: u]' in Proctor's Atlas], the distance between it and that of
+the three which is nearest being about 4 cubits [9� 20']. It is of the
+first magnitude; it is that which is marked on the southern astrolabe, and
+called _achir al-nahr_, 'the End of the River.' There are before this
+bright one two stars, one to the south, [[Greek: s] Eridani, not shown in
+Proctor's small Atlas], the other to the north [[Greek: i] Eridani];
+Ptolemy does not mention these. One of these stars is of the 4th
+magnitude, the other of the 5th. There is behind the same [that is, east
+of it] a star of the 4th magnitude distant from it two cubits [[Greek: e]
+Eridani]. To the south of the three stars which follow the bright one
+there are some stars of the 4th and 5th magnitudes, which he [Ptolemy] has
+not mentioned."
+
+Now, a glance at a star map of this region will show clearly that the
+bright star referred to by Al-Sufi is undoubtedly [Greek: th] Eridani,
+which is therefore the star known to the ancients as the "End of the
+River," or the "Last in the River."
+
+The position given by Ptolemy agrees fairly well with Al-Sufi's
+description, although the place is slightly erroneous, as is also the case
+with Fomalhaut and [Greek: b] Centauri. It is impossible to suppose that
+either Ptolemy or Al-Sufi could have seen [Greek: a] Eridani, as it is too
+far south to be visible from their stations, and, owing to the precession
+of the equinoxes, the star was still further south in ancient times.
+Al-Sufi says distinctly that the distance between Ptolemy's 33rd star
+(which is undoubtedly _h_ Eridani, or Proctor's [Greek: u]') and the 34th
+star was "4 cubits," or 9� 20'. The actual distance is about 9� 11', so
+that Al-Sufi's estimate was practically correct. Halley, in his _Catalogus
+Stellarium Australium_, identifies Ptolemy's star with [Greek: th]
+Eridani, and Baily agreed with him.[430] Ulugh Beigh also identifies the
+"Last in the River" with [Greek: th] Eridani. The Arabic observer Mohammed
+Ali Achsasi, who observed in the seventeenth century, called [Greek: th]
+Eridani _Achr al-nahr_, and rated it first magnitude.[431] To argue, as
+Bode and Flammarion have done, that Ptolemy and Al-Sufi may have heard of
+[Greek: a] Eridani from travellers in the southern hemisphere, is to beg
+the whole question at issue. This is especially true with reference to
+Al-Sufi, who says, in the preface to his work, that he has described the
+stars "as seen with my own eyes." [Greek: a] Eridani is over 11 "cubits"
+from _h_ Eridani instead of "4 cubits" as Al-Sufi says. This shows
+conclusively that the star seen by Al-Sufi was certainly _not_ [Greek: a]
+Eridani. The interest of the identification is that Al-Sufi rated [Greek:
+th] Eridani of the _first_ magnitude, whereas it is now only 3rd
+magnitude! It was measured 3�06 at Harvard and estimated 3�4 by Stanley
+Williams, so that it has evidently diminished greatly in brightness since
+Al-Sufi's time. There is an interesting paper on this subject by Dr.
+Anderson (the discoverer of Nova Aurig� and Nova Persei) in _Knowledge_
+for July, 1893, in which he states that the "Last in the River," according
+to the statements of Hipparchus and Ptolemy, _did_ rise above their
+horizon at a certain time of the year, which [Greek: a] Eridani could not
+possibly have done. This seems sufficient to settle the question in favour
+of [Greek: th] Eridani. Dr. Anderson says, "It is much to be regretted
+that Professor Schjellerup, the able and industrious translator of Sufi,
+has allowed this to escape his notice, and helped in the preface and note
+to his work to propagate the delusion that [Greek: a] Eridani is Ptolemy's
+'Last in the River'"; and in this opinion I fully concur. Al-Sufi's clear
+account places it beyond a doubt that the star known to Hipparchus,
+Ptolemy, Al-Sufi, and Ulugh Beigh as the "Last in the River" was [Greek:
+th] Eridani. [Greek: th] must have diminished greatly in brightness since
+Al-Sufi's time, for in ranking it as 1st magnitude he placed it in a very
+select list. He only rated thirteen stars in the whole heavens as being of
+the 1st magnitude. These are: Arcturus, Vega, Capella, Aldebaran, Regulus,
+[Greek: b] Leonis, Fomalhaut, Rigel, [Greek: th] Eridani, Sirius, Procyon,
+Canopus, and [Greek: a] Centauri. _All_ these stars were actually _seen_
+by Al-Sufi, _and described from his own observations_. He does not mention
+[Greek: a] Eridani, as it was not visible from his station in Persia.
+
+[Greek: th] Eridani is a splendid double star (3�40, 4�49: 8"�38, 1902,
+Tebbutt). I found the components white and light yellow with 3-inch
+refractor in the Punjab. Dr. Gould thinks that one of the components is
+variable to some extent. This is interesting, considering the brilliancy
+of the star in Al-Sufi's time. The brighter component was found to be a
+spectroscopic binary by Wright, so that on the whole the star is a most
+interesting object.
+
+The small constellation Lepus, the Hare, lies south of Orion. Pliny calls
+it Dasypus, and Virgil Auritus. In ancient Egypt it was the symbol of
+vigilance, prudence, fear, solitude, and speed.[432] It may perhaps
+represent the hare hunted by Orion; but some say it was placed in the sky
+to commemorate a terrible plague of hares which occurred in Sicily in
+ancient times.
+
+A little north-west of the star [Greek: m] Leporis is Hind's "crimson
+star" (R.A. 4{h} 53{m}, S. 14� 57', 1900) described by him as "of the most
+intense crimson, resembling a blood drop on the background of the sky; as
+regards depth of colour, no other star visible in these latitudes could be
+compared with it." It is variable from about the 6th to the 8th magnitude,
+with a period of about 436 days from maximum to maximum.
+
+The constellation Canis Major, the Great Dog, is remarkable for containing
+Sirius, the brightest star in the heavens. In the Greek mythology it was
+supposed to represent a dog given by Aurora to Cephalus as the swiftest of
+all dogs. Cephalus wished to match it against a fox which he thought
+surpassed all animals for speed. They both ran for so long a time, so the
+story goes, that Jupiter rewarded the dog by placing it among the stars.
+But probably the dog comes from Anubis, the dog-headed god of the ancient
+Egyptians. According to Brown, Theogirius (B.C. 544) refers to the
+constellation of the Dog.[433] He thinks that Canis Major is probably "a
+reduplication" of Orion; Sirius and [Greek: b] Canis Majoris corresponding
+to [Greek: a] and [Greek: g] Orionis; [Greek: d], 22, and [Greek: e] Canis
+Majoris to the stars in Orion's belt ([Greek: d, e], and [Greek: z]
+Orionis); and [Greek: �]; and [Greek: k] Canis Majoris with [Greek: k] and
+[Greek: b] Orionis.[434]
+
+The Arabic name of Sirius was _al-schira_, which might easily be corrupted
+into Sirius. The Hebrew name was Sihor. According to Plutarch, the
+Ethiopians paid regal honours to the Celestial Dog. The Romans used to
+sacrifice a dog in its honour at the fetes called Robigalia, which were
+held on the seventh day before the Calends of May, and nine days after the
+entry of the sun into Taurus. Pliny says, "Hoc tempus Varro determinat
+sole decimam partem Tauri obtinenti quod canis occidit, sidus per se
+vehemens," etc.[435]
+
+Owing to some remarks of Cicero, Horace, and Seneca, it has been supposed
+that in ancient times Sirius was of red colour. Seneca says, "Nec mirum
+est, si terra omnis generis et varia evaporatio est; quam in coelo
+quoque non unus appareat color rerum, sed acrior sit Canicul� rubor,
+Nartis remissior, Jovis nullus, in lucem puram nitore perducto."[436] It
+is now brilliantly white with a bluish tinge. But this change of colour is
+somewhat doubtful. The remarks of the ancient writers may possibly refer
+to its great brilliancy rather than its colour. Al-Sufi says nothing about
+its colour, and it was probably a white star in his time. If it were red
+in his day he would most probably have mentioned the fact, as he does in
+the case of several red stars. Brown, however, quotes the following from
+Ibn Alraqqa, an Arabian observer:--
+
+  "I recognize Sirius _shining red_, whilst the morning is becoming white.
+  The night fading away, has risen and left him,
+  The night is not afraid to lose him, since he follows her."
+
+Schjellerup thinks that it is very doubtful that Sirius was really red as
+seen by Hipparchus and Ptolemy. But in an exhaustive inquiry made by Dr.
+See on the supposed change of colour,[437] he comes to the conclusion that
+Sirius was really red in ancient times. Seneca states distinctly that it
+was redder than Mars (see extract above), and other ancient writers refer
+to its red colour. It has been generally supposed that the Arabian
+astronomer Alfraganus, in his translation of Ptolemy's _Almagest_, refers
+to only five red stars observed by Ptolemy, namely, Arcturus, Aldebaran,
+Betelgeuse, Antares, and Pollux. But Dr. See shows that this idea is due
+to a mistranslation of Alfraganus by Plato Tibertinus in 1537, and that
+Ptolemy did not speak of "five red stars," but five _nebulous_ stars, as
+stated by Christmann and Golius. Ptolemy described Sirius as [Greek:
+upokirros], "fiery red," the same word used with reference to the other
+stars mentioned above. The change of colour, if any, probably took place
+before Al-Sufi's time.
+
+Dr. See says--
+
+    "Prof. Newcomb rejects the former well-authenticated redness of
+    Sirius, because he cannot explain the fact. But the ink was scarcely
+    dry on his new book on the stars, in which he takes this position,
+    when Nova Persei blazed forth in 1901; and observers saw it change
+    colour from day to day and week to week. Could any one explain the
+    cause of these numerous and conspicuous changes of colour? Shall we,
+    then, deny the changes of colour in Nova Persei, some of which were
+    noticed when it was nearly as bright as Sirius?"[438]
+
+On the ceiling of the Memnonium at Thebes the heliacal rising of Sirius is
+represented under the form and name of Isis. The coincidence of this
+rising with the annual rising of the Nile is mentioned by Tibullus and
+Aclian. About 4000 B.C. the heliacal rising of Sirius coincided with the
+summer solstice (about June 21) and the beginning of the rising of the
+Nile. The festival in honour of this event was held by the Egyptians about
+July 20, and this marked the beginning of the sacred Egyptian year. On the
+summit of Mount Pelion in Thessaly there was a temple dedicated to Zeus,
+where sacrifices were offered at the rising of Sirius by men of rank who
+were chosen for the purpose by the priests and wore fresh sheepskins.
+
+Sirius seems to have been worshipped by the ancient Egyptians under the
+name of Sothis, and it was regarded as the star of Isis and Osiris. The
+last name without the initial O very much resembles our modern name.
+
+According to Al-Sufi, the Arabians called Sirius _al-schira al-ab�r_,
+"Sirius which has passed across," also _al-schira al Jam�nija_, "the
+Sirius of Y�men." He says it is called _al-ab�r_, "because it has passed
+across the Milky Way into the southern region." He relates a mythological
+story why Sirius "fled towards the south" and passed across the Milky Way
+towards Suhail (Canopus). The same story is told by Albufaragius[439]
+(thirteenth century). (The story was probably derived from Al-Sufi.) Now,
+it seems to me a curious and interesting fact that the large proper motion
+of Sirius would have carried it across the Milky Way from the eastern to
+the western border in a period of 60,000 years. Possibly the Arabian story
+may be based on a tradition of Sirius having been seen on the opposite, or
+eastern, side of the Milky Way by the men of the early Stone Age. However
+this may be, we know from the amount and direction of the star's proper
+motion that it must have passed across the Milky Way from east to west
+within the period above stated. The Arabic name _al-ab�r_ is not,
+therefore, a merely fanciful one, but denotes an _actual fact_. The
+proper motion of Sirius could not possibly have been known to the
+ancients, as it was only revealed by accurate modern observations.
+
+The little constellation Canis Minor, the Little Dog, lies south of Gemini
+and Cancer. Small as it is, it was one of the original forty-eight
+constellations of Ptolemy. In the Greek mythology it was supposed to
+represent either one of Diana's hunting dogs, or one of Orion's hounds.
+Ovid calls it the dog of Icarus. Others say it was the dog of Helen, who
+was carried off by Paris. According to the old poets, Orion's dog, or the
+dog of Icarus, threw himself into a well after seeing his master perish.
+The name Fovea, given to the constellation by Bayer, signifies a pit where
+corn was deposited. This comes from the fact that the rising of the star
+Procyon ([Greek: a] Canis Minoris) indicated the season of abundance. But
+Lalande thought it more probable that the idea of a pit came from the
+Greek [Greek: seiros], which means a corn store, and that it was
+confounded with Sirius.
+
+The name of the bright star Procyon ([Greek: a] Canis Minoris) is derived
+from the Greek [Greek: proku�n], "the advanced day," because it appeared
+in the morning sky before Sirius. Procyon was called by the Hindoos
+Hanouman after their famous monkey god, from whose tail a bridge is said
+to have been formed to enable the army of Rama to pass from India to
+Ceylon. Al-Sufi says that the star was marked on the old astrolabes as
+_al-schira al-schamia_, "the Syrian Sirius." It was also called, he says,
+_al-schira al-gumaisa_, "the Sirius with blear eyes" (!) from weeping
+because Sirius had passed across the Milky Way, Procyon remaining on the
+eastern side. Here we have the same legend again. The proper motion of
+Procyon (about the same in amount and direction as that of Sirius) shows
+that the star has been on the eastern side of the Milky Way for many ages
+past. About 60,000 years hence, Procyon will be near the star [Greek: th]
+Canis Majoris, and will then--like Sirius--have passed across the Milky
+Way.
+
+Argo, the Ship, is a large constellation south of Hydra, Monoceros, and
+Canis Major. It is called by Al-Sufi _al-saf�na_, "the Ship." It is
+supposed to represent the first ship ever built. The name is derived from
+the builder Argo, or from the Greek word [Greek: Argos]. This ship is said
+to have been built in Thessaly by order of Minerva and Neptune, to go on
+the expedition for the conquest of the golden fleece. The date of this
+expedition, commanded by Jason, is usually fixed at 1300 or 1400 B.C. With
+reference to the position of this supposed ship in the sky, Proctor says,
+"It is noteworthy that when we make due correction for the effects of
+precession during the past 4000 years, the old constellation Argo is set
+on an even keel, instead of being tilted some 45� to the horizon, as at
+present when due south." He connects Argo with Noah's Ark.
+
+The brightest star of Argo is Canopus, called Suha�l by Al-Sufi. It is the
+second brightest star in the heavens; but it is not visible in northern
+latitudes. The Harvard photometric measures make it nearly one magnitude
+brighter than the zero magnitude, about two magnitudes brighter than
+Aldebaran, and about half the brightness of Sirius. This fine star has
+been suspected of variable light. Webb says, "It was thought (1861) in
+Chili brighter than Sirius." Observing it in the Punjab, the present
+writer found it on several occasions but little inferior to Sirius,
+although very low on the southern horizon. From recent observations by Mr.
+H. C. McKay in Australia, he believes that it is variable to the extent of
+at least half a magnitude.[440] But it is difficult to establish
+variations of light in very bright stars. The parallax of Canopus is
+_very_ small, so its distance from the earth is very great, and it must be
+a sun of gigantic size. According to Al-Fargani, Canopus was called the
+star of St. Catherine by the Christian pilgrims in the tenth century.[441]
+It was called Suha�l by the old Arabians, a name apparently derived from
+the root _sahl_, "a plain"; and Schjellerup suggests that the name was
+probably applied to this and some other southern stars because they seem
+to move along a plain near the southern horizon. Al-Sufi says that he
+measured the latitude of Schiraz in Persia, where he observed, and found
+it to be 29� 36'; and hence for that place Canopus, when on the meridian,
+had an altitude of about 9�. Canopus was the ancient name of Aboukir in
+Egypt, and is said to have derived its name from the pilot of Menelaus,
+whose name was Kanobus, and who died there from the bite of a snake. The
+star is supposed to have been named after him, and it was worshipped by
+the ancient Egyptians.
+
+Al-Sufi does not mention the famous variable star [Greek: �] Arg�s, which,
+owing to the precession of the equinoxes, he might possibly have seen
+_close to the horizon_, if it had been a bright star in his day. It lies
+between [Greek: ph] Velorum and [Greek: a] Crucis. Both of these stars are
+mentioned by Al-Sufi, but he says nothing of any bright star (or indeed
+any star) between them. This negative evidence tends to show that [Greek:
+�] Arg�s was not visible to the naked eye in Al-Sufi's time. This
+extraordinary star has in modern times varied through all degrees of
+brightness from Sirius down to the 8th magnitude! Sch�nfeld thought that a
+regular period is very improbable. It seems to be a sort of connecting
+link between the long period variables and the _nov�_ or temporary stars.
+It is reddish in colour, and the spectrum of its light is very similar to
+that of the temporary stars. Whether it will ever become a brilliant
+object again, time alone can tell; but from the fact that it was
+presumably faint in Al-Sufi's time, and afterwards increased to the
+brightness of Sirius, it seems possible that its light may again revive.
+
+The long constellation Hydra lies south of Cancer, Leo, Crater, Corvus,
+Virgo, and Libra. It was also called Asina, Coluber, Anguis, Sublimatus,
+etc. In the Greek mythology it was supposed to represent the Lern�an
+serpent killed by Hercules. According to Ovid, who fixed its acronycal
+rising for February 14, it had a common origin with Corvus and Crater.
+Apollo, wishing to sacrifice to Jupiter, sent the Crow with a cup to fetch
+water. On his way to the well the Crow stopped at a fig tree and waited
+for the fruit to ripen! Afterwards, to excuse his delay, he said that a
+serpent had prevented him from drawing the water. But Apollo, to punish
+the Crow for his deception, changed his plumage from white to black, and
+ordered the serpent to prevent the Crow from drinking.[442] Hydra was
+called by Al-Sufi _al-schudja_, "the Serpent, or Hydra." He says that "it
+contains twenty-five stars in the figure and two 'outside', and its head
+is to the south of the southern scale of the Balance" ([Greek: a] Libr�).
+But this is clearly a mistake (one of the very few errors to be found in
+Al-Sufi's work), for he goes on to say that the head is composed of four
+stars forming a figure like the head of a horse, and he adds, "This head
+is in the middle between _al-shira al-gumaisa_ [Procyon] and _Kalb
+al-asad_ [Regulus] the Heart, inclining from these two stars a little to
+the south." This clearly indicates the stars [Greek: d, e, �], and [Greek:
+s] Hydr� which, with [Greek: z] Hydr�, have always been considered as
+forming the Hydra's head. These stars lie south of [Greek: a] and [Greek:
+b] Cancri, not south of Libra as Al-Sufi says (doubtless by a slip of the
+pen).
+
+Ptolemy's 12th star of Hydra ([Greek: a] Hydr�) is, Al-Sufi says, "the
+bright red star which is found at the end of the neck where the back
+begins; it is of the 2nd magnitude. It is that which is marked on the
+astrolabe as _unk al-schudja_, 'the neck of the serpent,' also _al-fard_,
+'the solitary one.'" Al-Sufi's estimate of its brightness agrees well with
+modern measures; but it has been suspected of variable light. Sir John
+Herschel's estimates at the Cape of Good Hope varied from 1�75 to 2�58
+magnitude. He thought that its apparent variation might be due to its
+reddish colour, and compares it to the case of [Greek: a] Cassiopei�. But
+as this latter star is now _known_ to be irregularly variable it seems
+probable that [Greek: a] Hydr� may be variable also. Gemmill found it
+remarkably bright on May 9, 1883, when he thought it nearly equal to
+Pollux (1�2 magnitude). On the other hand, Franks thought it nearer the
+3rd than the 2nd magnitude on March 2, 1878. On April 9, 1884, the
+present writer found it only slightly less than Regulus (1�3 magnitude).
+On April 6, 1886, how-ever, it was considerably less than Regulus, but
+half a magnitude brighter than [Greek: b] Canis Minoris, or about 2-1/2
+magnitude. In the Chinese Annals it is called the "Red Bird." In a list of
+thirty stars found on a tablet at Birs-Nimroud, it is called "The son of
+the supreme temple." Although to the naked eye deserving the name of
+Alphard or "the solitary one," it is by no means an isolated star when
+examined with a telescope. It has a faint and distant companion, observed
+by Admiral Smyth; and about 25' to the west of it Ward saw a small double
+star (8, 13: 90�: 50"). With a 3-inch refractor in the Punjab, I saw a
+small star of about 8-1/2 magnitude to the south and a little east of the
+bright star, probably identical with Smyth's companion. Farther off in the
+same direction I saw a fainter star, and others at greater distances in
+the field. There is also a faint star a little to the north. I also saw
+Ward's double with the 3-inch telescope.
+
+There is some difficulty in identifying the stars numbered by Ptolemy 13,
+14, and 15 in Hydra. Having plotted a map from Ptolemy's positions (as
+given by Al-Sufi), I have come to the conclusion that Ptolemy's stars are
+13 = [Greek: k] Hydr�; 14 = [Greek: u]; and 15 = [Greek: l] Hydr�,
+probably. From the clear description given by Al-Sufi of the stars
+observed by _him_, I find that _his_ stars are 13 = [Greek: u]_{1}; 14 =
+[Greek: u]_{2}; and 15 = [Greek: l] Hydr�. We must, therefore, conclude
+that Ptolemy and Al-Sufi saw only three stars where now there are
+four,[443] and that [Greek: k] Hydr� was not seen, or at least is not
+mentioned by Al-Sufi. [Greek: k] is, therefore, probably variable. It was
+rated 4 by Tycho Brah�, Bayer, and Hevelius; it is at present about 5th
+magnitude. If Ptolemy did not see [Greek: u]_{2} it is probably variable
+also, and, indeed, it has been suspected of variable light.[444]
+
+The small constellation of Crater, the Cup, lies north of Hydra, and south
+of Leo and Virgo. Al-Sufi calls it _al-batija_, "the Jar, or Cup." He says
+the Arabians called it _al-malif_, "the Crib, or Manger." According to
+Brown, the stars of Crater exactly form a Bakhian [Greek: kantharos], with
+its two handles rising above the two extremities of the
+circumference.[445] An Asia Minor legend "connected Crater with the mixing
+of human blood with wine in a bowl." Crater is referred to by Ovid in the
+lines--
+
+  "Dixit et antiqui monumenta perennia facti
+  Anguis, Avis, Crater sidera, juncta micunt."
+
+The star [Greek: a] Crateris was rated 4th magnitude by Al-Sufi and all
+other observers, and the Harvard measures make it 4�20, a satisfactory
+agreement. It has three companions noted by Admiral Smyth. One of these he
+called "intense blood colour." This is R Crateris, now known to be
+variable from above the 8th magnitude to below the 9th. Sir John Herschel
+called it an "intense scarlet star, a curious colour." With 3-inch
+refractor in the Punjab I found it "full scarlet." It is one of an open
+pair, the further of the two from [Greek: a]. There is a third star about
+9th magnitude a little south of it. Ward saw a 13th magnitude star between
+[Greek: a] and R with a 2-7/8-inch (Wray) refractor. This I saw "readily"
+with my 3-inch. Smyth does not mention this faint star, although he used a
+much larger telescope.
+
+Corvus, the Crow, is a small constellation, north of Hydra. Aratus says
+"the Crow form seems to peck the fold of the water snake" (Hydra). The
+victory which Valerius Corvinus is said to have owed to a crow has given
+it the name of Pomptina, because the victory took place near the Pontine
+marshes.[446] A quadrilateral figure is formed by its four brightest
+stars, [Greek: g, d, b], and [Greek: e] Corvi. This figure has sometimes
+been mistaken for the Southern Cross by those who are not familiar with
+the heavens. But the stars of the Southern Cross are much brighter.
+
+The constellation Centaurus, the Centaur, lies south of Hydra and Libra,
+and north of the Southern Cross. According to Dupuis, Centaurus represents
+the 3rd "labour of Hercules," his triumph over the Centaurs.[447] The
+Centaurs were supposed to be a people living in the vicinity of Mount
+Ossa, who first rode on horses. The constellation was also called Semivir,
+Chiron, Phobos, Minotaurus, etc. Al-Sufi says it "is represented by the
+figure of an animal, of which the forepart is the upper part of a man from
+the head to end of the back, and its hinder part is the hinder part of a
+horse, from the beginning of the back to the tail. It is to the south of
+the Balance [Libra] turning its face towards the east, and the hinder part
+of the beast towards the west."
+
+Al-Sufi describes very clearly the four bright stars of the famous
+"Southern Cross." Owing to precession these stars were some 7� further
+north in the tenth century than they are at present, and they could have
+been all seen by Al-Sufi, when on the meridian. In the time of Ptolemy and
+Hipparchus, they were still further north, and about 5000 years ago they
+were visible in the latitude of London. Dante speaks of these four stars
+as emblematical of the four cardinal virtues, Justice, Temperance,
+Fortitude, and Prudence.
+
+Closely south-east of [Greek: a] and [Greek: b] Crucis is the dark spot in
+the Milky Way known as the "Coal Sack," which forms such a conspicuous
+object near the Southern Cross. It was first described by Pinzon in 1499;
+and afterwards by Lacaille in 1755. Although to the naked eye apparently
+black, photographs show that it contains many faint stars, but, of course,
+much less numerous than in the surrounding regions. The dark effect is
+chiefly caused by contrast with the brilliancy of the Milky Way
+surrounding it.
+
+Al-Sufi also mentions the bright stars [Greek: a] and [Greek: b] Centauri
+which follow the Southern Cross. He says that the distance between them
+"is four cubits," that is about 9� 20', but it is less than this now.
+[Greek: a] has a large "proper motion" of 3"�67 per annum, and was farther
+from [Greek: b] in Al-Sufi's time than it is at present. This, however,
+would not _wholly_ account for the difference, and Al-Sufi's over-estimate
+is probably due to the well-known effect by which the distance between two
+stars is _apparently_ increased when they are near the horizon. Several of
+Al-Sufi's distances between southern stars are over-estimated, probably
+for the same reason.
+
+The constellation Lupus, the Wolf, is south of Libra and Scorpio. It lies
+along the western border of the Milky Way. According to ancient writers it
+represents Lycaon, King of Arcadia, a contemporary of Cecrops, who is said
+to have sacrificed human victims, and on account of his cruelty was
+changed into a wolf. Another fable is that it represents a wolf
+sacrificed by the Centaur Chiron. According to Brown, Lupus appears on the
+Euphratian planisphere discovered by George Smyth in the palace of
+Sennacherib. Al-Sufi called it _al-sabu_, "the Wild Beast." It was also
+called _al-fand_, "the Leopard," and _al-asada_, "the Lioness."
+
+Ara, the Altar, lies south of Scorpio. According to ancient writers it
+represents an altar built by Vulcan, when the gods made war against the
+Titans. It is called by Al-Sufi _al-midjman_, "the Scent Box," or "the
+Altar."
+
+The little constellation Corona Australis, the Southern Crown, lies south
+and west of Sagittarius, east of Scorpio, and west of Telescopium. Aratus
+refers to the stars in Corona Australis as--
+
+                          "Other few
+  Before the Archer under his forefeet
+  Led round in circle roll without a name."[449]
+
+But the constellation was known by the names Caduceus, Orbiculus, Corona
+Sagittarii, etc. The ancient poets relate that Bacchus placed this crown
+in the sky in honour of his mother Semele.[450] Others say that it
+represents the crown conferred on Corinne of Thebes, famous as a poet.
+
+The small constellation Piscis Australis, or the Southern Fish, lies
+south of Capricornus and Aquarius. In the most ancient maps it is
+represented as a fish drinking the water which flows from the urn of
+Aquarius.
+
+       *       *       *       *       *
+
+A good many constellations have been added to the heavens since the days
+of Al-Sufi, and notes on some of these may be of interest.
+
+CAMELOPARDALIS.--This constellation first appears on a celestial
+planisphere published by Bartschius in the year 1624. It was not formed by
+Bartschius himself, but by the navigators of the sixteenth century. It
+lies south of Ursa Minor, north of Perseus and Auriga, east of Draco, and
+west of Cassiopeia. It contains no star brighter than the 4th magnitude.
+
+LYNX.--This constellation is south of Camelopardalis and Ursa Major, and
+north of Gemini and Cancer. It was formed by Hevelius in 1660, and he
+called it the Lynx, because, he said, it contained only faint stars and
+"it was necessary to have the eyes of a lynx" to see them! Some of them
+were, however, observed by Ptolemy and Al-Sufi, and are mentioned by the
+latter under Ursa Major.
+
+CANES VENATICI, or the Hunting Dogs.--This was formed by Hevelius in 1660.
+It lies south of the Great Bear's tail, north of Coma Berenices, east of
+Ursa Major, and west of Bo�tis. Its brightest stars [Greek: a] (12) and
+[Greek: b] (8) were observed by Al-Sufi, and included by him in the
+"extern" stars of Ursa Major.
+
+COMA BERENICES.--This constellation lies between Canes Venatici and Virgo.
+Although it was not included among the old forty-eight constellations of
+Ptolemy, it is referred to by Al-Sufi as the Plat, or Tress of Hair, and
+he included its stars Flamsteed 12, 15, and 21 in the "extern" stars of
+Leo. It was originally formed by the poet Callimachus in the third century
+B.C., but was not generally accepted until reformed by Hevelius.
+Callimachus lived at Alexandria in the reigns of Ptolemy Philadelphus and
+Ptolemy Euergetes, and was chief librarian of the famous library of
+Alexandria from about B.C. 260 until his death in B.C. 240. Eratosthenes
+was one of his pupils. The history of the constellation is as follows:
+Berenice, wife of Ptolemy Euergetes, made a vow, when her husband was
+leaving her on a military expedition, that if he returned in safety she
+would cut off her hair and consecrate it in the temple of Mars. Her
+husband returned, and she fulfilled her vow. But on the next day the hair
+had disappeared--stolen from the temple--and Conon the mathematician
+showed Ptolemy seven stars near the constellation of the Lion which did
+not belong to any constellation. These were formed into a constellation
+and called Berenice's Hair. Conon is referred to by Catullus in the
+lines--
+
+  "Idem me ille Conon coeleste numine vidit
+  E. Berenico vertice C�sariem."
+
+Coma Berenices first occurs as a distinct constellation in the catalogue
+contained in the Rudolphine Tables formed by Kepler (epoch 1600) from the
+observations of Tycho Brah�.[451] Bayer substituted a sheaf of corn, an
+idea derived from an ancient manuscript.
+
+LEO MINOR.--This small constellation lies between Ursa Major and Leo, and
+east of the Lynx. It was formed by Halley about the year 1660; but is
+referred to by Al-Sufi, who includes one of its stars (Fl. 41) in the
+"extern" stars of Leo. There are, however, several brighter stars in the
+group. The brightest, Fl. 46, was measured 3�92 at Harvard. The star Fl.
+37 was called _pr�cipua_ (or brightest) by Tycho Brah�, and rated 3, but
+as it was measured only 4�77 at Harvard it may possibly have diminished in
+brightness.
+
+SEXTANS.--This constellation lies south of Leo, and north and east of
+Hydra. It was formed by Hevelius about the year 1680. According to the
+Harvard photometric measures its brightest star is Fl. 15 (4�50).
+
+MONOCEROS, or the Unicorn, lies south of Gemini and Canis Minor, north of
+Canis Major and Argo, east of Orion, and west of Hydra. It appears on the
+planisphere of Bartschius, published in 1624. According to Scaliger it is
+shown on an old Persian sphere. One of its stars, Fl. 22, is mentioned by
+Al-Sufi among the "extern" stars of Canis Major (No. 1). Another, Fl. 30,
+is given under Hydra ("Extern" No. 1) and Fl. 8, 13, and 15 are apparently
+referred to in Gemini. The star 15 Monocerotis is a little south of
+[Greek: x] Geminorum, and was measured 4�59 magnitude at Harvard. It was
+at one time supposed to be variable with a short period (about 3-1/2
+days), but this variation has not been confirmed. The spectrum is of the
+fifth type--with bright lines--a very rare type among naked-eye stars. It
+is a triple star (5, 8�8, 11�2: 2"�9, 16"�3) and should be seen with a
+4-inch telescope. It has several other small companions, one of which
+(139��2: 75"�7) has been suspected of variation in light. It was estimated
+8-1/2 by Main in 1863, but only 12 by Sadler in 1875. Observing it on
+March 28, 1889, with 3-inch refractor, I found it about one magnitude
+brighter than a star closely preceding, and estimated it 8 or 8-1/2
+magnitude. It is probably variable and should be watched.
+
+SCUTUM SOBIESKI.--This is, or was, a small constellation in the southern
+portion of Aquila, which was formed by Hevelius in 1660 in honour of the
+Polish hero Sobieski. Its principal stars, which lie south-west of [Greek:
+l] Aquil�, were mentioned by Al-Sufi and are referred to by him under that
+constellation. It contains a very bright spot of Milky Way light, which
+may be well seen in the month of July just below the star [Greek: l]
+Aquil�. Closely south of the star 6 Aquil� is a remarkable variable star R
+Scuti (R.A. 18{h} 42{m}�2, S. 5� 49'). It varies from 4�8 to 7�8 with an
+irregular period. All the light changes can be observed with a good
+opera-glass.
+
+VULPECULA, the Fox.--This modern constellation lies south of Cygnus, north
+of Sagitta and Delphinus, east of Hercules, and west of Pegasus. It was
+formed by Hevelius in 1660. One of its stars, 6 Vulpecul�, is mentioned by
+Al-Sufi in describing the constellation Cygnus. Closely north-west of 32
+Vulpecul� is the short-period variable T Vulpecul�. It varies from 5�5 to
+6�2 magnitude, and its period is 4�436 days. This is an interesting
+object, and all the changes of light can be observed with an opera-glass.
+
+LACERTA.--This little constellation lies south of Cepheus and north of
+Pegasus. Its formation was first suggested by Roger and Anthelm in 1679,
+and it was called by them "The Sceptre and the Hand of Justice." It was
+named Lacerta by Hevelius in 1690, and this name it still retains. Al-Sufi
+seems to refer to its stars in his description of Andromeda, but does not
+mention any star in particular. It brightest star Fl. 7 ([Greek: a]
+Lacert�) is about the 4th magnitude. About one degree south-west of 7 is 5
+Lacert�, a deep orange star with a blue companion in a fine field.
+
+There are some constellations south of the Equator which, although above
+Al-Sufi's horizon when on the meridian, are not described by him, as they
+were formed since his time. These are as follows:--
+
+SCULPTOR.--This constellation lies south of Aquarius and Cetus, and north
+of Phoenix. Some of its stars are referred to by Al-Sufi under Eridanus
+as lying within the large triangle formed by [Greek: b] Ceti, Fomalhaut,
+and [Greek: a] Phoenicis. The brightest star is [Greek: a], about 12�
+south of [Greek: b] Ceti (4�39 magnitude Harvard). About 7� south-east of
+[Greek: a] is the red and variable star R Sculptoris; variable from 6�2 to
+8�8 magnitude, with a period of about 376 days. Gould describes it as
+"intense scarlet." It has a spectrum of the fourth type.
+
+PHOENIX.--This constellation lies south of Sculptor. Some of its stars
+are referred to by Al-Sufi, under Eridanus, as forming a boat-shaped
+figure. These are evidently [Greek: a, k, m, b, n], and [Greek: g].
+[Greek: a] is at the south-eastern angle of Al-Sufi's triangle referred to
+above (under "Sculptor"). (See Proctor's Atlas, No. 3.)
+
+FORNAX, the Furnace, lies south of Cetus, west of Eridanus, and east of
+Sculptor and Phoenix. It was formed by Lacaille, and is supposed to
+represent a chemical furnace with an alembic and receiver! Its brightest
+star, [Greek: a] Fornacis, is identical with 12 Eridani.
+
+C�LUM, the Sculptor's Tools, is a small constellation east of Columba, and
+west of Eridanus. It was formed by Lacaille. The brightest stars are
+[Greek: a] and [Greek: g], which are about 4-1/2 magnitude. [Greek: a] has
+a faint companion; and [Greek: g] is a wide double star to the naked eye.
+
+ANTLIA, the Air Pump, lies south of Hydra, east and north of Argo, and
+west of Centaurus. It was formed by Lacaille. It contains no star brighter
+than 4th magnitude. The brightest, [Greek: a], has been variously rated
+from 4 to 5, and Stanley Williams thinks its variability "highly
+probable."
+
+NORMA, the Rule, lies south of Scorpio. It contains no star brighter than
+the 4th magnitude.
+
+TELESCOPIUM.--This modern constellation lies south of Corona Australis,
+and north of Pavo. Its stars [Greek: a, d], and [Greek: z], which lie near
+the northern boundary of the constellation, are referred to by Al-Sufi in
+his description of Ara.
+
+MICROSCOPIUM.--This small constellation is south of Capricornus, and west
+of Piscis Australis. Its stars seem to be referred to by Al-Sufi as having
+been seen by Ptolemy, but he does not specify their exact positions. It
+contains no star brighter than 4-1/2 magnitude.
+
+       *       *       *       *       *
+
+South of Al-Sufi's horizon are a number of constellations surrounding the
+south pole, which, of course, he could not see. Most of these have been
+formed since his time, and these will now be considered; beginning with
+that immediately surrounding the South Pole (Octans), and then following
+the others as nearly as possible in order of Right Ascension.
+
+OCTANS.--This is the constellation surrounding the South Pole of the
+heavens. There is no bright star near the Pole, the nearest visible to the
+naked eye being [Greek: s] Octantis, which is within one degree of the
+pole. It was estimated 5�8 at Cordoba. The brightest star in the
+constellation is [Greek: n] Octantis ([Greek: a], Proctor), which lies
+about 12 degrees from the pole in the direction of Indus and Microscopium.
+The Harvard measure is 3�74 magnitude.
+
+HYDRUS, the Water-Snake, is north of Octans in the direction of Achernar
+([Greek: a] Eridani). The brightest star is [Greek: b], which lies close
+to [Greek: th] Octantis. The Harvard measure is 2�90. Gould says its
+colour is "clear yellow." It has a large proper motion of 2"�28 per annum.
+Sir David Gill found a parallax of 0"�134, and this combined with the
+proper motion gives a velocity of 50 miles a second at right angles to the
+line of sight. [Greek: g] Hydri is a comparatively bright star of about
+the 3rd magnitude, about 15-1/2 degrees from the South Pole. It is
+reddish, with a spectrum of the third type.
+
+HOROLOGIUM, the Clock, is north of Hydra, and south of Eridanus. Three of
+its stars, [Greek: a, d], and [Greek: ps], at the extreme northern end of
+the constellation, seem to be referred to by Al-Sufi in his description
+of Eridanus, but he does not give their exact positions. Most of the stars
+forming this constellation were below Al-Sufi's horizon.
+
+RETICULUM, the Net, is a small constellation to the east of Hydrus and
+Horologium. The brightest star of the constellation is [Greek: a] (3�36
+Harvard, 3�3 Cordoba, and "coloured").
+
+DORADO, the Sword Fish, lies east of Reticulum and west of Pictor. It
+contains only two stars brighter than the 4th magnitude. These are [Greek:
+a] (3�47 Harvard) and [Greek: b] (3�81 Harvard, but suspected of
+variation). About 3� east of [Greek: a] Reticuli is the variable star R
+Doradus. It varies from 4�8 to 6�8, and its period is about 345 days.
+Gould calls it "excessively red." It may be followed through all its
+fluctuations of light with an opera-glass.
+
+MENSA, or Mons Mensa, the Table Mountain, lies between Dorado and the
+South Pole, and represents the Table Mountain of the Cape of Good Hope. It
+contains no star brighter than the 5th magnitude.
+
+PICTOR, the Painter's Easel, lies north of Doradus, and south of Columba.
+It contains no very bright stars, the brightest being [Greek: a] (3�30
+Harvard).
+
+VOLANS, the Flying Fish, is north of Mensa, and south and west of Argo.
+Its brighter stars, with the exception of [Greek: a] and [Greek: b], form
+an irregular six-sided figure. Its brightest star is [Greek: b] (3�65)
+according to the Harvard measures. The Cordoba estimates, however, range
+from 3�6 to 4�4, and Gould says its colour is "bright yellow." Williams
+rated it 3�8.
+
+CHAM�LION.--This small constellation lies south of Volans, and north of
+Mensa and Octans. None of its stars are brighter than the 4th magnitude,
+its brightest being [Greek: a] (4�08 Harvard) and [Greek: g] (4�10).
+
+ARGO.--This large constellation extends much further south than Al-Sufi
+could follow it. The most southern star he mentions is [Greek: e] Carin�,
+but south of this are several bright stars. [Greek: b] Carin� is 1�80
+according to the Harvard measures; [Greek: u] Carin�, 3�08; [Greek: th],
+3�03; [Greek: �], 3�56; and others. A little north-west of [Greek: i] is
+the long-period variable R Carin� (9{h} 29{m}�7, S. 62� 21', 1900). It
+varies from 4�5 at maximum to 10 at minimum, and the period is about 309�7
+days. A little east of R Carin� is another remarkable variable star, _l_
+Carin� (R.A. 9{h} 42{m}�5, S. 62� 3'). It varies from 3�6 to 5�0
+magnitude, with a period of 35-1/2 days from maximum to maximum. All the
+light changes can be observed with an opera-glass, or even with the naked
+eye. It was discovered at Cordoba. The spectrum is of the solar type (G).
+
+MUSCA, the Bee, is a small constellation south of the Southern Cross and
+Centaurus. Its brightest stars are [Greek: a] (2�84 Harvard) and [Greek:
+b] (3�26). These two stars form a fine pair south of [Greek: a] Crucis.
+Closely south-east of [Greek: a] is the short-period variable R Musc�. It
+varies from 6�5 to 7�6 magnitude, and its period is about 19 hours. All
+its changes of light may be observed with a good opera-glass.
+
+APUS, the Bird of Paradise, lies south-east of Musca, and north of Octans.
+Its brightest star is [Greek: a], about the 4th magnitude. Williams calls
+it "deep yellow." About 3� north-west of [Greek: a], in the direction of
+the Southern Cross, is [Greek: th] Apodis, which was found to be variable
+at Cordoba from 5-1/2 to 6-1/2. The spectrum is of the third type, which
+includes so many variable stars.
+
+TRIANGULUM AUSTRALIS, the Southern Triangle, is a small constellation
+north of Apus, and south of Norma. A fine triangle, nearly isosceles, is
+formed by its three bright stars, [Greek: a, b, g], the brightest [Greek:
+a] being at the vertex. These three stars form with [Greek: a] Centauri an
+elongated cross. The stars [Greek: b] and [Greek: g] are about 3rd
+magnitude. [Greek: b] is reddish. [Greek: e] (4�11, Harvard) is also
+reddish, and is nearly midway between [Greek: b] and [Greek: g], and near
+the centre of the cross above referred to. [Greek: a] is a fine star (1�88
+Harvard) and is one of the brightest stars in the sky--No. 33 in a list of
+1500 highest stars given by Pickering. About 1� 40' west of [Greek: e] is
+the short-period variable R Trianguli Australis (R.A. 15{h} 10{m}�8, S.
+66� 8') discovered at Cordoba in 1871. It varies from 6�7 to 7�4, and the
+period is about 3{d} 7{h}�2. Although not visible to ordinary eyesight it
+is given here, as it is an interesting object and all its light changes
+may be well seen with an opera-glass. A little south-east of [Greek: b] is
+another short-period variable, S Trianguli Australis (R.A. 15{h} 52{m}�2,
+S. 63� 30'), which varies from 6�4 to 7�4, with a period of 6�3 days; and
+all its fluctuations of light may also be observed with a good
+opera-glass.
+
+CIRCINUS, the Compass, is a very small constellation lying between
+Triangulum and Centaurus. Its brightest star, [Greek: a], is about 3-1/2
+magnitude, about 4� south of [Greek: a] Centauri.
+
+PAVO, the Peacock, lies north of Octans and Apus, and south of
+Telescopium. Its brightest star is [Greek: a], which is a fine bright star
+(2�12 Harvard). [Greek: k] is a short-period variable. It varies from 3�8
+to 5�2, and the period is about 9 days. This is an interesting object, as
+all the fluctations of light can be observed by the naked eye or an
+opera-glass. [Greek: e] Pavonis was measured 4�10 at Harvard, but the
+Cordoba estimates vary from 3�6 to 4�2. Gould says "it is of a remarkably
+blue colour."
+
+INDUS.--This constellation lies north of Octans, and south of Sagittarius,
+Microscopium, and Grus. One of its stars, [Greek: a], is probably referred
+to by Al-Sufi in his description of Sagittarius; it lies nearly midway
+between [Greek: b] Sagittarii and [Greek: a] Gruis, and is the brightest
+star of the constellation. The star [Greek: e] Indi (4�74 Harvard) has a
+remarkably large proper motion of 4"�68 per annum. Its parallax is about
+0"�28, and the proper motion indicates a velocity of about 49 miles a
+second at right angles to the line of sight.
+
+TOUCAN.--This constellation lies north of Octans, and south of Phoenix
+and Grus, east of Indus, and west of Hydrus. Its brightest star is [Greek:
+a], of about the 3rd magnitude.
+
+       *       *       *       *       *
+
+There are seven "celestial rivers" alluded to by the ancient
+astronomers:--
+
+1. The Fish River, which flows from the urn of Aquarius.
+
+2. The "River of the Bird," or the Milky Way in Cygnus.
+
+3. The River of the Birds--2, including Aquila.
+
+4. The River of Orion--Eridanus.
+
+5. The River of the god Marduk--perhaps the Milky Way in Perseus.
+
+6. The River of Serpents (Serpens, or Hydra).
+
+7. The River of Gan-gal (The High Cloud)--probably the Milky Way as a
+whole.
+
+There are four serpents represented among the constellations. These are
+Hydra, Hydrus, Serpens, and Draco.
+
+According to the late Mr. Proctor the date of the building of the Great
+Pyramid was about 3400 B.C.[452] At this time the Spring Equinox was in
+Taurus, and this is referred to by Virgil. But this was not so in Virgil's
+time, when--on account of the precession of the equinoxes--the equinoctial
+point had already entered Pisces, in which constellation it still remains.
+At the date 3400 B.C. the celestial equator ran along the whole length of
+the constellation Hydra, nearly through Procyon, and a little north of the
+bright red star Antares.
+
+The star Fomalhaut ([Greek: a] Piscis Australis) is interesting as being
+the most southern 1st magnitude star visible in England, its meridian
+altitude at Greenwich being little more than eight degrees.[453]
+
+With reference to the Greek letters given to the brighter stars by Bayer
+(in his Atlas published in 1603), and now generally used by astronomers,
+Mr. Lynn has shown that although "Bayer did uniformly designate the
+brightest stars in each constellation by the letter [Greek: a],"[454] it
+is a mistake to suppose--as has often been stated in popular books on
+astronomy--that he added the other Greek letters _in order of brightness_.
+That this is an error clearly appears from Bayer's own "Explicatio" to his
+Atlas, and was long since pointed out by Argelander (1832), and by Dr.
+Gould in his _Uranometria Argentina_. Gould says, "For the stars of each
+order, the sequence of the letters in no manner represents that of their
+brightness, but depended upon the positions of the stars in the figure,
+beginning usually at the head, and following its course until all the
+stars of that order of magnitude were exhausted." Mr. Lynn says, "Perhaps
+one of the most remarkable instances in which the lettering is seen at a
+glance not to follow the order of the letters is that of the three
+brightest stars in Aquila [Al-Sufi's 'three famous stars'], [Greek: g]
+being evidently brighter than [Greek: b]. But there is no occasion to
+conjecture from this that any change of relative brightness has taken
+place. Bayer reckoned both of these two of the third magnitude, and
+appears to have arranged [Greek: b] before [Greek: g], according to his
+usual custom, simply because [Greek: b] is in the neck of the supposed
+eagle, and [Greek: g] at the root of one of the wings."[455] Another good
+example is found in the stars of the "Plough," in which the stars are
+evidently arranged in the order of the figure and not in the order of
+relative brightness. In fact, Bayer is no guide at all with reference to
+star magnitudes. How different Al-Sufi was in this respect!
+
+The stars Aldebaran, Regulus, Antares, and Fomalhaut were called royal
+stars by the ancients. The reason of this was that they lie roughly about
+90� apart, that is 6 hours of Right Ascension. So, if through the north
+and south poles of the heavens and each of these stars we draw great
+circles of the sphere, these circles will divide the sphere into four
+nearly equal parts, and the ancients supposed that each of these stars
+ruled over a quarter of the sphere, an idea probably connected with
+astrology. As the position of Aldebaran is R.A. 4{h} 30{m}, Declination
+North 16� 19', and that of Antares is R.A. 16{h} 15{m}, Declination South
+25� 2', these two stars lie at nearly opposite points of the celestial
+sphere. From this it follows that our sun seen from Aldebaran would lie
+not very far from Antares, and seen from Antares it would appear not far
+from Aldebaran.
+
+The following may be considered as representative stars of different
+magnitudes. For those of first magnitude and fainter I have only given
+those for which all the best observers in ancient and modern times agree,
+and which have been confirmed by modern photometric measures. The Harvard
+measures are given:--
+
+  Brighter than "zero magnitude"    Sirius (-1�58); Canopus (-0�86)
+
+  Zero magnitude                    [Greek: a] Centauri (0�06)
+
+  0 to 0�4 magnitude                Vega (0�14); Capella (0�21);
+                                    Arcturus (0�24); Rigel (0�34)
+
+  0�5 magnitude                     Procyon (0�48)
+
+  1st     "                         Aldebaran (1�06)
+
+  2nd     "                         [Greek: a] Persei (1�90);
+                                    [Greek: b] Aurig� (2�07)
+
+  3rd     "                         [Greek: �] Bo�tis (3�08);
+                                    [Greek: z] Capricorni (2�98)
+
+  4th     "                         [Greek: r] Leonis (3�85);
+                                    [Greek: l] Scorpii (4�16);
+                                    [Greek: g] Crateris(4�14);
+                                    [Greek: r] Herculis (4�14)
+
+  5th     "                         [Greek: o] Pegasi (4�85);
+                                    [Greek: m] Capricorni (5�10)
+
+
+
+
+CHAPTER XX
+
+The Visible Universe
+
+
+Some researches on the distribution of stars in the sky have recently been
+made at the Harvard Observatory (U.S.A.). The principal results are:--(1)
+The number of stars on any "given area of the Milky Way is about twice as
+great as in an equal area of any other region." (2) This ratio does not
+increase for faint stars down to the 12th magnitude. (3) "The Milky Way
+covers about one-third of the sky and contains about half of the stars."
+(4) There are about 10,000 stars of magnitude 6�6 or brighter, 100,000
+down to magnitude 8�7, one million to magnitude 11, and two millions to
+magnitude 11�9. It is estimated that there are about 18 millions of stars
+down to the 15th magnitude visible in a telescope of 15 inches
+aperture.[456]
+
+According to Prof. Kapteyn's researches on stellar distribution, he finds
+that going out from the earth into space, the "star density"--that is,
+the number of stars per unit volume of space--is fairly constant until we
+reach a distance of about 200 "light years." From this point the density
+gradually diminishes out to a distance of 2500 "light years," at which
+distance it is reduced to about one-fifth of the density in the sun's
+vicinity.[457]
+
+In a letter to the late Mr. Proctor (_Knowledge_, November, 1885, p. 21),
+Sir John Herschel suggested that our Galaxy (or stellar system) "contained
+within itself miniatures of itself." This beautiful idea is probably true.
+In his account of the greater "Magellanic cloud," Sir John Herschel
+describes one of the numerous objects it contains as follows:--
+
+    "Very bright, very large; oval; very gradually pretty, much brighter
+    in the middle; a beautiful nebula; it has very much the resemblance to
+    the Nubecula Major itself as seen with the naked eye, but it is far
+    brighter and more impressive in its general aspect as if it were
+    doubled in intensity. Note--July 29, 1837. I well remember this
+    observation, it was the result of repeated comparisons between the
+    object seen in the telescope and the actual nubecula as seen high in
+    the sky on the meridian, and no vague estimate carelessly set down.
+    And who can say whether in this object, magnified and analysed by
+    telescopes infinitely superior to what we now possess, there may not
+    exist all the complexity of detail that the nubecula itself presents
+    to our examination?"[458]
+
+The late Lord Kelvin, in a remarkable address delivered before the
+Physical Science Section of the British Association at its meeting at
+Glasgow in 1901, considered the probable quantity of matter contained in
+our Visible Universe. He takes a sphere of radius represented by the
+distance of a star having a parallax of one-thousandth of a second (or
+about 3000 years' journey for light), and he supposes that uniformly
+distributed within this sphere there exists a mass of matter equal to 1000
+million times the sun's mass. With these data he finds that a body placed
+originally at the surface of the sphere would in 5 million years acquire
+by gravitational force a velocity of about 12-1/2 miles a second, and
+after 25 million of years a velocity of about 67 miles a second. As these
+velocities are of the same order as the observed velocities among the
+stars, Lord Kelvin concludes that there _is_ probably as much matter in
+our universe as would be represented by a thousand million suns. If we
+assumed a mass of ten thousand suns the velocities would be much too high.
+The most probable estimate of the total number of the visible stars is
+about 100 millions; so that if Lord Kelvin's calculations are correct we
+seem bound to assume that space contains a number of dark bodies. The
+nebul�, however, probably contain vast masses of matter, and this may
+perhaps account--partially, at least--for the large amount of matter
+estimated by Lord Kelvin. (See Chapter on "Nebul�.")
+
+In some notes on photographs of the Milky Way, Prof. Barnard says with
+reference to the great nebula near [Greek: r] Ophiuchi, "The peculiarity
+of this region has suggested to me the idea that the apparently small
+stars forming the ground work of the Milky Way here, are really very small
+bodies compared with our own sun"; and again, referring to the region near
+[Greek: b] Cygni, "One is specially struck with the apparent extreme
+smallness of the general mass of the stars in this region." Again, with
+reference to [Greek: ch] Cygni, he says, "The stars here also are
+remarkably uniform in size."[459]
+
+Eastman's results for parallax seem to show that "the fainter rather than
+the brighter stars are nearest to our system." But this apparent paradox
+is considered by Mr. Monck to be very misleading;[460] and the present
+writer holds the same opinion.
+
+Prof. Kapteyn finds "that stars whose proper motions exceed 0"�05 are not
+more numerous in the Milky Way than in other parts of the sky; or, in
+other words, if only the stars having proper motions of 0"�05 or upwards
+were mapped, there would be no aggregation of stars showing the existence
+of the Milky Way."[461]
+
+With reference to the number of stars visible on photographs, the late Dr.
+Isaac Roberts says--
+
+    "So far as I am able at present to judge, under the atmospheric
+    conditions prevalent in this country, the limit of the photographic
+    method of delineation will be reached at stellar, or nebular, light of
+    the feebleness of about 18th-magnitude stars. The reason for this
+    inference is that the general illumination of the atmosphere by
+    starlight concentrated upon a film by the instrument will mask the
+    light of objects that are fainter than about 18th-magnitude
+    stars."[462]
+
+With reference to blank spaces in the sky, the late Mr. Norman Pogson
+remarked--
+
+    "Near S Ophiuchi we find one of the most remarkable vacuities in this
+    hemisphere--an elliptic space of about 65' in length in the direction
+    of R.A., and 40' in width, in which there exists _no_ star larger than
+    the 13th magnitude ... it is impossible to turn a large telescope in
+    that direction and, if I may so express it, view such black darkness,
+    without a feeling that we are here searching into the remote regions
+    of space, far beyond the limits of our own sidereal system."[463]
+
+Prof. Barnard describes some regions in the constellation Taurus
+containing "dark lanes" in a groundwork of faint nebulosity. He gives two
+beautiful photographs of the regions referred to, and says that the dark
+holes and lanes are apparently darker than the sky in the immediate
+vicinity. He says, "A very singular feature in this connection is that the
+stars also are absent in general from the lanes." A close examination of
+these photographs has given the present writer the impression that the
+dark lanes and spots are _in_ the nebulosity, and that the nebulosity is
+mixed up with the stars. This would account for the fact that the stars
+are in general absent from the dark lanes. For if there is an intimate
+relation between the stars and the nebulosity, it would follow that where
+there is no nebulosity in this particular region there would be no stars.
+Prof. Barnard adds that the nebulosity is easily visible in a 12-inch
+telescope.[464]
+
+With reference to the life of the universe, Prof. F. R. Moulton well
+says--
+
+    "The lifetime of a man seems fairly long, and the epoch when Troy was
+    besieged, or when the Pharaohs piled up the pyramids in the valley of
+    the Nile, or when our ancestors separated on the high plateaux of
+    Asia, seems extremely remote, but these intervals are only moments
+    compared to the immense periods required for geological evolutions and
+    the enormously greater ones consumed in the developement of worlds
+    from widely extended nebulous masses. We recognize the existence of
+    only those forces whose immediate consequences are appreciable, and it
+    may be that those whose effects are yet unseen are really of the
+    highest importance. A little creature whose life extended over only
+    two or three hours of a summer's day might be led, if he were
+    sufficiently endowed with intelligence, to infer that passing clouds
+    were the chief influence at work in changing the climate instead of
+    perceiving that the sun's slow motion across the sky would bring on
+    the night and its southward motion the winter."[465]
+
+In a review of my book _Astronomical Essays_ in _The Observatory_,
+September, 1907, the following words occur. They seem to form a good and
+sufficient answer to people who ask, What is there beyond our visible
+universe? "If the stellar universe is contained in a sphere of say 1000
+stellar units radius, what is there beyond? To this the astronomer will
+reply that theories and hypotheses are put forward for the purpose of
+explaining observed facts; when there are no facts to be explained, no
+theory is required. As there are no observed facts as to what exists
+beyond the farthest stars, the mind of the astronomer is a complete blank
+on the subject. Popular imagination can fill up the blank as it pleases."
+With these remarks I fully concur.
+
+In his address to the British Association, Prof. G. H. Darwin (now Sir
+George Darwin) said--
+
+    "Man is but a microscopic being relatively to astronomical space, and
+    he lives on a puny planet circling round a star of inferior rank. Does
+    it not, then, seem futile to imagine that he can discover the origin
+    and tendency of the Universe as to expect a housefly to instruct us as
+    to the theory of the motions of the planets? And yet, so long as he
+    shall last, he will pursue his search, and will no doubt discover many
+    wonderful things which are still hidden. We may indeed be amazed at
+    all that man has been able to find out, but the immeasurable magnitude
+    of the undiscovered will throughout all time remain to humble his
+    pride. Our children's children will still be gazing and marvelling at
+    the starry heavens, but the riddle will never be read."
+
+The ancient philosopher Lucretius said--
+
+  "Globed from the atoms falling slow or swift
+  I see the suns, I see the systems lift
+  Their forms; and even the system and the suns
+  Shall go back slowly to the eternal drift."[466]
+
+But it has been well said that the structure of the universe "has a
+fascination of its own for most readers quite apart from any real progress
+which may be made towards its solution."[467]
+
+The Milky Way itself, Mr. Stratonoff considers to be an agglomeration of
+immense condensations, or stellar clouds, which are scattered round the
+region of the galactic equator. These clouds, or masses of stars,
+sometimes leave spaces between them, and sometimes they overlap, and in
+this way he accounts for the great rifts, like the Coal Sack, which allow
+us to see through this great circle of light. He finds other
+condensations of stars; the nearest is one of which our sun is a member,
+chiefly composed of stars of the higher magnitudes which "thin out rapidly
+as the Milky Way is approached." There are other condensations: one in
+stars of magnitudes 6�5 to 8�5; and a third, farther off, in stars of
+magnitudes 7�6 to 8. These may be called opera-glass, or field-glass
+stars.
+
+Stratonoff finds that stars with spectra of the first type (class A, B, C,
+and D of Harvard) which include the Sirian and Orion stars, are
+principally situated near the Milky Way, while those of type II. (which
+includes the solar stars) "are principally condensed in a region
+coinciding roughly with the terrestrial pole, and only show a slight
+increase, as compared with other stars, as the galaxy is approached."[468]
+
+Prof. Kapteyn thinks that "undoubtedly one of the greatest difficulties,
+if not the greatest of all, in the way of obtaining an understanding of
+the real distribution of the stars in space, lies in our uncertainty about
+the amount of loss suffered by the light of the stars on its way to the
+observer."[469] He says, "There can be little doubt in my opinion, about
+the existence of absorption in space, and I think that even a good guess
+as to the order of its amount can be made. For, first we know that space
+contains an enormous mass of meteoric matter. This matter must necessarily
+intercept some part of the star-light."
+
+This absorption, however, seems to be comparatively small. Kapteyn finds a
+value of 0�016 (about 1/60th) of a magnitude for a star at a distance
+corresponding to a parallax of one-tenth of a second (about 33 "light
+years"). This is a quantity almost imperceptible in the most delicate
+photometer. But for very great distances--such as 3000 "light years"--the
+absorption would evidently become very considerable, and would account
+satisfactorily for the gradual "thinning out" of the fainter stars. If
+this were fully proved, we should have to consider the fainter stars of
+the Milky Way to be in all probability fairly large suns, the light of
+which is reduced by absorption.
+
+That some of the ancients knew that the Milky Way is composed of stars is
+shown by the following lines translated from Ovid:--
+
+  "A way there is in heaven's extended plain
+  Which when the skies are clear is seen below
+  And mortals, by the name of Milky, know;
+  The groundwork is of stars, through which the road
+  Lies open to great Jupiter's abode."[470]
+
+From an examination of the distribution of the faint stars composing the
+Milky Way, and those shown in Argelander's charts of stars down to the
+9-1/2 magnitude, Easton finds that there is "a real connection between the
+distribution of 9th and 10th magnitude stars, and that of the faint stars
+of the Milky Way, and that consequently the faint or very faint stars of
+the galactic zone are at a distance which does not greatly exceed that of
+the 9th and 10th magnitude stars."[471] A similar conclusion was, I think,
+arrived at by Proctor many years ago. Now let us consider the meaning of
+this result. Taking stars of the 15th magnitude, if their faintness were
+merely due to greater distance, their actual brightness--if of the same
+size--would imply that they are at 10 times the distance of stars of the
+10th magnitude. But if at the same distance from us, a 10th magnitude star
+would be 100 times brighter than a 15th magnitude star, and if of the same
+density and "intrinsic brightness" (or luminosity of surface) the 10th
+magnitude would have 10 times the diameter of the fainter star, and hence
+its volume would be 1000 times greater (10{3}), and this great difference
+is not perhaps improbable.
+
+The constitution of the Milky Way is not the same in all its parts. The
+bright spot between [Greek: b] and [Greek: g] Cygni is due to relatively
+bright stars. Others equally dense but fainter regions in Auriga and
+Monoceros are only evident in stars of the 8th and 9th magnitude, and the
+light of the well-known luminous spot in "Sobieski's Shield," closely
+south of [Greek: l] Aquil�, is due to stars below magnitude 9-1/2.
+
+The correspondence in distribution between the stars of Argelander's
+charts and the fainter stars of the Milky Way shows, as Easton points out,
+that Herschel's hypothesis of a uniform distribution of stars of
+approximately equal size is quite untenable.
+
+It has been suggested that the Milky Way may perhaps form a ring of stars
+with the sun placed nearly, but not exactly, in the centre of the ring.
+But were it really a ring of uniform width with the sun eccentrically
+placed within it, we should expect to find the Milky Way wider at its
+nearest part, and gradually narrowing towards the opposite point. Now,
+Herschel's "gages" and Celoria's counts show that the Galaxy is wider in
+Aquila than in Monoceros. This is confirmed by Easton, who says, "_for the
+faint stars taken as a whole, the Milky Way is widest in its brightest
+part_" (the italics are Easton's). From this we should conclude that the
+Milky Way is nearer to us in the direction of Aquila than in that of
+Monoceros. Sir John Herschel suggested that the southern parts of the
+galactic zone are nearer to us on account of their greater _brightness_ in
+those regions.[472] But greater width is a safer test of distance than
+relative brightness. For it may be easily shown than the _intrinsic_
+brightness of an area containing a large number of stars would be the
+same for _all_ distances (neglecting the supposed absorption of light in
+space). For suppose any given area crowded with stars to be removed to a
+greater distance. The light of each star would be diminished inversely as
+the square of the distance. But the given area would also be diminished
+_directly_ as the square of the distance, so we should have a diminished
+amount of light on an equally diminished area, and hence the intrinsic
+brightness, or luminosity of the area per unit of surface, would remain
+unaltered. The increased brightness of the Milky Way in Aquila is
+accounted for by the fact that Herschel's "gages" show an increased number
+of stars, and hence the brightness in Aquila and Sagittarius does not
+necessarily imply that the Milky Way is nearer to us in those parts, but
+that it is richer in small stars than in other regions.
+
+Easton is of opinion that the annular hypothesis of the Milky Way is
+inconsistent with our present knowledge of the galactic phenomena, and he
+suggests that its actual constitution resembles more that of a spiral
+nebula.[473] On this hypothesis the increase in the number of stars in the
+regions above referred to may be due to our seeing one branch of the
+supposed "two-branched spiral" projected on another branch of the same
+spiral. This seems supported by Sir John Herschel's observations in the
+southern hemisphere, where he found in some places "a tissue as it were of
+large stars spread over another of very small ones, the immediate
+magnitudes being wanting." Again, portions of the spiral branches may be
+richer than others, as photographs of spiral nebul� seem to indicate.
+Celoria, rejecting the hypothesis of a single ring, suggests the existence
+of _two_ galactic rings inclined to each other at an angle of about 20�,
+one of these including the brighter stars, and the other the fainter. But
+this seems to be a more artificial arrangement then the hypothesis of a
+spiral. Further, the complicated structure of the Milky Way cannot be well
+explained by Celoria's hypothesis of two distinct rings one inside the
+other. From analogy the spiral hypothesis seems much more probable.
+
+Considering the Milky Way to represent a colossal spiral nebula viewed
+from a point not far removed from the centre of the spiral branches,
+Easton suggests that the bright region between [Greek: b] and [Greek: g]
+Cygni, which is very rich in comparatively bright stars, may possibly
+represent the "_central accumulations of the Milky Way_," that is, the
+portion corresponding to the nucleus of a spiral nebula. If this be so,
+this portion of the Milky Way should be nearer to us than others. Easton
+also thinks that the so-called "solar cluster" of Gould, Kapteyn, and
+Schiaparelli may perhaps be "the expression of the central condensation
+of the galactic system itself, composed of the most part of suns
+comparable with our own, and which would thus embrace most of the bright
+stars to the 9th or 10th magnitude. The distance of the galactic streams
+and convolutions would thus be comparable with the distances of these
+stars." He thinks that the sun lies within a gigantic spiral, "in a
+comparatively sparse region between the central nucleus and Orion."
+
+Scheiner thinks that "the irregularities of the Milky Way, especially in
+streams, can be quite well accounted for, as Easton has attempted to do,
+if they are regarded as a system of spirals, and not as a ring system."
+
+Evidence in favour of the spiral hypothesis of the Milky Way, as advocated
+by Easton and Scheiner, may be found in Kapteyn's researches on the proper
+motions of the stars. This eminent astronomer finds that stars with
+measurable proper motions--and therefore in all probability relatively
+near the earth--have mostly spectra of the solar type, and seem to cluster
+round "a point adjacent to the sun, in total disregard to the position of
+the Milky Way," and that stars with little or no proper motion collect
+round the galactic plain. He is also of opinion that the Milky Way
+resembles the Andromeda nebula, "the globular nucleus representing the
+solar cluster, and the far spreading wings or whorls the compressed layer
+of stars enclosed by the rings of the remote Galaxy."
+
+With reference to the plurality of inhabited worlds, it has been well said
+by the ancient writer Metrodorus (third century B.C.), "The idea that
+there is but a single world in all infinitude would be as absurd as to
+suppose that a vast field had been formed to produce a single blade of
+wheat."[474] With this opinion the present writer fully concurs.
+
+
+
+
+CHAPTER XXI
+
+General
+
+
+The achievements of Hipparchus in astronomy were very remarkable,
+considering the age in which he lived. He found the amount of the apparent
+motion of the stars due to the precession of the equinoxes (of which he
+was the discoverer) to be 59" per annum. The correct amount is about 50".
+He measured the length of the year to within 9 minutes of its true value.
+He found the inclination of the ecliptic to the plane of the equator to be
+23� 51'. It was then 23� 46'--as we now know by modern calculations--so
+that Hipparchus' estimation was a wonderfully close approximation to the
+truth. He computed the moon's parallax to be 57', which is about its
+correct value. He found the eccentricity of the sun's apparent orbit round
+the earth to be one twenty-fourth, the real value being then about
+one-thirteenth. He determined other motions connected with the earth and
+moon; and formed a catalogue of 1080 stars. All this work has earned for
+him the well-merited title of "The Father of Astronomy."[475]
+
+The following is a translation of a Greek passage ascribed to Ptolemy: "I
+know that I am mortal and the creature of a day, but when I search out the
+many rolling circles of the stars, my feet touch the earth no longer, but
+with Zeus himself I take my fill of ambrosia, the food of the gods."[476]
+This was inscribed (in Greek) on a silver loving cup presented to the late
+Professor C. A. Young, the famous American astronomer.[477]
+
+Some curious and interesting phenomena are recorded in the old Chinese
+Annals, which go back to a great antiquity. In 687 B.C. "a night" is
+mentioned "without clouds and without stars" (!) This may perhaps refer to
+a total eclipse of the sun; but if so, the eclipse is not mentioned in the
+Chinese list of eclipses. In the year 141 B.C., it is stated that the sun
+and moon appeared of a deep red colour during 5 days, a phenomenon which
+caused great terror among the people. In 74 B.C., it is related that a
+star as large as the moon appeared, and was followed in its motion by
+several stars of ordinary size. This probably refers to an unusually large
+"bolide" or "fireball." In 38 B.C., a fall of meteoric stones is recorded
+"of the size of a walnut." In A.D. 88, another fall of stones is
+mentioned. In A.D. 321, sun-spots were visible to the naked eye.
+
+Homer speaks of a curious darkness which occurred during one of the great
+battles in the last year of the Trojan war. Mr. Stockwell identifies this
+with an eclipse of the sun which took place on August 28, 1184 B.C. An
+eclipse referred to by Thucydides as having occurred during the first year
+of the Peloponnesian War, when the darkness was so great that some stars
+were seen, is identified by Stockwell with a total eclipse of the sun,
+which took place on August 2, 430 B.C.
+
+A great eclipse of the sun is supposed to have occurred in the year 43 or
+44 B.C., soon after the death of Julius C�sar. Baron de Zach and Arago
+mention it as the first annular eclipse on record. But calculations show
+that no solar eclipse whatever, visible in Italy, occurred in either of
+these years. The phenomenon referred to must therefore have been of
+atmospherical origin, and indeed this is suggested by a passage in
+Suetonius, one of the authors quoted on the subject.
+
+M. Guillaume thinks that the ninth Egyptian plague, the thick "darkness"
+(Exodus x. 21-23), may perhaps be explained by a total eclipse of the sun
+which occurred in 1332 B.C. It is true that the account states that the
+darkness lasted "three days," but this, M. Guillaume thinks, may be due to
+an error in the translation.[478] This explanation, however, seems very
+improbable.
+
+According to Hind, the moon was eclipsed on the generally received date
+of the Crucifixion, A.D. 33, April 3. He says, "I find she had emerged
+from the earth's dark shadow a quarter of an hour before she rose at
+Jerusalem (6{h} 36{m} p.m.); but the penumbra continued upon her disc for
+an hour afterwards." An eclipse could not have had anything to do with the
+"darkness over all the land" during the Crucifixion. For this lasted for
+three hours, and the totality of a solar eclipse can only last a few
+minutes at the most. As a matter of fact the "eclipse of Phlegon," a
+partial one (A.D. 29, November 24) was "the only solar eclipse that could
+have been visible in Jerusalem during the period usually fixed for the
+ministry of Christ."
+
+It is mentioned in the Anglo-Saxon Chronicle that a total eclipse of the
+sun took place in the year after King Alfred's great battle with the
+Danes. Now, calculation shows that this eclipse occurred on October 29,
+878 A.D. King Alfred's victory over the Danes must, therefore, have taken
+place in 877 A.D., and his death probably occurred in 899 A.D. This solar
+eclipse is also mentioned in the Annals of Ulster. From this it will be
+seen that in some cases the dates of historical events can be accurately
+fixed by astronomical phenomena.
+
+It is stated by some historians that an eclipse of the sun took place on
+the morning of the battle of Crecy, August 26, 1346. But calculation
+shows that there was no eclipse of the sun visible in England in that
+year. At the time of the famous battle the moon had just entered on her
+first quarter, and she was partially eclipsed six days afterwards--that is
+on the 1st of September. The mistake seems to have arisen from a
+mistranslation of the old French word _esclistre_, which means lightning.
+This was mistaken for _esclipse_. The account seems to indicate that there
+was a heavy thunderstorm on the morning of the battle.
+
+A dark shade was seen on the waning moon by Messrs. Hirst and J. C.
+Russell on October 21, 1878, "as dark as the shadow during an eclipse of
+the moon."[479] If this observation is correct, it is certainly most
+difficult to explain. Another curious observation is recorded by Mr. E.
+Stone Wiggins, who says that a partial eclipse of the sun by a dark body
+was observed in the State of Michigan (U.S.A.) on May 16, 1884, at 7 p.m.
+The "moon at that moment was 12 degrees south of the equator and the sun
+as many degrees north of it." The existence of a dark satellite of the
+earth has been suggested, but this seems highly improbable.
+
+The sun's corona seems to have been first noticed in the total eclipse of
+the sun which occurred at the death of the Roman emperor Domitian, A.D.
+95. Philostratus in his _Life of Apollonius_ says, with reference to this
+eclipse, "In the heavens there appeared a prodigy of this nature: a
+certain _corona_ resembling the Iris surrounded the orb of the sun, and
+obscured its light."[480] In more modern times the corona seems to have
+been first noticed by Clavius during the total eclipse of April 9,
+1567.[481] Kepler proved that this eclipse was total, not annular, so that
+the ring seen by Clavius must have been the corona.
+
+With reference to the visibility of planets and stars during total
+eclipses of the sun; in the eclipse of May 12, 1706, Venus, Mercury, and
+Aldebaran, and several other stars were seen. During the totality of the
+eclipse of May 3, 1715, about twenty stars were seen with the naked
+eye.[482] At the eclipse of May 22, 1724, Venus and Mercury, and a few
+fixed stars were seen.[483] The corona was also noticed. At the eclipse of
+May 2, 1733, Jupiter, the stars of the "Plough," Capella, and other stars
+were visible to the naked eye; and the corona was again seen.[483]
+
+During the total eclipses of February 9, 1766, June 24, 1778, and June 16,
+1806, the corona was again noticed. But its true character was then
+unknown.
+
+At the eclipse of July 8, 1842, it was noticed by observers at Lipesk
+that the stars Aldebaran and Betelgeuse ([Greek: a] Orionis), which are
+usually red, "appeared quite white."[484]
+
+There will be seven eclipses in the years 1917, 1935, and 1985. In the
+year 1935 there will be five eclipses of the sun, a rare event; and in
+1985 there will be three total eclipses of the moon, a most unusual
+occurrence.[485]
+
+Among the ancient Hindoos, the common people believed that eclipses were
+caused by the interposition of a monstrous demon called Raha. This absurd
+idea, and others equally ridiculous, were based on declarations in their
+sacred books, and no pious Hindoo would think of denying it.
+
+The following cases of darkenings of the sun are given by Humboldt:--
+
+According to Plutarch the sun remained pale for a whole year at the death
+of Julius C�sar, and gave less than its usual heat.[486]
+
+A sun-darkening lasting for two hours is recorded on August 22, 358 A.D.,
+before the great earthquake of Nicomedia.
+
+In 360 A.D. there was a sun-darkening from early morn till noon. The
+description given by the historians of the time corresponds to an eclipse
+of the sun, but the duration of the obscurity is inexplicable.
+
+In 409 A.D., when Alaric lay siege to Rome, "there was so great a
+darkness that the stars were seen by day."
+
+In 536 A.D. the sun is said to have been darkened for a year and two
+months!
+
+In 626 A.D., according to Abul Farag, half the sun's disc was darkened for
+eight months!
+
+In 934 A.D. the sun lost its brightness for two months in Portugal.
+
+In 1090 A.D. the sun was darkened for three hours.
+
+In 1096, sun-spots were seen with the naked eye on March 3.
+
+In 1206 A.D. on the last day of February, "there was complete darkness for
+six hours, turning the day into night." This seems to have occurred in
+Spain.
+
+In 1241 the sun was so darkened that stars could be seen at 3 p.m. on
+Michaelmas day. This happened in Vienna.[487]
+
+The sun is said to have been so darkened in the year 1547 A.D. for three
+days that stars were visible at midday. This occurred about the time of
+the battle of M�hlbergh.[488]
+
+Some of these darkenings may possibly have been due to an enormous
+development of sun-spots; but in some cases the darkness is supposed by
+Chladni and Schnurrer to have been caused by "the passage of meteoric
+masses before the sun's disc."
+
+The first observer of a transit of Venus was Jeremiah Horrocks, who
+observed the transit of November 24 (O.S.), 1639. He had previously
+corrected Kepler's predicted time of the transit from 8{h} 8{m} a.m. at
+Manchester to 5{h} 57{m} p.m. At the end of 1875 a marble scroll was
+placed on the pedestal of the monument of John Conduitt (nephew of Sir
+Isaac Newton, and who adopted Horrocks' theory of lunar motions) at the
+west end of the nave of Westminster Abbey, bearing this inscription from
+the pen of Dean Stanley--
+
+  "Ad majora avocatus
+  qu� ob h�c parerga negligi non decuit"
+  IN MEMORY OF
+  JEREMIAH HORROCKS
+  Curate of Hoole in Lancashire
+  Who died on the 3{d} of January, 1641, in or near his
+  22{d} year
+  Having in so short a life
+  Detected the long inequality in the mean motion of
+  Jupiter and Saturn
+  Discovered the orbit of the Moon to be an ellipse;
+  Determined the motion of the lunar aspe,
+  Suggested the physical cause of its revolution;
+  And predicted from his own observations, the
+  Transit of Venus
+  Which was seen by himself and his friend
+  WILLIAM CRABTREE
+  On Sunday, the 24th November (O.S.) 1639;
+  This Tablet, facing the Monument of Newton
+  Was raised after the lapse of more than two centuries
+  December 9, 1874.[489]
+
+The transit of Venus which occurred in 1761 was observed on board ship(!)
+by the famous but unfortunate French astronomer Le Gentil. The ship was
+the frigate _Sylphide_, sent to the help of Pondicherry (India) which was
+then being besieged by the English. Owing to unfavourable winds the
+_Sylphide_ was tossed about from March 25, 1761, to May 24 of the same
+year. When, on the later date, off the coast of Malabar, the captain of
+the frigate learned that Pondicherry had been captured by the English, the
+vessel returned to the Isle of France, where it arrived on June 23, after
+touching at Point de Galle on May 30. It was between these two places that
+Le Gentil made his observations of the transit of Venus under such
+unfavourable conditions. He had an object-glass of 15 feet (French) focus,
+and this he mounted in a tube formed of "four pine planks." This rough
+instrument was fixed to a small mast set up on the quarter-deck and worked
+by ropes. The observations made under such curious conditions, were not,
+as may be imagined, very satisfactory. As another transit was to take
+place on June 3, 1769, Le Gentil made the heroic resolution of remaining
+in the southern hemisphere to observe it! This determination was duly
+carried out, but his devotion to astronomy was not rewarded; for on the
+day of the long waited for transit the sky at Pondicherry (where he had
+gone to observe it) was clouded over during the whole phenomenon,
+"although for many days previous the sky had been cloudless." To add to
+his feeling of disappointment he heard that at Manilla, where he had been
+staying some time previously, the sky was quite clear, and two of his
+friends there had seen the transit without any difficulty.[490] Truly the
+unfortunate Le Gentil was a martyr to science.
+
+The famous German astronomer Bessel once said "that a practical astronomer
+could make observations of value if he had only a cart-wheel and a gun
+barrel"; and Watson said that "the most important part of the instrument
+is the person at the small end."[491]
+
+With reference to Father Hell's supposed forgery of his observations of
+the transit of Venus in 1769, and Littrow's criticism of some of the
+entries in Hell's manuscript being corrected with a different coloured
+ink, Professor Newcomb ascertained from Weiss that Littrow was colour
+blind, and could not distinguish between the colour of Aldebaran and the
+whitest star. Newcomb adds, "For half a century the astronomical world had
+based an impression on the innocent but mistaken evidence of a
+colour-blind man respecting the tint of ink in a manuscript."
+
+It is recorded that on February 26, B.C. 2012, the moon, Mercury, Venus,
+Jupiter, and Saturn, were in the same constellation, and within 14
+degrees of each other. On September 14, 1186 A.D., the sun, moon, and all
+the planets then known, are said to have been situated in Libra.[492]
+
+In the Sanscrit epic poem, "The Ramaya," it is stated that at the birth of
+Rama, the moon was in Cancer, the sun in Aries, Mercury in Taurus, Venus
+in Pisces, Mars in Capricornus, Jupiter in Cancer, and Saturn in Libra.
+From these data, Mr. Walter R. Old has computed that Rama was born on
+February 10, 1761 B.C.[493]
+
+A close conjunction of Mars and Saturn was observed by Denning on
+September 29, 1889, the bright star Regulus ([Greek: a] Leonis) being at
+the time only 47' distant from the planets.[494]
+
+An occultation of the Pleiades by the moon was observed by Timocharis at
+Alexandria on January 29, 282 B.C. Calculations by Schjellerup show that
+Alcyone ([Greek: �] Tauri) was occulted; but the exact time of the day
+recorded by Timocharis differs very considerably from that computed by
+Schjellerup.[495] Another occultation of the Pleiades is recorded by
+Agrippa in the reign of Domitian. According to Schjellerup the phenomenon
+occurred on November 29, A.D. 92.
+
+"Kepler states that on the 9th of January, 1591, M�stlin and himself
+witnessed an occultation of Jupiter by Mars. The red colour of the latter
+on that occasion plainly indicated that it was the inferior planet."[496]
+That is, that Mars was nearer to the sun than Jupiter. But as the
+telescope had not then been invented, this may have been merely a near
+approach of the two planets.
+
+According to Kepler, M�stlin saw an occultation of Mars by Venus on
+October 3, 1590. But this may also have been merely a near approach.[496]
+
+A curious paradox is that one can discover an object without seeing it,
+and see an object without discovering it! The planet Neptune was
+discovered by Adams and Leverrier by calculation before it was seen in the
+telescope by Galle; and it was actually seen by Lalande on May 8 and 10,
+1795, but he took it for a _star_ and thus missed the discovery. In fact,
+he _saw_ the planet, but did not _discover_ it. It actually appears as a
+star of the 8th magnitude in Harding's Atlas (1822). The great "new star"
+of February, 1901, known as Nova Persei, was probably seen by some people
+before its discovery was announced; and it was actually noticed by a
+well-known American astronomer, who thought it was some bright star with
+which he was not familiar! But this did not amount to a discovery. Any one
+absolutely ignorant of astronomy might have made the same observation. An
+object must be _identified_ as a _new_ object before a discovery can be
+claimed. Some years ago a well-known Irish naturalist discovered a spider
+new to science, and after its discovery he found that it was common in
+nearly every house in Dublin! But this fact did not detract in the least
+from the merit of its scientific discovery.
+
+There is a story of an eminent astronomer who had been on several eclipse
+expeditions, and yet was heard to remark that he had never seen a total
+eclipse of the sun. "But your observations of several eclipses are on
+record," it was objected. "Certainly, I have on several occasions made
+observations, but I have always been too busy to look at the eclipse." He
+was probably in a dark tent taking photographs or using a spectroscope
+during the totality. This was observing an eclipse without seeing it!
+
+Humboldt gives the credit of the invention of the telescope to Hans
+Lippershey, a native of Wesel and a spectacle-maker at Middleburgh; to
+Jacob Adreaansz, surnamed Metius, who is also said to have made
+burning-glasses of ice; and to Zachariah Jansen.[497]
+
+With reference to the parabolic figure of the large mirrors of reflecting
+telescopes, Dr. Robinson remarked at the meeting of the British
+Association at Cork in 1843, "between the spherical and parabolic figures
+the extreme difference is so slight, even in the telescope of 6-feet
+aperture [Lord Rosse's] that if the two surfaces touched at their vertex,
+the distance at the edge would not amount to the 1/10000th of an inch, a
+space which few can measure, and none without a microscope."[498]
+
+In the year 1758, Roger Long, Lowndean Professor of Astronomy at
+Cambridge, constructed an "orrery" on a novel principle. It was a hollow
+metal sphere of about 18 feet in diameter with its fixed axis parallel to
+the earth's axis. It was rotated, by means of a winch and rackwork. It
+held about thirty persons in its interior, where astronomical lectures
+were delivered. The constellations were painted on the interior surface;
+and holes pierced through the shell and illuminated from the outside
+represented the stars according to their different magnitudes. This
+ingenious machine was much neglected for many years, but was still in
+existence in Admiral Smyth's time, 1844.[499]
+
+A "temporary star" is said to have been seen by Hepidanus in the
+constellation Aries in either 1006 or 1012 A.D. The late M. Sch�nfeld, a
+great authority on variable stars, found from an Arabic and Syrian
+chronicle that 1012 is the correct year (396 of the Hegira), but that the
+word translated Aries would by a probable emendation mean Scorpio. The
+word in the Syrian record is not the word for Aries.[500]
+
+Mr. Heber D. Curtis finds that the faintest stars mentioned in Ptolemy's
+Catalogue are about 5�38 magnitude on the scale of the Harvard
+_Photometric Durchmustering_.[501] Heis and Houzeau saw stars of 6-7
+magnitude (about 6�4 on Harvard scale). The present writer found that he
+could see most of Heis' faintest stars in the west of Ireland (Co. Sligo)
+without optical aid (except short-sighted spectacles).
+
+With reference to the apparent changes in the stellar heavens produced by
+the precession of the equinoxes, Humboldt says--
+
+    "Canopus was fully 1� 20' below the horizon of Toledo (39� 54' north
+    latitude) in the time of Columbus; and now the same star is almost as
+    much above the horizon of Cadiz. While at Berlin, and in northern
+    latitudes, the stars of the Southern Cross, as well as [Greek: a] and
+    [Greek: b] Centauri, are receding more and more from view, the
+    Magellanic Clouds are slowly approaching our latitudes. Canopus was at
+    its greatest northern approximation during last century [eighteenth],
+    and is now moving nearer and nearer to the south, although very
+    slowly, owing to its vicinity to the south pole of the ecliptic. The
+    Southern Cross began to become invisible in 52� 30' north latitude
+    2900 years before our era, since, according to Galle, this
+    constellation might previously have reached an altitude of more than
+    10�. When it had disappeared from the horizon of the countries of the
+    Baltic, the great pyramid of Cheops had already been erected more than
+    five hundred years. The pastoral tribe of the Hyksos made their
+    incursion seven hundred years earlier. The past seems to be visibly
+    nearer to us when we connect its measurement with great and memorable
+    events."[502]
+
+With reference to the great Grecian philosopher and scientist Eratosthenes
+of Cyrene, keeper of the Alexandrian Library under Ptolemy Euergetes, Carl
+Snyder says, "Above all the Alexanders, C�sars, Tadema-Napoleons, I set
+the brain which first spanned the earth, over whose little patches these
+fought through their empty bootless lives. Why should we have no poet to
+celebrate so great a deed?"[503] And with reference to Aristarchus he
+says, "If grandeur of conceptions be a measure of the brain, or ingenuity
+of its powers, then we must rank Aristarchus as one of the three or four
+most acute intellects of the ancient world."[504]
+
+Lagrange, who often asserted Newton to be the greatest genius that ever
+existed, used to remark also--"and the most fortunate; we do not find more
+than once a system of the world to establish."[505]
+
+Grant says--
+
+    "Lagrange deserves to be ranked among the greatest mathematical
+    geniuses of ancient or modern times. In this respect he is worthy of a
+    place with Archimedes or Newton, although he was far from possessing
+    the sagacity in physical enquiries which distinguished these
+    illustrious sages. From the very outset of his career he assumed a
+    commanding position among the mathematicians of the age, and during
+    the course of nearly half a century previous to his death, he
+    continued to divide with Laplace the homage due to pre-eminence in the
+    exact sciences. His great rival survived him fourteen years, during
+    which he reigned alone as the prince of mathematicians and theoretical
+    astronomers."[506]
+
+A writer in _Nature_ (May 25, 1871) relates the following anecdote with
+reference to Sir John Herschel: "Some time after the death of Laplace, the
+writer of this notice, while travelling on the continent in company with
+the celebrated French _savant_ Biot, ventured to put to him the question,
+not altogether a wise one, 'And whom of all the philosophers of Europe do
+you regard as the most worthy successor of Laplace?' Probably no man was
+better able than Biot to form a correct conclusion, and the reply was more
+judicious than the question. It was this, 'If I did not love him so much I
+should unhesitatingly say, Sir John Herschel.'" Dr. Gill (now Sir David
+Gill), in an address at the Cape of Good Hope in June, 1898, spoke of Sir
+John Herschel as "the prose poet of science; his popular scientific works
+are models of clearness, and his presidential addresses teem with
+passages of surpassing beauty. His life was a pure and blameless one from
+first to last, full of the noblest effort and the noblest aim from the
+time when as a young Cambridge graduate he registered a vow 'to try to
+leave the world wiser than he found it'--a vow that his life amply
+fulfilled."[507]
+
+Prof. Newcomb said of Adams, the co-discoverer of Neptune with Leverrier,
+"Adams' intellect was one of the keenest I ever knew. The most difficult
+problem of mathematical astronomy and the most recondite principles that
+underlie the theory of the celestial motions were to him but child's
+play." Airy he regarded as "the most commanding figure in the astronomy of
+our time."[508] He spoke of Delaunay, the great French astronomer, as a
+most kindly and attractive man, and says, "His investigations of the
+moon's motion is one of the most extraordinary pieces of mathematical work
+ever turned out by a single person. It fills two quarto volumes, and the
+reader who attempts to go through any part of the calculations will wonder
+how one man could do the work in a lifetime."[509]
+
+Sir George B. Airy and Prof. J. C. Adams died in the same month. The
+former on January 2, 1892, and the latter on January 22 of the same year.
+
+It is known from the parish register of Burstow in Surrey that Flamsteed
+(Rev. John Flamsteed), the first Astronomer Royal at Greenwich, was buried
+in the church at that place on January 12, 1720; but a search for his
+grave made by Mr. J. Carpenter in 1866 and by Mr. Lynn in 1880 led to no
+result. In Mrs. Flamsteed's will a sum of twenty-five pounds was left for
+the purpose of erecting a monument to the memory of the great astronomer
+in Burstow Church; but it does not appear that any monument was ever
+erected. Flamsteed was Rector of the Parish of Burstow.[510] He was
+succeeded in 1720 by the Rev. James Pound, another well-known astronomer.
+Pound died in 1724.[511]
+
+Evelyn says in his Diary, 1676, September 10, "Dined with Mr. Flamsteed,
+the learned astrologer and mathematician, whom his Majesty had established
+in the new Observatory in Greenwich Park furnished with the choicest
+instruments. An honest sincere man."[512] This shows that in those days
+the term "astrologer" was synonymous with "astronomer."
+
+In an article on "Our Debt to Astronomy," by Prof. Russell Tracy Crawford
+(Berkeley Astronomical Department, California, U.S.A.), the following
+remarks occur:--
+
+    "Behind the artisan is a chemist, behind the chemist is a physicist,
+    behind the physicist is a mathematician, and behind the mathematician
+    is an astronomer." "Were it not for the data furnished by astronomers,
+    commerce by sea would practically stop. The sailing-master on the high
+    seas could not determine his position, nor in what direction to head
+    his ship in order to reach a desired harbour. Think what this means in
+    dollars and cents, and estimate it if you can. For this one service
+    alone the science of astronomy is worth more in dollars and cents to
+    the world in one week than has been expended upon it since the
+    beginning of civilization. Do you think that Great Britain, for
+    instance, would take in exchange an amount equal to its national debt
+    for what astronomy gives it? I answer for you most emphatically,
+    'No.'"
+
+In his interesting book, _Reminiscences of an Astronomer_, Prof. Simon
+Newcomb says with reference to the calculations for the _Nautical Almanac_
+(referred to in the above extract)--
+
+    "A more hopeless problem than this could not be presented to the
+    ordinary human intellect. There are tens of thousands of men who could
+    be successful in all the ordinary walks of life, hundreds who could
+    wield empires, thousands who could gain wealth, for one who could take
+    up this astronomical problem with any hope of success. The men who
+    have done it are, therefore, in intellect the select few of the human
+    race--an aristocracy ranking above all others in the scale of being.
+    The astronomical ephemeris is the last outcome of their productive
+    genius."
+
+In a paper on the "Aspects of American Astronomy," Prof. Newcomb says, "A
+great telescope is of no use without a man at the end of it, and what the
+telescope may do depends more upon this appendage than upon the instrument
+itself. The place which telescopes and observatories have taken in
+astronomical history are by no means proportional to their dimensions.
+Many a great instrument has been a mere toy in the hands of its owner.
+Many a small one has become famous. Twenty years ago there was here in
+your city [Chicago] a modest little instrument which, judged by its size,
+could not hold up its head with the great ones even of that day. It was
+the private property of a young man holding no scientific position and
+scarcely known to the public. And yet that little telescope is to-day
+among the famous ones of the world, having made memorable advances in the
+astronomy of double stars, and shown its owner to be a worthy successor of
+the Herschels and Struves in that line of work."[513] Here Prof. Newcomb
+evidently refers to Prof. Burnham, and the 6-inch telescope with which he
+made many of his remarkable discoveries of double stars. With reference to
+Burnham's work, Prof. Barnard says--
+
+    "It represents the labour of a struggling amateur, who during the day
+    led the drudging life of a stenographer in the United States court in
+    Chicago, and at night worked among the stars for the pure love of it.
+    Such work deserves an everlasting fame, and surely this has fallen to
+    Mr. Burnham."
+
+Admiral Smyth says--
+
+    "A man may prove a good astronomer without possessing a spacious
+    observatory: thus Kepler was wont to observe on the bridge at Prague;
+    Schr�ter studied the moon, and Harding found a planet from a
+    _gloriette_; while Olbers discovered two new planets from an attic of
+    his house."[514]
+
+It is probably not generally known that "some of the greatest astronomers
+of modern times, such as Kepler, Newton, Hansen, Laplace, and Leverrier,
+scarcely ever looked through a telescope."[515]
+
+Kepler, who always signed himself Keppler in German, is usually supposed
+to have been born on December 21, 1571, in the imperial town of Weil, but
+according to Baron von Breitschwert,[516] he was really born on December
+27, 1571, in the village of Magstadt in Wurtemberg.
+
+According to Lieut. Winterhalter, M. Perrotin of the Nice Observatory
+declared "that two hours' work with a large instrument is as fatiguing as
+eight with a small one, the labour involved increasing in proportion to
+the cube of the aperture, the chances of seeing decreasing in the same
+ratio, while it can hardly be said that the advantages increase in like
+proportion."[517]
+
+The late Mr. Proctor has well said--
+
+    "It is well to remember that the hatred which many entertain against
+    the doctrine of development as applied to solar systems and stellar
+    galaxies is not in reality a sign, as they imagine, of humility, but
+    is an effort to avoid the recognition of the nothingness of man in the
+    presence of the infinities of space and time and vitality presented
+    within the universe of God."[518]
+
+Humboldt says--
+
+    "That arrogant spirit of incredulity, which rejects facts without
+    attempting to investigate them, is in some cases almost more injurious
+    than an unquestioning credulity. Both are alike detrimental to the
+    force of investigations."[519]
+
+With reference to the precession of the equinoxes and the changes it
+produces in the position of the Pole Star, it is stated in a recent book
+on science that the entrance passage of the Great Pyramid of Ghizeh is
+inclined at an angle of 30� to the horizon, and therefore points to the
+celestial pole. But this is quite incorrect. The Great Pyramid, it is
+true, is situated close to the latitude of 30�. But the entrance passage
+does not point exactly to the pole. The inclination was measured by Col.
+Vyse, and found to be 26� 45'. For six out of the nine pyramids of
+Ghizeh, Col. Vyse found an _average_ inclination of 26� 47', these
+inclinations ranging from 25� 55' (2nd, or pyramid of Mycerinus) to 28� 0'
+(9th pyramid).[520] Sir John Herschel gives 3970 B.C. as the probable date
+of the erection of the Great Pyramid.[520] At that time the distance of
+[Greek: a] Draconis (the Pole Star of that day) from the pole was 3� 44'
+25", so that when on the meridian _below_ the pole (its lower culmination
+as it is termed) its altitude was 30� - 3� 44' 25" = 26� 15' 35", which
+agrees fairly well with the inclination of the entrance passage. Letronne
+found a date of 3430 B.C.; but the earlier date agrees better with the
+evidence derived from Egyptology.
+
+Emerson says--
+
+  "I am brother to him who squared the pyramids
+  By the same stars I watch."
+
+From February 6 to 15, 1908, all the bright planets were visible together
+at the same time. Mercury was visible above the western horizon after
+sunset, Venus very brilliant with Saturn a little above it, Mars higher
+still, all ranged along the ecliptic, and lastly Jupiter rising in the
+east.[521] This simultaneous visibility of all the bright planets is
+rather a rare occurrence.
+
+With reference to the great improbability of Laplace's original Nebular
+Hypothesis being true, Dr. See says, "We may calculate from the
+preponderance of small bodies actually found in the solar system--eight
+principal planets, twenty-five satellites (besides our moon), and 625
+asteroids--that the chances of a nebula devoid of hydrostatic pressure
+producing small bodies is about 2{658} to 1, or a decillion decillion
+(10{66}){6} to the sixth power, to unity. This figure is so very large
+that we shall content ourselves with illustrating a decillion decillion,
+and for this purpose we avail ourselves of a method employed by ARCHIMEDES
+to illustrate his system of enumeration. Imagine sand so fine that 10,000
+grains will be contained in the space occupied by a poppy seed, itself
+about the size of a pin's head; and then conceive a sphere described about
+our sun with a radius of 200,000 astronomical units[522] ([Greek: a]
+Centauri being at a distance of 275,000) entirely filled with this fine
+sand. The number of grains of sand in this sphere of the fixed stars would
+be a decillion decillion[523] (10{66}){6}. All these grains of sand
+against one is the probability that a nebula devoid of hydrostatical
+pressure, such as that which formed the planets and satellites, will lead
+to the genesis of such small bodies revolving about a greatly predominant
+central mass."[524] In other words, it is practically certain that the
+solar system was _not_ formed from a gaseous nebula in the manner
+originally proposed by Laplace. On the other hand, the evolution of the
+solar system from a rotating spiral nebula seems very probable.
+
+       *       *       *       *       *
+
+Some one has said that "the world knows nothing of its greatest men." The
+name of Mr. George W. Hill will probably be unknown to many of my readers.
+But the late Prof. Simon Newcomb said of him that he "will easily rank as
+the greatest master of mathematical astronomy during the last quarter of
+the nineteenth century."[525] Of Prof. Newcomb himself--also a great
+master in the same subject--Sir Robert Ball says he was "the most
+conspicuous figure among the brilliant band of contemporary American
+astronomers."[526]
+
+An astronomer is supposed to say, with reference to unwelcome visitors to
+his observatory, "Who steals my purse steals trash; but he that filches
+from me my clear nights, robs me of that which not enriches him, and makes
+me poor indeed."[527]
+
+Cicero said, "In the heavens there is nothing fortuitous, unadvised,
+inconstant, or variable; all there is order, truth, reason, and
+constancy"; and he adds, "The creation is as plain a signal of the being
+of a God, as a globe, a clock, or other artificial machine, is of a
+man."[528]
+
+"Of all the epigrams attributed rightly or wrongly to Plato, the most
+famous has been expanded by Shelley into the four glorious lines--
+
+  "'Thou wert the morning star among the living
+    Ere thy pure light had fled,
+  Now having died, thou art as Hesperus, giving
+    New splendour to the dead.'"[529]
+
+Sir David Brewster has well said,[530] "Isaiah furnishes us with a
+striking passage, in which the occupants of the earth and the heavens are
+separately described, 'I have made the earth, and created man upon it: I,
+even My hands, have stretched out the heavens, and all _their_ host have I
+commanded' (Isaiah xlv. 12). But in addition to these obvious references
+to life and things pertaining to life, we find in Isaiah the following
+remarkable passage: 'For thus saith the Lord that created the heavens; God
+Himself that formed the earth and made it; He hath established it, _He
+created it not_ IN VAIN, He formed _it to be inhabited_' (Isaiah xlv. 18).
+Here we have a distinct declaration from the inspired prophet that the
+_earth would have been created_ IN VAIN _if it had not been formed to be
+inhabited_; and hence we draw the conclusion that as the Creator cannot be
+supposed to have made the worlds of our system and those in the sidereal
+system in vain, they must have been formed to be inhabited." This seems to
+the present writer to be a good and sufficient reply to Dr. Wallace's
+theory that our earth is the only inhabited world in the Universe![531]
+Such a theory seems incredible.
+
+The recent discovery made by Prof. Kapteyn, and confirmed by Mr.
+Eddington, of two drifts of stars, indicating the existence of _two_
+universes, seems to render untenable Dr. Wallace's hypothesis of the
+earth's central position in a single universe.[531]
+
+
+NOTE ADDED IN THE PRESS.
+
+While these pages were in the Press, it was announced, by Dr. Max Wolf of
+Heidelberg, that he found Halley's comet on a photograph taken on the
+early morning of September 12, 1909. The discovery has been confirmed at
+Greenwich Observatory. The comet was close to the position predicted by
+the calculations of Messrs. Cowell and Crommelin of Greenwich Observatory
+(_Nature_, September 16, 1908).
+
+
+
+
+INDEX
+
+
+  A
+
+  Aboukir, 287
+
+  Aboul Hassan, 221
+
+  Abu Ali al Farisi, 225
+
+  Abu-Hanifa, 233, 234
+
+  Abul-fadl, 236
+
+  Accadians, 250, 252
+
+  Achernar, 275
+
+  Aclian, 282
+
+  Adam, 96, 347
+
+  Adhad-al-Davlat, 225, 236
+
+  Adonis, 261
+
+  Adreaansz, 342
+
+  Airy, Sir G. B., 87, 140, 347, 357
+
+  Aitken, 160
+
+  Al-Battani, 232, 233
+
+  Albrecht, 173
+
+  Albufaragius, 283
+
+  Alcor, 241
+
+  Alcyone, 137
+
+  Aldebaran, 60, 156, 236, 252, 257, 310, 311
+
+  Alfard, 236, 289
+
+  Alfargani, 286
+
+  Alfraganus, 281
+
+  Almagest, 281
+
+  Al-Sufi, 47, 149, 179, 189, 221, 224, 225-238, 244, 246, 250, 251, 253,
+      254, 261, 263, 264, 266-270, 272, 274-278, 285, 287, 289, 290, 293,
+      298, 300-302, 304, 307
+
+  Altair, 246
+
+  Ampelius, 262
+
+  Amphion, 257
+
+  Ancient eclipses, 52, 53
+
+  Anderson, 120, 277
+
+  Andromeda nebula, 198-206, 231
+
+  Annals of Ulster, 332
+
+  Antares, 60, 179, 310, 311
+
+  Anthelm, 300
+
+  Antinous, 248
+
+  Antlia, 302
+
+  Apollo, 257
+
+  Apparent diameter of moon, 49
+
+  Apple, 79
+
+  "Apples, golden," 258
+
+  Apus, 306
+
+  Aquarius, 268
+
+  Aquila, 246
+
+  Aquillus, 220
+
+  Ara 295
+
+  Arago, 26, 30, 57, 116, 193, 331
+
+  Aratus, 219, 242, 245, 250, 255, 256, 261, 263, 272
+
+  Archimedes, 346, 354
+
+  Arcturus, 148, 188, 244
+
+  Argelander, 29, 227, 229, 230, 240
+
+  Argo, 285-288, 305
+
+  Argon in sun, 4
+
+  Argonauts, 243, 250
+
+  Aries, 250
+
+  Aristotle, 49, 67
+
+  Arrhenius, 4, 8, 22, 45, 66
+
+  Ashtoreth, 260
+
+  _Astra Borbonia_, 4
+
+  Astr�a, 263
+
+  Astronomy, Laplace on, 44
+
+  _Astro Theology_, 23
+
+  Atarid, 232, 233
+
+  Atmosphere, height of, 33
+
+  Augean stables, 269
+
+  Augustus, 262
+
+  Auriga, 245
+
+  Aurora, 33, 41, 42
+
+  Auwers, 206
+
+  Axis of Mars, 59
+
+
+  B
+
+  Babilu, 267
+
+  Baily, 137, 144
+
+  Baker, 183
+
+  Ball, Sir Robert, 6, 355
+
+  Barnard, Prof., 29, 54, 57, 79, 80, 81, 85, 86, 91, 93, 103, 104, 114,
+      130, 132, 139, 192, 213, 316, 317, 350
+
+  Barnes, 78, 79
+
+  Bartlett, 35, 36
+
+  Bartschius, 296, 298
+
+  Bauschingen, 69, 70
+
+  Bayer, 179, 221, 272, 284, 309, 310
+
+  Bayeux Tapestry, 105
+
+  Becquerel, 8
+
+  "Beehive," 259
+
+  Beer, 20
+
+  Bel, 250
+
+  Bellatrix, 253
+
+  Benoit, 22
+
+  Berenice, 297
+
+  Berry, 25
+
+  Bessel, 339
+
+  Betelgeuse, 179, 222, 264
+
+  Bianchini, 21, 22, 77
+
+  Biela's comet, 99
+
+  Bifornis, 268
+
+  Binary stars, 162
+
+  Birmingham, 5, 114
+
+  "Black body," 3
+
+  "Blackness" of sun-spots, 6
+
+  "Blaze star," 180, 184
+
+  Bode, 276
+
+  Bohlin, 199, 200
+
+  Bond, 85
+
+  Bond (Jun.), 74
+
+  _Book of the Dead_, 264, 274
+
+  Borelly, 103
+
+  Boserup, 28
+
+  Boss, 152
+
+  Brah�, Tycho. _See_ Tycho Brah�
+
+  Brauner, 211
+
+  Bravais, 42
+
+  Bredikhin, 76
+
+  Bremiker, 94
+
+  Brenner, L�o, 13, 22, 87, 91, 133
+
+  Brewster, 356
+
+  Brightness of Mercury, 10-12
+
+      "      of nebul�, 193
+
+      "      of sun, 1, 2, 3
+
+      "      of Venus, 14, 17, 19, 31
+
+  Bright clouds, 33, 34
+
+    "    night, 45
+
+    "    stars, 278
+
+  Brooks, 118
+
+  Brown, 218, 219, 248, 255, 260, 267, 272, 279, 281, 291, 295
+
+  Browning, 25
+
+  Brugsch, 127
+
+  Buddha, 256
+
+  Bull, Pope's, 107
+
+  "Bull's foot," 253
+
+  Buonaparte, 30
+
+  Burnham, 160, 165-167, 180, 184, 260, 350, 351
+
+  Burns, 130
+
+  Buss, 4
+
+
+  C
+
+  Caaba, 125
+
+  Cacciatore, 72
+
+  C�lum, 302
+
+  Callimachus, 297
+
+  Callixtus III., 107
+
+  Calvisius, 53
+
+  Camelopardalis, 296
+
+  Cameron, 18
+
+  Campbell, 85, 153, 159, 178
+
+  "Canals" on Mars, 61-63
+
+  Cancer, 258, 259
+
+  Canes Venatici, 296
+
+  Canicula, 280
+
+  Canis Major, 279
+
+    "   Minor, 284
+
+  Canopus, 157, 286, 344
+
+  Capella, 156, 164, 189, 236, 245, 246
+
+  Capricornus, 267, 268
+
+  "Capture" of satellites, 58
+
+  Carbonic acid, 66
+
+  Cassini, 20, 22, 74, 78, 358
+
+  Cassiopeia's Chair, 244
+
+  Castor, 160, 257
+
+  Caswell, 52
+
+  Catullus, 297
+
+  Caussin, 225
+
+  Cecrops, 268
+
+  "Celestial Rivers," 308
+
+  Celoria, 324, 326
+
+  Centaurus, 292, 293
+
+  Centre of gravity, 8
+
+  Cephalus, 279
+
+  Cepheid variables, 187
+
+  Ceraski, 2, 176
+
+  Cerberus, 243, 257
+
+  Ceres, 260
+
+  Cerulli, 22, 62
+
+  Cetus, 272
+
+  Chacornac, 18, 84
+
+  Cham�lion, 305
+
+  Chamberlin, 194
+
+  Chambers, 72
+
+  "Charles' Wain," 240
+
+  Chinese Annals, 19, 30, 105, 186, 223, 267, 330
+
+  Childrey, 128
+
+  Chiron, 295
+
+  Christmann, 281
+
+  Chromosphere, sun's, 4
+
+  Cicero, 49, 262, 280, 355
+
+  Circinus, 307
+
+  Clavius, 334
+
+  Climate, 45
+
+  "Coal Sack," 293, 320
+
+  Cobham, 88, 102
+
+  Colbert, 175
+
+  Colours of stars, 140, 141, 188-190
+
+  Coma Berenices, 297, 298
+
+  Comets, number of, 98
+
+    "     tails of, 115, 116
+
+  Comet years, 104
+
+  Comiers, 99
+
+  Comstock, 90, 146
+
+  Condamine, 257
+
+  Conon, 297
+
+  Coon Butte mountain, 120, 121
+
+  Cooper, 3
+
+  Copeland, 76, 157
+
+  Corona, sun's, 1, 334
+
+    "     round moon, 35, 36
+
+  Corona Australis, 295
+
+  Corvinus, 292
+
+  Corvus, 292
+
+  Cotsworth, 46
+
+  Cowell, 105
+
+  Crabtree, 337
+
+  Crater, 291
+
+  Craters on moon, 55, 56
+
+  Crawford, 348
+
+  Crecy, Battle of, 333
+
+  Crescent of Venus, 19, 20
+
+  Crommelin, 105, 111
+
+  Crucifixion, 18
+
+  Curtis, 344
+
+  Cusps of Venus, 20
+
+  Cygnus, (61), 155
+
+  Cynocephalus, 222
+
+
+  D
+
+  Dante, 156, 258, 265
+
+  Dark shade on moon, 333
+
+  D'Arrest, 94
+
+  Darwin, Sir George, 158, 319
+
+  "David's Chariot," 241
+
+  Davis, 155
+
+  Dawes, 168
+
+  "Dawn proclaimer," 251
+
+  Delambre, 185
+
+  Delauney, 347
+
+  Dembowski, 190
+
+  Demetrius, 111
+
+  Denning, 11, 74, 77, 84, 86, 87, 89, 99, 118, 340
+
+  Derham, 21, 23
+
+  Deucalion, 268
+
+  De Vico, 21, 22
+
+  Diamonds in meteorites, 127
+
+  Dilkur, 251
+
+  Diodorus Siculus, 127
+
+  Diogenes Laertius, 41
+
+  Diomed, 272
+
+  Dione, 89
+
+  "Dipper," 241
+
+  Doberck, 160
+
+  Dollond, 24
+
+  Domitian, 334
+
+  Donati's comet, 100
+
+  Dorado, 304
+
+  Dordona, 256
+
+  Dorn, 245
+
+  Douglass, 81
+
+  Dragon, 242
+
+  Draper, 75
+
+  Drayton, 156
+
+  Dreyer, 115
+
+  Drifting stars, 152
+
+  Dryden, 242
+
+  Duncan, 187
+
+  Dunlop, 264
+
+  Dupret, 83
+
+  Dupuis, 245, 252, 257, 258, 259, 266, 267, 268
+
+  "Dusky star," 272
+
+
+  E
+
+  "Earthen jar," 247
+
+  Earth's attraction on moon, 55
+
+  Earth's motions, 39
+
+    "     rotation, 46
+
+    "     surface, 32
+
+  "Earthshine" on moon, 51, 52, 56, 57
+
+  Eastmann, 316
+
+  Easton, 323, 324, 325
+
+  Eclipses, ancient, 52, 53, 57, 58
+
+     "      dark, of moon, 53, 57, 58
+
+  Ecliptic, obliquity of, 47
+
+  Eddington, 357
+
+  Electra, 19
+
+  Elster, 39
+
+  Emerson, 353
+
+  Enceladus, 89
+
+  Encke, 113, 116, 240
+
+  Ennis, 189
+
+  Eratosthenes, 250, 297, 345
+
+  Eridanus, 274-278
+
+  Eros, 69, 70, 71
+
+  Eta Argus, 177, 287
+
+  Eudemus, 47
+
+  Eudoxus, 218, 219, 223
+
+  Euler, 56
+
+  Eunomia, 71
+
+  Europa, 252
+
+
+  F
+
+  Fabritius, 4, 101
+
+  Fabry, 1
+
+  Faint stars in telescope, 176
+
+  "False Cross," 156
+
+  "Famous stars," 246
+
+  Fath, 130, 213
+
+  Faye, 100
+
+  February, Five Sundays in, 36
+
+  Fergani, 189
+
+  "Fisher Stars," 256
+
+  "Fishes in Andromeda," 249
+
+  Fitzgerald, 127
+
+  Flammarion, 22, 26, 50, 138, 255, 265, 276
+
+  Flamsteed, 348
+
+  "Flat earth" theory, 32
+
+  Fomalhaut, 271, 309, 310
+
+  Fontana, 20
+
+  Fontenelle, 357
+
+  Forbes, 82, 95, 96
+
+  Fornax, 301
+
+  Fournier, 87
+
+  Fovea, 284
+
+  Freeman, 88
+
+  Fr�ret, 222
+
+  Frisby, 101
+
+  Fritsch, 21
+
+  Furner, 163
+
+
+  G
+
+  Gale, 78
+
+  Galileo, 3, 4, 80, 82
+
+  Galle, 94, 341
+
+  Ganymede, 268
+
+  Gaseous nebula, spectra of, 195-198, 212
+
+  Gassendi, 14, 139
+
+  Gathman, 118
+
+  Gaubil, 99
+
+  Gauthier, 103
+
+  Gegenschein, 131
+
+  Gemini, 257, 258
+
+  Geminid variables, 187
+
+  Gentil, Le, 338, 339
+
+  Gertel, 39
+
+  Ghizeh, Pyramids of, 353
+
+  Gibbous phase of Jupiter, 75
+
+  Gill, Sir David, 118, 215, 216, 346
+
+  Glacial epoch, 42
+
+  Gledhill, 76
+
+  Globular clusters, 214, 215
+
+  Goad, 12
+
+  Goatcher, 179
+
+  "Golden apples," 258
+
+  Golius, 281
+
+  Gould, 229, 278, 301, 304, 309, 310, 326
+
+  Grant, 82, 96, 345
+
+  Gravitation, Law of, 15, 40
+
+  Greely, 186
+
+  Greisbach, 80
+
+  Groombridge 1830, 159
+
+  Grubb, Sir Howard, 164
+
+  Gruithuisen, 21, 25, 26, 28
+
+  Gruson, 127
+
+  Guillaume, 331
+
+  Guthrie, 25
+
+
+  H
+
+  Habitability of Mars, 63-66
+
+       "       of planets, 40
+
+  Hadrian, 248
+
+  Halbert, 78
+
+  Hale, 148, 150
+
+  Hall, 15, 131
+
+  Halley, 14, 17, 99, 105, 106, 108, 109, 116, 143, 145, 276
+
+  Halm, 122
+
+  Halo, 35, 36
+
+  Hanouman, 284
+
+  Hansen, 351
+
+  Hansky, 27
+
+  Harding, 25, 26, 94
+
+  "Harris, Mrs.," 90
+
+  Hartwig, 88, 173
+
+  Harvests, 104
+
+  Heat of sun, 2, 3, 7
+
+  Height of atmosphere, 33
+
+  Heis, 132, 175, 189, 227, 229, 344
+
+  Helium, 4
+
+  Hepidanus, 267, 348
+
+  Hercules, 243, 259, 268
+
+  Herod, 18, 53
+
+  Herschel, Miss Caroline, 193, 194, 324, 357
+
+  Herschel, Sir John, 112, 177, 190, 207, 209, 210, 215, 289, 314, 346,
+      353
+
+  Herschel, Sir Wm., 3, 24, 80, 112, 114, 115, 116, 171, 178, 179, 190,
+      324, 325
+
+  Hesiod, 17, 220
+
+  Hesperus, 256
+
+  Hevelius, 99, 116, 221, 296, 299, 300
+
+  Hill, 87, 355
+
+  Hind, 19, 30, 54, 105, 111, 180
+
+  Hipparchus, 135, 221-223, 226, 250, 278, 281, 293, 329
+
+  Hippocrates, 258
+
+  Hirst, 333
+
+  Holetschak, 108
+
+  Homer, 17
+
+  Honorat, 84
+
+  Hooke, 74, 128
+
+  Horace, 280
+
+  Horologium, 303
+
+  Horus, 145, 258
+
+  Horrebow, 29
+
+  Horrocks, 337
+
+  Hortensus, Martinus, 139
+
+  Hough, 76
+
+  Houzeau, 227, 229, 262, 274, 344
+
+  Hovedin, Roger de, 53
+
+  Hubbard, 100
+
+  Huggins, Sir Wm., 91, 148, 180
+
+  Humboldt, 30, 82, 83, 124, 128, 134, 154, 157, 342, 352, 357
+
+  Hussey, 88
+
+  Hyades, 157, 252, 253, 257
+
+  Hydra, 288
+
+  Hydrus, 303
+
+  Hyperion, 88, 90
+
+
+  I
+
+  Ibn al-Aalam, 225
+
+  Ibn Alraqqa, 281
+
+  Icarus, 284
+
+  Indus, 307
+
+  Inhabited worlds, 328, 357
+
+  Innes, 78, 168
+
+  Intra-Mercurial planet, 14, 15, 29
+
+  Invention of telescope, 342
+
+  Io, 252
+
+  Ions, 27
+
+  Iris, 71
+
+  Isaiah, 17, 356
+
+  Isis, 252, 261, 282, 283
+
+  Istar, 260
+
+
+  J
+
+  Jansen, 342
+
+  Japetus, 89, 90
+
+  Jason, 257, 285
+
+  Johnson, Rev. S. J., 19
+
+  Jonckheere, 15
+
+  Jones, 129
+
+  Jordan, 174
+
+  Jupiter, chap. viii.
+
+     "     gibbous form of, 75
+
+     "     and sun, 8
+
+
+  K
+
+  Kalevala, 240
+
+  Kapteyn, 314, 316, 321, 322, 326, 357
+
+  Kazemerski, 244
+
+  Keeler, 86, 215
+
+  Kelvin, Lord, 206, 315, 316
+
+  Kempf, 174
+
+  Kepler, 52, 57, 298, 340, 341, 351
+
+  Khayyam, Omar, 127
+
+  Kimah, 255
+
+  Kimball, 51
+
+  Kimta, 255
+
+  Kirch, 23, 115
+
+  Kirkwood, 6
+
+  Kleiber, 123
+
+  Klein, 114, 183
+
+  Knobel, 238, 263
+
+  Konkoly, 183
+
+  Koran, 127, 270
+
+  Kreusler, 4
+
+  Kreutz, 101, 112
+
+
+  L
+
+  Lacaille, 294, 301, 302
+
+  Lacerta, 300
+
+  Lagrange, 345
+
+  La Hire, 20, 21
+
+  Lalande, 143, 144, 284
+
+  Landerer, 52
+
+  Langdon, 25
+
+  Langley, Prof., 3
+
+  Laplace, 43, 44, 98, 346, 351, 354
+
+  Larkin, 65
+
+  Lassell, 77, 128
+
+  "Last in the River," 275-298
+
+  Last year of century, 37
+
+  Lau, 178, 183
+
+  Leo, 259
+
+  Leo Minor, 298
+
+  Lepus, 278, 279
+
+  Lern�an marsh, 258
+
+  Leverrier, 44, 347, 351
+
+  Lewis, 156, 162
+
+  Lewis, Sir G. C., 17
+
+  Lexell's comet, 98
+
+  Libra, 262
+
+  Life, possible, in Mars, 63-65
+
+  Light of full moon, 1, 51
+
+  Lippershey, 342
+
+  Littrow, 339
+
+  Lockyer, Sir Norman, 144, 147
+
+  Lodge, Sir Oliver, 55
+
+  Long, 343, 357
+
+  Longfellow, 156, 273
+
+  Lottin, 42
+
+  Lowell, 22, 43, 59, 61, 64, 88
+
+  Lucifer, 17
+
+  Lucretius, 320
+
+  "Luminous clouds," 33, 34
+
+  Lunar craters, 55, 56
+
+    "   "mansions," 251
+
+    "   mountains, 58
+
+    "   theory, 56
+
+  Lunt, 179
+
+  Lupus, 294
+
+  Lyman, 25
+
+  Lynn, 37, 38, 96, 106, 179, 243, 244, 310
+
+  Lynx, 296
+
+  Lyra, 243, 244, 266
+
+
+  M
+
+  Maclear, 77
+
+  M�dler, 20, 22
+
+  M�stlin, 341
+
+  Magi, star of, 1, 18, 145
+
+  Magnitudes, star, 311
+
+  Maia, 19, 256
+
+  Mairan, 357
+
+  "Manger," 259
+
+  Manilius, 250, 259, 272
+
+  Marius, Simon, 82, 83, 231
+
+  Markree Castle, 3
+
+  Marmol, 76
+
+  Mars, chap. vi.;
+    axis of 59;
+    red colour of, 60;
+    water vapour in, 60;
+    clouds in, 61;
+    "canals" in, 61
+
+  Martial, 17
+
+  Mascari, 22
+
+  Ma-tuan-lin, 186, 267
+
+  Mayer, 24
+
+  May transits of Mercury, 15
+
+  Maxwell, Clerk, 86
+
+  McHarg, 16
+
+  McKay, 286
+
+  Medusa, 244
+
+  Mee, 88
+
+  Melotte, 82
+
+  Mendelief, 212
+
+  Mensa, 304
+
+  Mercury, chap, ii., 258
+
+  Merrill, 121
+
+  Messier, 114
+
+  Meteoric stones, 119
+
+  Meteors, 33
+
+  Metius, 342
+
+  Microscopium, 302
+
+  Milky Way, 320, 323, 325, 326, 328
+
+  Milton, 263
+
+  Mimas, 88, 89
+
+  Minor planets, chap. vii.
+
+  Mira Ceti, 178, 186, 272, 273
+
+  Mitchell, 4
+
+  Mithridates, 111
+
+  Mitra, 145
+
+  Molyneux, 80
+
+  Monck, 156, 181
+
+  Monoceros, 298
+
+  Montanari, 170, 171
+
+  Montigny, 34
+
+  Moon, light of, 1, 51
+
+    "   as seen through a telescope, 50
+
+  "Moon maiden," 52
+
+  Moon mountains, 58
+
+  Morehouse, 103, 110
+
+  Motions of stars in line of sight, 141, 142
+
+  Moulton, 133, 318
+
+  Mountains, lunar, 58
+
+  M�ller, 174
+
+  Musca, 305
+
+  Mycerinus, Pyramid of, 353
+
+
+  N
+
+  Nasmyth, 11
+
+  Nath, 253
+
+  Nautical Almanac, 349
+
+  Nebula in Andromeda, 198-206, 231
+
+  Nebul�, gaseous, 195-198, 212, 213
+
+  Nebul�, spiral, 213
+
+  Nebular hypothesis, 354
+
+  Nem�lian lion, 259
+
+  Nem�us, 259
+
+  Neon in sun, 4
+
+  Nepthys, 271
+
+  Neptune, 341
+
+  Newcomb, 13, 15, 33, 50, 65, 70, 129, 130, 153, 191, 203, 282, 339, 347,
+      349, 350, 355
+
+  Newton, 15, 351
+
+  Nicephorus, 127
+
+  Nicholls, 148, 154
+
+  Nineveh tablets, 17
+
+  Noble, 25
+
+  Norma, 302
+
+  Nov�, 180-182, 265, 267, 343
+
+  Nova Persei, 190
+
+  November transits of Mercury, 15
+
+  Number of nebul�, 191
+
+    "    of stars, 135, 136, 236, 237
+
+    "    of variable stars, 182, 183
+
+
+  O
+
+  Obliquity of ecliptic, 47
+
+  Occupations, 14, 15, 54, 67, 80, 84, 85, 259, 340, 341
+
+  Octans, 303
+
+  Odling, 122
+
+  Oeltzen, 72
+
+  Olbers, 104, 124
+
+  Old, 340
+
+  Orion, 49, 146, 273, 274
+
+  Osiris, 145, 259, 261, 283
+
+  "Ostriches," 266
+
+  Otawa, 240
+
+  Ovid, 242, 250, 255, 265, 288, 291, 322
+
+
+  P
+
+  Palisa, 71
+
+  Palmer, 182
+
+  Parker, 19
+
+  Parkhurst, 174
+
+  Paschen, 2
+
+  Pastorff, 25
+
+  Pavo, 307
+
+  Payne, 139
+
+  Pearson, 77
+
+  Peary, 119
+
+  Peck, 176
+
+  Pegasus, 248
+
+  Pelion, 282
+
+  Peritheus, 258
+
+  Perrine, 15, 76, 191, 192, 214
+
+  Perrotin, 351
+
+  Perseus, 244
+
+  Petosiris, 222
+
+  Philostratus, 334
+
+  Phlegon, 332
+
+  Phoebe, 90
+
+  Phoenix, 301
+
+  Phosphorus, 17
+
+  Photographic nebula, 192
+
+  Pickering, E. C., 125, 140, 144, 177
+
+  Pickering, W. H., 1, 12, 51, 61, 95, 102
+
+  Pictor, 304
+
+  Pierce, 228
+
+  "Pilgrim Star," 180, 185, 186
+
+  Pingr�, 54
+
+  Pinzon, 294
+
+  Pisces, 271
+
+  Piscis Australis, 295, 296
+
+  Planetary nebul�, 213
+
+  Platina, 107
+
+  Pleiades, 19, 52, 137, 154, 157, 235, 254-257
+
+  Pliny, 17, 265, 280
+
+  Plummer, W. E., 180
+
+  Plurality of worlds, 328, 356, 357
+
+  Pococke, 271
+
+  Pogson, 317
+
+  Polarization of moon's surface, 52
+
+  Polarization on Mars, 61
+
+  Pole of cold, 33
+
+    "  star, 138, 239, 240
+
+  Pollux, 257
+
+  Polydectus, 244
+
+  Poor, 15 (footnote)
+
+  Poynting, 130
+
+  Pr�sape, 259
+
+  Prince, 25
+
+  Proclus, 221
+
+  Proctor, 7, 49, 59, 123, 285, 308, 323, 352
+
+  Procyon, 156, 157, 236, 284
+
+  Ptolemy, 189, 221-223, 224, 227, 230, 231, 234, 238, 244, 252, 253, 260,
+      263, 264, 267, 269, 275, 278, 281, 284, 293, 302, 330
+
+  Pyramid, Great, 46, 47, 308, 353
+
+  Pytheas, 46
+
+
+  Q
+
+  Quadruple system, 168
+
+  Qu�nisset, 21, 133
+
+
+  R
+
+  Rabourdin, 103
+
+  Radium, 7, 8, 38
+
+  R�hu, 93
+
+  Rama, 284, 340
+
+  _Rational Almanac_, 46
+
+  "Red Bird," 290
+
+  Red star, 279, 292
+
+  Regulus, 30, 156, 235, 236, 260, 310, 340
+
+  Remote galaxies, 193, 204, 205
+
+  Reticulum, 304
+
+  Rhea, 89
+
+  Rheita, De, 144
+
+  Riccioli, 189
+
+  Ricco, 32
+
+  Rigel, 156, 157, 222
+
+  Rigge, 107
+
+  Ring nebula in Lyra, 211
+
+  Rings of Saturn, 85
+
+  Rishis, 240
+
+  Ritter, 76, 147
+
+  "Rivers, celestial," 308
+
+  Roberts, Dr. A. W., 172, 173
+
+  Roberts, Dr. I., 95, 154, 200, 201, 203, 317
+
+  Roberts, C., 84
+
+  Robigalia, 280
+
+  Robinson, 342, 357
+
+  Roedeckoer, 28
+
+  Rogovsky, 42, 43, 44, 75
+
+  Rosse, Lord, 76
+
+  Roszel, 70
+
+  Rotation of Mercury, 16
+
+     "     of Uranus, 91
+
+     "     of Venus, 22
+
+  Rub�iy�t, 127
+
+  Rudaux, 80, 89
+
+  Russell, H. C., 21
+
+  Russell, H. N., 146
+
+  Russell, J. C., 333
+
+  Rutherford, 38
+
+
+  S
+
+  Sadler, 78, 299
+
+  Safarik, 24, 25
+
+  Sagittarius, 265-267
+
+  _Sahu_, 274
+
+  Santini, 357
+
+  Satellite, eighth, of Jupiter, 82
+
+      "      possible lunar, 54
+
+      "      of Venus, 28, 29
+
+  Sawyer, 186
+
+  Sayce, 218, 261
+
+  Scaliger, 299
+
+  Schaeberle, 93
+
+  Schaer, 88
+
+  Scheiner, 4, 150, 188, 195
+
+  Scheuter, 30
+
+  Schiaparelli, 22, 326
+
+  Schjellerup, 226, 228, 230, 231, 264, 277, 281, 340
+
+  Schlesinger, 183
+
+  Sch�nfeld, 287
+
+  Schiraz, 47
+
+  Schmidt, 51, 188, 220, 271
+
+  Scholl, 79
+
+  Schr�ter, 13, 20, 21, 22, 24, 26, 48
+
+  Schuster, 2, 148, 149, 150
+
+  Schwabe, 5
+
+  Scorpio, 263-265
+
+  Sculptor, 301
+
+  Scutum, 299
+
+  Searle, 132
+
+  "Secondary light" of Venus, 23-28
+
+  See, Dr., 12, 13, 33, 58, 96, 161, 164, 165, 210, 211, 281, 282, 354
+
+  Seeliger, 181, 206
+
+  Seneca, 218, 220
+
+  Serapis, 145
+
+  Sestini, 190
+
+  "Seven Perfect Ones," 256
+
+  Sextans, 298
+
+  Shaler, 48
+
+  Sharpe, 357
+
+  Shelley, 356
+
+  Shicor, 274
+
+  "Ship," 285
+
+  "Sickle," 259
+
+  Signalling to Mars, 65
+
+  Sihor, 280
+
+  Silkit, 264
+
+  Silvestria, 124
+
+  Simeon of Durham, 53
+
+  Simonides, 255
+
+  "Singing Maidens," 256
+
+  Sirius, 138, 156, 157, 160, 163, 236, 274, 280, 282, 283
+
+  Slipher, 60, 87, 161, 178
+
+  Smart, 109
+
+  Smyth, Admiral, 12, 72, 77, 107, 136, 140, 145, 170, 176, 190, 194, 253,
+      259, 351
+
+  Snyder, Carl, 8, 345
+
+  Sobieski, 299
+
+  Sola, Comas, 81, 87
+
+  Somerville, Mrs., 357
+
+  Sothis, 286
+
+  Southern Cross, 293, 344
+
+  Spectra of double stars, 162
+
+  Spectrum of gaseous nebul�, 195-198, 212
+
+  Spectrum of sun's chromosphere, 4
+
+  Spencer, Herbert, 193
+
+  Sphinx, 261
+
+  Spica, 156, 236
+
+  Spiral nebul�, 213
+
+  Star magnitudes, 311
+
+  "Star of Bethlehem," 17, 18
+
+  Stars in daytime, 158
+
+  Stebbins, 51
+
+  Stockwell, 18, 331
+
+  "Stones from heaven," 125, 126
+
+  Stoney, 133
+
+  Strabo, 127
+
+  Stratonoff, 151, 320, 321
+
+  Stromgen, 88
+
+  Strutt, 7
+
+  Struve, 113, 240
+
+  Struyck, 54
+
+  Succul�, 253
+
+  Suhail, 283, 286
+
+  Sun darkenings, 5, 335, 336
+
+  Sun's heat, 7
+
+  Sunlight, 1, 2
+
+  Sun-spots, 5, 6
+
+  Swift, 102
+
+  _Sydera Austricea_, 5
+
+
+  T
+
+  Tacchini, 22
+
+  Tamerlane, 238
+
+  Tammuz, 261
+
+  Tard�, 4
+
+  Taurus, 251
+
+  Taylor, 40
+
+  T Coron�, 184
+
+  Tebbutt, 183, 278
+
+  Telescopium, 302
+
+  Temporary stars, 180-182, 265, 267, 343
+
+  Tennyson, 40
+
+  Terby, 88
+
+  Tethys, 89
+
+  Thales, 357
+
+  Thebes, 271
+
+  Themis, 88-90
+
+  Theogirus, 279
+
+  Theon, 245
+
+  Theseus, 257
+
+  Thome, 101
+
+  Thucydides, 331
+
+  Tibertinus, 281
+
+  Tibullus, 282
+
+  Tides, 40
+
+  Timocharis, 340
+
+  Tin, 179
+
+  Titan, 85, 88, 89
+
+  Titanium, 179
+
+  Toucan, 308
+
+  Transits of Mercury, 14, 15
+
+     "     of Venus, 337, 338, 339
+
+  Triangulum, 271
+
+       "      Australis, 306
+
+  Trio, 220
+
+  Triptolemus, 257
+
+  Triton, 93
+
+  Trouvelot, 21, 22, 78, 211
+
+  Tumlirz, 46
+
+  Turrinus, 220
+
+  Tycho Brah�, 10, 30, 99, 145, 179, 298
+
+  Typhon, 263, 272
+
+
+  U
+
+  Ulugh Beigh, 238, 276, 278
+
+  Underwood, 85
+
+  Uranus, chap. x.;
+    spectrum of, 91, 92
+
+  Urda, 71
+
+
+  V
+
+  Valz 72
+
+  "Vanishing star," 59
+
+  Varvadjah, 236
+
+  Vega, 148, 156, 244
+
+  Vencontre, 220
+
+  Venus, chap. iii.;
+    apparent motion of, 28;
+    supposed satellite of, 28, 29;
+    transit of, 337-339
+
+  Veronica, S, 145
+
+  Vesta, 70
+
+  Virgil, 17, 218, 242, 262, 309
+
+  Virgo, 260
+
+  Vogel, 180
+
+  Vogt, 122
+
+  Volans, 304
+
+  Voltaire, 15
+
+  Von Hahn, 24
+
+  Vulpecula, 300
+
+
+  W
+
+  Wallace, Dr., 212, 357
+
+  Wallis, 80
+
+  Ward, 88
+
+  Wargentin, 178
+
+  Watson, 339
+
+  Webb, 24, 25, 77, 190, 286
+
+  Weber, 183
+
+  Weinhand, 122
+
+  Wendell, 71, 103, 109
+
+  Werchojansk, 33
+
+  White spots on Jupiter's satellites, 81
+
+  White spots on Venus, 21
+
+  Whitmell, 50, 86
+
+  Wiggins, 333
+
+  Wilczyniski, 195
+
+  Williams, Stanley, 22, 277, 302
+
+  Wilsing, 155
+
+  Wilson, H. C., 137, 139
+
+  Wilson, Dr. W. E., 3, 148
+
+  Winnecke, 26, 188
+
+  Winterhalter, 351
+
+  Wolf, Dr. Max, 71, 72, 191, 211, Note p. 537
+
+  Wrangel, 240
+
+
+  Y
+
+  Young, Prof., 4, 7, 9
+
+  Young, Miss Anne S., 79
+
+  Yunis, Ibn, 30
+
+
+  Z
+
+  Zach, 331
+
+  Zenophon, 127
+
+  Zethas, 257
+
+  Z�llner, 27
+
+
+THE END
+
+
+PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLES.
+
+
+[Illustration]
+
+
+
+
+FOOTNOTES:
+
+[1] _Comptes Rendus_, 1903, December 7.
+
+[2] _Nature_, April 11, 1907.
+
+[3] _Astrophysical Journal_, vol. 19 (1904), p. 39.
+
+[4] _Astrophysical Journal_, vol. 21 (1905), p. 260.
+
+[5] _Knowledge_, July, 1902, p. 132.
+
+[6] _Nature_, April 30, 1903.
+
+[7] _Ibid._, May 18, 1905.
+
+[8] _Ibid._, May 18, 1905.
+
+[9] _Nature_, June 29, 1871.
+
+[10] _Nature_, October 15, 1903.
+
+[11] _The Life of the Universe_ (1909), vol. ii. p. 209.
+
+[12] _The World Machine_, p. 234.
+
+[13] Quoted in _The Observatory_, March 1908, p. 125.
+
+[14] _The Observatory_, September, 1906.
+
+[15] _Nature_, March 1, 1900.
+
+[16] _Cycle of Celestial Objects_, p. 96.
+
+[17] _Ast. Nach._ No. 3737.
+
+[18] _Observatory_, September, 1906.
+
+[19] _Nature_, November 29 and December 20, 1894.
+
+[20] _Bulletin, Ast. Soc. de France_, July, 1898.
+
+[21] _Observatory_, vol. 8 (1885), pp. 306-7.
+
+[22] _Nature_, October 30, 1902.
+
+[23] Charles Lane Poor, _The Solar System_, p. 170.
+
+[24] Smyth, _Celestial Cycle_, p. 60.
+
+[25] Denning, _Telescopic Work for Starlight Evenings_, p. 225.
+
+[26] _The Observatory_, 1894, p. 395.
+
+[27] _Ast. Nach._ 4333, quoted in _Nature_, July 1, 1909, p. 20.
+
+[28] _English Mechanic_, July 23, 1909.
+
+[29] _Nature_, December 22, 1892.
+
+[30] _Celestial Objects_, vol. i. p. 52, footnote.
+
+[31] _Ibid._, p. 54.
+
+[32] _Astronomy and Astrophysics_, 1892, p. 618.
+
+[33] _Nature_, August 7, 1879.
+
+[34] _The World of Space_, p. 56.
+
+[35] _Nature_, September 15, 1892.
+
+[36] _Observatory_, 1880, p. 574.
+
+[37] _Knowledge_, November 1, 1897, pp. 260, 261.
+
+[38] _Worlds in the Making_, p. 61.
+
+[39] _Ibid._, p. 48.
+
+[40] _Nature_, June 1, 1876.
+
+[41] _Cel. Objects_, vol. i. p. 66 (5th Edition).
+
+[42] _Celestial Objects_, vol. i. p. 65 (5th Edition).
+
+[43] _Ast. Nach._ No. 1863.
+
+[44] _Nature_, June 1, 1876.
+
+[45] _Ibid._, June 8, 1876.
+
+[46] _Nature_, October 17, 1895.
+
+[47] _Ibid._, July 27, 1905.
+
+[48] _Celestial Cycle_, p. 107.
+
+[49] _Nature_, October 6, 1887.
+
+[50] _Ast. Nach._, No. 4106.
+
+[51] _Copernicus_, vol. ii. p. 168.
+
+[52] _Cosmos_, vol. iv. p. 476, footnote.
+
+[53] Denning, _Telescopic Work for Starlight Evenings_, p. 153.
+
+[54] _Ibid._, p. 154.
+
+[55] _Nature_, July 13, 1876.
+
+[56] P. M. Ryves in _Knowledge_, June 1, 1897, p. 144.
+
+[57] _Bulletin, Ast. Soc. de France_, August, 1905.
+
+[58] _Nature_, April 5, 1894.
+
+[59] _Nature_, May 14, 1896. Some have attributed these "luminous clouds"
+to light reflected from the dust of the Krakatoa eruption (1883).
+
+[60] _The Observatory_, 1877, p. 90.
+
+[61] _Popular Astronomy_, vol. 11 (1903), p. 293.
+
+[62] _Popular Astronomy_, vol. 13 (1905), p. 226.
+
+[63] _Nature_, July 25, 1901 (from Flammarion).
+
+[64] _Popular Astronomy_, vol. 11 (1903), p. 496.
+
+[65] _Kinetic Theories of Gravitation_, Washington, 1877.
+
+[66] _The Observatory_, June, 1894, p. 208.
+
+[67] _Nature_, June 8, 1899.
+
+[68] _Astrophysical Journal_, vol. 14 (1901), p. 238, footnote.
+
+[69] _Mars as the Abode of Life_, p. 52.
+
+[70] Second Book of the Maccabees v. 1-4 (Revised Edition).
+
+[71] Humboldt's _Cosmos_, vol. i. p. 169 (Ott�'s translation).
+
+[72] Quoted by Grant in _History of Physical Astronomy_, p. 71.
+
+[73] _Ibid._, pp. 100, 101.
+
+[74] _Exposition du Syst�me du Monde_, quoted by Carl Snyder in _The World
+Machine_, p. 226.
+
+[75] _Worlds in the Making_, p. 63.
+
+[76] _Cosmos_, vol. i. p. 131.
+
+[77] _The Observatory_, June, 1909, p. 261.
+
+[78] _Astronomical Essays_, pp. 61, 62.
+
+[79] _Encyclop�dia Britannica_ (_Schiraz_).
+
+[80] _Monthly Notices_, R.A.S., February, 1905.
+
+[81] _Nature_, March 3, 1870.
+
+[82] _Ibid._, March 31, 1870, p. 557.
+
+[83] Prof. W. H. Pickering found 12 times (see p. 1).
+
+[84] _Nature_, January 30, 1908.
+
+[85] _Nature_, September 5, 1901.
+
+[86] _Ibid._, July 31, 1890.
+
+[87] _Nature_, October 16, 1884.
+
+[88] _Nature_, February 19, 1885.
+
+[89] _Nature_, January 14, 1909, p. 323.
+
+[90] _Photographic Atlas of the Moon, Annals of Harvard Observatory_, vol.
+li. pp. 14, 15.
+
+[91] _Nature_, January 18, 1906.
+
+[92] Humboldt's _Cosmos_, vol. iv. p. 481.
+
+[93] _Ibid._, p. 482.
+
+[94] _Monthly Notices_, R.A.S., June, 1895.
+
+[95] Humboldt's _Cosmos_, vol. iv. p. 483 (Ott�'s translation).
+
+[96] Grant, _History of Physical Astronomy_, p. 229.
+
+[97] _Popular Astronomy_, vol. xvii. No. 6, p. 387 (June-July, 1909).
+
+[98] _Nature_, October 7, 1875.
+
+[99] _Mars as an Abode of Life_ (1908), p. 281.
+
+[100] _Knowledge_, May 2, 1886.
+
+[101] _Nature_, March 12, 1908.
+
+[102] _Bulletin, Ast. Soc. de France_, April, 1899.
+
+[103] _Astronomy and Astrophysics_ (1894), p. 649.
+
+[104] _Nature_, April 20, 1905.
+
+[105] _Astrophysical Journal_, vol. 14 (1901), p. 258.
+
+[106] _Nature_, August 22, 1907.
+
+[107] _Popular Astronomy_, vol. 12 (1904), p. 679.
+
+[108] _Mars as an Abode of Life_, p. 69.
+
+[109] _Ibid._, p. 146.
+
+[110] _Worlds in the Making_, p. 49.
+
+[111] _Worlds in the Making_, p. 53.
+
+[112] Denning, _Telescopic Work for Starlight Evenings_, p. 158.
+
+[113] _Ibid._, p. 166.
+
+[114] _Nature_, July 13, 1876.
+
+[115] _Nature_, May 2, 1907.
+
+[116] _Nature_, May 30, 1907.
+
+[117] _Publications of the Astronomical Society of the Pacific_, August,
+1908.
+
+[118] _Monthly Notices_, R.A.S., 1902, p. 291.
+
+[119] _Monthly Notices_, R.A.S., February, 1902, p. 291.
+
+[120] _Nature_, May 24, 1894.
+
+[121] _Ibid._, February 14, 1895.
+
+[122] _Ibid._, September 14, 1905.
+
+[123] _Ibid._, September 21, 1905.
+
+[124] _Ibid._, September 28, 1905.
+
+[125] _Ibid._, July 13, 1905.
+
+[126] _Nature_, November 3, 1898.
+
+[127] _Ibid._, July 14, 1881, p. 235.
+
+[128] Quoted in _The Observatory_, February, 1896, p. 104, from _Ast.
+Nach._, No. 3319.
+
+[129] _Monthly Notices_, R.A.S., February, 1909.
+
+[130] _Celestial Objects_, vol. i. p. 163.
+
+[131] _Nature_, December 29, 1898.
+
+[132] _Celestial Objects_, vol. i. p. 166.
+
+[133] _Astrophysical Journal_, vol. 14 (1901), pp. 248-9.
+
+[134] _Nature_, August 27, 1908.
+
+[135] Webb's _Celestial Objects_, vol. i. p. 177.
+
+[136] _Ibid._, vol. i. p. 187.
+
+[137] _Celestial Objects_, vol. i. p. 186.
+
+[138] _Astronomy and Astrophysics_, 1892, p. 87.
+
+[139] _Ibid._, 1892, pp. 94-5.
+
+[140] _Observatory_, December, 1891.
+
+[141] _Popular Astronomy_, vol. 11 (1903), p. 574.
+
+[142] _Ibid._, October, 1908.
+
+[143] _Bulletin, Ast. Soc. de France_, August, 1907.
+
+[144] _Nature_, August, 29 1907.
+
+[145] _Ibid._, March 7, 1907.
+
+[146] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[147] _The Observatory_, October, 1903, p. 392.
+
+[148] _Astronomy and Astrophysics_, 1894, p. 277.
+
+[149] _Nature_, November 18, 1897.
+
+[150] _Journal_, B.A.A., January, 1907.
+
+[151] _Journal_, B.A.A., February, 1909, p. 161.
+
+[152] _Cosmos_, vol. ii. p. 703.
+
+[153] _Ibid._
+
+[154] Denning, _Telescopic Work for Starlight Evenings_, p. 349.
+
+[155] _Cosmos_, vol. iii. p. 75.
+
+[156] _Journal_, B.A.A., June, 1896.
+
+[157] _Celestial Objects_, vol. i. p. 191.
+
+[158] _Nature_, May 30, 1901.
+
+[159] _Bulletin, Ast. Soc. de France_, August, 1900.
+
+[160] _Astronomy and Astrophysics_, 1892.
+
+[161] _Astrophysical Journal_, January, 1908, p. 35.
+
+[162] _Nature_, May 22, 1902.
+
+[163] _Ibid._, July 9, 1903.
+
+[164] _Ibid._, July 16, 1903.
+
+[165] _Nature_, September 24, 1903.
+
+[166] _Ibid._, October 8, 1903.
+
+[167] _Astrophysical Journal_, vol. 26 (1907), p. 60.
+
+[168] _Nature_, January 30, 1908.
+
+[169] _Ibid._, October 15, 1908.
+
+[170] _Ibid._, October 29, 1908.
+
+[171] _Journal_, B.A.A., March, 1908, and June 22, 1908.
+
+[172] _Nature_, June 25, 1903.
+
+[173] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[174] _Pop. Ast._, vol. 12, pp. 408-9.
+
+[175] _Nature_, August 29, 1889.
+
+[176] _Astrophysical Journal_, vol. 26 (1907), p. 62.
+
+[177] _Bulletin, Ast. Soc. de France_, January, 1904.
+
+[178] Humboldt's _Cosmos_, vol. iv. p. 532.
+
+[179] _Copernicus_, vol. ii. p. 64.
+
+[180] _Knowledge_, May, 1909.
+
+[181] _Journal_, British Astronomical Association, January, 1909, p. 132.
+
+[182] _Ast. Nach._, No. 4308.
+
+[183] _History of Physical Astronomy_, p. 204.
+
+[184] Smyth's _Celestial Cycle_, pp. 210, 211.
+
+[185] Poor, _The Solar System_, p. 274.
+
+[186] _Celestial Cycle_, p. 246.
+
+[187] _Nature_, October 2, 1879.
+
+[188] _Ibid._, May 6, 1880.
+
+[189] _Ibid._, February 19, 1880.
+
+[190] _Nature_, September 30, 1897.
+
+[191] _Nature_, August 5, 1875.
+
+[192] _Ibid._, October 12, 1882, and _Copernicus_, vol. iii. p. 85.
+
+[193] _Nature_, May 8, 1884.
+
+[194] _Ibid._, June 16, 1887.
+
+[195] _Journal_, B.A.A., December 13, 1901.
+
+[196] _Nature_, September 20, 1900.
+
+[197] _Ast. Nach._, No. 3868, and _Nature_, March 12, 1903.
+
+[198] _Nature_, November 13, 1908.
+
+[199] _Nature_, December 7, 1905.
+
+[200] _Celestial Cycle_, p. 259.
+
+[201] _Celestial Cycle_, p. 260.
+
+[202] _Journal_, B.A.A., April, 1907.
+
+[203] _Monthly Notices_, R.A.S., March, 1908.
+
+[204] _Celestial Cycle_, p. 231.
+
+[205] _Journal_, B.A.A., July, 1908.
+
+[206] _Popular Astronomy_, October, 1908.
+
+[207] _Cape Obs._, p. 401.
+
+[208] _Nature_, July 2, 1908.
+
+[209] _Journal_, B.A.A., January 20, 1909, pp. 123-4.
+
+[210] Chambers' _Handbook of Astronomy_, Catalogue of Comets.
+
+[211] Seneca, quoted by Chambers, _Handbook_, vol. i. p. 554 (Fourth
+Edition).
+
+[212] _Ibid._
+
+[213] _Ibid._
+
+[214] _Ibid._, p. 534.
+
+[215] _Ibid._
+
+[216] Ma-tuoan-lin, quoted by Chambers, _Handbook_, p. 570.
+
+[217] _Astronomy and Astrophysics_, 1893, p. 798.
+
+[218] _The Observatory_, October, 1898.
+
+[219] Grant's _History of Physical Astronomy_, p. 293.
+
+[220] _Ibid._, p. 294.
+
+[221] Humboldt's _Cosmos_, vol. i. pp. 89, 90 (Ott�'s translation).
+
+[222] _Celestial Objects_, vol. i. p. 211, footnote.
+
+[223] Denning, _Telescopic Work for Starlight Evenings_, p. 248.
+
+[224] _Ibid._, p. 248.
+
+[225] _Ibid._, p. 250.
+
+[226] _Ibid._, p. 231.
+
+[227] Vol. iii. p. 106.
+
+[228] Grant's _History of Physical Astronomy_, p. 298.
+
+[229] _Ibid._, p. 305.
+
+[230] Humboldt's _Cosmos_, vol. i. p. 95.
+
+[231] _Nature_, April 30, 1908.
+
+[232] _Bulletin, Ast. Soc. de France_, May, 1906.
+
+[233] _Nature_, November 24, 1904.
+
+[234] _Ibid._, September 10, 1896.
+
+[235] _Ibid._, June 29, 1893.
+
+[236] _Journal_, B.A.A., May 22, 1903.
+
+[237] _Nature_, December 13, 1906, p. 159.
+
+[238] _Nature_, September 13, 1906.
+
+[239] _Nature_, October 12, 1905, p. 596.
+
+[240] _Knowledge_, January 13, 1882.
+
+[241] _Ibid._, January 20, 1882.
+
+[242] _Popular Astronomy_, June-July, 1908, p. 345.
+
+[243] _The Observatory_, March, 1896, p. 135.
+
+[244] _The Observatory_, February, 1900, pp. 106-7.
+
+[245] _Knowledge_, March, 1893, p. 51.
+
+[246] _Ibid._, July 3, 1885, p. 11.
+
+[247] _Cosmos_, vol. i. p. 108 (Ott�'s translation).
+
+[248] _Ibid._, vol. i. p. 124.
+
+[249] _Ibid._, vol. i. p. 119, footnote.
+
+[250] _Copernicus_, vol. i. p. 72.
+
+[251] _Ibid._
+
+[252] _Astrophysical Journal_, June, 1909, pp. 378-9.
+
+[253] _Knowledge_, July, 1909, p. 264.
+
+[254] Quoted by Miss Irene E. T. Warner in _Knowledge_, July, 1909, p.
+264.
+
+[255] _The Observatory_, November, 1900.
+
+[256] Or, "Before the phantom of false morning died" (4th edition); _The
+Observatory_, September, 1905, p. 356.
+
+[257] _The Observatory_, July, 1896, p. 274.
+
+[258] _Journal_, B.A.A., January 24, 1906.
+
+[259] _Ast. Soc. of the Pacific_, December, 1908, p. 280.
+
+[260] _Nature_, November 1, 1906.
+
+[261] _Ibid._, November 22, 1906, p. 93.
+
+[262] _Nature_, August 30, 1906.
+
+[263] _Cosmos_, vol. i. p. 131, footnote.
+
+[264] _Nature_, December 16, 1875.
+
+[265] _Ibid._, July 23, 1891.
+
+[266] _Bulletin, Ast. Soc. de France_, April, 1903.
+
+[267] _Bulletin, Ast. Soc. de France_, April, 1903.
+
+[268] _The Observatory_, May, 1896. The italics are Brenner's.
+
+[269] _Cosmos_, vol. iv. p. 563.
+
+[270] For details of this enumeration, see _Astronomical Essays_, p. 222.
+
+[271] _Nature_, June 11, 1908.
+
+[272] _Popular Astronomy_, vol. 14 (1906), p. 510.
+
+[273] _Bedford Catalogue_, p. 532.
+
+[274] _Popular Astronomy_, vol. 15 (1907), p. 194.
+
+[275] _Popular Astronomy_, vol. 15 (1907), p. 195.
+
+[276] _Bulletin, Ast. Soc. de France_, February, 1903.
+
+[277] Here [Greek: ch] is probably 17 Cygni, [Greek: ch] being the famous
+variable near it.
+
+[278] _Popular Astronomy_, vol. 13 (1904), p. 509.
+
+[279] _Astrophysical Journal_, December, 1895.
+
+[280] _The Observatory_, July, 1895, p. 290.
+
+[281] _Celestial Cycle_, p. 302.
+
+[282] _Nature_, December 13, 1894.
+
+[283] _Histoire Celeste_, p. 211.
+
+[284] _Nature_, October, 1887.
+
+[285] _Ibid._, August 29, 1889.
+
+[286] _Science Abstracts_, February 25, 1908, pp. 82, 83.
+
+[287] _Bedford Catalogue_, pp. 227-8.
+
+[288] _Knowledge_, February 1, 1888.
+
+[289] _Celestial Cycle_, p. 280.
+
+[290] _Popular Astronomy_, February, 1904.
+
+[291] _Ibid._, vol. 15 (1907), p. 444.
+
+[292] _Journal_, B.A.A., June, 1899.
+
+[293] _Astrophysical Journal_, vol. 8 (1898), p. 314.
+
+[294] _Astrophysical Journal_, vol. 8, p. 213.
+
+[295] _Ibid._, vol. 17, January to June, 1902.
+
+[296] _Astronomy and Astrophysics_, 1894, pp. 569-70.
+
+[297] _The Study of Stellar Evolution_ (1908), p. 171.
+
+[298] _Astrophysical Journal_, January, 1905.
+
+[299] _Journal_, B.A.A., June, 1901.
+
+[300] _Ast. Soc. of the Pacific_, December, 1908.
+
+[301] _The Observatory_, November, 1902, p. 391.
+
+[302] _Cosmos_, vol. iv. p. 567 (Ott�'s translation).
+
+[303] _Journal_, B.A.A., February, 1898.
+
+[304] _The Observatory_, April, 1887.
+
+[305] _Evangeline_, Part the Second, III.
+
+[306] _Legend of Robert, Duke of Normandy._
+
+[307] _Copernicus_, vol. iii. p. 231.
+
+[308] _Ibid._, p. 61.
+
+[309] _Cosmos_, vol. i. p. 142.
+
+[310] These apertures are computed from the formula, minimum visible = 9 +
+5 log. aperture.
+
+[311] _Cosmos_, vol. iii. p. 73.
+
+[312] _Darwin and Modern Science_, p. 563.
+
+[313] _Journal_, B.A.A., October, 1895.
+
+[314] Burnham's _General Catalogue of Double Stars_, p. 494.
+
+[315] _Journal_, B.A.A., November 18, 1896.
+
+[316] _Ibid._, B.A.A., January, 1907.
+
+[317] _Studies in Astronomy_, p. 185.
+
+[318] _Knowledge_, June, 1891.
+
+[319] Seen by Drs. Ludendorff and Eberhard, _The Observatory_, April,
+1906, p. 166, quoted from _Ast. Nach._, No. 4067.
+
+[320] _The Observatory_, January, 1907, p. 61.
+
+[321] _Astronomy and Astrophysics_, 1894.
+
+[322] Smyth's _Celestial Cycle_, p. 223.
+
+[323] _Nature_, February 7, 1907.
+
+[324] _Ibid._, March 19, 1908.
+
+[325] _Popular Astronomy_, vol. 15 (1907), p. 9.
+
+[326] _Astrophysical Journal_, June, 1907, p. 330.
+
+[327] _Ibid._, vol. 22, p. 172.
+
+[328] _Nature_, November 18, 1886.
+
+[329] _Astrophysical Journal_, vol. 17 (1903), p. 282.
+
+[330] _Astrophysical Journal_, vol. 12 (1900), p. 54.
+
+[331] _Nature_, March 21, 1878.
+
+[332] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[333] _Journal_, B.A.A., vol. 17 (1903), p. 282.
+
+[334] _Nature_, June 20, 1909.
+
+[335] _The Observatory_, vol. 7 (1884), p. 17.
+
+[336] _The Observatory_, vol. 14 (1891), p. 69.
+
+[337] _Astronomy and Astrophysics_, 1896, p. 54
+
+[338] _Nature_, August 28, 1902.
+
+[339] _Astrophysical Journal_, October, 1903.
+
+[340] _Nature_, May 30, 1907.
+
+[341] _Popular Astronomy_, February, 1909, p. 125.
+
+[342] _The Observatory_, May, 1907, p. 216.
+
+[343] _Astrophysical Journal_, May, 1907.
+
+[344] _Histoire de l'Astronomie Moderne_, vol. i. pp. 185-6.
+
+[345] Humboldt's _Cosmos_, vol. iii. p. 210 (Ott�'s translation).
+
+[346] _Ibid._, vol. iii. pp. 213-14.
+
+[347] J. C. Duncan, _Lick Observatory Bulletin_, No. 151.
+
+[348] _Astrophysical Journal_, vol. 17, p. 283.
+
+[349] _The Origin of the Stars_, p. 143.
+
+[350] _Ibid._, p. 135.
+
+[351] Quoted by Ennis in _The Origin of the Stars_, p. 133.
+
+[352] _Astrophysical Journal_, vol. 20 (1904), p. 357.
+
+[353] _Nature_, March 8, 1906.
+
+[354] _Astronomical Society of the Pacific_, August, 1908.
+
+[355] _Astronomy and Astrophysics_, 1894, p. 812.
+
+[356] _The Observatory_, May, 1905.
+
+[357] This is a misquotation. See my _Astronomical Essays_, p. 135.
+
+[358] _Nature_, February 3, 1870.
+
+[359] _Bedford Catalogue_, p. 14.
+
+[360] _Ibid._, p. 307.
+
+[361] _Astrophysical Journal_, vol. 14, p. 37.
+
+[362] _Ibid._, vol. 9, p. 149.
+
+[363] _Nature_, July 20, 1899.
+
+[364] _Ast. Nach._, No. 3476.
+
+[365] _Astronomische Nachrichten_, No. 4213.
+
+[366] _Astrophysical Journal_, vol. 9, p. 149.
+
+[367] _Cape Observations_, p. 61.
+
+[368] _Ibid._, p. 85.
+
+[369] _Cape Observations_, p. 98.
+
+[370] _Transactions_, Royal Dublin Society, vol. 2.
+
+[371] _Ast. Nach._, 3628, quoted in _The Observatory_, April, 1900.
+
+[372] _Nature_, April 8, 1909.
+
+[373] _Problems in Astrophysics_, p. 477.
+
+[374] _Ibid._, p. 499.
+
+[375] _Copernicus_, vol. iii. p. 55.
+
+[376] _Lick Observatory Bulletin_, No. 149.
+
+[377] _Ibid._
+
+[378] _Ibid._
+
+[379] _Monthly Notices_, R.A.S., April, 1908, pp. 465-481.
+
+[380] _Lick Observatory Bulletin_, No. 155 (February, 1909).
+
+[381] _Outlines of Astronomy_, par. 870 (Edition of 1875).
+
+[382] _Georgics_, i. II. 217-18.
+
+[383] See paper by Mr. and Mrs. Maunder in _Monthly Notices_, R.A.S.,
+March, 1904, p. 506.
+
+[384] _Primitive Constellations_, vol. ii. p. 143.
+
+[385] _Recherches sur l'Histoire de l'Astronomie Ancienne_, by Paul
+Tannery (1893), p. 298.
+
+[386] _Primitive Constellations_, vol. ii. p. 225.
+
+[387] _Nature_, October 2, 1890.
+
+[388] Lalande's _Astronomie_, vol. i. pp. 243-4.
+
+[389] Lalande's _Astronomie_, vol. i. pp. 242-3.
+
+[390] There are three copies of Al-Sufi's work in the Imperial Library at
+Paris, but these are inaccurate. There is also one in the British Museum
+Library, and another in the India Office Library; but these are imperfect,
+considerable portions of the original work being missing.
+
+[391] _Harvard Annals_, vol. ix. p. 51.
+
+[392] The science of the risings and settings of the stars was called _ilm
+el-anwa_ (Caussin, _Notices et Extraits des Manuscrits de la Biblioth�que
+due Roi_, tome xii. p. 237).
+
+[393] See Mr. E. B. Knobel's papers on this subject in the _Monthly
+Notices_, R.A.S., for 1879 and 1884.
+
+[394] In reading this chapter the reader is recommended to have a Star
+Atlas beside him for reference; Proctor's smaller Star Atlas will be found
+very convenient for this purpose. On the title-page of this useful work
+the author quotes Carlyle's words, "Why did not somebody teach me the
+constellations and make me at home in the starry heavens which are always
+overhead, and which I don't half know to this day?"
+
+[395] _Bedford Catalogue_, p. 29.
+
+[396] _Cosmos_, vol. iii. p. 87.
+
+[397] _Heavenly Display_, 579-85.
+
+[398] _Bedford Catalogue_, p. 385.
+
+[399] Lalande's _Astronomie_, vol. iv. p. 529.
+
+[400] Lalande's _Astronomie_, vol. i. pp. 268-9.
+
+[401] _Primitive Constellations_, vol. i. p. 48.
+
+[402] _Bedford Catalogue_, pp. 27, 28.
+
+[403] Lalande's _Astronomie_, vol. iv. p. 492.
+
+[404] _Bedford Catalogue_, p. 120.
+
+[405] _Primitive Constellations_, vol. i. p. 143.
+
+[406] Perseus.
+
+[407] _Heavenly Display_, 254-8, 261-5, quoted by Brown in _Primitive
+Constellations_, vol. i. p. 274.
+
+[408] Lalande's _Astronomie_, vol. iv. p. 493.
+
+[409] _Primitive Constellations_, vol. i. p. 292.
+
+[410] _Paradiso_, xxii. 111.
+
+[411] Lalande's _Astronomie_, vol. iv. p. 493.
+
+[412] _Bedford Catalogue_, p. 225.
+
+[413] _Nature_, April 6, 1882.
+
+[414] _Primitive Constellations_, vol. i. p. 68.
+
+[415] _Ibid._, vol. i. p. 71.
+
+[416] _Bibliographie G�n�rale de l'Astronomie_, vol. i. Introduction, pp.
+131, 132.
+
+[417] Lalande's _Astronomie_, vol. i. p. 296.
+
+[418] _Primitive Constellations_, vol. i. p. 74.
+
+[419] _Cape Observations_, p. 116.
+
+[420] _Metamorphoses_, xv. 371.
+
+[421] Lalande's _Astronomie_, vol. iv. p. 487.
+
+[422] _Monthly Notices_, R.A.S., April 14, 1848.
+
+[423] _Prim. Const._, vol. ii. p. 45.
+
+[424] Lalande's _Astronomie_, pp. 472-3.
+
+[425] Lalande's _Astronomie_, vol. iv. p. 485.
+
+[426] This star is not shown in Proctor's small Atlas, but it lies between
+[Greek: m] and [Greek: n], nearer to [Greek: m].
+
+[427] Lalande's _Astronomie_, vol. i. p. 247.
+
+[428] Lalande's _Astronomie_, vol. iv. p. 489.
+
+[429] _Primitive Constellations_, vol. i. p. 91.
+
+[430] _Memoirs_, R.A.S., vol. xiii. 61.
+
+[431] _Monthly Notices_, R.A.S., June, 1895.
+
+[432] Lalande's _Astronomie_, vol. i. p. 274.
+
+[433] _Primitive Constellations_, vol. i. p. 143.
+
+[434] _Primitive Constellations_, vol. i. p. 278.
+
+[435] Lalande's _Astronomie_, vol. iv. p. 468.
+
+[436] _Qu�st. Nat._, Lib. 1, Cap. I. � 6; quoted by Dr. See. "Canicula" is
+Sirius, and "Nartis," Mars.
+
+[437] _Astronomy and Astrophysics_, vol. 11, 1892.
+
+[438] _The Observatory_, April, 1906, p. 175.
+
+[439] Houzeau, _Bibliographie G�n�rale de l'Astronomie_, vol. i.,
+Introduction, p. 129.
+
+[440] _English Mechanic_, March 25, 1904, p. 145.
+
+[441] Humboldt's _Cosmos_, vol. iii. p. 185, footnote (Ott�'s
+translation).
+
+[442] Lalande's _Astronomie_, vol, i. p. 277.
+
+[443] This was pointed out by Flammarion in his work _Les �toiles_, page
+532; but his identifications do not agree exactly with mine.
+
+[444] See Proctor's Map 7, now x.
+
+[445] _Primitive Constellations_, vol. i. p. 106.
+
+[446] Lalande's _Astronomie_, vol. i. p. 278.
+
+[447] Lalande's _Astronomie_, vol. iv.
+
+[448] _Primitive Constellations_, vol. i. p. 112.
+
+[449] _Ibid._, vol. i. p. 113.
+
+[450] Lalande's _Astronomie_, vol. i.
+
+[451] W. T. Lynn in _The Observatory_, vol. 22, p. 236.
+
+[452] _Knowledge_, May 1, 1889. Sir John Herschel, however, gives 3970
+B.C.
+
+[453] _The Observatory_, November 1907, p. 412.
+
+[454] This is not, however, _invariably_ the case, as pointed out by Mr.
+Denning in _The Observatory_, 1885, p. 340.
+
+[455] _The Observatory_, vol. 8 (1885), pp. 246-7.
+
+[456] _Harvard College Observatory Annals_, vol. xlviii. No. 5.
+
+[457] _Popular Astronomy_, vol. 15 (1907), p. 529.
+
+[458] _Cape Observations_, p. 77.
+
+[459] _Monthly Notices_, R.A.S., March, 1899.
+
+[460] _Nature_, February 13, 1890.
+
+[461] _Popular Astronomy_, vol. 15 (1907), p. 530.
+
+[462] _Photographs of Star-Clusters and Nebul�_, vol. ii. p. 17.
+
+[463] _Monthly Notices_, R.A.S., May 9, 1856.
+
+[464] _Astrophysical Journal_, vol. 25 (1907), p. 219.
+
+[465] _Popular Astronomy_, vol. 11 (1903), p. 293.
+
+[466] Translated by W. H. Mallock, _Nature_, February 8, 1900, p. 352.
+
+[467] Howard Payn, _Nature_, May 16, 1901, p. 56.
+
+[468] Howard Payn, _Nature_, May 16, 1901, p. 56.
+
+[469] _Contributions from the Mount Wilson Solar Observatory_, No. 31.
+
+[470] Quoted by Denning in _Telescopic Work for Starlight Evenings_, p.
+297.
+
+[471] _Astrophysical Journal_, March, 1895.
+
+[472] _Outlines of Astronomy_, Tenth Edition, p. 571.
+
+[473] _Astrophysical Journal_, vol. 12, p. 136.
+
+[474] _De Placitis._ Quoted by Carl Snyder in _The World Machine_ p. 354.
+
+[475] _Popular Astronomy_, vol. 14 (1906), p. 638.
+
+[476] Article on "The Greek Anthology," _Nineteenth Century_, April, 1907,
+quoted in _The Observatory_, May, 1907.
+
+[477] _Popular Astronomy_, vol. 13 (1905), p. 346.
+
+[478] _Bulletin de la Soc. Ast. de France_, April, 1908.
+
+[479] _The Observatory_, vol. 11, p. 375.
+
+[480] Grant, _History of Physical Astronomy_, p. 364.
+
+[481] _Ibid._, p. 377.
+
+[482] _Ibid._, p. 366.
+
+[483] _Ibid._, p. 367.
+
+[484] Grant, _History of Physical Astronomy_, p. 370.
+
+[485] _Nature_, July 25, 1889.
+
+[486] _Cosmos_, vol. iv. p. 381.
+
+[487] _Cosmos_, vol. iv. pp. 381-6.
+
+[488] _Ibid._, vol. i. p. 121.
+
+[489] _The Observatory_, vol. 6 (1883), pp. 327-8.
+
+[490] _Nature_, June 25, 1874.
+
+[491] _Popular Astronomy_, May, 1895, "Reflectors or Refractors."
+
+[492] Denning, _Telescopic Work for Starlight Evenings_, p. 225.
+
+[493] _Nature_, November 2, 1893.
+
+[494] _Telescopic Work_, p. 226.
+
+[495] _Copernicus_, vol. i. p. 229.
+
+[496] Grant, _History of Physical Astronomy_, p. 433.
+
+[497] _Cosmos_, vol. ii. p. 699.
+
+[498] Grant, _History of Physical Astronomy_, p. 536, footnote.
+
+[499] _Bedford Catalogue_, p. 179.
+
+[500] _The Observatory_, July, 1891.
+
+[501] _Nature_, September 3, 1903.
+
+[502] _Cosmos_, vol. ii. p. 669.
+
+[503] _The World Machine_, p. 80.
+
+[504] _Ibid._, p. 89.
+
+[505] Grant, _History of Physical Astronomy_, p. 107.
+
+[506] Grant, _History of Physical Astronomy_, p. 113.
+
+[507] _Nature_, August 11, 1898.
+
+[508] _Ibid._, August 18, 1898.
+
+[509] _Ibid._, October 20, 1898.
+
+[510] _The Observatory_, vol. iv. (1881), p. 234.
+
+[511] W. T. Lynn, _The Observatory_, July, 1909, p. 291.
+
+[512] Quoted in _The Observatory_, July, 1902, p. 281.
+
+[513] _Astrophysical Journal_, vol. 6, 1897, p. 304.
+
+[514] _Celestial Cycle_, p. 367.
+
+[515] _The Observatory_, vol. 5 (1882), p. 251.
+
+[516] Quoted by Humboldt in _Cosmos_, vol. ii. p. 696, footnote.
+
+[517] Quoted by Denning in _Telescopic Work_, p. 347.
+
+[518] _Knowledge_, February 20, 1885, p. 149.
+
+[519] Humboldt's _Cosmos_, vol. i. p. 123.
+
+[520] _Outlines of Astronomy_, par. 319; edition of 1875.
+
+[521] _Bulletin de la Soc. Ast. de France_, March, 1908, p. 146.
+
+[522] An "astronomical unit" is the sun's mean distance from the earth.
+
+[523] This is on the American and French system of notation, but on the
+English system, 10{66} = 10{60} � 10{6} would be a million decillion.
+
+[524] _Astronomical Society of the Pacific_, April, 1909 (No. 125), and
+_Popular Astronomy_, May, 1909.
+
+[525] _Nature_, July 22, 1909.
+
+[526] _Ibid._
+
+[527] _The Observatory_, vol. 9 (December, 1886), p. 389.
+
+[528] _De Nat. Deorum_, quoted in Smyth's _Cycle_, p. 19.
+
+[529] _The Observatory_, May, 1907.
+
+[530] _More Worlds than Ours_, p. 17.
+
+[531] _Man's Place in Nature._
+
+
+
+
+Transcriber's Notes:
+
+Passages in italics are indicated by _italics_.
+
+Superscripted characters are indicated by {superscript}.
+
+Subscripted characters are indicated by _{subscript}.
+
+The original text includes Greek characters. For this text version these
+letters have been replaced with transliterations.
+
+Foonote 48 appears on page 28 of the text, but there is no corresponding
+marker on the page.
+
+Foonote 448 appears on page 295 of the text, but there is no corresponding
+marker on the page.
+
+
+
+
+
+
+End of Project Gutenberg's Astronomical Curiosities, by J. Ellard Gore
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+    <title>
+      Astronomical Curiosities: Facts and Fallacies, by J. Ellard Gore&mdash;A Project Gutenberg eBook
+    </title>
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+
+The Project Gutenberg EBook of Astronomical Curiosities, by J. Ellard Gore
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org/license
+
+
+Title: Astronomical Curiosities
+       Facts and Fallacies
+
+Author: J. Ellard Gore
+
+Release Date: March 25, 2012 [EBook #39263]
+
+Language: English
+
+Character set encoding: ISO-8859-1
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+*** START OF THIS PROJECT GUTENBERG EBOOK ASTRONOMICAL CURIOSITIES ***
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+Produced by The Online Distributed Proofreading Team at
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+</pre>
+
+
+
+<div class="figcenter"><img src="images/cover.jpg" alt="" /></div>
+<p>&nbsp;</p><p>&nbsp;</p>
+
+<h1>ASTRONOMICAL CURIOSITIES</h1>
+<p class="center"><span class="huge">FACTS AND FALLACIES</span></p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<p class="center"><span class="huge">ASTRONOMICAL<br />
+CURIOSITIES</span></p>
+<p class="center"><span class="large">FACTS AND FALLACIES</span></p>
+<p>&nbsp;</p>
+<p class="center"><small>BY</small><br />
+<span class="large">J. ELLARD GORE</span><br />
+<small>MEMBER OF THE ROYAL IRISH ACADEMY<br />
+FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY<br />
+CORRESPONDING MEMBER OF THE ROYAL ASTRONOMICAL SOCIETY OF CANADA<br />
+ETC.<br />
+AUTHOR OF &#8220;ASTRONOMICAL ESSAYS,&#8221; &#8220;STUDIES IN ASTRONOMY,&#8221;<br />
+&#8220;THE VISIBLE UNIVERSE,&#8221; ETC.</small></p>
+<p>&nbsp;</p>
+<p class="center">LONDON<br />
+CHATTO &amp; WINDUS<br />
+1909</p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<p class="center">PRINTED BY<br />
+WILLIAM CLOWES AND SONS, LIMITED<br />
+LONDON AND BECCLES</p>
+
+<p class="center"><i>All rights reserved</i></p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<h2>PREFACE</h2>
+
+<div class="note">
+<p>The curious facts, fallacies, and paradoxes contained in the following
+pages have been collected from various sources. Most of the information
+given will not, I think, be found in popular works on astronomy, and will,
+it is hoped, prove of interest to the general reader.</p>
+
+<p class="right">J. E. G.</p>
+
+<p><i>September, 1909.</i></p></div>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p class="title">CONTENTS</p>
+
+<table border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td><small>CHAPTER</small></td>
+    <td>&nbsp;</td>
+    <td align="right"><small>PAGE</small></td></tr>
+<tr><td align="right"><a href="#CHAPTER_I">I.</a></td>
+    <td>THE SUN</td>
+    <td align="right"><a href="#Page_1">1</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_II">II.</a></td>
+    <td>MERCURY</td>
+    <td align="right"><a href="#Page_10">10</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_III">III.</a></td>
+    <td>VENUS</td>
+    <td align="right"><a href="#Page_17">17</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_IV">IV.</a></td>
+    <td>THE EARTH</td>
+    <td align="right"><a href="#Page_32">32</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_V">V.</a></td>
+    <td>THE MOON</td>
+    <td align="right"><a href="#Page_48">48</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_VI">VI.</a></td>
+    <td>MARS</td>
+    <td align="right"><a href="#Page_59">59</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_VII">VII.</a></td>
+    <td>THE MINOR PLANETS</td>
+    <td align="right"><a href="#Page_68">68</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_VIII">VIII.</a></td>
+    <td>JUPITER</td>
+    <td align="right"><a href="#Page_74">74</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_IX">IX.</a></td>
+    <td>SATURN</td>
+    <td align="right"><a href="#Page_84">84</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_X">X.</a></td>
+    <td>URANUS AND NEPTUNE</td>
+    <td align="right"><a href="#Page_91">91</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XI">XI.</a></td>
+    <td>COMETS</td>
+    <td align="right"><a href="#Page_97">97</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XII">XII.</a></td>
+    <td>METEORS</td>
+    <td align="right"><a href="#Page_117">117</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XIII">XIII.</a></td>
+    <td>THE ZODIACAL LIGHT AND GEGENSCHEIN</td>
+    <td align="right"><a href="#Page_127">127</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XIV">XIV.</a></td>
+    <td>THE STARS</td>
+    <td align="right"><a href="#Page_135">135</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XV">XV.</a></td>
+    <td>DOUBLE AND BINARY STARS</td>
+    <td align="right"><a href="#Page_160">160</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XVI">XVI.</a></td>
+    <td>VARIABLE STARS</td>
+    <td align="right"><a href="#Page_170">170</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XVII">XVII.</a></td>
+    <td>NEBUL&AElig; AND CLUSTERS</td>
+    <td align="right"><a href="#Page_191">191</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XVIII">XVIII.</a></td>
+    <td>HISTORICAL</td>
+    <td align="right"><a href="#Page_217">217</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XIX">XIX.</a></td>
+    <td>THE CONSTELLATIONS</td>
+    <td align="right"><a href="#Page_239">239</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XX">XX.</a></td>
+    <td>THE VISIBLE UNIVERSE</td>
+    <td align="right"><a href="#Page_313">313</a></td></tr>
+<tr><td align="right"><a href="#CHAPTER_XXI">XXI.</a></td>
+    <td>GENERAL</td>
+    <td align="right"><a href="#Page_329">329</a></td></tr>
+<tr><td>&nbsp;</td>
+    <td>INDEX</td>
+    <td align="right"><a href="#Page_359">359</a></td></tr></table>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p class="title">ILLUSTRATIONS</p>
+
+<table border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td colspan="2">&nbsp;</td>
+    <td align="right"><small>PAGE</small></td></tr>
+<tr><td>AL-SUFI&#8217;S &#8220;EARTHEN JAR&#8221;</td>
+    <td><span class="spacer">&nbsp;</span></td>
+    <td align="right"><a href="#Page_248">247</a></td></tr>
+<tr><td>AL-SUFI&#8217;S &#8220;FISHES&#8221; IN ANDROMEDA</td>
+    <td>&nbsp;</td>
+    <td align="right"><a href="#Page_250">249</a></td></tr></table>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
+<p class="center"><span class="giant">ASTRONOMICAL CURIOSITIES</span></p>
+<p>&nbsp;</p>
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I</h2>
+<p class="title">The Sun</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Some</span> observations recently made by Prof. W. H. Pickering in Jamaica, make
+the value of sunlight 540,000 times that of moonlight. This makes the
+sun&#8217;s &#8220;stellar magnitude&#8221; minus 26&middot;83, and that of moonlight minus 12&middot;5.
+Prof. Pickering finds that the light of the full moon is equal to 100,000
+stars of zero magnitude. He finds that the moon&#8217;s &#8220;albedo&#8221; is about
+0&middot;0909; or in other words, the moon reflects about one-tenth of the light
+which falls on it from the sun. He also finds that the light of the full
+moon is about twelve times the light of the half moon: a curious and
+rather unexpected result.</p>
+
+<p>M. C. Fabry found that during the total eclipse of the sun on August 30,
+1905, the light of the corona at a distance of five minutes of arc from
+the sun&#8217;s limit, and in the vicinity of the sun&#8217;s equator, was about 720
+candle-power. Comparing this<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span> with the intrinsic light of the full moon
+(2600 candle-power) we have the ratio of 0&middot;28 to 1. He finds that the
+light of the sun in the zenith, and at its mean distance from the earth,
+is 100,000 times greater than the light of a &#8220;decimal candle&#8221; placed at a
+distance of one metre from the eye.<a name='fna_1' id='fna_1' href='#f_1'><small>[1]</small></a> He also finds that sunlight is
+equal to 60,000 million times the light of Vega. This would make the sun&#8217;s
+&#8220;stellar magnitude&#8221; minus 26&middot;7, which does not differ much from Prof.
+Pickering&#8217;s result, given above, and is probably not far from the truth.</p>
+
+<p>From experiments made in 1906 at Moscow, Prof. Ceraski found that the
+light of the sun&#8217;s limb is only 31&middot;4 to 38&middot;4 times brighter than the
+illumination of the earth&#8217;s atmosphere very near the limb. This is a very
+unexpected result; and considering the comparative faintness of the sun&#8217;s
+corona during a total eclipse, it is not surprising that all attempts to
+photograph it without an eclipse have hitherto failed.<a name='fna_2' id='fna_2' href='#f_2'><small>[2]</small></a></p>
+
+<p>From Paschen&#8217;s investigations on the heat of the sun&#8217;s surface, he finds a
+result of 5961&deg; (absolute), &#8220;assuming that the sun is a perfectly black
+body.&#8221;<a name='fna_3' id='fna_3' href='#f_3'><small>[3]</small></a> Schuster finds that &#8220;There is a stratum near the sun&#8217;s surface
+having an average temperature of approximately 5500&deg; C., to which about
+0&middot;3 of the sun&#8217;s radiation is due. The<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span> remaining portion of the radiation
+has an intensity equal to that due to a black body having a temperature of
+about 6700&deg; C.&#8221; The above results agree fairly well with those found by
+the late Dr. W. E. Wilson.<a name='fna_4' id='fna_4' href='#f_4'><small>[4]</small></a> The assumption of the sun being &#8220;a black
+body&#8221; seems a curious paradox; but the simple meaning of the statement is
+that the sun is assumed to act as a radiator as <i>if it were a perfectly
+black body heated to the high temperature given above</i>.</p>
+
+<p>According to Prof. Langley, the sun&#8217;s photosphere is 5000 times brighter
+than the molten metal in a &#8220;Bessemer convertor.&#8221;<a name='fna_5' id='fna_5' href='#f_5'><small>[5]</small></a></p>
+
+<p>Observations of the sun even with small telescopes and protected by dark
+glasses are very dangerous to the eyesight. Galileo blinded himself in
+this way; Sir William Herschel lost one of his eyes; and some modern
+observers have also suffered. The present writer had a narrow escape from
+permanent injury while observing the transit of Venus, in 1874, in India,
+the dark screen before the eyepiece of a 3-inch telescope having
+blistered&mdash;that is, partially fused during the observation. Mr. Cooper,
+Markree Castle, Ireland, in observing the sun, used a &#8220;drum&#8221; of alum water
+and dark spectacles, and found this sufficient protection against the
+glare in using his large refracting telescope of 13&middot;3-inches aperture.</p>
+
+<p><span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span>Prof. Mitchell, of Columbia University (U.S.A.), finds that lines due to
+the recently discovered atmospherical gases argon and neon are present in
+the spectrum of the sun&#8217;s chromosphere. The evidence for the existence of
+krypton and xenon is, however, inconclusive. Prof. Mitchell suggests that
+these gases may possibly have reached the earth&#8217;s atmosphere from the sun.
+This would agree with the theory advanced by Arrhenius that &#8220;ionised
+particles are constantly being repulsed by the pressure of light, and thus
+journey from one sun to another.&#8221;<a name='fna_6' id='fna_6' href='#f_6'><small>[6]</small></a></p>
+
+<p>Prof. Young in 1870, and Dr. Kreusler in June, 1904, observed the helium
+line D<sub>3</sub> as a <i>dark</i> line &#8220;in the spectrum of the region about a
+sun-spot.&#8221;<a name='fna_7' id='fna_7' href='#f_7'><small>[7]</small></a> This famous line, from which helium was originally
+discovered in the sun, and by which it was long afterwards detected in
+terrestrial minerals, usually appears as a <i>bright</i> line in the spectrum
+of the solar chromosphere and &#8220;prominences.&#8221; It has also been seen <i>dark</i>
+by Mr. Buss in sun-spot regions.<a name='fna_8' id='fna_8' href='#f_8'><small>[8]</small></a></p>
+
+<p>The discovery of sun-spots was claimed by Hariotte, in 1610, and by
+Galileo, Fabricius, and Scheiner, in 1611. The latter wrote 800 pages on
+them, and thought they were small planets revolving round the sun! This
+idea was also held by Tard&egrave;, who called them <i>Astra Borbonia</i>, and by<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span> C.
+Malapert, who termed them <i>Sydera Austricea</i>. But they seem to have been
+noticed by the ancients.</p>
+
+<p>Although in modern times there has been no extraordinary development of
+sun-spots at the epoch of maximum, it is not altogether impossible that in
+former times these spots may have occasionally increased to such an
+extent, both in number and size, as to have perceptibly darkened the sun&#8217;s
+light. A more probable explanation of recorded sun-darkenings seems,
+however, to be the passing of a meteoric or nebulous cloud between the sun
+and the earth. A remarkable instance of sun-darkening recorded in Europe
+occurred on May 22, 1870, when the sun&#8217;s light was observed to be
+considerably reduced in a cloudless sky in the west of Ireland, by the
+late John Birmingham; at Greenwich on the 23rd; and on the same date, but
+at a later hour, in North-Eastern France&mdash;&#8220;a progressive manifestation,&#8221;
+Mr. Birmingham says, &#8220;that seems to accord well with the hypothesis of
+moving nebulous matter.&#8221; A similar phenomenon was observed in New England
+(U.S.A.), on September 6, 1881.</p>
+
+<p>One of the largest spots ever seen on the sun was observed in June, 1843.
+It remained visible for seven or eight days. According to Schwabe&mdash;the
+discoverer of the sun-spot period&mdash;its diameter was 74,000 miles, so that
+its area was many times<span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> that of the earth&#8217;s surface. The most curious
+thing about this spot was that it appeared near a <i>minimum</i> of the
+sun-spot cycle! and was therefore rather an anomalous phenomenon. It was
+suggested by the late Daniel Kirkwood that this great spot was caused by
+the fall of meteoric matter into the sun; and that it had possibly some
+connection with the great comet of 1843, which approached the sun nearer
+than any other recorded comet, its distance from the sun at perihelion
+being about 65,000 miles, or less than one-third of the moon&#8217;s distance
+from the earth. This near approach of the comet to the sun occurred about
+three months before the appearance of the great sun-spot; and it seems
+probable that the spot was caused by the downfall of a large meteorite
+travelling in the wake of the comet.<a name='fna_9' id='fna_9' href='#f_9'><small>[9]</small></a> The connection between comets and
+meteors is well known.</p>
+
+<p>The so-called blackness of sun-spots is merely relative. They are really
+very bright. The most brilliant light which can be produced artificially
+looks like a black spot when projected on the sun&#8217;s disc.</p>
+
+<p>According to Sir Robert Ball a pound of coal striking a body with a
+velocity of five miles a second would develop as much heat as it would
+produce by its combustion. A body falling into the sun from infinity would
+have a velocity of<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span> 450 miles a second when it reached the sun&#8217;s surface.
+Now as the momentum varies as the square of the velocity we have a pound
+of coal developing 90<sup>2</sup> (= <span style="font-size: 0.8em;"><sup>450</sup></span>&frasl;<span style="font-size: 0.6em;">5</span>)<sup>2</sup>,
+or 8,100 times as much heat as would be produced by its combustion. If the sun were formed of coal it would be
+consumed in about 3000 years. Hence it follows that the contraction of the
+sun&#8217;s substance from infinity would produce a supply of heat for 3000 &times;
+8100, or 24,300,000 years.</p>
+
+<p>The late Mr. Proctor and Prof. Young believed &#8220;that the contraction theory
+of the sun&#8217;s heat is the true and only available theory.&#8221; The theory is,
+of course, a sound one; but it may now be supplemented by supposing the
+sun to contain a certain small amount of radium. This would bring physics
+and geology into harmony. Proctor thought the &#8220;sun&#8217;s real globe is very
+much smaller than the globe we see. In other words the process of
+contraction has gone on further than, judging from the sun&#8217;s apparent
+size, we should suppose it to have done, and therefore represents more sun
+work&#8221; done in past ages.</p>
+
+<p>With reference to the suggestion, recently made, that a portion, at least,
+of the sun&#8217;s heat may be due to radium, and the experiments which have
+been made with negative results, Mr. R. T. Strutt&mdash;the eminent
+physicist&mdash;has made some calculations on the subject and says, &#8220;even if
+all<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span> the sun&#8217;s heat were due to radium, there does not appear to be the
+smallest possibility that the Becquerel radiation from it could ever be
+detected at the earth&#8217;s surface.&#8221;<a name='fna_10' id='fna_10' href='#f_10'><small>[10]</small></a></p>
+
+<p>The eminent Swedish physicist Arrhenius, while admitting that a large
+proportion of the sun&#8217;s heat is due to contraction, considers that it is
+probably the chemical processes going on in the sun, and not the
+contraction which constitute the <i>chief</i> source of the solar heat.<a name='fna_11' id='fna_11' href='#f_11'><small>[11]</small></a></p>
+
+<p>As the centre of gravity of the sun and Jupiter lies at a distance of
+about 460,000 miles from the sun&#8217;s centre, and the sun&#8217;s radius is only
+433,000 miles, it follows that the centre of gravity of the sun and planet
+is about 27,000 miles <i>outside</i> the sun&#8217;s surface. The attractions of the
+other planets perpetually change the position of the centre of gravity of
+the solar system; but in some books on astronomy it is erroneously stated
+that the centre of gravity of the system is <i>always</i> within the sun&#8217;s
+surface. If <i>all</i> the planets lay on the same side of the sun at the same
+time (as might possibly happen), then the centre of gravity of the whole
+system would lie considerably more than 27,000 miles outside the sun&#8217;s
+surface.</p>
+
+<p>With reference to the sun&#8217;s great size, Carl Snyder has well said, &#8220;It was
+as if in Vulcan&#8217;s<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> smithy the gods had moulded one giant ball, and the
+planets were but bits and small shot which had spattered off as the
+glowing ingot was cast and set in space. Little man on a little part of a
+little earth&mdash;a minor planet, a million of which might be tumbled into the
+shell of the central sun&mdash;was growing very small; his wars, the
+convulsions of a state, were losing consequence. Human endeavour, human
+ambitions could now scarce possess the significance they had when men
+could regard the earth as the central fact of the universe.&#8221;<a name='fna_12' id='fna_12' href='#f_12'><small>[12]</small></a></p>
+
+<p>With reference to the late Prof. C. A. Young (U.S.A.)&mdash;a great authority
+on the sun&mdash;an American writer has written the following lines:&mdash;</p>
+
+<p class="poem">&#8220;The destined course of whirling worlds to trace,<br />
+To plot the highways of the universe,<br />
+And hear the morning stars their song rehearse,<br />
+And find the wandering comet in his place;<br />
+This is the triumph written in his face,<br />
+And in the gleaming eye that read the sun<br />
+Like open book, and from the spectrum won<br />
+The secrets of immeasurable space.&#8221;<a name='fna_13' id='fna_13' href='#f_13'><small>[13]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span></p>
+<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II</h2>
+<p class="title">Mercury</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">As</span> the elongation of Mercury from the sun seldom exceeds 18&deg;, it is a
+difficult object, at least in this country, to see without a telescope. As
+the poet says, the planet&mdash;</p>
+
+<p class="poem">&#8220;Can scarce be caught by philosophic eye<br />
+Lost in the near effulgence of its blaze.&#8221;</p>
+
+<p>Tycho Brah&eacute;, however, records several observations of Mercury with the
+unaided vision in Denmark.</p>
+
+<p>It can be occasionally caught with the naked eye in this country after
+sunset, when it is favourably placed for observation, and I have so seen
+it several times in Ireland. On February 19, 1888, I found it very visible
+in strong twilight near the western horizon, and apparently brighter than
+an average star of the first magnitude would be in the same position. In
+the clear air of the Punjab sky I observed Mercury on November 24-29,
+1872, near the western horizon after sunset. Its appearance was that of a
+reddish star of the first magnitude. On November 29 I compared its
+brilliancy<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> with that of Saturn, which was some distance above it, and
+making allowance for the glare near the horizon in which Mercury was
+immersed, its brightness appeared to me to be quite equal to that of
+Saturn. In June, 1874, I found it equal to Aldebaran, and of very much the
+same colour. Mr. W. F. Denning, the famous observer of meteors, states
+that he observed Mercury with the naked eye about 150 times during the
+years 1868 to 1905.<a name='fna_14' id='fna_14' href='#f_14'><small>[14]</small></a></p>
+
+<p>He found that the duration of visibility after sunset is about 1<sup>h</sup> 40<sup>m</sup>
+when seen in March, 1<sup>h</sup> 30<sup>m</sup> in April, and 1<sup>h</sup> 20<sup>m</sup> in May. He thinks
+that the planet is, at its brightest, &#8220;certainly much brighter than a
+first magnitude star.&#8221;<a name='fna_15' id='fna_15' href='#f_15'><small>[15]</small></a> In February, 1868, he found that its brightness
+rivalled that of Jupiter, then only 2&deg; or 3&deg; distant. In November, 1882,
+it seemed brighter than Sirius. In 1876 it was more striking than Mars,
+but the latter was then &#8220;faint and at a considerable distance from the
+earth.&#8221;</p>
+
+<p>In 1878, when Mercury and Venus were in the same field of view of a
+telescope, Nasmyth found that the surface brightness (or &#8220;intrinsic
+brightness,&#8221; as it is called) of Venus was at least twice as great as that
+of Mercury; and Z&ouml;llner found that from a photometric point of view the
+surface of Mercury is comparable with that of the moon.</p>
+
+<p><span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span>With reference to the difficulty of seeing Mercury, owing to its proximity
+to the sun, Admiral Smyth says, &#8220;Although Mercury is never in <i>opposition</i>
+to the earth, he was, when in the house of Mars, always viewed by
+astrologers as a most malignant planet, and one full of evil influences.
+The sages stigmatized him as a false deceitful star (<i>sidus dolosum</i>), the
+eternal torment of astronomers, eluding them as much as terrestrial
+mercury did the alchemists; and Goad, who in 1686 published a whole folio
+volume full of astro-meteorological aphorisms, unveiling the choicest
+secrets of nature, contemptuously calls Mercury a &#8216;squinting lacquey of
+the sun, who seldom shows his head in these parts, as if he was in debt.&#8217;
+His extreme mobility is so striking that chemists adopted his symbol to
+denote quicksilver.&#8221;<a name='fna_16' id='fna_16' href='#f_16'><small>[16]</small></a></p>
+
+<p>Prof. W. H. Pickering thinks that the shortness of the cusps (or &#8220;horns&#8221;)
+of Mercury&#8217;s disc indicates that the planet&#8217;s atmosphere is of small
+density&mdash;even rarer than that of Mars.</p>
+
+<p>The diameter of Mercury is usually stated at about 3000 miles; but a long
+series of measures made by Prof. See in the year 1901 make the real
+diameter about 2702 miles. This would make the planet smaller than some of
+the satellites of the large planets, probably smaller than satellites III.
+and IV. of Jupiter, less than Saturn&#8217;s satellite<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> Titan, and possibly
+inferior in size to the satellite of Neptune. Prof. Pickering thinks that
+the density of Mercury is about 3 (water = 1). Dr. See&#8217;s observations show
+&#8220;no noticeable falling off in the brightness of Mercury near the limb.&#8221;
+There is therefore no evidence of any kind of atmospheric absorption in
+Mercury, and the observer &#8220;gets the impression that the physical condition
+of the planet is very similar to that of our moon.&#8221;<a name='fna_17' id='fna_17' href='#f_17'><small>[17]</small></a></p>
+
+<p>Schr&ouml;ter (1780-1815) observed markings on Mercury, from which he inferred
+that the planet&#8217;s surface was mountainous, and one of these mountains he
+estimated at about 11 miles in height!<a name='fna_18' id='fna_18' href='#f_18'><small>[18]</small></a> But this seems very doubtful.</p>
+
+<p>To account for the observed irregularities in the motion of Mercury in its
+orbit, Prof. Newcomb thinks it possible that there may exist a ring or
+zone of &#8220;asteroids&#8221; a little &#8220;outside the orbit of Mercury&#8221; and having a
+combined mass of &#8220;one-fiftieth to one-three-hundredth of the mass of
+Venus, according to its distance from Mercury.&#8221; Prof. Newcomb, however,
+considers that the existence of such a ring is extremely improbable, and
+regards it &#8220;more as a curiosity than a reality.&#8221;<a name='fna_19' id='fna_19' href='#f_19'><small>[19]</small></a></p>
+
+<p>M. L&eacute;o Brenner thinks that he has seen the<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span> dark side of Mercury, in the
+same way that the dark side of Venus has been seen by many observers. In
+the case of Mercury the dark side appeared <i>darker</i> than the background of
+the sky. Perhaps this may be due to its being projected on the zodiacal
+light, or outer envelope of the sun.<a name='fna_20' id='fna_20' href='#f_20'><small>[20]</small></a></p>
+
+<p>Mercury is said to have been occulted by Venus in the year 1737.<a name='fna_21' id='fna_21' href='#f_21'><small>[21]</small></a> But
+whether this was an actual occultation, or merely a near approach does not
+seem to be certain.</p>
+
+<p>The first transit of Mercury across the sun&#8217;s disc was observed by
+Gassendi on November 6, 1631, and Halley observed one on November 7, 1677,
+when in the island of St. Helena.</p>
+
+<p>Seen from Mercury, Venus would appear brighter than even we see it, and as
+it would be at its brightest when in opposition to the sun, and seen on a
+dark sky with a full face, it must present a magnificent appearance in the
+midnight sky of Mercury. The earth will also form a brilliant object, and
+the moon would be distinctly visible. The other planets would appear very
+much as they do to us, but with somewhat less brilliancy owing to their
+greater distance.</p>
+
+<p>As the existence of an intra-Mercurial planet (that is a planet revolving
+round the sun within the orbit of Mercury) seems now to be very<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span>
+improbable, Prof. Perrine suggests that possibly &#8220;the finely divided
+matter which produces the zodiacal light when considered in the aggregate
+may be sufficient to cause the perturbations in the orbit of Mercury.&#8221;<a name='fna_22' id='fna_22' href='#f_22'><small>[22]</small></a>
+Prof. Newcomb, however, questions the exact accuracy of Newton&#8217;s law, and
+seems to adopt Hall&#8217;s hypothesis that gravity does not act <i>exactly</i> as
+the inverse square of the distance, and that the exponent of the distance
+is not 2, but 2&middot;0000001574.<a name='fna_23' id='fna_23' href='#f_23'><small>[23]</small></a></p>
+
+<p>Voltaire said, &#8220;If Newton had been in Portugal, and any Dominican had
+discovered a heresy in his inverse ratio of the squares of the distances,
+he would without hesitation have been clothed in a <i>san benito</i>, and burnt
+as a sacrifice to God at an <i>auto da f&eacute;</i>.&#8221;<a name='fna_24' id='fna_24' href='#f_24'><small>[24]</small></a></p>
+
+<p>An occultation of Mercury by Venus was observed with a telescope on May
+17, 1737.<a name='fna_25' id='fna_25' href='#f_25'><small>[25]</small></a></p>
+
+<p>May transits of Mercury across the sun&#8217;s disc will occur in the years
+1924, 1957, and 1970; and November transits in the years 1914, 1927, and
+1940.<a name='fna_26' id='fna_26' href='#f_26'><small>[26]</small></a></p>
+
+<p>From measurements of the disc of Mercury during the last transit, M. R.
+Jonckheere concludes that the <i>polar</i> diameter of the planet is greater<span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span>
+than the <i>equatorial</i>! His result, which is very curious, if true, seems
+to be supported by the observations of other observers.<a name='fna_27' id='fna_27' href='#f_27'><small>[27]</small></a></p>
+
+<p>The rotation period of Mercury, or the length of its day, seems to be
+still in doubt. From a series of observations made in the years 1896 to
+1909, Mr. John McHarg finds a period of 1&middot;0121162 day, or 1<sup>d</sup> 0<sup>h</sup> 17<sup>m</sup>
+26<sup>s</sup>&middot;8. He thinks that &#8220;the planet possesses a considerable atmosphere
+not so clear as that of Mars&#8221;; that &#8220;its axis is very considerably
+tilted&#8221;; and that it &#8220;has fairly large sheets of water.&#8221;<a name='fna_28' id='fna_28' href='#f_28'><small>[28]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span></p>
+<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III</h2>
+<p class="title">Venus</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Venus</span> was naturally&mdash;owing to its brightness&mdash;the first of the planets
+known to the ancients. It is mentioned by Hesiod, Homer, Virgil, Martial,
+and Pliny; and Isaiah&#8217;s remark about &#8220;Lucifer, son of the morning&#8221; (Isaiah
+xiv. 12) probably refers to Venus as a &#8220;morning star.&#8221; An observation of
+Venus is found on the Nineveh tablets of date <span class="smcaplc">B.C.</span> 684. It was observed in
+daylight by Halley in July, 1716.</p>
+
+<p>In <i>very</i> ancient times Venus, when a morning star, was called Phosphorus
+or Lucifer, and when an evening star Hesperus; but, according to Sir G. C.
+Lewis, the identity of the two objects was known so far back as 540 <span class="smcaplc">B.C.</span></p>
+
+<p>When Venus is at its greatest brilliancy, and appears as a morning star
+about Christmas time (which occurred in 1887, and again in 1889), it has
+been mistaken by the public for a return of the &#8220;Star of Bethlehem.&#8221;<a name='fna_29' id='fna_29' href='#f_29'><small>[29]</small></a>
+But whatever &#8220;the star<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> of the Magi&#8221; was it certainly was <i>not</i> Venus. It,
+seems, indeed absurd to suppose that &#8220;the wise men&#8221; of the East should
+have mistaken a familiar object like Venus for a strange apparition. There
+seems to be nothing whatever in the Bible to lead us to expect that the
+star of Bethlehem will reappear.</p>
+
+<p>Mr. J. H. Stockwell has suggested that the &#8220;Star of Bethlehem&#8221; may perhaps
+be explained by a conjunction of the planets Venus and Jupiter which
+occurred on May 8, <span class="smcaplc">B.C.</span> 6, which was two years before the death of Herod.
+From this it would follow that the Crucifixion took place on April 3, <span class="smcaplc">A.D.</span>
+33. But it seems very doubtful that the phenomenon recorded in the Bible
+refers to any conjunction of planets.</p>
+
+<p>Chacornac found the intrinsic brightness of Venus to be ten times greater
+than the most luminous parts of the moon.<a name='fna_30' id='fna_30' href='#f_30'><small>[30]</small></a> But this estimate is
+probably too high.</p>
+
+<p>When at its brightest, the planet is visible in broad daylight to good
+eyesight, if its exact position in the sky is known. In the clear air of
+Cambridge (U.S.A.) it is said to be possible to see it in this way in all
+parts of its orbit, except when the planet is within 10&deg; of the sun.<a name='fna_31' id='fna_31' href='#f_31'><small>[31]</small></a>
+Mr. A. Cameron, of Yarmouth, Nova Scotia, has, however, seen Venus with
+the naked eye three<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> days before conjunction when the planet was only
+6&#188;&deg; from the sun.<a name='fna_32' id='fna_32' href='#f_32'><small>[32]</small></a> This seems a remarkable observation, and shows
+that the observer&#8217;s eyesight must have been very keen. In a private letter
+dated October 22, 1888, the late Rev. S. J. Johnson informed the present
+writer that he saw Venus with the naked eye only four days before
+conjunction with the sun in February, 1878, and February, 1886.</p>
+
+<p>The crescent shape of Venus is said to have been seen with the naked eye
+by Theodore Parker in America when he was only 12 years old. Other
+observers have stated the same thing; but the possibility of such an
+observation has been much disputed in recent years.</p>
+
+<p>In the Chinese Annals some records are given of Venus having been seen in
+the Pleiades. On March 16, <span class="smcaplc">A.D.</span> 845, it is said that &#8220;Venus eclipsed the
+Pleiades.&#8221; This means, of course, that the cluster was apparently effaced
+by the brilliant light of the planet. Computing backwards for the above
+date, Hind found that on the evening of March 16, 845, Venus was situated
+near the star Electra; and on the following evening the planet passed
+close to Maia; thus showing the accuracy of the Chinese record. Another
+&#8220;eclipse&#8221; of the Pleiades by Venus is recorded in the same annals as
+having occurred on March 10, <span class="smcaplc">A.D.</span> 1002.<a name='fna_33' id='fna_33' href='#f_33'><small>[33]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span>When Venus is in the crescent phase, that is near &#8220;Inferior conjunction&#8221;
+with the sun, it will be noticed, even by a casual observer, that the
+crescent is not of the same shape as that of the crescent moon. The horns
+or &#8220;cusps&#8221; of the planetary crescent are more prolonged than in the case
+of the moon, and extend beyond the hemisphere. This appearance is caused
+by refraction of the sun&#8217;s light through the planetary atmosphere, and is,
+in fact, a certain proof that Venus has an atmosphere similar to that of
+the earth. Observations further show that this atmosphere is denser than
+ours.</p>
+
+<p>Seen from Venus, the earth and moon, when in opposition, must present a
+splendid spectacle. I find that the earth would shine as a star about half
+as bright again as Venus at her brightest appears to us, and the moon
+about equal in brightness to Sirius! the two forming a superb &#8220;naked eye
+double star&#8221;&mdash;perhaps the finest sight of its kind in the solar
+system.<a name='fna_34' id='fna_34' href='#f_34'><small>[34]</small></a></p>
+
+<p>Some of the earlier observers, such as La Hire, Fontana, Cassini, and
+Schr&ouml;ter, thought they saw evidence of mountains on Venus. Schr&ouml;ter
+estimated some of these to be 27 or 28 miles in height! but this seems
+very doubtful. Sir William Herschel severely attacked these supposed
+discoveries. Schr&ouml;ter defended himself, and was supported by Beer and
+M&auml;dler, the famous<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> lunar observers. Several modern observers seem to
+confirm Schr&ouml;ter&#8217;s conclusions; but very little is really known about the
+topography of Venus.</p>
+
+<p>The well-known French astronomer Trouvelot&mdash;a most excellent observer&mdash;saw
+white spots on Venus similar to those on Mars. These were well seen and
+quite brilliant in July and August, 1876, and in February and November,
+1877. The observations seem to show that these spots do not (unlike Mars)
+increase and decrease with the planet&#8217;s seasons. These white spots had
+been previously noticed by former observers, including Bianchini, Derham,
+Gruithuisen, and La Hire; but these early observers do not seem to have
+considered them as snow caps, like those of Mars. Trouvelot was led by his
+own observations to conclude that the period of rotation of Venus is
+short, and the best result he obtained was 23<sup>h</sup> 49<sup>m</sup> 28<sup>s</sup>. This does
+not differ much from the results previously found by De Vico, Fritsch, and
+Schr&ouml;ter.<a name='fna_35' id='fna_35' href='#f_35'><small>[35]</small></a></p>
+
+<p>A white spot near the planet&#8217;s south pole was seen on several occasions by
+H. C. Russell in May and June, 1876.<a name='fna_36' id='fna_36' href='#f_36'><small>[36]</small></a></p>
+
+<p>Photographs of Venus taken on March 18 and April 29, 1908, by M. Qu&eacute;nisset
+at the Observatory of Juvissy, France, show a white polar spot. The<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> spot
+was also seen at the same observatory by M. A. Benoit on May 20, 1903.</p>
+
+<p>The controversy on the period of rotation of Venus, or the length of its
+day, is a very curious one and has not yet been decided. Many good
+observers assert confidently that it is short (about 24 hours); while
+others affirm with equal confidence that it is long (about 225 days, the
+period of the planet&#8217;s revolution round the sun). Among the observers who
+favour the short period of rotation are: D. Cassini (1667), J. Cassini
+(1730), Schr&ouml;ter (1788-93), M&auml;dler (1836), De Vico (1840?) Trouvelot
+(1871-79), Flammarion, L&eacute;o Brenner, Stanley Williams, and J. McHarg; and
+among those who support the long period are: Bianchini (1727),
+Schiaparelli, Cerulli, Tacchini, Mascari, and Lowell. Some recent
+spectroscopic observations seem to favour the short period.</p>
+
+<p>Flammarion thinks that &#8220;nothing certain can be descried upon the surface
+of Venus, and that whatever has hitherto been written regarding its period
+of rotation must be considered null and void&#8221;; and again he says, &#8220;Nothing
+can be affirmed regarding the rotation of Venus, inasmuch as the
+absorption of its immense atmosphere certainly prevents any detail on its
+surface from being perceived.&#8221;<a name='fna_37' id='fna_37' href='#f_37'><small>[37]</small></a></p>
+
+<p>The eminent Swedish physicist Arrhenius thinks, however, that the dense
+atmosphere and clouds<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span> of Venus are in favour of a rapid rotation on its
+axis.<a name='fna_38' id='fna_38' href='#f_38'><small>[38]</small></a> He thinks that the mean temperature of Venus may &#8220;not differ
+much from the calculated temperature 104&deg; F.&#8221; &#8220;Under these circumstances
+the assumption would appear plausible that a very considerable portion of
+the surface of Venus, and particularly the districts about the poles,
+would be favourable to organic life.&#8221;<a name='fna_39' id='fna_39' href='#f_39'><small>[39]</small></a></p>
+
+<p>The &#8220;secondary light of Venus,&#8221; or the visibility of the dark side, seems
+to have been first mentioned by Derham in his <i>Astro Theology</i> published
+in 1715. He speaks of the visibility of the dark part of the planet&#8217;s disc
+&#8220;by the aid of a light of a somewhat dull and ruddy colour.&#8221; The date of
+Derham&#8217;s observation is not given, but it seems to have been previous to
+the year 1714. The light seems to have been also seen by a friend of
+Derham. We next find observations by Christfried Kirch, assistant
+astronomer to the Berlin Academy of Sciences, on June 7, 1721, and March
+8, 1726. These observations are found in his original papers, and were
+printed in the <i>Astronomische Nachrichten</i>, No. 1586. On the first date
+the telescopic image of the planet was &#8220;rather tremulous,&#8221; but in 1726 he
+noticed that the dark part of the circle seemed to belong to a smaller
+circle than the illuminated portion of the disc.<a name='fna_40' id='fna_40' href='#f_40'><small>[40]</small></a> The same effect was
+also noted by<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> Webb.<a name='fna_41' id='fna_41' href='#f_41'><small>[41]</small></a> A similar illusion is seen in the case of the
+crescent moon, and this has given rise to the saying, &#8220;the old moon in the
+new moon&#8217;s arms.&#8221;</p>
+
+<p>We next come, in order of date, to an observation made by Andreas Mayer,
+Professor of Mathematics at Griefswald in Prussia. The observation was
+made on October 20, 1759, and the dark part of Venus was seen distinctly
+by Mayer. As the planet&#8217;s altitude at the time was not more than 14&deg; above
+the horizon, and its apparent distance from the sun only 10&deg;, the
+phenomenon&mdash;as Professor Safarik has pointed out&mdash;&#8220;must have had a most
+unusual intensity.&#8221;</p>
+
+<p>Sir William Herschel makes no mention of having ever seen the &#8220;secondary
+light&#8221; of Venus, although he noticed the extension of the horns beyond a
+semicircle.</p>
+
+<p>In the spring and summer of the year 1793, Von Hahn of Remplin in
+Mecklenburg, using excellent telescopes made by Dollond and Herschel, saw
+the dark part of Venus on several occasions, and describes the light as
+&#8220;grey verging upon brown.&#8221;</p>
+
+<p>Schr&ouml;ter of Lilienthal&mdash;the famous observer of the moon&mdash;saw the horns of
+the crescent of Venus extended many degrees beyond the semicircle on
+several occasions in 1784 and 1795, and the border of the dark part
+faintly lit up by a dusky grey light. On February 14, 1806, at<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span>
+7 <span class="smcaplc">P.M.</span> he saw the whole of the dark part visible with an ash-coloured light, and he
+was satisfied that there was no illusion. On January 24 of the same year,
+1806, Harding at G&ouml;ttingen, using a reflector of 9 inches aperture and
+power 84, saw the dark side of Venus &#8220;shining with a pale ash-coloured
+light,&#8221; and very visible against the dark background of the sky. The
+appearance was seen with various magnifying powers, and he thought that
+there could be no illusion. In fact the phenomenon was as evident as in
+the case of the moon. Harding again saw it on February 28 of the same
+year, the illumination being of a reddish grey colour, &#8220;like that of the
+moon in a total eclipse.&#8221;</p>
+
+<p>The &#8220;secondary light&#8221; was also seen by Pastorff in 1822, and by
+Gruithuisen in 1825. Since 1824 observations of the &#8220;light&#8221; were made by
+Berry, Browning, Guthrie, Langdon, Noble, Prince, Webb, and others. Webb
+saw it with powers of 90 and 212 on a 9&middot;38-inch mirror, and found it
+&#8220;equally visible when the bright crescent was hidden by a field bar.&#8221;<a name='fna_42' id='fna_42' href='#f_42'><small>[42]</small></a></p>
+
+<p>Captain Noble&#8217;s observation was rather unique. He found that the dark side
+was &#8220;always distinctly and positively <i>darker</i> than the background upon
+which it is projected.&#8221;</p>
+
+<p>The &#8220;light&#8221; was also seen by Lyman in America in 1867, and by Safarik at
+Prague. In<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> 1871 the whole disc of Venus was seen by Professor
+Winnecke.<a name='fna_43' id='fna_43' href='#f_43'><small>[43]</small></a> On the other hand, Winnecke stated that he only saw it twice
+in 24 years; and the great observers Dawes and M&auml;dler never saw it at
+all!<a name='fna_44' id='fna_44' href='#f_44'><small>[44]</small></a></p>
+
+<p>Various attempts have been made to explain the visibility&mdash;at times&mdash;of
+the &#8220;dark side&#8221; of Venus. The following may be mentioned<a name='fna_45' id='fna_45' href='#f_45'><small>[45]</small></a>:&mdash;(1)
+Reflected earth-light, analogous to the dark side of the crescent moon.
+This explanation was advocated by Harding, Schr&ouml;ter, and others. But,
+although the earth is undoubtedly a bright object in the sky of Venus, the
+explanation is evidently quite inadequate. (2) Phosphorescence of the
+planet&#8217;s atmosphere. This has been suggested by some observers. (3)
+Visibility by contrast, a theory advanced by the great French astronomer
+Arago. (4) Illumination of the planet&#8217;s surface by an aurora borealis.
+This also seems rather inadequate, but would account for the light being
+sometimes visible and sometimes not. (5) Luminosity of the oceans&mdash;if
+there be any&mdash;on Venus. But this also seems inadequate. (6) A planetary
+surface glowing with intense heat. But this seems improbable. (7) The
+Kunstliche Feuer (artificial fire) of Gruithuisen, a very fanciful theory.
+Flammarion thinks that the visibility of the dark side may perhaps be
+explained by its<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span> projection on a somewhat lighter background, such as the
+zodiacal light, or an extended solar envelope.<a name='fna_46' id='fna_46' href='#f_46'><small>[46]</small></a></p>
+
+<p>It will be seen that none of these explanations are entirely satisfactory,
+and the phenomenon, if real, remains a sort of astronomical enigma. The
+fact that the &#8220;light&#8221; is visible on some occasions and not on others would
+render some of the explanations improbable or even inadmissible. But the
+condition of the earth&#8217;s atmosphere at times might account for its
+invisibility on many occasions.</p>
+
+<p>A curious suggestion was made by Z&ouml;llner, namely, that if the secondary
+light of Venus could be observed with the spectroscope it would show
+bright lines! But such an observation would be one of extreme difficulty.</p>
+
+<p>M. Hansky finds that the visibility of the &#8220;light&#8221; is greater during
+periods of maximum solar activity&mdash;that is, at the maxima of sun spots.
+This he explains by the theory of Arrhenius, in which electrified &#8220;ions
+emitted by the sun cause the phenomena of terrestrial magnetic storms and
+auroras.&#8221; &#8220;In the same way the dense atmosphere of Venus is rendered more
+phosphorescent, and therefore more easily visible by the increased solar
+activity.&#8221;<a name='fna_47' id='fna_47' href='#f_47'><small>[47]</small></a> This seems a very plausible hypothesis.</p>
+
+<p>On the whole the occasional illumination of the<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> night side of Venus by a
+very brilliant aurora (explanation (4) above) seems to the present writer
+to be the most probable explanation. Gruithuisen&#8217;s hypothesis (7) seems
+utterly improbable.</p>
+
+<p>There is a curious apparent anomaly about the motion of Venus in the sky.
+Although the planet&#8217;s period of revolution round the sun is 224&middot;7 days, it
+remains on the same side of the sun, as seen from the earth, for 290 days.
+The reason of this is that the earth is going at the same time round the
+sun in the same direction, though at a slower pace; and Venus must
+continue to appear on the same side of the sun until the excess of her
+daily motion above that of the earth amounts to 179&deg;, and this at the
+daily rate of 37&prime; will be about 290 days.</p>
+
+<p>Several observations have been recorded of a supposed satellite of Venus.
+But the existence of such a body has never been verified. In the year
+1887, M. Stroobant investigated the various accounts, and came to the
+conclusion that in several at least of the recorded observations the
+object seen was certainly a star. Thus, in the observation made by
+R&oelig;dick&oelig;r and Boserup on August 4, 1761, a satellite and star are
+recorded as having been seen near the planet. M. Stroobant finds that the
+supposed &#8220;satellite&#8221; was the star &#967;<sub>4</sub> Orionis, and the &#8220;star&#8221;
+<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span>&#967;<sub>3</sub> Orionis. A supposed observation of a satellite made by
+Horrebow on January 3, 1768, was undoubtedly &#952; Libr&aelig;. M.
+Stroobant found that the supposed motion of the &#8220;satellite&#8221; as seen by
+Horrebow is accurately represented by the motion of Venus itself during
+the time of observation. In most of the other supposed observations of a
+satellite a satisfactory identification has also been found. M. Stroobant
+finds that with a telescope of 6 inches aperture, a star of the 8th or
+even the 9th magnitude can be well seen when close to Venus.<a name='fna_49' id='fna_49' href='#f_49'><small>[49]</small></a></p>
+
+<p>On the night of August 13, 1892, Professor Barnard, while examining Venus
+with the great 36-inch telescope of the Lick Observatory, saw a star of
+the 7th magnitude in the same field with the planet. He carefully
+determined the exact position of this star, and found that it is not in
+Argelander&#8217;s great catalogue, the <i>Durchmusterung</i>. Prof. Barnard finds
+that owing to elongation of Venus from the sun at the time of observation
+the star could not possibly be an intra-Mercurial planet (that is, a
+planet revolving round the sun inside the orbit of Mercury); but that
+possibly it might be a planet revolving between the orbits of Venus and
+Mercury. As the brightest of the minor planets&mdash;Ceres, Pallas, Juno, and
+Vesta&mdash;were not at the time near the position of the observed object, the
+observation<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> remains unexplained. It might possibly have been a <i>nova</i>, or
+temporary star.<a name='fna_50' id='fna_50' href='#f_50'><small>[50]</small></a></p>
+
+<p>Scheuten is said to have seen a supposed satellite of Venus following the
+planet across the sun at the end of the transit of June 6, 1761.<a name='fna_51' id='fna_51' href='#f_51'><small>[51]</small></a></p>
+
+<p>Humboldt speaks of the supposed satellite of Venus as among &#8220;the
+astronomical myths of an uncritical age.&#8221;<a name='fna_52' id='fna_52' href='#f_52'><small>[52]</small></a></p>
+
+<p>An occultation of Venus by the moon is mentioned in the Chinese Annals as
+having occurred on March 19, 361 <span class="smcaplc">A.D.</span>, and Tycho Brah&eacute; observed another on
+May 23, 1587.<a name='fna_53' id='fna_53' href='#f_53'><small>[53]</small></a></p>
+
+<p>A close conjunction of Venus and Regulus (&#945; Leonis) is recorded
+by the Arabian astronomer, Ibn Yunis, as having occurred on September 9,
+885 <span class="smcaplc">A.D.</span> Calculations by Hind show that the planet and star were within 2&prime;
+of arc on that night, and consequently would have appeared as a single
+star to the naked eye. The telescope had not then been invented.<a name='fna_54' id='fna_54' href='#f_54'><small>[54]</small></a></p>
+
+<p>Seen from Venus, the maximum apparent distance between the earth and moon
+would vary from about 5&prime; to 31&prime;.<a name='fna_55' id='fna_55' href='#f_55'><small>[55]</small></a></p>
+
+<p>It is related by Arago that Buonaparte, when going to the Luxembourg in
+Paris, where the<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> Directory were giving a f&ecirc;te in his honour, was very
+much surprised to find the crowd assembled in the Rue de Touracour &#8220;pay
+more attention to a region of the heavens situated above the palace than
+to his person or the brilliant staff that accompanied him. He inquired the
+cause and learned that these curious persons were observing with
+astonishment, although it was noon, a star, which they supposed to be that
+of the conqueror of Italy&mdash;an allusion to which the illustrious general
+did not seem indifferent, when he himself, with his piercing eyes,
+remarked the radiant body.&#8221; The &#8220;star&#8221; in question was Venus.<a name='fna_56' id='fna_56' href='#f_56'><small>[56]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span></p>
+<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV</h2>
+<p class="title">The Earth</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">The</span> earth being our place of abode is, of course, to us the most important
+planet in the solar system. It is a curious paradox that the moon&#8217;s
+surface (at least the visible portion) is better known to us than the
+surface of the earth. Every spot on the moon&#8217;s visible surface equal in
+size to say Liverpool or Glasgow is well known to lunar observers, whereas
+there are thousands of square miles on the earth&#8217;s surface&mdash;for example,
+near the poles and in the centre of Australia&mdash;which are wholly unknown to
+the earth&#8217;s inhabitants; and are perhaps likely to remain so.</p>
+
+<p>Many attempts have been made by &#8220;paradoxers&#8221; to show that the earth is a
+flat plane and not a sphere. But M. Ricco has found by actual experiment
+that the reflected image of the setting sun from a smooth sea is an
+elongated ellipse. This proves mathematically beyond all doubt that the
+surface of the sea is spherical; for the reflection from a plane surface
+would be<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> necessarily <i>circular</i>. The theory of a &#8220;flat earth&#8221; is
+therefore proved to be quite untenable, and all the arguments (?) of the
+&#8220;earth flatteners&#8221; have now been&mdash;like the French Revolution&mdash;&#8220;blown into
+space.&#8221;</p>
+
+<p>The pole of minimum temperature in the northern hemisphere, or &#8220;the pole
+of cold,&#8221; as it has been termed, is supposed to lie near Werchojansk in
+Siberia, where a temperature of nearly -70&deg; has been observed.</p>
+
+<p>From a series of observations made at Annapolis (U.S.A.) on the gradual
+disappearance of the blue of the sky after sunset, Dr. See finds that the
+extreme height of the earth&#8217;s atmosphere is about 130 miles. Prof. Newcomb
+finds that meteors first appear at a mean height of about 74 miles.<a name='fna_57' id='fna_57' href='#f_57'><small>[57]</small></a></p>
+
+<p>An aurora seen in Canada on July 15, 1893, was observed from stations 110
+miles apart, and from these observations the aurora was found to lie at a
+height of 166 miles above the earth&#8217;s surface. It was computed that if the
+auroral &#8220;arch maintained an equal height above the earth its ends were
+1150 miles away, so that the magnificent sight was presented of an auroral
+belt in the sky with 2300 miles between its two extremities.&#8221;<a name='fna_58' id='fna_58' href='#f_58'><small>[58]</small></a></p>
+
+<p>&#8220;Luminous clouds&#8221; are bright clouds sometimes seen at night near the end
+of June and beginning<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> of July. They appear above the northern horizon
+over the sun&#8217;s place about midnight, and evidently lie at a great height
+above the earth&#8217;s surface. Observations made in Germany by Dr. Jesse, and
+in England by Mr. Backhouse, in the years 1885-91, show that the height of
+these clouds is nearly constant at about 51 miles.<a name='fna_59' id='fna_59' href='#f_59'><small>[59]</small></a> The present writer
+has seen these remarkable clouds on one or two occasions in County Sligo,
+Ireland, during the period above mentioned.</p>
+
+<p>M. Montigny has shown that &#8220;the approach of violent cyclones or other
+storms is heralded by an increase of scintillation&#8221; (or twinkling of the
+stars). The effect is also very evident when such storms pass at a
+considerable distance. He has also made some interesting observations
+(especially on the star Capella), which show that, not only does
+scintillation increase in rainy weather, but that &#8220;it is very evident, at
+such times, in stars situated at an altitude at which on other occasions
+it would not be perceptible at all; thus confirming the remark of
+Humboldt&#8217;s with regard to the advent of the wet season in tropical
+countries.&#8221;<a name='fna_60' id='fna_60' href='#f_60'><small>[60]</small></a></p>
+
+<p>In a paper on the subject of &#8220;Optical Illusions&#8221; in <i>Popular Astronomy</i>,
+February, 1906, Mr.<span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span> Arthur K. Bartlett, of Batter Creek, Michigan
+(U.S.A.), makes the following interesting remarks:&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The lunar halo which by many persons is regarded as a remarkable and
+unexplained luminosity associated with the moon, is to meteorological
+students neither a mysterious nor an anomalous occurrence. It has been
+frequently observed and for many years thoroughly understood, and at
+the present time admits of an easy scientific explanation. It is an
+atmospheric exhibition due to the refraction and dispersion of the
+moon&#8217;s light through very minute ice crystals floating at great
+elevations above the earth, and it is explained by the science of
+meteorology, to which it properly belongs; for it is not of cosmical
+origin, and in no way pertains to astronomy, as most persons suppose,
+except as it depends on the moon, whose light passing through the
+atmosphere, produces the luminous halo, which as will be seen, is
+simply an optical illusion, originating, not in the vicinity of the
+moon&mdash;two hundred and forty thousand miles away&mdash;but just above the
+earth&#8217;s surface, and within the aqueous envelope that surrounds it on
+all sides.... A halo may form round the sun as well as the moon ...
+but a halo is more frequently noticed round the moon for the reason
+that we are too much dazzled by the sun&#8217;s light to distinguish faint
+colours surrounding its disc, and to see them it is necessary to look
+through smoked glass, or view the sun by reflection from the surface
+of still water, by which its brilliancy is very much reduced.&#8221;...</p></div>
+
+<p>&#8220;A &#8216;corona&#8217; is an appearance of faintly coloured rings often seen around
+the sun and moon when<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span> a light fleecy cloud passes over them, and should
+not be mistaken for a halo, which is much larger and more complicated in
+its structure. These two phenomena are frequently confounded by
+inexperienced observers.&#8221; With these remarks the present writer fully
+concurs.</p>
+
+<p>Mr. Bartlett adds&mdash;</p>
+
+<div class="blockquot"><p>&#8220;As a halo is never seen except when the sky is hazy, it indicates
+that moisture is accumulating in the atmosphere which will form
+clouds, and usually result in a storm. But the popular notion that the
+number of bright stars visible within the circle indicates the number
+of days before the storm will occur, is without any foundation
+whatever, and the belief is almost too absurd to be refuted. In
+whatever part of the sky a lunar halo is seen, one or more bright
+stars are always sure to be noticed inside the luminous ring, and the
+number visible depends entirely upon the position of the moon.
+Moreover, when the sky within the circle is examined with even a small
+telescope, hundreds of stars are visible where only one, or perhaps
+two or three, are perceived with the naked eye.&#8221;</p></div>
+
+<p>It is possible to have five Sundays in February (the year must of course
+be a &#8220;leap year&#8221;). This occurred in the year 1880, Sunday falling on
+February 1, 8, 15, 22, and 29. But this will not happen again till the
+year 1920. No century year (such as 1900, 2000, etc.) could possibly have
+five Sundays in February, and the Rev. Richard Campbell, who investigated
+this matter, finds<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span> the following sequence of years in which five Sundays
+occur in February: 1604, 1632, 1660, 1688, 1728, 1756, 1784, 1824, 1852,
+1880, 1920, 1948, 1976.<a name='fna_61' id='fna_61' href='#f_61'><small>[61]</small></a></p>
+
+<p>In an article on &#8220;The Last Day and Year of the Century: Remarks on Time
+Reckoning,&#8221; in <i>Nature</i>, September 10, 1896, Mr. W. T. Lynn, the eminent
+astronomer, says, &#8220;The late Astronomer Royal, Sir George Airy, once
+received a letter requesting him to settle a dispute which had arisen in
+some local debating society, as to which would be the first day of the
+next century. His reply was, &#8216;A very little consideration will suffice to
+show that the first day of the twentieth century will be January 1, 1901.&#8217;
+Simple as the matter seems, the fact that it is occasionally brought into
+question shows that there is some little difficulty connected with it.
+Probably, however, this is in a great measure due to the circumstance that
+the actual figures are changed on January 1, 1900, the day preceding being
+December 31, 1899. A century is a very definite word for an interval
+respecting which there is no possible room for mistake or difference of
+opinion. But the date of its ending depends upon that of its beginning.
+Our double system of backward and forward reckoning leads to a good deal
+of inconvenience. Our reckoning supposes (what we know was not the case,
+but as an era the date<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> does equally well) that Christ was born at the end
+of <span class="smcaplc">B.C.</span> 1. At the end of <span class="smcaplc">A.D.</span> 1, therefore, one year had elapsed from the
+event, at the end of <span class="smcaplc">A.D.</span> 100, one century, and at the end of 1900,
+nineteen centuries.... It is clear, then, that the year, as we call it, is
+an ordinal number, and that 1900 years from the birth of Christ (reckoning
+as we do from <span class="smcaplc">B.C.</span> 1) will not be completed until the end of December 31
+in that year, the twentieth century beginning with January 1, 1901, that
+is (to be exact) at the previous midnight, when the day commences by civil
+reckoning.&#8221; With these remarks of Mr. Lynn I fully concur, and, so far as
+I know, all astronomers agree with him. As the discussion will probably
+again arise at the end of the twentieth century, I would like to put on
+record here what the scientific opinion was at the close of the nineteenth
+century.</p>
+
+<p>Prof. E. Rutherford, the well-known authority on radium, suggests that
+possibly radium is a source of heat from within the earth. Traces of
+radium have been detected in many rocks and soils, and even in sea water.
+Calculation shows that the total amount distributed through the earth&#8217;s
+crust is enormously large, although relatively small &#8220;compared with the
+annual output of coal for the world.&#8221; The amount of radium necessary to
+compensate for the present loss of heat from the earth &#8220;corresponds to
+only five parts in one hundred million<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span> millions per unit mass,&#8221; and the
+&#8220;observations of Elster and Gertel show that the radio-activity observed
+in soils corresponds to the presence of about this proportion of
+radium.&#8221;<a name='fna_62' id='fna_62' href='#f_62'><small>[62]</small></a></p>
+
+<p>The earth has 12 different motions. These are as follows:&mdash;</p>
+
+<p>1. Rotation on its axis, having a period of 24 hours.</p>
+
+<p>2. Revolution round the sun; period 365&#188; days.</p>
+
+<p>3. Precession; period of about 25,765 years.</p>
+
+<p>4. Semi-lunar gravitation; period 28 days.</p>
+
+<p>5. Nutation; period 18&#189; years.</p>
+
+<p>6. Variation in obliquity of the ecliptic; about 47&Prime; in 100 years.</p>
+
+<p>7. Variation of eccentricity of orbit.</p>
+
+<p>8. Change of line of apsides; period about 21,000 years.</p>
+
+<p>9. Planetary perturbations.</p>
+
+<p>10. Change of centre of gravity of whole solar system.</p>
+
+<p>11. General motion of solar system in space.</p>
+
+<p>12. Variation of latitude with several degrees of periodicity.<a name='fna_63' id='fna_63' href='#f_63'><small>[63]</small></a></p>
+
+<div class="blockquot"><p>&#8220;An amusing story has been told which affords a good illustration of
+the ignorance and popular notions regarding the tides prevailing even
+among persons of average intelligence. &#8216;Tell me,&#8217; said a man to an
+eminent living English<span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span> astronomer not long ago, &#8216;is it still
+considered probable that the tides are caused by the moon?&#8217; The man of
+science replied that to the best of his belief it was, and then asked
+in turn whether the inquirer had any serious reason for questioning
+the relationship. &#8216;Well, I don&#8217;t know,&#8217; was the answer; &#8216;sometimes
+when there is no moon there seems to be a tide all the same.&#8217;&#8221;!<a name='fna_64' id='fna_64' href='#f_64'><small>[64]</small></a></p></div>
+
+<p>With reference to the force of gravitation, on the earth and other bodies
+in the universe, Mr. William B. Taylor has well said, &#8220;With each revolving
+year new demonstrations of its absolute precision and of its universal
+domination serves only to fill the mind with added wonder and with added
+confidence in the stability and the supremacy of the power in which has
+been found no variableness neither shadow of turning, but which&mdash;the same
+yesterday, to-day and for ever&mdash;</p>
+
+<p class="poem">&#8220;Lives through all life, extends through all extent,<br />
+Spreads undivided, operates unspent.&#8221;<a name='fna_65' id='fna_65' href='#f_65'><small>[65]</small></a></p>
+
+<p>With reference to the habitability of other planets, Tennyson has
+beautifully said&mdash;</p>
+
+<p class="poem">&#8220;Venus near her! smiling downwards at this earthlier earth of ours,<br />
+Closer on the sun, perhaps a world of never fading flowers.<br />
+Hesper, whom the poets call&#8217;d the Bringer home of all good things;<br />
+<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span>All good things may move in Hesper; perfect people, perfect kings.<br />
+Hesper&mdash;Venus&mdash;were we native to that splendour, or in Mars,<br />
+We should see the globe we groan in fairest of their evening stars.<br />
+Could we dream of war and carnage, craft and madness, lust and spite,<br />
+Roaring London, raving Paris, in that spot of peaceful light?<br />
+Might we not in glancing heavenward on a star so silver fair,<br />
+Yearn and clasp the hands, and murmur, &#8216;Would to God that we were there!&#8217;&#8221;</p>
+
+<p>The ancient Greek writer, Diogenes Laertius, states that Anaximander
+(610-547 <span class="smcaplc">B.C.</span>) believed that the earth was a sphere. The Greek words are:
+&#956;&#8055;&#963;&#951;&#957; &#964;&#949; &#964;&#8052;&#957; &#947;&#8053;&#957; &#954;&#949;&#8150;&#963;&#952;&#945;&#953;,
+&#954;&#8051;&#957;&#964;&#961;&#965; &#964;&#8049;&#958;&#953;&#957; &#7952;&#960;&#949;&#967;&#959;&#8166;&#963;&#945;&#957;
+&#959;&#8016;&#963;&#945;&#957; &#963;&#966;&#945;&#953;&#961;&#959;&#949;&#953;&#948;&#8134;.<a name='fna_66' id='fna_66' href='#f_66'><small>[66]</small></a></p>
+
+<p>With reference to the Aurora Borealis, the exact nature of which is not
+accurately known, &#8220;a good story used to be told some years ago of a
+candidate who, undergoing the torture of a <i>viv&acirc; voce</i> examination, was
+unable to reply satisfactorily to any of the questions asked. &#8216;Come, sir,&#8217;
+said the examiner, with the air of a man asking the simplest question,
+&#8216;explain to me the cause of the aurora borealis.&#8217; &#8216;Sir,&#8217; said the unhappy
+aspirant for physical honours, &#8216;I could have explained it perfectly
+yesterday, but nervousness has, I think, made me lose my memory.&#8217; &#8216;This is
+very unfortunate,&#8217; said the examiner; &#8216;you are the only man who could have
+explained this mystery, and you have forgotten it.&#8217;&#8221;<a name='fna_67' id='fna_67' href='#f_67'><small>[67]</small></a> This was written
+in the year 1899, and probably the<span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span> phenomenon of the aurora remains
+nearly as great a mystery to-day. In 1839, MM. Bravais and Lottin made
+observations on the aurora in Norway in about N. latitude 70&deg;. Bravais
+found the height to be between 62 and 93 miles above the earth&#8217;s surface.</p>
+
+<p>The cause of the so-called Glacial Epoch in the earth&#8217;s history has been
+much discussed. The Russian physicist, Rogovsky, has advanced the
+following theory&mdash;</p>
+
+<div class="blockquot"><p>&#8220;If we suppose that the temperature of the sun at the present time is
+still increasing, or at least has been increasing until now, the
+glacial epoch can be easily accounted for. Formerly the earth had a
+high temperature of its own, but received a lesser quantity of heat
+from the sun than now; on cooling gradually, the earth&#8217;s surface
+attained such a temperature as caused a great part of the surface of
+the northern and southern hemispheres to be covered with ice; but the
+sun&#8217;s radiation increasing, the glaciers melted, and the climatic
+conditions became as they are now. In a word, the temperature of the
+earth&#8217;s surface is a function of two quantities: one decreasing (the
+earth&#8217;s own heat), and the other increasing (the sun&#8217;s radiation), and
+consequently there may be a minimum, and this minimum was the glacial
+epoch, which, as shown by recent investigations, those of Luigi de
+Marchi (Report of <i>G. Schiaparelli, Meteorolog. Zeitschr.</i>, 30,
+130-136, 1895), are not local, but general for the whole earth&#8221; (see
+also M. Neumahr, <i>Erdegeschicht</i>).<a name='fna_68' id='fna_68' href='#f_68'><small>[68]</small></a></p></div>
+
+<p><span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span>Prof. Percival Lowell thinks that the life of geological pal&aelig;ozoic times
+was supported by the earth&#8217;s internal heat, which maintained the ocean at
+a comparatively warm temperature.<a name='fna_69' id='fna_69' href='#f_69'><small>[69]</small></a></p>
+
+<p>The following passage in the Book of the Maccabees may possibly refer to
+an aurora&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Now about this time Antiochus made his second inroad into Egypt. And
+it <i>so</i> befell that throughout all the city, for the space of almost
+forty days, there appeared in the midst of the sky horsemen in swift
+motion, wearing robes inwrought with gold and <i>carrying</i> spears,
+equipped in troops for battle; and drawing of swords; and <i>on the
+other side</i> squadrons of horse in array; and encounters and pursuits
+of both armies; and shaking of shields, and multitudes of lances, and
+casting of darts, and flashing of golden trappings, and girding on of
+all sorts of armour. Wherefore all men besought that the vision might
+have been given for food.&#8221;<a name='fna_70' id='fna_70' href='#f_70'><small>[70]</small></a></p></div>
+
+<p>According to Laplace &#8220;the decrease of the mean heat of the earth during a
+period of 2000 years has not, taking the extremist limits, diminished as
+much as <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">300</span>th of a degree Fahrenheit.&#8221;<a name='fna_71' id='fna_71' href='#f_71'><small>[71]</small></a></p>
+
+<p>From his researches on the cause of the Precession of the Equinoxes,
+Laplace concluded that &#8220;the motion of the earth&#8217;s axis is the same as if
+the<span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span> whole sea formed a solid
+mass adhering to its surface.&#8221;<a name='fna_72' id='fna_72' href='#f_72'><small>[72]</small></a></p>
+
+<p>Laplace found that the major (or longer) axis of the earth&#8217;s orbit
+coincided with the line of Equinoxes in the year 4107 <span class="smcaplc">B.C.</span> The earth&#8217;s
+perigee then coincided with the autumnal equinox. The epoch at which the
+major axis was perpendicular to the line of equinoxes fell in the year
+1250 <span class="smcaplc">A.D.</span><a name='fna_73' id='fna_73' href='#f_73'><small>[73]</small></a></p>
+
+<p>Leverrier has found the minimum eccentricity of the earth&#8217;s orbit round
+the sun to be 0&middot;0047; so that the orbit will never become absolutely
+circular, as some have imagined.</p>
+
+<p>Laplace says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Astronomy considered in its entirety is the finest monument of the
+human mind, the noblest essay of its intelligence. Seduced by the
+illusions of the senses and of self-pride, for a long time man
+considered himself as the centre of the movement of the stars; his
+vain-glory has been punished by the terrors which his own ideas have
+inspired. At last the efforts of several centuries brushed aside the
+veil which concealed the system of the world. We discover ourselves
+upon a planet, itself almost imperceptible in the vast extent of the
+solar system, which in its turn is only an insensible point in the
+immensity of space. The sublime results to which this discovery has
+led should suffice to console us for our extreme littleness, and the
+rank which it assigns to the earth. Let us treasure with<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span> solicitude,
+let us add to as we may, this store of higher knowledge, the most
+exquisite treasure of thinking beings.&#8221;<a name='fna_74' id='fna_74' href='#f_74'><small>[74]</small></a></p></div>
+
+<p>With reference to probable future changes in climate, the great physicist,
+Arrhenius, says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;We often hear lamentation that the coal stored up in the earth is
+wasted by the present generation without any thought of the future,
+and we are terrified by the awful destruction of life and property
+which has followed the volcanic eruptions of our days. We may find a
+kind of consolation in the consideration that here, as in every other
+case, there is good mixed with evil. By the influence of the
+increasing percentage of carbonic acid in the atmosphere, we may hope
+to enjoy ages with more equable and better climates, especially as
+regards the colder regions of the earth, ages when the earth will
+bring forth much more abundant crops than at present, for the benefit
+of rapidly propagating mankind.&#8221;<a name='fna_75' id='fna_75' href='#f_75'><small>[75]</small></a></p></div>
+
+<p>The night of July 1, 1908, was unusually bright. This was noticed in
+various parts of England and Ireland, and by the present writer in Dublin.
+Humboldt states that &#8220;at the time of the new moon at midnight in 1743, the
+phosphorescence was so intense that objects could be distinctly recognized
+at a distance of more than 600 feet.&#8221;<a name='fna_76' id='fna_76' href='#f_76'><small>[76]</small></a></p>
+
+<p>An interesting proof of the earth&#8217;s rotation on its axis has recently been
+found.</p>
+
+<div class="blockquot"><p><span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span>&#8220;In a paper in the
+<i>Proceedings</i> of the Vienna Academy (June, 1908) by Herr Tumlirz, it is shown mathematically that if a liquid is flowing
+outwards between two horizontal discs, the lines of flow will be
+strictly straight only if the discs and vessel be at rest, and will
+assume certain curves if that vessel and the discs are in rotation,
+as, for example, due to the earth&#8217;s rotation. An experimental
+arrangement was set up with all precautions, and the stream lines were
+marked with coloured liquids and photographed. These were in general
+accord with the predictions of theory and the supposition that the
+earth is rotating about an axis.&#8221;<a name='fna_77' id='fna_77' href='#f_77'><small>[77]</small></a></p></div>
+
+<p>In a book published in 1905 entitled <i>The Rational Almanac</i>, by Moses B.
+Cotsworth, of York, the author states that (p. 397), &#8220;The explanation is
+apparent from the Great Pyramid&#8217;s Slope, which conclusively proves that
+when it was built the latitude of that region was 7&deg;&middot;1 more than at
+present. Egyptian Memphis now near Cairo was then in latitude 37&deg;&middot;1, where
+Asia Minor now ranges, whilst Syria would then be where the Caucasus
+regions now experience those rigorous winters formerly experienced in
+Syria.&#8221; But the reality of this comparatively great change of latitude in
+the position of the Great Pyramid can be easily disproved. Pytheas of
+Marseilles&mdash;who lived in the time of Alexander the Great, about 330
+<span class="smcaplc">B.C.</span>&mdash;measured the latitude of Marseilles by means of a gnomon, and found
+it to be about 42&deg; 56&prime;&#189;. As the present latitude of Marseilles is<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span> 43&deg;
+17&prime; 50&Prime;, no great change in the latitude could have taken place in over
+2000 years.<a name='fna_78' id='fna_78' href='#f_78'><small>[78]</small></a> From this we may conclude that the latitude of the Great
+Pyramid has <i>not</i> changed by 7&deg;&middot;1 since its construction. There is, it is
+true, a slow diminution going on in the obliquity of the ecliptic (or
+inclination of the earth&#8217;s axis), but modern observations show that this
+would not amount to as much as one degree in 6000 years. Eudemus of
+Rhodes&mdash;a disciple of Aristotle (who died in 322 <span class="smcaplc">B.C.</span>)&mdash;found the
+obliquity of the ecliptic to be 24&deg;, which differs but little from its
+present value, 23&deg; 27&prime;. Al-Sufi in the tenth century measured the latitude
+of Schiraz in Persia, and found it 29&deg; 36&prime;. Its present latitude is 29&deg;
+36&prime; 30&Prime;,<a name='fna_79' id='fna_79' href='#f_79'><small>[79]</small></a> so that evidently there has been no change in the latitude in
+900 years.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span></p>
+<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V</h2>
+<p class="title">The Moon</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">The</span> total area of the moon&#8217;s surface is about equal to that of North and
+South America. The actual surface visible at any one time is about equal
+to North America.</p>
+
+<p>The famous lunar observer, Schr&ouml;ter, thought that the moon had an
+atmosphere, but estimated its height at only a little over a mile. Its
+density he supposed to be less than that of the vacuum in an air-pump.
+Recent investigations, however, seem to show that owing to its small mass
+and attractive force the moon could not retain an atmosphere like that of
+the earth.</p>
+
+<p>Prof. N. S. Shaler, of Harvard (U.S.A.), finds from a study of the moon
+(from a geological point of view) with the 15-inch refractor of the
+Harvard Observatory, that our satellite has no atmosphere nor any form of
+organic life, and he believes that its surface &#8220;was brought to its present
+condition before the earth had even a solid crust.&#8221;<a name='fna_80' id='fna_80' href='#f_80'><small>[80]</small></a></p>
+
+<p>There is a curious illusion with reference to the<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span> moon&#8217;s apparent
+diameter referred to by Proctor.<a name='fna_81' id='fna_81' href='#f_81'><small>[81]</small></a> If, when the moon is absent in the
+winter months, we ask a person whether the moon&#8217;s diameter is greater or
+less than the distance between the stars &#948; and &#949;, and
+&#949; and &#950; Orionis, the three well-known stars in the &#8220;belt
+of Orion,&#8221; the answer will probably be that the moon&#8217;s apparent diameter
+is about equal to each of these distances. But in reality the apparent
+distance between &#948; and &#949; Orionis (or between &#949;
+and &#950;, which is about the same) is more than double the moon&#8217;s
+apparent diameter. This seems at first sight a startling statement; but
+its truth is, of course, beyond all doubt and is not open to argument.
+Proctor points out that if a person estimates the moon as a foot in
+diameter, as its apparent diameter is about half a degree, this would
+imply that the observer estimates the circumference of the star sphere as
+about 720 feet (360&deg; &times; 2), and hence the radius (or the moon&#8217;s distance
+from the earth) about 115 feet. But in reality all such estimates have no
+scientific (that is, accurate) meaning. Some of the ancients, such as
+Aristotle, Cicero, and Heraclitus, seem to have estimated the moon&#8217;s
+apparent diameter at about a foot.<a name='fna_82' id='fna_82' href='#f_82'><small>[82]</small></a> This shows that even great minds
+may make serious mistakes.</p>
+
+<p>It has been stated by some writer that the moon as seen with the highest
+powers of the great<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> Yerkes telescope (40 inches aperture) appears &#8220;just
+as it would be seen with the naked eye if it were suspended 60 miles over
+our heads.&#8221; But this statement is quite erroneous. The moon as seen with
+the naked eye or with a telescope shows us nearly a whole hemisphere of
+its surface. But if the eye were placed only 60 miles from the moon&#8217;s
+surface, we should see only a small portion of its surface. In fact, it is
+a curious paradox that the nearer the eye is to a sphere the less we see
+of its surface! The truth of this will be evident from the fact that on a
+level plain an eye placed at a height, say 5 feet, sees a very small
+portion indeed of the earth&#8217;s surface, and the higher we ascend the more
+of the surface we see. I find that at a distance of 60 miles from the
+moon&#8217;s surface we should only see a small portion of its visible
+hemisphere (about <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">90</span>th). The lunar features would also appear under a
+different aspect. The view would be more of a landscape than that seen in
+any telescope. This view of the matter is not new. It has been previously
+pointed out, especially by M. Flammarion and Mr. Whitmell, but its truth
+is not, I think, generally recognized. Prof. Newcomb doubts whether with
+any telescope the moon has ever been seen so well as it would be if
+brought within 500 miles of the earth.</p>
+
+<p>A relief map of the moon 19 feet in diameter was added, in 1898, to the
+Field Columbian<span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span> Museum (U.S.A.). It was prepared with great care from the
+lunar charts of Beer and M&auml;dler, and Dr. Schmidt of the Athens
+Observatory, and it shows the lunar features very accurately. Its
+construction took five years.</p>
+
+<p>On a photograph of a part of the moon&#8217;s surface near the crater
+Eratosthenes, Prof. William H. Pickering finds markings which very much
+resemble the so-called &#8220;canals&#8221; of Mars. The photograph was taken in
+Jamaica, and a copy of it is given in Prof. Pickering&#8217;s book on the Moon,
+and in <i>Popular Astronomy</i>, February, 1904.</p>
+
+<p>Experiments made in America by Messrs. Stebbins and F. C. Brown, by means
+of selenium cells, show that the light of the full moon is about nine
+times that of the half moon;<a name='fna_83' id='fna_83' href='#f_83'><small>[83]</small></a> and that &#8220;the moon is brighter between
+the first quarter and full than in the corresponding phase after full
+moon.&#8221; They also find that the light of the full moon is equal to &#8220;0&middot;23
+candle power,&#8221;<a href='#f_83'><small>[83]</small></a> that is, according to the method of measurement used in
+America, its light is equal to 0&middot;23 of a standard candle placed at a
+distance of one metre (39&middot;37 inches) from the eye.<a name='fna_84' id='fna_84' href='#f_84'><small>[84]</small></a></p>
+
+<p>Mr. H. H. Kimball finds that no less than 52 per cent. of the observed
+changes in intensity of the &#8220;earth-shine&#8221; visible on the moon when at or
+near the crescent phase is due to the eccentricity<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span> of the lunar orbit,
+and &#8220;this is probably much greater than could be expected from any
+increase or diminution in the average cloudiness over the hemisphere of
+the earth reflecting light to the moon.&#8221;<a name='fna_85' id='fna_85' href='#f_85'><small>[85]</small></a></p>
+
+<p>The &#8220;moon maiden&#8221; is a term applied to a fancied resemblance of a portion
+of the Sinus Iridum to a female head. It forms the &#8220;promontory&#8221; known as
+Cape Heraclides, and may be looked for when the moon&#8217;s &#8220;age&#8221; is about 11
+days. Mr. C. J. Caswell, who observed it on September 29, 1895, describes
+it as resembling &#8220;a beautiful silver statuette of a graceful female figure
+with flowing hair.&#8221;</p>
+
+<p>M. Landerer finds that the angle of polarization of the moon&#8217;s
+surface&mdash;about 33&deg;&mdash;agrees well with the polarizing angle for many
+specimens of igneous rocks (30&deg; 51&prime; to 33&deg; 46&prime;). The polarizing angle for
+ice is more than 37&deg;, and this fact is opposed to the theories of lunar
+glaciation advanced by some observers.<a name='fna_86' id='fna_86' href='#f_86'><small>[86]</small></a></p>
+
+<p>Kepler states in his <i>Somnium</i> that he saw the moon in the crescent phase
+on the morning and evening of the <i>same</i> day (that is, before and after
+conjunction with the sun). Kepler could see 14 stars in the Pleiades with
+the naked eye, so his eyesight must have been exceptionally keen.</p>
+
+<p>Investigations on ancient eclipses of the moon show that the eclipse
+mentioned by Josephus as<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> having occurred before the death of Herod is
+probably that which took place on September 15, <span class="smcaplc">B.C.</span> 5. This occurred
+about 9.45 p.m.; and probably about six months before the death of Herod
+(St. Matthew ii. 15).</p>
+
+<p>The total lunar eclipse which occurred on October 4, 1884, was remarkable
+for the almost total disappearance of the moon during totality. One
+observer says that &#8220;in the open air, if one had not known exactly where to
+look for it, one might have searched for some time without discovering it.
+I speak of course of the naked eye appearance.&#8221;<a name='fna_87' id='fna_87' href='#f_87'><small>[87]</small></a> On the other hand the
+same observer, speaking of the total eclipse of the moon on August 23,
+1877, which was a bright one, says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The moon even in the middle of the total phase was a conspicuous
+object in the sky, and the ruddy colour was well marked. In the very
+middle of the eclipse the degree of illumination was as nearly as
+possible equal all round the edge of the moon, the central parts being
+darker than those near the edge.&#8221;</p></div>
+
+<p>In Roger de Hovedin&#8217;s <i>Chronicle</i> (<span class="smcaplc">A.D.</span> 756) an account is given of the
+occultation of &#8220;a bright star,&#8221; by the moon during a total eclipse. This
+is confirmed by Simeon of Durham, who also dates the eclipse <span class="smcaplc">A.D.</span> 756.
+This is, however, a mistake, the eclipse having occurred on the evening of
+November 23, <span class="smcaplc">A.D.</span> 755. Calvisius supposed that
+<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> the occulted &#8220;star&#8221; might
+have been Aldebaran. Pingr&eacute;, however, showed that this was impossible, and
+Struyck, in 1740, showed that the planet Jupiter was the &#8220;star&#8221; referred
+to by the early observer. Further calculations by Hind (1885) show
+conclusively that Struyck was quite correct, and that the phenomenon
+described in the old chronicles was the occultation of Jupiter by a
+totally eclipsed moon&mdash;a rather unique phenomenon.<a name='fna_88' id='fna_88' href='#f_88'><small>[88]</small></a></p>
+
+<p>An occultation of Mars by the moon is recorded by the Chinese, on February
+14, <span class="smcaplc">B.C.</span> 69, and one of Venus, on March 30, <span class="smcaplc">A.D.</span> 361. These have also been
+verified by Hind, and his calculations show the accuracy of these old
+Chinese records.</p>
+
+<p>It has been suggested that the moon may possibly have a satellite
+revolving round it, as the moon itself revolves round the earth. This
+would, of course, form an object of great interest. During the total lunar
+eclipses of March 10 and September 3, 1895, a careful photographic search
+was made by Prof. Barnard for a possible lunar satellite. The eclipse of
+March 10 was not very suitable for the purpose owing to a hazy sky, but
+that of September 3 was &#8220;entirely satisfactory,&#8221; as the sky was very
+clear, and the duration of totality was very long. On the latter occasion
+&#8220;six splendid&#8221; photographs were obtained of the total phase with a 6-inch
+Willard lens. The result<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> was that none of these photographs &#8220;show
+anything which might be taken for a lunar satellite,&#8221; at least any
+satellite as bright as the 10th or 12th magnitude. It is, of course, just
+possible that the supposed satellite might have been behind the moon
+during the totality.</p>
+
+<p>With reference to the attraction between the earth and moon, Sir Oliver
+Lodge says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The force with which the moon is held in its orbit would be great
+enough to tear asunder a steel rod 400 miles thick, with a tenacity of
+30 tons to the square inch, so that if the moon and earth were
+connected by steel instead of gravity, a forest of pillars would be
+necessary to whirl the system once a month round their common centre
+of gravity. Such a force necessarily implies enormous tensure or
+pressure in the medium. Maxwell calculates that the gravitational
+stress near the earth, which we must suppose to exist in the invisible
+medium, is 3000 times greater than what the strongest steel can stand,
+and near the sun it should be 2500 times as great as that.&#8221;<a name='fna_89' id='fna_89' href='#f_89'><small>[89]</small></a></p></div>
+
+<p>With reference to the names given to &#8220;craters&#8221; on the moon, Prof. W. H.
+Pickering says,<a name='fna_90' id='fna_90' href='#f_90'><small>[90]</small></a> &#8220;The system of nomenclature is, I think, unfortunate.
+The names of the chief craters are generally those of men who have done
+little or nothing for selenography, or even for astronomy, while the men
+who should be really commemorated are<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span> represented in general by small and
+unimportant craters,&#8221; and again&mdash;</p>
+
+<div class="blockquot"><p>&#8220;A serious objection to the whole system of nomenclature lies in the
+fact that it has apparently been used by some selenographers, from the
+earliest times up to the present, as a means of satisfying their spite
+against some of their contemporaries. Under the guise of pretending to
+honour them by placing their names in perpetuity upon the moon, they
+have used their names merely to designate the smallest objects that
+their telescopes were capable of showing. An interesting illustration
+of this point is found in the craters of Galileo and Riccioli, which
+lie close together on the moon. It will be remembered that Galileo was
+the discoverer of the craters on the moon. Both names were given by
+Riccioli, and the relative size and importance of the craters
+[Riccioli large, and Galileo very small] probably indicates to us the
+relative importance that he assigned to the two men themselves. Other
+examples might be quoted of craters named in the same spirit after men
+still living.... With the exception of Maedler, one might almost say,
+the more prominent the selenographer the more insignificant the
+crater.&#8221;</p></div>
+
+<p>The mathematical treatment of the lunar theory is a problem of great
+difficulty. The famous mathematician, Euler, described it as <i>incredibile
+stadium atque indefessus labor</i>.<a name='fna_91' id='fna_91' href='#f_91'><small>[91]</small></a></p>
+
+<p>With reference to the &#8220;earth-shine&#8221; on the moon when in the crescent
+phase, Humboldt says, &#8220;Lambert made the remarkable observation<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span> (14th of
+February, 1774) of a change of the ash-coloured moonlight into an
+olive-green colour, bordering upon yellow. The moon, which then stood
+vertically over the Atlantic Ocean, received upon its night side the green
+terrestrial light, which is reflected towards her when the sky is clear by
+the forest districts of South America.&#8221;<a name='fna_92' id='fna_92' href='#f_92'><small>[92]</small></a> Arago said, &#8220;Il n&#8217;est donc pas
+impossible, malgr&eacute; tout ce qu&#8217;un pareil r&eacute;sultat exciterait de surprise au
+premier coup d&#8217;&oelig;il qu&#8217;un jour les m&eacute;t&eacute;orologistes aillent puiser dans
+l&#8217;aspect de la Lune des notions pr&eacute;cieuses sur <i>l&#8217;etat moyen</i> de
+diaphanit&eacute; de l&#8217;atmosph&egrave;re terrestre, dans les hemisph&egrave;res qui
+successivement concurrent &agrave; la production de la lumi&egrave;re cendr&eacute;e.&#8221;<a name='fna_93' id='fna_93' href='#f_93'><small>[93]</small></a></p>
+
+<p>The &#8220;earth-shine&#8221; on the new moon was successfully photographed in
+February, 1895, by Prof. Barnard at the Lick Observatory, with a 6-inch
+Willard portrait lens. He says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The earth-lit globe stands out beautifully round, encircled by the
+slender crescent. All the &#8216;seas&#8217; are conspicuously visible, as are
+also the other prominent features, especially the region about
+<i>Tycho</i>. <i>Aristarchus</i> and <i>Copernicus</i> appear as bright specks, and
+the light streams from <i>Tycho</i> are very distinct.&#8221;<a name='fna_94' id='fna_94' href='#f_94'><small>[94]</small></a></p></div>
+
+<p>Kepler found that the moon completely disappeared during the total eclipse
+of December 9,<span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span> 1601, and Hevelius observed the same phenomenon during the
+eclipse of April 25, 1642, when &#8220;not a vestige of the moon could be
+seen.&#8221;<a name='fna_95' id='fna_95' href='#f_95'><small>[95]</small></a> In the total lunar eclipse of June 10, 1816, the moon during
+totality was not visible in London, even with a telescope!<a href='#f_95'><small>[95]</small></a></p>
+
+<p>The lunar mountains are <i>relatively</i> much higher than those on the earth.
+Beer and M&auml;dler found the following heights: D&ouml;rfel, 23,174 feet; Newton,
+22,141; Casatus, 21,102; Curtius, 20,632; Callippus, 18,946; and Tycho,
+18,748 feet.<a name='fna_96' id='fna_96' href='#f_96'><small>[96]</small></a></p>
+
+<p>Taking the earth&#8217;s diameter at 7912 miles, the moon&#8217;s diameter, 2163
+miles, and the height of Mount Everest as 29,000 feet, I find that</p>
+
+<table border="0" cellpadding="0" cellspacing="0" summary="table">
+<tr><td align="center" class="botbor">Everest</td>
+    <td rowspan="2" align="center">&nbsp; = &nbsp;</td>
+    <td align="center" class="botbor">1</td>
+    <td rowspan="2" align="center"> , and &nbsp;</td>
+    <td align="center" class="botbor">D&ouml;rfel</td>
+    <td rowspan="2" align="center">&nbsp; = &nbsp;</td>
+    <td align="center" class="botbor">1</td></tr>
+<tr><td align="center">Earth&#8217;s diameter</td>
+    <td align="center">1440</td>
+    <td align="center">moon&#8217;s diameter</td>
+    <td align="center">492</td></tr></table>
+
+<p>From which it follows that the lunar mountains are <i>proportionately</i> about
+three times higher than those on the earth.</p>
+
+<p>According to an hypothesis recently advanced by Dr. See, all the
+satellites of the solar system, including our moon, were &#8220;captured&#8221; by
+their primaries. He thinks, therefore, that the &#8220;moon came to earth from
+heavenly space.&#8221;<a name='fna_97' id='fna_97' href='#f_97'><small>[97]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span></p>
+<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI</h2>
+<p class="title">Mars</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Mars</span> was called by the ancients &#8220;the vanishing star,&#8221; owing to the long
+periods during which it is practically invisible from the earth.<a name='fna_98' id='fna_98' href='#f_98'><small>[98]</small></a> It
+was also called &#960;&#965;&#961;&#8057;&#949;&#953;&#962; and Hercules.</p>
+
+<p>I have seen it stated in a book on the &#8220;Solar System&#8221; by a well-known
+astronomer that the <i>axis</i> of Mars &#8220;is inclined to the plane of the orbit&#8221;
+at an angle of 24&deg; 50&prime;! But this is quite erroneous. The angle given is
+the angle between <i>the plane of the planet&#8217;s equator</i> and the plane of its
+orbit, which is quite a different thing. This angle, which may be called
+the obliquity of Mars&#8217; ecliptic, does not differ much from that of the
+earth. Lowell finds it 23&deg; 13&prime; from observations in 1907.<a name='fna_99' id='fna_99' href='#f_99'><small>[99]</small></a></p>
+
+<p>The late Mr. Proctor thought that Mars is &#8220;far the reddest star in the
+heavens; Aldebaran and Antares are pale beside him.&#8221;<a name='fna_100' id='fna_100' href='#f_100'><small>[100]</small></a> But this does
+not<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> agree with my experience. Antares is to my eye quite as red as Mars.
+Its name is derived from two Greek words implying &#8220;redder than Mars.&#8221; The
+colour of Aldebaran is, I think, quite comparable with that of the &#8220;ruddy
+planet.&#8221; In the telescope the colour of Mars is, I believe, more yellow
+than red, but I have not seen the planet very often in a telescope. Sir
+John Herschel suggested that the reddish colour of Mars may possibly be
+due to red rocks, like those of the Old Red Sandstone, and the red soil
+often associated with such rocks, as I have myself noticed near Torquay
+and other places in Devonshire.</p>
+
+<p>The ruddy colour of Mars was formerly thought to be due to the great
+density of its atmosphere. But modern observations seem to show that the
+planet&#8217;s atmosphere is, on the contrary, much rarer than that of the
+earth. The persistent visibility of the markings on its surface shows that
+its atmosphere cannot be cloud-laden like ours; and the spectroscope shows
+that the water vapour present is&mdash;although perceptible&mdash;less than that of
+our terrestrial envelope.</p>
+
+<p>The existence of water vapour is clearly shown by photographs of the
+planet&#8217;s spectrum taken by Mr. Slipher at the Lowell Observatory in 1908.
+These show that the water vapour bands <i>a</i> and near D are stronger in the
+spectrum of Mars than in that of the moon at the same altitude.<a name='fna_101' id='fna_101' href='#f_101'><small>[101]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span>The dark markings on Mars were formerly supposed to represent water and
+the light parts land. But this idea has now been abandoned. Light
+reflected from a water surface is polarized at certain angles. Prof. W. H.
+Pickering, in his observations on Mars, finds no trace of polarization in
+the light reflected from the dark parts of the planet. But under the same
+conditions he finds that the bluish-black ring surrounding the white polar
+cap shows a well-marked polarization of light, thus indicating that this
+dark ring is probably water.<a name='fna_102' id='fna_102' href='#f_102'><small>[102]</small></a></p>
+
+<p>Projections on the limb of the planet have frequently been observed in
+America. These are known <i>not</i> to be mountains, as they do not reappear
+under similar conditions. They are supposed to be clouds, and one seen in
+December, 1900, has been explained as a cloud lying at a height of some 13
+miles above the planet&#8217;s surface and drifting at the rate of about 27
+miles an hour. If there are any mountains on Mars they have not yet been
+discovered.</p>
+
+<p>The existence of the so-called &#8220;canals&#8221; of Mars is supposed to be
+confirmed by Lowell&#8217;s photographs of the planet. But what these &#8220;canals&#8221;
+really represent, that is the question. They have certainly an artificial
+look about them, and they form one of the most curious and interesting
+problems in the heavens. Prof. Lowell says&mdash;</p>
+
+<div class="blockquot"><p><span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span>&#8220;Most suggestive of all Martian phenomena are the canals. Were they
+more generally observable the world would have been spared much
+scepticism and more theory. They may of course not be artificial, but
+observations here [Flagstaff] indicate that they are; as will, I
+think, appear from the drawings. For it is one thing to see two or
+three canals and quite another to have the planet&#8217;s disc mapped with
+them on a most elaborate system of triangulation. In the first place
+they are this season (August, 1894) bluish-green, of the same colour
+as the seas into which the longer ones all eventually debouch. In the
+next place they are almost without exception geodetically straight,
+supernaturally so, and this in spite of their leading in every
+possible direction. Then they are of apparently nearly uniform width
+throughout their length. What they are is another matter. Their mere
+aspect, however, is enough to cause all theories about glaciation
+fissures or surface cracks to die an instant and natural death.&#8221;<a name='fna_103' id='fna_103' href='#f_103'><small>[103]</small></a></p></div>
+
+<p>Some of the observed colour-changes on Mars are very curious. In April,
+1905, Mr. Lowell observed that the marking known as Mare Erythr&aelig;um, just
+above Syrtis, had &#8220;changed from a blue-green to a chocolate-brown colour.&#8221;
+The season on Mars corresponded with our February.</p>
+
+<p>Signor V. Cerulli says that, having observed Mars regularly for ten years,
+he has come to the conclusion that the actual existence of the &#8220;canals&#8221; is
+as much a subject for physiological<span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span> as for astronomical investigation. He
+states that &#8220;the phenomena observed are so near the limit of the range of
+the human eye that in observing them one really experiences an effect
+accompanying the &#8216;birth of vision.&#8217; That is to say, the eye sees more and
+more as it becomes accustomed, or strained, to the delicate markings, and
+thus the joining up of spots to form &#8216;canals&#8217; and the gemination of the
+latter follow as a physiological effect, and need not necessarily be
+subjective phenomena seen by the unaccustomed eye.&#8221;<a name='fna_104' id='fna_104' href='#f_104'><small>[104]</small></a></p>
+
+<p>The possibility of life on Mars has been recently much discussed; some
+denying, others asserting. M. E. Rogovsky says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;As free oxygen and carbonic dioxide may exist in the atmosphere of
+<i>Mars</i>, vegetable and animal life is quite possible. If the
+temperature which prevails upon <i>Mars</i> is nearer to -36&deg; C. than to
+-73&deg; C., the existence of living beings like ourselves is possible. In
+fact, the ice of some Greenland and Alpine glaciers is covered by red
+alg&aelig; (<i>Sph&aelig;rella nivalis</i>); we find there also different species of
+rotaloria, variegated spiders, and other animals on the snow fields
+illuminated by the sun; at the edges of glacier snows in the Tyrol we
+see violet bells of <i>Soldanella pusilla</i>, the stalks of which make
+their way through the snow by producing heat which melts it round
+about them. Finally the Siberian town Verkhociansk, near Yakutsk,
+exists, though the temperature there falls to -69&deg;&middot;8 C. and the mean
+temperature of January to -51&deg;&middot;2, and the mean pressure of the vapour
+of water is<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span> less than 0&middot;05mm. It is possible, therefore, that living
+beings have become adapted to the conditions now prevailing upon
+<i>Mars</i> after the lapse of many ages, and live at an even lower
+temperature than upon the earth, developing the necessary heat
+themselves.&#8221;</p></div>
+
+<p>M. Rogovsky adds, &#8220;Water in organisms is mainly a liquid or solvent, and
+many other liquids may be the same. We have no reason to believe that life
+is possible only under the same conditions and with the same chemical
+composition of organisms as upon the earth, although indeed we cannot
+affirm that they actually exist on Mars.&#8221;<a name='fna_105' id='fna_105' href='#f_105'><small>[105]</small></a> With the above views the
+present writer fully concurs.</p>
+
+<p>Prof. Lowell thinks that the polar regions of Mars, both north and south,
+are actually warmer than the corresponding regions of the earth, although
+the mean temperature of the planet is probably twelve degrees lower than
+the earth&#8217;s mean temperature.<a name='fna_106' id='fna_106' href='#f_106'><small>[106]</small></a></p>
+
+<p>A writer in <i>Astronomy and Astrophysics</i> (1892, p. 748) says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Whether the planet Mars is inhabited or not seems to be the
+all-absorbing question with the ordinary reader. With the astronomer
+this query is almost the last thing about the planet that he would
+think of when he has an opportunity to study its surface markings ...
+no<span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span> astronomer claims to know whether the planet is inhabited or not.&#8221;</p></div>
+
+<p>Several suggestions have been made with reference to the possibility of
+signalling to Mars. But, as Mr. Larkin of Mount Lowe (U.S.A.) points out,
+all writers on this subject seem to forget the fact that the night side of
+two planets are never turned towards each other. &#8220;When the sun is between
+them it is day on the side of Mars which is towards us, and also day on
+the side of the earth which is towards Mars. When they are on the same
+side of the sun, it is day on Mars when night on the earth, and for this
+reason they could never see our signals. This should make it apparent that
+the task of signalling to Mars is a more difficult one than the most
+hopeful theorist has probably considered. All this is under the
+supposition that the Martians (if there are such) are beings like
+ourselves. If they are not like us, we cannot guess what they are
+like.&#8221;<a name='fna_107' id='fna_107' href='#f_107'><small>[107]</small></a> These views seem to me to be undoubtedly correct, and show the
+futility of visual signals. Electricity might, however, be conceivably
+used for the purpose; but even this seems highly improbable.</p>
+
+<p>Prof. Newcomb, in his work <i>Astronomy for Everybody</i>, says with reference
+to this question, &#8220;The reader will excuse me from saying nothing in this
+chapter about the possible inhabitants of<span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span> Mars. He knows just as much
+about the subject as I do, and that is nothing at all.&#8221;</p>
+
+<p>It is, however, quite possible that life <i>in some form</i> may exist on Mars.
+As Lowell well says, &#8220;Life but waits in the wings of existence for its cue
+to enter the scene the moment the stage is set.&#8221;<a name='fna_108' id='fna_108' href='#f_108'><small>[108]</small></a> With reference to
+the &#8220;canals&#8221; he says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;It is certainly no exaggeration to say that they are the most
+astonishing objects to be viewed in the heavens. There are celestial
+sights more dazzling, spectacles that inspire more awe, but to the
+thoughtful observer who is privileged to see them well, there is
+nothing in the sky so profoundly impressive as these canals of
+Mars.&#8221;<a name='fna_109' id='fna_109' href='#f_109'><small>[109]</small></a></p></div>
+
+<p>The eminent Swedish physicist Arrhenius thinks that the mean annual
+temperature on Mars may possibly be as high as 50&deg; F. He says, &#8220;Sometimes
+the snow-caps on the poles of Mars disappear entirely during the Mars
+summer; this never happens on our terrestrial poles. The mean temperature
+of Mars must therefore be above zero, probably about +10&deg; [Centigrade =
+50&deg; Fahrenheit]. Organic life may very probably thrive, therefore, on
+Mars.&#8221;<a name='fna_110' id='fna_110' href='#f_110'><small>[110]</small></a> He thinks that this excess of mean temperature above the
+calculated temperature may be due to an increased amount of carbonic acid
+in the planet&#8217;s atmosphere, and says &#8220;any doubling of the percentage of
+carbon<span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span> dioxide in the air would raise the temperature of the earth&#8217;s
+surface by 4&deg;; and if the carbon dioxide were increased fourfold, the
+temperature would rise by 8&deg;.&#8221;<a name='fna_111' id='fna_111' href='#f_111'><small>[111]</small></a></p>
+
+<p>Denning says,&mdash;<a name='fna_112' id='fna_112' href='#f_112'><small>[112]</small></a></p>
+
+<div class="blockquot"><p>&#8220;A few years ago, when christening celestial formations was more in
+fashion than it is now, a man simply had to use a telescope for an
+evening or two on Mars or the moon, and spice the relation of his
+seeings with something in the way of novelty, when his name would be
+pretty certainly attached to an object and hung in the heavens for all
+time! A writer in the <i>Astronomical Register</i> for January, 1879,
+humorously suggested that &#8216;the matter should be put into the hands of
+an advertising agent,&#8217; and &#8216;made the means of raising a revenue for
+astronomical purposes.&#8217; Some men would not object to pay handsomely
+for the distinction of having their names applied to the seas and
+continents of Mars or the craters of the moon.&#8221;</p></div>
+
+<p>An occultation of Mars by the moon is recorded by Aristotle as having
+occurred on April 4, 357 <span class="smcaplc">B.C.</span><a name='fna_113' id='fna_113' href='#f_113'><small>[113]</small></a></p>
+
+<p>Seen from Mars the maximum apparent distance between the earth and moon
+would vary from 3&#189;&prime; to nearly 17&prime;.<a name='fna_114' id='fna_114' href='#f_114'><small>[114]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span></p>
+<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII</h2>
+<p class="title">The Minor Planets</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Up</span> to 1908 the number of minor planets (or asteroids) certainly known
+amounted to over 650.</p>
+
+<p>From an examination of the distribution of the first 512 of these small
+bodies, Dr. P. Stroobant finds that a decided maximum in number occurs
+between the limits of distance of 2&middot;55 and 2&middot;85 (earth&#8217;s mean distance
+from sun = 1), &#8220;199 of the asteroids considered revolving in this
+annulus.&#8221; He finds that nearly all the asteroidal matter is concentrated
+near to the middle of the ring in the neighbourhood of the mean distance
+of 2&middot;7, and the smallest asteroids are relatively less numerous in the
+richest zones.<a name='fna_115' id='fna_115' href='#f_115'><small>[115]</small></a></p>
+
+<p>There are some &#8220;striking similarities&#8221; in the orbits of some of the
+asteroids. Thus, in the small planets Sophia (No. 251 in order of
+discovery) and Magdalena (No. 318) we have the mean distance of Sophia
+3&middot;10, and that of Magdalena 3&middot;19 (earth&#8217;s mean distance = 1).<span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span> The
+eccentricities of the orbits are 0&middot;09 and 0&middot;07; and the inclinations of
+the orbits to the plane of the ecliptic 10&deg; 29&prime; and 10&deg; 33&prime;
+respectively.<a name='fna_116' id='fna_116' href='#f_116'><small>[116]</small></a> This similarity may be&mdash;and probably is&mdash;merely
+accidental, but it is none the less curious and interesting.</p>
+
+<p>Some very interesting discoveries have recently been made among the minor
+planets. The orbit of Eros intersects the orbit of Mars; and the following
+have nearly the same mean distance from the sun as Jupiter:&mdash;</p>
+
+<p class="poem">Achilles (1906 TG), No. 588,<br />
+Patrocles (1906 XY), No. 617,<br />
+Hector (1907 XM), No. 624,</p>
+
+<p>and another (No. 659) has been recently found. Each of these small planets
+&#8220;moves approximately in a vertex of an equilateral triangle that it forms
+with Jupiter and the sun.&#8221;<a name='fna_117' id='fna_117' href='#f_117'><small>[117]</small></a> The minor planet known provisionally as HN
+is remarkable for the large eccentricity of its orbit (0&middot;38), and its
+small perihelion distance (1&middot;6). When discovered it had a very high South
+Declination (61&#189;&deg;), showing that the inclination of the plane of its
+orbit to the plane of the ecliptic is considerable.<a name='fna_118' id='fna_118' href='#f_118'><small>[118]</small></a></p>
+
+<p>Dr. Bauschinger has made a study of the minor planets discovered up to the
+end of 1900.<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span> He finds that the ascending nodes of the orbits show a
+marked tendency to cluster near the ascending node of Jupiter&#8217;s orbit, a
+fact which agrees well with Prof. Newcomb&#8217;s theoretical results. There
+seems to be a slight tendency for large inclinations and great
+eccentricities to go together; but there appears to be no connection
+between the eccentricity and the mean distance from the sun. The
+longitudes of the perihelia of these small planets &#8220;show a well-marked
+maximum near the longitude of <i>Jupiter&#8217;s</i> perihelion, and equally
+well-marked minimum near the longitude of his aphelion,&#8221; which is again in
+good agreement with Newcomb&#8217;s calculations.<a name='fna_119' id='fna_119' href='#f_119'><small>[119]</small></a> Dr. Bauschinger&#8217;s
+diameter for Eros is 20 miles. He finds that the whole group, including
+those remaining to be discovered, would probably form a sphere of about
+830 miles in diameter.</p>
+
+<p>The total mass of the minor planets has been frequently estimated, but
+generally much too high. Mr. B. M. Roszel of the John Hopkins University
+(U.S.A.) has made a calculation of the probable mass from the known
+diameter of Vesta (319 miles, Pickering), and finds the volume of the
+first 216 asteroids discovered. From this calculation it appears that it
+would take 310 asteroids of the 6th magnitude, or 1200 of the 7th to equal
+the moon in volume. Mr. Roszel concludes that the probable mass of the
+whole<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span> asteroidal belt is between
+<span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">50</span>th
+and <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">100</span>th of that of the
+moon.<a name='fna_120' id='fna_120' href='#f_120'><small>[120]</small></a> Subsequently Mr. Roszel extended his study to the mass of 311
+asteroids,<a name='fna_121' id='fna_121' href='#f_121'><small>[121]</small></a> and found a combined mass of about
+<span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">40</span>th of the moon&#8217;s mass.</p>
+
+<p>Dr. Palisa finds that the recently discovered minor planet (1905 QY)
+varies in light to a considerable extent.<a name='fna_122' id='fna_122' href='#f_122'><small>[122]</small></a> This planet was discovered
+by Dr. Max Wolf on August 23, 1905; but it was subsequently found that it
+is identical with one previously known, (167) Urda.<a name='fna_123' id='fna_123' href='#f_123'><small>[123]</small></a> The light
+variation is said to be from the 11th to the 13th magnitude.<a name='fna_124' id='fna_124' href='#f_124'><small>[124]</small></a>
+Variation in some of the other minor planets has also been suspected.
+Prof. Wendell found a variation of about half a magnitude in the planet
+Eunomia (No. 15). He also found that Iris (No. 7) varies about a quarter
+of a magnitude in a period of about 6<sup>h</sup> 12<sup>m</sup>.<a name='fna_125' id='fna_125' href='#f_125'><small>[125]</small></a> But these variations
+are small, and perhaps doubtful. The variability of Eros is well known.</p>
+
+<p>The planet Eros is a very interesting one. The perihelion portion of its
+orbit lies between the orbits of Mars and the earth, and the aphelion part
+is outside the orbit of Mars. Owing to the great variation in its distance
+from the earth the brightness of Eros varies from the 6th to the 12th
+magnitude. That is, when brightest, it is 250<span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span> times brighter than when it
+is faintest.<a name='fna_126' id='fna_126' href='#f_126'><small>[126]</small></a> This variation of light, is of course, merely due to the
+variation of distance; but some actual variation in the brightness of the
+planet has been observed.</p>
+
+<p>It has been shown by Oeltzen and Valz that Cacciatore&#8217;s supposed distant
+comet, mentioned by Admiral Smyth in his <i>Bedford Catalogue</i>, must have
+been a minor planet.<a name='fna_127' id='fna_127' href='#f_127'><small>[127]</small></a></p>
+
+<p>Dr. Max Wolf discovered 36 new minor planets by photography in the years
+1892-95. Up to the latter year he had never seen one of these through a
+telescope! His words are, &#8220;Ich selsbt habe noch nie einen meinen kleinen
+Planeten am Himmel gesehen.&#8221;<a name='fna_128' id='fna_128' href='#f_128'><small>[128]</small></a></p>
+
+<p>These small bodies have now become so numerous that it is a matter of much
+difficulty to follow them. At the meeting of the Royal Astronomical
+Society on January 8, 1909, Mr. G. F. Chambers made the following
+facetious remarks&mdash;</p>
+
+<div class="blockquot"><p>&#8220;I would like to make a suggestion that has been in my mind for
+several years past&mdash;that it should be made an offence punishable by
+fine or imprisonment to discover any more minor planets. They seem to
+be an intolerable nuisance, and are a great burden upon the literary
+gentlemen who have to keep pace with them and record them. I have
+never seen, during the last few<span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span> years at any rate, any good come from
+them, or likely to come, and I should like to see the supply stopped,
+and the energies of the German gentlemen who find so many turned into
+more promising channels.&#8221;</p></div>
+
+<p>Among the minor planets numbered 1 to 500, about 40 &#8220;have not been seen
+since the year of their discovery, and must be regarded as lost.&#8221;<a name='fna_129' id='fna_129' href='#f_129'><small>[129]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span></p>
+<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII</h2>
+<p class="title">Jupiter</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">This</span> brilliant planet&mdash;only inferior to Venus in brightness&mdash;was often
+seen by Bond (Jun.) with the naked eye in &#8220;high and clear sunshine&#8221;; also
+by Denning, who has very keen eyesight. Its brightness on such occasions
+is so great, that&mdash;like Venus&mdash;it casts a distinct shadow in a dark
+room.<a name='fna_130' id='fna_130' href='#f_130'><small>[130]</small></a></p>
+
+<p>The great &#8220;red spot&#8221; on Jupiter seems to have been originally discovered
+by Robert Hooke on May 9, 1664, with a telescope of 2 inches aperture and
+12 feet focus. It seems to have existed ever since; at least the evidence
+is, according to Denning, in favour of the identity of Hooke&#8217;s spot with
+the red spot visible in recent years. The spot was also observed by
+Cassini in the years 1665-72, and is sometimes called &#8220;Cassini&#8217;s spot.&#8221;
+But the real discoverer was Hooke.<a name='fna_131' id='fna_131' href='#f_131'><small>[131]</small></a></p>
+
+<p>The orbit of Jupiter is so far outside the earth&#8217;s<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span> orbit that there can
+be little visible in the way of &#8220;phase&#8221;&mdash;as in the case of Mars, where the
+&#8220;gibbous&#8221; phase is sometimes very perceptible. Some books on astronomy
+state that Jupiter shows no phase. But this is incorrect. A distinct,
+although very slight, gibbous appearance is visible when the planet is
+near quadrature. Webb thought it more conspicuous in twilight than in a
+dark sky. With large telescopes, Jupiter&#8217;s satellites II. and III. have
+been seen&mdash;in consequence of Jupiter&#8217;s phase&mdash;to emerge from occultation
+&#8220;at a sensible distance from the limb.&#8221;<a name='fna_132' id='fna_132' href='#f_132'><small>[132]</small></a></p>
+
+<p>According to M. E. Rogovsky, the high &#8220;albedo of Jupiter, the appearance
+of the clear (red) and dark spots on its surface and their continual
+variation, the different velocity of rotation of the equatorial and other
+zones of its surface, and particularly its small density (1&middot;33, water as
+unity), all these facts afford irrefragable proofs of the high temperature
+of this planet. The dense and opaque atmosphere hides its glowing surface
+from our view, and we see therefore only the external surface of its
+clouds. The objective existence of this atmosphere is proved by the bands
+and lines of absorption in its spectrum. The interesting photograph
+obtained by Draper, September 27, 1879, in which the blue and green parts
+are more brilliant for the equatorial zone than for the<span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span> adjacent parts of
+the surface, appears to show that <i>Jupiter</i> emits its proper light. It is
+possible that the constant red spot noticed on its surface by several
+observers, as Gledhill, Lord Rosse, and Copeland (1873), Russel and
+Bredikhin (1876), is the summit of a high glowing mountain. G. W. Hough
+considers Jupiter to be gaseous, and A. Ritter inferred from his formul&aelig;
+that in this case the temperature at the centre would be 600,000&deg; C.&#8221;<a name='fna_133' id='fna_133' href='#f_133'><small>[133]</small></a></p>
+
+<p>The four brighter satellites of Jupiter are usually known by numbers I.,
+II., III., and IV.; I. being the nearest to the planet, and IV. the
+farthest. III. is usually the brightest, and IV. the faintest, but
+exceptions to this rule have been noticed.</p>
+
+<p>With reference to the recently discovered sixth and seventh satellites of
+Jupiter, Prof. Perrine has suggested that the large inclination of their
+orbits to the plane of the planet&#8217;s equator seems to indicate that neither
+of these bodies was originally a member of Jupiter&#8217;s family, but has been
+&#8220;captured by the planet.&#8221; This seems possible as the orbits of some of the
+minor planets lie near the orbit of Jupiter (see &#8220;Minor Planets&#8221;). A
+similar suggestion has been made by Prof. del Marmol.<a name='fna_134' id='fna_134' href='#f_134'><small>[134]</small></a></p>
+
+<p>Many curious observations have been recorded<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span> with reference to Jupiter&#8217;s
+satellites; some very difficult of explanation. In 1711 Bianchini saw
+satellite IV. so faint for more than an hour that it was hardly visible! A
+similar observation was made by Lassell with a more powerful telescope on
+June 13, 1849. Key, T. T. Smyth, and Denning have also recorded unusual
+faintness.<a name='fna_135' id='fna_135' href='#f_135'><small>[135]</small></a> A very remarkable phenomenon was seen by Admiral Smyth,
+Maclear, and Pearson on June 26, 1828. Satellite II., &#8220;having fairly
+entered on Jupiter, was found 12 or 13 minutes afterwards <i>outside the
+limb</i>, where it remained visible for at least 4 minutes, and then suddenly
+vanished.&#8221; As Webb says, &#8220;Explanation is here set at defiance;
+demonstrably neither in the atmosphere of the earth, nor Jupiter, where
+and what could have been the cause? At present we can get no answer.&#8221;<a name='fna_136' id='fna_136' href='#f_136'><small>[136]</small></a>
+When Jupiter is in opposition to the sun&mdash;that is, on the meridian at
+midnight&mdash;satellite I. has been seen projected on its own shadow, the
+shadow appearing as a dark ring round the satellite.</p>
+
+<p>On January 28, 1848, at Cambridge (U.S.A.) satellite III. was seen in
+transit lying between the shadows of I. and II. and so black that it could
+not be distinguished from the shadows, &#8220;except by the place it occupied.&#8221;
+This seems to suggest inherent light in the planet&#8217;s surface, as the
+satellite was at the time illuminated by full<span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span> sunshine; its apparent
+blackness being due to the effect of contrast. Cassini on one occasion
+failed to find the shadow of satellite I. when it should have been on the
+planet&#8217;s disc,<a name='fna_137' id='fna_137' href='#f_137'><small>[137]</small></a> an observation which again points to the glowing light
+of Jupiter&#8217;s surface. Sadler and Trouvelot saw the shadow of satellite I.
+double! an observation difficult to explain&mdash;but the same phenomenon was
+again seen on the evening of September 19, 1891, by Mr. H. S. Halbert of
+Detroit, Michigan (U.S.A.). He says that the satellite &#8220;was in transit
+nearing egress, and it appeared as a white disc against the dark southern
+equatorial belt; following it was the usual shadow, and at an equal
+distance from this was a second shadow, smaller and not so dark as the
+true one, and surrounded by a faint penumbra.&#8221;<a name='fna_138' id='fna_138' href='#f_138'><small>[138]</small></a></p>
+
+<p>A dark transit of satellite III. was again seen on the evening of December
+19, 1891, by two observers in America. One observer noted that the
+satellite, when on the disc of the planet, was intensely black. To the
+other observer (Willis L. Barnes) it appeared as an ill-defined <i>dark</i>
+image.<a name='fna_139' id='fna_139' href='#f_139'><small>[139]</small></a> A similar observation was made on October 9 of the same year
+by Messrs. Gale and Innes.<a name='fna_140' id='fna_140' href='#f_140'><small>[140]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span>A &#8220;black transit&#8221; of satellite IV. was seen by several observers in 1873,
+and by Prof. Barnard on May 4, 1886. The same phenomenon was observed on
+October 30, 1903, in America, by Miss Anne S. Young and Willis S. Barnes.
+Miss Young says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The ingress of the satellite took place at 8<sup>h</sup> 50<sup>m</sup> (E. standard
+time) when it became invisible upon the background of the planet. An
+hour later it was plainly visible as a dark round spot upon the
+planet. It was decidedly darker than the equatorial belt.&#8221;<a name='fna_141' id='fna_141' href='#f_141'><small>[141]</small></a></p></div>
+
+<p>The rather rare phenomenon of an occultation of one of Jupiter&#8217;s
+satellites by another was observed by Mr. Apple, director of the Daniel
+Scholl Observatory, Franklin and Marshall College, Lancaster, Pa.
+(U.S.A.), on the evening of March 16, 1908. The satellites in question
+were I. and II., and they were so close that they could not be separated
+with the 11&middot;5-inch telescope of the Observatory.<a name='fna_142' id='fna_142' href='#f_142'><small>[142]</small></a> One of the present
+writer&#8217;s first observations with a telescope is dated May 17, 1873, and is
+as follows: &#8220;Observed one of Jupiter&#8217;s satellites occulted (or very nearly
+so) by another. Appeared as one with power 133&#8221; (on 3-inch refractor in
+the Punjab). These satellites were probably I. and II.</p>
+
+<p>Jupiter has been seen on several occasions apparently without his
+satellites; some being<span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span> behind the disc, some eclipsed in his shadow, and
+some in transit across the disc. This phenomenon was seen by Galileo,
+March 15, 1611; by Molyneux, on November 12, 1681; by Sir William
+Herschel, May 23, 1802; by Wallis, April 15, 1826; by Greisbach, September
+27, 1843; and by several observers on four occasions in the years
+1867-1895.<a name='fna_143' id='fna_143' href='#f_143'><small>[143]</small></a> The phenomenon again occurred on October 3, 1907, No. 1
+being eclipsed and occulted, No. 2 in transit, No. 3 eclipsed, and No. 4
+occulted.<a name='fna_144' id='fna_144' href='#f_144'><small>[144]</small></a> It was not, however, visible in Europe, but could have been
+seen in Asia and Oceania.<a href='#f_144'><small>[144]</small></a> The phenomenon will occur again on October
+22, 1913.<a name='fna_145' id='fna_145' href='#f_145'><small>[145]</small></a></p>
+
+<p>On the night of September 19, 1903, a star of magnitude 6&#189; was occulted
+by the disc of Jupiter. This curious and rare phenomenon was photographed
+by M. Lucien Rudaux at the Observatory of Donville, France.<a name='fna_146' id='fna_146' href='#f_146'><small>[146]</small></a> The star
+was Lalande 45698 (= BAC 8129).<a name='fna_147' id='fna_147' href='#f_147'><small>[147]</small></a></p>
+
+<p>Prof. Barnard, using telescopes with apertures from 5 inches up to 36
+inches (Lick), has failed to see a satellite through the planet&#8217;s limb (an
+observation which has been claimed by other astronomers). He says, &#8220;To my
+mind this has<span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span> been due to either poor seeing, a poor telescope, or an
+excited observer.&#8221;<a name='fna_148' id='fna_148' href='#f_148'><small>[148]</small></a> He adds&mdash;</p>
+
+<div class="blockquot"><p>&#8220;I think it is high time that the astronomers reject the idea that the
+satellites of Jupiter can be seen through his limb at occultation.
+When the seeing is bad there is a spurious limb to Jupiter that well
+might give the appearance of transparency at the occultation of a
+satellite. But under first-class conditions the limb of Jupiter is
+perfectly opaque. It is quibbling and begging the question altogether
+to say the phenomenon of transparency may be a rare one and so have
+escaped my observations. Has any one said that the moon was
+transparent when a star has been seen projected on it when it ought to
+have been behind it?&#8221;</p></div>
+
+<p>Prof. Barnard and Mr. Douglass have seen white polar caps on the third and
+fourth satellites of Jupiter. The former says they are &#8220;exactly like those
+on Mars.&#8221; &#8220;Both caps of the fourth satellite have been clearly
+distinguished, that at the north being sometimes exceptionally large,
+covering a surface equal to one-quarter or one-third of the diameter of
+the satellite.&#8221;<a name='fna_149' id='fna_149' href='#f_149'><small>[149]</small></a> This was confirmed on November 23, 1906, when Signor
+J. Comas Sola observed a brilliant white spot surrounded by a dark marking
+in the north polar region of the third satellite. There were other dark
+markings visible, and the satellite presented the appearance of a
+miniature of Mars.<a name='fna_150' id='fna_150' href='#f_150'><small>[150]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span>An eighth satellite of Jupiter has recently been discovered by Mr. Melotte
+at the Greenwich Observatory by means of photography. It moves in a
+retrograde direction round Jupiter in an orbit inclined about 30&deg; to that
+of the planet. The period of revolution is about two years. The orbit is
+very eccentric, the eccentricity being about one-third, or greater than
+that of any other satellite of the solar system. When nearest to Jupiter
+it is about 9 millions of miles from the planet, and when farthest about
+20 millions.<a name='fna_151' id='fna_151' href='#f_151'><small>[151]</small></a> It has been suggested by Mr. George Forbes that this
+satellite may possibly be identical with the lost comet of Lexell which at
+its return in the year 1779 became entangled in Jupiter&#8217;s system, and has
+not been seen since. If this be the case, we should have the curious
+phenomenon of a comet revolving round a planet!</p>
+
+<p>According to Humboldt the four bright satellites of Jupiter were seen
+almost simultaneously and quite independently by Simon Marius at Ausbach
+on December 29, 1609, and by Galileo at Padua on January 7, 1610.<a name='fna_152' id='fna_152' href='#f_152'><small>[152]</small></a> The
+actual priority, therefore, seems to rest with Simon Marius, but the
+publication of the discovery was first made by Galileo in his <i>Nuncius
+Siderius</i> (1610).<a name='fna_153' id='fna_153' href='#f_153'><small>[153]</small></a> Grant, however, in his <i>History of Physical
+Astronomy</i>,<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span> calls Simon Marius an &#8220;impudent pretender&#8221;! (p. 79).</p>
+
+<p>M. Dupret at Algiers saw Jupiter with the naked eye on September 26, 1890,
+twenty minutes before sunset.<a name='fna_154' id='fna_154' href='#f_154'><small>[154]</small></a></p>
+
+<p>Humboldt states that he saw Jupiter with the naked eye when the sun was
+from 18&deg; to 20&deg; above the horizon.<a name='fna_155' id='fna_155' href='#f_155'><small>[155]</small></a> This was in the plains of South
+America near the sea-level.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span></p>
+<h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX</h2>
+<p class="title">Saturn</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">To</span> show the advantages of large telescopes over small ones, Mr. C. Roberts
+says that &#8220;with the 25-inch refractor of the Cambridge Observatory the
+view of the planet Saturn is indescribably glorious; everything I had ever
+seen before was visible at a glance, and an enormous amount of detail that
+I had never even glimpsed before, after a few minutes&#8217; observation.&#8221;<a name='fna_156' id='fna_156' href='#f_156'><small>[156]</small></a></p>
+
+<p>Chacornac found that the illumination of Saturn&#8217;s disc is the reverse of
+that of Jupiter, the edges of Saturn being brighter than the centre of the
+disc, while in the case of Jupiter&mdash;as in that of the sun&mdash;the edges are
+fainter than the centre.<a name='fna_157' id='fna_157' href='#f_157'><small>[157]</small></a> According to Mr. Denning, Saturn bears
+satisfactorily &#8220;greater magnifying power than either Mars or
+Jupiter.&#8221;<a name='fna_158' id='fna_158' href='#f_158'><small>[158]</small></a></p>
+
+<p>At an occultation of Saturn by the moon, which occurred on June 13, 1900,
+M. M. Honorat<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span> noticed the great contrast between the slightly yellowish
+colour of the moon and the greenish tint of the planet.<a name='fna_159' id='fna_159' href='#f_159'><small>[159]</small></a></p>
+
+<p>In the year 1892, when the rings of Saturn had nearly disappeared, Prof.
+L. W. Underwood, of the Underwood Observatory, Appleton, Wisconsin
+(U.S.A.), saw one of Saturn&#8217;s satellites (Titan) apparently moving along
+the needlelike appendage to the planet presented by the rings. &#8220;The
+apparent diameter of the satellite so far exceeded the apparent thickness
+of the ring that it gave the appearance of a beautiful golden bead moving
+very slowly along a fine golden thread.&#8221;<a name='fna_160' id='fna_160' href='#f_160'><small>[160]</small></a></p>
+
+<p>In 1907, when the rings of Saturn became invisible in ordinary telescopes,
+Professor Campbell, observing with the great Lick telescope, noticed
+&#8220;prominent bright knots, visible ... in Saturn&#8217;s rings. The knots were
+symmetrically placed, two being to the east and two to the west.&#8221; This was
+confirmed by Mr. Lowell, who says, &#8220;Condensations in Saturn&#8217;s rings
+confirmed here and measured repeatedly. Symmetric and permanent.&#8221; This
+phenomenon was previously seen by Bond in the years 1847-56. Measures of
+these light spots made by Prof. Barnard with the 40-inch Yerkes telescope
+show that the outer one corresponded in position with the outer edge<span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span> of
+the middle ring close to the Cassini division, and the inner condensation,
+curious to say, seemed to coincide in position with the &#8220;crape ring.&#8221;
+Prof. Barnard thinks that the thickness of the rings &#8220;must be greatly
+under 100 miles, and probably less than 50 miles,&#8221; and he says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The important fact clearly brought out at this apparition of <i>Saturn</i>
+is that the bright rings are not opaque to the light of the sun&mdash;and
+this is really what we should expect from the nature of their
+constitution as shown by the theory of Clerk Maxwell, and the
+spectroscopic results of Keeler.&#8221;<a name='fna_161' id='fna_161' href='#f_161'><small>[161]</small></a></p></div>
+
+<p>Under certain conditions it would be theoretically possible, according to
+Mr. Whitmell, to see the globe of Saturn through the Cassini division in
+the ring. But the observation would be one of great difficulty and
+delicacy. The effect would be that, of the arc of the division which
+crosses the planet&#8217;s disc, &#8220;a small portion will appear bright instead of
+dark, and may almost disappear.&#8221;<a name='fna_162' id='fna_162' href='#f_162'><small>[162]</small></a></p>
+
+<p>A remarkable white spot was seen on Saturn on June 23, 1903, by Prof.
+Barnard, and afterwards by Mr. Denning.<a name='fna_163' id='fna_163' href='#f_163'><small>[163]</small></a> Another white spot was seen
+by Denning on July 9 of the same year.<a name='fna_164' id='fna_164' href='#f_164'><small>[164]</small></a> From numerous observations of
+these spots, Denning found a rotation period for the planet of about<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span>
+10<sup>h</sup> 39<sup>m</sup> 21<sup>s</sup>.<a name='fna_165' id='fna_165' href='#f_165'><small>[165]</small></a> From observations of the same spots Signor Comas
+Sola found a period 10<sup>h</sup> 38<sup>m</sup>&middot;4, a close agreement with Denning&#8217;s
+result. For Saturn&#8217;s equator, Prof. Hill found a rotation period of 10<sup>h</sup>
+14<sup>m</sup> 23<sup>s</sup>&middot;8, so that&mdash;as in the case of Jupiter&mdash;the rotation is faster
+at the equator than in the northern latitudes of the planet. A similar
+phenomenon is observed in the sun. Mr. Denning&#8217;s results were fully
+confirmed by Herr Leo Brenner, and other German astronomers.<a name='fna_166' id='fna_166' href='#f_166'><small>[166]</small></a></p>
+
+<p>Photographs taken by Prof. V. M. Slipher in America show that the spectrum
+of Saturn is similar to that of Jupiter. None of the bands observed in the
+planet&#8217;s spectrum are visible in the spectrum of the rings. This shows
+that if the rings possess an atmosphere at all, it must be much rarer than
+that surrounding the ball of the planet. Prof. Slipher says that &#8220;none of
+the absorption bands in the spectrum of <i>Saturn</i> can be identified with
+those bands due to absorption in the earth&#8217;s atmosphere,&#8221; and there is no
+trace of aqueous vapour.<a name='fna_167' id='fna_167' href='#f_167'><small>[167]</small></a></p>
+
+<p>In September, 1907, M. G. Fournier suspected the existence of a &#8220;faint
+transparent and luminous ring&#8221; outside the principal rings of Saturn. He
+thinks that it may possibly be subject to periodical fluctuations of
+brightness, sometimes being visible<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span> and sometimes not.<a name='fna_168' id='fna_168' href='#f_168'><small>[168]</small></a> This dusky
+ring was again suspected at the Geneva Observatory in October, 1908.<a name='fna_169' id='fna_169' href='#f_169'><small>[169]</small></a>
+M. Schaer found it a difficult object with a 16-inch Cassegrain reflector.
+Prof. Stromgen at Copenhagen, and Prof. Hartwig at Bamberg, however,
+failed to see any trace of the supposed ring.<a name='fna_170' id='fna_170' href='#f_170'><small>[170]</small></a> It was seen at
+Greenwich in October, 1908.</p>
+
+<p>A &#8220;dark transit&#8221; of Saturn&#8217;s satellite Titan across the disc of the planet
+has been observed on several occasions. It was seen by Mr. Isaac W. Ward,
+of Belfast, on March 27, 1892, with a 4&middot;3-inch Wray refractor. The
+satellite appeared smaller than its shadow. The phenomenon was also seen
+on March 12 of the same year by the Rev. A. Freeman, Mr. Mee, and M. F.
+Terby; and again on November 6, 1907, by Mr. Paul Chauleur and Mr. A. B.
+Cobham.<a name='fna_171' id='fna_171' href='#f_171'><small>[171]</small></a></p>
+
+<p>The recently discovered tenth satellite of Saturn, Themis, was discovered
+by photography, and has never been seen by the eye even with the largest
+telescopes! But its existence is beyond all doubt, and its orbit round the
+planet has been calculated.</p>
+
+<p>Prof. Hussey of the Lick Observatory finds that Saturn&#8217;s satellite Mimas
+is probably larger than Hyperion. He also finds from careful measurements
+that the diameter of Titan is certainly<span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span> overestimated, and that its
+probable diameter is about 2500 miles.<a name='fna_172' id='fna_172' href='#f_172'><small>[172]</small></a></p>
+
+<p>The French astronomer, M. Lucien Rudaux, finds the following variation in
+the light of the satellites of Saturn:&mdash;</p>
+
+<table border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td>Japetus</td>
+    <td>from</td>
+    <td>9th</td>
+    <td>magnitude to</td>
+    <td>12th</td></tr>
+<tr><td>Rhea</td>
+    <td align="center">"</td>
+    <td>9</td>
+    <td align="center">"</td>
+    <td>10&middot;6</td></tr>
+<tr><td>Dione</td>
+    <td align="center">"</td>
+    <td>9&middot;5</td>
+    <td align="center">"</td>
+    <td>10&middot;5</td></tr>
+<tr><td>Tethys</td>
+    <td align="center">"</td>
+    <td>9&middot;8</td>
+    <td align="center">"</td>
+    <td>10&middot;5</td></tr>
+<tr><td>Titan</td>
+    <td align="center">"</td>
+    <td>8</td>
+    <td align="center">"</td>
+    <td><span style="margin-left: .5em;">8&middot;6</span></td></tr></table>
+
+<p>The variation of light is, he thinks, due to the fact that the period of
+rotation of each satellite is equal to that of their revolution round the
+planet; as in the case of our moon.<a name='fna_173' id='fna_173' href='#f_173'><small>[173]</small></a></p>
+
+<p>The names of the satellites of Saturn are derived from the ancient heathen
+mythology. They are given in order of distance from the planet, the
+nearest being Mimas and the farthest Themis.</p>
+
+<p>1. Mimas was a Trojan born at the same time as Paris.</p>
+
+<p>2. Enceladus was son of Tartarus and Ge.</p>
+
+<p>3. Tethys was wife of Oceanus, god of ocean currents. She became mother of
+all the chief rivers in the universe, as also the Oceanides or sea nymphs.</p>
+
+<p>4. Dione was one of the wives of Zeus.</p>
+
+<p>5. Rhea was a daughter of Uranus. She married Saturn, and became the
+mother of Vesta, Ceres, Juno, and Pluto.</p>
+
+<p><span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span>6. Titan was the eldest son of Uranus.</p>
+
+<p>7. Hyperion was the god of day, and the father of sun and moon.</p>
+
+<p>8. Japetus was the fifth son of Uranus, and father of Atlas and
+Prometheus.<a name='fna_174' id='fna_174' href='#f_174'><small>[174]</small></a></p>
+
+<p>9. Ph&oelig;be was daughter of Uranus and Ge.</p>
+
+<p>10. Themis was daughter of Uranus and Ge, and, therefore, sister of
+Ph&oelig;be.</p>
+
+<p>In a review of Prof. Comstock&#8217;s <i>Text Book of Astronomy</i> in <i>The
+Observatory</i>, November, 1901, the remark occurs, &#8220;We are astonished to see
+that Mr. Comstock alludes with apparent seriousness to the <i>nine</i>
+satellites of Saturn. As regards the ninth satellite, we thought that all
+astronomers held with Mrs. Betsy Prig on the subject of this astronomical
+Mrs. Harris.&#8221; This reads curiously now (1909) when the existence of the
+ninth satellite (Ph&oelig;be) has been fully confirmed, and a tenth satellite
+discovered.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span></p>
+<h2><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X</h2>
+<p class="title">Uranus and Neptune</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">From</span> observations of Uranus made in 1896, M. Leo Brenner concluded that
+the planet rotates on its axis in about 8&#189; hours (probably 8<sup>h</sup> 27<sup>m</sup>).
+This is a short period, but considering the short periods of Jupiter and
+Saturn there seems to be nothing improbable about it.</p>
+
+<p>Prof. Barnard finds that the two inner satellites of Uranus are difficult
+objects even with the great 36-inch telescope of the Lick Observatory!
+They have, however, been photographed at Cambridge (U.S.A.) with a 13-inch
+lens, although they are &#8220;among the most difficult objects known.&#8221;<a name='fna_175' id='fna_175' href='#f_175'><small>[175]</small></a></p>
+
+<p>Sir William Huggins in 1871 found strong absorption lines (six strong
+lines) in the spectrum of Uranus. One of these lines indicated the
+presence of hydrogen, a gas which does not exist in our atmosphere. Three
+of the other lines seen were situated near lines in the spectrum of
+atmospheric air. Neither carbonic acid nor sodium<span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span> showed any indications
+of their presence in the planet&#8217;s spectrum. A photograph by Prof. Slipher
+of Neptune&#8217;s spectrum &#8220;shows the spectrum of this planet to contain many
+strong absorption bands. These bands are so pronounced in the part of the
+spectrum between the Fraunhofer lines F and D, as to leave the solar
+spectrum unrecognizable.... Neptune&#8217;s spectrum is strikingly different
+from that of <i>Uranus</i>, the bands in the latter planet all being reinforced
+in <i>Neptune</i>. In this planet there are also new bands which have not been
+observed in any of the other planets. The F line of hydrogen is remarkably
+dark ... this band is of more than solar strength in the spectrum of
+Uranus also. Thus free hydrogen seems to be present in the atmosphere of
+both these planets. This and the other dark bands in these planets bear
+evidence of an enveloping atmosphere of gases which is quite unlike that
+which surrounds the earth.&#8221;<a name='fna_176' id='fna_176' href='#f_176'><small>[176]</small></a></p>
+
+<p>With the 18-inch equatorial telescope of the Strasburgh Observatory, M.
+Wirtz measured the diameter of Neptune, and found from forty-nine measures
+made between December 9, 1902, and March 28, 1903, a value of 2&Prime;&middot;303 at a
+distance of 30&middot;1093 (earth&#8217;s distance from sun = 1). This gives a diameter
+of 50,251 kilometres, or about 31,225 miles,<a name='fna_177' id='fna_177' href='#f_177'><small>[177]</small></a> and a mean density of
+1&middot;54 (water = 1;<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span> earth&#8217;s mean density = 5&middot;53). Prof. Barnard&#8217;s measures
+gave a diameter of 32,900 miles, a fairly close agreement, considering the
+difficulty of measuring so small a disc as that shown by Neptune.</p>
+
+<p>The satellite of Neptune was photographed at the Pulkown Observatory in
+the year 1899. The name Triton has been suggested for it. In the old Greek
+mythology Triton was a son of Neptune, so the name would be an appropriate
+one.</p>
+
+<p>The existence of a second satellite of Neptune is suspected by Prof.
+Schaeberle, who thinks he once saw it with the 36-inch telescope of the
+Lick Observatory &#8220;on an exceptionally fine night&#8221; in 1895.<a name='fna_178' id='fna_178' href='#f_178'><small>[178]</small></a> But this
+supposed discovery has not yet been confirmed. Lassell also thought he had
+discovered a second satellite, but this supposed discovery was never
+confirmed.<a href='#f_178'><small>[178]</small></a></p>
+
+<p>The ancient Burmese mention eight planets, the sun, the moon, Mercury,
+Venus, Mars, Jupiter, Saturn, and another named R&acirc;hu, which is invisible.
+It has been surmised that &#8220;R&acirc;hu&#8221; is Uranus, which is just visible to the
+naked eye, and may possibly have been discovered by keen eyesight in
+ancient times. The present writer has seen it several times without
+optical aid in the West of Ireland, and with a binocular field-glass of 2
+inches aperture he found it quite a conspicuous object.</p>
+
+<p><span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span>When Neptune was <i>visually</i> discovered by Galle, at Berlin, he was
+assisted in his observation by Prof. d&#8217;Arrest. The incident is thus
+described by Dr. Dreyer, &#8220;On the night of June 14, 1874, while observing
+Coggia&#8217;s comet together, I reminded Prof. d&#8217;Arrest how he had once said in
+the course of a lecture, that he had been present at the finding of
+Neptune, and that &#8216;he might say it would not have been found without him.&#8217;
+He then told me (and I wrote it down the next day), how he had suggested
+the use of Bremiker&#8217;s map (as first mentioned by Dr. Galle in 1877) and
+continued, &#8216;We then went back to the dome, where there was a kind of desk,
+at which I placed myself with the map, while Galle, looking through the
+refractor, described the configurations of the stars he saw. I followed
+them on the map one by one, until he said: &#8220;And then there is a star of
+the 8th magnitude, in such and such a position,&#8221; whereupon I immediately
+exclaimed: &#8220;That star is not on the map.&#8221;&#8217;&#8221;<a name='fna_179' id='fna_179' href='#f_179'><small>[179]</small></a> This was the planet. But
+it seems to the present writer that if Galle or d&#8217;Arrest had access to
+Harding&#8217;s Atlas (as they probably had) they might easily have found the
+planet with a good binocular field-glass. As a matter of fact Neptune is
+shown in Harding&#8217;s Atlas (1822) as a star of the 8th magnitude, having
+been mistaken for a star by Lalande on May 8 and 10, 1795; and the present
+writer has<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span> found Harding&#8217;s 8th magnitude stars quite easy objects with a
+binocular field-glass having object-glasses of two inches diameter, and a
+power of about six diameters.</p>
+
+<p><span class="smcap">Supposed Planet beyond Neptune.</span>&mdash;The possible existence of a planet beyond
+Neptune has been frequently suggested. From considerations on the aphelia
+of certain comets, Prof. Forbes in 1880 computed the probable position of
+such a body. He thought this hypothetical planet would be considerably
+larger than Jupiter, and probably revolve round the sun at a distance of
+about 100 times the earth&#8217;s mean distance from the sun. The place
+indicated was between R.A. 11<sup>h</sup> 24<sup>m</sup> and 12<sup>h</sup> 12<sup>m</sup>, and declination 0&deg;
+0&prime; to 6&deg; 0&prime; north. With a view to its discovery, the late Dr. Roberts took
+a series of eighteen photographs covering the region indicated. The result
+of an examination of these photographs showed, Dr. Roberts says, that &#8220;no
+planet of greater brightness than a star of the 15th magnitude exists on
+the sky area herein indicated.&#8221; Prof. W. H. Pickering has recently revived
+the question, and has arrived at the following results: Mean distance of
+the planet from the sun, 51&middot;9 (earth&#8217;s mean distance = 1); period of
+revolution, 373&#189; years; mass about twice the earth&#8217;s mass; probable
+position for 1909 about R.A. 7<sup>h</sup> 47<sup>m</sup>, north declination 21&deg;, or about
+5&deg; south-east of the star &#954; Geminorum. The supposed planet would
+be faint, its brightness<span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span> being from 11&#189; to 13&#189;, according to the
+&#8220;albedo&#8221; (or reflecting power) it may have.<a name='fna_180' id='fna_180' href='#f_180'><small>[180]</small></a></p>
+
+<p>Prof. Forbes has again attacked the question of a possible ultra-Neptunian
+planet, and from a consideration of the comets of 1556, 1843 I, 1880 I,
+and 1882 II, finds a mean distance of 105&middot;4, with an inclination of the
+orbit of 52&deg; to the plane of the ecliptic. This high inclination implies
+that &#8220;during the greatest part of its revolution it is beyond the zodiac,&#8221;
+and this, Mr. W. T. Lynn thinks, &#8220;may partly account for its not having
+hitherto been found by observation.&#8221;<a name='fna_181' id='fna_181' href='#f_181'><small>[181]</small></a></p>
+
+<p>From a consideration of the approximately circular shape of the orbits of
+all the large planets of the solar system, Dr. See suggests the existence
+of three planets outside Neptune, with approximate distances from the sun
+of 42, 56, and 72 respectively (earth&#8217;s distance = 1), and recommends a
+photographic search for them. He says, &#8220;To suppose the planetary system to
+terminate with an orbit so round as that of Neptune is as absurd as to
+suppose that Jupiter&#8217;s system terminates with the orbit of the fourth
+satellite.&#8221;<a name='fna_182' id='fna_182' href='#f_182'><small>[182]</small></a></p>
+
+<p>According to Grant, even twenty years before the discovery of Neptune the
+error of Prof. Adams&#8217; first approximation amounted to little more than
+10&deg;.<a name='fna_183' id='fna_183' href='#f_183'><small>[183]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span></p>
+<h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI</h2>
+<p class="title">Comets</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">We</span> learn from Pliny that comets were classified in ancient times,
+according to their peculiar forms, into twelve classes, of which the
+principal were: <i>Pogonias</i>, bearded; <i>Lampadias</i>, torch-like; <i>Xiphias</i>,
+sword-like; <i>Pitheus</i>, tun-like; <i>Acontias</i>, javelin-like; <i>Ceratias</i>,
+horn-like; <i>Disceus</i>, quoit-like; and <i>Hippias</i>, horse-mane-like.<a name='fna_184' id='fna_184' href='#f_184'><small>[184]</small></a></p>
+
+<p>Of the numerous comets mentioned in astronomical records, comparatively
+few have been visible to the naked eye. Before the invention of the
+telescope (1610) only those which were so visible <i>could</i>, of course, be
+recorded. These number about 400. Of the 400 observed since then, some 70
+or 80 only have been visible by unaided vision; and most of these now
+recorded could never have been seen without a telescope. During the last
+century, out of 300 comets discovered, only 13 were very visible to the
+naked eye. Hence, when we read in the newspapers that a comet has been
+discovered the<span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span> chances are greatly against it becoming visible to the
+naked eye.<a name='fna_185' id='fna_185' href='#f_185'><small>[185]</small></a></p>
+
+<p>Although comparatively few comets can be seen without a telescope, they
+are sometimes bright enough to be visible in daylight! Such were those of
+<span class="smcaplc">B.C.</span> 43, <span class="smcaplc">A.D.</span> 1106, 1402, 1532, 1577, 1744, 1843, and the &#8220;great September
+comet&#8221; of 1882.</p>
+
+<p>If we except the great comet of 1861, through the tail of which the earth
+is supposed to have passed, the comet which came nearest to the earth was
+that of 1770, known as Lexell&#8217;s, which approached us within two millions
+of miles, moving nearly in the plane of the ecliptic. It produced,
+however, no effect on the tides, nor on the moon&#8217;s motion, which shows
+that its mass must have been very small. It was computed by Laplace that
+if its mass had equalled that of the earth, the length of our year would
+have been shortened by 2 hours 47 minutes, and as there was no perceptible
+change Laplace concluded that the comet&#8217;s mass did not exceed
+<span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">5000</span>th of
+the earth&#8217;s mass. This is the comet which passed so near to Jupiter that
+its period was reduced to 5&#189; years. Owing to another near approach in
+1779 it became invisible from the earth, and is now lost.<a name='fna_186' id='fna_186' href='#f_186'><small>[186]</small></a> Its
+identity with the recently discovered eighth satellite of Jupiter has been
+suggested by Mr. George Forbes (see under &#8220;Jupiter&#8221;). At the near approach
+of Lexell&#8217;s comet to the earth in 1770, Messier, &#8220;the comet ferret,&#8221;<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span> found
+that its head had an apparent diameter of 2&#189;&deg;, or nearly five times
+that of the moon!</p>
+
+<p>Another case of near approach to the earth was that of Biela&#8217;s comet at
+its appearance in 1805. On the evening of December 9 of that year, the
+comet approached the earth within 3,380,000 miles.<a name='fna_187' id='fna_187' href='#f_187'><small>[187]</small></a></p>
+
+<p>The comet of <span class="smcaplc">A.D.</span> 1106 is stated to have been seen in daylight close to
+the sun. This was on February 4 of that year. On February 10 it had a tail
+of 60&deg; in length, according to Gaubil.<a name='fna_188' id='fna_188' href='#f_188'><small>[188]</small></a></p>
+
+<p>The comet of 1577 seems to have been one of the brightest on record.
+According to Tycho Brah&eacute;, it was visible in broad daylight. He describes
+the head as &#8220;round, bright, and of a yellowish light,&#8221; with a curved tail
+of a reddish colour.<a name='fna_189' id='fna_189' href='#f_189'><small>[189]</small></a></p>
+
+<p>The comet of 1652 was observed for about three weeks only, and Hevelius
+and Comiers state that it was equal to the moon in apparent size! This
+would indicate a near approach to the earth. An orbit computed by Halley
+shows that the least distance was about 12 millions of miles, and the
+diameter of the comet&#8217;s head rather less than 110,000 miles, or about 14
+times the earth&#8217;s diameter.</p>
+
+<p>According to Mr. Denning, &#8220;most of the periodical comets at perihelion are
+outside the earth&#8217;s orbit, and hence it follows that they escape<span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span>
+observation unless the earth is on the same side of the sun as the
+comet.&#8221;<a name='fna_190' id='fna_190' href='#f_190'><small>[190]</small></a></p>
+
+<p>It was computed by M. Faye that the <i>volume</i> of the famous Donati&#8217;s comet
+(1858) was about 500 times that of the sun! On the other hand, he
+calculated that its <i>mass</i> (or quantity of matter it contained) was only a
+fraction of the earth&#8217;s mass. This shows how almost inconceivably tenuous
+the material forming the comet must have been&mdash;much more rarefied, indeed,
+than the most perfect vacuum which can be produced in an air-pump. This
+tenuity is shown by the fact that stars were seen through the tail &#8220;as if
+the tail did not exist.&#8221; A mist of a few hundred yards in thickness is
+sufficient to hide the stars from our view, while a thickness of thousands
+of miles of cometary matter does not suffice even to dim their brilliancy!</p>
+
+<p>At the time of the appearance of the great comet of 1843, it was doubtful
+whether the comet had transited the sun&#8217;s disc. But it is now known, from
+careful calculations by Prof. Hubbard, that a transit really took place
+between 11<sup>h</sup> 28<sup>m</sup> and 12<sup>h</sup> 29<sup>m</sup> on February 27, 1843, and might have
+been observed in the southern hemisphere. The distance of this remarkable
+comet from the sun at its perihelion passage was less than that of any
+known comet. A little before 10 p.m. on February 27, the comet passed
+within 81,500 miles of<span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span> the sun&#8217;s surface with the enormous velocity of
+348 miles a second! It remained less than 2&#188; hours north of the
+ecliptic, passing from the ascending to the descending node of its orbit
+in 2<sup>h</sup> 13<sup>m</sup>&middot;4.<a name='fna_191' id='fna_191' href='#f_191'><small>[191]</small></a> The great comet of 1882 transited the sun&#8217;s disc on
+Sunday, September 17, of that year, the ingress taking place at 4<sup>h</sup> 50<sup>m</sup>
+58<sup>s</sup>, Cape mean time. When on the sun the comet was absolutely invisible,
+showing that there was nothing solid about it. It was visible near the sun
+with the naked eye a little before the transit took place.<a name='fna_192' id='fna_192' href='#f_192'><small>[192]</small></a> This great
+comet was found by several computors to have been travelling in an
+elliptic orbit with a period of about eight centuries. Morrison found 712
+years; Frisby, 794; Fabritius, 823; and Kreutz, 843 years.<a name='fna_193' id='fna_193' href='#f_193'><small>[193]</small></a></p>
+
+<p>The great southern comet of 1887 may be described as a comet without a
+head! The popular idea of a comet is a star with a tail. But in this case
+there was no head visible&mdash;to the naked eye at least. Dr. Thome of the
+Cordoba Observatory&mdash;its discoverer&mdash;describes it as &#8220;a beautiful
+object&mdash;a narrow, straight, sharply defined, graceful tail, over 40&deg; long,
+shining with a soft starry light against a dark sky, beginning apparently
+without a head, and gradually widening and fading as it extended
+upwards.&#8221;<a name='fna_194' id='fna_194' href='#f_194'><small>[194]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span>The great southern comet of 1901 had five tails on May 6 of that year. Two
+were fairly bright, and the remaining three rather faint. Mr. Gale saw a
+number of faint stars through the tails. The light of these seem to have
+been &#8220;undimmed.&#8221; Mr. Cobham noticed that the stars Rigel and &#946;
+Eridani shone through one of the faint tails, and &#8220;showed no perceptible
+difference.&#8221;<a name='fna_195' id='fna_195' href='#f_195'><small>[195]</small></a></p>
+
+<p>Prof. W. H. Pickering says that &#8220;the head of a comet, as far as our
+present knowledge is concerned, seems therefore to be merely a meteor
+swarm containing so much gaseous material that when electrified by its
+approach to the sun it will be rendered luminous&#8221; (<i>Harvard Annual</i>, vol.
+xxxii. part ii. p. 295) &#8220;... if the meteors and their atmospheres are
+sufficiently widely separated from one another, the comet may be brilliant
+and yet transparent at the same time.&#8221;</p>
+
+<p>In the case of Swift&#8217;s comet of 1892 some periodical differences of
+appearance were due, according to Prof. W. H. Pickering, to a rotation of
+the comet round an axis passing longitudinally through the tail, and he
+estimated the period of rotation at about 94 to 97 hours. He computed that
+in this comet the repulsive force exerted by the sun on the comet&#8217;s tail
+was &#8220;about 39&middot;5 times the gravitational force.&#8221;<a name='fna_196' id='fna_196' href='#f_196'><small>[196]</small></a></p>
+
+<p>The comet known as 1902<i>b</i> approached the<span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span> planet Mercury within two
+millions of miles on November 29 of that year. Prof. O. C. Wendell, of
+Harvard Observatory, made some observations on the transparency of this
+comet. He found with the aid of a photometer and the 15-inch telescope of
+the observatory that in the case of two faint stars over which the comet
+passed on October 14, 1902, the absorption of light by the comet was
+insensible, and possibly did not exceed one or two hundredths of a
+magnitude,<a name='fna_197' id='fna_197' href='#f_197'><small>[197]</small></a> an amount quite imperceptible to the naked eye, and shows
+conclusively how almost inconceivably rarefied the substance of this comet
+must be.</p>
+
+<p>The comet known as Morehouse (1908<i>c</i>) showed some curious and wonderful
+changes. Mr. Borelly found that five tails are visible on a photographic
+plate taken on October 3, 1908, and the trail of an occulted star
+indicates a slight absorption effect. According to M. L. Rabourdin, great
+changes took place from day to day, and even during the course of an hour!
+Similar changes were recorded by G. M. Gauthier; and Prof. Barnard, who
+photographed the comet on 30 nights from September 2 to October 13, states
+that the photographs of September 30 &#8220;are unique, whilst the
+transformation which took place between the taking of these and the taking
+of the next one on October 1 was very wonderful.&#8221;<a name='fna_198' id='fna_198' href='#f_198'><small>[198]</small></a> The spectrum<span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span>
+showed the lines of cyanogen instead of the hydrocarbon spectrum shown by
+most comets.</p>
+
+<p>Prof. Barnard has suggested that all the phenomena of comets&#8217; tails cannot
+be explained by a repulsive force from the sun. Short tails issuing from
+the comet&#8217;s nucleus at considerable angles with the main tail point to
+eruptive action in the comet itself. The rapid changes and distortions
+frequently observed in the tails of some comets suggest motion through a
+resisting medium; and the sudden increase of light also occasionally
+observed points in the same direction.<a name='fna_199' id='fna_199' href='#f_199'><small>[199]</small></a></p>
+
+<p>It was computed by Olbers that if a comet having a mass of
+<span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">2000</span>th of the
+earth&#8217;s mass&mdash;which would form a globe of about 520 miles in diameter and
+of the density of granite&mdash;collided with the earth, with a velocity of 40
+miles a second, our globe would be shattered into fragments.<a name='fna_200' id='fna_200' href='#f_200'><small>[200]</small></a> But that
+any comet has a solid nucleus of this size seems very doubtful; and we may
+further say that the collision of the earth with <i>any</i> comet is highly
+improbable.</p>
+
+<p>It seems to be a common idea that harvests are affected by comets, and
+even &#8220;comet wines&#8221; are sometimes spoken of. But we know that the earth
+receives practically no heat from the brightest comet. Even in the case of
+the brilliant comet of 1811, one of the finest on record, it was<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span> found
+that &#8220;all the efforts to concentrate its rays did not produce the
+slightest effect on the blackened bulb of the most sensitive thermometer.&#8221;
+Arago found that the year 1808, in which several comets were visible, was
+a cold year, &#8220;and 1831, in which there was no comet, enjoyed a much higher
+temperature than 1819, when there were three comets, one of which was very
+brilliant.&#8221;<a name='fna_201' id='fna_201' href='#f_201'><small>[201]</small></a> We may, therefore, safely conclude that even a large
+comet has no effect whatever on the weather.</p>
+
+<p>From calculations on the orbit of Halley&#8217;s comet, the next return of which
+is due in 1910, Messrs. Cowell and Crommelin find that the identity of the
+comet shown on the Bayeux Tapestry with Halley&#8217;s comet is now &#8220;fully
+established.&#8221; They find that the date of perihelion passage was March 25,
+1066, which differs by only 4 days from the date found by Hind. The
+imposing aspect of the comet in 1066 described in European chronicles of
+that time is confirmed by the Chinese Annals. In the latter records the
+brightness is compared to that of Venus, and even with that of the moon!
+The comparison with the moon was probably an exaggeration, but the comet
+doubtless made a very brilliant show. In the Bayeux Tapestry the
+inscription on the wall behind the spectators reads: &#8220;<i>isti mirant
+stella</i>.&#8221; Now, this is bad Latin, and Mr. W. T.<span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span> Lynn has made the
+interesting suggestion that some of the letters are hidden by the
+buildings in front and that the real sentence is &#8220;<i>isti mirantur
+stellam</i>.&#8221;<a name='fna_202' id='fna_202' href='#f_202'><small>[202]</small></a> The present writer has examined the copy of the Bayeux
+Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn&#8217;s
+suggestion seems very plausible. But the last letter of <i>stellam</i> is
+apparently hidden by the comet&#8217;s tail, which does not seem very probable!</p>
+
+<p>The conditions under which the comet will appear in 1910 are not unlike
+those of 1066 and 1145. &#8220;In each year the comet was discovered as a
+morning star, then lost in the sun&#8217;s rays; on its emergence it was near
+the earth and moved with great rapidity, finally becoming stationary in
+the neighbourhood of Hydra, where it was lost to view.&#8221;<a name='fna_203' id='fna_203' href='#f_203'><small>[203]</small></a> In 1910 it
+will probably be an evening star before March 17, and after May 11, making
+a near approach to the earth about May 12. About this time its apparent
+motion in the sky will be very rapid. As, however, periodical comets&mdash;such
+as Halley&#8217;s&mdash;seem to become fainter at each return, great expectations
+with reference to its appearance in 1910 should not be indulged in.</p>
+
+<p>The appearance of Halley&#8217;s comet in <span class="smcaplc">A.D.</span> 1222 is thus described by
+Pingr&eacute;&mdash;a great authority on comets&mdash;(quoting from an ancient writer)&mdash;</p>
+
+<div class="blockquot"><p><span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span>&#8220;In autumn, that
+is to say in the months of August and September, a star of the first magnitude was seen, very red, and accompanied by a
+great tail which extended towards the top of the sky in the form of a
+cone extremely pointed. It appeared to be very near the earth. It was
+observed (at first?) near the place of the setting sun in the month of
+December.&#8221;</p></div>
+
+<p>With reference to its appearance in the year 1456, when it was of &#8220;vivid
+brightness,&#8221; and had a tail of 60&deg; in length, Admiral Smyth says,<a name='fna_204' id='fna_204' href='#f_204'><small>[204]</small></a> &#8220;To
+its malign influence were imputed the rapid successes of Mahomet II.,
+which then threatened all Christendom. The general alarm was greatly
+aggravated by the conduct of Pope Callixtus III., who, though otherwise a
+man of abilities, was a poor astronomer; for that pontiff daily ordered
+the church bells to be rung at noon-tide, extra <i>Ave-Marias</i> to be
+repeated, and a special protest and excommunication was composed,
+exorcising equally the Devil, the Turks, and the comet.&#8221; With reference to
+this story, Mr. G. F. Chambers points out<a name='fna_205' id='fna_205' href='#f_205'><small>[205]</small></a> that it is probably based
+on a passage in Platina&#8217;s <i>Vit&aelig; Pontificum</i>. But in this passage there is
+no mention made of excommunication or exorcism, so that the story, which
+has long been current, is probably mythical. In confirmation of this view,
+the Rev. W. F. Rigge has shown conclusively<a name='fna_206' id='fna_206' href='#f_206'><small>[206]</small></a> that no bull was ever
+issued<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span> by Pope Callixtus III. containing a reference to <i>any</i> comet. The
+story would therefore seem to be absolutely without foundation, and should
+be consigned to the limbo of all such baseless myths.</p>
+
+<p>With reference to the appearance of Halley&#8217;s comet, at his last return in
+1835, Sir John Herschel, who observed it at the Cape of Good Hope, says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Among the innumerable stars of all magnitudes, from the ninth
+downwards, which at various times were seen through it, and some
+extremely near to the nucleus (though not <i>exactly on it</i>) there never
+appeared the least ground for presuming any extinction of their light
+in traversing it. Very minute stars indeed, on entering its brightest
+portions, were obliterated, as they would have been by an equal
+illumination of the field of view; but stars which before their entry
+appeared bright enough to bear that degree of illumination, were in no
+case, so far as I could judge, affected to a greater extent than they
+would have been by so much lamp-light artificially introduced.&#8221;<a name='fna_207' id='fna_207' href='#f_207'><small>[207]</small></a></p></div>
+
+<p>It is computed by Prof. J. Holetschak that, early in October, 1909,
+Halley&#8217;s comet should have the brightness of a star of about 14&#189;
+magnitude.<a name='fna_208' id='fna_208' href='#f_208'><small>[208]</small></a> It should then&mdash;if not detected before&mdash;be discoverable
+with some of the large telescopes now available.</p>
+
+<p>According to the computations of Messrs. Cowell and Crommelin, the comet
+should enter Pisces<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span> from Aries in January, 1910. &#8220;Travelling westward
+towards the star &#947; Piscium until the beginning of May, and then
+turning eastward again, it will travel back through the constellations
+Cetus, Orion, Monoceros, Hydra, and Sextans.&#8221; From this it seems that
+observers in the southern hemisphere will have a better view of the comet
+than those in northern latitudes. The computed brightness varies from 1 on
+January 2, 1910, to 1112 on May 10. But the actual brightness of a comet
+does not always agree with theory. It is sometimes brighter than
+calculation would indicate.</p>
+
+<p>According to Prof. O. C. Wendell, Halley&#8217;s comet will, on May 12, 1910,
+approach the earth&#8217;s orbit within 4&middot;6 millions of miles; and he thinks
+that possibly the earth may &#8220;encounter some meteors,&#8221; which are presumably
+connected with the comet. He has computed the &#8220;radiant point&#8221; of these
+meteors (that is, the point from which they appear to come), and finds its
+position to be R.A. 22<sup>h</sup> 42<sup>m</sup>&middot;9, Decl. N. 1&deg; 18&prime;. This point lies a
+little south-west of the star &#946; Piscium.</p>
+
+<p>According to Dr. Smart, the comet will, on June 2, &#8220;cross the Equator
+thirteen degrees south of Regulus, and will then move slowly in the
+direction of &#966; Leonis. The comet will be at its descending node
+on the ecliptic in the morning of May 16, and the earth will pass through
+the node on the comet&#8217;s orbit about two and a half<span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span> days later. The
+comet&#8217;s orbit at the node is about 13 million miles within that of the
+earth. Matter repelled from the comet&#8217;s nucleus by the sun with a velocity
+of about 216,000 miles per hour, would just meet the earth when crossing
+the comet&#8217;s orbit plane. Matter expelled with a velocity of 80,000 miles
+per hour, as in the case of Comet Morehouse, would require seven days for
+the journey. Cometary matter is said to have acquired greater velocities
+than this, for (according to Webb, who quotes Chacornac) Comet II., 1862,
+shot luminous matter towards the sun, with a velocity of nearly 2200 miles
+per second. It is therefore possible that matter thrown off by the comet
+at the node may enter our atmosphere, in which case we must hope that
+cyanogen, which so often appears in cometary spectra, may not be
+inconveniently in evidence.&#8221;<a name='fna_209' id='fna_209' href='#f_209'><small>[209]</small></a></p>
+
+<p>Cyanogen is, of course, a poisonous gas, but cometary matter is so
+rarefied that injurious effects on the earth need not be feared.</p>
+
+<p>If we can believe the accounts which have been handed down to us, some
+very wonderful comets were visible in ancient times. The following may be
+mentioned:&mdash;</p>
+
+<p>B.C. 165. The sun is said to have been &#8220;seen for several hours in the
+night.&#8221; If this was a comet it must have been one of extraordinary
+brilliancy.<a name='fna_210' id='fna_210' href='#f_210'><small>[210]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span>B.C. 146. &#8220;After the death of Demetrius, king of Syria, the father of
+Demetrius and Antiochus, a little before the war in Achaia, there appeared
+a comet as large as the sun. Its disc was first red, and like fire,
+spreading sufficient light to dissipate the darkness of night; after a
+little while its size diminished, its brilliancy became weakened, and at
+length it entirely disappeared.&#8221;<a name='fna_211' id='fna_211' href='#f_211'><small>[211]</small></a></p>
+
+<p>B.C. 134. It is recorded that at the birth of Mithridates a great comet
+appeared which &#8220;occupied the fourth part of the sky, and its brilliancy
+was superior to that of the sun.&#8221; (?)<a name='fna_212' id='fna_212' href='#f_212'><small>[212]</small></a></p>
+
+<p>B.C. 75. A comet is described as equal in size to the moon, and giving as
+much light as the sun on a cloudy day. (!)<a name='fna_213' id='fna_213' href='#f_213'><small>[213]</small></a></p>
+
+<p>A.D. 531. In this year a great comet was observed in Europe and China. It
+is described as &#8220;a very large and fearful comet,&#8221; and was visible in the
+west for three weeks. Hind thinks that this was an appearance of Halley&#8217;s
+comet,<a name='fna_214' id='fna_214' href='#f_214'><small>[214]</small></a> and this has been confirmed by Mr. Crommelin.</p>
+
+<p>A.D. 813, August 4. A comet is said to have appeared on this date, of
+which the following curious description is given: &#8220;It resembled two moons
+joined together; they separated, and having taken different forms, at
+length appeared like a man without a head.&#8221; (!)<a name='fna_215' id='fna_215' href='#f_215'><small>[215]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span>A.D. 893. A great comet is said to have appeared in this year with a tail
+100&deg; in length, which afterwards increased to 200&deg;!<a name='fna_216' id='fna_216' href='#f_216'><small>[216]</small></a></p>
+
+<p>A.D. 1402. A comet appeared in February of this year, which was visible in
+daylight for eight days. &#8220;On Palm Sunday, March 19, its size was
+prodigious.&#8221; Another comet, visible in the daytime, was seen from June to
+September of the same year.</p>
+
+<p>When the orbit of the comet known as 1889 V was computed, it was found
+that it had passed through Jupiter&#8217;s system in 1886 (July 18-21). The
+calculations show that it must have passed within a distance of 112,300
+miles of the planet itself&mdash;or less than half the moon&#8217;s distance from the
+earth&mdash;and &#8220;its centre may possibly have grazed the surface of
+Jupiter.&#8221;<a name='fna_217' id='fna_217' href='#f_217'><small>[217]</small></a></p>
+
+<p>Sir John Herschel thought that the great comet of 1861 was by far the
+brightest comet he had ever seen, those of 1811 and 1858 (Donati&#8217;s) not
+excepted.<a name='fna_218' id='fna_218' href='#f_218'><small>[218]</small></a> Prof. Kreutz found its period of revolution round the sun
+to be about 409 years, with the plane of the orbit nearly at right angles
+to the plane of the ecliptic.</p>
+
+<hr style="width: 25%;" />
+
+<p>On November 9, 1795, Sir William Herschel saw the comet of that year pass
+centrally over<span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span> a small double star of the 11th and 12th magnitudes, and
+the fainter of the two components remained distinctly visible during the
+comet&#8217;s transit over the star. This comet was an appearance of the comet
+now known as Encke&#8217;s.<a name='fna_219' id='fna_219' href='#f_219'><small>[219]</small></a> Struve saw a star of the 10th magnitude through
+nearly the brightest part of Encke&#8217;s comet on November 7, 1828, but the
+star&#8217;s light was not dimmed by the comet.</p>
+
+<p>Sir John Herschel saw a cluster of stars of the 16th or 17th magnitude
+through Biela&#8217;s comet, although the interposed cometary matter must have
+been at least 50,000 miles in thickness.<a name='fna_220' id='fna_220' href='#f_220'><small>[220]</small></a></p>
+
+<p>Bessel found that on September 29, 1835, a star of the 10th magnitude
+shone with undimmed lustre through the tail of Halley&#8217;s comet within 8
+seconds of arc of the central point of the head. At Dorpat (Russia) Struve
+saw the same star &#8220;in conjunction only 2&Prime;&middot;2 from the brightest point of
+the comet. The star remained continuously visible, and its light was not
+perceptibly diminished whilst the nucleus of the comet seemed to be almost
+extinguished before the radiance of the small star of the 9th or 10th
+magnitude.&#8221;<a name='fna_221' id='fna_221' href='#f_221'><small>[221]</small></a></p>
+
+<p>Webb says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Donati saw a 7 mg. star enlarged so as to show a sensible disc, when
+the nucleus of comet III.,<span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span> 1860, passed very near it. Stars are said
+to have started, or become tremulous, during occultations by comets.
+Birmingham observed the comet of Encke illuminated by a star over
+which it passed, August 23, 1868; and Klein, in 1861, remarked an
+exceptional twinkling in 5 mg. stars involved in the tail.&#8221;<a name='fna_222' id='fna_222' href='#f_222'><small>[222]</small></a></p></div>
+
+<p>The comet of 1729 had the greatest perihelion distance of any known
+comet;<a name='fna_223' id='fna_223' href='#f_223'><small>[223]</small></a> that is, when nearest to the sun, it did not approach the
+central luminary within four times the earth&#8217;s distance from the sun!</p>
+
+<p>Barnard&#8217;s comet, 1889 I., although it never became visible to the naked
+eye, was visible with a telescope from September 2, 1888, to August 18,
+1890, or 715 days&mdash;the longest period of visibility of any comet on
+record. When last seen it was 6&#188; times the earth&#8217;s distance from the
+sun, or about 580 millions of miles,<a name='fna_224' id='fna_224' href='#f_224'><small>[224]</small></a> or beyond the orbit of Jupiter!</p>
+
+<p>Messier, who was called &#8220;the comet ferret,&#8221; discovered &#8220;all his comets
+with a small 2-foot telescope of 2&#188; inches aperture, magnifying 5
+times, and with a field of 4&deg;.&#8221;<a name='fna_225' id='fna_225' href='#f_225'><small>[225]</small></a></p>
+
+<p>It is a very curious fact that Sir William Herschel, &#8220;during all his
+star-gaugings and sweeps for nebul&aelig;, never discovered a comet;&#8221;<a name='fna_226' id='fna_226' href='#f_226'><small>[226]</small></a> that
+is<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span> an object which was afterwards <i>proved</i> to be a comet. Possibly,
+however, some of his nebul&aelig; which are now missing, may have been really
+comets.</p>
+
+<p>Sir William Herschel found the diameter of the head of the great comet of
+1811 to be 127,000 miles. The surrounding envelope he estimated to be at
+least 643,000 miles, or about three-fourths of the sun&#8217;s diameter.</p>
+
+<p>On a drawing of the tails of the great comet of 1744 given in a little
+book printed in Berlin in that year, no less than 12 tails are shown!
+These vary in length and brightness. A copy of this drawing is given in
+<i>Copernicus</i>.<a name='fna_227' id='fna_227' href='#f_227'><small>[227]</small></a> The observations were made by &#8220;einen geschichten
+Frauenzimmer,&#8221; who Dr. Dreyer identifies with Christian Kirch, or one of
+her two sisters, daughters of the famous Gottfried and Maria Margaretta
+Kirch (<i>Idem</i>, p. 107). Dr. Dreyer thinks that the drawing &#8220;seems to have
+been carefully made, and not to be a mere rough sketch as I had at first
+supposed&#8221; (<i>Idem</i>, p. 185).</p>
+
+<p>The tails of some comets were of immense length. That of the comet of 1769
+had an absolute length of 38 millions of miles. That of 1680, 96 million
+of miles, or more than the sun&#8217;s distance from the earth. According to Sir
+William Herschel, the tail of the great comet of 1811 was over 100
+millions of miles in length. That of the<span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span> great comet of 1843&mdash;one of the
+finest in history&mdash;is supposed to have reached a length of 150 millions of
+miles!<a name='fna_228' id='fna_228' href='#f_228'><small>[228]</small></a></p>
+
+<p>In width the tails of comets were in some cases enormous. According to Sir
+William Herschel, the tail of the comet of 1811 had a diameter of 15
+millions of miles! Its volume was, therefore, far greater than that of the
+sun!<a href='#f_228'><small>[228]</small></a></p>
+
+<p>According to Hevelius the comet of 1652 was of such a magnitude that it
+&#8220;resembled the moon when half full; only it shone with a pale and dismal
+light.&#8221;<a name='fna_229' id='fna_229' href='#f_229'><small>[229]</small></a></p>
+
+<p>Halley&#8217;s comet at its next appearance will be examined with the
+spectroscope for the first time in its history. At its last return in
+1835, the spectroscope had not been invented.</p>
+
+<p>For the great comet of 1811, Arago computed a period of 3065 years; and
+Encke found a period of 8800 years for the great comet of 1680.<a name='fna_230' id='fna_230' href='#f_230'><small>[230]</small></a></p>
+
+<p>The variation in the orbital velocity of some comets is enormous. The
+velocity of the comet of 1680 when passing round the sun (perihelion) was
+about 212 miles a second! Whereas at its greatest distance from the sun
+(aphelion) the velocity is reduced to about 10 feet a second!</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span></p>
+<h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII</h2>
+<p class="title">Meteors</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Mr. Denning</span> thinks that the meteor shower of the month of May, known as
+the Aquarids, is probably connected with Halley&#8217;s comet. The meteors
+should be looked for after 1 a.m. during the first week in May, and may
+possibly show an enhanced display in May, 1910, when Halley&#8217;s comet will
+be near the sun and earth.<a name='fna_231' id='fna_231' href='#f_231'><small>[231]</small></a></p>
+
+<p>On November 29, 1905, Sir David Gill observed a fireball with an apparent
+diameter equal to that of the moon, which remained visible for 5 minutes
+and disappeared in a hazy sky. Observed from another place, Mr. Fuller
+found that the meteor was visible 2 hours later! Sir David Gill stated
+that he does not know of any similar phenomenon.<a name='fna_232' id='fna_232' href='#f_232'><small>[232]</small></a></p>
+
+<p>Mr. Denning finds that swiftly moving meteors become visible at a greater
+height above the earth&#8217;s surface than the slower ones. Thus, for the
+Leonids and Perseids, which are both swift,<span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span> it has been found that the
+Leonids appear at an average height of 84 miles, and disappear at a height
+of 56 miles; and the Perseids at 80 and 54 miles respectively. &#8220;On the
+other hand, the mean height of the very slow meteors average about 65
+miles at the beginning and 38 miles at the end of their appearance.&#8221;<a name='fna_233' id='fna_233' href='#f_233'><small>[233]</small></a></p>
+
+<p>During the night of July 21-22, 1896, Mr. William Brooks, the well-known
+astronomer, and director of the Smith Observatory at Geneva (New York),
+saw a round dark body pass slowly across the moon&#8217;s bright disc, the moon
+being nearly full at the time. The apparent diameter of the object was
+about one minute of arc, and the duration of the transit 3 or 4 seconds,
+the direction of motion being from east to west. On August 22 of the same
+year, Mr. Gathman (an American observer) saw a meteor crossing the <i>sun&#8217;s</i>
+disc, the transit lasting about 8 seconds.<a name='fna_234' id='fna_234' href='#f_234'><small>[234]</small></a></p>
+
+<p>A meteor which appeared in Italy on July 7, 1892, was shown by Prof. von
+Niessl to have had an <i>ascending</i> path towards the latter end of its
+course! The length of its path was computed to be 683 miles. When first
+seen, its height above the earth was about 42 miles, and when it
+disappeared its height had increased to about 98 miles, showing that its
+motion was directed upwards!<a name='fna_235' id='fna_235' href='#f_235'><small>[235]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span>In the case of the fall of meteoric stones, which occasionally occur, it
+has sometimes been noticed that the sound caused by the explosion of the
+meteorite, or its passage through the air, is heard before the meteorite
+is seen to fall. This has been explained by the fact that owing to the
+resistance of the air to a body moving at first with a high velocity its
+speed is so reduced that it strikes the earth with a velocity less than
+that of sound. Hence the sound reaches the earth before the body strikes
+the ground.<a name='fna_236' id='fna_236' href='#f_236'><small>[236]</small></a></p>
+
+<p>The largest meteoric stone preserved in a museum is that known as the
+Anighita, which weighs 36&#189; tons, and was found at Cape York in
+Greenland. It was brought to the American Museum of Natural History by
+Commander R. E. Peary, the Arctic explorer.</p>
+
+<p>The second largest known is that of Bacubirito in Mexico, the weight of
+which is estimated at 27&#189; tons.</p>
+
+<p>The third largest is that known as the Williamette, which was found in
+1902 near the town of that name in Western Oregon (U.S.A.). It is composed
+of metallic nickel-iron, and weighs about 13&#189; tons. It is now in the
+American Museum of Natural History.</p>
+
+<p>A large meteorite was actually seen, from the deck of the steamer <i>African
+Prince</i>, to fall into the Atlantic Ocean, on October 7, 1906! The captain<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span>
+of the vessel, Captain Anderson, describes it as having a train of light
+resembling &#8220;an immense broad electric-coloured band, gradually turning to
+orange, and then to the colour of molten metal. When the meteor came into
+the denser atmosphere close to the earth, it appeared, as nearly as is
+possible to describe it, like a molten mass of metal being poured out. It
+entered the water with a hissing noise close to the ship.&#8221;<a name='fna_237' id='fna_237' href='#f_237'><small>[237]</small></a> This was a
+very curious and perhaps unique phenomenon, and it would seem that the
+vessel had a narrow escape from destruction.</p>
+
+<p>In Central Arizona (U.S.A.) there is a hill called Coon Butte, or Coon
+Mountain. This so-called &#8220;mountain&#8221; rises to a height of only 130 to 160
+feet above the surrounding plain, and has on its top a crater of 530 to
+560 feet deep; the bottom of the crater&mdash;which is dry&mdash;being thus 400 feet
+below the level of the surrounding country. This so-called &#8220;crater&#8221; is
+almost circular and nearly three-quarters of a mile in diameter. It has
+been suggested that this &#8220;crater&#8221; was formed by the fall of an enormous
+iron meteorite, or small asteroid. The &#8220;crater&#8221; has been carefully
+examined by a geologist and a physicist. From the evidence and facts
+found, the geologist (Mr. Barringer) states that &#8220;they do not leave, in my
+mind, a scintilla of doubt that this mountain and its crater were produced
+by the impact<span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span> of a huge meteorite or small asteroid.&#8221; The physicist (Mr.
+Tilghmann) says that he &#8220;is justified, under due reserve as to
+subsequently developed facts, in announcing that the formation at this
+locality is due to the impact of a meteor of enormous and unprecedented
+size.&#8221; There are numerous masses of meteoric iron in the vicinity of the
+&#8220;crater.&#8221; The so-called Canyon Diabolo meteorite was found in a canyon of
+that name about 2&#189; miles from the Coon Mountain. The investigators
+estimate that the great meteoric fall took place &#8220;not more than 5000 years
+ago, perhaps much less.&#8221; Cedar trees about 700 years old are now growing
+on the rim of the mountain. From the results of artillery experiments, Mr.
+Gilbert finds that &#8220;a spherical projectile striking solid limestone with a
+velocity of 1800 feet a second will penetrate to a depth of something less
+than two diameters,&#8221; and from this Mr. L. Fletcher concludes &#8220;that a
+meteorite of large size would not be prevented by the earth&#8217;s atmosphere
+from having a penetration effect sufficient for the production of such a
+crater.&#8221;<a name='fna_238' id='fna_238' href='#f_238'><small>[238]</small></a></p>
+
+<p>The meteoric origin of this remarkable &#8220;crater&#8221; is strongly favoured by
+Mr. G. P. Merrill, Head Curator of Geology, U.S. National Museum.</p>
+
+<p>The Canyon Diabolo meteorite above referred to was found to contain
+diamonds! some black, others transparent. So some have said that &#8220;the<span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span>
+diamond is a gift from Heaven,&#8221; conveyed to earth in meteoric
+showers.<a name='fna_239' id='fna_239' href='#f_239'><small>[239]</small></a> But diamond-bearing meteorites would seem to be rather a
+freak of nature. It does not follow that <i>all</i> diamonds had their origin
+in meteoric stones. The mineral known as periodot is frequently found in
+meteoric stones, but it is also a constituent of terrestrial rocks.</p>
+
+<p>In the year 1882 it was stated by Dr. Halm and Dr. Weinhand that they had
+found fossil sponges, corals, and crinoids in meteoric stones! Dr.
+Weinhand thought he had actually determined three genera!<a name='fna_240' id='fna_240' href='#f_240'><small>[240]</small></a> But this
+startling result was flatly contradicted by Carl Vogt, who stated that the
+supposed fossils are merely crystalline conformations.<a name='fna_241' id='fna_241' href='#f_241'><small>[241]</small></a></p>
+
+<p>Some meteorites contain a large quantity of occluded gases, hydrogen,
+helium, and carbon oxides. It is stated that Dr. Odling once &#8220;lighted up
+the theatre of the Royal Institution with gas brought down from
+interstellar space by meteorites&#8221;!<a name='fna_242' id='fna_242' href='#f_242'><small>[242]</small></a></p>
+
+<p>On February 10, 1896, a large meteorite burst over Madrid with a loud
+report. The concussion was so great that many windows in the city were
+broken, and some partitions in houses were shaken down!<a name='fna_243' id='fna_243' href='#f_243'><small>[243]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span>A very brilliant meteor or fireball was seen in daylight on June 9, 1900,
+at 2<sup>h</sup> 55<sup>m</sup> p.m. from various places in Surrey, Sussex, and near London.
+Calculations showed that &#8220;the meteor began 59 miles in height over a point
+10 miles east of Valognes, near Cherbourg, France. Meteor ended 23 miles
+in height, over Calais, France. Length of path 175 miles. Radiant point,
+280&deg;, 12&deg;.&#8221;<a name='fna_244' id='fna_244' href='#f_244'><small>[244]</small></a></p>
+
+<p>It was decided some years ago &#8220;in the American Supreme Court that a
+meteorite, though a stone fallen from heaven, belongs to the owner of the
+freehold interest in the land on which it falls, and not to the
+tenant.&#8221;<a name='fna_245' id='fna_245' href='#f_245'><small>[245]</small></a></p>
+
+<p>With reference to the fall of meteoric matter on the earth, Mr. Proctor
+says, &#8220;It is calculated by Dr. Kleiber of St. Petersburgh that 4250 lbs.
+of meteoric dust fall on the earth every hour&mdash;that is, 59 tons a day, and
+more than 11,435 tons a year. I believe this to be considerably short of
+the truth. It sounds like a large annual growth, and the downfall of such
+an enormous mass of meteoric matter seems suggestive of some degree of
+danger. But in reality, Dr. Kleiber&#8217;s estimate gives only about 25
+millions of pounds annually, which is less than 2 ounces annually to each
+square mile of the earth&#8217;s surface,&#8221;<a name='fna_246' id='fna_246' href='#f_246'><small>[246]</small></a> a quantity which is, of course,
+quite insignificant.</p>
+
+<p><span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span>According to Humboldt, Chladni states that a Franciscan monk was killed by
+the fall of an a&euml;rolite at Milan in the year 1660.<a name='fna_247' id='fna_247' href='#f_247'><small>[247]</small></a> Humboldt also
+mentions the death by meteoric stones of a monk at Crema on September 4,
+1511, and two Swedish sailors on board ship in 1674.<a name='fna_248' id='fna_248' href='#f_248'><small>[248]</small></a></p>
+
+<p>It is a curious fact that, according to Olbers, &#8220;no fossil meteoric
+stones&#8221; have ever been discovered.<a name='fna_249' id='fna_249' href='#f_249'><small>[249]</small></a> Considering the number which are
+supposed to have fallen to the earth in the course of ages, this fact
+seems a remarkable one.</p>
+
+<p>On May 10, 1879, a shower of meteorites fell at Eitherville, Iowa
+(U.S.A.). Some of the fragments found weighed 437, 170, 92&#189;, 28,
+10&#189;, 4 and 2 lbs. in weight. In the following year (1880) when the
+prairie grass had been consumed by a fire, about &#8220;5000 pieces were found
+from the size of a pin to a pound in weight.&#8221;<a name='fna_250' id='fna_250' href='#f_250'><small>[250]</small></a></p>
+
+<p>According to Prof. Silvestria of Catania, a shower of meteoric dust mixed
+with rain fell on the night of March 29, 1880. The dust contained a large
+proportion of iron in the metallic state. In size the particles varied
+from a tenth to a hundredth of a millimetre.<a name='fna_251' id='fna_251' href='#f_251'><small>[251]</small></a></p>
+
+<p>It is sometimes stated that the average mass of a &#8220;shooting star&#8221; is only
+a few grains. But from<span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span> comparisons with an electric arc light, Prof. W.
+H. Pickering concludes that a meteor as bright as a third magnitude star,
+composed of iron or stone, would probably have a diameter of 6 or 7
+inches. An average bright fireball would perhaps measure 5 or 6 feet in
+diameter.<a name='fna_252' id='fna_252' href='#f_252'><small>[252]</small></a></p>
+
+<p>In the Book of Joshua we are told &#8220;that the <span class="smcap">Lord</span> cast down great stones
+from heaven upon them unto Azekah, and they died&#8221; (Joshua x. 11). In the
+latter portion of the verse &#8220;hailstones&#8221; are mentioned, but as the
+original Hebrew word means stones in general (not hailstones), it seems
+very probable that the stones referred to were a&euml;rolites.<a name='fna_253' id='fna_253' href='#f_253'><small>[253]</small></a></p>
+
+<p>The stone mentioned in the Acts of the Apostles, from which was found &#8220;the
+<i>image</i> which fell down from Jupiter&#8221; (Acts xix. 35), was evidently a
+meteoric stone.<a href='#f_253'><small>[253]</small></a></p>
+
+<p>The famous stone in the Caaba at Mecca, is probably a stone of meteoric
+origin.<a href='#f_253'><small>[253]</small></a></p>
+
+<p class="poem"><span style="margin-left: 7em;">I</span><br />
+&#8220;Stones from Heaven! Can you wonder,<br />
+<span style="margin-left: 1em;">You who scrutinize the Earth,</span><br />
+At the love and veneration<br />
+<span style="margin-left: 1em;">They received before the birth</span><br />
+Of our scientific methods?<br />
+<br />
+<br />
+<span style="margin-left: 6.75em;">II</span><br />
+&#8220;Stones from Heaven! we can handle<br />
+<span style="margin-left: 1em;">Fragments fallen from realms of Space;</span><br />
+<span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span>Oh! the marvel and the mystery,<br />
+<span style="margin-left: 1em;">Could we understand their place</span><br />
+In the scheme of things created!<br />
+<br />
+<br />
+<span style="margin-left: 6.5em;">III</span><br />
+&#8220;Stones from Heaven! With a mighty<br />
+<span style="margin-left: 1em;">Comet whirling formed they part?</span><br />
+Fell they from their lofty station<br />
+<span style="margin-left: 1em;">Like a brilliant fiery dart,</span><br />
+Hurl&#8217;d from starry fields of Night?&#8221;<a name='fna_254' id='fna_254' href='#f_254'><small>[254]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span></p>
+<h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII</h2>
+<p class="title">The Zodiacal Light and Gegenschein</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">According</span> to Gruson and Brugsch, the Zodiacal Light was known in ancient
+times, and was even worshipped by the Egyptians. Strabo does not mention
+it; but Diodorus Siculus seems to refer to it (<span class="smcaplc">B.C.</span> 373), and he probably
+obtained his information from some Greek writers before his time, possibly
+from Zenophon, who lived in the sixth century <span class="smcaplc">B.C.</span><a name='fna_255' id='fna_255' href='#f_255'><small>[255]</small></a> Coming to the
+Christian era, it was noticed by Nicephorus, about 410 <span class="smcaplc">B.C.</span> In the Koran,
+it is called the &#8220;false Aurora&#8221;; and it is supposed to be referred to in
+the &#8220;Rub&aacute;iy&aacute;t&#8221; of Omar Khayyam, the Persian astronomical poet, in the
+second stanza of that poem (Edward Fitzgerald&#8217;s translation)&mdash;</p>
+
+<p class="poem">&#8220;Dreaming when Dawn&#8217;s Left Hand was in the Sky,<a name='fna_256' id='fna_256' href='#f_256'><small>[256]</small></a><br />
+I heard a voice within the Tavern cry,<br />
+Awake, my Little ones, and fill the Cup,<br />
+Before Life&#8217;s Liquor in its Cup be dry.&#8221;</p>
+
+<p>It was observed by Cassini in 1668,<a name='fna_257' id='fna_257' href='#f_257'><small>[257]</small></a> and by<span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span> Hooke in 1705. A short
+description of its appearance will be found in Childrey&#8217;s <i>Britannia
+Baconica</i> (1661), p. 183.</p>
+
+<p>The finest displays of this curious light seem to occur between the middle
+of January and the middle of February. In February, 1856, Secchi found it
+brighter than he had ever seen it before. It was yellowish towards the
+axis of the cone, and it seemed to be brighter than the Milky Way in
+Cygnus. He described it as &#8220;un grande spectacle.&#8221; In the middle of
+February, 1866, Mr. Lassell, during his last residence in Malta, saw a
+remarkable display of the Zodiacal Light. He found it at least twice as
+bright as the brightest part of the Milky Way, and much brighter than he
+had previously seen it. He found that the character of its light differed
+considerably from that of the Milky Way. It was of a much redder hue than
+the Galaxy. In 1874 very remarkable displays were seen in the
+neighbourhood of London in January and February of that year; and in 1875
+on January 24, 25, and 30. On January 24 it was noticed that the &#8220;light&#8221;
+was distinctly reddish and much excelled in brightness any portion of the
+Milky Way.</p>
+
+<p>Humboldt, who observed it from Andes (at a height of 13,000 to 15,000
+feet), from Venezuela and from Cumana, tells us that he has seen the
+Zodiacal Light equal in brightness to the Milky Way in Sagittarius.</p>
+
+<p><span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span>As probably many people have never seen the &#8220;light,&#8221; a caution may be
+given to those who care to look for it. It is defined by the Rev. George
+Jones, Chaplain to the &#8220;United States&#8217; Japan Expedition&#8221; (1853-55), as &#8220;a
+brightness that appears in the western sky after sunset, and in the east
+before sunrise; following nearly or quite the line of the ecliptic in the
+heavens, and stretching upwards to various elevations according to the
+season of the year.&#8221; From the description some might suppose that the
+light is visible <i>immediately</i> after sunset. But this is not so; it never
+appears until twilight is over and &#8220;the night has fully set in.&#8221;</p>
+
+<p>The &#8220;light&#8221; is usually seen after sunset or before sunrise. But attempts
+have recently been made by Prof. Simon Newcomb to observe it north of the
+sun. To avoid the effects of twilight the sun must be only slightly more
+than 18&deg; below the horizon (that is, a little before or after the longest
+day). This condition limits the place of observation to latitudes not much
+south of 46&deg;; and to reduce atmospheric absorption the observing station
+should be as high as possible above the level of the sea. Prof. Newcomb,
+observing from the Brienzer Rothorn in Switzerland (latitude 46&deg; 47&prime; N.,
+longitude 8&deg; 3&prime; E.), succeeded in tracing the &#8220;light&#8221; to a distance of 35&deg;
+north of the sun. It would seem, therefore, that the Zodiacal Light
+envelops the sun on all<span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span> sides, but has a greater extension in the
+direction of the ecliptic.<a name='fna_258' id='fna_258' href='#f_258'><small>[258]</small></a> From observations at the Lick Observatory,
+Mr. E. A. Fath found an extension of 46&deg; north of the sun.<a name='fna_259' id='fna_259' href='#f_259'><small>[259]</small></a></p>
+
+<p>From observations of the &#8220;light&#8221; made by Prof. Barnard at the Yerkes
+Observatory during the summer of 1906, he finds that it extends to at
+least 65&deg; north of the sun, a considerably higher value than that found by
+Prof. Newcomb.<a name='fna_260' id='fna_260' href='#f_260'><small>[260]</small></a> The difference may perhaps be explained by actual
+variation of the meteoric matter producing the light. Prof. J. H. Poynting
+thinks that possibly the Zodiacal Light is due to the &#8220;dust of long dead
+comets.&#8221;<a name='fna_261' id='fna_261' href='#f_261'><small>[261]</small></a></p>
+
+<p>From careful observations of the &#8220;light,&#8221; Mr. Gavin J. Burns finds that
+its luminosity is &#8220;some 40 or 50 per cent. brighter than the background of
+the sky. Prof. Newcomb has made a precisely similar remark about the
+luminosity of the Milky Way, viz. that it is surprisingly small.&#8221; This
+agrees with my own observations during many years. It is only on the
+finest and clearest nights that the Milky Way forms a conspicuous object
+in the night sky. And this only in the country. The lights of a city
+almost entirely obliterate it. Mr. Burns finds that the Zodiacal Light<span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span>
+appears &#8220;to be of a yellowish tint; or if we call it white, then the Milky
+Way is comparatively of a bluish tint.&#8221; During my residence in the Punjab
+the Zodiacal Light seemed to me constantly visible in the evening sky in
+the spring months. In the west of Ireland I have seen it nearly as bright
+as the brightest portions of the Milky Way visible in this country
+(February 20, 1890). The &#8220;meteoric theory&#8221; of the &#8220;light&#8221; seems to be the
+one now generally accepted by astronomers, and in this opinion I fully
+concur.</p>
+
+<p>From observations made in Jamaica in the years 1899 and 1901, Mr. Maxwell
+Hall arrived at the conclusion that &#8220;the Zodiacal Light is caused by
+reflection of sunlight from masses of meteoric matter still contained in
+the invariable plane, which may be considered the original plane of the
+solar system.&#8221;<a name='fna_262' id='fna_262' href='#f_262'><small>[262]</small></a> According to Humboldt, Cassini believed that the
+Zodiacal Light &#8220;consisted of innumerably small planetary bodies revolving
+round the sun.&#8221;<a name='fna_263' id='fna_263' href='#f_263'><small>[263]</small></a></p>
+
+<p><span class="smcap">The Gegenschein</span>, or <span class="smcap">Counter-glow</span>.&mdash;This is a faint patch of light seen
+opposite the sun&#8217;s place in the sky, that is on the meridian at midnight.
+It is usually elliptical in shape, with its longer axis lying nearly in
+the plane of the ecliptic. It seems to have been first detected by Brorsen
+(the discoverer of the short-period comet<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span> of 1846) about the middle of
+the nineteenth century. But it is not easy to see, for the famous Heis of
+M&uuml;nster, who had very keen eyesight, did not succeed in seeing it for
+several years after Brorsen&#8217;s announcement.<a name='fna_264' id='fna_264' href='#f_264'><small>[264]</small></a> It was afterwards
+independently discovered by Backhouse, and Barnard.</p>
+
+<p>Prof. Barnard&#8217;s earlier observations seemed to show that the Gegenschein
+does not lie exactly opposite to the sun, but very nearly so. He found its
+longitude is within one degree of 180&deg;, and its latitude about 1&deg;&middot;3 north
+of the ecliptic.<a name='fna_265' id='fna_265' href='#f_265'><small>[265]</small></a> But from subsequent observations he came to the
+conclusion that the differences in longitude and apparent latitude are due
+to atmospheric absorption, and that the object really lies in the ecliptic
+and <i>exactly</i> opposite to the sun.<a name='fna_266' id='fna_266' href='#f_266'><small>[266]</small></a></p>
+
+<p>Barnard finds that the Gegenschein is not so faint as is generally
+supposed. He says &#8220;it is best seen by averted vision, the face being
+turned 60&deg; or 70&deg; to the right or left, and the eyes alone turned towards
+it.&#8221; It is invisible in June and December, while in September it is round,
+with a diameter of 20&deg;, and very distinct. No satisfactory theory has yet
+been advanced to account for this curious phenomenon. Prof. Arthur Searle
+of Harvard attributes it to a number of<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span> asteroids too small to be seen
+individually. When in &#8220;opposition&#8221; to the sun these would be fully
+illuminated and nearest to the earth. Its distance from the earth probably
+exceeds that of the moon. Dr. Johnson Stoney thinks that the Gegenschein
+may possibly be due to a &#8220;tail&#8221; of hydrogen and helium gases repelled from
+the earth by solar action; this &#8220;tail&#8221; being visible to us by reflected
+sunlight.</p>
+
+<p>It was observed under favourable circumstances in January and February,
+1903, by the French astronomer, M. F. Qu&eacute;nisset. He found that it was
+better seen when the atmosphere was less clear, contrary to his experience
+of the Zodiacal Light. Prof. Barnard&#8217;s experience confirms this. M.
+Qu&eacute;nisset notes that&mdash;as in the case of the Zodiacal Light&mdash;the southern
+border of the Gegenschein is sharper than the northern. He found that its
+brightness is less than that of the Milky Way between Betelgeuse and
+&#947; Geminorum; and thinks that it is merely a strengthening of the
+Zodiacal Light.<a name='fna_267' id='fna_267' href='#f_267'><small>[267]</small></a></p>
+
+<p>A meteoritic theory of the Gegenschein has been advanced by Prof. F. R.
+Moulton, which explains it by light reflected from a swarm of meteorites
+revolving round the sun at a distance of 930,240 miles outside the earth&#8217;s
+orbit.</p>
+
+<p>Both the Zodiacal Light and Gegenschein were observed by Herr Leo Brenner
+on the evening of<span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span> March 4, 1896. He found the Zodiacal Light on this
+evening to be &#8220;<i>perhaps eight times brighter</i> than the Milky Way in
+Perseus.&#8221; The &#8220;<i>Gegenschein distinctly visible</i> as a round, bright,
+cloud-like nebula below Leo (Virgo), and about twice the brightness of the
+Milky Way in Monoceros between Canis Major and Canis Minor.&#8221;<a name='fna_268' id='fna_268' href='#f_268'><small>[268]</small></a></p>
+
+<p>Humboldt thought that the fluctuations in the brilliancy of the Zodiacal
+Light were probably due to a real variation in the intensity of the
+phenomenon rather than to the elevated position of the observer.<a name='fna_269' id='fna_269' href='#f_269'><small>[269]</small></a> He
+says that he was &#8220;astonished in the tropical climates of South America, to
+observe the variable intensity of the light.&#8221;</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span></p>
+<h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV</h2>
+<p class="title">The Stars</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Pliny</span> says that Hipparchus &#8220;ventured to count the stars, a work arduous
+even for the Deity.&#8221; But this was quite a mistaken idea. Those visible to
+the naked eye are comparatively few in number, and the enumeration of
+those visible in an opera-glass&mdash;which of course far exceed those which
+can be seen by unaided vision&mdash;is a matter of no great difficulty. Those
+visible in a small telescope of 2&#190; inches aperture have all been
+observed and catalogued; and even those shown on photographs taken with
+large telescopes can be easily counted. The present writer has made an
+attempt in this direction, and taking an average of a large number of
+counts in various parts of the sky, as shown on stellar photographs, he
+finds a total of about 64 millions for the whole sky in both
+hemispheres.<a name='fna_270' id='fna_270' href='#f_270'><small>[270]</small></a> Probably the total number will not exceed 100 millions.
+But this is a comparatively small<span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span> number, even when compared with the
+human population of our little globe.</p>
+
+<p>With reference to the charts made by photography in the International
+scheme commenced some years ago, it has now been estimated that the charts
+will probably contain a total of about 9,854,000 stars down to about the
+14th magnitude (13&middot;7). The &#8220;catalogue plates&#8221; (taken with a shorter
+exposure) will, it is expected, include about 2,676,500 stars down to
+11&#189; magnitude. These numbers may, however, be somewhat increased when
+the work has been completed.<a name='fna_271' id='fna_271' href='#f_271'><small>[271]</small></a> If this estimate proves to be correct,
+the number of stars visible down to the 14th magnitude will be
+considerably less than former estimates have made it.</p>
+
+<p>Prof. E. C. Pickering estimates that the total number of stars visible on
+photographs down to the 16th magnitude (about the faintest visible in the
+great Lick telescope) will be about 50 millions.<a name='fna_272' id='fna_272' href='#f_272'><small>[272]</small></a> In the present
+writer&#8217;s enumeration, above referred to, many stars fainter than the 16th
+magnitude were included.</p>
+
+<p>Admiral Smyth says, with reference to Sir William Herschel&mdash;perhaps the
+greatest observer that ever lived&mdash;&#8220;As to Sir William himself, he could
+unhesitatingly call every star down to the 6th magnitude, by its name,
+letter, or number.&#8221;<a name='fna_273' id='fna_273' href='#f_273'><small>[273]</small></a><span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span> This shows great powers of observation, and a
+wonderful memory.</p>
+
+<p>On a photographic plate of the Pleiades taken with the Bruce telescope and
+an exposure of 6 hours, Prof. Bailey of Harvard has counted &#8220;3972 stars
+within an area 2&deg; square, having Alcyone at its centre.&#8221;<a name='fna_274' id='fna_274' href='#f_274'><small>[274]</small></a> This would
+give a total of about 41 millions for the whole sky, if of the same
+richness.</p>
+
+<p>With an exposure of 16 hours, Prof. H. C. Wilson finds on an area of less
+that 110&prime; square a total of 4621 stars. He thinks, &#8220;That all of these
+stars belong to the Pleiades group is not at all probable. The great
+majority of them probably lie at immense distances beyond the group, and
+simply appear in it by projection.&#8221;<a href='#f_274'><small>[274]</small></a> He adds, &#8220;It has been found,
+however, by very careful measurements made during the last 75 years at the
+K&ouml;nigsbergh and Yale Observatories, that of the sixty-nine brighter stars,
+including those down to the 9th magnitude, only eight show any certain
+movement with reference to Alcyone. Since Alcyone has a proper motion or
+drift of 6&Prime; per century, this means that all the brightest stars except
+the eight mentioned are drifting with Alcyone and so form a true cluster,
+at approximately the same distance from the earth. Six of the eight stars
+which show relative drift are moving in the opposite direction to the<span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span>
+movement of Alcyone, and at nearly the same rate, so that their motion is
+only apparent. They are really stationary, while Alcyone and the rest of
+the cluster are moving past them.&#8221;<a name='fna_275' id='fna_275' href='#f_275'><small>[275]</small></a> This tends to show that the faint
+stars are really <i>behind</i> the cluster, and are unconnected with it.</p>
+
+<p>It is a popular idea with some people that the Pole Star is the nearest of
+all the stars to the celestial pole. But photographs show that there are
+many faint stars nearer to the pole than the Pole Star. The Pole Star is
+at present at a distance of 1&deg; 13&prime; from the real pole of the heavens, but
+it is slowly approaching it. The minimum distance will be reached in the
+year 2104. From photographs taken by M. Flammarion at the Juvisy
+Observatory, he finds that there are at least 128 stars nearer to the pole
+than the Pole Star! The nearest star to the pole was, in the year 1902, a
+small star of about 12&#189; magnitude, which was distant about 4 minutes of
+arc from the pole.<a name='fna_276' id='fna_276' href='#f_276'><small>[276]</small></a> The estimated magnitude shows that the Pole Star
+is nearly 10,000 times brighter than this faint star!</p>
+
+<p>It has been found that Sirius is bright enough to cast a shadow under
+favourable conditions. On March 22, 1903, the distinguished French
+astronomer Touchet succeeded in photographing<span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span> the shadow of a brooch cast
+by this brilliant star. The exposure was 1<sup>h</sup> 5<sup>m</sup>.</p>
+
+<p>Martinus Hortensius seems to have been the first to see stars in daylight,
+perhaps early in the seventeenth century. He mentions the fact in a letter
+to Gassendi dated October 12, 1636, but does not give the date of his
+observation. Schickard saw Arcturus in broad daylight early in 1632. Morin
+saw the same bright star half an hour after sunset in March, 1635.</p>
+
+<p>Some interesting observations were made by Professors Payne and H. C.
+Wilson, in the summer of 1904, at Midvale, Montana (U.S.A.), at a height
+of 4790 feet above sea-level. At this height they found the air very clear
+and transparent. &#8220;Many more stars were visible at a glance, and the
+familiar stars appeared more brilliant.... In the great bright cloud of
+the Milky Way, between &#946; and &#947; Cygni, one could count
+easily sixteen or seventeen stars, besides the bright ones &#951; and
+&#967;,<a name='fna_277' id='fna_277' href='#f_277'><small>[277]</small></a> while at Northfield it is difficult to distinctly see
+eight or nine with the naked eye.&#8221; Some nebul&aelig; and star fields were
+photographed with good results by the aid of a 2&#189;-inch Darlot lens and
+3 hours&#8217; exposure.<a name='fna_278' id='fna_278' href='#f_278'><small>[278]</small></a></p>
+
+<p>Prof. Barnard has taken some good stellar photographs with a lens of only
+1&#189; inches in diameter,<span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span> and 4 or 5 inches focus belonging to an
+ordinary &#8220;magic lantern&#8221;! He says that these &#8220;photographs with the small
+lens show us in the most striking manner how the most valuable and
+important information may be obtained with the simplest means.&#8221;<a name='fna_279' id='fna_279' href='#f_279'><small>[279]</small></a></p>
+
+<p>With reference to the rising and setting of the stars due to the earth&#8217;s
+rotation on its axis, the late Sir George B. Airy, Astronomer Royal of
+England, once said to a schoolmaster, &#8220;I should like to know how far your
+pupils go into the first practical points for which reading is scarcely
+necessary. Do they know that the stars rise and set? Very few people in
+England know it. I once had a correspondence with a literary man of the
+highest rank on a point of Greek astronomy, and found that he did not know
+it!&#8221;<a name='fna_280' id='fna_280' href='#f_280'><small>[280]</small></a></p>
+
+<p>Admiral Smyth says, &#8220;I have been struck with the beautiful blue tint of
+the smallest stars visible in my telescope. This, however, may be
+attributed to some optical peculiarity.&#8221; This bluish colour of small stars
+agrees with the conclusion arrived at by Prof. Pickering in recent years,
+that the majority of faint stars in the Milky Way have spectra of the
+Sirian type and, like that brilliant star, are of a bluish white colour.
+Sir William Herschel saw many stars of a redder tinge than other observers
+have noticed. Admiral Smyth<span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span> says, &#8220;This may be owing to the effect of his
+metallic mirror or to some peculiarity of vision, or perhaps both.&#8221;<a name='fna_281' id='fna_281' href='#f_281'><small>[281]</small></a></p>
+
+<p>The ancient astronomers do not mention any coloured stars except white and
+red. Among the latter they only speak of Arcturus, Aldebaran, Pollux,
+Antares, and Betelgeuse as of a striking red colour. To these Al-Sufi adds
+Alphard (&#945; Hydr&aelig;).</p>
+
+<p>Sir William Herschel remarked that no decidedly green or blue star &#8220;has
+ever been noticed unassociated with a companion brighter than itself.&#8221; An
+exception to Herschel&#8217;s rule seems to be found in the case of the star
+&#946; Libr&aelig;, which Admiral Smyth called &#8220;pale emerald.&#8221; Mr. George
+Knott observed it on May 19, 1852, as &#8220;beautiful pale green&#8221; (3&middot;7 inches
+achromatic, power 80), and on May 9, 1872, as &#8220;fine pale green&#8221; (5&middot;5
+inches achromatic, power 65).</p>
+
+<p>The motion of stars in the line of sight, as shown by the
+spectroscope&mdash;should theoretically alter their brightness in the course of
+time; those approaching the earth becoming gradually brighter, while those
+receding should become fainter. But the distance of the stars is so
+enormous that even with very high velocities the change would not become
+perceptible for ages. Prof. Oudemans found that to change the brightness
+of a star by only one-tenth of a magnitude&mdash;a quantity barely<span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span> perceptible
+to the eye-a number of years would be necessary, which is represented by
+the formula</p>
+
+<table border="0" cellpadding="0" cellspacing="0" summary="table">
+<tr><td align="center" class="botbor">5916 years</td></tr>
+<tr><td align="center">parallax &times; motion</td></tr></table>
+
+<p>for a star approaching the earth, and for a receding star</p>
+
+<table border="0" cellpadding="0" cellspacing="0" summary="table">
+<tr><td align="center" class="botbor">6195 years</td></tr>
+<tr><td align="center">p &times; m</td></tr></table>
+
+<p>This is in geographical miles, 1 geographical mile being equal to 4&middot;61
+English miles.</p>
+
+<p>Reducing the above to English miles, and taking an average for both
+approaching and receding stars, we have</p>
+
+<table border="0" cellpadding="0" cellspacing="0" summary="table">
+<tr><td align="center" class="botbor">27,660 years</td></tr>
+<tr><td align="center">p &times; m</td></tr></table>
+
+<p>where p = parallax in seconds of arc, and m = radial velocity in English
+miles per second.</p>
+
+<p>Prof. Oudemans found that the only star which could have changed in
+brightness by one-tenth of a magnitude since the time of Hipparchus is
+Aldebaran. This is taking its parallax as 0&Prime;&middot;52. But assuming the more
+reliable parallax 0&Prime;&middot;12 found by Dr. Elkin, this period is 4&#8531; times
+longer. For Procyon, the period would be 5500 years.<a name='fna_282' id='fna_282' href='#f_282'><small>[282]</small></a> The above
+calculation shows how absurd it is to suppose that any star could have
+gained or lost in brightness by motion in the line of sight during
+historical times. The &#8220;secular variation&#8221; of stars<span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span> is quite another
+thing. This is due to physical changes in the stars themselves.</p>
+
+<p>The famous astronomer Halley, the second Astronomer Royal at Greenwich,
+says (<i>Phil. Trans.</i>, 1796), &#8220;Supposing the number of 1st magnitude stars
+to be 13, at twice the distance from the sun there may be placed four
+times as many, or 52; which with the same allowance would nearly represent
+the star we find to be of the 2nd magnitude. So 9 &times; 13, or 117, for those
+at three times the distance; and at ten times the distance 100 &times; 13, or
+1300 stars; of which distance may probably diminish the light of any of
+the stars of the 1st magnitude to that of the 6th, it being but the
+hundredth part of what, at their present distance, they appear with.&#8221; This
+agrees with the now generally accepted &#8220;light ratio&#8221; of 2&middot;512 for each
+magnitude, which makes a first magnitude star 100 times the light of a 6th
+magnitude.</p>
+
+<p>On the 4th of March, 1796,<a name='fna_283' id='fna_283' href='#f_283'><small>[283]</small></a> the famous French astronomer Lalande
+observed on the meridian a star of small 6th magnitude, the exact position
+of which he determined. On the 15th of the same month he again observed
+the star, and the places found for 1800 refer to numbers 16292-3 of the
+reduced catalogue. In the observation of March 4 he attached the curious
+remark, &#8220;&Eacute;toile singuli&egrave;re&#8221; (the observation of March 15 is without<span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span>
+note). This remark of Lalande has puzzled observers who failed to find any
+peculiarity about the star. Indeed, &#8220;the remark is a strange one for the
+observer of so many thousands of stars to attach unless there was really
+something singular in the star&#8217;s aspect at the time.&#8221; On the evening of
+April 18, 1887, the star was examined by the present writer, and the
+following is the record in his observing book, &#8220;Lalande&#8217;s &eacute;toile
+singuli&egrave;re (16292-3) about half a magnitude less than &#951; Cancri.
+With the binocular I see two streams of small stars branching out from it,
+north preceding like the tails of comet.&#8221; This may perhaps have something
+to do with Lalande&#8217;s curious remark.</p>
+
+<p>The star numbered 1647 in Baily&#8217;s <i>Flamsteed Catalogue</i> is now known to
+have been an observation of the planet Uranus.<a name='fna_284' id='fna_284' href='#f_284'><small>[284]</small></a></p>
+
+<p>Prof. Pickering states that the fainter stars photographed with the 8-inch
+telescope at Cambridge (U.S.A.) are invisible to the eye in the 15-inch
+telescope.<a name='fna_285' id='fna_285' href='#f_285'><small>[285]</small></a></p>
+
+<p>Sir Norman Lockyer finds that the lines of sulphur are present in the
+spectrum of the bright star Rigel (&#946; Orionis).<a name='fna_286' id='fna_286' href='#f_286'><small>[286]</small></a></p>
+
+<p>About 8&#189;&deg; south of the bright star Regulus (&#945; Leonis) is a
+faint nebula (H I, 4 Sextantis). On or near this spot the Capuchin monk De
+Rheita fancied he saw, in the year 1643, a<span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span> group of stars representing
+the napkin of S. Veronica&mdash;&#8220;sudarium Veronic&aelig; sive faciem Domini maxima
+similitudina in astris expressum.&#8221; And he gave a picture of the napkin and
+star group. But all subsequent observers have failed to find any trace of
+the star group referred to by De Rheita!<a name='fna_287' id='fna_287' href='#f_287'><small>[287]</small></a></p>
+
+<p>The Bible story of the star of the Magi is also told in connection with
+the birth of the sun-gods Osiris, Horus, Mithra, Serapis, etc.<a name='fna_288' id='fna_288' href='#f_288'><small>[288]</small></a> The
+present writer has also heard it suggested that the phenomenon may have
+been an apparition of Halley&#8217;s comet! But as this famous comet is known to
+have appeared in the year <span class="smcaplc">B.C.</span> 11, and as the date of the Nativity was
+probably not earlier than <span class="smcaplc">B.C.</span> 5, the hypothesis seems for this (and other
+reasons) to be inadmissible. It has also been suggested that the
+phenomenon might have been an appearance of Tycho Brah&eacute;&#8217;s temporary star
+of 1572, known as the &#8220;Pilgrim star&#8221;; but there seems to be no real
+foundation for such an hypothesis. There is no reason to think that
+&#8220;temporary&#8221; or new stars ever appear a second time.</p>
+
+<p>Admiral Smyth has well said, &#8220;It checks one&#8217;s pride to recollect that if
+our sun with the whole system of planets, asteroids, and moons, and comets
+were to be removed from the spectator<span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span> to the distance of the nearest
+fixed star, not one of them would be visible, except the sun, which would
+then appear but as a star of perhaps the 2nd magnitude. Nay, more, were
+the whole system of which our globe forms an insignificant member, with
+its central luminary, suddenly annihilated, no effect would be produced on
+those unconnected and remote bodies; and the only annunciation of such a
+catastrophe in the Sidereal &#8220;Times&#8221; would be that a small star once seen
+in a distant quarter of the sky had ceased to shine.&#8221;<a name='fna_289' id='fna_289' href='#f_289'><small>[289]</small></a></p>
+
+<p>Prof. George C. Comstock finds that the average parallax of 67 selected
+stars ranging in brightness between the 9th and the 12th magnitude, is of
+the value of 0&Prime;&middot;0051.<a name='fna_290' id='fna_290' href='#f_290'><small>[290]</small></a> This gives a distance representing a journey
+for light of about 639 years!</p>
+
+<p>Mr. Henry Norris Russell thinks that nearly all the bright stars in the
+constellation of Orion are practically at the same distance from the
+earth. His reasons for this opinion are: (1) the stars are similar in
+their spectra and proper motions, (2) their proper motions are small,
+which suggests a small parallax, and therefore a great distance from the
+earth. Mr. Russell thinks that the average parallax of these stars may
+perhaps be 0&Prime;&middot;005, which gives a distance of about 650 &#8220;light
+years.&#8221;<a name='fna_291' id='fna_291' href='#f_291'><small>[291]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span>According to Sir Norman Lockyer&#8217;s classification of the stars, the order
+of <i>increasing</i> temperature is represented by the following, beginning
+with those in the earliest stage of stellar evolution:&mdash;Nebul&aelig;, Antares,
+Aldebaran, Polaris, &#945; Cygni, Rigel, &#949; Tauri, &#946;
+Crucis. Then we have the hottest stars represented by &#949; Puppis,
+&#947; Argus, and Alnitam (&#949; Orionis). <i>Decreasing</i>
+temperature is represented by (in order), Achernar, Algol, Markab, Sirius,
+Procyon, Arcturus, 19 Piscium, and the &#8220;Dark Stars.&#8221;<a name='fna_292' id='fna_292' href='#f_292'><small>[292]</small></a> But other
+astronomers do not agree with this classification. Antares and Aldebaran
+are by some authorities considered to be <i>cooling</i> suns.</p>
+
+<p>According to Ritter&#8217;s views of the Constitution of the Celestial Bodies,
+if we &#8220;divide the stars into three classes according to age corresponding
+to these three stages of development, we shall assign to the first class,
+A, those stars still in the nebular phase of development; to the second
+class, B, those in the transient stage of greatest brilliancy; and to the
+class C, those stars which have already entered into the long period of
+slow extinction. It should be noted in this classification that we refer
+to relative and not absolute age, since a star of slight mass passes
+through the successive phases of its development more rapidly than the
+star of greater mass.&#8221;<a name='fna_293' id='fna_293' href='#f_293'><small>[293]</small></a> Ritter<span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span> comes to the conclusion that &#8220;the
+duration of the period in which the sun as a star had a greater brightness
+than at present was very short in comparison with the period in which it
+had and will continue to have a brightness differing only slightly from
+its present value.&#8221;<a name='fna_294' id='fna_294' href='#f_294'><small>[294]</small></a></p>
+
+<p>In a valuable and interesting paper on &#8220;The Evolution of Solar
+Stars,&#8221;<a name='fna_295' id='fna_295' href='#f_295'><small>[295]</small></a> Prof. Schuster says that &#8220;measurements by E. F. Nichols on
+the heat of Vega and Arcturus indicated a lower temperature for Arcturus,
+and confirms the conclusion arrived at on other grounds, that the hydrogen
+stars have a higher temperature than the solar stars.&#8221; &#8220;An inspection of
+the ultraviolet region of the spectrum gives the same result. These
+different lines of argument, all leading to the same result, justify us in
+saying that the surface temperature of the hydrogen stars is higher than
+that of the solar stars. An extension of the same reasoning leads to the
+belief that the helium stars have a temperature which is higher still.&#8221;
+Hence we have Schuster, Hale, and Sir William Huggins in agreement that
+the Sirian stars are hotter than the solar stars; and personally I agree
+with these high authorities. The late Dr. W. E. Wilson, however, held the
+opinion that the sun is hotter that Sirius!</p>
+
+<p>Schuster thinks that Lane&#8217;s law does not apply<span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span> to the temperature of the
+photosphere and the absorbing layers of the sun and stars, but only to the
+portions between the photosphere and the centre, which probably act like a
+perfect gas. On this view he says the interior might become &#8220;hotter and
+hotter until the condensation had reached a point at which the laws of
+gaseous condensation no longer hold.&#8221;</p>
+
+<p>With reference to the stars having spectra of the 3rd and 4th type
+(usually orange and red in colour), Schuster says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The remaining types of spectra belong to lower temperature still, as
+in place of metallic lines, or in addition to them, certain bands
+appear which experiments show us invariably belong to lower
+temperature than the lines of the same element.</p>
+
+<p>&#8220;If an evolutionary process has been going on, which is similar for
+all stars, there is little doubt that from the bright-line stars down
+to the solar stars the order has been (1) helium or <i>Orion</i> stars, (2)
+hydrogen or Sirian stars, (3) calcium or Procyon stars, (4) solar or
+Capellan stars.&#8221;</p></div>
+
+<p>My investigations on &#8220;The Secular Variation of Starlight&#8221; (<i>Studies in
+Astronomy</i>, chap. 17, and <i>Astronomical Essays</i>, chap. 12) based on a
+comparison of Al-Sufi&#8217;s star magnitudes (tenth century) with modern
+estimates and measures, tend strongly to confirm the above views.</p>
+
+<p>With regard to the 3rd-type stars, such as Betelgeuse and Mira Ceti,
+Schuster says, &#8220;It has been already mentioned that observers differ as<span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span> to
+whether their position is anterior to the hydrogen or posterior to the
+solar stars, and there are valid arguments on both sides.&#8221;</p>
+
+<p>Scheiner, however, shows, from the behaviour of the lines of magnesium,
+that stars of type I. (Sirian) are the hottest, and type III. the coolest,
+and he says, we have &#8220;for the first time a direct proof of the correctness
+of the physical interpretation of Vogel&#8217;s spectral classes, according to
+which class II. is developed by cooling from I., and III. by a further
+process of cooling from II.&#8221;<a name='fna_296' id='fna_296' href='#f_296'><small>[296]</small></a></p>
+
+<p>Prof. Hale says that &#8220;the resemblance between the spectra of sun-spots and
+of 3rd-type stars is so close as to indicate that the same cause is
+controlling the relative intensities of many lines in both instances. This
+cause, as the laboratory work indicates, is to be regarded as reduced
+temperature.&#8221;<a name='fna_297' id='fna_297' href='#f_297'><small>[297]</small></a></p>
+
+<p>According to Prof. Schuster, &#8220;a spectrum of bright lines may be given by a
+mass of luminous gas, even if the gas is of great thickness. There is,
+therefore, no difficulty in explaining the existence of stars giving
+bright lines.&#8221; He thinks that the difference between &#8220;bright line&#8221; stars
+and those showing dark lines depends upon the rate of increase of the
+temperature from the surface towards the centre. If this rate is slow,
+bright lines will be seen. If the rate of increase<span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span> is rapid, the
+dark-line spectrum shown by the majority of the stars will appear. This
+rate, he thinks, is regulated by the gravitational force. So that in the
+early stages of condensation bright lines are more likely to occur. &#8220;If
+the light is not fully absorbed,&#8221; both bright and dark lines of the same
+element may be visible in the same star. Schuster considers it quite
+possible that if we could remove the outer layers of the Sun&#8217;s atmosphere,
+we should obtain a spectrum of bright lines.<a name='fna_298' id='fna_298' href='#f_298'><small>[298]</small></a></p>
+
+<p>M. Stratonoff finds that stars having spectra of the Orion and Sirian
+types&mdash;supposed to represent an early stage in stellar evolution&mdash;tend to
+congregate in or near the Milky Way. Star clusters in general show a
+similar tendency, &#8220;but to this law the globular clusters form an
+exception.&#8221;<a name='fna_299' id='fna_299' href='#f_299'><small>[299]</small></a> We may add that the spiral nebul&aelig;&mdash;which seem to be
+scattered indifferently over all parts of the sky&mdash;also seem to form an
+exception; for the spectra of these wonderful objects seem to show that
+they are really star clusters, in which the components are probably
+relatively small; that is, small in comparison with our sun.</p>
+
+<p>If we accept the hypothesis that suns and systems were evolved from
+nebul&aelig;, and if we consider the comparatively small number of<span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span> nebul&aelig;
+hitherto discovered in the largest telescopes&mdash;about half a million; and
+if we further consider the very small number of red stars, or those having
+spectra of the third and fourth types&mdash;usually considered to be dying-out
+suns&mdash;we seem led to the conclusion that our sidereal system is now at
+about the zenith of its life-history; comparatively few nebul&aelig; being left
+to consolidate into stars, and comparatively few stars having gone far on
+the road to the final extinction of their light.</p>
+
+<p>Prof. Boss of Albany (U.S.A.) finds that about forty stars of magnitudes
+from 3&#189; to 7 in the constellation Taurus are apparently drifting
+together towards one point. These stars are included between about R.A.
+3<sup>h</sup> 47<sup>m</sup> to 5<sup>h</sup> 4<sup>m</sup>, and Declination + 5&deg; to + 23&deg; (that is, in the
+region surrounding the Hyades). These motions apparently converge to a
+point near R.A. 6<sup>h</sup>, Declination + 7&deg; (near Betelgeuse). Prof. Boss has
+computed the velocity of the stars in this group to be 45&middot;6 kilometres
+(about 28 miles) a second towards the &#8220;vanishing point,&#8221; and he estimated
+the average parallax of the group to be 0&Prime;&middot;025&mdash;about 130 years&#8217; journey
+for light. Although the motions are apparently converging to a point, it
+does not follow that the stars in question will, in the course of ages,
+meet at the &#8220;vanishing point.&#8221; On the contrary, the observed motions show
+that the stars are moving in parallel lines through space.<span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span> About 15
+kilometres of the observed speed is due to the sun&#8217;s motion through space
+in the opposite direction. Prof. Campbell finds from spectroscopic
+measures that of these forty stars, nine are receding from the earth with
+velocities varying from 12 to 60 kilometres a second, and twenty-three
+others with less velocities than 38 kilometres.<a name='fna_300' id='fna_300' href='#f_300'><small>[300]</small></a> It will be obvious
+that, as there is a &#8220;vanishing point,&#8221; the motion in the line of sight
+must be one of <i>recession</i> from the earth.</p>
+
+<p>It has been found that on an average the parallax of a star is about
+one-seventh of its &#8220;proper motion.&#8221;<a name='fna_301' id='fna_301' href='#f_301'><small>[301]</small></a></p>
+
+<p>Adopting Prof. Newcomb&#8217;s parallax of 0&Prime;&middot;14 for the famous star 1830
+Groombridge, the velocity perpendicular to the line of sight is about 150
+miles a second. The velocity <i>in</i> the line of sight&mdash;as shown by the
+spectroscope&mdash;is 59 miles a second approaching the earth. Compounding
+these two velocities we find a velocity through space of about 161 miles a
+second!</p>
+
+<p>An eminent American writer puts into the mouth of one of his characters, a
+young astronomer, the following:&mdash;</p>
+
+<p class="poem"><span style="margin-left: 9em;">&#8220;I read the page</span><br />
+Where every letter is a glittering sun.&#8221;</p>
+
+<p>From an examination of the heat radiated by<span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span> some bright stars, made by
+Dr. E. F. Nicholls in America with a very sensitive radiometer of his own
+construction, he finds that &#8220;we do not receive from Arcturus more heat
+than we should from a candle at a distance of 5 or 6 miles.&#8221;</p>
+
+<p>With reference to the progressive motion of light, and the different times
+taken by light to reach the earth from different stars, Humboldt says,
+&#8220;The aspect of the starry heavens presents to us objects of <i>unequal
+date</i>. Much has long ceased to exist before the knowledge of its presence
+reaches us; much has been otherwise arranged.&#8221;<a name='fna_302' id='fna_302' href='#f_302'><small>[302]</small></a></p>
+
+<p>The photographic method of charting the stars, although a great
+improvement on the old system, seems to have its disadvantages. One of
+these is that the star images are liable to disappear from the plates in
+the course of time. The reduction of stellar photograph plates should,
+therefore, be carried out as soon as possible after they are taken. The
+late Dr. Roberts found that on a plate originally containing 364 stars, no
+less than 130 had completely disappeared in 9&#188; years!</p>
+
+<p>It has been assumed by some writers on astronomy that the faint stars
+visible on photographs of the Pleiades are at practically the same
+distance from the earth as the brighter stars of the cluster, and that
+consequently there must be an enormous difference in actual size between
+the<span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span> brighter and fainter stars. But there is really no warrant for any
+such assumption. Photographs of the vicinity show that the sky all round
+the Pleiades is equally rich in faint stars. It seems, therefore, more
+reasonable to suppose that most of the faint stars visible in the Pleiades
+are really far behind the cluster in space. For if <i>all</i> the faint stars
+visible on photographs belonged to the cluster, then if we imagine the
+cluster removed, a &#8220;hole&#8221; would be left in the sky, which is of course
+utterly improbable, and indeed absurd. An examination of the proper
+motions tends to confirm this view of the matter, and indicates that the
+Pleiades cluster is a comparatively small one and simply projected on a
+background of fainter stars.</p>
+
+<p>It has long been suspected that the famous star 61 Cygni, which is a
+double star, forms a binary system&mdash;that is, that the two stars composing
+it revolve round their common centre of gravity and move together through
+space. But measures of parallax made by Herman S. Davis and Wilsing seem
+to show a difference of parallax between the two components of about 0&middot;08
+of a second of arc. This difference of parallax implies a distance of
+about 2&#188; &#8220;light years&#8221; between the two stars, and &#8220;if this is correct,
+the stars are too remote to form a binary system. The proper motions of
+5&Prime;&middot;21 and 5&Prime;&middot;15 seem to show that they are moving in nearly parallel
+directions; but are<span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span> probably slowly separating.&#8221; Mr. Lewis, however,
+thinks that a physical connection probably exists.<a name='fna_303' id='fna_303' href='#f_303'><small>[303]</small></a></p>
+
+<p>Dante speaks of the four bright stars of the Southern Cross as
+emblematical of the four cardinal virtues, Justice, Temperance, Fortitude,
+and Prudence; and he seems to refer to the stars Canopus, Achernar, and
+Foomalhaut under the symbols of Faith, Hope, and Charity. The so-called
+&#8220;False Cross&#8221; is said to be formed by the stars &#954;, &#948;,
+&#949;, and &#953; of the constellation Argo Navis. But it seems
+to me that a better (although larger) cross is formed by the stars &#945; Centauri
+and &#945;, &#946;, and &#947; of Triangulum Australis.</p>
+
+<p>Mr. Monck has pointed out that the names of the brightest stars seem to be
+arranged alphabetically in order of colour, beginning with red and ending
+with blue. Thus we have Aldebaran, Arcturus, Betelgeuse, Capella, Procyon,
+Regulus, Rigel, Sirius, Spica and Vega. But as the origin of these names
+is different, this must be merely a curious coincidence.<a name='fna_304' id='fna_304' href='#f_304'><small>[304]</small></a> And, to my
+eye at least, Betelgeuse is redder than Arcturus.</p>
+
+<p>The poet Longfellow speaks of the&mdash;</p>
+
+<p class="poem">&#8220;Stars, the thoughts of God in the heavens,&#8221;<a name='fna_305' id='fna_305' href='#f_305'><small>[305]</small></a></p>
+
+<p>and Drayton says&mdash;</p>
+
+<p class="poem">&#8220;The stars to me an everlasting book<br />
+In that eternal register, the sky.&#8221;<a name='fna_306' id='fna_306' href='#f_306'><small>[306]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span>Observing at a height of 12,540 feet on the Andes, the late Dr. Copeland
+saw Sirius with the naked eye less than 10 minutes before sunset.<a name='fna_307' id='fna_307' href='#f_307'><small>[307]</small></a> He
+also saw Jupiter 3<sup>m</sup> 47<sup>s</sup> before sunset; and the following bright
+stars&mdash;Canopus, 0<sup>m</sup> 52<sup>s</sup> before sunset; Rigel (&#946; Orionis) 16<sup>m</sup>
+32<sup>s</sup> after sunset; and Procyon 11<sup>m</sup> 28<sup>s</sup> after sunset. From a height of
+12,050 feet at La Paz, Bolivia, he saw with the naked eye in February,
+1883, ten stars in the Pleiades in full moonlight, and seventeen stars in
+the Hyades. He also saw &#963; Tauri double.<a name='fna_308' id='fna_308' href='#f_308'><small>[308]</small></a></p>
+
+<p>Humboldt says, &#8220;In whatever point the vault of heaven has been pierced by
+powerful and far-penetrating telescopic instruments, stars or luminous
+nebul&aelig; are everywhere discoverable, the former in some cases not exceeding
+the 20th or 24th degree of telescopic magnitude.&#8221;<a name='fna_309' id='fna_309' href='#f_309'><small>[309]</small></a> But this is a
+mistake. No star of even the 20th magnitude has ever been seen by any
+telescope. Even on the best photographic plates it is doubtful that any
+stars much below the 18th magnitude are visible. To show a star of the
+20th magnitude&mdash;if such stars exist&mdash;would require a telescope of 144
+inches or 12 feet in aperture. To show a star of the 24th magnitude&mdash;if
+such there be&mdash;an aperture of 33 feet would be necessary!<a name='fna_310' id='fna_310' href='#f_310'><small>[310]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span>It is a popular idea that stars may be seen in the daytime from the bottom
+of a deep pit or high chimney. But this has often been denied. Humboldt
+says, &#8220;While practically engaged in mining operations, I was in the habit,
+during many years, of passing a great portion of the day in mines where I
+could see the sky through deep shafts, yet I never was able to observe a
+star.&#8221;<a name='fna_311' id='fna_311' href='#f_311'><small>[311]</small></a></p>
+
+<p>Stars may, however, be seen in the daytime with even small telescopes. It
+is said that a telescope of 1 inch aperture will show stars of the 2nd
+magnitude; 2 inches, stars of the 3rd magnitude; and 4 inches, stars of
+the 4th magnitude. But I cannot confirm this from personal observation. It
+may be so, but I have not tried the experiment.</p>
+
+<p>Sir George Darwin says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Human life is too short to permit us to watch the leisurely procedure
+of cosmical evolution, but the celestial museum contains so many
+exhibits that it may become possible, by the aid of theory, to piece
+together, bit by bit, the processes through which stars pass in the
+course of their evolutions.&#8221;<a name='fna_312' id='fna_312' href='#f_312'><small>[312]</small></a></p></div>
+
+<p>The so-called &#8220;telluric lines&#8221; seen in the solar spectrum, are due to
+water vapour in the earth&#8217;s atmosphere. As the light of the stars also
+passes through the atmosphere, it is evident that these lines should also
+be visible in the spectra<span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span> of the stars. This is found to be the case by
+Prof. Campbell, Director of the Lick Observatory, who has observed all the
+principal bands in the spectrum of every star he has examined.<a name='fna_313' id='fna_313' href='#f_313'><small>[313]</small></a></p>
+
+<p>The largest &#8220;proper motion&#8221; now known is that of a star of the 8&#189;
+magnitude in the southern hemisphere, known as Cordoba Zone V. No. 243.
+Its proper motion is 8&middot;07 seconds of arc per annum, thus exceeding that of
+the famous &#8220;runaway star,&#8221; 1830 Groombridge, which has a proper motion of
+7&middot;05 seconds per annum. This greater motion is, however, only apparent.
+Measures of parallax show that the southern &#8220;runaway&#8221; is much nearer to us
+than its northern rival, its parallax being 0&Prime;&middot;32, while that of
+Groombridge 1830 is only 0&Prime;&middot;14. With these data the actual velocity across
+the line of sight can be easily computed. That of the southern star comes
+out 80 miles a second, while that of Groombridge 1830 is 148 miles a
+second. The actual velocity of Arcturus is probably still greater.</p>
+
+<p>The poet Barton has well said&mdash;</p>
+
+<p class="poem">&#8220;The stars! the stars! go forth at night,<br />
+<span style="margin-left: 1em;">Lift up thine eyes on high,</span><br />
+And view the countless orbs of light,<br />
+<span style="margin-left: 1em;">Which gem the midnight sky.</span><br />
+Go forth in silence and alone,<br />
+<span style="margin-left: 1em;">This glorious sight to scan,</span><br />
+And bid the humbled spirit own<br />
+<span style="margin-left: 1em;">The littleness of man.&#8221;</span></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span></p>
+<h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV</h2>
+<p class="title">Double and Binary Stars</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Prof. R. G. Aitken</span>, the eminent American observer of double stars, finds
+that of all the stars down to the 9th magnitude&mdash;about the faintest
+visible in a powerful binocular field-glass&mdash;1 in 18, or 1 in 20, on the
+average, are double, with the component stars less than 5 seconds of arc
+apart. This proportion of double stars is not, however, the same for all
+parts of the sky; while in some regions double stars are very scarce, in
+other places the proportion rises to 1 in 8.</p>
+
+<p>For the well-known binary star Castor (&#945; Geminorum), several
+orbits have been computed with periods ranging from 232 years (M&auml;dler) to
+1001 years (Doberck). But Burnham finds that &#8220;the orbit is absolutely
+indeterminate at this time, and likely to remain so for another century or
+longer.&#8221;<a name='fna_314' id='fna_314' href='#f_314'><small>[314]</small></a> Both components are spectroscopic binaries, and the system
+is a most interesting one.</p>
+
+<p>The well-known companion of Sirius became<span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span> invisible in all telescopes in
+the year 1890, owing to its near approach to its brilliant primary. It
+remained invisible until August 20, 1896, when it was again seen by Dr.
+See at the Lowell Observatory.<a name='fna_315' id='fna_315' href='#f_315'><small>[315]</small></a> Since then its distance has been
+increasing, and it has been regularly measured. The maximum distance will
+be attained about the year 1922.</p>
+
+<p>The star &#946; Cephei has recently been discovered to be a
+spectroscopic binary with the wonderfully short period of 4<sup>h</sup> 34<sup>m</sup>
+11<sup>s</sup>. The orbital velocity is about 10&#189; miles a second, and as this
+velocity is not very great, the distance between the components must be
+very small, and possibly the two component bodies are revolving in actual
+contact. The spectrum is of the &#8220;Orion type.&#8221;<a name='fna_316' id='fna_316' href='#f_316'><small>[316]</small></a></p>
+
+<p>According to Slipher the spectroscopic binary &#947; Geminorum has the
+comparatively long period (for a spectroscopic binary) of about 3&#189;
+years. This period is comparable with that of the telescopic binary
+system, &#948; Equulei (period about 5&middot;7 years). The orbit is quite
+eccentric. I have shown elsewhere<a name='fna_317' id='fna_317' href='#f_317'><small>[317]</small></a> that &#947; Geminorum has
+probably increased in brightness since the time of Al-Sufi (tenth
+century). Possibly its spectroscopic duplicity may have something to do
+with the variation in its light.</p>
+
+<p><span class="pagenum"><a name="Page_162" id="Page_162">[Pg 162]</a></span>With reference to the spectra of double stars, Mr. Maunder suggests that
+the fact of the companion of a binary star showing a Sirian spectrum while
+the brighter star has a solar spectrum may be explained by supposing that,
+on the theory of fission, &#8220;the smaller body when thrown off consisted of
+the lighter elements, the heavier remaining in the principal star. In
+other words, in these cases spectral type depends upon original chemical
+constitution, and not upon the stage of stellar development
+attained.&#8221;<a name='fna_318' id='fna_318' href='#f_318'><small>[318]</small></a></p>
+
+<p>A curious paradox with reference to binary stars has recently come to
+light. For many years it was almost taken for granted that the brighter
+star of a pair had a larger mass than the fainter component. This was a
+natural conclusion, as both stars are practically at the same distance
+from the earth. But it has been recently found that in some binary stars
+the fainter component has actually the larger mass! Thus, in the binary
+star &#949; Hydr&aelig;, the &#8220;magnitude&#8221; of the component stars are 3 and 6,
+indicating that the brighter star is about 16 times brighter than the
+fainter component. Yet calculations by Lewis show that the fainter star
+has 6 times the mass of the brighter, that is, contains 6 times the
+quantity of matter! In the well-known binary 70 Ophiuchi, Prey finds that
+the fainter star has about 4 times the<span class="pagenum"><a name="Page_163" id="Page_163">[Pg 163]</a></span> mass of the brighter! In 85
+Pegasi, the brighter star is about 40 times brighter than its companion,
+while Furner finds that the mass of the fainter star is about 4 times that
+of the brighter! And there are other similar cases. In fact, in these
+remarkable combinations of suns the fainter star is really the &#8220;primary,&#8221;
+and is, so far as mass is concerned, &#8220;the predominant partner.&#8221; This is a
+curious anomaly, and cannot be well explained in the present state of our
+knowledge of stellar systems. In the case of &#945; Centauri the
+masses of the components are about equal, while the primary star is about
+3 times brighter than the other. But here the discrepancy is
+satisfactorily explained by the difference in character of the spectra,
+the brighter component having a spectrum of the solar type, while the
+fainter seems further advanced on the downward road of evolution, that is,
+more consolidated and having, perhaps, less intrinsic brightness of
+surface.</p>
+
+<p>In the case of Sirius and its faint attendant, the mass of the bright star
+is about twice the mass of the satellite, while its light is about 40,000
+times greater! Here the satellite is either a cooled-down sun or perhaps a
+gaseous nebula. There seems to be no other explanation of this curious
+paradox. The same remark applies to Procyon, where the bright star is
+about 100,000 times brighter than its faint companion, although its mass
+is only 5 times greater.</p>
+
+<p><span class="pagenum"><a name="Page_164" id="Page_164">[Pg 164]</a></span>The bright star Capella forms a curious anomaly or paradox. Spectroscopic
+observations show that it is a very close binary pair. It has been seen
+&#8220;elongated&#8221; at the Greenwich Observatory with the great 28-inch
+refractor&mdash;the work of Sir Howard Grubb&mdash;and the spectroscopic and visual
+measurements agree in indicating that its mass is about 18 times the mass
+of the sun. But its parallax (about 0&Prime;&middot;08) shows that it is about 128
+times brighter than the sun! This great brilliancy is inconsistent with
+the star&#8217;s computed mass, which would indicate a much smaller brightness.
+The sun placed at the distance of Capella would, I find, shine as a star
+of about 5&#189; magnitude, while Capella is one of the brightest stars in
+the sky. As the spectrum of Capella&#8217;s light closely resembles the solar
+spectrum, we seem justified in assuming that the two bodies have pretty
+much the same physical composition. The discrepancy between the computed
+and actual brightness of the star cannot be explained satisfactorily, and
+the star remains an astronomical enigma.</p>
+
+<p>Three remarkable double-star systems have been discovered by Dr. See in
+the southern hemisphere. The first of these is the bright star &#945;
+Ph&oelig;nicis, of which the magnitude is 2&middot;4, or only very slightly fainter
+than the Pole Star. It is attended by a faint star of the 13th magnitude
+at a distance of less than 10 seconds (1897). The<span class="pagenum"><a name="Page_165" id="Page_165">[Pg 165]</a></span> bright star is of a
+deep orange or reddish colour, and the great difference in brightness
+between the component stars &#8220;renders the system both striking and
+difficult.&#8221; The second is &#956; Velorum, a star of the 3rd magnitude,
+which has a companion of the 11th magnitude, and only 2&#189;&Prime; from its
+bright primary (1897). Dr. See describes this pair as &#8220;one of the most
+extraordinary in the heavens.&#8221; The third is &#951; Centauri, of 2&#189;
+magnitude, with a companion of 13&#189; magnitude at a distance of 5&Prime;&middot;65
+(1897); colours yellow and purple. This pair is &#8220;extremely difficult,
+requiring a powerful telescope to see it.&#8221; Dr. See thinks that these three
+objects &#8220;may be regarded as amongst the most splendid in the heavens.&#8221;</p>
+
+<p>The following notes are from Burnham&#8217;s recently published <i>General
+Catalogue of Double Stars</i>.</p>
+
+<p>The Pole Star has a well-known companion of about the 9th magnitude, which
+is a favourite object for small telescopes. Burnham finds that the bright
+star and its faint companion are &#8220;relatively fixed,&#8221; and are probably only
+an &#8220;optical pair.&#8221; Some other companions have been suspected by amateur
+observers, but Burnham finds that &#8220;there is nothing nearer&#8221; than the known
+companion within the reach of the great 36-inch telescope of the Lick
+Observatory (<i>Cat.</i>, p. 299).</p>
+
+<p>The well-known companion to the bright star<span class="pagenum"><a name="Page_166" id="Page_166">[Pg 166]</a></span> Rigel (&#946; Orionis)
+has been suspected for many years to be a close double star. Burnham
+concludes that it is really a binary star, and its &#8220;period may be shorter
+than that of any known pair&#8221; (<i>Cat.</i>, p. 411).</p>
+
+<p>Burnham finds that the four brighter stars in the trapezium in the great
+Orion nebula (in the &#8220;sword&#8221;) are relatively fixed (<i>Cat.</i>, p. 426).</p>
+
+<p>&#947; Leonis. This double star was for many years considered to be a
+binary, but Burnham has shown that all the measures may be satisfactorily
+represented by a straight line, and that consequently the pair merely
+forms an &#8220;optical double.&#8221;</p>
+
+<p>42 Com&aelig; Berenices. This is a binary star of which the orbit plane passes
+nearly through the earth. The period is about 25&#189; years, and Burnham
+says the orbit &#8220;is as accurately known as that of any known binary.&#8221;</p>
+
+<p>&#963; Coron&aelig; Borealis. Burnham says that the orbits hitherto
+computed&mdash;with periods ranging from 195 years (Jacob) to 846 years
+(Doberck) are &#8220;mere guess work,&#8221; and it will require the measures of at
+least another century, and perhaps a much longer time, to give an
+approximate period (<i>Cat.</i>, p. 209). So here is some work left for
+posterity to do in this field.</p>
+
+<p>70 Ophiuchi. With reference to this well-known binary star, Burnham says,
+&#8220;the elements of the orbit are very accurately known.&#8221; The<span class="pagenum"><a name="Page_167" id="Page_167">[Pg 167]</a></span> periods
+computed range from 86&middot;66 years (Doolittle) to 98&middot;15 years (Powell). The
+present writer found a period of 87&middot;84 years, which cannot be far from the
+truth. Burnham found 87&middot;75 years (<i>Cat.</i>, p. 774). In this case there is
+not much left for posterity to accomplish.</p>
+
+<p>61 Cygni. With reference to this famous star Burnham says, &#8220;So far the
+relative motion is practically rectilinear. If the companion is moving in
+a curved path, it will require the measures of at least another
+half-century to make this certain. The deviation of the measured positions
+during the last 70 years from a right line are less than the average
+errors of the observations.&#8221;</p>
+
+<p>Burnham once saw a faint companion to Sirius of the 16th magnitude, and
+measured its position with reference to the bright star (280&deg;&middot;6: 40&Prime;&middot;25:
+1899&middot;86). But he afterwards found that it was &#8220;not a real object but a
+reflection from Sirius&#8221; (in the eye-piece). Such false images are called
+&#8220;ghosts.&#8221;</p>
+
+<p>With reference to the well-known double (or rather quadruple) star &#949;
+Lyr&aelig;, near Vega, and supposed faint stars near it, Burnham says, &#8220;From
+time to time various small stars in the vicinity have been mapped, and
+much time wasted in looking for and speculating about objects which only
+exist in the imagination of the observer.&#8221; He believes that many of these
+faint<span class="pagenum"><a name="Page_168" id="Page_168">[Pg 168]</a></span> stars, supposed to have been seen by various observers, are merely
+&#8220;ghosts produced by reflection.&#8221;</p>
+
+<p>The binary star &#950; Bo&ouml;tis, which has long been suspected of small
+and irregular variation of light, showed remarkable spectral changes in
+the year 1905,<a name='fna_319' id='fna_319' href='#f_319'><small>[319]</small></a> somewhat similar to those of a <i>nova</i>, or temporary
+star. It is curious that such changes should occur in a star having an
+ordinary Sirian type of spectrum!</p>
+
+<p>A curious quadruple system has been discovered by Mr. R. T. A. Innes in
+the southern hemisphere. The star &#954; Toucani is a binary star with
+components of magnitudes 5 and 7&middot;7, and a period of revolution of perhaps
+about 1000 years. Within 6&prime; of this pair is another star (Lacaille 353),
+which is also a binary, with a period of perhaps 72 years. Both pairs have
+the same proper motion through space, and evidently form a vast quadruple
+system; for which Mr. Innes finds a possible period of 300,000 years.<a name='fna_320' id='fna_320' href='#f_320'><small>[320]</small></a></p>
+
+<p>It is a curious fact that the performance of a really good refracting
+telescope actually exceeds what theory would indicate! at least so far as
+double stars are concerned. For example, the famous double-star observer
+Dawes found that the distance between the components of a double<span class="pagenum"><a name="Page_169" id="Page_169">[Pg 169]</a></span> star
+which can just be divided, is found by dividing 4&Prime;&middot;56 by the aperture of
+the object-glass in inches. Now theory gives 5&Prime;&middot;52 divided by the
+aperture. &#8220;The actual telescope&mdash;if a really good one&mdash;thus exceeds its
+theoretical requirements. The difference between theory and practice in
+this case seems to be due to the fact that in the &#8216;spurious&#8217; star disc
+shown by good telescopes, the illumination at the edges of the star disc
+is very feeble, so that its full size is not seen except in the case of a
+very bright star.&#8221;<a name='fna_321' id='fna_321' href='#f_321'><small>[321]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_170" id="Page_170">[Pg 170]</a></span></p>
+<h2><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI</h2>
+<p class="title">Variable Stars</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">In</span> that interesting work <i>A Cycle of Celestial Objects</i>, Admiral Smyth
+says (p. 275), &#8220;Geminiano Montanari, as far back as 1670, was so struck
+with the celestial changes, that he projected a work to be intituled the
+<i>Instabilities of the Firmament</i>, hoping to show such alterations as would
+be sufficient to make even Aristotle&mdash;were he alive&mdash;reverse his opinion
+on the incorruptibility of the spangled sky: &#8216;There are now wanting in the
+heavens,&#8217; said he, &#8216;two stars of the 2nd magnitude in the stem and yard of
+the ship Argo. I and others observed them in the year 1664, upon occasion
+of the comet that appeared in that year. When they first disappeared I
+know not; only I am sure that on April 10, 1668, there was not the least
+glimpse of them to be seen.&#8217;&#8221; Smyth adds, &#8220;Startling as this account
+is&mdash;and I am even disposed to question the fact&mdash;it must be recollected
+that Montanari was a man of integrity, and well versed in the theory and
+practice of astronomy;<span class="pagenum"><a name="Page_171" id="Page_171">[Pg 171]</a></span> and his account of the wonder will be found&mdash;in
+good set Latin&mdash;in page 2202 of the <i>Philosophical Transactions</i> for
+1671.&#8221;</p>
+
+<p>There must be, I think&mdash;as Smyth suggests&mdash;some mistake in Montanari&#8217;s
+observations, for it is quite certain that of the stars mentioned by
+Ptolemy (second century <span class="smcaplc">A.D.</span>) there is no star of the 2nd magnitude now
+missing. It is true that Al-Sufi (tenth century) mentions a star of the
+<i>third</i> magnitude mentioned by Ptolemy in the constellation of the Centaur
+(about 2&deg; east of the star &#949; Centauri) which he could not find.
+But this has nothing to do with Montanari&#8217;s stars. Montanari&#8217;s words are
+very clear. He says, &#8220;<i>Desunt in C&oelig;lo du&aelig; stell&aelig;</i> Secund&aelig; Magnitudinis
+<i>in</i> Puppi Navis <i>ejusve Transtris</i> Bayero &#946; et &#947;,
+<i>prope</i> Canem Majoris, <i>&agrave; me et aliis, occasione pr&aelig;sertim Comet&aelig;</i> A. 1664
+<i>observat&aelig; et recognit&aelig;. Earum Disparitionem</i> cui Anno debeam, non novi;
+<i>hoc indubium, quod &agrave; die</i> 10 April, 1668, <i>ne</i> vestigium quidem <i>illarum
+adesse amplius observe; c&aelig;teris circa eas etium quart&aelig; et quint&aelig;
+magnitudinis, immotis.</i>&#8221; So the puzzle remains unsolved.</p>
+
+<p>Sir William Herschel thought that &#8220;of all stars which are singly visible,
+about one in thirty are undergoing an observable change.&#8221;<a name='fna_322' id='fna_322' href='#f_322'><small>[322]</small></a> Now taking
+the number of stars visible to the naked eye at 6000, this would give
+about 200 variable stars<span class="pagenum"><a name="Page_172" id="Page_172">[Pg 172]</a></span> visible at maximum to the unaided vision. But
+this estimate seems too high. Taking all the stars visible in the largest
+telescopes&mdash;possibly about 100 millions&mdash;the proportion of variable stars
+will probably be much smaller still.</p>
+
+<p>The theory that the variation of light in the variable stars of the Algol
+type is due to a partial eclipse by a companion star (not necessarily a
+dark body) is now well established by the spectroscope, and is accepted by
+all astronomers. The late Miss Clarke has well said &#8220;to argue this point
+would be <i>enforcer une porte ouverte</i>.&#8221;</p>
+
+<p>According to Dr. A. W. Roberts, the components of the following &#8220;Algol
+variables&#8221; &#8220;revolve in contact&#8221;: V Puppis, X Carin&aelig;, &#946; Lyr&aelig;, and
+&#965; Pegasi. Of those V Puppis and &#946; Lyr&aelig; are known
+spectroscopic binaries. The others are beyond the reach of the
+spectroscope, owing to their faintness.</p>
+
+<p>A very curious variable star of the Algol type is that known as R R
+Draconis. Its normal magnitude is 10, but at minimum it becomes invisible
+in a 7&#189;-inch refracting telescope. The variation must, therefore, be
+over 3 magnitudes, that is, at minimum its light must be reduced to about
+one-sixteenth of its normal brightness. The period of variation from
+maximum to minimum is about 2&middot;83 days. The variation of light near minimum
+is extraordinarily rapid, the<span class="pagenum"><a name="Page_173" id="Page_173">[Pg 173]</a></span> light decreasing by about 1 magnitude in
+half an hour.<a name='fna_323' id='fna_323' href='#f_323'><small>[323]</small></a></p>
+
+<p>A very remarkable variable star has been recently discovered in the
+constellation Auriga. Prof. Hartwig found it of the 9th magnitude on March
+6, 1908, the star &#8220;having increased four magnitudes in one day, whilst
+within eight days it was less than the 14th magnitude.&#8221;<a name='fna_324' id='fna_324' href='#f_324'><small>[324]</small></a> In other
+words its light increased at least one-hundredfold in eight days!</p>
+
+<p>The period of the well-known variable star &#946; Lyr&aelig; seems to be
+slowly increasing. This Dr. Roberts (of South Africa) considers to be due
+to the component stars slowly receding from each other. He finds that &#8220;a
+very slight increase of one-thousandth part of the radius of the orbit
+would account for the augmentation in time, 30<sup>m</sup> in a century.&#8221; According
+to the theory of stellar evolution the lengthening of the period of
+revolution of a binary star would be due to the &#8220;drag&#8221; caused by the tides
+formed by each component on the other.<a name='fna_325' id='fna_325' href='#f_325'><small>[325]</small></a></p>
+
+<p>M. Sebastian Albrecht finds that in the short-period variable star known
+as T Vulpecul&aelig; (and other variables of this class, such as Y Ophiuchi),
+there can be no eclipse to explain the variation of light (as in the case
+of Algol). The star is a spectroscopic binary, it is true, but the
+maximum<span class="pagenum"><a name="Page_174" id="Page_174">[Pg 174]</a></span> of light coincides with the greatest velocity of <i>approach</i> in
+the line of sight, and the minimum with the greatest velocity of
+<i>recession</i>. Thus the light curve and the spectroscopic velocity curve are
+very similar in shape, but one is like the other turned upside down. &#8220;That
+is, the two curves have a very close correspondence in phase in addition
+to correspondence of shape and period.&#8221;<a name='fna_326' id='fna_326' href='#f_326'><small>[326]</small></a></p>
+
+<p>The star now known as W Urs&aelig; Majoris (the variability of which was
+discovered by M&uuml;ller and Kempf in 1902), and which lies between the stars
+&#952; and &#965; of that constellation, has the marvellously
+short period of 4 hours (from maximum to maximum). Messrs. Jordan and
+Parkhurst (U.S.A.), find from photographic plates that the star varies
+from 7&middot;24 to 8&middot;17 magnitude.<a name='fna_327' id='fna_327' href='#f_327'><small>[327]</small></a> The light at maximum is, therefore, more
+than double the light at minimum. A sun which loses more than half its
+light and recovers it again in the short period of 4 hours is certainly a
+curious and wonderful object.</p>
+
+<p>In contrast with the above, the same astronomers have discovered a star in
+Perseus which seems to vary from about the 6th to the 7th magnitude in the
+very long period of 7&#189; years! It is now known as X Persei, and its
+position for 1900 is R.A. 3<sup>h</sup> 49<sup>m</sup> 8<sup>s</sup>, Dec. N. 30&deg; 46&prime;, or about one
+degree south-east of the star &#950; Persei.<span class="pagenum"><a name="Page_175" id="Page_175">[Pg 175]</a></span> It seems to be a
+variable of the Algol type, as the star remained constant in light at
+about the 6th magnitude from 1887 to 1891. It then began to fade, and on
+December 1, 1897, it was reduced to about the 7th magnitude.</p>
+
+<p>On the night of August 20, 1886, Prof. Colbert, of Chicago, noticed that
+the star &#950; Cassiopei&aelig; increased in brightness &#8220;by quite half a
+magnitude, and about half an hour afterwards began to return to its normal
+magnitude.&#8221;<a name='fna_328' id='fna_328' href='#f_328'><small>[328]</small></a> This curious outburst of light in a star usually constant
+in brightness is (if true) a very unusual phenomenon. But a somewhat
+similar fluctuation of light is recorded by the famous German astronomer
+Heis. On September 26, 1850, he noted that the star &#8220;&#950; Lyr&aelig;
+became, for a moment, <i>very bright</i>, and then again faint.&#8221; (The words in
+his original observing book are: &#8220;&#950; Lyr&aelig; wurde einen <i>Moment sehr
+hell</i> und hierauf wieder dunkel.&#8221;) As Heis was a remarkably accurate
+observer of star brightness, the above remark deserves the highest
+confidence.<a name='fna_329' id='fna_329' href='#f_329'><small>[329]</small></a></p>
+
+<p>The variable star known as the V Delphini was found to be invisible in the
+great 40-inch telescope of the Yerkes Observatory on July 20, 1900. Its
+magnitude was, therefore, below the 17th. At its maximum brightness it is
+about 7&#189;, or easily visible in an ordinary opera-glass, so that its<span class="pagenum"><a name="Page_176" id="Page_176">[Pg 176]</a></span>
+range of variation is nearly, or quite, ten magnitudes. That is, its light
+at maximum is about 10,000 times its light at minimum. That a sun should
+vary in light to this enormous extent is certainly a wonderful fact. A
+variable discovered by Ceraski (and numbered 7579 in Chandlers&#8217; Catalogue)
+&#8220;had passed below the limit of the 40-inch in June, 1900, and was,
+therefore, not brighter than 17 mag.&#8221;<a name='fna_330' id='fna_330' href='#f_330'><small>[330]</small></a></p>
+
+<p>The late Sir C. E. Peck and his assistant, Mr. Grover, made many valuable
+observations of variable stars at the Rousden Observatory during many
+years past. Among other interesting things noted, Peck sometimes saw faint
+stars in the field of view of his telescope which were at other times
+invisible for many months, and he suggested that these are faint variable
+stars with a range of brightness from the 13th to the 20th magnitude. He
+adds, &#8220;Here there is a practically unemployed field for the largest
+telescopes.&#8221; Considering the enormous number of faint stars visible on
+stellar photographs the number of undiscovered variable stars must be very
+large.</p>
+
+<p>Admiral Smyth describes a small star near &#946; Leonis, about 5&prime;
+distant, of about 8th magnitude, and dull red. In 1864 Mr. Knott measured
+a faint star close to Smyth&#8217;s position, but estimated it only 11&middot;6
+magnitude. The Admiral&#8217;s star would thereupon seem to be variable.<a name='fna_331' id='fna_331' href='#f_331'><small>[331]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_177" id="Page_177">[Pg 177]</a></span>The famous variable star &#951; Argus, which Sir John Herschel, when
+at the Cape of Good Hope in 1838, saw involved in dense nebulosity, was in
+April, 1869, &#8220;seen on the bare sky,&#8221; with the great Melbourne telescope,
+&#8220;the nebula having disappeared for some distance round it.&#8221; Other changes
+were noticed in this remarkable nebula. The Melbourne observers saw &#8220;three
+times as many stars as were seen by Herschel.&#8221; But of course their
+telescope is much larger&mdash;48 inches aperture, compared with Herschel&#8217;s 20
+inches.</p>
+
+<p>Prof. E. C. Pickering thinks that the fluctuations of light of the
+well-known variable star R Coron&aelig; (in the Northern Crown), &#8220;are unlike
+those of any known variable.&#8221; This very curious object&mdash;one of the most
+curious in the heavens&mdash;sometimes remains for many months almost constant
+in brightness (just visible to the naked eye), and then rapidly fades in
+light by several magnitudes! Thus its changes of light in April and May,
+1905, were as follows:&mdash;</p>
+
+<table border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td>1905,</td>
+    <td>April</td>
+    <td align="right">1</td>
+    <td> &nbsp; ... &nbsp; ... &nbsp; </td>
+    <td align="right">6&middot;0</td>
+    <td>magnitude</td></tr>
+<tr><td>&nbsp;</td>
+    <td align="center">"</td>
+    <td align="right">11</td>
+    <td> &nbsp; ... &nbsp; ... &nbsp; </td>
+    <td align="right">7&middot;3</td>
+    <td align="center">"</td></tr>
+<tr><td>&nbsp;</td>
+    <td align="center">"</td>
+    <td align="right">12</td>
+    <td> &nbsp; ... &nbsp; ... &nbsp; </td>
+    <td align="right">8&middot;4</td>
+    <td align="center">"</td></tr>
+<tr><td>&nbsp;</td>
+    <td>May</td>
+    <td align="right">1</td>
+    <td> &nbsp; ... &nbsp; ... &nbsp; </td>
+    <td align="right">11&middot;4</td>
+    <td align="center">"</td></tr>
+<tr><td>&nbsp;</td>
+    <td align="center">"</td>
+    <td align="right">7</td>
+    <td> &nbsp; ... &nbsp; ... &nbsp; </td>
+    <td align="right">12&middot;5</td>
+    <td align="center">"</td></tr></table>
+
+<p>Thus between April 1 and May 1, its light was reduced by over 5
+magnitudes. In other words, the light of the star on May 1 was reduced to
+less than one-hundredth of its light on April 1. If our<span class="pagenum"><a name="Page_178" id="Page_178">[Pg 178]</a></span> sun were to
+behave in this way nearly all life would soon be destroyed on the face of
+the earth.</p>
+
+<p>M. H. E. Lau finds that the short-period variable star &#948; Cephei
+varies slightly in colour as well as in light, and that the colour curve
+is parallel to the light curve. Near the minimum of light the colour is
+reddish yellow, almost as red as &#950; Cephei; a day later it is pure
+yellow, and of about the same colour as the neighbouring &#949;
+Cephei.<a name='fna_332' id='fna_332' href='#f_332'><small>[332]</small></a> But it would not be easy to fully establish such slight
+variations of tint.</p>
+
+<p>A remarkably bright maximum of the famous variable Mira Ceti occurred in
+1906. In December of that year it was fully 2nd magnitude. The present
+writer estimated it 1&middot;8, or nearly equal to the brightest on record&mdash;1&middot;7
+observed by Sir William Herschel and Wargentin in the year 1779. From
+photographs of the spectrum taken by Mr. Slipher at the Lowell Observatory
+in 1907, he finds strong indications of the presence of the rather rare
+element vanadium in the star&#8217;s surroundings. Prof. Campbell finds with the
+Mills spectrograph attached to the great 36-inch telescope of the Lick
+Observatory that Mira is receding from the earth at the apparently
+constant velocity of about 38 miles a second.<a name='fna_333' id='fna_333' href='#f_333'><small>[333]</small></a> This, of course, has
+nothing to do with the variation in the star&#8217;s light. Prof. Campbell
+failed to see any trace of the green line<span class="pagenum"><a name="Page_179" id="Page_179">[Pg 179]</a></span> of hydrogen in the star&#8217;s
+spectrum, while two other lines of the hydrogen series &#8220;glowed with
+singular intensity.&#8221;</p>
+
+<p>Mr. Newall has found evidence of the element titanium in the spectrum of
+Betelgeuse (&#945; Orionis); Mr. Goatcher and Mr. Lunt (of the Cape
+Observatory) find tin in Antares (and Scorpii). If the latter observation
+is confirmed it will be the first time this metal has been found in a
+star&#8217;s atmosphere.<a name='fna_334' id='fna_334' href='#f_334'><small>[334]</small></a></p>
+
+<p>It is a curious fact that Al-Sufi (tenth century) does not mention the
+star &#949; Aquil&aelig;, which lies closely north-west of &#950;
+Aquil&aelig;, as it is now quite conspicuous to the naked eye. It was suspected
+of variation by Sir William Herschel. It was first recorded by Tycho Brah&eacute;
+about 1590, and he called it 3rd magnitude. Bayer also rated it 3, and
+since his time it has been variously estimated from 3&#189; to 4. If it was
+anything like its present brightness (4&middot;21 Harvard) in the tenth century
+it seems difficult to explain how it could have escaped Al-Sufi&#8217;s careful
+scrutiny of the heavens, unless it is variable. Its colour seems reddish
+to me.</p>
+
+<p>Mr. W. T. Lynn has shown&mdash;and I think conclusively&mdash;that the so-called
+&#8220;new star&#8221; of <span class="smcaplc">A.D.</span> 389 (which is said to have appeared near Altair in the
+Eagle) was really a comet.<a name='fna_335' id='fna_335' href='#f_335'><small>[335]</small></a></p>
+
+<p>Near the place of Tycho Brah&eacute;&#8217;s great new star<span class="pagenum"><a name="Page_180" id="Page_180">[Pg 180]</a></span> of 1572 (the &#8220;Pilgrim
+Star&#8221;), Hind and W. E. Plummer observed a small star (No. 129 of
+d&#8217;Arrest&#8217;s catalogue of the region) which seemed to show small
+fluctuations of light, which &#8220;scarcely include a whole magnitude.&#8221; This
+may possibly be identical with Tycho Brah&eacute;&#8217;s wonderful star, and should be
+watched by observers. The place of this small star is (for 1865) R.A. 0<sup>h</sup>
+17<sup>m</sup> 18<sup>s</sup>, N.P.D. 26&deg; 37&prime;&middot;1. The region was examined by Prof. Burnham in
+1890 with the 36-inch telescope of the Lick Observatory. &#8220;None of the
+faint stars near the place presented any peculiarity worthy of remark, but
+three double stars were found.&#8221;<a name='fna_336' id='fna_336' href='#f_336'><small>[336]</small></a></p>
+
+<p>With reference to the famous Nova (T) Coron&aelig;&mdash;the &#8220;Blaze Star&#8221; of
+1866&mdash;Prof. Barnard finds from careful comparisons with small stars in its
+vicinity that &#8220;the Nova is now essentially of the same brightness it was
+before the outburst of 1866 ... there seems to be no indication of motion
+in the <i>Nova</i>.&#8221;</p>
+
+<p>With reference to the cause of &#8220;temporary&#8221; stars, or <i>nov&aelig;</i>, as they are
+now called by astronomers&mdash;the late Prof. H. C. Vogel said&mdash;</p>
+
+<div class="blockquot"><p>&#8220;A direct collision of two celestial bodies is not regarded by Huggins
+as an admissible explanation of the Nova; a partial collision has
+little probability, and the most that can be admitted is perhaps the
+mutual penetration and admixture of the outer<span class="pagenum"><a name="Page_181" id="Page_181">[Pg 181]</a></span> gaseous envelopes of
+the two bodies at the time of their closest approach. A more probable
+explanation is given by an hypothesis which we owe to Klinkerfues, and
+which has more recently been further developed by Wilsing, viz. that
+by the very close passage of two celestial bodies enormous tidal
+disturbances are produced and thereby changes in the brightness of the
+bodies. In the case of the two bodies which form the Nova, it must be
+assumed that these phenomena are displayed in the highest degree of
+development, and that changes of pressure have been produced which
+have caused enormous eruptions from the heated interior of the bodies;
+the eruptions are perhaps accompanied by electrical actions, and are
+comparable with the outbursts in our own sun, although they are on a
+much larger scale.&#8221;<a name='fna_337' id='fna_337' href='#f_337'><small>[337]</small></a></p></div>
+
+<p>It will be noticed that this hypothesis agrees with the fundamental
+assumption of the &#8220;Planetesimal Hypothesis&#8221; advocated by Professors
+Chamberlin and Moulton (see my <i>Astronomical Essays</i>, p. 324).</p>
+
+<p>The rush of a comparatively small body through a mass of gaseous matter
+seems also a very plausible hypothesis. This idea was originally advanced
+by Prof. Seeliger, and independently by Mr. Monck.</p>
+
+<p>With reference to the nebula which was observed round the great new star
+of 1901&mdash;Nova Persei&mdash;Prof. Lewis Bell supports the theory of Seeliger,
+which accounts for the apparent movements of the brightest portions of the
+nebula by<span class="pagenum"><a name="Page_182" id="Page_182">[Pg 182]</a></span> supposing that the various parts of the highly tenuous matter
+were successively lighted up by the effects of a travelling
+electro-magnetic wavefront, and he shows that this theory agrees well with
+the observed phenomenon.<a name='fna_338' id='fna_338' href='#f_338'><small>[338]</small></a> The &#8220;collision theory&#8221; which explained the
+sudden outburst of light by the meeting of two dark bodies in space, seems
+to be now abandoned by the best astronomers. The rapid cooling down of the
+supposed bodies indicated by the rapid decrease of light is quite
+inconsistent with this hypothesis.</p>
+
+<p>The rapid diminution in the light of some of these &#8220;new stars&#8221; is very
+remarkable. Thus the new star which suddenly blazed out near the nucleus
+of the great nebula in Andromeda in August, 1885, faded down in 5 months
+from &#8220;the limit of visibility to the naked eye to that of a 26-inch
+telescope&#8221;! A <i>large</i> body could not cool in this way.</p>
+
+<p>Mr. Harold K. Palmer thinks that the &#8220;complete and astonishingly rapid
+changes of spectral type observed in the case of <i>Nova Cygni</i> and <i>Nova
+Aurig&aelig;</i>, and likewise those observed in <i>Nova Norm&aelig;</i>, <i>Nova Sagittarii</i>
+and <i>Nova Persei</i>, leave little doubt that the masses of these objects are
+small.&#8221;<a name='fna_339' id='fna_339' href='#f_339'><small>[339]</small></a></p>
+
+<p>No less than 3748 variable stars had been discovered up to May, 1907. Of
+these 2909 were<span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span> found at Harvard Observatory (U.S.A.) chiefly by means of
+photography.<a name='fna_340' id='fna_340' href='#f_340'><small>[340]</small></a></p>
+
+<p>The star 14. 1904 Cygni has a period of only 3 hours 14 minutes, which is
+the shortest period known for a variable star.</p>
+
+<p>A very interesting discovery has recently been made with reference to the
+star &#956; Herculis. It has been long suspected of variable light
+with a period of 35 or 40 days, or perhaps irregular. Frost and Adams now
+find it to be a spectroscopic binary, and further observations at Harvard
+Observatory show that it is a variable of the Algol (or perhaps &#946;
+Lyr&aelig;) type. The Algol variation of light was suggested by MM. Baker and
+Schlesinger. The period seems to be about 2&middot;05 days.<a name='fna_341' id='fna_341' href='#f_341'><small>[341]</small></a></p>
+
+<p>The northern of the two &#8220;pointers&#8221; in the Plough (so called because they
+nearly point to the Pole Star) is about the 2nd magnitude, as Al-Sufi
+rated it. It was thought to be variable in colour by Klein, Konkoly, and
+Weber; and M. Lau has recently found a period of 50 days with a maximum of
+&#8220;jaune rouge&acirc;tre&#8221; on April 2, 1902.</p>
+
+<p>The famous variable star &#951; Argus did &#8220;not exceed the 8th
+magnitude&#8221; in February, 1907, according to Mr. Tebbutt.<a name='fna_342' id='fna_342' href='#f_342'><small>[342]</small></a> This is the
+faintest ever recorded for this wonderful star.</p>
+
+<p><span class="pagenum"><a name="Page_184" id="Page_184">[Pg 184]</a></span>It is stated in <i>Knowledge</i> (vol. 5, p. 3, January 4, 1884) that the
+temporary star of 1876 (in the constellation of Cygnus) &#8220;had long been
+known and catalogued as a telescopic star of the 9th magnitude with
+nothing to distinguish it from the common herd.&#8221; But this is quite
+erroneous. The star was quite unknown before it was discovered by Schmidt
+at Athens on November 24 of that year. The remark apparently refers to the
+&#8220;Blaze Star&#8221; of 1866 in Corona Borealis, which <i>was</i> known previously as a
+star of about the 9th magnitude before its sudden outburst on May 12 of
+that year.</p>
+
+<p>This &#8220;new star&#8221; of 1866&mdash;T Coron&aelig;, as it is now called&mdash;was, with the
+possible exception of Nova Persei (1901), the only example of a <i>nova</i>
+which was known to astronomers as a small star previous to the great
+outburst of light. It is the brightest of the <i>nov&aelig;</i> still visible. It was
+the first of these interesting objects to be examined with the
+spectroscope. It was observed by Burnham in the years 1904-1906 with the
+great 40-inch telescope of the Yerkes Observatory (U.S.A.). He found its
+colour white, or only slightly tinged with yellow. In August and
+September, 1906, he estimated its magnitude at about 9&middot;3, and &#8220;it would
+seem therefore that the Nova is now essentially of the same brightness it
+was before the outburst in 1866.&#8221; It shows no indication of motion.
+Burnham found no<span class="pagenum"><a name="Page_185" id="Page_185">[Pg 185]</a></span> peculiarity about its telescopic image. A small and very
+faint nebula was found by Burnham a little following (that is east of) the
+<i>nova</i>.<a name='fna_343' id='fna_343' href='#f_343'><small>[343]</small></a></p>
+
+<p>The following details of the great new star of 1572&mdash;the &#8220;Pilgrim Star&#8221; of
+Tycho Brah&eacute;&mdash;are given by Delambre.<a name='fna_344' id='fna_344' href='#f_344'><small>[344]</small></a> In November, 1572, it was
+brighter than Sirius, Vega, and Jupiter, and almost equal to Venus at its
+brightest. During December it resembled Jupiter in brightness. In January,
+1573, it was fainter and only a little brighter than stars of the 1st
+magnitude. In February and March it was equal to 1st magnitude stars, and
+in April and May was reduced to the 2nd magnitude. In June and July it was
+3rd magnitude; in September of the 4th, and at the end of 1573 it was
+reduced to the 5th magnitude. In February, 1574, it was 6th magnitude, and
+in March of the same year it became invisible to the naked eye.</p>
+
+<p>From this account it will be seen that the decrease in light of this
+curious object was much slower than that of Nova Persei (1901) (&#8220;the new
+star of the new century&#8221;). This would suggest that it was a much larger
+body.</p>
+
+<p>There were also changes in its colour. When it was of the brightness of
+Venus or Jupiter it shone with a white light. It then became golden, and
+afterwards reddish like Mars, Aldebaran, or<span class="pagenum"><a name="Page_186" id="Page_186">[Pg 186]</a></span> Betelgeuse. It afterwards
+became of a livid white colour like Saturn, and this it retained as long
+as it was visible. Tycho Brah&eacute; thought that its apparent diameter might
+have been about 3&#189; minutes of arc, and that it was possibly 361 times
+smaller than the earth(!) But we now know that these estimates were
+probably quite erroneous.</p>
+
+<p>Temporary stars were called by the ancient Chinese &#8220;Ke-sing,&#8221; or guest
+stars.<a name='fna_345' id='fna_345' href='#f_345'><small>[345]</small></a></p>
+
+<p>A temporary star recorded by Ma-tuan-lin (Chinese Annals) in February,
+1578, is described as &#8220;a star as large as the sun.&#8221; But its position is
+not given.<a name='fna_346' id='fna_346' href='#f_346'><small>[346]</small></a></p>
+
+<p>About the middle of September, 1878, Mr. Greely, of Boston (U.S.A.),
+reported to Mr. E. F. Sawyer (the eminent observer of variable stars)
+that, about the middle of August of that year, he had seen the famous
+variable star Mira Ceti of about the 2nd magnitude, although the star did
+not attain its usual maximum until early in October, 1878. Mr. Greely
+stated that several nights after he first saw Mira it had faded to the 4th
+or 5th magnitude. If there was no mistake in this observation (and Sawyer
+could find none) it was quite an unique phenomenon, as nothing of the sort
+has been observed before or since in the history of this famous star. It
+looks as if Mr. Greely had observed a new or &#8220;temporary&#8221; star near the<span class="pagenum"><a name="Page_187" id="Page_187">[Pg 187]</a></span>
+place of Mira Ceti; but as the spot is far from the Milky Way, which is
+the usual seat of such phenomena, this hypothesis seems improbable.</p>
+
+<p>In the so-called Cepheid and Geminid variables of short period, the
+principal characteristics of the light variation are as follows:&mdash;</p>
+
+<div class="blockquot"><p>&#8220;1. The light varies without pause.</p>
+
+<p>&#8220;2. The amount of their light variation is usually about 1 magnitude.</p>
+
+<p>&#8220;3. Their periods are short&mdash;a few days only.</p>
+
+<p>&#8220;4. They are of a spectral type approximately solar; no Orion, Sirian
+or Arcturian stars having been found among them.</p>
+
+<p>&#8220;5. They seem to be found in greater numbers in certain parts of the
+sky, notably in the Milky Way, but exhibit no tendency to form
+clusters.</p>
+
+<p>&#8220;6. All those stars whose radial velocities have been studied have
+been found to be binaries whose period of orbital revolution coincides
+with that of their light change.</p>
+
+<p>&#8220;7. The orbits, so far as determined, are all small, <i>a</i> sin <i>i</i> being
+2,000,000 kilometres or less.</p>
+
+<p>&#8220;8. Their maximum light synchronizes with their maximum velocity of
+approach, and minimum light with maximum velocity of recession.</p>
+
+<p>&#8220;9. No case has been found in which the spectrum of more than one
+component has been bright enough to be recorded in the
+spectrograms.&#8221;<a name='fna_347' id='fna_347' href='#f_347'><small>[347]</small></a></p></div>
+
+<p>It is very difficult to find an hypothesis which will explain
+satisfactorily <i>all</i> these characteristics, and attempts in this direction
+have not proved very successful. Mr. J. C. Duncan suggests the<span class="pagenum"><a name="Page_188" id="Page_188">[Pg 188]</a></span> action of
+an absorbing atmosphere surrounding the component stars.</p>
+
+<p>On March 30, 1612, Scheiner saw a star near Jupiter. It was at first equal
+in brightness to Jupiter&#8217;s satellites. It gradually faded, and on April 8
+of the same year it was only seen with much difficulty in a very clear
+sky. &#8220;After that date it was never seen again, although carefully looked
+for under favourable conditions.&#8221;</p>
+
+<p>An attempted identification of Scheiner&#8217;s star was made in recent years by
+Winnecke. He found that its position, as indicated by Scheiner, agrees
+with that of the Bonn <i>Durchmusterung</i> star 15&deg;, 2083 (8&#189; magnitude).
+This star is not a known variable. Winnecke watched it for 17 years, but
+found no variation of light. From Scheiner&#8217;s recorded observations his
+star seems to have reached the 6th magnitude, which is considerably
+brighter than the <i>Durchmusterung</i> star watched by Winnecke.<a name='fna_348' id='fna_348' href='#f_348'><small>[348]</small></a></p>
+
+<p>With reference to the colours of the stars, the supposed change of colour
+in Sirius from red to white is well known, and will be considered in the
+chapter on the Constellations. The bright star Arcturus has also been
+suspected of variation in colour. About the middle of the nineteenth
+century Dr. Julius Schmidt, of Athens, the well-known observer of variable
+stars, thought it one of the reddest stars in the sky, especially in the
+year<span class="pagenum"><a name="Page_189" id="Page_189">[Pg 189]</a></span> 1841, when he found its colour comparable with that of the planet
+Mars.<a name='fna_349' id='fna_349' href='#f_349'><small>[349]</small></a> In 1852, however, he was surprised to find it yellow and devoid
+of any reddish tinge; in colour it was lighter than that of Capella. In
+1863, Mr. Jacob Ennis found it &#8220;decidedly orange.&#8221; Ptolemy and Al-Sufi
+called it red.</p>
+
+<p>Mr. Ennis speaks of Capella as &#8220;blue&#8221; (classing it with Rigel), and
+comparing its colour with that of Vega!<a name='fna_350' id='fna_350' href='#f_350'><small>[350]</small></a> But the present writer has
+never seen it of this colour. To his eye it seems yellowish or orange. It
+was called red by Ptolemy, El Fergani, and Riccioli; but Al-Sufi says
+nothing about its colour.</p>
+
+<p>Of &#946; Urs&aelig; Minoris, Heis, the eminent German astronomer said, &#8220;I
+have had frequent opportunities of convincing myself that the colour of
+this star is not always equally red; at times it is more or less yellow,
+at others most decidedly red.&#8221;<a name='fna_351' id='fna_351' href='#f_351'><small>[351]</small></a></p>
+
+<p>Among double stars there are many cases in which variation of colour has
+been suspected. In some of these the difference in the recorded colour may
+possibly be due to &#8220;colour blindness&#8221; in some of the observers; but in
+others there seems to be good evidence in favour of a change. The
+following may be mentioned:&mdash;</p>
+
+<p><span class="pagenum"><a name="Page_190" id="Page_190">[Pg 190]</a></span>&#951; Cassiopei&aelig;. Magnitudes of the components about 4 and 7&#189;.
+Recorded as red and green by Sir John Herschel and South; but yellow and
+orange by Sestini.</p>
+
+<p>&#953; Trianguli. Magnitudes 5&#189; and 7. Secchi estimated them as
+white or yellow and blue; but Webb called them yellow and green (1862).</p>
+
+<p>&#947; Leonis, 2 and 3&#189;. Sir William Herschel noted them white and
+reddish white; but Webb, light orange and greenish yellow.</p>
+
+<p>12 Canum Venaticorum, 2&#189; and 6&#189;. White and red, Sir William
+Herschel; but Sir John Herschel says in 1830, &#8220;With all attention I could
+perceive no contrast of colours in the two stars.&#8221; Struve found them both
+white in 1830, thus agreeing with Sir John Herschel. Sestini saw them
+yellow and blue in 1844; Smyth, in 1855, pale reddish white and lilac;
+Dembowski, in 1856, white and pale olive blue; and Webb, in 1862, flushed
+white and pale lilac.</p>
+
+<p>On October 13, 1907, Nova Persei, the great new star of 1901, was
+estimated to be only 11&middot;44 magnitude, or about 11&#189;. When at its
+brightest this famous star was about zero magnitude; so that it has in
+about 6 years faded about 11&#189; magnitudes in brightness; in other words,
+it has been reduced to <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">40000</span> of its greatest brilliancy!</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_191" id="Page_191">[Pg 191]</a></span></p>
+<h2><a name="CHAPTER_XVII" id="CHAPTER_XVII"></a>CHAPTER XVII</h2>
+<p class="title">Nebul&aelig; and Clusters</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">In</span> his interesting and valuable work on &#8220;The Stars,&#8221; the late Prof.
+Newcomb said&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Great numbers of the nebul&aelig; are therefore thousands of times the
+dimensions of the earth&#8217;s orbit, and most of them are thousands of
+times the dimensions of the whole solar system. That they should be
+completely transparent through such enormous dimensions shows their
+extreme tenuity. Were our solar system placed in the midst of one of
+them it is probable that we should not be able to find any evidence of
+its existence&#8221;!</p></div>
+
+<p>Prof. Perrine thinks that the total number of the nebul&aelig; will ultimately
+be found to exceed a million.<a name='fna_352' id='fna_352' href='#f_352'><small>[352]</small></a></p>
+
+<p>Dr. Max Wolf has discovered a number of small nebul&aelig; in the regions near
+Algol and Nova Persei (the great &#8220;new star&#8221; of 1901). He says, &#8220;They
+mostly lie in two bands,&#8221; and are especially numerous where the two bands
+meet, a region of 12 minutes of arc square containing no less than 148 of
+them. They are usually &#8220;round with<span class="pagenum"><a name="Page_192" id="Page_192">[Pg 192]</a></span> central condensation,&#8221; and form of
+Andromeda nebula.<a name='fna_353' id='fna_353' href='#f_353'><small>[353]</small></a></p>
+
+<p>Some small nebul&aelig; have been found in the vicinity of the globular
+clusters. They are described by Prof. Perrine as very small and like an
+&#8220;out of focus&#8221; image of a small star. &#8220;They appear to be most numerous
+about clusters which are farthest from the galaxy.&#8221; Prof. Perrine says,
+&#8220;Practically all the small nebul&aelig; about the globular clusters are
+elliptical or circular. Those large enough to show structure are spirals.
+Doubtless the majority of these are spirals.&#8221;<a name='fna_354' id='fna_354' href='#f_354'><small>[354]</small></a> This seems further
+evidence in favour of the &#8220;spiral nebular hypothesis&#8221; of Chamberlin and
+Moulton.</p>
+
+<p>A great photographic nebula in Orion was discovered by Prof. Barnard in
+1894. In a drawing he gives of the nebula,<a name='fna_355' id='fna_355' href='#f_355'><small>[355]</small></a> it forms a long streak
+beginning a little south of &#947; Orionis (Bellatrix), passing
+through the star 38 Orionis north of 51 and south of 56 and 60 Orionis.
+Then turning south it sweeps round a little north of &#954; Orionis;
+then over 29 Orionis, and ends a little to the west of &#951; Orionis.
+There is an outside patch west of Rigel. Barnard thinks that the whole
+forms a vast spiral structure; probably connected with the &#8220;great nebula&#8221;
+in the &#8220;sword of Orion,&#8221; which it surrounds.</p>
+
+<p><span class="pagenum"><a name="Page_193" id="Page_193">[Pg 193]</a></span>From calculations of the brightness of surface (&#8220;intrinsic brightness&#8221;) of
+several &#8220;planetary&#8221; nebul&aelig; made by the present writer in the year 1905, he
+finds that the luminosity is very small compared with that of the moon.
+The brightest of those examined (<i>h</i> 3365, in the southern hemisphere,
+near the Southern Cross) has a surface luminosity of only
+<span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">400</span> of that of
+the moon.<a name='fna_356' id='fna_356' href='#f_356'><small>[356]</small></a> The great nebul&aelig; in Orion and Andromeda seem to have &#8220;still
+smaller intrinsic brightness.&#8221;</p>
+
+<p>Arago says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The spaces which precede or which follow simple nebul&aelig;, and <i>a
+fortiori</i> groups of nebul&aelig;, contain generally few stars. Herschel
+found this rule to be invariable. Thus every time that, during a short
+interval, no star appeared, in virtue of the diurnal motion, to place
+itself in the field of his motionless telescope, he was accustomed to
+say to the secretary who assisted him (Miss Caroline Herschel),
+&#8216;Prepare to write; nebul&aelig; are about to arrive.&#8217;&#8221;<a name='fna_357' id='fna_357' href='#f_357'><small>[357]</small></a></p></div>
+
+<p>Commenting on this remark of Arago, the late Herbert Spencer says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;How does this fact consist with the hypothesis that nebul&aelig; are remote
+galaxies? If there were but one nebula, it would be a curious
+coincidence were this one nebula so placed in the distant regions of
+space as to agree in direction with a starless spot in our sidereal
+system! If there were but two nebul&aelig;, and both were so placed, the
+coincidence would be excessively strange.<span class="pagenum"><a name="Page_194" id="Page_194">[Pg 194]</a></span> What shall we say on
+finding that they are habitually so placed? (the last five words
+replace some that are possibly a little too strong).... When to the
+fact that the general mass of nebul&aelig; are antithetical in position to
+the general mass of the stars, we add the fact that local regions of
+nebul&aelig; are regions where stars are scarce, and the further fact that
+single nebul&aelig; are habitually found in comparatively starless spots,
+does not the proof of a physical connection become overwhelming?&#8221;<a name='fna_358' id='fna_358' href='#f_358'><small>[358]</small></a></p></div>
+
+<p>With reference to the small elongated nebula discovered by Miss Caroline
+Herschel in 1783 near the great nebula in Andromeda, Admiral Smyth says,
+&#8220;It lies between two sets of stars, consisting of four each, and each
+disposed like the figure 7, the preceding group being the smallest.&#8221;<a name='fna_359' id='fna_359' href='#f_359'><small>[359]</small></a></p>
+
+<p>Speaking of the &#8220;nebula&#8221; Messier 3&mdash;a globular cluster in Canes
+Venatici&mdash;Admiral Smyth says, &#8220;This mass is one of those balls of compact
+and wedged stars whose laws of aggregation it is so impossible to assign;
+but the rotundity of the figure gives full indication of some general
+attractive bond of union.&#8221;<a name='fna_360' id='fna_360' href='#f_360'><small>[360]</small></a> The terms &#8220;compact and wedged&#8221; are,
+however, too strong, for we know that in the globular clusters the
+component stars must be separated from each other by millions of miles!</p>
+
+<p>Prof. Chamberlin suggests that the secondary nebula (as it is called) in
+the great spiral in Canes<span class="pagenum"><a name="Page_195" id="Page_195">[Pg 195]</a></span> Venatici (Messier 51) may possibly represent
+the body which collided with the other (the chief nucleus) in a grazing
+collision, and is now escaping. He considers this secondary body to have
+been &#8220;a dead sun&#8221;&mdash;that is, a dark body.<a name='fna_361' id='fna_361' href='#f_361'><small>[361]</small></a> This would be very
+interesting if it could be proved. But it seems to me more probable that
+the secondary nucleus is simply a larger portion of the ejected matter,
+which is now being gradually detached from the parent mass.</p>
+
+<p>Scheiner says &#8220;the previous suspicion that the spiral nebul&aelig; are star
+clusters is now raised to a certainty,&#8221; and that the spectrum of the
+Andromeda nebula is very similar to that of the sun. He says there is &#8220;a
+surprising agreement of the two, even in respect to the relative intensity
+of the separate spectral regions.&#8221;<a name='fna_362' id='fna_362' href='#f_362'><small>[362]</small></a></p>
+
+<p>In the dynamical theory of spiral nebul&aelig;, Dr. E. J. Wilczynski thinks that
+the age of a spiral nebula may be indicated by the number of its coils;
+those having the largest number of coils being the oldest, from the point
+of view of evolution.<a name='fna_363' id='fna_363' href='#f_363'><small>[363]</small></a> This seems to be very probable.</p>
+
+<p>In the spectrum of the gaseous nebul&aelig;, the F line of hydrogen (H&#946;)
+is visible, but not the C line (H&#945;). The invisibility of the
+C line is explained by Scheiner as due to a physiological<span class="pagenum"><a name="Page_196" id="Page_196">[Pg 196]</a></span> cause, &#8220;the eye
+being less sensitive to that part of the spectrum in which the line
+appears than to the part containing the F line.&#8221;<a name='fna_364' id='fna_364' href='#f_364'><small>[364]</small></a></p>
+
+<p>An apparent paradox is found in the case of the gaseous nebul&aelig;. The
+undefined outlines of these objects render any attempt at measuring their
+parallax very difficult, if not impossible. Their distance from the earth
+is therefore unknown, and perhaps likely to remain so for many years to
+come. It is possible that they may not be farther from us than some of the
+stars visible in their vicinity. On the other hand, they may lie far
+beyond them in space. But whatever their distance from the earth may be,
+it may be easily shown that their attraction on the sun is directly
+proportioned to their distance&mdash;that is, the greater their distance, the
+greater the attraction! This is evidently a paradox, and rather a
+startling one too. But it is nevertheless mathematically true, and can be
+easily proved. For, <i>their distance being unknown</i>, they may be of any
+dimensions. They might be comparatively small bodies relatively near the
+earth, or they may be immense masses at a vast distance from us. The
+latter is, of course, the more probable. In either case the <i>apparent</i>
+size would be the same. Take the case of any round gaseous nebula.
+Assuming it to be of a globular form, its <i>real</i> diameter will depend on
+its distance from<span class="pagenum"><a name="Page_197" id="Page_197">[Pg 197]</a></span> the earth&mdash;the greater the distance, the greater the
+diameter. Now, as the volumes of spheres vary as the cubes of their
+diameters, it follows that the volume of the nebula will vary as the cube
+of its distance from the earth. As the mass of an attracting body depends
+on its volume and density, its real mass will depend on the cube of its
+distance, the density (although unknown) being a fixed quantity. If at a
+certain distance its mass is <i>m</i>, at double the distance (the <i>apparent</i>
+diameter being the same) it would have a mass of eight times <i>m</i> (8 being
+the cube of 2), and at treble the distance its mass would be 27 <i>m</i>, and
+so on, its <i>apparent</i> size being known, but not its <i>real</i> size. This is
+obvious. Now, the attractive power of a body varies directly as its
+mass&mdash;the greater the mass, the greater the attraction. Again, the
+attraction varies <i>inversely</i> as the square of the distance, according to
+the well-known law of Newton. Hence if <i>d</i> be the unknown distance of the
+nebula, we have its attractive power varying as <i>d</i><sup>3</sup> divided by <i>d</i><sup>2</sup>,
+or directly as the distance <i>d</i>. We have then the curious paradox that for
+a nebula whose distance from the earth is unknown, its attractive power on
+the sun (or earth) will vary directly as the distance&mdash;the greater the
+distance the greater the attraction, and, of course, conversely, the
+smaller the distance the less the attractive power. This result seems at
+first sight absurd and incredible,<span class="pagenum"><a name="Page_198" id="Page_198">[Pg 198]</a></span> but a little consideration will show
+that it is quite correct. Consider a small wisp of cloud in our
+atmosphere. Its mass is almost infinitesimal and its attractive power on
+the earth practically <i>nil</i>. But a gaseous nebula having the same
+<i>apparent size</i> would have an enormous volume, and, although probably
+formed of very tenuous gas, its mass would be very great, and its
+attractive power considerable. The large apparent size of the Orion nebula
+shows that its volume is probably enormous, and as its attraction on the
+sun is not appreciable, its density must be excessively small, less than
+the density of the air remaining in the receiver of the best air-pump
+after the air has been exhausted. How such a tenuous gas can shine as it
+does forms another paradox. Its light is possibly due to some
+phosphorescent or electrical action.</p>
+
+<p>The apparent size of &#8220;the great nebula in Andromeda&#8221; shows that it must be
+an object of vast dimensions. The nearest star to the earth, Alpha
+Centauri, although probably equal to our sun in volume, certainly does not
+exceed one-hundredth of a second in diameter as seen from the earth. But
+in the case of the Andromeda nebula we have an object of considerable
+apparent size, not measured by seconds of arc, but showing an area about
+three times greater than that of the full moon. The nebula certainly lies
+in the region of the stars&mdash;much farther off than<span class="pagenum"><a name="Page_199" id="Page_199">[Pg 199]</a></span> Alpha Centauri&mdash;and its
+great apparent size shows that it must be of stupendous dimensions. A
+moment&#8217;s consideration will show that whatever its distance may be, the
+farther it is from the earth the larger it must be in actual size. The sun
+is vastly larger than the moon, but its apparent size is about the same
+owing to its greater distance. Sir William Herschel thought the Andromeda
+nebula to be &#8220;undoubtedly the nearest of all the great nebul&aelig;,&#8221; and he
+estimated its distance at 2000 times the distance of Sirius. This would
+not, however, indicate a relatively near object, as it would imply a
+&#8220;light journey&#8221; of over 17,000 years! (The distance of Sirius is about 88
+&#8220;light years.&#8221;)</p>
+
+<p>It has been generally supposed that this great nebula lies at a vast
+distance from the earth, possibly far beyond most of the stars seen in the
+same region of the sky; but perhaps not quite so far as Herschel&#8217;s
+estimate would imply. Recently, however, Prof. Bohlin of Stockholm has
+found from three series of measures made in recent years a parallax of
+0&Prime;&middot;17.<a name='fna_365' id='fna_365' href='#f_365'><small>[365]</small></a></p>
+
+<p>This indicates a distance of 1,213,330 times the sun&#8217;s distance from the
+earth, and a &#8220;light journey&#8221; of about 19 years. This would make the
+distance of the nebula more than twice the distance of Sirius, about four
+times the distance of &#945; Centauri, but less than that of Capella.</p>
+
+<p><span class="pagenum"><a name="Page_200" id="Page_200">[Pg 200]</a></span>Prof. Bohlin&#8217;s result is rather unexpected, and will require confirmation
+before it can be accepted. But it will be interesting to inquire what this
+parallax implies as to the real dimensions and probable mass of this vast
+nebula. The extreme length of the nebula may be taken to represent its
+
+diameter considered as circular. For, although a circle seen obliquely is
+always foreshortened into an ellipse, still the longer axis of the ellipse
+will always represent the real diameter of the circle. This may be seen by
+holding a penny at various angles to the eye. Now, Dr. Roberts found that
+the apparent length of the Andromeda nebula is 2&#8531; degrees, or 8400
+seconds of arc. The diameter in seconds divided by the parallax will give
+the real diameter of the nebula in terms of the sun&#8217;s distance from the
+earth taken as unity. Now, 8400 divided by 0&Prime;&middot;17 gives nearly 50,000, that
+is, the real diameter of the Andromeda nebula would be&mdash;on Bohlin&#8217;s
+parallax&mdash;nearly 50,000 times the sun&#8217;s distance from the earth. As light
+takes about 500 seconds to come from the sun to the earth, the above
+figures imply that light would take about 290 days, or over 9 months to
+cross the diameter of this vast nebula.</p>
+
+<p>Elementary geometrical considerations will show that if the Andromeda
+nebula lies at a greater distance from the earth than that indicated by
+Bohlin&#8217;s parallax, its real diameter, and therefore its volume and mass,
+will be greater. If, therefore,<span class="pagenum"><a name="Page_201" id="Page_201">[Pg 201]</a></span> we assume the parallax found by Bohlin,
+we shall probably find a <i>minimum</i> value for the size and mass of this
+marvellous object.</p>
+
+<p>Among Dr. Roberts&#8217; photographs of spiral nebul&aelig; (and the Andromeda nebula
+is undoubtedly a spiral) there are some which are apparently seen nearly
+edgeways, and show that these nebul&aelig; are very thin in proportion to their
+diameter. From a consideration of these photographs we may, I think,
+assume a thickness of about one-hundredth of the diameter. This would give
+a thickness for the Andromeda nebul&aelig; of about 500 times the sun&#8217;s distance
+from the earth. This great thickness will give some idea of the vast
+proportions of the object we are dealing with. The size of the whole solar
+system&mdash;large as it is&mdash;is small in comparison. The diameter and thickness
+found above can easily be converted into miles, and from these dimensions
+the actual volume of the nebula can be compared with that of the sun. It
+is merely a question of simple mensuration, and no problem of &#8220;high
+mathematics&#8221; is involved. Making the necessary calculations, I find that
+the volume of the Andromeda nebula would be about 2&middot;32 trillion times
+(2&middot;32 &times; 10<sup>18</sup>) the sun&#8217;s volume! Now, assuming that the nebulous matter
+fills only one-half of the apparent volume of the nebula (allowing for
+spaces between the spiral branches), we have the volume = 1&middot;16 &times; 10<sup>18</sup>.
+If the nebula had the same<span class="pagenum"><a name="Page_202" id="Page_202">[Pg 202]</a></span> density as the sun, this would be its mass in
+terms of the sun&#8217;s mass taken as unity, a mass probably exceeding the
+combined mass of all the <i>stars</i> visible in the largest telescopes! But
+this assumption is, of course, inadmissible, as the sun is evidently quite
+opaque, whereas the nebula is, partially at least, more or less
+transparent. Let us suppose that the nebula has a <i>mean</i> density equal to
+that of atmospheric air. As water is about 773 times heavier than air, and
+the sun&#8217;s density is 1&middot;4 (water = 1) we have the mass of the nebula equal
+to 1&middot;16 &times; 10<sup>18</sup> divided by 773 &times; 1&middot;4, or about 10<sup>15</sup> times the sun&#8217;s
+mass, which is still much greater than the probable combined mass of all
+the <i>visible</i> stars. As it seems unreasonable to suppose that the mass of
+an individual member of our sidereal system should exceed the combined
+mass of the remainder of the system, we seem compelled to further reduce
+the density of the Andromeda nebula. Let us assume a mean density of, say,
+a millionth of hydrogen gas (a sufficiently low estimate) which is about
+14&middot;44 times lighter than air, and we obtain a mass of about 8 &times; 10<sup>7</sup> or
+80 million times the mass of the sun, which is still an enormous mass.</p>
+
+<p>As possibly I may have assumed too great a thickness for the nebula, let
+us take a thickness of one-tenth of that used above, or one thousandth of
+the length of the nebula. This gives a mass of 8 million times the sun&#8217;s
+mass. This seems<span class="pagenum"><a name="Page_203" id="Page_203">[Pg 203]</a></span> a more probable mass if the nebula is&mdash;as Bohlin&#8217;s
+parallax implies&mdash;a member of our sidereal system.</p>
+
+<p>If we assume a parallax of say 0&Prime;&middot;01&mdash;or one-hundredth of a second of
+arc&mdash;which would still keep the nebula within the bounds of our sidereal
+system&mdash;we have the dimensions of the nebula increased 17 times, and hence
+its mass nearly 5000 times greater (17<sup>3</sup>) than that found above. The mass
+would then be 40,000 million times the sun&#8217;s mass! This result seems
+highly improbable, for even this small parallax would imply a light
+journey of only 326 years, whereas the distance of the Milky Way has been
+estimated by Prof. Newcomb at about 3000 years&#8217; journey for light.</p>
+
+<p>In Dr. Roberts&#8217; photograph many small stars are seen scattered over the
+surface of the nebula; but these do not seem to be quite so numerous as in
+the surrounding sky. If the nebula lies nearer to us than the fainter
+stars visible on the photograph, some of them may be obscured by the
+denser portions of the nebula; some may be visible through the openings
+between the spiral branches; while others may be nearer to us and simply
+projected on the nebula.</p>
+
+<p>To add to the difficulty of solving this celestial problem, the
+spectroscope shows that the Andromeda nebula is not gaseous. The spectrum
+is, according to Scheiner, very similar to that of the sun, and &#8220;there is
+a surprising agreement of<span class="pagenum"><a name="Page_204" id="Page_204">[Pg 204]</a></span> the two, even in respect to the relative
+intensities of the separate spectral regions.&#8221;<a name='fna_366' id='fna_366' href='#f_366'><small>[366]</small></a> He thinks that &#8220;the
+greater part of the stars comprising the nucleus of the nebula belong to
+the second spectral class&#8221; (solar), and that the nebula &#8220;is now in an
+advanced stage of development. No trace of bright nebular lines are
+present, so that the interstellar space in the Andromeda nebula, just as
+in our stellar system, is not appreciably occupied by gaseous
+matter.&#8221;<a href='#f_366'><small>[366]</small></a> He suggests that the inner part of the nebula [the
+&#8220;nucleus&#8221;] &#8220;corresponds to the complex of those stars which do not belong
+to the Milky Way, while the latter corresponds to the spirals of the
+Andromeda nebula.&#8221;<a href='#f_366'><small>[366]</small></a> On this view of the matter we may suppose that the
+component particles are small bodies widely separated, and in this way the
+<i>mean</i> density of the Andromeda nebula may be very small indeed. They
+cannot be large bodies, as the largest telescopes have failed to resolve
+the nebula into stars, and photographs show no sign of resolution.</p>
+
+<p>It has often been suggested, and sometimes definitely stated, that the
+Andromeda nebula may possibly be an &#8220;external&#8221; universe, that is an
+universe entirely outside our sidereal system, and comparable with it in
+size. Let us examine the probability of such hypothesis. Assuming that the
+nebula has the same diameter as the Milky<span class="pagenum"><a name="Page_205" id="Page_205">[Pg 205]</a></span> Way, or about 6000 &#8220;light
+years,&#8221; as estimated by Prof. Newcomb, I find that its distance from the
+earth would be about 150,000 &#8220;light years.&#8221; As this is about 8000 times
+the distance indicated by Bohlin&#8217;s parallax, its dimensions would be 8000
+times as great, and hence its volume and mass would be 8000 cubed, or
+512,000,000,000 times greater than that found above. That is, about 4
+trillion (4 &times; 10<sup>18</sup>) times the sun&#8217;s mass! As this appears an incredibly
+large mass to be compressed into a volume even so large as that of our
+sidereal system, we seem compelled to reject the hypothesis that the
+nebula represents an external universe. The sun placed at the distance
+corresponding to 150,000 light years would, I find, shine as a star of
+less than the 23rd magnitude, a magnitude which would be invisible in the
+largest telescope that man could ever construct. But the combined light of
+4 trillion of stars of even the 23rd magnitude would be equal to one of
+minus 23&middot;5 magnitude, that is, 23&#189; magnitude brighter than the zero
+magnitude, or not very much inferior to the sun in brightness. As the
+Andromeda nebula shines only as a star of about the 5th magnitude the
+hypothesis of an external universe seems to be untenable.</p>
+
+<p>It is evident, however, that the mass of the Andromeda nebula must be
+enormous; and if it belongs to our sidereal system, and if the other great
+nebul&aelig; have similar masses, it seems quite<span class="pagenum"><a name="Page_206" id="Page_206">[Pg 206]</a></span> possible that the mass of the
+<i>visible</i> universe may much exceed that of the <i>visible</i> stars, and may be
+equal to 1000 million times the sun&#8217;s mass&mdash;as supposed by the late Lord
+Kelvin&mdash;or even much more.</p>
+
+<p>With reference to the small star which suddenly blazed out near the
+nucleus of the Andromeda nebula in August, 1885, Prof. Seeliger has
+investigated the decrease in the light of the star on the hypothesis that
+it was a cooling body which had suddenly been raised to an intense heat by
+the shock of a collision, and finds a fair agreement between theory and
+observation. Prof. Auwers points out the similarity between this outburst
+and that of the &#8220;temporary star&#8221; of 1860, which appeared in the cluster 80
+Messier, and he thinks it very probable that both phenomena were due to
+physical changes in the nebul&aelig; in which they appeared.</p>
+
+<p>The appearance of this temporary star in the Andromeda nebula seems to
+afford further evidence against the hypothesis of the nebula being an
+external universe. For, as I have shown above, our sun, if placed at a
+distance of 150,000 light years, would shine only as a star of the 23rd
+magnitude, or over 15 magnitudes fainter than the temporary star. This
+would imply that the star shone with a brightness of over a million times
+that of the sun, and would therefore indicate a body of enormous size. But
+the rapid<span class="pagenum"><a name="Page_207" id="Page_207">[Pg 207]</a></span> fading of its light would, on the contrary, imply a body of
+comparatively small dimensions. We must, therefore, conclude that the
+nebula, whatever it may be, is not an external universe, but forms a
+member of our own sidereal system.</p>
+
+<p>In Sir John Herschel&#8217;s catalogue of Nebul&aelig; and Clusters of Stars,
+published in 1833, in the <i>Philosophical Transactions</i> of the Royal
+Society, there are many curious objects mentioned. Of these I have
+selected the following:&mdash;</p>
+
+<p>No. 496 is described as &#8220;a superb cluster which fills the whole field;
+stars 9, 10 ... 13 magnitude and none below, but the whole ground of the
+sky on which it stands is singularly dotted over with infinitely minute
+points.&#8221; This is No. 22 of Sir William Herschel&#8217;s 6th class, and will be
+found about 3 degrees south and a little east of the triple star 29
+Monocerotis.</p>
+
+<p>No. 650. This object lies about 3 degrees north of the star &#956;
+Leonis, the most northern of the bright stars in the well-known &#8220;Sickle,&#8221;
+and is thus described by Sir John Herschel: &#8220;A star 12th magnitude with an
+extremely faint nebulous atmosphere about 10&Prime; to 12&Prime;. It is between a star
+8-9 magnitude north preceding, and one 10th magnitude south following,
+neither of which are so affected. A curious object.&#8221;</p>
+
+<p>No. 1558. Messier 53. A little north-east of the star &#945; Com&aelig;
+Berenices. Described as &#8220;a most beautiful highly compressed cluster.
+Stars<span class="pagenum"><a name="Page_208" id="Page_208">[Pg 208]</a></span> very small, 12th ... 20th magnitude, with scattered stars to a
+considerable distance; irregularly round, but not globular. Comes up to a
+blaze in the centre; indicating a round mass of pretty equable density.
+Extremely compressed. A most beautiful object. A mass of close-wedged
+stars 5&prime; in diameter; a few 12th magnitude, the rest of the smallest size
+and innumerable.&#8221; Webb says, &#8220;Not very bright with 3<span style="font-size: 0.8em;"><sup>7</sup></span>&frasl;<span style="font-size: 0.6em;">10</span> inches;
+beautiful with 9 inches.&#8221; This should be a magnificent object with a very
+large telescope, like the Lick or Yerkes.</p>
+
+<p>No. 2018. &#8220;A more than usually condensed portion of the enormous cluster
+of the Milky Way. The field has 200 or 300 stars in it at once.&#8221; This lies
+about 2&deg; south-west of the star 6 Aquil&aelig;, which is near the northern edge
+of the bright spot of Milky Way light in &#8220;Sobieski&#8217;s Shield&#8221;&mdash;one of the
+brightest spots in the sky.</p>
+
+<p>No. 2093. &#8220;A most wonderful phenomenon. A very large space 20&prime; or 30&prime;
+broad in Polar Distance, and 1<sup>m</sup> or 2<sup>m</sup> in Right Ascension, full of
+nebula and stars mixed. The nebula is decidedly attached to the stars, and
+is as decidedly not stellar. It forms irregular lace-work marked out by
+stars, but some parts are decidedly nebulous, wherein no star can be
+seen.&#8221; Sir John Herschel gives a figure of this curious spot, which he
+says represents its &#8220;general character, but not the minute<span class="pagenum"><a name="Page_209" id="Page_209">[Pg 209]</a></span> details of
+this object, which would be extremely difficult to give with any degree of
+fidelity.&#8221; It lies about 3 degrees west of the bright star &#950;
+Cygni.</p>
+
+<p>Among the numerous curious objects observed by Sir John Herschel during
+his visit to the Cape of Good Hope, the following may be mentioned:&mdash;</p>
+
+<p><i>h</i> 2534 (H iv. 77). Near &#964;<sup>4</sup> Eridani. Sir John Herschel says,
+&#8220;Attached cometically to a 9th magnitude star which forms its head. It is
+an exact resemblance to Halley&#8217;s comet as seen in a night glass.&#8221;... &#8220;A
+complete telescopic comet; a perfect miniature of Halley&#8217;s comet, only the
+tail is rather broader in proportion.&#8221;<a name='fna_367' id='fna_367' href='#f_367'><small>[367]</small></a></p>
+
+<p><i>h</i> 3075. Between &#947; Monocerotis and &#947; Canis Majoris. &#8220;A
+very singular nebula, and much like the profile of a bust (head, neck, and
+shoulders) or a silhouette portrait, very large, pretty well defined,
+light nearly uniform, about 12&prime; diameter. In a crowded field of Milky Way
+stars, many of which are projected on it.&#8221;<a name='fna_368' id='fna_368' href='#f_368'><small>[368]</small></a></p>
+
+<p><i>h</i> 3315 (Dunlop 323). In the Milky Way; about 3&deg; east of the Eta Arg&ucirc;s
+nebula. Sir John Herschel says, &#8220;A glorious cluster of immense magnitude,
+being at least 2 fields in extent every way. The stars are 8, 9, 10, and
+11th magnitudes, but chiefly 10th magnitude, of which there must be at
+least 200. It is the most brilliant object of the kind I have ever seen&#8221;
+... &#8220;has several<span class="pagenum"><a name="Page_210" id="Page_210">[Pg 210]</a></span> elegant double stars, and many orange-coloured
+stars.&#8221;<a name='fna_369' id='fna_369' href='#f_369'><small>[369]</small></a> This should form a fine object in even a comparatively small
+telescope, and may be recommended to observers in the southern hemisphere.
+A telescope of 3-inches aperture should show it well.</p>
+
+<p>Among astronomical curiosities may be counted &#8220;clusters within clusters.&#8221;
+A cluster in Gemini (N.G.C. 2331) has a small group of &#8220;six or seven stars
+close together and well isolated from the rest.&#8221;</p>
+
+<p>Lord Rosse describes No. 4511 of Sir John Herschel&#8217;s General Catalogue of
+Nebul&aelig; and Clusters (<i>Phil. Trans.</i>, 1864) as &#8220;a most gorgeous cluster,
+stars 12-15 magnitude, full of holes.&#8221;<a name='fna_370' id='fna_370' href='#f_370'><small>[370]</small></a> His sketch of this cluster
+shows 3 rings of stars in a line, each ring touching the next on the
+outside. Sir John Herschel described it as &#8220;Cluster; very large; very
+rich; stars 11-15 magnitude (Harding, 1827),&#8221; but says nothing about the
+rings. This cluster lies about 5 degrees south of &#948; Cygni.</p>
+
+<p>Dr. See, observing with the large telescope of the Lowell Observatory,
+found that when the sky is clear, the moon absent, and the seeing perfect,
+&#8220;the sky appeared in patches to be of a brownish colour,&#8221; and suggests
+that this colour owes its existence to immense cosmical clouds, which are
+shining by excessively feeble light!<span class="pagenum"><a name="Page_211" id="Page_211">[Pg 211]</a></span> Dr. See found that these brown
+patches seem to cluster in certain regions of the Milky Way.<a name='fna_371' id='fna_371' href='#f_371'><small>[371]</small></a></p>
+
+<p>From a comparison of Trouvelot&#8217;s drawing of the small elongated nebula
+near the great nebula in Andromeda with recent photographs, Mr. Easton
+infers that this small nebula has probably rotated through an angle of
+about 15&deg; in 25 years. An examination I have made of photographs taken in
+different years seems to me to confirm this suspicion, which, if true, is
+evidently a most interesting phenomenon.</p>
+
+<p>Dr. Max Wolf of Heidelberg finds, by spectrum photography, that the
+well-known &#8220;ring nebula&#8221; in Lyra consists of four rings composed of four
+different gases. Calling the inner ring A, the next B, the next C, and the
+outer D, he finds that A is the smallest ring, and is composed of an
+unknown gas; the next largest, B, is composed of hydrogen gas; the next,
+C, consists of helium gas; and the outer and largest ring, D, is
+composed&mdash;like A&mdash;of an unknown gas. As the molecular weight of hydrogen
+is 2&middot;016, and that of helium is 3&middot;96, Prof. Bohuslav Brauner suggests that
+the molecular weight of the gas composing the inner ring A is smaller than
+that of hydrogen, and the molecular weight of the gas forming the outer
+ring D is greater than that of helium. He also suggests that the gas of
+ring A may possibly be identical with the &#8220;coronium&#8221; of the solar<span class="pagenum"><a name="Page_212" id="Page_212">[Pg 212]</a></span> corona,
+for which Mendelief found a hypothetical atomic and molecular weight of
+0&middot;4.<a name='fna_372' id='fna_372' href='#f_372'><small>[372]</small></a></p>
+
+<p>With reference to the nebular hypothesis of Laplace, Dr. A. R. Wallace
+argues that &#8220;if there exists a sun in a state of expansion in which our
+sun was when it extended to the orbit of Neptune, it would, even with a
+parallax of <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">60</span>th of a second, show a disc of half a second, which could
+be seen with the Lick telescope.&#8221; My reply to this objection is, that with
+such an expansion there would probably be very little &#8220;intrinsic
+brightness,&#8221; and if luminous enough to be visible the spectrum would be
+that of a gaseous nebula, and no known <i>star</i> gives such a spectrum. But
+some planetary nebul&aelig; look like small stars, and with high powers on large
+telescopes would probably show a disc. On these considerations, Dr.
+Wallace&#8217;s objection does not seem to be valid.</p>
+
+<p>It is usually stated in popular works on astronomy that the spectra of
+gaseous nebul&aelig; show only three or four bright lines on a faint continuous
+background. But this is quite incorrect. No less than forty bright lines
+have been seen and measured in the spectra of gaseous nebul&aelig;.<a name='fna_373' id='fna_373' href='#f_373'><small>[373]</small></a> This
+includes 2 lines of &#8220;nebulium,&#8221; 11 of hydrogen, 5 of helium, 1 of oxygen
+(?), 3 of nitrogen (?), 1 of silicon (?), and 17 of an unknown substance.
+In the great nebul&aelig; in Orion 30 bright lines have been photographed.<a name='fna_374' id='fna_374' href='#f_374'><small>[374]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_213" id="Page_213">[Pg 213]</a></span>D&#8217;Arrest found that &#8220;gaseous
+nebul&aelig; are rarely met with outside the Milky Way, and never at a considerable distance from it.&#8221;<a name='fna_375' id='fna_375' href='#f_375'><small>[375]</small></a></p>
+
+<p>Mr. A. E. Fath thinks that &#8220;no spiral nebula investigated has a truly
+continuous spectrum.&#8221; He finds that so feeble is the intensity of the
+light of the spiral nebul&aelig; that, while a spectrogram of Arcturus can be
+secured with the Mills spectrograph &#8220;in less than two minutes,&#8221; &#8220;an
+exposure of about 500 hours would be required for the great nebula in
+Andromeda, which is of the same spectral type.&#8221;<a name='fna_376' id='fna_376' href='#f_376'><small>[376]</small></a> Mr. Fath thinks that
+in the case of the Andromeda nebula, the &#8220;star cluster&#8221; theory &#8220;seems to
+be the only one that can at all adequately explain the spectrum
+obtained.&#8221;<a name='fna_377' id='fna_377' href='#f_377'><small>[377]</small></a></p>
+
+<p>Prof. Barnard finds that the great cluster in Hercules (Messier 13) is
+&#8220;composed of stars of different spectral types.&#8221; This result was confirmed
+by Mr. Fath.<a name='fna_378' id='fna_378' href='#f_378'><small>[378]</small></a></p>
+
+<p>From observations with the great 40-inch telescope of the Yerkes
+Observatory (U.S.A.), Prof. Barnard finds that the nucleus of the planetary
+nebula H. iv. 18 in Andromeda is variable to the extent of at least 3
+magnitudes. At its brightest it is about the 12th magnitude; and the
+period seems to be about 28 days. Barnard says, &#8220;I think this is the first
+case in<span class="pagenum"><a name="Page_214" id="Page_214">[Pg 214]</a></span> which the nucleus of a planetary or other nebula has been shown
+to be certainly variable.&#8221; &#8220;The normal condition seems to be faint&mdash;the
+nucleus remaining bright for a few days only. In an ordinary telescope it
+looks like a small round disc of a bluish green colour.&#8221; He estimated the
+brightness of the nebula as that of a star of 8&middot;2 magnitude.<a name='fna_379' id='fna_379' href='#f_379'><small>[379]</small></a> Even in
+a telescope of 4 inches aperture, this would be a fairly bright object. It
+lies about 3&#189; degrees south-west of the star &#953; Andromed&aelig;.</p>
+
+<p>The so-called &#8220;globular clusters&#8221; usually include stars of different
+brightness; comparatively bright telescopic stars of the 10th to 13th
+magnitude with faint stars of the 15th to 17th magnitude. Prof. Perrine of
+the Lick Observatory finds that (<i>a</i>) &#8220;the division of the stars in
+globular clusters into groups, differing widely in brightness, is
+characteristic of these objects&#8221;; (<i>b</i>) &#8220;the globular clusters are devoid
+of true nebulosity&#8221;; and (<i>c</i>) &#8220;stars fainter than 15th magnitude
+predominate in the Milky Way and globular clusters, but elsewhere are
+relatively scarce.&#8221; He found that &#8220;exposures of one hour or thereabouts
+showed as many stars as exposures four to six times as long; the only
+effect of the longer exposures being in the matter of density.&#8221; This last
+result confirms the late Dr. Roberts&#8217; conclusions. Perrine finds that for
+clusters in the Milky Way, the faint stars (15th to 17th magnitude) &#8220;are
+about as<span class="pagenum"><a name="Page_215" id="Page_215">[Pg 215]</a></span> numerous in proportion to the bright stars (10th to 13th
+magnitude) as in the globular clusters themselves.&#8221; This is, however, not
+the case with globular clusters at a distance from the Milky Way. In these
+latter clusters he found that &#8220;in the regions outside the limits of the
+cluster there are usually very few faint stars, hardly more than
+one-fourth or one-tenth as many as there are bright stars&#8221;; and he thinks
+that &#8220;this paucity of faint stars&#8221; in the vicinity of these clusters
+&#8220;gives rise to the suspicion that all regions at a distance from the
+Galaxy may be almost devoid of these very faint stars.&#8221; The late Prof.
+Keeler&#8217;s series of nebular photographs &#8220;in or near the Milky Way&#8221; tend to
+confirm the above conclusions. Perrine finds the northernmost region of
+the Milky Way &#8220;to be almost, if not entirely, devoid of globular
+clusters.&#8221;<a name='fna_380' id='fna_380' href='#f_380'><small>[380]</small></a></p>
+
+<p>According to Sir John Herschel, &#8220;the sublimity of the spectacle afforded&#8221;
+by Lord Rosse&#8217;s great telescope of 6 feet in diameter of some of the
+&#8220;larger globular and other clusters&#8221; &#8220;is declared by all who have
+witnessed it, to be such that no words can express.&#8221;<a name='fna_381' id='fna_381' href='#f_381'><small>[381]</small></a></p>
+
+<p>In his address to the British Association at Leicester in 1907, Sir David
+Gill said&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Evidence upon evidence has accumulated to show that nebul&aelig; consist of
+the matter out of<span class="pagenum"><a name="Page_216" id="Page_216">[Pg 216]</a></span> which stars have been and are being evolved.... The
+fact of such an evolution with the evidence before us, can hardly be
+doubted. I most fully believe that, when the modifications of
+terrestrial spectra under sufficiently varied conditions of
+temperature, pressure, and environment, have been further studied,
+this connection will be greatly strengthened.&#8221;</p></div>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_217" id="Page_217">[Pg 217]</a></span></p>
+<h2><a name="CHAPTER_XVIII" id="CHAPTER_XVIII"></a>CHAPTER XVIII</h2>
+<p class="title">Historical</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">The</span> grouping of the stars into constellations is of great antiquity. The
+exact date of their formation is not exactly known, but an approximate
+result may be arrived at from the following considerations. On the
+celestial spheres, or &#8220;globes,&#8221; used by the ancient astronomers, a portion
+of the southern heavens of a roughly circular form surrounding the South
+Pole was left blank. This space presumably contained the stars in the
+southern hemisphere which they could not see from their northern stations.
+Now, the centre of this circular blank space most probably coincided with
+the South Pole of the heavens at the time when the constellations were
+first formed. Owing to the &#8220;Precession of the Equinoxes&#8221; this centre has
+now moved away from the South Pole to a considerable distance. It can be
+easily computed at what period this centre coincided with the South Pole,
+and calculations show that this was the case about 2700 <span class="smcaplc">B.C.</span> The position
+of this circle also indicates that the<span class="pagenum"><a name="Page_218" id="Page_218">[Pg 218]</a></span> constellations were formed at a
+place between 36&deg; and 40&deg; north latitude, and therefore probably somewhere
+in Asia Minor north of Mesopotamia. Again, the most ancient observations
+refer to Taurus as the equinoxial constellation. Virgil says&mdash;</p>
+
+<p class="poem">&#8220;Candidus auratis aperit cum cornibus annum Taurus.&#8221;<a name='fna_382' id='fna_382' href='#f_382'><small>[382]</small></a></p>
+
+<p>This would indicate a date about 3000 <span class="smcaplc">B.C.</span> There is no tradition, however,
+that the constellation Gemini was ever <i>seen</i> to occupy this position, so
+that 3000 <span class="smcaplc">B.C.</span> seems to be the earliest date admissible.<a name='fna_383' id='fna_383' href='#f_383'><small>[383]</small></a></p>
+
+<p>Prof. Sayce thinks that the &#8220;signs of the Zodiac&#8221; had their origin in the
+plains of Mesopotamia in the twentieth or twenty-third century <span class="smcaplc">B.C.</span>, and
+Brown gives the probable date as 2084 <span class="smcaplc">B.C.</span><a name='fna_384' id='fna_384' href='#f_384'><small>[384]</small></a></p>
+
+<p>According to Seneca, the study of astronomy among the Greeks dates back to
+about 1400 <span class="smcaplc">B.C.</span>; and the ancient constellations were already classical in
+the time of Eudoxus in the fourth century <span class="smcaplc">B.C.</span> Eudoxus (408-355 <span class="smcaplc">B.C.</span>)
+observed the positions of forty-seven stars visible in Greece, thus
+forming the most ancient star catalogue which has been preserved. He was a
+son of<span class="pagenum"><a name="Page_219" id="Page_219">[Pg 219]</a></span> Eschinus, and a pupil of Archytas and probably Plato.</p>
+
+<p>The work of Eudoxus was put into verse by the poet Aratus (third century
+<span class="smcaplc">B.C.</span>). This poem describes all the old constellations now known, except
+Libra, the Balance, which was at that time included in the Claws of the
+Scorpion. About <span class="smcaplc">B.C.</span> 50, the Romans changed the Claws, or Chel&aelig;, into
+Libra. Curious to say, Aratus states that the constellation Lyra contained
+no bright star!<a name='fna_385' id='fna_385' href='#f_385'><small>[385]</small></a> Whereas its principal star, Vega, is now one of the
+brightest stars in the heavens!</p>
+
+<p>With reference to the origin of the constellations, Aratus says&mdash;</p>
+
+<p class="poem"><span style="margin-left: 7.5em;">&#8220;Some men of yore</span><br />
+A nomenclature thought of and devised<br />
+And forms sufficient found.&#8221;</p>
+
+<p>This shows that even in the time of Aratus the constellations were of
+great antiquity.</p>
+
+<p>Brown says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Writers have often told us, speaking only from the depths of their
+ignorance, how &#8216;Chaldean&#8217; shepherds were wont to gaze at the brilliant
+nocturnal sky, and to <i>imagine</i> that such and such stars resemble this
+or that figure. But all this is merely the old effort to make capital
+out of nescience, and the stars are before our eyes to prove the
+contrary. Having already certain fixed ideas and figures in his mind,
+the constellation-former, when he came to his task, applied his<span class="pagenum"><a name="Page_220" id="Page_220">[Pg 220]</a></span>
+figures to the stars and the stars to his figures as harmoniously as
+possible.&#8221;<a name='fna_386' id='fna_386' href='#f_386'><small>[386]</small></a> &#8220;Thus <i>e.g.</i> he arranged the stars of <i>Andromeda</i> into
+the representation of a chained lady, not because they naturally
+reminded him (or anybody else) of such a figure, but because he
+desired to express that idea.&#8221;</p></div>
+
+<p>A coin of Manius Aquillus, <span class="smcaplc">B.C.</span> 94, shows four stars in Aquila, and seems
+to be the oldest representation extant of a star group. On a coin of <span class="smcaplc">B.C.</span>
+43, Dr. Vencontre found five stars, one of which was much larger than the
+others, and concludes that it represents the Hyades (in Taurus). He
+attributes the coin to P. Clodius Turrinus, who probably used the
+constellation Taurus or Taurinus as a phonetic reference to his surname. A
+coin struck by L. Lucretius Trio in 74 <span class="smcaplc">B.C.</span>, shows the seven stars of the
+Plough, or as the ancients called them Septem Triones. Here we have an
+allusion to the name of the magistrate Trio.<a name='fna_387' id='fna_387' href='#f_387'><small>[387]</small></a></p>
+
+<p>In a work published in Berne in 1760, Schmidt contends that the ancient
+Egyptians gave to the constellations of the Zodiac the names of their
+divinities, and expressed them by the signs which were used in their
+hieroglyphics.<a name='fna_388' id='fna_388' href='#f_388'><small>[388]</small></a></p>
+
+<p>Hesiod mentions Orion, the Pleiades, Sirius, Aldebaran, and Arcturus; and
+Homer refers to Orion, Arcturus, the Pleiades, the Hyades, the<span class="pagenum"><a name="Page_221" id="Page_221">[Pg 221]</a></span> Great Bear
+(under the name of Amaxa, the Chariot), and the tail of the Little Bear,
+or &#8220;Cynosura.&#8221;</p>
+
+<p>Hipparchus called the constellations Asterisms (&#7936;&#963;&#964;&#949;&#961;&#8055;&#963;&#956;&#959;&#962;),
+Aristotle and Hyginus &#931;&#959;&#956;&#8049;&#964;&#945; (bodies), and Ptolemy
+&#931;&#967;&#951;&#956;&#8049;&#964;&#945; (figures). By some they were called &#924;&#959;&#961;&#966;&#8061;&#963;&#949;&#953;&#962;
+(configurations), and by others &#924;&#949;&#964;&#949;&#8061;&#961;&#949;. Proclus called those
+near the ecliptic &#918;&#969;&#948;&#8055;&#945; (animals). Hence our modern name Zodiac.</p>
+
+<p>Hipparchus, Ptolemy, and Al-Sufi referred the positions of the stars to
+the ecliptic. They are now referred to the equator. Aboul Hassan in the
+thirteenth century (1282) was the first to use Right Ascensions and
+Declinations instead of Longitudes and Latitudes. The ancient writers
+described the stars by their positions in the ancient figures. Thus they
+spoke of &#8220;the star in the head of Hercules,&#8221; &#8220;the bright star in the left
+foot of Orion&#8221; (Rigel); but Bayer in 1603 introduced the Greek letters to
+designate the brighter stars, and these are now universally used by
+astronomers. These letters being sometimes insufficient, Hevelius added
+numbers, but the numbers in <i>Flamsteed&#8217;s Catalogue</i> are now generally
+used.</p>
+
+<p>Ptolemy and all the ancient writers described the constellation figures as
+they are seen on globes, that is from the outside. Bayer in his Atlas,
+published in 1603, reversed the figures to show them as they would be seen
+from the <i>interior</i><span class="pagenum"><a name="Page_222" id="Page_222">[Pg 222]</a></span> of a hollow globe and as, of course, they are seen in
+the sky. Hevelius again reversed Bayer&#8217;s figures to make them correspond
+with those of Ptolemy. According to Bayer&#8217;s arrangement, Betelgeuse
+(&#945; Orionis) would be on the left shoulder of Orion, instead of
+the right shoulder according to Ptolemy and Al-Sufi, and Rigel (&#946;
+Orionis) on the right foot (Bayer) instead of the left foot (Ptolemy).
+This change of position has led to some confusion; but at present the
+positions of the stars are indicated by their Right Ascensions and
+Declinations, without any reference to their positions in the ancient
+figures.</p>
+
+<p>The classical constellations of Hipparchus and Ptolemy number forty-eight,
+and this is the number described by Al-Sufi in his &#8220;Description of the
+Fixed Stars&#8221; written in the tenth century <span class="smcaplc">A.D.</span></p>
+
+<p>Firminicus gives the names of several constellations not mentioned by
+Ptolemy. M. Fr&eacute;ret thought that these were derived from the Egyptian
+sphere of Petosiris. Of these a Fox was placed north of the Scorpion; a
+constellation called Cynocephalus near the southern constellation of the
+Altar (Ara); and to the north of Pisces was placed a Stag. But all these
+have long since been discarded. Curious to say neither the Dragon nor
+Cepheus appears on the old Egyptian sphere.<a name='fna_389' id='fna_389' href='#f_389'><small>[389]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_223" id="Page_223">[Pg 223]</a></span>Other small constellations have also been formed by various astronomers
+from time to time, but these have disappeared from our modern star maps.
+The total number of constellations now recognized in both hemispheres
+amounts to eighty-four.</p>
+
+<p>The first catalogue formed was nominally that of Eudoxus in the fourth
+century <span class="smcaplc">B.C.</span> (about 370 <span class="smcaplc">B.C.</span>). But this can hardly be dignified by the
+name of catalogue, as it contained only forty-seven stars, and it omits
+several of the brighter stars, notably Sirius! The first complete (or
+nearly complete) catalogue of stars visible to the naked eye was that of
+Hipparchus about 129 <span class="smcaplc">B.C.</span> Ptolemy informs us that it was the sudden
+appearance of a bright new or &#8220;temporary star&#8221; in the year 134 <span class="smcaplc">B.C.</span> in the
+constellation Scorpio which led Hipparchus to form his catalogue, and
+there seems to be no reason to doubt the accuracy of this statement, as
+the appearance of this star is recorded in the Chinese Annals. The
+Catalogue of Hipparchus contains only 1080 stars; but as many more are
+visible to the naked eye, Hipparchus must have omitted those which are not
+immediately connected with the old constellation figures of men and
+animals.</p>
+
+<p>Hipparchus&#8217; Catalogue was revised by Ptolemy in his famous work the
+<i>Almagest</i>. Ptolemy reduced the positions of the stars given by Hipparchus
+to the year 137 <span class="smcaplc">A.D.</span>; but used a<span class="pagenum"><a name="Page_224" id="Page_224">[Pg 224]</a></span>
+wrong value of the precession which only corresponded to about 50 <span class="smcaplc">A.D.</span>; and he probably adopted the star magnitudes
+of Hipparchus without any revision. Indeed, it seems somewhat doubtful
+whether Ptolemy made any observations of the brightness of the stars
+himself. Ptolemy&#8217;s catalogue contains 1022 stars.</p>
+
+<p>Prof. De Morgan speaks of Ptolemy as &#8220;a splendid mathematician and an
+indifferent observer&#8221;; and from my own examination of Al-Sufi&#8217;s work on
+the Fixed Stars, which was based on Ptolemy&#8217;s work, I think that De
+Morgan&#8217;s criticism is quite justified.</p>
+
+<p>Al-Sufi&#8217;s <i>Description of the Fixed Stars</i> was written in the tenth
+century and contains 1018 stars. He seems to have adopted the <i>positions</i>
+of the stars given by Ptolemy, merely correcting them for the effects of
+precession; but he made a very careful revision of the star magnitudes of
+Ptolemy (or Hipparchus) from his own observations, and this renders his
+work the most valuable, from this point of view, of all the ancient
+catalogues.</p>
+
+<p>Very little is known about Al-Sufi&#8217;s life, and the few details we have are
+chiefly derived from the works of the historians Abu&#8217;-l-faradji and
+Casiri, and the Oriental writers Hyde, Caussin, Sedillot, etc. Al-Sufi&#8217;s
+complete name was Abd-al-Rahm&auml;n Bin Umar Bin Muhammad Bin Sahl
+Abu&#8217;l-husa&iuml;n al-Sufi al-Razi. The name Sufi indicates that he<span class="pagenum"><a name="Page_225" id="Page_225">[Pg 225]</a></span> belonged to
+the sect of Sufis (Dervishes), and the name Razi that he lived in the town
+of Ra&iuml; in Persia, to the east of Teheran. He was born on December 7, 903
+<span class="smcaplc">A.D.</span>, and died on May 25, 986, so that, like many other astronomers, he
+lived to a good old age. According to ancient authorities, Al-Sufi&mdash;as he
+is usually called&mdash;was a very learned man, who lived at the courts of
+Schiraz and Baghdad under Adhad-al-Davlat&mdash;of the dynasty of the
+Bu&iuml;des&mdash;who was then the ruler of Persia. Al-Sufi was held in high esteem
+and great favour by this prince, who said of him, &#8220;Abd-al-Rahm&auml;n al-Sufi
+taught me to know the names and positions of the fixed stars, Scharif Ibn
+al-Aalam the use of astronomical tables, and Abu Ali al-Farisi instructed
+me in the principles of grammar.&#8221; Prince Adhad-al-Davlat died on March 26,
+983. According to Caussin, Al-Sufi also wrote a book on astrology, and a
+work entitled <i>Al-Ardjouze</i>, which seems to have been written in verse,
+but its subject is unknown. He also seems to have determined the exact
+length of the year, and to have undertaken geodetic measurements. The
+al-Aalam mentioned above was also an able astronomer, and in addition to
+numerous observations made at Baghdad, he determined with great care the
+precession of the equinoxes. He found the annual constant of precession to
+be 51&Prime;&middot;4, a value which differs but little from modern results.</p>
+
+<p><span class="pagenum"><a name="Page_226" id="Page_226">[Pg 226]</a></span>In the year 1874, the late M. Schjellerup, the eminent Danish astronomer,
+published a French translation of two Arabic manuscripts written by
+Al-Sufi and entitled &#8220;A Description of the Fixed Stars.&#8221; One of these
+manuscripts is preserved in the Royal Library at Copenhagen, and the other
+in the Imperial Library at St. Petersburgh.<a name='fna_390' id='fna_390' href='#f_390'><small>[390]</small></a></p>
+
+<p>Al-Sufi seems to have been a most careful and accurate observer, and
+although, as a rule, his estimates of the relative brightness of stars are
+in fairly good agreement with modern estimates and photometric measures,
+there are many remarkable and interesting differences. Al-Sufi&#8217;s
+observations have an important bearing on the supposed &#8220;secular variation&#8221;
+of the stars; that is, the slow variation in light which may have occurred
+in the course of ages in certain stars, apart from the periodical
+variation which is known to occur in the so-called variable stars. More
+than 900 years have now elapsed since the date of Al-Sufi&#8217;s observations
+(about <span class="smcaplc">A.D.</span> 964) and over 2000 years in the case of Hipparchus, and
+although these periods are of course very short in the life-history of any
+star, still <i>some</i> changes may possibly have taken place in the brightness
+of some of them.<span class="pagenum"><a name="Page_227" id="Page_227">[Pg 227]</a></span> There are several cases in which a star seems to have
+diminished in light since Al-Sufi&#8217;s time. This change seems to have
+certainly occurred in the case of &#952; Eridani, &#946; Leonis,
+&#950; Piscis Australis, and some others. On the other hand, some
+stars seem to have certainly increased in brightness, and the bearing of
+these changes on the question of &#8220;stellar evolution&#8221; will be obvious.</p>
+
+<p>In most cases Al-Sufi merely mentions the magnitude which he estimated a
+star to be; such as &#8220;third magnitude,&#8221; &#8220;fourth,&#8221; &#8220;small third magnitude,&#8221;
+&#8220;large fourth,&#8221; etc. In some cases, however, he directly states that a
+certain star is a little brighter than another star near it. Such
+cases&mdash;unfortunately not numerous&mdash;are very valuable for comparison with
+modern estimates and measures, when variation is suspected in the light of
+a star. The estimates of Argelander, Heis, and Houzeau are based on the
+same scale as that used by Ptolemy and Al-Sufi. Al-Sufi&#8217;s estimates are
+given in thirds of a magnitude. Thus, &#8220;small third magnitude&#8221; means 3&#8531;,
+or 3&middot;33 magnitude in modern measures; &#8220;large fourth,&#8221; 3&#8532; or 3&middot;66
+magnitude. These correspond with the estimates of magnitude given by
+Argelander, Heis, and Houzeau in their catalogues of stars visible to the
+naked eye, and so the estimates can be directly compared.</p>
+
+<p>I have made an independent identification of all the stars mentioned by
+Al-Sufi. In the<span class="pagenum"><a name="Page_228" id="Page_228">[Pg 228]</a></span> majority of cases my identifications concur with those of
+Schjellerup; but in some cases I cannot agree with him. In a few cases I
+have found that Al-Sufi himself, although accurately describing the
+position of the stars observed by <i>him</i>, has apparently misidentified the
+star observed by Hipparchus and Ptolemy. This becomes evident when we plot
+Ptolemy&#8217;s positions (as given by Al-Sufi) and compare them with Al-Sufi&#8217;s
+descriptions of the stars observed by him. This I have done in all cases
+where there seemed to be any doubt; and in this way I have arrived at some
+interesting results which have escaped the notice of Schjellerup. This
+examination shows clearly, I think, that Al-Sufi did not himself measure
+the <i>positions</i> of the stars he observed, but merely adopted those of
+Ptolemy, corrected for the effect of precession. The great value of his
+work, however, consists in his estimates of star magnitudes, which seem to
+have been most carefully made, and from this point of view, his work is
+invaluable. Prof. Pierce says, &#8220;The work which the learning of M.
+Schjellerup has brought to light is so important that the smallest errors
+of detail become interesting.&#8221;<a name='fna_391' id='fna_391' href='#f_391'><small>[391]</small></a></p>
+
+<p>Although Al-Sufi&#8217;s work is mentioned by the writers referred to above, no
+complete translation of his manuscript was made until the task was
+undertaken by Schjellerup, and even now Al-Sufi&#8217;s<span class="pagenum"><a name="Page_229" id="Page_229">[Pg 229]</a></span> name is not mentioned
+in some popular works on astronomy! But he was certainly the best of all
+the old observers, and his work is deserving of the most careful
+consideration.</p>
+
+<p>Al-Sufi&#8217;s descriptions of the stars were, it is true, based on Ptolemy&#8217;s
+catalogue, but his work is not a mere translation of that of his
+predecessor. It is, on the contrary, a careful and independent survey of
+the heavens, made from his own personal observations, each of Ptolemy&#8217;s
+stars having been carefully examined as to its position and magnitude, and
+Ptolemy&#8217;s mistakes corrected. In examining his descriptions, Schjellerup
+says, &#8220;We soon see the vast extent of his labours, his perseverance, and
+the minute accuracy and almost modern criticism with which he executed his
+work.&#8221; In fact, Al-Sufi has given us a careful description of the starry
+sky as it appeared in his time, and one which deserves the greatest
+confidence. It far surpasses the work of Ptolemy, which had been without a
+rival for eight centuries previously, and it has only been equalled in
+modern times by the surveys of Argelander, Gould, Heis, and Houzeau. Plato
+remarked with reference to the catalogue of Hipparchus, <i>C&oelig;lam posteris
+in hereditatem relictum</i>, and the same may be said of Al-Sufi&#8217;s work. In
+addition to his own estimates of star magnitudes, Al-Sufi adds the
+magnitudes given by Ptolemy whenever Ptolemy&#8217;s estimate differs<span class="pagenum"><a name="Page_230" id="Page_230">[Pg 230]</a></span> from his
+own; and this makes his work still more valuable, as Ptolemy&#8217;s magnitudes
+given in all the editions of the <i>Almagest</i> now extant are quite
+untrustworthy.</p>
+
+<p>In the preface to his translation of Al-Sufi&#8217;s work, Schjellerup mentions
+some remarkable discrepancies between the magnitudes assigned to certain
+stars by Ptolemy and Argelander. This comparison is worthy of confidence
+as it is known that both Al-Sufi and Argelander adopted Ptolemy&#8217;s (or
+Hipparchus&#8217;) scale of magnitudes. For example, all these observers agree
+that &#946; Urs&aelig; Minoris (Ptolemy&#8217;s No. 6 of that constellation) is of
+the 2nd magnitude, while in the case of &#947; Urs&aelig; Minoris (Ptolemy&#8217;s
+No. 7), Ptolemy called it 2nd, and Argelander rated it 3rd; Argelander
+thus making &#947; one magnitude fainter than Ptolemy&#8217;s estimate. Now,
+Al-Sufi, observing over 900 years ago, rated &#947; of the 3rd
+magnitude, thus correcting Ptolemy and agreeing with Argelander. Modern
+photometric measures confirm the estimates of Al-Sufi and Argelander. But
+it is, of course, possible that one or both stars may be variable in
+light, and &#946; has actually been suspected of variation. Almost all
+the constellations afford examples of this sort. In the majority of cases,
+however, Al-Sufi agrees well with Argelander and Heis, but there are in
+some cases differences which suggest a change in relative brightness.</p>
+
+<p><span class="pagenum"><a name="Page_231" id="Page_231">[Pg 231]</a></span>Among other remarkable things contained in Al-Sufi&#8217;s most interesting work
+may be mentioned the great nebula in Andromeda, which was first noticed in
+Europe as visible to the naked eye by Simon Marius in 1612. Al-Sufi,
+however, speaks of it as a familiar object in his time.</p>
+
+<p>Schjellerup says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;For a long time many of the stars in Ptolemy&#8217;s catalogue could not be
+identified in the sky. Most of these discordances were certainly due
+to mistakes in copying, either in longitude or latitude. Many of these
+differences were, however, corrected by the help of new manuscripts.
+For this purpose Al-Sufi&#8217;s work is of great importance. By a direct
+examination of the sky he succeeded in finding nearly all the stars
+reported by Ptolemy (or Hipparchus). And even if his criticism may
+sometimes seem inconclusive, his descriptions are not subject to
+similar defects, his positions not depending solely on the places
+given in Ptolemy&#8217;s catalogue. For, in addition to the longitudes and
+latitudes quoted from Ptolemy, he has described by alignment the
+positions of the stars referred to. In going from the brightest and
+best known stars of each constellation he indicates the others either
+by describing some peculiarity in their position, or by giving their
+mutual distance as so many cubits (<i>dzir&acirc;</i>), or a span (<i>schibr</i>),
+units of length which were used at that time to measure apparent
+celestial distances. The term <i>dzir&acirc;</i> means literally the fore-arm
+from the bone of the elbow to the tip of the middle finger, or an ell.
+We should not, however, conclude from this that the Arabians were so
+unscientific as to measure celestial distances by an ell, as this
+would be quite in contradiction to<span class="pagenum"><a name="Page_232" id="Page_232">[Pg 232]</a></span> their well-known knowledge of
+Geometry and Trigonometry.&#8221;</p></div>
+
+<p>With reference to the arc or angular distance indicated by the &#8220;cubit,&#8221;
+Al-Sufi states in his description of the constellation Auriga that the
+<i>dzir&acirc;</i> (or cubit) is equal to 2&deg; 20&prime;. Three cubits, therefore, represent
+7&deg;, and 4 cubits 9&deg; 20&prime;.</p>
+
+<p>In Al-Sufi&#8217;s own preface to his work, after first giving glory to God and
+blessings on &#8220;his elected messenger Muhammed and his family,&#8221; he proceeds
+to state that he had often &#8220;met with many persons who wished to know the
+fixed stars, their positions on the celestial vault, and the
+constellations, and had found that these persons may be divided into two
+classes. One followed the method of astronomers and trust to spheres
+designed by artists, who not knowing, the stars themselves, take only the
+longitudes and latitudes which they find in the books, and thus place the
+stars on the sphere, without being able to distinguish truth from error.
+It then follows that those who really know the stars in the sky find on
+examining these spheres that many stars are otherwise than they are in the
+sky. Among these are Al-Battani, At&acirc;rid and others.&#8221;</p>
+
+<p>Al-Sufi seems rather hard on Al-Battani (or Albategnius as he is usually
+called) for he is generally considered to have been the most<span class="pagenum"><a name="Page_233" id="Page_233">[Pg 233]</a></span>
+distinguished of the Arabian astronomers. His real name was Mohammed Ibn
+Jaber Ibn Senan Abu Abdallah Al-Harrani. He was born about <span class="smcaplc">A.D.</span> 850 at
+Battan, near Harran in Mesopotamia, and died about <span class="smcaplc">A.D.</span> 929. He was the
+first to make use of sines instead of chords, and versed sines. The
+<i>Alphonsine Tables</i> of the moon&#8217;s motions were based on his observations.</p>
+
+<p>After some severe criticisms on the work of Al-Battani and At&acirc;rid, Al-Sufi
+goes on to say that the other class of amateurs who desire to know the
+fixed stars follow the method of the Arabians in the science of
+<i>Anva</i><a name='fna_392' id='fna_392' href='#f_392'><small>[392]</small></a> and the mansions of the moon and the books written on this
+subject. Al-Sufi found many books on the <i>anva</i>, the best being those of
+Abu Hanifa al-D&icirc;navari. This work shows that the author knew the Arabic
+tradition better than any of the other writers on the subject. Al-Sufi,
+however, doubts that he had a good knowledge of the stars themselves, for
+if he had he would not have followed the errors of his predecessors.</p>
+
+<p>According to Al-Sufi, those who know one of these methods do not know the
+other. Among these is Abu-Hanifa, who states in his book that the names of
+the twelve signs (of the Zodiac) did not originate from the arrangement
+or<span class="pagenum"><a name="Page_234" id="Page_234">[Pg 234]</a></span> configuration of the stars resembling the figure from which the name
+is derived. The stars, Abu-Hanifa said, &#8220;change their places, and although
+the names of the signs do not change, yet the arrangement of the stars
+ceases to be the same. This shows that he was not aware of the fact that
+the arrangement of the stars does not change, and their mutual distances
+and their latitudes, north and south of the ecliptic, are neither
+increased nor diminished.&#8221; &#8220;The stars,&#8221; Al-Sufi says, &#8220;do not change with
+regard to their configurations, because they are carried along together by
+a physical motion and by a motion round the poles of the ecliptic. This is
+why they are called fixed. Abu-Hanifa supposed that they are termed fixed
+because their motion is very slow in comparison with that of the planets.&#8221;
+&#8220;These facts,&#8221; he says, &#8220;can only be known to those who follow the method
+of the astronomers and are skilled in mathematics.&#8221;</p>
+
+<p>Al-Sufi says that the stars of the Zodiac have a certain movement
+following the order of the signs, which according to Ptolemy and his
+predecessors is a degree in 100 years. But according to the authors of
+<i>al-mumtahan</i> and those who have observed subsequently to Ptolemy, it is a
+degree in 66 years. According to modern measures, the precession is about
+50&Prime;&middot;35 per annum, or one degree in 71&#189; years.</p>
+
+<p>Al-Sufi says that the Arabians did not make<span class="pagenum"><a name="Page_235" id="Page_235">[Pg 235]</a></span> use of the figures of the
+Zodiac in their proper signification, because they divided the
+circumference of the sky by the number of days which the moon took to
+describe it&mdash;about 28 days&mdash;and they looked for conspicuous stars at
+intervals which, to the eye, the moon appeared to describe in a day and a
+night. They began with <i>al-scharata&iuml;n</i>, &#8220;the two marks&#8221; (&#945; and
+&#946; Arietis) which were the first striking points following the
+point of the spring equinox. They then sought behind these two marks
+another point at a distance from them, equal to the space described by the
+moon in a day and a night. In this way they found <i>al-buta&iuml;n</i> (&#949;,
+&#948;, and &#961; Arietis); after that <i>al-tsuraija</i>, the
+Pleiades; then <i>al-dabaran</i>, the Hyades, and thus all the &#8220;mansions&#8221; of
+the moon. They paid no attention to the signs of the Zodiac, nor to the
+extent of the figures which composed them. This is why they reckoned among
+the &#8220;mansions&#8221; <i>al-haka</i> (&#955; Orionis) which forms no part of the
+signs of the Zodiac, since it belongs to the southern constellation of the
+Giant (Orion). And similarly for other stars near the Zodiac, of which
+Al-Sufi gives some details. He says that Regulus (&#945; Leonis) was
+called by the Arabians <i>al-maliki</i>, the Royal Star, and that <i>al-anva</i>
+consists of five stars situated in the two wings of the Virgin. These
+stars seem to be &#946;, &#951;, &#947;, &#948;, and
+&#949; Virginis, which form with Spica (&#945; Virginis) a
+Y-shaped<span class="pagenum"><a name="Page_236" id="Page_236">[Pg 236]</a></span> figure. Spica was called <i>simak al-azal</i>, the unarmed <i>simak</i>;
+the &#8220;armed <i>simak</i>&#8221; being Arcturus, <i>simak al-ramih</i>. These old Arabic
+names seem very fanciful.</p>
+
+<p>Al-Sufi relates that in the year 337 of the Hegira (about <span class="smcaplc">A.D.</span> 948) he
+went to Ispahan with Prince Abul-fadhl, who introduced him to an
+inhabitant of that city, named Varvadjah, well known in that country, and
+famous for his astronomical acquirements. Al-Sufi asked him the names of
+the stars on an astrolabe which he had, and he named Aldebaran, the two
+bright stars in the Twins (Castor and Pollux), Regulus, Sirius, and
+Procyon, the two Simaks, etc. Al-Sufi also asked him in what part of the
+sky <i>Al-fard</i> (&#945; Hydr&aelig;) was, but he did not know! Afterwards, in
+the year 349, this same man was at the court of Prince Adhad-al-Davlat,
+and in the presence of the Prince, Al-Sufi asked him the name of a bright
+star&mdash;it was <i>al-nasr al-vaki</i>, the falling Vulture (Vega), and he
+replied, &#8220;That is <i>al-aijuk</i>&#8221; (Capella)! thus showing that he only knew
+the <i>names</i> of the stars, but did not know them when he saw them in the
+sky. Al-Sufi adds that all the women &#8220;who spin in their houses&#8221; knew this
+star (Vega) by the name of <i>al-atsafi</i>, the Tripod. But this could not be
+said even of &#8220;educated women&#8221; at the present day.</p>
+
+<p>With reference to the number of stars which<span class="pagenum"><a name="Page_237" id="Page_237">[Pg 237]</a></span> can be seen with the naked
+eye, Al-Sufi says, &#8220;Many people believe that the total number of fixed
+stars is 1025, but this is an evident error. The ancients only observed
+this number of stars, which they divided into six classes according to
+magnitude. They placed the brightest in the 1st magnitude; those which are
+a little smaller in the 2nd; those which are a little smaller again in the
+3rd; and so on to the 6th. As to those which are below the 6th magnitude,
+they found that their number was too great to count; and this is why they
+have omitted them. It is easy to convince one&#8217;s self of this. If we
+attentively fix our gaze on a constellation of which the stars are well
+known and registered, we find in the spaces between them many other stars
+which have not been counted. Take, for example, the Hen [Cygnus]; it is
+composed of seventeen internal stars, the first on the beak, the brightest
+on the tail, the others on the wings, the neck and the breast; and below
+the left wing are two stars which do not come into the figure. Between
+these different stars, if you examine with attention, you will perceive a
+multitude of stars, so small and so crowded that we cannot determine their
+number. It is the same with all the other constellations.&#8221; These remarks
+are so correct that they might have been written by a modern astronomer.
+It should be added, however, that <i>all</i> the faint stars referred to by
+Al-Sufi&mdash;and thousands of<span class="pagenum"><a name="Page_238" id="Page_238">[Pg 238]</a></span> others still fainter&mdash;have now been mapped down
+and their positions accurately determined.</p>
+
+<p>About the year 1437, Ulugh Beigh, son of Shah Rokh, and grandson of the
+Mogul Emperor Tamerlane, published a catalogue of stars in which he
+corrected Ptolemy&#8217;s positions. But he seems to have accepted Al-Sufi&#8217;s
+star magnitudes without any attempt at revision. This is unfortunate, for
+an <i>independent</i> estimate of star magnitudes made in the fifteenth century
+would now be very valuable for comparison with Al-Sufi&#8217;s work and with
+modern measures. Ulugh Beigh&#8217;s catalogue contains 1018 stars, nearly the
+same number as given by Ali-Sufi.<a name='fna_393' id='fna_393' href='#f_393'><small>[393]</small></a></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_239" id="Page_239">[Pg 239]</a></span></p>
+<h2><a name="CHAPTER_XIX" id="CHAPTER_XIX"></a>CHAPTER XIX</h2>
+<p class="center"><span class="title">The Constellations</span><a name='fna_394' id='fna_394' href='#f_394'><small>[394]</small></a></p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Curious</span> to say, Al-Sufi rated the Pole Star as 3rd magnitude; for it is
+now only slightly less than the 2nd. At present it is about the same
+brightness as &#946; of the same constellation (Ursa Minor) which
+Al-Sufi rated 2nd magnitude. It was, however, also rated 3rd magnitude by
+Ptolemy (or Hipparchus), and it may possibly have varied in brightness
+since ancient times. Admiral Smyth says that in his time (1830) it was
+&#8220;not even a very bright third size&#8221; (!)<a name='fna_395' id='fna_395' href='#f_395'><small>[395]</small></a> Spectroscopic measures show
+that it is approaching the earth at the rate of 16 miles a second; but
+this would have no perceptible effect on its brightness in historical
+times. This may seem difficult to understand, and to some perhaps<span class="pagenum"><a name="Page_240" id="Page_240">[Pg 240]</a></span>
+incredible; but the simple explanation is that its distance from the earth
+is so great that a journey of even 2000 years with the above velocity
+would make no <i>appreciable</i> difference in its distance! This is
+undoubtedly true, as a simple calculation will show, and the fact will
+give some idea of the vast distance of the stars. The well-known 9th
+magnitude companion to the Pole Star was seen <i>by day</i> in the Dorpat
+telescope by Struve and Wrangel; and &#8220;on one occasion by Encke and
+Argelander.&#8221;<a name='fna_396' id='fna_396' href='#f_396'><small>[396]</small></a></p>
+
+<p>The star &#946; Urs&aelig; Minoris was called by the Arabians <i>Kaukab
+al-sham&aacute;li</i>, the North Star, as it was&mdash;owing to the precession of the
+Equinoxes&mdash;nearer to the Pole in ancient times than our present Pole Star
+was <i>then</i>.</p>
+
+<p>The &#8220;Plough&#8221; (or Great Bear) is supposed to represent a waggon and horses.
+&#8220;Charles&#8217; Wain&#8221; is a corruption of &#8220;churl&#8217;s wain,&#8221; or peasant&#8217;s cart. The
+Arabians thought that the four stars in the quadrilateral represented a
+bier, and the three in the &#8220;tail&#8221; the children of the deceased following
+as mourners! In the Greek mythology, Ursa Major represented the nymph
+Callisto, a daughter of Lycaon, who was loved by Jupiter, and turned into
+a bear by the jealous Juno. Among the old Hindoos the seven stars
+represented the seven Rishis. It is the Otawa of the great Finnish epic,
+the &#8220;Kalevala.&#8221; It was also called<span class="pagenum"><a name="Page_241" id="Page_241">[Pg 241]</a></span>
+&#8220;David&#8217;s Chariot,&#8221; and in America it is known as &#8220;The Dipper.&#8221;</p>
+
+<p>Closely north of the star &#952; in Ursa Major is a small star known
+as Flamsteed 26. This is not mentioned by Al-Sufi, but is now, I find from
+personal observation, very visible, and indeed conspicuous, to the naked
+eye. I find, however, that owing to the large &#8220;proper motion&#8221; of the
+bright star (1&Prime;&middot;1 per annum) the two stars were much closer together in
+Al-Sufi&#8217;s time than they are at present, and this probably accounts for
+Al-Sufi&#8217;s omission. This is an interesting and curious fact, and shows the
+small changes which occur in the heavens during the course of ages.</p>
+
+<p>Close to the star &#950;, the middle star of the &#8220;tail&#8221; of Ursa Major
+(or handle of the &#8220;Plough&#8221;), is a small star known as Alcor, which is
+easily visible to good eyesight without optical aid. It is mentioned by
+Al-Sufi, who says the Arabians called it <i>al-suha</i>, &#8220;the little unnoticed
+one.&#8221; He says that &#8220;Ptolemy does not mention it, and it is a star which
+seems to test the powers of the eyesight.&#8221; He adds, however, an Arabian
+proverb, &#8220;I show him <i>al-suha</i>, and he shows me the moon,&#8221; which seems to
+suggest that to some eyes, at least, it was no test of sight at all. It
+has, however, been suspected of variation in light. It was rated 5th
+magnitude by Argelander, Heis, and Houzeau, but was measured 4&middot;02 at
+Harvard<span class="pagenum"><a name="Page_242" id="Page_242">[Pg 242]</a></span> Observatory. It has recently been found to be a spectroscopic
+binary.</p>
+
+<p>The constellation of the Dragon (Draco) is probably referred to in Job
+(chap. xxvi. v. 13), where it is called &#8220;the crooked serpent.&#8221; In the
+Greek mythology it is supposed to represent the dragon which guarded the
+golden apples in the Garden of the Hesperides. Some have suggested that it
+represented the serpent which tempted Eve. Dryden says, in his translation
+of Virgil&mdash;</p>
+
+<p class="poem">&#8220;Around our Pole the spiry Dragon glides,<br />
+And like a wand&#8217;ring stream the Bears divides.&#8221;</p>
+
+<p>The fact that the constellation Bo&ouml;tis rises quickly and sets slowly,
+owing to its lying horizontally when rising and vertically when setting,
+was noted by Aratus, who says&mdash;</p>
+
+<p class="poem">&#8220;The Bearward now, past seen,<br />
+But more obscured, near the horizon lies;<br />
+For with the four Signs the Ploughman, as he sinks,<br />
+The deep receives; and when tired of day<br />
+At even lingers more than half the night,<br />
+When with the sinking sun he likewise sets<br />
+These nights from his late setting bear their name.&#8221;<a name='fna_397' id='fna_397' href='#f_397'><small>[397]</small></a></p>
+
+<p>The cosmical setting of Bo&ouml;tis&mdash;that is, when he sets at sunset&mdash;is stated
+by Ovid to occur on March 5 of each year.</p>
+
+<p>With reference to the constellation Hercules, Admiral Smyth says&mdash;</p>
+
+<div class="blockquot"><p><span class="pagenum"><a name="Page_243" id="Page_243">[Pg 243]</a></span>&#8220;The kneeling posture has given rise to momentous discussion; and
+whether it represents Lycaon lamenting his daughter&#8217;s transformation,
+or Prometheus sentenced, or Ixion ditto, or Thamyrus mourning his
+broken fiddle, remains still uncertain. But in process of time, this
+figure became a lion, and Hyginus mentions both the lion&#8217;s skin and
+the club; while the right foot&#8217;s being just over the head of the
+Dragon, satisfied the mythologists that he was crushing the Lern&aelig;an
+hydra.... Some have considered the emblem as typifying the serpent
+which infested the vicinity of Cape T&aelig;narus, whence a sub-genus of
+Ophidians still derives its name. At all events a poet, indignant at
+the heathen exaltation of Hevelius, has said&mdash;</p>
+
+<p class="poem">&#8220;&#8216;To Cerberus, too, a place is given&mdash;<br />
+His home of old was far from heaven.&#8217;&#8221;<a name='fna_398' id='fna_398' href='#f_398'><small>[398]</small></a></p></div>
+
+<p>Aratus speaks of Hercules as &#8220;the Phantom whose name none can tell.&#8221;</p>
+
+<p>There were several heroes of the name of Hercules, but the most famous was
+Hercules the Theban, son of Jupiter and Alcmene wife of Amphitryon, King
+of Thebes, who is said to have lived some years before the siege of Troy,
+and went on the voyage of the Argonauts about 1300 <span class="smcaplc">B.C.</span> According to some
+ancient writers, another Hercules lived about 2400 <span class="smcaplc">B.C.</span>, and was a
+contemporary of Atlas and Theseus. But according to P&eacute;tau, Atlas lived
+about 1638 <span class="smcaplc">B.C.</span>, and Lalande thought that this chronology is the more
+probable.</p>
+
+<p>The small constellation Lyra, which contains<span class="pagenum"><a name="Page_244" id="Page_244">[Pg 244]</a></span> the bright star Vega, is
+called by Al-Sufi the Lyre, the Goose, the Persian harp, and the Tortoise.
+In his translation of Al-Sufi&#8217;s work, Schjellerup suggests that the name
+&#8220;Goose&#8221; may perhaps mean a plucked goose, which somewhat resembles a Greek
+lyre, and also a tortoise. The name of the bright star Vega is a
+corruption of the Arabic <i>v&acirc;ki</i>. Ptolemy and Al-Sufi included all the very
+brightest stars in the &#8220;first magnitude,&#8221; making no distinction between
+them, but it is evident at a glance that several of them, such as Arcturus
+and Vega, are brighter than an average star of the first magnitude, like
+Aldebaran.</p>
+
+<p>The constellation Perseus, which lies south-east of &#8220;Cassiopeia&#8217;s Chair,&#8221;
+may be recognized by the festoon formed by some of its stars, the bright
+star &#945; Persei being among them. It is called by Al-Sufi
+&#8220;<i>barsch&acirc;nsch</i>, &#928;&#949;&#961;&#963;&#949;&#8059;&#962;, Perseus, who is <i>hamil r&acirc;s al-gul</i>, the
+Bearer of the head of <i>al-gul</i>.&#8221; According to Kazimirski, &#8220;<i>Gul</i> was a
+kind of demon or ogre who bewilders travellers and devours them, beginning
+at the feet. In general any mischievous demon capable of taking all sorts
+of forms.&#8221; In the Greek mythology Perseus was supposed to be the son of
+Jupiter and Dan&aelig;. He is said to have been cast into the sea with his
+mother and saved by King Polydectus. He afterwards cut off the head of
+Medusa, one of the Gorgons, while she slept, and armed with this he
+delivered Andromeda from the sea-monster.</p>
+
+<p><span class="pagenum"><a name="Page_245" id="Page_245">[Pg 245]</a></span>The constellation Auriga lies east of Perseus and contains the bright star
+Capella, one of the three brightest stars in the northern hemisphere (the
+others being Arcturus and Vega). Theon, in his commentary on Aratus, says
+that Bellerophon invented the chariot, and that it is represented in the
+heavens by Auriga, the celestial coachman. According to Dupuis, Auriga
+represents Ph&aelig;ton, who tried to drive the chariot of the sun, and losing
+his head fell into the river Eridanus. The setting of Eridanus precedes by
+a few minutes that of Auriga, which was called by some of the ancient
+writers Amnis Pha&iuml;-tontis.<a name='fna_399' id='fna_399' href='#f_399'><small>[399]</small></a> Auriga is called by Al-Sufi <i>numsick
+al-ainna</i>&mdash;He who holds the reins, the Coachman; also <i>al-in&acirc;z</i>, the
+She-goat. M. Dorn found in Ptolemy&#8217;s work, the Greek name &#8216;&#919;&#957;&#8055;&#959;&#967;&#959;&#953;,
+Auriga, written in Arabic characters. Al-Sufi says, &#8220;This
+constellation is represented by the figure of a standing man behind &#8216;He
+who holds the head of <i>al-g&ucirc;l</i>&#8217; [Perseus], and between the Pleiades and
+the Great Bear.&#8221;</p>
+
+<p>Capella is, Al-Sufi says, &#8220;the bright and great star of the first
+magnitude which is on the left shoulder [of the ancient figure] on the
+eastern edge of the Milky Way. It is that which is marked on the astrolabe
+as <i>al-aij&ucirc;k</i>.&#8221; The real meaning of this name is unknown. Schjellerup
+thought, contrary to what Ideler says, that the name is<span class="pagenum"><a name="Page_246" id="Page_246">[Pg 246]</a></span> identical with
+the Greek word &#913;&#970;&#958; (a goat). Capella was observed at Babylon
+about 2000 <span class="smcaplc">B.C.</span>, and was then known as Dilgan. The Assyrian name was
+<i>Icu</i>, and the Persian name <i>colca</i>. It was also called Capra Hircus,
+Cabrilla, Amalthea, and Olenia. In ancient times the rising of Capella was
+supposed to presage the approach of storms. Ovid says, &#8220;Olenia sidus
+pluviale Capell&aelig;.&#8221;</p>
+
+<p>The constellation Aquila is called by Al-Sufi <i>al-ukab</i>, the Eagle, or
+<i>al-nasr al-t&acirc;&iuml;r</i>, the flying vulture. According to the ancient poets the
+eagle carried nectar to Jupiter when he was hidden in a cave in Crete.
+This eagle also assisted Jupiter in his victory over the Giants and
+contributed to his other pleasures. For these reasons the eagle was
+consecrated to Jupiter, and was placed in the sky. Al-Sufi says, &#8220;There
+are in this figure three famous stars [&#947;, &#945;, and &#946;
+Aquil&aelig;], which are called <i>al-nasr al-t&acirc;&iuml;r</i>.&#8221; Hence is derived the
+modern name Altair for the bright star &#945; Aquil&aelig;. Al-Sufi says
+that the &#8220;common people&#8221; call &#8220;the three famous stars&#8221; <i>al-m&icirc;z&acirc;n</i>, the
+Balance, on account of the equality of the stars.&#8221; This probably refers to
+the approximately equal distances between &#947; and &#945;, and
+&#945; and &#946;, and not to their relative brightness. He says
+&#8220;Between the bright one of the tail [&#958; Aquil&aelig;] and the star in
+the beak of the Hen [&#946; Cygni] in the thinnest part of the Milky
+Way, we see the figure of a little earthen jar, of which the<span class="pagenum"><a name="Page_247" id="Page_247">[Pg 247]</a></span> stars begin
+at the bright one in the tail, and extend towards the north-west. [This
+seems to refer to &#949; Aquil&aelig; and the small stars near it.] They
+then turn towards the east in the base of the jar, and then towards the
+south-east to a little cloud [4, 5, etc. Vulpecul&aelig;, a well-known group of
+small stars] which is found to the north of the two stars in the shaft of
+the Arrow [&#945; and &#946; Sagitt&aelig;]. The cloud is on the eastern
+edge of the jar, and the bright one on the tail on the western edge; the
+orifice is turned towards the flying Vulture [Aquila], and the base
+towards the north. Among these are distinguished some of the fourth,
+fifth, and sixth magnitudes [including, probably, 110, 111, 112, 113
+Hercules, and 1 Vulpecul&aelig;] and Ptolemy says nothing of this figure, except
+the bright star in the tail of the<span class="pagenum"><a name="Page_248" id="Page_248">[Pg 248]</a></span> Eagle&#8221; (see figure). The above is a
+good example of the minute accuracy of detail in Al-Sufi&#8217;s description.</p>
+
+<p>&nbsp;</p>
+<div class="figcenter"><img src="images/img1.jpg" alt="" /></div>
+<p class="caption">AL-SUFI&#8217;S &#8220;EARTHEN JAR.&#8221;</p>
+<p>&nbsp;</p>
+
+<p>The southern portion of Aquila was formerly called Antinous, who was said
+to have been a young man of great beauty born at Claudiopolis in Bithynia,
+and drowned in the Nile. Others say that he sacrificed his life to save
+that of the Emperor Hadrian, who afterwards raised altars in his honour
+and placed his image on coins.<a name='fna_400' id='fna_400' href='#f_400'><small>[400]</small></a></p>
+
+<p>The constellation Pegasus, Al-Sufi says, &#8220;is represented by the figure of
+a horse, which has the head, legs, and forepart of the body to the end of
+the back, but it has neither hind quarters nor hind legs.&#8221; According to
+Brown, Pegasus was the horse of Poseidon, the sea god. Half of it was
+supposed to be hidden in the sea, into which the river Eridanus
+flowed.<a name='fna_401' id='fna_401' href='#f_401'><small>[401]</small></a> In the Greek mythology it was supposed to represent the
+winged horse produced by the blood which fell from the head of Medusa when
+she was killed by Perseus! Some think that it represents Bellerophon&#8217;s
+horse, and others the horse of Nimrod. It was also called Sagmaria and
+Ephippiatus, and was sometimes represented with a saddle instead of wings.</p>
+
+<p>In describing the constellation Andromeda, Al-Sufi speaks of two series of
+stars which start from the great nebula in Andromeda; one series<span class="pagenum"><a name="Page_249" id="Page_249">[Pg 249]</a></span> going
+through 32 Andromed&aelig;, &#960;, &#948;, and &#949; to &#950; and
+&#951;; and the other through &#957;, &#956;, &#946; Andromed&aelig; into the
+constellation Pisces. He says they enclose a fish-shaped figure called by
+the Arabians <i>al-h&ucirc;t</i>, the Fish, <i>par excellence</i>. He speaks of two other
+series of stars which begin at &#964; and &#965;, and diverging
+meet again at &#967; Persei, forming another &#8220;fish-like figure.&#8221; The
+eastern stream starts from &#964; and passes through 55, &#947;,
+60, 62, 64, and 65 Andromed&aelig;; and the western stream from &#965;
+through &#967; 51, 54, and <i>g</i> Persei up to<span class="pagenum"><a name="Page_250" id="Page_250">[Pg 250]</a></span> &#967; Persei. The
+head of the first &#8220;fish,&#8221; <i>al-h&ucirc;t</i>, is turned towards the north, and that
+of the second towards the south (see figure).</p>
+
+<p>&nbsp;</p>
+<div class="figcenter"><img src="images/img2.jpg" alt="" /></div>
+<p class="caption">AL-SUFI&#8217;S &#8220;FISHES&#8221; IN ANDROMEDA.</p>
+<p>&nbsp;</p>
+
+<p>Al-Sufi says that the stars &#945; Persei, &#947;, &#946;, &#948;, and
+&#945; Andromed&aelig;, and &#946; Pegasi form a curved line. This is
+quite correct, and this fine curve of bright stars may be seen at a glance
+on a clear night in September, when all the stars are high in the sky.</p>
+
+<p>The first constellation of the Zodiac, Aries, the Ram, was called,
+according to Aratus and Eratosthenes, &#954;&#961;&#8055;&#959;&#962;. It is mentioned by
+Ovid under the name of Hellas. It was also called by the ancients the Ram
+with the golden horns. Manilius (fourth century <span class="smcaplc">B.C.</span>) called it &#8220;The
+Prince.&#8221; It is supposed to have represented the god Bel. Among the
+Accadians the sign meant &#8220;He who dwells on the altar of uprightness.&#8221; It
+first appears on the Egyptian Zodiac; and it was sacred to Jupiter Ammon.
+In the Greek mythology it was supposed to represent the ram, the loss of
+whose fleece led to the voyage of the Argonauts. In the time of
+Hipparchus, about 2000 years ago, it was the first sign of the Zodiac, or
+that in which the sun is situated at the Vernal Equinox (about March 21 in
+each year). But owing to the precession of the equinoxes, this point has
+now moved back into Pisces.</p>
+
+<p>The brightest star of Aries (&#945;) is sometimes<span class="pagenum"><a name="Page_251" id="Page_251">[Pg 251]</a></span> called Hamal,
+derived from the Arabic <i>al-hamal</i>, a name given to the constellation
+itself by Al-Sufi. In the Accadian language it was called <i>Dilkur</i>, &#8220;the
+dawn proclaimer.&#8221; Ali-Sufi says that close to &#945;, &#8220;as if it were
+attached to it,&#8221; is a small star of the 6th magnitude, not mentioned by
+Ptolemy. This is clearly &#954; Arietis. The fact of Al-Sufi having
+seen and noticed this small star, which modern measures show to be below
+the 5th magnitude, is good evidence of his keen eyesight and accuracy of
+observation.</p>
+
+<p>According to Al-Sufi, the stars &#946; and &#947; Arietis were
+called by the Arabians <i>al-scharatain</i>, &#8220;the two marks.&#8221; They marked the
+&#8220;first mansion of the moon,&#8221; and &#949;, &#948;, and &#961; the second
+mansion. With reference to these so-called &#8220;mansions of the moon,&#8221; Admiral
+Smyth says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The famous <i>Manazil al-kamar</i>, i.e. Lunar mansions, constituted a
+supposed broad circle in Oriental astronomy divided into twenty-eight
+unequal parts, corresponding with the moon&#8217;s course, and therefore
+called the abodes of the moon. This was not a bad arrangement for a
+certain class of gazers, since the luminary was observed to be in or
+near one or other of these parts, or constellations every night.
+Though tampered with by astrologers, these Lunar mansions are probably
+the earliest step in ancient astronomy.&#8221;<a name='fna_402' id='fna_402' href='#f_402'><small>[402]</small></a></p></div>
+
+<p>Taurus, the second constellation of the Zodiac,<span class="pagenum"><a name="Page_252" id="Page_252">[Pg 252]</a></span> was in ancient times
+represented by the figure of a bull, the hinder part of which is turned
+towards the south-west, and the fore part towards the east. It had no hind
+legs, and the head was turned to one side, with the horns extended towards
+the east. Its most ancient name was <i>Te</i>, possibly a corruption of the
+Accadian <i>dimmena</i>, &#8220;a foundation-stone.&#8221; The Greek name is &#7936;&#952;&#8061;&#961;
+(&#952;&#969;&#8061;&#961;, Eusebius). In the old Egyptian mythology Taurus
+represented the god Apis. According to Dupuis it also represented the 10th
+&#8220;labour of Hercules,&#8221; namely, his victory over the cows of Geryon, King of
+Spain.<a name='fna_403' id='fna_403' href='#f_403'><small>[403]</small></a> It was also supposed to represent the bull under the form of
+which Jupiter carried off Europa, daughter of Agenor, King of the
+Ph&oelig;nicians. It may also refer to Io or Isis, who is supposed to have
+taught the ancient Egyptians the art of agriculture.</p>
+
+<p>Aldebaran is the well-known bright red star in the Hyades. It was called
+by Ptolemy <i>Fulgur succularum</i>. Ali-Sufi says it was marked on the old
+astrolabes as <i>al-dabaran</i>, &#8220;the Follower&#8221; (because it follows the Hyades
+in the diurnal motion), and also <i>ain al-tsaur</i>, the eye of the bull. It
+may be considered as a standard star of the 1st magnitude. Modern
+observations show that it has a parallax of 0&Prime;&middot;107. It is receding from
+the earth, according to Vogel, at the rate<span class="pagenum"><a name="Page_253" id="Page_253">[Pg 253]</a></span> of about 30 miles a second;
+but even with this high velocity it will take thousands of years before
+its brightness is perceptibly diminished. It has a faint companion of
+about the 10th magnitude at the distance of 118&Prime;, which forms a good
+&#8220;light test&#8221; for telescopes of 3 or 4 inches aperture. I saw it well with
+a 4-inch Wray in the Punjab sky. The Hyades were called <i>Succul&aelig;</i> by the
+Romans, and in the Greek mythology were said to be children of Atlas.</p>
+
+<p>The star &#946; Tauri, sometimes called Nath, from the Arabic
+<i>al-n&aacute;tih</i>, the butting, is a bright star between Capella and &#947;
+Orionis (Bellatrix). It is on the tip of the horn in the ancient figure of
+Taurus, and &#8220;therefore&#8221; (says Admiral Smyth) &#8220;at the greatest distance
+from the hoof; can this have given rise to the otherwise pointless sarcasm
+of not knowing B from a bull&#8217;s foot?&#8221;<a name='fna_404' id='fna_404' href='#f_404'><small>[404]</small></a> Al-Sufi says that an imaginary
+line drawn from the star now known as A Tauri to &#964; Tauri would
+pass between &#965; and &#954; Tauri, which is quite correct,
+another proof of the accuracy of his observations. He also says that the
+star &#969; Tauri is exactly midway between A and &#949;, which is
+again correct. He points out that Ptolemy&#8217;s position of &#969; is
+incorrect. This is often the case with Ptolemy&#8217;s positions, and tends to
+show that Ptolemy adopted the position given by Hipparchus without
+attempting to verify their position in the sky.<span class="pagenum"><a name="Page_254" id="Page_254">[Pg 254]</a></span> Al-Sufi himself adopts
+the longitudes and latitudes of the stars as given by Ptolemy in the
+<i>Almagest</i>, but corrects the positions in his <i>descriptions</i>, when he
+found Ptolemy&#8217;s places erroneous.</p>
+
+<p>The famous group of the Pleiades is well known; but there is great
+difficulty in understanding Al-Sufi&#8217;s description of the cluster. He says,
+&#8220;The 29th star (of Taurus) is the more northern of the anterior side of
+the Pleiades themselves, and the 30th is the southern of the same side;
+the 31st is the following vertex of the Pleiades, and is in the more
+narrow part. The 32nd is situated outside the northern side. Among these
+stars, the 32nd is of the 4th magnitude, the others of the 5th.&#8221; Now, it
+is very difficult or impossible to identify these stars with the stars in
+the Pleiades as they are at present. The brightest of all, Alcyone
+(&#951; Tauri), now about 3rd magnitude, does not seem to be mentioned
+at all by Al-Sufi! as he says distinctly that &#8220;the brightest star&#8221; (No 32
+of Taurus) is &#8220;outside&#8221; the Pleiades &#8220;on the northern side.&#8221; It seems
+impossible to suppose that Al-Sufi could have overlooked Alcyone had it
+the same brightness it has now. The 32nd star seems to have disappeared,
+or at least diminished greatly in brightness, since the days of Al-Sufi.
+More than four stars were, however, seen by Al-Sufi, for he adds, &#8220;It is
+true that the stars of the Pleiades must exceed the four<span class="pagenum"><a name="Page_255" id="Page_255">[Pg 255]</a></span> mentioned above,
+but I limit myself to these four because they are very near each other and
+the largest [that is, the brightest]; this is why I have mentioned them,
+neglecting the others.&#8221; A full examination of the whole question is given
+by Flammarion in his interesting work <i>Les &Eacute;toiles</i> (pp. 289-307), and I
+must refer my readers to this investigation for further details.</p>
+
+<p>According to Brown, Simonides of Keos (<span class="smcaplc">B.C.</span> 556-467) says, &#8220;Atlas was the
+sire of seven daughters with violet locks, who are called the heavenly
+<i>Peleiades</i>.&#8221;<a name='fna_405' id='fna_405' href='#f_405'><small>[405]</small></a> The name is by some supposed to be derived from the
+Greek &#960;&#955;&#949;&#8055;&#969;&#957;, full. The Old Testament word <i>Kimah</i> (Job ix. 9 and
+xxviii. 31) and Amos (v. 8) is derived from the Assyrian <i>Kimta</i>, a
+&#8220;family.&#8221; Aratus describes the Pleiades in the following lines:&mdash;</p>
+
+<p class="poem">&#8220;Near his<a name='fna_406' id='fna_406' href='#f_406'><small>[406]</small></a> left thigh together sweep along<br />
+The flock of Clusterers. Not a mighty span<br />
+Holds all, and they themselves are dim to see,<br />
+And seven paths aloft men say they take,<br />
+Yet six alone are viewed by mortal eye.<br />
+These seven are called by name Alkyon&icirc;<br />
+Kelain&icirc;, Merop&icirc; and Sterop&icirc;<br />
+Tayget&icirc;, Elecktr&icirc;, Maia queen.<br />
+They thus together small and faint roll on<br />
+Yet notable at morn and eve through Zeus.&#8221;<a name='fna_407' id='fna_407' href='#f_407'><small>[407]</small></a></p>
+
+<p>The Pleiades are mentioned by Ovid. According to the ancient poets they
+were supposed to<span class="pagenum"><a name="Page_256" id="Page_256">[Pg 256]</a></span> represent the children of Atlas and Hesperus, and on
+this account they were called Atlantids or Hesperides. From the
+resemblance in sound to the word &#960;&#955;&#949;&#8055;&#945;&#962;, a pigeon, they were
+sometimes called &#8220;the doves,&#8221; and for the same reason the word
+&#960;&#955;&#949;&#8150;&#957;, to navigate, led to their being called the &#8220;shipping stars.&#8221; The
+word &#960;&#955;&#949;&#8055;&#945;&#962; was also applied to the priestesses of the god Zeus
+(Jupiter) at Dordona, in the groves of which temple there were a number of
+pigeons. This is, perhaps, what Aratus refers to in the last line of the
+extract quoted above. According to Neapolitan legends, the name of
+Virgil&#8217;s mother was Maia. The mother of Buddha, the Hindoo <i>avatar</i>, was
+also named Maia. In Italy the Pleiades were called <i>Gallinata</i>, and in
+France <i>poussini&egrave;re</i>, both of which mean the hen and chickens, a term also
+given to them by Al-Sufi. The old Blackfoot Indians called them &#8220;The Seven
+Perfect Ones.&#8221; The Crees and Ojibway Indians called them the &#8220;Fisher
+Stars.&#8221; The Adipones of Brazil and some other nations claimed that they
+sprang from the Pleiades! The Wyandot Indians called them &#8220;The Singing
+Maidens.&#8221;</p>
+
+<p>Photographs show that the brighter stars of the Pleiades are involved in
+nebulosity. That surrounding Maia seems to be of a spiral form. Now, there
+is a Sanscrit myth which represents Maia as &#8220;weaving the palpable
+universe,&#8221; for which reason she was &#8220;typified as a spider.&#8221;<span class="pagenum"><a name="Page_257" id="Page_257">[Pg 257]</a></span> This seems
+very appropriate, considering the web of nebulous light which surrounds
+the stars of the group. Maia was also considered as a type of the
+universe, which again seems appropriate, as probably most of the stars
+were evolved from spiral nebul&aelig;.</p>
+
+<p>The name Hyades is supposed to be derived from the Greek word &#8017;&#949;&#8150;&#957;,
+to rain, because in ancient times they rose at the rainy season.</p>
+
+<p>In ancient Egypt, Aldebaran was called <i>ary</i>; and the Pleiades <i>chooa</i>, a
+word which means &#8220;thousands.&#8221; The name Aldebaran seems to have been
+originally applied to the whole of the Hyades group. Aldebaran was also
+called by the Arabians <i>al-fanik</i>, the great Camel, and the Hyades
+<i>al-kilas</i>, the young Camels. The two close stars &#965; and &#954;
+Tauri were called <i>al-kalba&iuml;n</i>, the dogs of Aldebaran. La Condamine
+states that the Indians of the Amazon saw in the Hyades the head of a
+bull.</p>
+
+<p>Gemini, the Twins, is the third constellation of the Zodiac. It was also
+called Gemelli, etc. According to Dupuis it represents the 11th &#8220;labour of
+Hercules&#8221;&mdash;his triumph over the dog Cerberus.<a name='fna_408' id='fna_408' href='#f_408'><small>[408]</small></a> But some of Dupuis&#8217;
+ideas seem very fanciful. The Twins are usually called Castor and Pollux,
+but they were also called by the ancient writers Apollo and Hercules;
+Jason and Triptolemus; Amphion and Zethus; and Theseus<span class="pagenum"><a name="Page_258" id="Page_258">[Pg 258]</a></span> and Peritheus. In
+Egypt they represented the deities Horus and Hippocrates. Brown thinks
+that the &#8220;Great Twins&#8221; were originally the sun and moon, &#8220;who live
+alternately. As one is born the other dies; as one rises the other
+sets.&#8221;<a name='fna_409' id='fna_409' href='#f_409'><small>[409]</small></a> This applies to the full moon, but does not seem applicable to
+the other lunar phases.</p>
+
+<p>Gemini was the constellation to which Dante supposed himself transported
+when he visited the stellar heavens.<a name='fna_410' id='fna_410' href='#f_410'><small>[410]</small></a> He says he was born under the
+influence of this &#8220;sign.&#8221;</p>
+
+<p>Cancer, the Crab, is the next sign of the Zodiac. In the Greek mythology
+it was supposed to have been placed in the sky by Juno to commemorate the
+crab which pinched the toes of Hercules in the Lern&aelig;an marsh. The Greek
+name was &#964;&#965;&#946;&#8055;. According to Dupuis it represents the 12th &#8220;labour
+of Hercules&#8221;&mdash;his capture of the golden apples in the Garden of the
+Hesperides, which were guarded by a Dragon. This Dragon is Draco, which
+was also called Custos Hesperidum.<a name='fna_411' id='fna_411' href='#f_411'><small>[411]</small></a> But the connection between a crab
+and the myth of the golden apples is not obvious&mdash;unless some reference to
+&#8220;crab apples&#8221; is intended! Among the Romans, Cancer was consecrated to
+Mercury, and by the ancient Egyptians to their god Anubis.</p>
+
+<p>The well-known cluster in Cancer called the<span class="pagenum"><a name="Page_259" id="Page_259">[Pg 259]</a></span> Pr&aelig;sape, Al-Sufi says, is &#8220;a
+little spot which resembles a cloud, and is surrounded by four stars, two
+to the west [&#951; and &#952; Cancri] and two to the east&#8221;
+[&#947; and &#948;]. This cluster is mentioned by Aratus, who
+calls it the &#8220;Manger.&#8221; The word Pr&aelig;sape is often translated &#8220;Beehive,&#8221; but
+there can be no doubt that it really means &#8220;Manger,&#8221; referring to the
+stars &#947; and &#948; Cancri, which the ancients called Aselli,
+the ass&#8217;s colts. These were supposed to represent the asses which in the
+war of Jupiter against the Giants helped his victory by their braying!</p>
+
+<p>Admiral Smyth says in his <i>Bedford Catalogue</i> (p. 202) that he found
+&#947; and &#948; Cancri both of 4th magnitude; but the
+photometric measures show that &#948; is now distinctly brighter than
+&#947;. An occultation of &#948; Cancri by the moon is recorded as
+having occurred on September 3, <span class="smcaplc">B.C.</span> 240.</p>
+
+<p>The fine constellation Leo, the Lion, is the next &#8220;sign&#8221; of the Zodiac,
+and is marked by the well-known &#8220;Sickle.&#8221; According to Dupuis, it
+represents the first &#8220;labour of Hercules&#8221;&mdash;the killing of the Nem&aelig;lian
+lion. Manilius called it Nem&aelig;us. It was also called Janonus sidus, Bacchi
+sidus, etc. The Greek name was &#956;&#949;&#967;&#8055;&#961;, &#956;&#949;&#967;&#949;&#8055;&#961;, or
+&#956;&#949;&#967;&#8057;&#962;. In ancient Egypt, Leo was sacred to Osiris, and many of
+the Egyptian monuments are ornamented with lions&#8217; heads. It is stated in
+the Horapolla that its appearance was supposed to announce the annual
+rising of the Nile.</p>
+
+<p><span class="pagenum"><a name="Page_260" id="Page_260">[Pg 260]</a></span>Regulus (&#945; Leonis) is the brightest and most southern of the
+stars in the &#8220;Sickle.&#8221; Al-Sufi says &#8220;it is situated in the heart and is of
+the 1st magnitude. It is that which is called <i>al-maliki</i>, the royal star.
+It is marked on the astrolabe as <i>kalb al-asad</i>, the Heart of the Lion&#8221;
+(whence the name Cor Leonis). Modern photometric measures make it about
+1&middot;3 magnitude. It has an 8&#189; magnitude companion at about 177&Prime; distance
+(Burnham) which is moving through space with the bright star, and is
+therefore at probably the same distance from the earth as its brilliant
+primary. This companion is double (8&middot;5, 12&middot;5: 3&Prime;&middot;05, Burnham). The
+spectroscope shows that Regulus is approaching the earth at the rate of
+5&#189; miles a second. Its parallax is very small&mdash;about 0&Prime;&middot;022, according
+to Dr. Elkin&mdash;which indicates that it is at a vast distance from the
+earth; and its brightness shows that it must be a sun of enormous size.
+Ptolemy called it &#946;&#945;&#963;&#953;&#955;&#8055;&#963;&#954;&#959;&#962;, whence its Latin name Regulus,
+first used by Copernicus as the diminutive of <i>rex</i>.<a name='fna_412' id='fna_412' href='#f_412'><small>[412]</small></a></p>
+
+<p>The next constellation of the Zodiac is Virgo, the Virgin. It was also
+called by the ancients Ceres, Isis, Erigone, Fortuna, Concorda, Astr&aelig;a,
+and Themis. The Greek name was &#966;&#945;&#956;&#8051;&#957;&#969;&#952;. Ceres was the goddess
+of the harvest. Brown thinks that it probably represents the ancient
+goddess Istar, and also Ashtoreth. According to Prof.<span class="pagenum"><a name="Page_261" id="Page_261">[Pg 261]</a></span> Sayce it is the
+same as the Accadian sign of &#8220;the errand of Istar, a name due to the
+belief that it was in August that the goddess Astarte descended into Hades
+in search of her betrothed, the sun god Tammuz, or Adonis, who had been
+slain by the boar&#8217;s tusk.&#8221;<a name='fna_413' id='fna_413' href='#f_413'><small>[413]</small></a> The ear of corn (Spica) is found on the
+ancient Egyptian monuments, and is supposed to represent the fertility
+caused by the annual rising of the Nile. According to Aratus, the Virgin
+lived on earth during the golden age under the name of Justice, but that
+in the bronze age she left the earth and took up her abode in the heavens.</p>
+
+<p class="poem">&#8220;Justice, loathing that race of men,<br />
+Winged her flight to heaven.&#8221;</p>
+
+<p>The Sphinx near the Great Pyramid has the head of a virgin on the body of
+a lion, representing the goddess Isis (Virgo) and her husband Osiris
+(Leo).</p>
+
+<p>Al-Sufi&#8217;s 5th star of Virgo is Flamsteed 63 Virginis. Al-Sufi says it is a
+double star of the 5th magnitude. In Al-Sufi&#8217;s time it formed a &#8220;naked-eye
+double&#8221; with 61 Virginis, but owing to large proper motion, 61 has now
+moved about 26 minutes of arc towards the south, and no longer forms a
+double with 63. This interesting fact was first pointed out by Flammarion
+in his work <i>Les &Eacute;toiles</i> (p. 373).</p>
+
+<p><span class="pagenum"><a name="Page_262" id="Page_262">[Pg 262]</a></span>Libra, the Balance, is one of the &#8220;signs&#8221; of the Zodiac, but originally
+formed the claws of the Scorpion. It was called Juguna by Cicero, and
+Mochos by Ampelius. The Greek name was &#966;&#945;&#961;&#956;&#959;&#965;&#952;&#8051;. Virgil
+suggests that it represented the justice of the emperor Augustus, honoured
+by the name of a constellation; but probably this refers to the birth of
+Augustus under the sign of Libra, as Scaliger has pointed out. According
+to Brown, &#8220;the daily seizing of the dying western sun by the claws of the
+Scorpion of darkness is reduplicated annually at the Autumnal Equinox,
+when the feeble waning sun of shortening days falls ever earlier into his
+enemy&#8217;s grasp;&#8221;<a name='fna_414' id='fna_414' href='#f_414'><small>[414]</small></a> and he says, &#8220;The Balance or Scales (Libra), which it
+will be observed is in itself neither diurnal nor nocturnal, is the only
+one of the zodiacal signs not Euphratean in origin, having been imported
+from Egypt and representing originally the balance of the sun at the
+horizon between the upper and under worlds; and secondarily the equality
+of the days and nights at the equinox.&#8221;<a name='fna_415' id='fna_415' href='#f_415'><small>[415]</small></a></p>
+
+<p>According to Houzeau, Libra was formed at the beginning of the second
+century <span class="smcaplc">B.C.</span>, and it does not appear in any writings before those of
+Geminus and Varron.<a name='fna_416' id='fna_416' href='#f_416'><small>[416]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_263" id="Page_263">[Pg 263]</a></span>Milton says in <i>Paradise Lost</i>:&mdash;</p>
+
+<p class="poem">&#8220;The Eternal to prevent such horrid fray,<br />
+Hung forth in heaven his golden scales, yet seen<br />
+Betwixt Astr&aelig;a and the Scorpion&#8217;s sign.&#8221;</p>
+
+<p>(Here Astr&aelig;a is Virgo.)</p>
+
+<p>It is worth noticing that both Ptolemy and Al-Sufi rated the star &#954;
+Libr&aelig; as two magnitudes brighter than &#955; Libr&aelig;. The two stars
+are now practically of equal brightness (5th magnitude), and it seems
+impossible to believe that this could have been the case in Al-Sufi&#8217;s
+time. Surely a careful observer like Al-Sufi, who estimated the relative
+brightness of stars to a third of a magnitude, could not possibly have
+made an error of two magnitudes in the brightness of two stars near each
+other! It should be stated, however, that &#954; Libr&aelig; was rated 5th
+magnitude by Argelander and Heis, and &#955;, 6th magnitude by the
+same excellent observers.</p>
+
+<p>The next &#8220;sign&#8221; of the Zodiac, Scorpion, was consecrated by the Romans to
+Mars, and by the Egyptians to Typhon.<a name='fna_417' id='fna_417' href='#f_417'><small>[417]</small></a> It was called <i>Nepa</i> by Cicero,
+<i>Martis sidus</i> by Manilius, and <i>Fera magna</i> by Aratus. The Greek name was
+&#960;&#8049;&#967;&#959;&#957;.</p>
+
+<p>Mr. E. B. Knobel has called attention to a curious remark of Ptolemy with
+reference to the bright star Antares (&#945; Scorpii), &#8220;Media earum
+qu&aelig; <i>tendit ad rapinam</i> qu&aelig; dicitur Cor Scorpionis&#8221;; and he made a similar
+remark with<span class="pagenum"><a name="Page_264" id="Page_264">[Pg 264]</a></span> reference to Betelgeuse (&#945; Orionis) and others. But
+Mr. Robert Brown<a name='fna_418' id='fna_418' href='#f_418'><small>[418]</small></a> explains the remark by the fact that in ancient
+times these stars rose in the morning at a time when caravans were exposed
+to dangers from robbers. Thus the term had nothing to do with the aspect
+or colour of these stars, but was merely a reference to their supposed
+astrological influence on human affairs.</p>
+
+<p>In the Egyptian <i>Book of the Dead</i>, Silkit was a goddess who assumed the
+form of a scorpion in the sky. She was supposed to be the daughter of
+<i>Ra</i>.</p>
+
+<p>With reference to stars &#8220;outside&#8221; the ancient figure of Scorpio, the
+first, Al-Sufi says, &#8220;is a star which immediately follows <i>al-schaulat</i>&#8221;
+[&#955;] and &#954;, &#8220;it is of small 4th magnitude; Ptolemy calls
+it &#957;&#949;&#966;&#949;&#955;&#959;&#949;&#8055;&#948;&#951;&#962;&#8221; [nebulous]. Schjelerup, in his translation of
+Al-Sufi&#8217;s work, does not identify this object; but it is very evidently
+&#947; Telescopii, which lies exactly in the position described by
+Al-Sufi. Now, it is a very interesting and curious fact that Ptolemy
+called it nebulous, for in the same telescopic field with it is the nebula
+<i>h</i> 3705 (= Dunlop 557). Dunlop describes it as a &#8220;small well-defined
+rather bright nebula, about 20&Prime; in diameter; a very small star precedes
+it, but is not involved; following &#947; Telescopii.&#8221; Sir John
+Herschel at the Cape found it fairly resolved into very faint stars, and
+adds, &#8220;The whole <i>ground</i><span class="pagenum"><a name="Page_265" id="Page_265">[Pg 265]</a></span> of the heavens, for an immense extent is
+thickly sown with such stars. A beautiful object.&#8221;<a name='fna_419' id='fna_419' href='#f_419'><small>[419]</small></a> This perhaps
+accounts for the nebulous appearance of the star as seen by Ptolemy.</p>
+
+<p>Several <i>nov&aelig;</i> or temporary stars are recorded as having appeared in
+Scorpio. One in the year <span class="smcaplc">B.C.</span> 134 is stated by Pliny to have induced
+Hipparchus to form his catalogue of stars. This star was also observed in
+China. Its exact position is unknown, but Flammarion thinks it may
+possibly have appeared about 4&deg; north of the star &#946; Scorpii.
+Another new star is said to have appeared in <span class="smcaplc">A.D.</span> 393, somewhere in the
+Scorpion&#8217;s tail. One in <span class="smcaplc">A.D.</span> 1203 and another in 1584 are also mentioned,
+the latter near &#960; Scorpii.</p>
+
+<p>The constellation Scorpio seems to be referred to by Dante in his
+<i>Purgatorio</i> (ix. 4-6) in the lines&mdash;</p>
+
+<p class="poem">&#8220;De gemma la sua fronte era lucenta<br />
+Poste in figura del fredda animale<br />
+Che con la coda percota la genta,&#8221;</p>
+
+<p>perhaps suggested by Ovid&#8217;s remark&mdash;</p>
+
+<p class="poem">&#8220;Scorpius exhibit caudaque menabitur unca.&#8221;<a name='fna_420' id='fna_420' href='#f_420'><small>[420]</small></a></p>
+
+<p>Next to Scorpio comes Sagittarius, the Archer. It is said to have been
+placed in the sky as a symbol of Hercules, a hero who was held in the
+greatest veneration by the ancient Egyptians.<span class="pagenum"><a name="Page_266" id="Page_266">[Pg 266]</a></span> The horse, usually
+associated with this constellation, was a symbol of war. It was also
+called by the ancients Chiron, Arcitenens, Minotaurus, Croton, etc. The
+Greek name was &#960;&#945;&#965;&#957;&#8055;, or &#960;&#945;&#969;&#957;&#8055;. Chiron was supposed to
+be the son of Saturn and Phillyra, and first taught men to ride on horses.
+The name is derived from the Greek &#967;&#949;&#8055;&#961;, a hand. Some writers,
+however, think that Chiron is represented by the constellation of the
+Centaur, and others say that Sagittarius represents the Minotaur loved by
+Persephone. According to Dupuis, Sagittarius represents the 5th &#8220;labour of
+Hercules,&#8221; which consisted in hunting the birds of the lake Stymphalus,
+which ravaged the neighbouring countries. These birds are perhaps
+represented by Cygnus, Altair, and the Vulture (Lyra). The Lyre probably
+represents the musical instrument which Hercules used to frighten the
+birds.<a name='fna_421' id='fna_421' href='#f_421'><small>[421]</small></a></p>
+
+<p>According to Al-Sufi, the Arabians called the stars &#947;, &#948;, &#949;, and
+&#951; Sagittarii which form a quadrilateral figure, &#8220;the Ostrich
+which goes to the watering place,&#8221; because they compared the Milky Way to
+a river. They compared the stars &#963;, &#966;, &#964;, and &#950;
+Sagittarii, which form another quadrilateral, to an ostrich which has
+drunk and returns from the &#8220;watering place.&#8221; He says that the star &#955;
+Sagittarii forms with these two &#8220;ostriches&#8221; a tent, and certainly the
+figure formed by &#955;, &#966;, &#950;, &#949;,<span class="pagenum"><a name="Page_267" id="Page_267">[Pg 267]</a></span> and &#948; is not unlike a
+tent. Al-Sufi says more about these &#8220;ostriches&#8221;; but the ideas of the old
+Arabians about the stars seem very fanciful.</p>
+
+<p>A &#8220;temporary star&#8221; is recorded in the Chinese Annals of Ma-touan-lin as
+having appeared in May, <span class="smcaplc">B.C.</span> 48, about 4&deg; distant from &#956;
+Sagittarii. Another in the year 1011 <span class="smcaplc">A.D.</span> appeared near the quadrilateral
+figure formed by the stars &#963;, &#964;, &#950;, and &#966; Sagittarii.
+This may perhaps be identified with the object referred to by Hepidannus
+in the year 1012, which was of extraordinary brilliancy, and remained
+visible &#8220;in the southern part of the heavens during three months.&#8221; Another
+is mentioned near the same place in <span class="smcaplc">A.D.</span> 386 (April to July).<a name='fna_422' id='fna_422' href='#f_422'><small>[422]</small></a> The
+number of &#8220;temporary stars&#8221; recorded in this part of the heavens is very
+remarkable.</p>
+
+<p>According to Brown, Sagittarius is depicted on a stone, cir. <span class="smcaplc">B.C.</span> 1100,
+found at B&acirc;bilu, and now in the British Museum.<a name='fna_423' id='fna_423' href='#f_423'><small>[423]</small></a></p>
+
+<hr style="width: 25%;" />
+
+<p>The next of the &#8220;signs of the Zodiac&#8221; is Capricornus, the Goat. In the
+Arabo-Latin edition of Ptolemy&#8217;s <i>Almagest</i> it is called Alcaucurus. It is
+supposed to represent Amalthea, the goat which nursed Jupiter. According
+to Dupuis it represented the 6th &#8220;labour of Hercules,&#8221; which was the
+cleaning out of the Augean stables.<a name='fna_424' id='fna_424' href='#f_424'><small>[424]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_268" id="Page_268">[Pg 268]</a></span>&#945;<sub>2</sub> Capricorni is the northern of two stars of the 4th
+magnitude (&#945; and &#946; Capricorni). It really consists of
+two stars visible to the naked eye. The second of these two stars (&#945;<sub>1</sub>)
+is not mentioned by Al-Sufi, but I find that, owing to proper
+motion, they were nearer together in his time (tenth century), and were
+evidently seen by him as one star. &#946; Capricorni (about 3rd
+magnitude) is a very wide double star (3&#189;, 6; 205&Prime;), which may be seen
+with any small telescope. The fainter star was found to be a close double
+by Burnham. At present &#946; is brighter than &#945;, although
+rated of the same brightness by Al-Sufi.</p>
+
+<p>Aquarius is the next &#8220;sign of the Zodiac.&#8221; It is supposed to represent a
+man pouring water out of an urn or bucket. Other names given to this
+constellation were Arist&aelig;us, Ganymede, Cecrops, Amphora, Urna, and Aqua
+tyrannus. According to Dupuis it represents the 7th &#8220;labour of Hercules,&#8221;
+which was his victory over the famous bull which ravaged Crete.<a name='fna_425' id='fna_425' href='#f_425'><small>[425]</small></a> But
+the connection between a bull and a bucket is not obvious. Aquarius is
+represented in several places on the Egyptian monuments. Some of the
+ancient poets supposed that it represented Deucalion (the Noah of the
+Greek story of the Deluge); others thought that it represented Cecrops,
+who came to Greece from Egypt, built Athens, and was also called Bifornis.
+Others say that he was Ganymede, the cup-bearer of the gods.</p>
+
+<p><span class="pagenum"><a name="Page_269" id="Page_269">[Pg 269]</a></span>There is some difficulty about the identification of some of Al-Sufi&#8217;s
+stars in Aquarius. His sixth star (Fl. 7) is nearly 10&deg; south-west of
+&#946; Aquarii, and is, Al-Sufi says, &#8220;the following of three stars in
+the left hand, and precedes the fourth [&#946;] ... it is of the 6th
+magnitude. Ptolemy calls it third, but in reality it is very faint&#8221; [now
+about 6th magnitude]. The seventh [&#956;] is the middle one of the
+three and about 4&#189; magnitude, although Al-Sufi calls it &#8220;small fifth&#8221;
+[Ptolemy rated it 4]. The eighth star, &#949;, is the preceding of the
+three and about 3&middot;8, agreeing closely with Al-Sufi&#8217;s 4&middot;3. Ptolemy rated it
+3. This star is mentioned under the name <i>nou</i> in the time of
+<i>Tcheou-Kong</i> in the twelfth century <span class="smcaplc">B.C.</span> Al-Sufi says, &#8220;These three stars
+are followed by a star of the 5th magnitude which Ptolemy has not
+mentioned. It is brighter than the sixth star&#8221; [Fl. 7]. This is evidently
+&#957; Aquarii. If, however, we plot Ptolemy&#8217;s positions as given by
+Al-Sufi, it seems probable that <i>Ptolemy&#8217;s</i> sixth star was really &#957;,
+and that either &#956; or Fl. 7 was not seen by him. As Ptolemy
+called his seventh star 4th magnitude, and his sixth and eighth stars 3rd
+magnitude, some considerable change of brightness seems to have taken
+place in these stars; as &#957; is now only 4&#189; and Fl. 7 only a
+bright sixth. Variation was suspected in Fl. 7<a name='fna_426' id='fna_426' href='#f_426'><small>[426]</small></a> by Gould. I found it
+very<span class="pagenum"><a name="Page_270" id="Page_270">[Pg 270]</a></span> reddish with binocular in October, 1892. Burnham found it to be a
+close double star, the companion being about 12th magnitude at a distance
+of only 2&Prime;. It is probably a binary.</p>
+
+<p>According to Al-Sufi, the Arabians called the second and third stars of
+the figure (&#945; and &#959; Aquarii) <i>sad al-malik</i> (<i>malk</i> or
+<i>mulk</i>), &#8220;the Good Fortune of the king.&#8221; They called the fourth and fifth
+stars (&#946; and &#958; Aquarii) with the twenty-eighth star of
+Capricornus (<i>c</i>) <i>sad al-sund</i>, &#8220;the Good Fortune of the Happy Events.&#8221;
+&#8220;This is the 24th mansion of the moon.&#8221; These stars rose at the time of
+year when the cold ends, and they set at the time the heat ends. Hence,
+Al-Sufi says, &#8220;when they rise the rains begin, and when they set the
+unhealthy winds cease, fertility abounds, and the dew falls.&#8221; Hence
+probably the Arabic names. This, of course, applies to the climate of
+Persia and Arabia, and not to the British Isles. Al-Sufi says, &#8220;They call
+the 6th, 7th, and 8th stars <i>sad bula</i>, &#8216;The Good Fortune which swallows
+up!&#8217; This is the 23rd mansion of the moon. They say that it is so called
+because that at the time of the Deluge it rose at the moment when God
+said, &#8216;O earth! absorb the waters&#8217; (Koran, chap, xi., v. 46). They called
+the stars &#947;, &#960;, &#950; and &#951; Aquarii <i>sad al-achbija</i>, &#8216;the
+the Good Fortune of the tents&#8217;; this is the 25th mansion of the moon, and
+they give them this name because of these four stars, three form a
+triangle, the fourth [&#950;] being in the<span class="pagenum"><a name="Page_271" id="Page_271">[Pg 271]</a></span> middle.&#8221; The three were
+considered to form a tent.</p>
+
+<p>The Arabians called the bright star Fomalhaut &#8220;in the mouth of the
+southern fish <i>al-dhifda al-auval</i>, &#8216;the first Frog,&#8217; as the bright one on
+the southern point of the tail of K&icirc;tus [Cetus] is called <i>al-dhifda
+al-tsani</i> [&#946; Ceti], &#8216;the second Frog.&#8217;&#8221; Fomalhaut was also called
+<i>al-zhalim</i>, &#8220;the male ostrich.&#8221;</p>
+
+<p>Al-Sufi says, &#8220;Some of the Arabians state that a ship is situated to the
+south of Aquarius.&#8221; The stars in the Southern Fish (Piscis Australis) seem
+to be here referred to.</p>
+
+<p>The constellation Pisces, the Fishes, is the last of the &#8220;signs of the
+Zodiac.&#8221; The Fishes appear on an ancient Greek obelisk described by
+Pococke. Among the Greeks this sign was consecrated to Venus; and in Egypt
+to Nepthys, wife of Typhon and goddess of the sea. Pisces is said to end
+the Zodiac as the Mediterranean Sea terminated Egypt. This idea was
+suggested by Schmidt, who also conjectured that the Ram (Aries) was placed
+at the beginning of the Zodiac because Thebes, a town sacred to Jupiter
+Ammon, was at the beginning of Egypt in ancient times; and he thought that
+the constellation Triangulum, the Triangle, represented the Nile Delta,
+Eridanus being the Nile.<a name='fna_427' id='fna_427' href='#f_427'><small>[427]</small></a> The constellation was represented in ancient
+times by two fishes connected by a cord<span class="pagenum"><a name="Page_272" id="Page_272">[Pg 272]</a></span> tied to their tails. The southern
+of these &#8220;fishes&#8221; lies south of the &#8220;Square of Pegasus,&#8221; and the northern
+between Andromeda and Aries. According to Manilius, the origin of these
+fishes is as follows: Venus, seeing Typhon on the banks of the river
+Euphrates, cast herself with her son into the river and they were
+transformed into fishes!</p>
+
+<p>Some of the Arabians substituted a swallow for the northern of the two
+fishes&mdash;the one below Andromeda. The swallow was a symbol of Spring.
+According to Dupuis, Pisces represents the 8th &#8220;labour of Hercules,&#8221; his
+triumph over the mares of Diomed which emitted fire from their
+nostrils.<a name='fna_428' id='fna_428' href='#f_428'><small>[428]</small></a> But the connection between fishes and mares is not obvious,
+and some of Dupuis&#8217; ideas seem very fanciful. Here he seems to have found
+a &#8220;mare&#8217;s nest.&#8221;</p>
+
+<p>The constellation Cetus, the Whale, represents, according to ancient
+writers, the sea monster sent by Neptune to devour Andromeda when she was
+chained to the rock. Aratus calls Cetus the &#8220;dusky monster,&#8221; and Brown
+remarks that &#8220;the &#8216;Dusky Star&#8217; would be peculiarly appropriate to Mira
+(the wondrous &#959; Ceti).&#8221;<a name='fna_429' id='fna_429' href='#f_429'><small>[429]</small></a> Cetus was also called Canis
+Tritonis, or Dog of the Sea, Bayer in his Atlas (1603) shows a dragon
+instead of a whale, finding it so represented on some ancient spheres.
+Al-Sufi calls it K&icirc;tus or &#954;&#951;&#964;&#959;&#962;, the whale. He says,<span class="pagenum"><a name="Page_273" id="Page_273">[Pg 273]</a></span> &#8220;it is
+represented by the figure of a marine animal, of which the fore part is
+turned towards the east, to the south of the Ram, and the hinder part
+towards the west behind the three &#8216;extern&#8217; stars of Aquarius.&#8221;</p>
+
+<p>Al-Sufi does not mention the variable star &#959; Ceti, now called
+Mira, or the &#8220;wonderful,&#8221; nor does he refer to any star in its immediate
+vicinity. We may, therefore, conclude that it was near a minimum of light
+at the time of his observation of the stars of Cetus.</p>
+
+<p>The constellation of Orion, one of the finest in the heavens, was called
+by Al-Sufi <i>al-djabbar</i>, &#8220;the Giant,&#8221; and also <i>al-djauza</i>, &#8220;the Spouse.&#8221;
+The poet Longfellow says&mdash;</p>
+
+<p class="poem">&#8220;Sirius was rising in the east<br />
+And, slow ascending one by one,<br />
+The kindling constellations shone<br />
+Begirt with many a blazing star<br />
+Stood the great giant Al-gebar<br />
+Orion, hunter of the beast!<br />
+His sword hung gleaming at his side<br />
+And on his arm, the lion&#8217;s hide&mdash;<br />
+Scattered across the midnight air<br />
+The golden radiance of its hair.&#8221;</p>
+
+<p>Al-Sufi says it &#8220;is represented by the figure of a standing man, to the
+south of the sun&#8217;s path. This constellation very much resembles a human
+figure with a head and two shoulders. It is called <i>al-djabbar</i>, &#8216;the
+Giant,&#8217; because it has two thrones, holds a club in his hand, and is
+girded with a sword.&#8221; Orion is supposed to have been a son of<span class="pagenum"><a name="Page_274" id="Page_274">[Pg 274]</a></span> Neptune;
+but there are many stories of the origin of the name. It is also said to
+be derived from the Greek word &#8036;&#961;&#945;, because the constellation was
+used to mark the different times of the year. According to the ancient
+fable, Orion was killed by a scorpion, and was placed in the sky at the
+request of Diana. According to Houzeau, the name comes from <i>oriri</i>, to be
+born. Scorpio rises when Orion sets, and he thinks that the idea of the
+ancients was that the Scorpion in this way kills the giant Orion.</p>
+
+<p>In ancient Egypt Orion was called <i>Sahu</i>. This name occurs on the
+monuments of the Ptolemies, and also on those of the Pharaohs. It is also
+mentioned in the <i>Book of the Dead</i>. It seems to have been considered of
+great importance in ancient Egypt, as its heliacal rising announced that
+of Sirius, which heralded the annual rising of the Nile.</p>
+
+<p>The constellation Eridanus lies south of Taurus, east of Cetus, and west
+of Lepus. In ancient times it was supposed to represent the Nile or the
+Po. Ptolemy merely calls it &#928;&#959;&#964;&#945;&#956;&#959;&#8166;
+&#7936;&#963;&#964;&#949;&#961;&#953;&#963;&#956;&#8056;&#962;, or asterism of
+the river. It was called Eridanus by the Greeks, and Fluvius by the
+Romans. It appears to correspond with the Hebrew Shicor. Al-Sufi calls it
+<i>al-nahr</i>, &#8220;the River.&#8221;</p>
+
+<p>One of the most interesting points in Al-Sufi&#8217;s most interesting work is
+the identity of the bright star known to the ancient astronomers as<span class="pagenum"><a name="Page_275" id="Page_275">[Pg 275]</a></span>
+<i>achir al-nahr</i>, &#8220;the End of the River,&#8221; and called by Ptolemy
+&#8217;&#917;&#963;&#967;&#945;&#964;&#959;&#962; &#964;&#959;&#8166; &#960;&#959;&#964;&#945;&#956;&#959;&#8166;,
+&#8220;the Last in the River.&#8221; Some astronomers have
+identified this star with &#945; Eridani (Achernar), a bright southern
+star of the 1st magnitude, south of Eridanus. But Al-Sufi&#8217;s description
+shows clearly that the star he refers to is really &#952; Eridani;
+and the reader will find it interesting to follow his description with a
+star map before him. Describing Ptolemy&#8217;s 34th star of Eridanus (the star
+in question), he says, &#8220;the 34th star is found before [that is west of]
+these three stars [the 31st, 32nd, and 33rd, which are &#965;<sup>2</sup>, Du,
+and &#965;&prime; in Proctor&#8217;s Atlas], the distance between it and that of
+the three which is nearest being about 4 cubits [9&deg; 20&prime;]. It is of the
+first magnitude; it is that which is marked on the southern astrolabe, and
+called <i>achir al-nahr</i>, &#8216;the End of the River.&#8217; There are before this
+bright one two stars, one to the south, [&#963; Eridani, not shown in
+Proctor&#8217;s small Atlas], the other to the north [&#953; Eridani];
+Ptolemy does not mention these. One of these stars is of the 4th
+magnitude, the other of the 5th. There is behind the same [that is, east
+of it] a star of the 4th magnitude distant from it two cubits [&#949;
+Eridani]. To the south of the three stars which follow the bright one
+there are some stars of the 4th and 5th magnitudes, which he [Ptolemy] has
+not mentioned.&#8221;</p>
+
+<p>Now, a glance at a star map of this region will<span class="pagenum"><a name="Page_276" id="Page_276">[Pg 276]</a></span> show clearly that the
+bright star referred to by Al-Sufi is undoubtedly &#952; Eridani,
+which is therefore the star known to the ancients as the &#8220;End of the
+River,&#8221; or the &#8220;Last in the River.&#8221;</p>
+
+<p>The position given by Ptolemy agrees fairly well with Al-Sufi&#8217;s
+description, although the place is slightly erroneous, as is also the case
+with Fomalhaut and &#946; Centauri. It is impossible to suppose that
+either Ptolemy or Al-Sufi could have seen &#945; Eridani, as it is too
+far south to be visible from their stations, and, owing to the precession
+of the equinoxes, the star was still further south in ancient times.
+Al-Sufi says distinctly that the distance between Ptolemy&#8217;s 33rd star
+(which is undoubtedly <i>h</i> Eridani, or Proctor&#8217;s &#965;&prime;) and the 34th
+star was &#8220;4 cubits,&#8221; or 9&deg; 20&prime;. The actual distance is about 9&deg; 11&prime;, so
+that Al-Sufi&#8217;s estimate was practically correct. Halley, in his <i>Catalogus
+Stellarium Australium</i>, identifies Ptolemy&#8217;s star with &#952;
+Eridani, and Baily agreed with him.<a name='fna_430' id='fna_430' href='#f_430'><small>[430]</small></a> Ulugh Beigh also identifies the
+&#8220;Last in the River&#8221; with &#952; Eridani. The Arabic observer Mohammed
+Ali Achsasi, who observed in the seventeenth century, called &#952;
+Eridani <i>Achr al-nahr</i>, and rated it first magnitude.<a name='fna_431' id='fna_431' href='#f_431'><small>[431]</small></a> To argue, as
+Bode and Flammarion have done, that Ptolemy and Al-Sufi may have heard of
+&#945; Eridani from travellers in the southern<span class="pagenum"><a name="Page_277" id="Page_277">[Pg 277]</a></span> hemisphere, is to beg
+the whole question at issue. This is especially true with reference to
+Al-Sufi, who says, in the preface to his work, that he has described the
+stars &#8220;as seen with my own eyes.&#8221; &#945; Eridani is over 11 &#8220;cubits&#8221;
+from <i>h</i> Eridani instead of &#8220;4 cubits&#8221; as Al-Sufi says. This shows
+conclusively that the star seen by Al-Sufi was certainly <i>not</i> &#945;
+Eridani. The interest of the identification is that Al-Sufi rated &#952;
+Eridani of the <i>first</i> magnitude, whereas it is now only 3rd
+magnitude! It was measured 3&middot;06 at Harvard and estimated 3&middot;4 by Stanley
+Williams, so that it has evidently diminished greatly in brightness since
+Al-Sufi&#8217;s time. There is an interesting paper on this subject by Dr.
+Anderson (the discoverer of Nova Aurig&aelig; and Nova Persei) in <i>Knowledge</i>
+for July, 1893, in which he states that the &#8220;Last in the River,&#8221; according
+to the statements of Hipparchus and Ptolemy, <i>did</i> rise above their
+horizon at a certain time of the year, which &#945; Eridani could not
+possibly have done. This seems sufficient to settle the question in favour
+of &#952; Eridani. Dr. Anderson says, &#8220;It is much to be regretted
+that Professor Schjellerup, the able and industrious translator of Sufi,
+has allowed this to escape his notice, and helped in the preface and note
+to his work to propagate the delusion that &#945; Eridani is Ptolemy&#8217;s
+&#8216;Last in the River&#8217;&#8221;; and in this opinion I fully concur. Al-Sufi&#8217;s clear
+account places it beyond a doubt that the star<span class="pagenum"><a name="Page_278" id="Page_278">[Pg 278]</a></span> known to Hipparchus,
+Ptolemy, Al-Sufi, and Ulugh Beigh as the &#8220;Last in the River&#8221; was &#952;
+Eridani. &#952; must have diminished greatly in brightness since
+Al-Sufi&#8217;s time, for in ranking it as 1st magnitude he placed it in a very
+select list. He only rated thirteen stars in the whole heavens as being of
+the 1st magnitude. These are: Arcturus, Vega, Capella, Aldebaran, Regulus,
+&#946; Leonis, Fomalhaut, Rigel, &#952; Eridani, Sirius, Procyon,
+Canopus, and &#945; Centauri. <i>All</i> these stars were actually <i>seen</i>
+by Al-Sufi, <i>and described from his own observations</i>. He does not mention
+&#945; Eridani, as it was not visible from his station in Persia.</p>
+
+<p>&#952; Eridani is a splendid double star (3&middot;40, 4&middot;49: 8&Prime;&middot;38, 1902,
+Tebbutt). I found the components white and light yellow with 3-inch
+refractor in the Punjab. Dr. Gould thinks that one of the components is
+variable to some extent. This is interesting, considering the brilliancy
+of the star in Al-Sufi&#8217;s time. The brighter component was found to be a
+spectroscopic binary by Wright, so that on the whole the star is a most
+interesting object.</p>
+
+<p>The small constellation Lepus, the Hare, lies south of Orion. Pliny calls
+it Dasypus, and Virgil Auritus. In ancient Egypt it was the symbol of
+vigilance, prudence, fear, solitude, and speed.<a name='fna_432' id='fna_432' href='#f_432'><small>[432]</small></a> It may perhaps
+represent the hare hunted by Orion;<span class="pagenum"><a name="Page_279" id="Page_279">[Pg 279]</a></span> but some say it was placed in the sky
+to commemorate a terrible plague of hares which occurred in Sicily in
+ancient times.</p>
+
+<p>A little north-west of the star &#956; Leporis is Hind&#8217;s &#8220;crimson
+star&#8221; (R.A. 4<sup>h</sup> 53<sup>m</sup>, S. 14&deg; 57&prime;, 1900) described by him as &#8220;of the most
+intense crimson, resembling a blood drop on the background of the sky; as
+regards depth of colour, no other star visible in these latitudes could be
+compared with it.&#8221; It is variable from about the 6th to the 8th magnitude,
+with a period of about 436 days from maximum to maximum.</p>
+
+<p>The constellation Canis Major, the Great Dog, is remarkable for containing
+Sirius, the brightest star in the heavens. In the Greek mythology it was
+supposed to represent a dog given by Aurora to Cephalus as the swiftest of
+all dogs. Cephalus wished to match it against a fox which he thought
+surpassed all animals for speed. They both ran for so long a time, so the
+story goes, that Jupiter rewarded the dog by placing it among the stars.
+But probably the dog comes from Anubis, the dog-headed god of the ancient
+Egyptians. According to Brown, Theogirius (<span class="smcaplc">B.C.</span> 544) refers to the
+constellation of the Dog.<a name='fna_433' id='fna_433' href='#f_433'><small>[433]</small></a> He thinks that Canis Major is probably &#8220;a
+reduplication&#8221; of Orion; Sirius and &#946; Canis Majoris corresponding
+to &#945; and &#947; Orionis; &#948;, 22, and &#949; Canis
+Majoris to the stars in Orion&#8217;s belt (&#948;, &#949;, and<span class="pagenum"><a name="Page_280" id="Page_280">[Pg 280]</a></span> &#950;
+Orionis); and &#951;; and &#954; Canis Majoris with &#954; and
+&#946; Orionis.<a name='fna_434' id='fna_434' href='#f_434'><small>[434]</small></a></p>
+
+<p>The Arabic name of Sirius was <i>al-schira</i>, which might easily be corrupted
+into Sirius. The Hebrew name was Sihor. According to Plutarch, the
+Ethiopians paid regal honours to the Celestial Dog. The Romans used to
+sacrifice a dog in its honour at the fetes called Robigalia, which were
+held on the seventh day before the Calends of May, and nine days after the
+entry of the sun into Taurus. Pliny says, &#8220;Hoc tempus Varro determinat
+sole decimam partem Tauri obtinenti quod canis occidit, sidus per se
+vehemens,&#8221; etc.<a name='fna_435' id='fna_435' href='#f_435'><small>[435]</small></a></p>
+
+<p>Owing to some remarks of Cicero, Horace, and Seneca, it has been supposed
+that in ancient times Sirius was of red colour. Seneca says, &#8220;Nec mirum
+est, si terra omnis generis et varia evaporatio est; quam in c&oelig;lo
+quoque non unus appareat color rerum, sed acrior sit Canicul&aelig; rubor,
+Nartis remissior, Jovis nullus, in lucem puram nitore perducto.&#8221;<a name='fna_436' id='fna_436' href='#f_436'><small>[436]</small></a> It
+is now brilliantly white with a bluish tinge. But this change of colour is
+somewhat doubtful. The remarks of the ancient writers may possibly refer
+to its great brilliancy rather than its colour. Al-Sufi says nothing about
+its colour, and it was probably<span class="pagenum"><a name="Page_281" id="Page_281">[Pg 281]</a></span> a white star in his time. If it were red
+in his day he would most probably have mentioned the fact, as he does in
+the case of several red stars. Brown, however, quotes the following from
+Ibn Alraqqa, an Arabian observer:&mdash;</p>
+
+<p class="poem">&#8220;I recognize Sirius <i>shining red</i>, whilst the morning is becoming white.<br />
+The night fading away, has risen and left him,<br />
+The night is not afraid to lose him, since he follows her.&#8221;</p>
+
+<p>Schjellerup thinks that it is very doubtful that Sirius was really red as
+seen by Hipparchus and Ptolemy. But in an exhaustive inquiry made by Dr.
+See on the supposed change of colour,<a name='fna_437' id='fna_437' href='#f_437'><small>[437]</small></a> he comes to the conclusion that
+Sirius was really red in ancient times. Seneca states distinctly that it
+was redder than Mars (see extract above), and other ancient writers refer
+to its red colour. It has been generally supposed that the Arabian
+astronomer Alfraganus, in his translation of Ptolemy&#8217;s <i>Almagest</i>, refers
+to only five red stars observed by Ptolemy, namely, Arcturus, Aldebaran,
+Betelgeuse, Antares, and Pollux. But Dr. See shows that this idea is due
+to a mistranslation of Alfraganus by Plato Tibertinus in 1537, and that
+Ptolemy did not speak of &#8220;five red stars,&#8221; but five <i>nebulous</i> stars, as
+stated by Christmann and Golius. Ptolemy described Sirius as &#8017;&#960;&#8057;&#954;&#953;&#961;&#961;&#959;&#962;,
+&#8220;fiery red,&#8221; the same word used with reference to the other
+stars mentioned above. The change<span class="pagenum"><a name="Page_282" id="Page_282">[Pg 282]</a></span> of colour, if any, probably took place
+before Al-Sufi&#8217;s time.</p>
+
+<p>Dr. See says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Prof. Newcomb rejects the former well-authenticated redness of
+Sirius, because he cannot explain the fact. But the ink was scarcely
+dry on his new book on the stars, in which he takes this position,
+when Nova Persei blazed forth in 1901; and observers saw it change
+colour from day to day and week to week. Could any one explain the
+cause of these numerous and conspicuous changes of colour? Shall we,
+then, deny the changes of colour in Nova Persei, some of which were
+noticed when it was nearly as bright as Sirius?&#8221;<a name='fna_438' id='fna_438' href='#f_438'><small>[438]</small></a></p></div>
+
+<p>On the ceiling of the Memnonium at Thebes the heliacal rising of Sirius is
+represented under the form and name of Isis. The coincidence of this
+rising with the annual rising of the Nile is mentioned by Tibullus and
+Aclian. About 4000 <span class="smcaplc">B.C.</span> the heliacal rising of Sirius coincided with the
+summer solstice (about June 21) and the beginning of the rising of the
+Nile. The festival in honour of this event was held by the Egyptians about
+July 20, and this marked the beginning of the sacred Egyptian year. On the
+summit of Mount Pelion in Thessaly there was a temple dedicated to Zeus,
+where sacrifices were offered at the rising of Sirius by men of rank who
+were chosen for the purpose by the priests and wore fresh sheepskins.</p>
+
+<p><span class="pagenum"><a name="Page_283" id="Page_283">[Pg 283]</a></span>Sirius seems to have been worshipped by the ancient Egyptians under the
+name of Sothis, and it was regarded as the star of Isis and Osiris. The
+last name without the initial O very much resembles our modern name.</p>
+
+<p>According to Al-Sufi, the Arabians called Sirius <i>al-schira al-ab&ucirc;r</i>,
+&#8220;Sirius which has passed across,&#8221; also <i>al-schira al Jam&acirc;nija</i>, &#8220;the
+Sirius of Y&eacute;men.&#8221; He says it is called <i>al-ab&ucirc;r</i>, &#8220;because it has passed
+across the Milky Way into the southern region.&#8221; He relates a mythological
+story why Sirius &#8220;fled towards the south&#8221; and passed across the Milky Way
+towards Suhail (Canopus). The same story is told by Albufaragius<a name='fna_439' id='fna_439' href='#f_439'><small>[439]</small></a>
+(thirteenth century). (The story was probably derived from Al-Sufi.) Now,
+it seems to me a curious and interesting fact that the large proper motion
+of Sirius would have carried it across the Milky Way from the eastern to
+the western border in a period of 60,000 years. Possibly the Arabian story
+may be based on a tradition of Sirius having been seen on the opposite, or
+eastern, side of the Milky Way by the men of the early Stone Age. However
+this may be, we know from the amount and direction of the star&#8217;s proper
+motion that it must have passed across the Milky Way from east to west
+within the period above stated. The Arabic name <i>al-ab&ucirc;r</i> is not,
+therefore, a merely fanciful<span class="pagenum"><a name="Page_284" id="Page_284">[Pg 284]</a></span> one, but denotes an <i>actual fact</i>. The
+proper motion of Sirius could not possibly have been known to the
+ancients, as it was only revealed by accurate modern observations.</p>
+
+<p>The little constellation Canis Minor, the Little Dog, lies south of Gemini
+and Cancer. Small as it is, it was one of the original forty-eight
+constellations of Ptolemy. In the Greek mythology it was supposed to
+represent either one of Diana&#8217;s hunting dogs, or one of Orion&#8217;s hounds.
+Ovid calls it the dog of Icarus. Others say it was the dog of Helen, who
+was carried off by Paris. According to the old poets, Orion&#8217;s dog, or the
+dog of Icarus, threw himself into a well after seeing his master perish.
+The name Fovea, given to the constellation by Bayer, signifies a pit where
+corn was deposited. This comes from the fact that the rising of the star
+Procyon (&#945; Canis Minoris) indicated the season of abundance. But
+Lalande thought it more probable that the idea of a pit came from the
+Greek &#963;&#949;&#953;&#961;&#8056;&#962;, which means a corn store, and that it was
+confounded with Sirius.</p>
+
+<p>The name of the bright star Procyon (&#945; Canis Minoris) is derived
+from the Greek &#960;&#961;&#959;&#954;&#8059;&#969;&#957;, &#8220;the advanced day,&#8221; because it appeared
+in the morning sky before Sirius. Procyon was called by the Hindoos
+Hanouman after their famous monkey god, from whose tail a bridge is said
+to have been formed to enable the army of Rama to pass from India to
+Ceylon. Al-Sufi says that the star was<span class="pagenum"><a name="Page_285" id="Page_285">[Pg 285]</a></span> marked on the old astrolabes as
+<i>al-schira al-schamia</i>, &#8220;the Syrian Sirius.&#8221; It was also called, he says,
+<i>al-schira al-gumaisa</i>, &#8220;the Sirius with blear eyes&#8221; (!) from weeping
+because Sirius had passed across the Milky Way, Procyon remaining on the
+eastern side. Here we have the same legend again. The proper motion of
+Procyon (about the same in amount and direction as that of Sirius) shows
+that the star has been on the eastern side of the Milky Way for many ages
+past. About 60,000 years hence, Procyon will be near the star &#952;
+Canis Majoris, and will then&mdash;like Sirius&mdash;have passed across the Milky
+Way.</p>
+
+<p>Argo, the Ship, is a large constellation south of Hydra, Monoceros, and
+Canis Major. It is called by Al-Sufi <i>al-saf&icirc;na</i>, &#8220;the Ship.&#8221; It is
+supposed to represent the first ship ever built. The name is derived from
+the builder Argo, or from the Greek word &#8217;&#913;&#961;&#947;&#8056;&#962;. This ship is said
+to have been built in Thessaly by order of Minerva and Neptune, to go on
+the expedition for the conquest of the golden fleece. The date of this
+expedition, commanded by Jason, is usually fixed at 1300 or 1400 <span class="smcaplc">B.C.</span> With
+reference to the position of this supposed ship in the sky, Proctor says,
+&#8220;It is noteworthy that when we make due correction for the effects of
+precession during the past 4000 years, the old constellation Argo is set
+on an even keel, instead of being tilted some 45&deg; to the horizon, as at
+present when<span class="pagenum"><a name="Page_286" id="Page_286">[Pg 286]</a></span> due south.&#8221; He connects Argo with Noah&#8217;s Ark.</p>
+
+<p>The brightest star of Argo is Canopus, called Suha&iuml;l by Al-Sufi. It is the
+second brightest star in the heavens; but it is not visible in northern
+latitudes. The Harvard photometric measures make it nearly one magnitude
+brighter than the zero magnitude, about two magnitudes brighter than
+Aldebaran, and about half the brightness of Sirius. This fine star has
+been suspected of variable light. Webb says, &#8220;It was thought (1861) in
+Chili brighter than Sirius.&#8221; Observing it in the Punjab, the present
+writer found it on several occasions but little inferior to Sirius,
+although very low on the southern horizon. From recent observations by Mr.
+H. C. McKay in Australia, he believes that it is variable to the extent of
+at least half a magnitude.<a name='fna_440' id='fna_440' href='#f_440'><small>[440]</small></a> But it is difficult to establish
+variations of light in very bright stars. The parallax of Canopus is
+<i>very</i> small, so its distance from the earth is very great, and it must be
+a sun of gigantic size. According to Al-Fargani, Canopus was called the
+star of St. Catherine by the Christian pilgrims in the tenth century.<a name='fna_441' id='fna_441' href='#f_441'><small>[441]</small></a>
+It was called Suha&iuml;l by the old Arabians, a name apparently derived from
+the root <i>sahl</i>, &#8220;a plain&#8221;; and Schjellerup suggests that the name was
+probably applied to this and some other southern<span class="pagenum"><a name="Page_287" id="Page_287">[Pg 287]</a></span> stars because they seem
+to move along a plain near the southern horizon. Al-Sufi says that he
+measured the latitude of Schiraz in Persia, where he observed, and found
+it to be 29&deg; 36&prime;; and hence for that place Canopus, when on the meridian,
+had an altitude of about 9&deg;. Canopus was the ancient name of Aboukir in
+Egypt, and is said to have derived its name from the pilot of Menelaus,
+whose name was Kanobus, and who died there from the bite of a snake. The
+star is supposed to have been named after him, and it was worshipped by
+the ancient Egyptians.</p>
+
+<p>Al-Sufi does not mention the famous variable star &#951; Arg&ucirc;s, which,
+owing to the precession of the equinoxes, he might possibly have seen
+<i>close to the horizon</i>, if it had been a bright star in his day. It lies
+between &#966; Velorum and &#945; Crucis. Both of these stars are
+mentioned by Al-Sufi, but he says nothing of any bright star (or indeed
+any star) between them. This negative evidence tends to show that &#951;
+Arg&ucirc;s was not visible to the naked eye in Al-Sufi&#8217;s time. This
+extraordinary star has in modern times varied through all degrees of
+brightness from Sirius down to the 8th magnitude! Sch&ouml;nfeld thought that a
+regular period is very improbable. It seems to be a sort of connecting
+link between the long period variables and the <i>nov&aelig;</i> or temporary stars.
+It is reddish in colour, and the spectrum of its light is very similar to
+that of the temporary stars. Whether it will<span class="pagenum"><a name="Page_288" id="Page_288">[Pg 288]</a></span> ever become a brilliant
+object again, time alone can tell; but from the fact that it was
+presumably faint in Al-Sufi&#8217;s time, and afterwards increased to the
+brightness of Sirius, it seems possible that its light may again revive.</p>
+
+<p>The long constellation Hydra lies south of Cancer, Leo, Crater, Corvus,
+Virgo, and Libra. It was also called Asina, Coluber, Anguis, Sublimatus,
+etc. In the Greek mythology it was supposed to represent the Lern&aelig;an
+serpent killed by Hercules. According to Ovid, who fixed its acronycal
+rising for February 14, it had a common origin with Corvus and Crater.
+Apollo, wishing to sacrifice to Jupiter, sent the Crow with a cup to fetch
+water. On his way to the well the Crow stopped at a fig tree and waited
+for the fruit to ripen! Afterwards, to excuse his delay, he said that a
+serpent had prevented him from drawing the water. But Apollo, to punish
+the Crow for his deception, changed his plumage from white to black, and
+ordered the serpent to prevent the Crow from drinking.<a name='fna_442' id='fna_442' href='#f_442'><small>[442]</small></a> Hydra was
+called by Al-Sufi <i>al-schudja</i>, &#8220;the Serpent, or Hydra.&#8221; He says that &#8220;it
+contains twenty-five stars in the figure and two &#8216;outside&#8217;, and its head
+is to the south of the southern scale of the Balance&#8221; (&#945; Libr&aelig;).
+But this is clearly a mistake (one of the very few errors to be found in
+Al-Sufi&#8217;s work), for he goes on to say that the head is composed of four
+stars<span class="pagenum"><a name="Page_289" id="Page_289">[Pg 289]</a></span> forming a figure like the head of a horse, and he adds, &#8220;This head
+is in the middle between <i>al-shira al-gumaisa</i> [Procyon] and <i>Kalb
+al-asad</i> [Regulus] the Heart, inclining from these two stars a little to
+the south.&#8221; This clearly indicates the stars &#948;, &#949;, &#951;, and &#963;
+Hydr&aelig; which, with &#950; Hydr&aelig;, have always been considered as
+forming the Hydra&#8217;s head. These stars lie south of &#945; and &#946;
+Cancri, not south of Libra as Al-Sufi says (doubtless by a slip of the
+pen).</p>
+
+<p>Ptolemy&#8217;s 12th star of Hydra (&#945; Hydr&aelig;) is, Al-Sufi says, &#8220;the
+bright red star which is found at the end of the neck where the back
+begins; it is of the 2nd magnitude. It is that which is marked on the
+astrolabe as <i>unk al-schudja</i>, &#8216;the neck of the serpent,&#8217; also <i>al-fard</i>,
+&#8216;the solitary one.&#8217;&#8221; Al-Sufi&#8217;s estimate of its brightness agrees well with
+modern measures; but it has been suspected of variable light. Sir John
+Herschel&#8217;s estimates at the Cape of Good Hope varied from 1&middot;75 to 2&middot;58
+magnitude. He thought that its apparent variation might be due to its
+reddish colour, and compares it to the case of &#945; Cassiopei&aelig;. But
+as this latter star is now <i>known</i> to be irregularly variable it seems
+probable that &#945; Hydr&aelig; may be variable also. Gemmill found it
+remarkably bright on May 9, 1883, when he thought it nearly equal to
+Pollux (1&middot;2 magnitude). On the other hand, Franks thought it nearer the
+3rd than the 2nd magnitude on March 2, 1878. On April 9, 1884, the<span class="pagenum"><a name="Page_290" id="Page_290">[Pg 290]</a></span>
+present writer found it only slightly less than Regulus (1&middot;3 magnitude).
+On April 6, 1886, how-ever, it was considerably less than Regulus, but
+half a magnitude brighter than &#946; Canis Minoris, or about 2&#189;
+magnitude. In the Chinese Annals it is called the &#8220;Red Bird.&#8221; In a list of
+thirty stars found on a tablet at Birs-Nimroud, it is called &#8220;The son of
+the supreme temple.&#8221; Although to the naked eye deserving the name of
+Alphard or &#8220;the solitary one,&#8221; it is by no means an isolated star when
+examined with a telescope. It has a faint and distant companion, observed
+by Admiral Smyth; and about 25&prime; to the west of it Ward saw a small double
+star (8, 13: 90&deg;: 50&Prime;). With a 3-inch refractor in the Punjab, I saw a
+small star of about 8&#189; magnitude to the south and a little east of the
+bright star, probably identical with Smyth&#8217;s companion. Farther off in the
+same direction I saw a fainter star, and others at greater distances in
+the field. There is also a faint star a little to the north. I also saw
+Ward&#8217;s double with the 3-inch telescope.</p>
+
+<p>There is some difficulty in identifying the stars numbered by Ptolemy 13,
+14, and 15 in Hydra. Having plotted a map from Ptolemy&#8217;s positions (as
+given by Al-Sufi), I have come to the conclusion that Ptolemy&#8217;s stars are
+13 = &#954; Hydr&aelig;; 14 = &#965;; and 15 = &#955; Hydr&aelig;,
+probably. From the clear description given by Al-Sufi of the stars
+<span class="pagenum"><a name="Page_291" id="Page_291">[Pg 291]</a></span>observed by <i>him</i>, I find that <i>his</i> stars are 13 = &#965;<sub>1</sub>; 14 =
+&#965;<sub>2</sub>; and 15 = &#955; Hydr&aelig;. We must, therefore, conclude
+that Ptolemy and Al-Sufi saw only three stars where now there are
+four,<a name='fna_443' id='fna_443' href='#f_443'><small>[443]</small></a> and that &#954; Hydr&aelig; was not seen, or at least is not
+mentioned by Al-Sufi. &#954; is, therefore, probably variable. It was
+rated 4 by Tycho Brah&eacute;, Bayer, and Hevelius; it is at present about 5th
+magnitude. If Ptolemy did not see &#965;<sub>2</sub> it is probably variable
+also, and, indeed, it has been suspected of variable light.<a name='fna_444' id='fna_444' href='#f_444'><small>[444]</small></a></p>
+
+<p>The small constellation of Crater, the Cup, lies north of Hydra, and south
+of Leo and Virgo. Al-Sufi calls it <i>al-batija</i>, &#8220;the Jar, or Cup.&#8221; He says
+the Arabians called it <i>al-malif</i>, &#8220;the Crib, or Manger.&#8221; According to
+Brown, the stars of Crater exactly form a Bakhian &#954;&#8049;&#957;&#952;&#945;&#961;&#959;&#962;, with
+its two handles rising above the two extremities of the
+circumference.<a name='fna_445' id='fna_445' href='#f_445'><small>[445]</small></a> An Asia Minor legend &#8220;connected Crater with the mixing
+of human blood with wine in a bowl.&#8221; Crater is referred to by Ovid in the
+lines&mdash;</p>
+
+<p class="poem">&#8220;Dixit et antiqui monumenta perennia facti<br />
+Anguis, Avis, Crater sidera, juncta micunt.&#8221;</p>
+
+<p>The star &#945; Crateris was rated 4th magnitude by<span class="pagenum"><a name="Page_292" id="Page_292">[Pg 292]</a></span> Al-Sufi and all
+other observers, and the Harvard measures make it 4&middot;20, a satisfactory
+agreement. It has three companions noted by Admiral Smyth. One of these he
+called &#8220;intense blood colour.&#8221; This is R Crateris, now known to be
+variable from above the 8th magnitude to below the 9th. Sir John Herschel
+called it an &#8220;intense scarlet star, a curious colour.&#8221; With 3-inch
+refractor in the Punjab I found it &#8220;full scarlet.&#8221; It is one of an open
+pair, the further of the two from &#945;. There is a third star about
+9th magnitude a little south of it. Ward saw a 13th magnitude star between
+&#945; and R with a 2&#8542;-inch (Wray) refractor. This I saw &#8220;readily&#8221;
+with my 3-inch. Smyth does not mention this faint star, although he used a
+much larger telescope.</p>
+
+<p>Corvus, the Crow, is a small constellation, north of Hydra. Aratus says
+&#8220;the Crow form seems to peck the fold of the water snake&#8221; (Hydra). The
+victory which Valerius Corvinus is said to have owed to a crow has given
+it the name of Pomptina, because the victory took place near the Pontine
+marshes.<a name='fna_446' id='fna_446' href='#f_446'><small>[446]</small></a> A quadrilateral figure is formed by its four brightest
+stars, &#947;, &#948;, &#946;, and &#949; Corvi. This figure has sometimes
+been mistaken for the Southern Cross by those who are not familiar with
+the heavens. But the stars of the Southern Cross are much brighter.</p>
+
+<p>The constellation Centaurus, the Centaur, lies<span class="pagenum"><a name="Page_293" id="Page_293">[Pg 293]</a></span> south of Hydra and Libra,
+and north of the Southern Cross. According to Dupuis, Centaurus represents
+the 3rd &#8220;labour of Hercules,&#8221; his triumph over the Centaurs.<a name='fna_447' id='fna_447' href='#f_447'><small>[447]</small></a> The
+Centaurs were supposed to be a people living in the vicinity of Mount
+Ossa, who first rode on horses. The constellation was also called Semivir,
+Chiron, Phobos, Minotaurus, etc. Al-Sufi says it &#8220;is represented by the
+figure of an animal, of which the forepart is the upper part of a man from
+the head to end of the back, and its hinder part is the hinder part of a
+horse, from the beginning of the back to the tail. It is to the south of
+the Balance [Libra] turning its face towards the east, and the hinder part
+of the beast towards the west.&#8221;</p>
+
+<p>Al-Sufi describes very clearly the four bright stars of the famous
+&#8220;Southern Cross.&#8221; Owing to precession these stars were some 7&deg; further
+north in the tenth century than they are at present, and they could have
+been all seen by Al-Sufi, when on the meridian. In the time of Ptolemy and
+Hipparchus, they were still further north, and about 5000 years ago they
+were visible in the latitude of London. Dante speaks of these four stars
+as emblematical of the four cardinal virtues, Justice, Temperance,
+Fortitude, and Prudence.</p>
+
+<p>Closely south-east of &#945; and &#946; Crucis is the dark spot in
+the Milky Way known as the &#8220;Coal Sack,&#8221;<span class="pagenum"><a name="Page_294" id="Page_294">[Pg 294]</a></span> which forms such a conspicuous
+object near the Southern Cross. It was first described by Pinzon in 1499;
+and afterwards by Lacaille in 1755. Although to the naked eye apparently
+black, photographs show that it contains many faint stars, but, of course,
+much less numerous than in the surrounding regions. The dark effect is
+chiefly caused by contrast with the brilliancy of the Milky Way
+surrounding it.</p>
+
+<p>Al-Sufi also mentions the bright stars &#945; and &#946; Centauri
+which follow the Southern Cross. He says that the distance between them
+&#8220;is four cubits,&#8221; that is about 9&deg; 20&prime;, but it is less than this now.
+&#945; has a large &#8220;proper motion&#8221; of 3&Prime;&middot;67 per annum, and was farther
+from &#946; in Al-Sufi&#8217;s time than it is at present. This, however,
+would not <i>wholly</i> account for the difference, and Al-Sufi&#8217;s over-estimate
+is probably due to the well-known effect by which the distance between two
+stars is <i>apparently</i> increased when they are near the horizon. Several of
+Al-Sufi&#8217;s distances between southern stars are over-estimated, probably
+for the same reason.</p>
+
+<p>The constellation Lupus, the Wolf, is south of Libra and Scorpio. It lies
+along the western border of the Milky Way. According to ancient writers it
+represents Lycaon, King of Arcadia, a contemporary of Cecrops, who is said
+to have sacrificed human victims, and on account of his cruelty was
+changed into a wolf. Another fable<span class="pagenum"><a name="Page_295" id="Page_295">[Pg 295]</a></span> is that it represents a wolf
+sacrificed by the Centaur Chiron. According to Brown, Lupus appears on the
+Euphratian planisphere discovered by George Smyth in the palace of
+Sennacherib. Al-Sufi called it <i>al-sabu</i>, &#8220;the Wild Beast.&#8221; It was also
+called <i>al-fand</i>, &#8220;the Leopard,&#8221; and <i>al-asada</i>, &#8220;the Lioness.&#8221;</p>
+
+<p>Ara, the Altar, lies south of Scorpio. According to ancient writers it
+represents an altar built by Vulcan, when the gods made war against the
+Titans. It is called by Al-Sufi <i>al-midjman</i>, &#8220;the Scent Box,&#8221; or &#8220;the
+Altar.&#8221;</p>
+
+<p>The little constellation Corona Australis, the Southern Crown, lies south
+and west of Sagittarius, east of Scorpio, and west of Telescopium. Aratus
+refers to the stars in Corona Australis as&mdash;</p>
+
+<p class="poem"><span style="margin-left: 9em;">&#8220;Other few</span><br />
+Before the Archer under his forefeet<br />
+Led round in circle roll without a name.&#8221;<a name='fna_449' id='fna_449' href='#f_449'><small>[449]</small></a></p>
+
+<p>But the constellation was known by the names Caduceus, Orbiculus, Corona
+Sagittarii, etc. The ancient poets relate that Bacchus placed this crown
+in the sky in honour of his mother Semele.<a name='fna_450' id='fna_450' href='#f_450'><small>[450]</small></a> Others say that it
+represents the crown conferred on Corinne of Thebes, famous as a poet.</p>
+
+<p>The small constellation Piscis Australis, or the<span class="pagenum"><a name="Page_296" id="Page_296">[Pg 296]</a></span> Southern Fish, lies
+south of Capricornus and Aquarius. In the most ancient maps it is
+represented as a fish drinking the water which flows from the urn of
+Aquarius.</p>
+
+<hr style="width: 25%;" />
+
+<p>A good many constellations have been added to the heavens since the days
+of Al-Sufi, and notes on some of these may be of interest.</p>
+
+<p><span class="smcap">Camelopardalis.</span>&mdash;This constellation first appears on a celestial
+planisphere published by Bartschius in the year 1624. It was not formed by
+Bartschius himself, but by the navigators of the sixteenth century. It
+lies south of Ursa Minor, north of Perseus and Auriga, east of Draco, and
+west of Cassiopeia. It contains no star brighter than the 4th magnitude.</p>
+
+<p><span class="smcap">Lynx.</span>&mdash;This constellation is south of Camelopardalis and Ursa Major, and
+north of Gemini and Cancer. It was formed by Hevelius in 1660, and he
+called it the Lynx, because, he said, it contained only faint stars and
+&#8220;it was necessary to have the eyes of a lynx&#8221; to see them! Some of them
+were, however, observed by Ptolemy and Al-Sufi, and are mentioned by the
+latter under Ursa Major.</p>
+
+<p><span class="smcap">Canes Venatici</span>, or the Hunting Dogs.&mdash;This was formed by Hevelius in 1660.
+It lies south of the Great Bear&#8217;s tail, north of Coma Berenices, east of
+Ursa Major, and west of Bo&ouml;tis. Its brightest stars &#945; (12) and
+&#946; (8) were observed by Al-Sufi,<span class="pagenum"><a name="Page_297" id="Page_297">[Pg 297]</a></span> and included by him in the
+&#8220;extern&#8221; stars of Ursa Major.</p>
+
+<p><span class="smcap">Coma Berenices.</span>&mdash;This constellation lies between Canes Venatici and Virgo.
+Although it was not included among the old forty-eight constellations of
+Ptolemy, it is referred to by Al-Sufi as the Plat, or Tress of Hair, and
+he included its stars Flamsteed 12, 15, and 21 in the &#8220;extern&#8221; stars of
+Leo. It was originally formed by the poet Callimachus in the third century
+<span class="smcaplc">B.C.</span>, but was not generally accepted until reformed by Hevelius.
+Callimachus lived at Alexandria in the reigns of Ptolemy Philadelphus and
+Ptolemy Euergetes, and was chief librarian of the famous library of
+Alexandria from about <span class="smcaplc">B.C.</span> 260 until his death in <span class="smcaplc">B.C.</span> 240. Eratosthenes
+was one of his pupils. The history of the constellation is as follows:
+Berenice, wife of Ptolemy Euergetes, made a vow, when her husband was
+leaving her on a military expedition, that if he returned in safety she
+would cut off her hair and consecrate it in the temple of Mars. Her
+husband returned, and she fulfilled her vow. But on the next day the hair
+had disappeared&mdash;stolen from the temple&mdash;and Conon the mathematician
+showed Ptolemy seven stars near the constellation of the Lion which did
+not belong to any constellation. These were formed into a constellation
+and called Berenice&#8217;s Hair. Conon is referred to by Catullus in the
+lines&mdash;</p>
+
+<p class="poem"><span class="pagenum"><a name="Page_298" id="Page_298">[Pg 298]</a></span>
+&#8220;Idem me ille Conon c&oelig;leste numine vidit<br />
+E. Berenico vertice C&aelig;sariem.&#8221;</p>
+
+<p>Coma Berenices first occurs as a distinct constellation in the catalogue
+contained in the Rudolphine Tables formed by Kepler (epoch 1600) from the
+observations of Tycho Brah&eacute;.<a name='fna_451' id='fna_451' href='#f_451'><small>[451]</small></a> Bayer substituted a sheaf of corn, an
+idea derived from an ancient manuscript.</p>
+
+<p><span class="smcap">Leo Minor.</span>&mdash;This small constellation lies between Ursa Major and Leo, and
+east of the Lynx. It was formed by Halley about the year 1660; but is
+referred to by Al-Sufi, who includes one of its stars (Fl. 41) in the
+&#8220;extern&#8221; stars of Leo. There are, however, several brighter stars in the
+group. The brightest, Fl. 46, was measured 3&middot;92 at Harvard. The star Fl.
+37 was called <i>pr&aelig;cipua</i> (or brightest) by Tycho Brah&eacute;, and rated 3, but
+as it was measured only 4&middot;77 at Harvard it may possibly have diminished in
+brightness.</p>
+
+<p><span class="smcap">Sextans.</span>&mdash;This constellation lies south of Leo, and north and east of
+Hydra. It was formed by Hevelius about the year 1680. According to the
+Harvard photometric measures its brightest star is Fl. 15 (4&middot;50).</p>
+
+<p><span class="smcap">Monoceros</span>, or the Unicorn, lies south of Gemini and Canis Minor, north of
+Canis Major and Argo, east of Orion, and west of Hydra. It appears on the
+planisphere of Bartschius, published in<span class="pagenum"><a name="Page_299" id="Page_299">[Pg 299]</a></span> 1624. According to Scaliger it is
+shown on an old Persian sphere. One of its stars, Fl. 22, is mentioned by
+Al-Sufi among the &#8220;extern&#8221; stars of Canis Major (No. 1). Another, Fl. 30,
+is given under Hydra (&#8220;Extern&#8221; No. 1) and Fl. 8, 13, and 15 are apparently
+referred to in Gemini. The star 15 Monocerotis is a little south of
+&#958; Geminorum, and was measured 4&middot;59 magnitude at Harvard. It was
+at one time supposed to be variable with a short period (about 3&#189;
+days), but this variation has not been confirmed. The spectrum is of the
+fifth type&mdash;with bright lines&mdash;a very rare type among naked-eye stars. It
+is a triple star (5, 8&middot;8, 11&middot;2: 2&Prime;&middot;9, 16&Prime;&middot;3) and should be seen with a
+4-inch telescope. It has several other small companions, one of which
+(139&deg;&middot;2: 75&Prime;&middot;7) has been suspected of variation in light. It was estimated
+8&#189; by Main in 1863, but only 12 by Sadler in 1875. Observing it on
+March 28, 1889, with 3-inch refractor, I found it about one magnitude
+brighter than a star closely preceding, and estimated it 8 or 8&#189;
+magnitude. It is probably variable and should be watched.</p>
+
+<p><span class="smcap">Scutum Sobieski.</span>&mdash;This is, or was, a small constellation in the southern
+portion of Aquila, which was formed by Hevelius in 1660 in honour of the
+Polish hero Sobieski. Its principal stars, which lie south-west of &#955;
+Aquil&aelig;, were mentioned by Al-Sufi and are referred to by him under that
+constellation. It contains a very bright spot of<span class="pagenum"><a name="Page_300" id="Page_300">[Pg 300]</a></span> Milky Way light, which
+may be well seen in the month of July just below the star &#955;
+Aquil&aelig;. Closely south of the star 6 Aquil&aelig; is a remarkable variable star R
+Scuti (R.A. 18<sup>h</sup> 42<sup>m</sup>&middot;2, S. 5&deg; 49&prime;). It varies from 4&middot;8 to 7&middot;8 with an
+irregular period. All the light changes can be observed with a good
+opera-glass.</p>
+
+<p><span class="smcap">Vulpecula</span>, the Fox.&mdash;This modern constellation lies south of Cygnus, north
+of Sagitta and Delphinus, east of Hercules, and west of Pegasus. It was
+formed by Hevelius in 1660. One of its stars, 6 Vulpecul&aelig;, is mentioned by
+Al-Sufi in describing the constellation Cygnus. Closely north-west of 32
+Vulpecul&aelig; is the short-period variable T Vulpecul&aelig;. It varies from 5&middot;5 to
+6&middot;2 magnitude, and its period is 4&middot;436 days. This is an interesting
+object, and all the changes of light can be observed with an opera-glass.</p>
+
+<p><span class="smcap">Lacerta.</span>&mdash;This little constellation lies south of Cepheus and north of
+Pegasus. Its formation was first suggested by Roger and Anthelm in 1679,
+and it was called by them &#8220;The Sceptre and the Hand of Justice.&#8221; It was
+named Lacerta by Hevelius in 1690, and this name it still retains. Al-Sufi
+seems to refer to its stars in his description of Andromeda, but does not
+mention any star in particular. It brightest star Fl. 7 (&#945;
+Lacert&aelig;) is about the 4th magnitude. About one degree south-west of 7 is 5
+Lacert&aelig;, a deep orange star with a blue companion in a fine field.</p>
+
+<p><span class="pagenum"><a name="Page_301" id="Page_301">[Pg 301]</a></span>There are some constellations south of the Equator which, although above
+Al-Sufi&#8217;s horizon when on the meridian, are not described by him, as they
+were formed since his time. These are as follows:&mdash;</p>
+
+<p><span class="smcap">Sculptor.</span>&mdash;This constellation lies south of Aquarius and Cetus, and north
+of Ph&oelig;nix. Some of its stars are referred to by Al-Sufi under Eridanus
+as lying within the large triangle formed by &#946; Ceti, Fomalhaut,
+and &#945; Ph&oelig;nicis. The brightest star is &#945;, about 12&deg;
+south of &#946; Ceti (4&middot;39 magnitude Harvard). About 7&deg; south-east of
+&#945; is the red and variable star R Sculptoris; variable from 6&middot;2 to
+8&middot;8 magnitude, with a period of about 376 days. Gould describes it as
+&#8220;intense scarlet.&#8221; It has a spectrum of the fourth type.</p>
+
+<p><span class="smcap">Ph&oelig;nix.</span>&mdash;This constellation lies south of Sculptor. Some of its stars
+are referred to by Al-Sufi, under Eridanus, as forming a boat-shaped
+figure. These are evidently &#945;, &#954;, &#956;, &#946;, &#957;, and &#947;.
+&#945; is at the south-eastern angle of Al-Sufi&#8217;s triangle referred to
+above (under &#8220;Sculptor&#8221;). (See Proctor&#8217;s Atlas, No. 3.)</p>
+
+<p><span class="smcap">Fornax</span>, the Furnace, lies south of Cetus, west of Eridanus, and east of
+Sculptor and Ph&oelig;nix. It was formed by Lacaille, and is supposed to
+represent a chemical furnace with an alembic and receiver! Its brightest
+star, &#945; Fornacis, is identical with 12 Eridani.</p>
+
+<p><span class="pagenum"><a name="Page_302" id="Page_302">[Pg 302]</a></span><span class="smcap">C&aelig;lum</span>,
+the Sculptor&#8217;s Tools, is a small constellation east of Columba, and
+west of Eridanus. It was formed by Lacaille. The brightest stars are
+&#945; and &#947;, which are about 4&#189; magnitude. &#945; has
+a faint companion; and &#947; is a wide double star to the naked eye.</p>
+
+<p><span class="smcap">Antlia</span>, the Air Pump, lies south of Hydra, east and north of Argo, and
+west of Centaurus. It was formed by Lacaille. It contains no star brighter
+than 4th magnitude. The brightest, &#945;, has been variously rated
+from 4 to 5, and Stanley Williams thinks its variability &#8220;highly
+probable.&#8221;</p>
+
+<p><span class="smcap">Norma</span>, the Rule, lies south of Scorpio. It contains no star brighter than
+the 4th magnitude.</p>
+
+<p><span class="smcap">Telescopium.</span>&mdash;This modern constellation lies south of Corona Australis,
+and north of Pavo. Its stars &#945;, &#948;, and &#950;, which lie near
+the northern boundary of the constellation, are referred to by Al-Sufi in
+his description of Ara.</p>
+
+<p><span class="smcap">Microscopium.</span>&mdash;This small constellation is south of Capricornus, and west
+of Piscis Australis. Its stars seem to be referred to by Al-Sufi as having
+been seen by Ptolemy, but he does not specify their exact positions. It
+contains no star brighter than 4&#189; magnitude.</p>
+
+<hr style="width: 25%;" />
+
+<p>South of Al-Sufi&#8217;s horizon are a number of constellations surrounding the
+south pole, which, of course, he could not see. Most of these have been
+formed since his time, and these will now be<span class="pagenum"><a name="Page_303" id="Page_303">[Pg 303]</a></span> considered; beginning with
+that immediately surrounding the South Pole (Octans), and then following
+the others as nearly as possible in order of Right Ascension.</p>
+
+<p><span class="smcap">Octans.</span>&mdash;This is the constellation surrounding the South Pole of the
+heavens. There is no bright star near the Pole, the nearest visible to the
+naked eye being &#963; Octantis, which is within one degree of the
+pole. It was estimated 5&middot;8 at Cordoba. The brightest star in the
+constellation is &#957; Octantis (&#945;, Proctor), which lies
+about 12 degrees from the pole in the direction of Indus and Microscopium.
+The Harvard measure is 3&middot;74 magnitude.</p>
+
+<p><span class="smcap">Hydrus</span>, the Water-Snake, is north of Octans in the direction of Achernar
+(&#945; Eridani). The brightest star is &#946;, which lies close
+to &#952; Octantis. The Harvard measure is 2&middot;90. Gould says its
+colour is &#8220;clear yellow.&#8221; It has a large proper motion of 2&Prime;&middot;28 per annum.
+Sir David Gill found a parallax of 0&Prime;&middot;134, and this combined with the
+proper motion gives a velocity of 50 miles a second at right angles to the
+line of sight. &#947; Hydri is a comparatively bright star of about
+the 3rd magnitude, about 15&#189; degrees from the South Pole. It is
+reddish, with a spectrum of the third type.</p>
+
+<p><span class="smcap">Horologium</span>, the Clock, is north of Hydra, and south of Eridanus. Three of
+its stars, &#945;, &#948;, and &#968;, at the extreme northern end of
+the constellation,<span class="pagenum"><a name="Page_304" id="Page_304">[Pg 304]</a></span> seem to be referred to by Al-Sufi in his description
+of Eridanus, but he does not give their exact positions. Most of the stars
+forming this constellation were below Al-Sufi&#8217;s horizon.</p>
+
+<p><span class="smcap">Reticulum</span>, the Net, is a small constellation to the east of Hydrus and
+Horologium. The brightest star of the constellation is &#945; (3&middot;36
+Harvard, 3&middot;3 Cordoba, and &#8220;coloured&#8221;).</p>
+
+<p><span class="smcap">Dorado</span>, the Sword Fish, lies east of Reticulum and west of Pictor. It
+contains only two stars brighter than the 4th magnitude. These are &#945;
+(3&middot;47 Harvard) and &#946; (3&middot;81 Harvard, but suspected of
+variation). About 3&deg; east of &#945; Reticuli is the variable star R
+Doradus. It varies from 4&middot;8 to 6&middot;8, and its period is about 345 days.
+Gould calls it &#8220;excessively red.&#8221; It may be followed through all its
+fluctuations of light with an opera-glass.</p>
+
+<p><span class="smcap">Mensa</span>, or Mons Mensa, the Table Mountain, lies between Dorado and the
+South Pole, and represents the Table Mountain of the Cape of Good Hope. It
+contains no star brighter than the 5th magnitude.</p>
+
+<p><span class="smcap">Pictor</span>, the Painter&#8217;s Easel, lies north of Doradus, and south of Columba.
+It contains no very bright stars, the brightest being &#945; (3&middot;30
+Harvard).</p>
+
+<p><span class="smcap">Volans</span>, the Flying Fish, is north of Mensa, and south and west of Argo.
+Its brighter stars, with the exception of &#945; and &#946;, form
+an irregular six-sided figure. Its brightest star is &#946; (3&middot;65)
+according<span class="pagenum"><a name="Page_305" id="Page_305">[Pg 305]</a></span> to the Harvard measures. The Cordoba estimates, however, range
+from 3&middot;6 to 4&middot;4, and Gould says its colour is &#8220;bright yellow.&#8221; Williams
+rated it 3&middot;8.</p>
+
+<p><span class="smcap">Cham&aelig;lion.</span>&mdash;This small constellation lies south of Volans, and north of
+Mensa and Octans. None of its stars are brighter than the 4th magnitude,
+its brightest being &#945; (4&middot;08 Harvard) and &#947; (4&middot;10).</p>
+
+<p><span class="smcap">Argo.</span>&mdash;This large constellation extends much further south than Al-Sufi
+could follow it. The most southern star he mentions is &#949; Carin&aelig;,
+but south of this are several bright stars. &#946; Carin&aelig; is 1&middot;80
+according to the Harvard measures; &#965; Carin&aelig;, 3&middot;08; &#952;,
+3&middot;03; &#969;, 3&middot;56; and others. A little north-west of &#953; is
+the long-period variable R Carin&aelig; (9<sup>h</sup> 29<sup>m</sup>&middot;7, S. 62&deg; 21&prime;, 1900). It
+varies from 4&middot;5 at maximum to 10 at minimum, and the period is about 309&middot;7
+days. A little east of R Carin&aelig; is another remarkable variable star, <i>l</i>
+Carin&aelig; (R.A. 9<sup>h</sup> 42<sup>m</sup>&middot;5, S. 62&deg; 3&prime;). It varies from 3&middot;6 to 5&middot;0
+magnitude, with a period of 35&#189; days from maximum to maximum. All the
+light changes can be observed with an opera-glass, or even with the naked
+eye. It was discovered at Cordoba. The spectrum is of the solar type (G).</p>
+
+<p><span class="smcap">Musca</span>, the Bee, is a small constellation south of the Southern Cross and
+Centaurus. Its brightest stars are &#945; (2&middot;84 Harvard) and &#946;
+(3&middot;26). These two stars form a fine pair south of<span class="pagenum"><a name="Page_306" id="Page_306">[Pg 306]</a></span> &#945; Crucis.
+Closely south-east of &#945; is the short-period variable R Musc&aelig;. It
+varies from 6&middot;5 to 7&middot;6 magnitude, and its period is about 19 hours. All
+its changes of light may be observed with a good opera-glass.</p>
+
+<p><span class="smcap">Apus</span>, the Bird of Paradise, lies south-east of Musca, and north of Octans.
+Its brightest star is &#945;, about the 4th magnitude. Williams calls
+it &#8220;deep yellow.&#8221; About 3&deg; north-west of &#945;, in the direction of
+the Southern Cross, is &#952; Apodis, which was found to be variable
+at Cordoba from 5&#189; to 6&#189;. The spectrum is of the third type, which
+includes so many variable stars.</p>
+
+<p><span class="smcap">Triangulum Australis</span>, the Southern Triangle, is a small constellation
+north of Apus, and south of Norma. A fine triangle, nearly isosceles, is
+formed by its three bright stars, &#945;, &#946;, &#947;, the brightest &#945;
+being at the vertex. These three stars form with &#945; Centauri an
+elongated cross. The stars &#946; and &#947; are about 3rd
+magnitude. &#946; is reddish. &#949; (4&middot;11, Harvard) is also
+reddish, and is nearly midway between &#946; and &#947;, and near
+the centre of the cross above referred to. &#945; is a fine star (1&middot;88
+Harvard) and is one of the brightest stars in the sky&mdash;No. 33 in a list of
+1500 highest stars given by Pickering. About 1&deg; 40&prime; west of &#949; is
+the short-period variable R Trianguli Australis (R.A. 15<sup>h</sup> 10<sup>m</sup>&middot;8, S.
+66&deg; 8&prime;) discovered at Cordoba in 1871. It varies from 6&middot;7 to 7&middot;4, and the
+period is about 3<sup>d</sup> 7<sup>h</sup>&middot;2. Although not visible to ordinary<span class="pagenum"><a name="Page_307" id="Page_307">[Pg 307]</a></span> eyesight it
+is given here, as it is an interesting object and all its light changes
+may be well seen with an opera-glass. A little south-east of &#946; is
+another short-period variable, S Trianguli Australis (R.A. 15<sup>h</sup> 52<sup>m</sup>&middot;2,
+S. 63&deg; 30&prime;), which varies from 6&middot;4 to 7&middot;4, with a period of 6&middot;3 days; and
+all its fluctuations of light may also be observed with a good
+opera-glass.</p>
+
+<p><span class="smcap">Circinus</span>, the Compass, is a very small constellation lying between
+Triangulum and Centaurus. Its brightest star, &#945;, is about 3&#189;
+magnitude, about 4&deg; south of &#945; Centauri.</p>
+
+<p><span class="smcap">Pavo</span>, the Peacock, lies north of Octans and Apus, and south of
+Telescopium. Its brightest star is &#945;, which is a fine bright star
+(2&middot;12 Harvard). &#954; is a short-period variable. It varies from 3&middot;8
+to 5&middot;2, and the period is about 9 days. This is an interesting object, as
+all the fluctations of light can be observed by the naked eye or an
+opera-glass. &#949; Pavonis was measured 4&middot;10 at Harvard, but the
+Cordoba estimates vary from 3&middot;6 to 4&middot;2. Gould says &#8220;it is of a remarkably
+blue colour.&#8221;</p>
+
+<p><span class="smcap">Indus.</span>&mdash;This constellation lies north of Octans, and south of Sagittarius,
+Microscopium, and Grus. One of its stars, &#945;, is probably referred
+to by Al-Sufi in his description of Sagittarius; it lies nearly midway
+between &#946; Sagittarii and &#945; Gruis, and is the brightest
+star of the constellation. The star &#949; Indi (4&middot;74 Harvard) has a
+remarkably large<span class="pagenum"><a name="Page_308" id="Page_308">[Pg 308]</a></span> proper motion of 4&Prime;&middot;68 per annum. Its parallax is about
+0&Prime;&middot;28, and the proper motion indicates a velocity of about 49 miles a
+second at right angles to the line of sight.</p>
+
+<p><span class="smcap">Toucan.</span>&mdash;This constellation lies north of Octans, and south of Ph&oelig;nix
+and Grus, east of Indus, and west of Hydrus. Its brightest star is &#945;, of about the 3rd magnitude.</p>
+
+<hr style="width: 25%;" />
+
+<p>There are seven &#8220;celestial rivers&#8221; alluded to by the ancient
+astronomers:&mdash;</p>
+
+<p>1. The Fish River, which flows from the urn of Aquarius.</p>
+
+<p>2. The &#8220;River of the Bird,&#8221; or the Milky Way in Cygnus.</p>
+
+<p>3. The River of the Birds&mdash;2, including Aquila.</p>
+
+<p>4. The River of Orion&mdash;Eridanus.</p>
+
+<p>5. The River of the god Marduk&mdash;perhaps the Milky Way in Perseus.</p>
+
+<p>6. The River of Serpents (Serpens, or Hydra).</p>
+
+<p>7. The River of Gan-gal (The High Cloud)&mdash;probably the Milky Way as a
+whole.</p>
+
+<p>There are four serpents represented among the constellations. These are
+Hydra, Hydrus, Serpens, and Draco.</p>
+
+<p>According to the late Mr. Proctor the date of the building of the Great
+Pyramid was about 3400 <span class="smcaplc">B.C.</span><a name='fna_452' id='fna_452' href='#f_452'><small>[452]</small></a> At this time the Spring
+Equinox was in<span class="pagenum"><a name="Page_309" id="Page_309">[Pg 309]</a></span>
+Taurus, and this is referred to by Virgil. But this was not so in Virgil&#8217;s
+time, when&mdash;on account of the precession of the equinoxes&mdash;the equinoctial
+point had already entered Pisces, in which constellation it still remains.
+At the date 3400 <span class="smcaplc">B.C.</span> the celestial equator ran along the whole length of
+the constellation Hydra, nearly through Procyon, and a little north of the
+bright red star Antares.</p>
+
+<p>The star Fomalhaut (&#945; Piscis Australis) is interesting as being
+the most southern 1st magnitude star visible in England, its meridian
+altitude at Greenwich being little more than eight degrees.<a name='fna_453' id='fna_453' href='#f_453'><small>[453]</small></a></p>
+
+<p>With reference to the Greek letters given to the brighter stars by Bayer
+(in his Atlas published in 1603), and now generally used by astronomers,
+Mr. Lynn has shown that although &#8220;Bayer did uniformly designate the
+brightest stars in each constellation by the letter &#945;,&#8221;<a name='fna_454' id='fna_454' href='#f_454'><small>[454]</small></a> it
+is a mistake to suppose&mdash;as has often been stated in popular books on
+astronomy&mdash;that he added the other Greek letters <i>in order of brightness</i>.
+That this is an error clearly appears from Bayer&#8217;s own &#8220;Explicatio&#8221; to his
+Atlas, and was long since pointed out by Argelander (1832), and by Dr.
+Gould in his <i>Uranometria Argentina</i>. Gould says,<span class="pagenum"><a name="Page_310" id="Page_310">[Pg 310]</a></span> &#8220;For the stars of each
+order, the sequence of the letters in no manner represents that of their
+brightness, but depended upon the positions of the stars in the figure,
+beginning usually at the head, and following its course until all the
+stars of that order of magnitude were exhausted.&#8221; Mr. Lynn says, &#8220;Perhaps
+one of the most remarkable instances in which the lettering is seen at a
+glance not to follow the order of the letters is that of the three
+brightest stars in Aquila [Al-Sufi&#8217;s &#8216;three famous stars&#8217;], &#947;
+being evidently brighter than &#946;. But there is no occasion to
+conjecture from this that any change of relative brightness has taken
+place. Bayer reckoned both of these two of the third magnitude, and
+appears to have arranged &#946; before &#947;, according to his
+usual custom, simply because &#946; is in the neck of the supposed
+eagle, and &#947; at the root of one of the wings.&#8221;<a name='fna_455' id='fna_455' href='#f_455'><small>[455]</small></a> Another good
+example is found in the stars of the &#8220;Plough,&#8221; in which the stars are
+evidently arranged in the order of the figure and not in the order of
+relative brightness. In fact, Bayer is no guide at all with reference to
+star magnitudes. How different Al-Sufi was in this respect!</p>
+
+<p>The stars Aldebaran, Regulus, Antares, and Fomalhaut were called royal
+stars by the ancients. The reason of this was that they lie roughly about
+90&deg; apart, that is 6 hours of Right Ascension. So, if through the north
+and south poles of the<span class="pagenum"><a name="Page_311" id="Page_311">[Pg 311]</a></span> heavens and each of these stars we draw great
+circles of the sphere, these circles will divide the sphere into four
+nearly equal parts, and the ancients supposed that each of these stars
+ruled over a quarter of the sphere, an idea probably connected with
+astrology. As the position of Aldebaran is R.A. 4<sup>h</sup> 30<sup>m</sup>, Declination
+North 16&deg; 19&prime;, and that of Antares is R.A. 16<sup>h</sup> 15<sup>m</sup>, Declination South
+25&deg; 2&prime;, these two stars lie at nearly opposite points of the celestial
+sphere. From this it follows that our sun seen from Aldebaran would lie
+not very far from Antares, and seen from Antares it would appear not far
+from Aldebaran.</p>
+
+<p>The following may be considered as representative stars of different
+magnitudes. For those of first magnitude and fainter I have only given
+those for which all the best observers in ancient and modern times agree,
+and which have been confirmed by modern photometric measures. The Harvard
+measures are given:&mdash;</p>
+
+<table border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td colspan="2">Brighter &nbsp; than</td>
+    <td>&#8220;zero magnitude&#8221;</td>
+    <td>Sirius (-1&middot;58); Canopus (-0&middot;86)</td></tr>
+<tr><td colspan="2">Zero magnitude</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>&#945; Centauri (0&middot;06)</td></tr>
+<tr><td colspan="2">0 to 0&middot;4 magnitude</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>Vega (0&middot;14); Capella (0&middot;21);<br /><span style="margin-left: 1em;">Arcturus (0&middot;24); Rigel (0&middot;34)</span></td></tr>
+<tr><td>0&middot;5</td>
+    <td>magnitude</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>Procyon (0&middot;48)</td></tr>
+<tr><td>1st</td>
+    <td align="center">"</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>Aldebaran (1&middot;06)</td></tr>
+<tr><td>2nd</td>
+    <td align="center">"</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>&#945; Persei (1&middot;90); &#946; Aurig&aelig; (2&middot;07)</td></tr>
+<tr><td><span class="pagenum"><a name="Page_312" id="Page_312">[Pg 312]</a></span>3rd</td>
+    <td align="center">"</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>&#951; Bo&ouml;tis (3&middot;08); &#950; Capricorni (2&middot;98)</td></tr>
+<tr><td>4th</td>
+    <td align="center">"</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>&#961; Leonis (3&middot;85); &#955; Scorpii (4&middot;16);<br />
+    <span style="margin-left: 1em;">&#947; Crateris(4&middot;14); &#961; Herculis (4&middot;14)</span></td></tr>
+<tr><td>5th</td>
+    <td align="center">"</td>
+    <td align="center">... &nbsp; ... &nbsp; ...</td>
+    <td>&#959; Pegasi (4&middot;85); &#956; Capricorni (5&middot;10)</td></tr></table>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_313" id="Page_313">[Pg 313]</a></span></p>
+<h2><a name="CHAPTER_XX" id="CHAPTER_XX"></a>CHAPTER XX</h2>
+<p class="title">The Visible Universe</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">Some</span> researches on the distribution of stars in the sky have recently been
+made at the Harvard Observatory (U.S.A.). The principal results are:&mdash;(1)
+The number of stars on any &#8220;given area of the Milky Way is about twice as
+great as in an equal area of any other region.&#8221; (2) This ratio does not
+increase for faint stars down to the 12th magnitude. (3) &#8220;The Milky Way
+covers about one-third of the sky and contains about half of the stars.&#8221;
+(4) There are about 10,000 stars of magnitude 6&middot;6 or brighter, 100,000
+down to magnitude 8&middot;7, one million to magnitude 11, and two millions to
+magnitude 11&middot;9. It is estimated that there are about 18 millions of stars
+down to the 15th magnitude visible in a telescope of 15 inches
+aperture.<a name='fna_456' id='fna_456' href='#f_456'><small>[456]</small></a></p>
+
+<p>According to Prof. Kapteyn&#8217;s researches on stellar distribution, he finds
+that going out from the earth into space, the &#8220;star density&#8221;&mdash;that is,<span class="pagenum"><a name="Page_314" id="Page_314">[Pg 314]</a></span>
+the number of stars per unit volume of space&mdash;is fairly constant until we
+reach a distance of about 200 &#8220;light years.&#8221; From this point the density
+gradually diminishes out to a distance of 2500 &#8220;light years,&#8221; at which
+distance it is reduced to about one-fifth of the density in the sun&#8217;s
+vicinity.<a name='fna_457' id='fna_457' href='#f_457'><small>[457]</small></a></p>
+
+<p>In a letter to the late Mr. Proctor (<i>Knowledge</i>, November, 1885, p. 21),
+Sir John Herschel suggested that our Galaxy (or stellar system) &#8220;contained
+within itself miniatures of itself.&#8221; This beautiful idea is probably true.
+In his account of the greater &#8220;Magellanic cloud,&#8221; Sir John Herschel
+describes one of the numerous objects it contains as follows:&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Very bright, very large; oval; very gradually pretty, much brighter
+in the middle; a beautiful nebula; it has very much the resemblance to
+the Nubecula Major itself as seen with the naked eye, but it is far
+brighter and more impressive in its general aspect as if it were
+doubled in intensity. Note&mdash;July 29, 1837. I well remember this
+observation, it was the result of repeated comparisons between the
+object seen in the telescope and the actual nubecula as seen high in
+the sky on the meridian, and no vague estimate carelessly set down.
+And who can say whether in this object, magnified and analysed by
+telescopes infinitely superior to what we now possess, there may not
+exist all the complexity of detail that the nubecula itself presents
+to our examination?&#8221;<a name='fna_458' id='fna_458' href='#f_458'><small>[458]</small></a></p></div>
+
+<p><span class="pagenum"><a name="Page_315" id="Page_315">[Pg 315]</a></span>The late Lord Kelvin, in a remarkable address delivered before the
+Physical Science Section of the British Association at its meeting at
+Glasgow in 1901, considered the probable quantity of matter contained in
+our Visible Universe. He takes a sphere of radius represented by the
+distance of a star having a parallax of one-thousandth of a second (or
+about 3000 years&#8217; journey for light), and he supposes that uniformly
+distributed within this sphere there exists a mass of matter equal to 1000
+million times the sun&#8217;s mass. With these data he finds that a body placed
+originally at the surface of the sphere would in 5 million years acquire
+by gravitational force a velocity of about 12&#189; miles a second, and
+after 25 million of years a velocity of about 67 miles a second. As these
+velocities are of the same order as the observed velocities among the
+stars, Lord Kelvin concludes that there <i>is</i> probably as much matter in
+our universe as would be represented by a thousand million suns. If we
+assumed a mass of ten thousand suns the velocities would be much too high.
+The most probable estimate of the total number of the visible stars is
+about 100 millions; so that if Lord Kelvin&#8217;s calculations are correct we
+seem bound to assume that space contains a number of dark bodies. The
+nebul&aelig;, however, probably contain vast masses of matter, and this may
+perhaps account&mdash;partially, at least&mdash;for the large amount of<span class="pagenum"><a name="Page_316" id="Page_316">[Pg 316]</a></span> matter
+estimated by Lord Kelvin. (See Chapter on &#8220;Nebul&aelig;.&#8221;)</p>
+
+<p>In some notes on photographs of the Milky Way, Prof. Barnard says with
+reference to the great nebula near &#961; Ophiuchi, &#8220;The peculiarity
+of this region has suggested to me the idea that the apparently small
+stars forming the ground work of the Milky Way here, are really very small
+bodies compared with our own sun&#8221;; and again, referring to the region near
+&#946; Cygni, &#8220;One is specially struck with the apparent extreme
+smallness of the general mass of the stars in this region.&#8221; Again, with
+reference to &#967; Cygni, he says, &#8220;The stars here also are
+remarkably uniform in size.&#8221;<a name='fna_459' id='fna_459' href='#f_459'><small>[459]</small></a></p>
+
+<p>Eastman&#8217;s results for parallax seem to show that &#8220;the fainter rather than
+the brighter stars are nearest to our system.&#8221; But this apparent paradox
+is considered by Mr. Monck to be very misleading;<a name='fna_460' id='fna_460' href='#f_460'><small>[460]</small></a> and the present
+writer holds the same opinion.</p>
+
+<p>Prof. Kapteyn finds &#8220;that stars whose proper motions exceed 0&Prime;&middot;05 are not
+more numerous in the Milky Way than in other parts of the sky; or, in
+other words, if only the stars having proper motions of 0&Prime;&middot;05 or upwards
+were mapped, there would be no aggregation of stars showing the existence
+of the Milky Way.&#8221;<a name='fna_461' id='fna_461' href='#f_461'><small>[461]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_317" id="Page_317">[Pg 317]</a></span>With reference to the number of stars visible on photographs, the late Dr.
+Isaac Roberts says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;So far as I am able at present to judge, under the atmospheric
+conditions prevalent in this country, the limit of the photographic
+method of delineation will be reached at stellar, or nebular, light of
+the feebleness of about 18th-magnitude stars. The reason for this
+inference is that the general illumination of the atmosphere by
+starlight concentrated upon a film by the instrument will mask the
+light of objects that are fainter than about 18th-magnitude
+stars.&#8221;<a name='fna_462' id='fna_462' href='#f_462'><small>[462]</small></a></p></div>
+
+<p>With reference to blank spaces in the sky, the late Mr. Norman Pogson
+remarked&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Near S Ophiuchi we find one of the most remarkable vacuities in this
+hemisphere&mdash;an elliptic space of about 65&prime; in length in the direction
+of R.A., and 40&prime; in width, in which there exists <i>no</i> star larger than
+the 13th magnitude ... it is impossible to turn a large telescope in
+that direction and, if I may so express it, view such black darkness,
+without a feeling that we are here searching into the remote regions
+of space, far beyond the limits of our own sidereal system.&#8221;<a name='fna_463' id='fna_463' href='#f_463'><small>[463]</small></a></p></div>
+
+<p>Prof. Barnard describes some regions in the constellation Taurus
+containing &#8220;dark lanes&#8221; in a groundwork of faint nebulosity. He gives two
+beautiful photographs of the regions referred to, and says that the dark
+holes and lanes are<span class="pagenum"><a name="Page_318" id="Page_318">[Pg 318]</a></span> apparently darker than the sky in the immediate
+vicinity. He says, &#8220;A very singular feature in this connection is that the
+stars also are absent in general from the lanes.&#8221; A close examination of
+these photographs has given the present writer the impression that the
+dark lanes and spots are <i>in</i> the nebulosity, and that the nebulosity is
+mixed up with the stars. This would account for the fact that the stars
+are in general absent from the dark lanes. For if there is an intimate
+relation between the stars and the nebulosity, it would follow that where
+there is no nebulosity in this particular region there would be no stars.
+Prof. Barnard adds that the nebulosity is easily visible in a 12-inch
+telescope.<a name='fna_464' id='fna_464' href='#f_464'><small>[464]</small></a></p>
+
+<p>With reference to the life of the universe, Prof. F. R. Moulton well
+says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;The lifetime of a man seems fairly long, and the epoch when Troy was
+besieged, or when the Pharaohs piled up the pyramids in the valley of
+the Nile, or when our ancestors separated on the high plateaux of
+Asia, seems extremely remote, but these intervals are only moments
+compared to the immense periods required for geological evolutions and
+the enormously greater ones consumed in the developement of worlds
+from widely extended nebulous masses. We recognize the existence of
+only those forces whose immediate consequences are appreciable, and it
+may be that those whose effects are yet unseen are really of the
+highest importance. A little creature whose<span class="pagenum"><a name="Page_319" id="Page_319">[Pg 319]</a></span> life extended over only
+two or three hours of a summer&#8217;s day might be led, if he were
+sufficiently endowed with intelligence, to infer that passing clouds
+were the chief influence at work in changing the climate instead of
+perceiving that the sun&#8217;s slow motion across the sky would bring on
+the night and its southward motion the winter.&#8221;<a name='fna_465' id='fna_465' href='#f_465'><small>[465]</small></a></p></div>
+
+<p>In a review of my book <i>Astronomical Essays</i> in <i>The Observatory</i>,
+September, 1907, the following words occur. They seem to form a good and
+sufficient answer to people who ask, What is there beyond our visible
+universe? &#8220;If the stellar universe is contained in a sphere of say 1000
+stellar units radius, what is there beyond? To this the astronomer will
+reply that theories and hypotheses are put forward for the purpose of
+explaining observed facts; when there are no facts to be explained, no
+theory is required. As there are no observed facts as to what exists
+beyond the farthest stars, the mind of the astronomer is a complete blank
+on the subject. Popular imagination can fill up the blank as it pleases.&#8221;
+With these remarks I fully concur.</p>
+
+<p>In his address to the British Association, Prof. G. H. Darwin (now Sir
+George Darwin) said&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Man is but a microscopic being relatively to astronomical space, and
+he lives on a puny planet circling round a star of inferior rank. Does
+it not, then, seem futile to imagine that he can discover<span class="pagenum"><a name="Page_320" id="Page_320">[Pg 320]</a></span> the origin
+and tendency of the Universe as to expect a housefly to instruct us as
+to the theory of the motions of the planets? And yet, so long as he
+shall last, he will pursue his search, and will no doubt discover many
+wonderful things which are still hidden. We may indeed be amazed at
+all that man has been able to find out, but the immeasurable magnitude
+of the undiscovered will throughout all time remain to humble his
+pride. Our children&#8217;s children will still be gazing and marvelling at
+the starry heavens, but the riddle will never be read.&#8221;</p></div>
+
+<p>The ancient philosopher Lucretius said&mdash;</p>
+
+<p class="poem">&#8220;Globed from the atoms falling slow or swift<br />
+I see the suns, I see the systems lift<br />
+Their forms; and even the system and the suns<br />
+Shall go back slowly to the eternal drift.&#8221;<a name='fna_466' id='fna_466' href='#f_466'><small>[466]</small></a></p>
+
+<p>But it has been well said that the structure of the universe &#8220;has a
+fascination of its own for most readers quite apart from any real progress
+which may be made towards its solution.&#8221;<a name='fna_467' id='fna_467' href='#f_467'><small>[467]</small></a></p>
+
+<p>The Milky Way itself, Mr. Stratonoff considers to be an agglomeration of
+immense condensations, or stellar clouds, which are scattered round the
+region of the galactic equator. These clouds, or masses of stars,
+sometimes leave spaces between them, and sometimes they overlap, and in
+this way he accounts for the great rifts, like the Coal Sack, which allow
+us to see through this great<span class="pagenum"><a name="Page_321" id="Page_321">[Pg 321]</a></span> circle of light. He finds other
+condensations of stars; the nearest is one of which our sun is a member,
+chiefly composed of stars of the higher magnitudes which &#8220;thin out rapidly
+as the Milky Way is approached.&#8221; There are other condensations: one in
+stars of magnitudes 6&middot;5 to 8&middot;5; and a third, farther off, in stars of
+magnitudes 7&middot;6 to 8. These may be called opera-glass, or field-glass
+stars.</p>
+
+<p>Stratonoff finds that stars with spectra of the first type (class A, B, C,
+and D of Harvard) which include the Sirian and Orion stars, are
+principally situated near the Milky Way, while those of type II. (which
+includes the solar stars) &#8220;are principally condensed in a region
+coinciding roughly with the terrestrial pole, and only show a slight
+increase, as compared with other stars, as the galaxy is approached.&#8221;<a name='fna_468' id='fna_468' href='#f_468'><small>[468]</small></a></p>
+
+<p>Prof. Kapteyn thinks that &#8220;undoubtedly one of the greatest difficulties,
+if not the greatest of all, in the way of obtaining an understanding of
+the real distribution of the stars in space, lies in our uncertainty about
+the amount of loss suffered by the light of the stars on its way to the
+observer.&#8221;<a name='fna_469' id='fna_469' href='#f_469'><small>[469]</small></a> He says, &#8220;There can be little doubt in my opinion, about
+the existence of absorption in space, and I think that even a good guess
+as to the order of its amount can be made. For, first<span class="pagenum"><a name="Page_322" id="Page_322">[Pg 322]</a></span> we know that space
+contains an enormous mass of meteoric matter. This matter must necessarily
+intercept some part of the star-light.&#8221;</p>
+
+<p>This absorption, however, seems to be comparatively small. Kapteyn finds a
+value of 0&middot;016 (about <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">60</span>th) of a magnitude for a star at a distance
+corresponding to a parallax of one-tenth of a second (about 33 &#8220;light
+years&#8221;). This is a quantity almost imperceptible in the most delicate
+photometer. But for very great distances&mdash;such as 3000 &#8220;light years&#8221;&mdash;the
+absorption would evidently become very considerable, and would account
+satisfactorily for the gradual &#8220;thinning out&#8221; of the fainter stars. If
+this were fully proved, we should have to consider the fainter stars of
+the Milky Way to be in all probability fairly large suns, the light of
+which is reduced by absorption.</p>
+
+<p>That some of the ancients knew that the Milky Way is composed of stars is
+shown by the following lines translated from Ovid:&mdash;</p>
+
+<p class="poem">&#8220;A way there is in heaven&#8217;s extended plain<br />
+Which when the skies are clear is seen below<br />
+And mortals, by the name of Milky, know;<br />
+The groundwork is of stars, through which the road<br />
+Lies open to great Jupiter&#8217;s abode.&#8221;<a name='fna_470' id='fna_470' href='#f_470'><small>[470]</small></a></p>
+
+<p>From an examination of the distribution of the faint stars composing the
+Milky Way, and those shown in Argelander&#8217;s charts of stars down to the<span class="pagenum"><a name="Page_323" id="Page_323">[Pg 323]</a></span>
+9&#189; magnitude, Easton finds that there is &#8220;a real connection between the
+distribution of 9th and 10th magnitude stars, and that of the faint stars
+of the Milky Way, and that consequently the faint or very faint stars of
+the galactic zone are at a distance which does not greatly exceed that of
+the 9th and 10th magnitude stars.&#8221;<a name='fna_471' id='fna_471' href='#f_471'><small>[471]</small></a> A similar conclusion was, I think,
+arrived at by Proctor many years ago. Now let us consider the meaning of
+this result. Taking stars of the 15th magnitude, if their faintness were
+merely due to greater distance, their actual brightness&mdash;if of the same
+size&mdash;would imply that they are at 10 times the distance of stars of the
+10th magnitude. But if at the same distance from us, a 10th magnitude star
+would be 100 times brighter than a 15th magnitude star, and if of the same
+density and &#8220;intrinsic brightness&#8221; (or luminosity of surface) the 10th
+magnitude would have 10 times the diameter of the fainter star, and hence
+its volume would be 1000 times greater (10<sup>3</sup>), and this great difference
+is not perhaps improbable.</p>
+
+<p>The constitution of the Milky Way is not the same in all its parts. The
+bright spot between &#946; and &#947; Cygni is due to relatively
+bright stars. Others equally dense but fainter regions in Auriga and
+Monoceros are only evident in stars of the 8th and 9th magnitude, and the
+light of the well-known luminous spot in &#8220;Sobieski&#8217;s Shield,&#8221;<span class="pagenum"><a name="Page_324" id="Page_324">[Pg 324]</a></span> closely
+south of &#955; Aquil&aelig;, is due to stars below magnitude 9&#189;.</p>
+
+<p>The correspondence in distribution between the stars of Argelander&#8217;s
+charts and the fainter stars of the Milky Way shows, as Easton points out,
+that Herschel&#8217;s hypothesis of a uniform distribution of stars of
+approximately equal size is quite untenable.</p>
+
+<p>It has been suggested that the Milky Way may perhaps form a ring of stars
+with the sun placed nearly, but not exactly, in the centre of the ring.
+But were it really a ring of uniform width with the sun eccentrically
+placed within it, we should expect to find the Milky Way wider at its
+nearest part, and gradually narrowing towards the opposite point. Now,
+Herschel&#8217;s &#8220;gages&#8221; and Celoria&#8217;s counts show that the Galaxy is wider in
+Aquila than in Monoceros. This is confirmed by Easton, who says, &#8220;<i>for the
+faint stars taken as a whole, the Milky Way is widest in its brightest
+part</i>&#8221; (the italics are Easton&#8217;s). From this we should conclude that the
+Milky Way is nearer to us in the direction of Aquila than in that of
+Monoceros. Sir John Herschel suggested that the southern parts of the
+galactic zone are nearer to us on account of their greater <i>brightness</i> in
+those regions.<a name='fna_472' id='fna_472' href='#f_472'><small>[472]</small></a> But greater width is a safer test of distance than
+relative brightness. For it may be easily shown than the <i>intrinsic</i>
+brightness of an<span class="pagenum"><a name="Page_325" id="Page_325">[Pg 325]</a></span> area containing a large number of stars would be the
+same for <i>all</i> distances (neglecting the supposed absorption of light in
+space). For suppose any given area crowded with stars to be removed to a
+greater distance. The light of each star would be diminished inversely as
+the square of the distance. But the given area would also be diminished
+<i>directly</i> as the square of the distance, so we should have a diminished
+amount of light on an equally diminished area, and hence the intrinsic
+brightness, or luminosity of the area per unit of surface, would remain
+unaltered. The increased brightness of the Milky Way in Aquila is
+accounted for by the fact that Herschel&#8217;s &#8220;gages&#8221; show an increased number
+of stars, and hence the brightness in Aquila and Sagittarius does not
+necessarily imply that the Milky Way is nearer to us in those parts, but
+that it is richer in small stars than in other regions.</p>
+
+<p>Easton is of opinion that the annular hypothesis of the Milky Way is
+inconsistent with our present knowledge of the galactic phenomena, and he
+suggests that its actual constitution resembles more that of a spiral
+nebula.<a name='fna_473' id='fna_473' href='#f_473'><small>[473]</small></a> On this hypothesis the increase in the number of stars in the
+regions above referred to may be due to our seeing one branch of the
+supposed &#8220;two-branched spiral&#8221; projected on another branch of the same
+spiral. This seems supported by Sir John Herschel&#8217;s<span class="pagenum"><a name="Page_326" id="Page_326">[Pg 326]</a></span> observations in the
+southern hemisphere, where he found in some places &#8220;a tissue as it were of
+large stars spread over another of very small ones, the immediate
+magnitudes being wanting.&#8221; Again, portions of the spiral branches may be
+richer than others, as photographs of spiral nebul&aelig; seem to indicate.
+Celoria, rejecting the hypothesis of a single ring, suggests the existence
+of <i>two</i> galactic rings inclined to each other at an angle of about 20&deg;,
+one of these including the brighter stars, and the other the fainter. But
+this seems to be a more artificial arrangement then the hypothesis of a
+spiral. Further, the complicated structure of the Milky Way cannot be well
+explained by Celoria&#8217;s hypothesis of two distinct rings one inside the
+other. From analogy the spiral hypothesis seems much more probable.</p>
+
+<p>Considering the Milky Way to represent a colossal spiral nebula viewed
+from a point not far removed from the centre of the spiral branches,
+Easton suggests that the bright region between &#946; and &#947;
+Cygni, which is very rich in comparatively bright stars, may possibly
+represent the &#8220;<i>central accumulations of the Milky Way</i>,&#8221; that is, the
+portion corresponding to the nucleus of a spiral nebula. If this be so,
+this portion of the Milky Way should be nearer to us than others. Easton
+also thinks that the so-called &#8220;solar cluster&#8221; of Gould, Kapteyn, and
+Schiaparelli may perhaps be &#8220;the expression of<span class="pagenum"><a name="Page_327" id="Page_327">[Pg 327]</a></span> the central condensation
+of the galactic system itself, composed of the most part of suns
+comparable with our own, and which would thus embrace most of the bright
+stars to the 9th or 10th magnitude. The distance of the galactic streams
+and convolutions would thus be comparable with the distances of these
+stars.&#8221; He thinks that the sun lies within a gigantic spiral, &#8220;in a
+comparatively sparse region between the central nucleus and Orion.&#8221;</p>
+
+<p>Scheiner thinks that &#8220;the irregularities of the Milky Way, especially in
+streams, can be quite well accounted for, as Easton has attempted to do,
+if they are regarded as a system of spirals, and not as a ring system.&#8221;</p>
+
+<p>Evidence in favour of the spiral hypothesis of the Milky Way, as advocated
+by Easton and Scheiner, may be found in Kapteyn&#8217;s researches on the proper
+motions of the stars. This eminent astronomer finds that stars with
+measurable proper motions&mdash;and therefore in all probability relatively
+near the earth&mdash;have mostly spectra of the solar type, and seem to cluster
+round &#8220;a point adjacent to the sun, in total disregard to the position of
+the Milky Way,&#8221; and that stars with little or no proper motion collect
+round the galactic plain. He is also of opinion that the Milky Way
+resembles the Andromeda nebula, &#8220;the globular nucleus representing the
+solar cluster, and the far spreading wings or whorls the<span class="pagenum"><a name="Page_328" id="Page_328">[Pg 328]</a></span> compressed layer
+of stars enclosed by the rings of the remote Galaxy.&#8221;</p>
+
+<p>With reference to the plurality of inhabited worlds, it has been well said
+by the ancient writer Metrodorus (third century <span class="smcaplc">B.C.</span>), &#8220;The idea that
+there is but a single world in all infinitude would be as absurd as to
+suppose that a vast field had been formed to produce a single blade of
+wheat.&#8221;<a name='fna_474' id='fna_474' href='#f_474'><small>[474]</small></a> With this opinion the present writer fully concurs.</p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_329" id="Page_329">[Pg 329]</a></span></p>
+<h2><a name="CHAPTER_XXI" id="CHAPTER_XXI"></a>CHAPTER XXI</h2>
+<p class="title">General</p>
+
+<p>&nbsp;</p>
+<p class="dropcap"><span class="caps">The</span> achievements of Hipparchus in astronomy were very remarkable,
+considering the age in which he lived. He found the amount of the apparent
+motion of the stars due to the precession of the equinoxes (of which he
+was the discoverer) to be 59&Prime; per annum. The correct amount is about 50&Prime;.
+He measured the length of the year to within 9 minutes of its true value.
+He found the inclination of the ecliptic to the plane of the equator to be
+23&deg; 51&prime;. It was then 23&deg; 46&prime;&mdash;as we now know by modern calculations&mdash;so
+that Hipparchus&#8217; estimation was a wonderfully close approximation to the
+truth. He computed the moon&#8217;s parallax to be 57&prime;, which is about its
+correct value. He found the eccentricity of the sun&#8217;s apparent orbit round
+the earth to be one twenty-fourth, the real value being then about
+one-thirteenth. He determined other motions connected with the earth and
+moon; and formed a catalogue of 1080 stars. All this work has earned for
+him the well-merited title of &#8220;The Father of Astronomy.&#8221;<a name='fna_475' id='fna_475' href='#f_475'><small>[475]</small></a></p>
+
+<p><span class="pagenum"><a name="Page_330" id="Page_330">[Pg 330]</a></span>The following is a translation of a Greek passage ascribed to Ptolemy: &#8220;I
+know that I am mortal and the creature of a day, but when I search out the
+many rolling circles of the stars, my feet touch the earth no longer, but
+with Zeus himself I take my fill of ambrosia, the food of the gods.&#8221;<a name='fna_476' id='fna_476' href='#f_476'><small>[476]</small></a>
+This was inscribed (in Greek) on a silver loving cup presented to the late
+Professor C. A. Young, the famous American astronomer.<a name='fna_477' id='fna_477' href='#f_477'><small>[477]</small></a></p>
+
+<p>Some curious and interesting phenomena are recorded in the old Chinese
+Annals, which go back to a great antiquity. In 687 <span class="smcaplc">B.C.</span> &#8220;a night&#8221; is
+mentioned &#8220;without clouds and without stars&#8221; (!) This may perhaps refer to
+a total eclipse of the sun; but if so, the eclipse is not mentioned in the
+Chinese list of eclipses. In the year 141 <span class="smcaplc">B.C.</span>, it is stated that the sun
+and moon appeared of a deep red colour during 5 days, a phenomenon which
+caused great terror among the people. In 74 <span class="smcaplc">B.C.</span>, it is related that a
+star as large as the moon appeared, and was followed in its motion by
+several stars of ordinary size. This probably refers to an unusually large
+&#8220;bolide&#8221; or &#8220;fireball.&#8221; In 38 <span class="smcaplc">B.C.</span>, a fall of meteoric stones is recorded
+&#8220;of the size of a walnut.&#8221; In <span class="smcaplc">A.D.</span> 88, another fall of stones is
+mentioned. In <span class="smcaplc">A.D.</span> 321, sun-spots were visible to the naked eye.</p>
+
+<p><span class="pagenum"><a name="Page_331" id="Page_331">[Pg 331]</a></span>Homer speaks of a curious darkness which occurred during one of the great
+battles in the last year of the Trojan war. Mr. Stockwell identifies this
+with an eclipse of the sun which took place on August 28, 1184 <span class="smcaplc">B.C.</span> An
+eclipse referred to by Thucydides as having occurred during the first year
+of the Peloponnesian War, when the darkness was so great that some stars
+were seen, is identified by Stockwell with a total eclipse of the sun,
+which took place on August 2, 430 <span class="smcaplc">B.C.</span></p>
+
+<p>A great eclipse of the sun is supposed to have occurred in the year 43 or
+44 <span class="smcaplc">B.C.</span>, soon after the death of Julius C&aelig;sar. Baron de Zach and Arago
+mention it as the first annular eclipse on record. But calculations show
+that no solar eclipse whatever, visible in Italy, occurred in either of
+these years. The phenomenon referred to must therefore have been of
+atmospherical origin, and indeed this is suggested by a passage in
+Suetonius, one of the authors quoted on the subject.</p>
+
+<p>M. Guillaume thinks that the ninth Egyptian plague, the thick &#8220;darkness&#8221;
+(Exodus x. 21-23), may perhaps be explained by a total eclipse of the sun
+which occurred in 1332 <span class="smcaplc">B.C.</span> It is true that the account states that the
+darkness lasted &#8220;three days,&#8221; but this, M. Guillaume thinks, may be due to
+an error in the translation.<a name='fna_478' id='fna_478' href='#f_478'><small>[478]</small></a> This explanation, however, seems very
+improbable.</p>
+
+<p>According to Hind, the moon was eclipsed on<span class="pagenum"><a name="Page_332" id="Page_332">[Pg 332]</a></span> the generally received date
+of the Crucifixion, <span class="smcaplc">A.D.</span> 33, April 3. He says, &#8220;I find she had emerged
+from the earth&#8217;s dark shadow a quarter of an hour before she rose at
+Jerusalem (6<sup>h</sup> 36<sup>m</sup> p.m.); but the penumbra continued upon her disc for
+an hour afterwards.&#8221; An eclipse could not have had anything to do with the
+&#8220;darkness over all the land&#8221; during the Crucifixion. For this lasted for
+three hours, and the totality of a solar eclipse can only last a few
+minutes at the most. As a matter of fact the &#8220;eclipse of Phlegon,&#8221; a
+partial one (<span class="smcaplc">A.D.</span> 29, November 24) was &#8220;the only solar eclipse that could
+have been visible in Jerusalem during the period usually fixed for the
+ministry of Christ.&#8221;</p>
+
+<p>It is mentioned in the Anglo-Saxon Chronicle that a total eclipse of the
+sun took place in the year after King Alfred&#8217;s great battle with the
+Danes. Now, calculation shows that this eclipse occurred on October 29,
+878 <span class="smcaplc">A.D.</span> King Alfred&#8217;s victory over the Danes must, therefore, have taken
+place in 877 <span class="smcaplc">A.D.</span>, and his death probably occurred in 899 <span class="smcaplc">A.D.</span> This solar
+eclipse is also mentioned in the Annals of Ulster. From this it will be
+seen that in some cases the dates of historical events can be accurately
+fixed by astronomical phenomena.</p>
+
+<p>It is stated by some historians that an eclipse of the sun took place on
+the morning of the battle of<span class="pagenum"><a name="Page_333" id="Page_333">[Pg 333]</a></span> Crecy, August 26, 1346. But calculation
+shows that there was no eclipse of the sun visible in England in that
+year. At the time of the famous battle the moon had just entered on her
+first quarter, and she was partially eclipsed six days afterwards&mdash;that is
+on the 1st of September. The mistake seems to have arisen from a
+mistranslation of the old French word <i>esclistre</i>, which means lightning.
+This was mistaken for <i>esclipse</i>. The account seems to indicate that there
+was a heavy thunderstorm on the morning of the battle.</p>
+
+<p>A dark shade was seen on the waning moon by Messrs. Hirst and J. C.
+Russell on October 21, 1878, &#8220;as dark as the shadow during an eclipse of
+the moon.&#8221;<a name='fna_479' id='fna_479' href='#f_479'><small>[479]</small></a> If this observation is correct, it is certainly most
+difficult to explain. Another curious observation is recorded by Mr. E.
+Stone Wiggins, who says that a partial eclipse of the sun by a dark body
+was observed in the State of Michigan (U.S.A.) on May 16, 1884, at 7 p.m.
+The &#8220;moon at that moment was 12 degrees south of the equator and the sun
+as many degrees north of it.&#8221; The existence of a dark satellite of the
+earth has been suggested, but this seems highly improbable.</p>
+
+<p>The sun&#8217;s corona seems to have been first noticed in the total eclipse of
+the sun which occurred at the death of the Roman emperor<span class="pagenum"><a name="Page_334" id="Page_334">[Pg 334]</a></span>
+Domitian, <span class="smcaplc">A.D.</span> 95. Philostratus in his <i>Life of Apollonius</i> says, with reference to this
+eclipse, &#8220;In the heavens there appeared a prodigy of this nature: a
+certain <i>corona</i> resembling the Iris surrounded the orb of the sun, and
+obscured its light.&#8221;<a name='fna_480' id='fna_480' href='#f_480'><small>[480]</small></a> In more modern times the corona seems to have
+been first noticed by Clavius during the total eclipse of April 9,
+1567.<a name='fna_481' id='fna_481' href='#f_481'><small>[481]</small></a> Kepler proved that this eclipse was total, not annular, so that
+the ring seen by Clavius must have been the corona.</p>
+
+<p>With reference to the visibility of planets and stars during total
+eclipses of the sun; in the eclipse of May 12, 1706, Venus, Mercury, and
+Aldebaran, and several other stars were seen. During the totality of the
+eclipse of May 3, 1715, about twenty stars were seen with the naked
+eye.<a name='fna_482' id='fna_482' href='#f_482'><small>[482]</small></a> At the eclipse of May 22, 1724, Venus and Mercury, and a few
+fixed stars were seen.<a name='fna_483' id='fna_483' href='#f_483'><small>[483]</small></a> The corona was also noticed. At the eclipse of
+May 2, 1733, Jupiter, the stars of the &#8220;Plough,&#8221; Capella, and other stars
+were visible to the naked eye; and the corona was again seen.<a href='#f_483'><small>[483]</small></a></p>
+
+<p>During the total eclipses of February 9, 1766, June 24, 1778, and June 16,
+1806, the corona was again noticed. But its true character was then
+unknown.</p>
+
+<p>At the eclipse of July 8, 1842, it was noticed by<span class="pagenum"><a name="Page_335" id="Page_335">[Pg 335]</a></span> observers at Lipesk
+that the stars Aldebaran and Betelgeuse (&#945; Orionis), which are
+usually red, &#8220;appeared quite white.&#8221;<a name='fna_484' id='fna_484' href='#f_484'><small>[484]</small></a></p>
+
+<p>There will be seven eclipses in the years 1917, 1935, and 1985. In the
+year 1935 there will be five eclipses of the sun, a rare event; and in
+1985 there will be three total eclipses of the moon, a most unusual
+occurrence.<a name='fna_485' id='fna_485' href='#f_485'><small>[485]</small></a></p>
+
+<p>Among the ancient Hindoos, the common people believed that eclipses were
+caused by the interposition of a monstrous demon called Raha. This absurd
+idea, and others equally ridiculous, were based on declarations in their
+sacred books, and no pious Hindoo would think of denying it.</p>
+
+<p>The following cases of darkenings of the sun are given by Humboldt:&mdash;</p>
+
+<p>According to Plutarch the sun remained pale for a whole year at the death
+of Julius C&aelig;sar, and gave less than its usual heat.<a name='fna_486' id='fna_486' href='#f_486'><small>[486]</small></a></p>
+
+<p>A sun-darkening lasting for two hours is recorded on August 22, 358 <span class="smcaplc">A.D.</span>,
+before the great earthquake of Nicomedia.</p>
+
+<p>In 360 <span class="smcaplc">A.D.</span> there was a sun-darkening from early morn till noon. The
+description given by the historians of the time corresponds to an eclipse
+of the sun, but the duration of the obscurity is inexplicable.</p>
+
+<p>In 409 <span class="smcaplc">A.D.</span>, when Alaric lay siege to Rome,
+<span class="pagenum"><a name="Page_336" id="Page_336">[Pg 336]</a></span> &#8220;there was so great a
+darkness that the stars were seen by day.&#8221;</p>
+
+<p>In 536 <span class="smcaplc">A.D.</span> the sun is said to have been darkened for a year and two
+months!</p>
+
+<p>In 626 <span class="smcaplc">A.D.</span>, according to Abul Farag, half the sun&#8217;s disc was darkened for
+eight months!</p>
+
+<p>In 934 <span class="smcaplc">A.D.</span> the sun lost its brightness for two months in Portugal.</p>
+
+<p>In 1090 <span class="smcaplc">A.D.</span> the sun was darkened for three hours.</p>
+
+<p>In 1096, sun-spots were seen with the naked eye on March 3.</p>
+
+<p>In 1206 <span class="smcaplc">A.D.</span> on the last day of February, &#8220;there was complete darkness for
+six hours, turning the day into night.&#8221; This seems to have occurred in
+Spain.</p>
+
+<p>In 1241 the sun was so darkened that stars could be seen at 3 p.m. on
+Michaelmas day. This happened in Vienna.<a name='fna_487' id='fna_487' href='#f_487'><small>[487]</small></a></p>
+
+<p>The sun is said to have been so darkened in the year 1547 <span class="smcaplc">A.D.</span> for three
+days that stars were visible at midday. This occurred about the time of
+the battle of M&uuml;hlbergh.<a name='fna_488' id='fna_488' href='#f_488'><small>[488]</small></a></p>
+
+<p>Some of these darkenings may possibly have been due to an enormous
+development of sun-spots; but in some cases the darkness is supposed by
+Chladni and Schnurrer to have been caused by &#8220;the passage of meteoric
+masses before the sun&#8217;s disc.&#8221;</p>
+
+<p><span class="pagenum"><a name="Page_337" id="Page_337">[Pg 337]</a></span>The first observer of a transit of Venus was Jeremiah Horrocks, who
+observed the transit of November 24 (O.S.), 1639. He had previously
+corrected Kepler&#8217;s predicted time of the transit from 8<sup>h</sup> 8<sup>m</sup> a.m. at
+Manchester to 5<sup>h</sup> 57<sup>m</sup> p.m. At the end of 1875 a marble scroll was
+placed on the pedestal of the monument of John Conduitt (nephew of Sir
+Isaac Newton, and who adopted Horrocks&#8217; theory of lunar motions) at the
+west end of the nave of Westminster Abbey, bearing this inscription from
+the pen of Dean Stanley&mdash;</p>
+
+<table style="margin-left: 15%;" border="0" cellpadding="0" cellspacing="5" summary="table">
+<tr><td align="center">&#8220;Ad majora avocatus<br />
+qu&aelig; ob h&aelig;c parerga negligi non decuit&#8221;<br />
+<span class="smcap">In Memory of</span><br />
+JEREMIAH HORROCKS<br />
+Curate of Hoole in Lancashire<br />
+Who died on the 3<sup>d</sup> of January, 1641, in or near his<br />
+22<sup>d</sup> year<br />
+Having in so short a life<br />
+Detected the long inequality in the mean motion of<br />
+Jupiter and Saturn<br />
+Discovered the orbit of the Moon to be an ellipse;<br />
+Determined the motion of the lunar aspe,<br />
+Suggested the physical cause of its revolution;<br />
+And predicted from his own observations, the<br />
+Transit of Venus<br />
+Which was seen by himself and his friend<br />
+WILLIAM CRABTREE<br />
+On Sunday, the 24th November (O.S.) 1639;<br />
+This Tablet, facing the Monument of Newton<br />
+Was raised after the lapse of more than two centuries<br />
+December 9, 1874.<a name='fna_489' id='fna_489' href='#f_489'><small>[489]</small></a></td></tr></table>
+
+<p><span class="pagenum"><a name="Page_338" id="Page_338">[Pg 338]</a></span>The transit of Venus which occurred in 1761 was observed on board ship(!)
+by the famous but unfortunate French astronomer Le Gentil. The ship was
+the frigate <i>Sylphide</i>, sent to the help of Pondicherry (India) which was
+then being besieged by the English. Owing to unfavourable winds the
+<i>Sylphide</i> was tossed about from March 25, 1761, to May 24 of the same
+year. When, on the later date, off the coast of Malabar, the captain of
+the frigate learned that Pondicherry had been captured by the English, the
+vessel returned to the Isle of France, where it arrived on June 23, after
+touching at Point de Galle on May 30. It was between these two places that
+Le Gentil made his observations of the transit of Venus under such
+unfavourable conditions. He had an object-glass of 15 feet (French) focus,
+and this he mounted in a tube formed of &#8220;four pine planks.&#8221; This rough
+instrument was fixed to a small mast set up on the quarter-deck and worked
+by ropes. The observations made under such curious conditions, were not,
+as may be imagined, very satisfactory. As another transit was to take
+place on June 3, 1769, Le Gentil made the heroic resolution of remaining
+in the southern hemisphere to observe it! This determination was duly
+carried out, but his devotion to astronomy was not rewarded; for on the
+day of the long waited for transit the sky at Pondicherry (where he had
+gone to observe it) was clouded over<span class="pagenum"><a name="Page_339" id="Page_339">[Pg 339]</a></span> during the whole phenomenon,
+&#8220;although for many days previous the sky had been cloudless.&#8221; To add to
+his feeling of disappointment he heard that at Manilla, where he had been
+staying some time previously, the sky was quite clear, and two of his
+friends there had seen the transit without any difficulty.<a name='fna_490' id='fna_490' href='#f_490'><small>[490]</small></a> Truly the
+unfortunate Le Gentil was a martyr to science.</p>
+
+<p>The famous German astronomer Bessel once said &#8220;that a practical astronomer
+could make observations of value if he had only a cart-wheel and a gun
+barrel&#8221;; and Watson said that &#8220;the most important part of the instrument
+is the person at the small end.&#8221;<a name='fna_491' id='fna_491' href='#f_491'><small>[491]</small></a></p>
+
+<p>With reference to Father Hell&#8217;s supposed forgery of his observations of
+the transit of Venus in 1769, and Littrow&#8217;s criticism of some of the
+entries in Hell&#8217;s manuscript being corrected with a different coloured
+ink, Professor Newcomb ascertained from Weiss that Littrow was colour
+blind, and could not distinguish between the colour of Aldebaran and the
+whitest star. Newcomb adds, &#8220;For half a century the astronomical world
+had based an impression on the innocent but mistaken evidence of a
+colour-blind man respecting the tint of ink in a manuscript.&#8221;</p>
+
+<p>It is recorded that on February 26, <span class="smcaplc">B.C.</span> 2012, the moon, Mercury, Venus,
+Jupiter, and Saturn,<span class="pagenum"><a name="Page_340" id="Page_340">[Pg 340]</a></span> were in the same constellation, and within 14
+degrees of each other. On September 14, 1186 <span class="smcaplc">A.D.</span>, the sun, moon, and all
+the planets then known, are said to have been situated in Libra.<a name='fna_492' id='fna_492' href='#f_492'><small>[492]</small></a></p>
+
+<p>In the Sanscrit epic poem, &#8220;The Ramaya,&#8221; it is stated that at the birth of
+Rama, the moon was in Cancer, the sun in Aries, Mercury in Taurus, Venus
+in Pisces, Mars in Capricornus, Jupiter in Cancer, and Saturn in Libra.
+From these data, Mr. Walter R. Old has computed that Rama was born on
+February 10, 1761 <span class="smcaplc">B.C.</span><a name='fna_493' id='fna_493' href='#f_493'><small>[493]</small></a></p>
+
+<p>A close conjunction of Mars and Saturn was observed by Denning on
+September 29, 1889, the bright star Regulus (&#945; Leonis) being at
+the time only 47&prime; distant from the planets.<a name='fna_494' id='fna_494' href='#f_494'><small>[494]</small></a></p>
+
+<p>An occultation of the Pleiades by the moon was observed by Timocharis at
+Alexandria on January 29, 282 <span class="smcaplc">B.C.</span> Calculations by Schjellerup show that
+Alcyone (&#951; Tauri) was occulted; but the exact time of the day
+recorded by Timocharis differs very considerably from that computed by
+Schjellerup.<a name='fna_495' id='fna_495' href='#f_495'><small>[495]</small></a> Another occultation of the Pleiades is recorded by
+Agrippa in the reign of Domitian. According to Schjellerup the phenomenon
+occurred on November 29, <span class="smcaplc">A.D.</span> 92.</p>
+
+<p>&#8220;Kepler states that on the 9th of January, 1591,<span class="pagenum"><a name="Page_341" id="Page_341">[Pg 341]</a></span> M&aelig;stlin and himself
+witnessed an occultation of Jupiter by Mars. The red colour of the latter
+on that occasion plainly indicated that it was the inferior planet.&#8221;<a name='fna_496' id='fna_496' href='#f_496'><small>[496]</small></a>
+That is, that Mars was nearer to the sun than Jupiter. But as the
+telescope had not then been invented, this may have been merely a near
+approach of the two planets.</p>
+
+<p>According to Kepler, M&aelig;stlin saw an occultation of Mars by Venus on
+October 3, 1590. But this may also have been merely a near approach.<a href='#f_496'><small>[496]</small></a></p>
+
+<p>A curious paradox is that one can discover an object without seeing it,
+and see an object without discovering it! The planet Neptune was
+discovered by Adams and Leverrier by calculation before it was seen in the
+telescope by Galle; and it was actually seen by Lalande on May 8 and 10,
+1795, but he took it for a <i>star</i> and thus missed the discovery. In fact,
+he <i>saw</i> the planet, but did not <i>discover</i> it. It actually appears as a
+star of the 8th magnitude in Harding&#8217;s Atlas (1822). The great &#8220;new star&#8221;
+of February, 1901, known as Nova Persei, was probably seen by some people
+before its discovery was announced; and it was actually noticed by a
+well-known American astronomer, who thought it was some bright star with
+which he was not familiar! But this did not amount to a discovery. Any one
+absolutely ignorant of astronomy might have made the same observation. An
+object must be <i>identified</i> as a<span class="pagenum"><a name="Page_342" id="Page_342">[Pg 342]</a></span> <i>new</i> object before a discovery can be
+claimed. Some years ago a well-known Irish naturalist discovered a spider
+new to science, and after its discovery he found that it was common in
+nearly every house in Dublin! But this fact did not detract in the least
+from the merit of its scientific discovery.</p>
+
+<p>There is a story of an eminent astronomer who had been on several eclipse
+expeditions, and yet was heard to remark that he had never seen a total
+eclipse of the sun. &#8220;But your observations of several eclipses are on
+record,&#8221; it was objected. &#8220;Certainly, I have on several occasions made
+observations, but I have always been too busy to look at the eclipse.&#8221; He
+was probably in a dark tent taking photographs or using a spectroscope
+during the totality. This was observing an eclipse without seeing it!</p>
+
+<p>Humboldt gives the credit of the invention of the telescope to Hans
+Lippershey, a native of Wesel and a spectacle-maker at Middleburgh; to
+Jacob Adreaansz, surnamed Metius, who is also said to have made
+burning-glasses of ice; and to Zachariah Jansen.<a name='fna_497' id='fna_497' href='#f_497'><small>[497]</small></a></p>
+
+<p>With reference to the parabolic figure of the large mirrors of reflecting
+telescopes, Dr. Robinson remarked at the meeting of the British
+Association at Cork in 1843, &#8220;between the spherical and parabolic figures
+the extreme difference is so<span class="pagenum"><a name="Page_343" id="Page_343">[Pg 343]</a></span> slight, even in the telescope of 6-feet
+aperture [Lord Rosse&#8217;s] that if the two surfaces touched at their vertex,
+the distance at the edge would not amount to the <span style="font-size: 0.8em;"><sup>1</sup></span>&frasl;<span style="font-size: 0.6em;">10000</span>
+of an inch, a space which few can measure, and none without a microscope.&#8221;<a name='fna_498' id='fna_498' href='#f_498'><small>[498]</small></a></p>
+
+<p>In the year 1758, Roger Long, Lowndean Professor of Astronomy at
+Cambridge, constructed an &#8220;orrery&#8221; on a novel principle. It was a hollow
+metal sphere of about 18 feet in diameter with its fixed axis parallel to
+the earth&#8217;s axis. It was rotated, by means of a winch and rackwork. It
+held about thirty persons in its interior, where astronomical lectures
+were delivered. The constellations were painted on the interior surface;
+and holes pierced through the shell and illuminated from the outside
+represented the stars according to their different magnitudes. This
+ingenious machine was much neglected for many years, but was still in
+existence in Admiral Smyth&#8217;s time, 1844.<a name='fna_499' id='fna_499' href='#f_499'><small>[499]</small></a></p>
+
+<p>A &#8220;temporary star&#8221; is said to have been seen by Hepidanus in the
+constellation Aries in either 1006 or 1012 <span class="smcaplc">A.D.</span> The late M. Sch&ouml;nfeld, a
+great authority on variable stars, found from an Arabic and Syrian
+chronicle that 1012 is the correct year (396 of the Hegira), but that the
+word translated Aries would by a probable emendation mean<span class="pagenum"><a name="Page_344" id="Page_344">[Pg 344]</a></span> Scorpio. The
+word in the Syrian record is not the word for Aries.<a name='fna_500' id='fna_500' href='#f_500'><small>[500]</small></a></p>
+
+<p>Mr. Heber D. Curtis finds that the faintest stars mentioned in Ptolemy&#8217;s
+Catalogue are about 5&middot;38 magnitude on the scale of the Harvard
+<i>Photometric Durchmustering</i>.<a name='fna_501' id='fna_501' href='#f_501'><small>[501]</small></a> Heis and Houzeau saw stars of 6-7
+magnitude (about 6&middot;4 on Harvard scale). The present writer found that he
+could see most of Heis&#8217; faintest stars in the west of Ireland (Co. Sligo)
+without optical aid (except short-sighted spectacles).</p>
+
+<p>With reference to the apparent changes in the stellar heavens produced by
+the precession of the equinoxes, Humboldt says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Canopus was fully 1&deg; 20&prime; below the horizon of Toledo (39&deg; 54&prime; north
+latitude) in the time of Columbus; and now the same star is almost as
+much above the horizon of Cadiz. While at Berlin, and in northern
+latitudes, the stars of the Southern Cross, as well as &#945; and
+&#946; Centauri, are receding more and more from view, the
+Magellanic Clouds are slowly approaching our latitudes. Canopus was at
+its greatest northern approximation during last century [eighteenth],
+and is now moving nearer and nearer to the south, although very
+slowly, owing to its vicinity to the south pole of the ecliptic. The
+Southern Cross began to become invisible in 52&deg; 30&prime; north latitude
+2900 years before our era, since, according to Galle, this
+constellation might previously have reached an altitude of more than
+10&deg;. When it<span class="pagenum"><a name="Page_345" id="Page_345">[Pg 345]</a></span> had disappeared from the horizon of the countries of the
+Baltic, the great pyramid of Cheops had already been erected more than
+five hundred years. The pastoral tribe of the Hyksos made their
+incursion seven hundred years earlier. The past seems to be visibly
+nearer to us when we connect its measurement with great and memorable
+events.&#8221;<a name='fna_502' id='fna_502' href='#f_502'><small>[502]</small></a></p></div>
+
+<p>With reference to the great Grecian philosopher and scientist Eratosthenes
+of Cyrene, keeper of the Alexandrian Library under Ptolemy Euergetes, Carl
+Snyder says, &#8220;Above all the Alexanders, C&aelig;sars, Tadema-Napoleons, I set
+the brain which first spanned the earth, over whose little patches these
+fought through their empty bootless lives. Why should we have no poet to
+celebrate so great a deed?&#8221;<a name='fna_503' id='fna_503' href='#f_503'><small>[503]</small></a> And with reference to Aristarchus he
+says, &#8220;If grandeur of conceptions be a measure of the brain, or ingenuity
+of its powers, then we must rank Aristarchus as one of the three or four
+most acute intellects of the ancient world.&#8221;<a name='fna_504' id='fna_504' href='#f_504'><small>[504]</small></a></p>
+
+<p>Lagrange, who often asserted Newton to be the greatest genius that ever
+existed, used to remark also&mdash;&#8220;and the most fortunate; we do not find more
+than once a system of the world to establish.&#8221;<a name='fna_505' id='fna_505' href='#f_505'><small>[505]</small></a></p>
+
+<p>Grant says&mdash;</p>
+
+<div class="blockquot"><p><span class="pagenum"><a name="Page_346" id="Page_346">[Pg 346]</a></span>&#8220;Lagrange deserves
+to be ranked among the greatest mathematical geniuses of ancient or modern times. In this respect he is worthy of a
+place with Archimedes or Newton, although he was far from possessing
+the sagacity in physical enquiries which distinguished these
+illustrious sages. From the very outset of his career he assumed a
+commanding position among the mathematicians of the age, and during
+the course of nearly half a century previous to his death, he
+continued to divide with Laplace the homage due to pre-eminence in the
+exact sciences. His great rival survived him fourteen years, during
+which he reigned alone as the prince of mathematicians and theoretical
+astronomers.&#8221;<a name='fna_506' id='fna_506' href='#f_506'><small>[506]</small></a></p></div>
+
+<p>A writer in <i>Nature</i> (May 25, 1871) relates the following anecdote with
+reference to Sir John Herschel: &#8220;Some time after the death of Laplace, the
+writer of this notice, while travelling on the continent in company with
+the celebrated French <i>savant</i> Biot, ventured to put to him the question,
+not altogether a wise one, &#8216;And whom of all the philosophers of Europe do
+you regard as the most worthy successor of Laplace?&#8217; Probably no man was
+better able than Biot to form a correct conclusion, and the reply was more
+judicious than the question. It was this, &#8216;If I did not love him so much I
+should unhesitatingly say, Sir John Herschel.&#8217;&#8221; Dr. Gill (now Sir David
+Gill), in an address at the Cape of Good Hope in June, 1898, spoke of Sir
+John Herschel as &#8220;the prose poet of science; his popular scientific works
+are models of<span class="pagenum"><a name="Page_347" id="Page_347">[Pg 347]</a></span> clearness, and his presidential addresses teem with
+passages of surpassing beauty. His life was a pure and blameless one from
+first to last, full of the noblest effort and the noblest aim from the
+time when as a young Cambridge graduate he registered a vow &#8216;to try to
+leave the world wiser than he found it&#8217;&mdash;a vow that his life amply
+fulfilled.&#8221;<a name='fna_507' id='fna_507' href='#f_507'><small>[507]</small></a></p>
+
+<p>Prof. Newcomb said of Adams, the co-discoverer of Neptune with Leverrier,
+&#8220;Adams&#8217; intellect was one of the keenest I ever knew. The most difficult
+problem of mathematical astronomy and the most recondite principles that
+underlie the theory of the celestial motions were to him but child&#8217;s
+play.&#8221; Airy he regarded as &#8220;the most commanding figure in the astronomy of
+our time.&#8221;<a name='fna_508' id='fna_508' href='#f_508'><small>[508]</small></a> He spoke of Delaunay, the great French astronomer, as a
+most kindly and attractive man, and says, &#8220;His investigations of the
+moon&#8217;s motion is one of the most extraordinary pieces of mathematical work
+ever turned out by a single person. It fills two quarto volumes, and the
+reader who attempts to go through any part of the calculations will wonder
+how one man could do the work in a lifetime.&#8221;<a name='fna_509' id='fna_509' href='#f_509'><small>[509]</small></a></p>
+
+<p>Sir George B. Airy and Prof. J. C. Adams died in the same month. The
+former on January 2,<span class="pagenum"><a name="Page_348" id="Page_348">[Pg 348]</a></span> 1892, and the latter on January 22 of the same year.</p>
+
+<p>It is known from the parish register of Burstow in Surrey that Flamsteed
+(Rev. John Flamsteed), the first Astronomer Royal at Greenwich, was buried
+in the church at that place on January 12, 1720; but a search for his
+grave made by Mr. J. Carpenter in 1866 and by Mr. Lynn in 1880 led to no
+result. In Mrs. Flamsteed&#8217;s will a sum of twenty-five pounds was left for
+the purpose of erecting a monument to the memory of the great astronomer
+in Burstow Church; but it does not appear that any monument was ever
+erected. Flamsteed was Rector of the Parish of Burstow.<a name='fna_510' id='fna_510' href='#f_510'><small>[510]</small></a> He was
+succeeded in 1720 by the Rev. James Pound, another well-known astronomer.
+Pound died in 1724.<a name='fna_511' id='fna_511' href='#f_511'><small>[511]</small></a></p>
+
+<p>Evelyn says in his Diary, 1676, September 10, &#8220;Dined with Mr. Flamsteed,
+the learned astrologer and mathematician, whom his Majesty had established
+in the new Observatory in Greenwich Park furnished with the choicest
+instruments. An honest sincere man.&#8221;<a name='fna_512' id='fna_512' href='#f_512'><small>[512]</small></a> This shows that in those days
+the term &#8220;astrologer&#8221; was synonymous with &#8220;astronomer.&#8221;</p>
+
+<p>In an article on &#8220;Our Debt to Astronomy,&#8221; by Prof. Russell Tracy Crawford
+(Berkeley<span class="pagenum"><a name="Page_349" id="Page_349">[Pg 349]</a></span> Astronomical Department, California, U.S.A.), the following
+remarks occur:&mdash;</p>
+
+<div class="blockquot"><p>&#8220;Behind the artisan is a chemist, behind the chemist is a physicist,
+behind the physicist is a mathematician, and behind the mathematician
+is an astronomer.&#8221; &#8220;Were it not for the data furnished by astronomers,
+commerce by sea would practically stop. The sailing-master on the high
+seas could not determine his position, nor in what direction to head
+his ship in order to reach a desired harbour. Think what this means in
+dollars and cents, and estimate it if you can. For this one service
+alone the science of astronomy is worth more in dollars and cents to
+the world in one week than has been expended upon it since the
+beginning of civilization. Do you think that Great Britain, for
+instance, would take in exchange an amount equal to its national debt
+for what astronomy gives it? I answer for you most emphatically,
+&#8216;No.&#8217;&#8221;</p></div>
+
+<p>In his interesting book, <i>Reminiscences of an Astronomer</i>, Prof. Simon
+Newcomb says with reference to the calculations for the <i>Nautical Almanac</i>
+(referred to in the above extract)&mdash;</p>
+
+<div class="blockquot"><p>&#8220;A more hopeless problem than this could not be presented to the
+ordinary human intellect. There are tens of thousands of men who could
+be successful in all the ordinary walks of life, hundreds who could
+wield empires, thousands who could gain wealth, for one who could take
+up this astronomical problem with any hope of success. The men who
+have done it are, therefore, in intellect the select few of the human
+race&mdash;an aristocracy ranking above all others in the scale of being.
+The astronomical ephemeris is the last outcome of their productive
+genius.&#8221;</p></div>
+
+<p><span class="pagenum"><a name="Page_350" id="Page_350">[Pg 350]</a></span>In a paper on the &#8220;Aspects of American Astronomy,&#8221; Prof. Newcomb says, &#8220;A
+great telescope is of no use without a man at the end of it, and what the
+telescope may do depends more upon this appendage than upon the instrument
+itself. The place which telescopes and observatories have taken in
+astronomical history are by no means proportional to their dimensions.
+Many a great instrument has been a mere toy in the hands of its owner.
+Many a small one has become famous. Twenty years ago there was here in
+your city [Chicago] a modest little instrument which, judged by its size,
+could not hold up its head with the great ones even of that day. It was
+the private property of a young man holding no scientific position and
+scarcely known to the public. And yet that little telescope is to-day
+among the famous ones of the world, having made memorable advances in the
+astronomy of double stars, and shown its owner to be a worthy successor of
+the Herschels and Struves in that line of work.&#8221;<a name='fna_513' id='fna_513' href='#f_513'><small>[513]</small></a> Here Prof. Newcomb
+evidently refers to Prof. Burnham, and the 6-inch telescope with which he
+made many of his remarkable discoveries of double stars. With reference to
+Burnham&#8217;s work, Prof. Barnard says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;It represents the labour of a struggling amateur, who during the day
+led the drudging life of a stenographer in the United States court<span class="pagenum"><a name="Page_351" id="Page_351">[Pg 351]</a></span> in
+Chicago, and at night worked among the stars for the pure love of it.
+Such work deserves an everlasting fame, and surely this has fallen to
+Mr. Burnham.&#8221;</p></div>
+
+<p>Admiral Smyth says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;A man may prove a good astronomer without possessing a spacious
+observatory: thus Kepler was wont to observe on the bridge at Prague;
+Schr&ouml;ter studied the moon, and Harding found a planet from a
+<i>gloriette</i>; while Olbers discovered two new planets from an attic of
+his house.&#8221;<a name='fna_514' id='fna_514' href='#f_514'><small>[514]</small></a></p></div>
+
+<p>It is probably not generally known that &#8220;some of the greatest astronomers
+of modern times, such as Kepler, Newton, Hansen, Laplace, and Leverrier,
+scarcely ever looked through a telescope.&#8221;<a name='fna_515' id='fna_515' href='#f_515'><small>[515]</small></a></p>
+
+<p>Kepler, who always signed himself Keppler in German, is usually supposed
+to have been born on December 21, 1571, in the imperial town of Weil, but
+according to Baron von Breitschwert,<a name='fna_516' id='fna_516' href='#f_516'><small>[516]</small></a> he was really born on December
+27, 1571, in the village of Magstadt in Wurtemberg.</p>
+
+<p>According to Lieut. Winterhalter, M. Perrotin of the Nice Observatory
+declared &#8220;that two hours&#8217; work with a large instrument is as fatiguing as
+eight with a small one, the labour involved increasing in proportion to
+the cube of the aperture, the chances of seeing decreasing in the same
+ratio,<span class="pagenum"><a name="Page_352" id="Page_352">[Pg 352]</a></span> while it can hardly be said that the advantages increase in like
+proportion.&#8221;<a name='fna_517' id='fna_517' href='#f_517'><small>[517]</small></a></p>
+
+<p>The late Mr. Proctor has well said&mdash;</p>
+
+<div class="blockquot"><p>&#8220;It is well to remember that the hatred which many entertain against
+the doctrine of development as applied to solar systems and stellar
+galaxies is not in reality a sign, as they imagine, of humility, but
+is an effort to avoid the recognition of the nothingness of man in the
+presence of the infinities of space and time and vitality presented
+within the universe of God.&#8221;<a name='fna_518' id='fna_518' href='#f_518'><small>[518]</small></a></p></div>
+
+<p>Humboldt says&mdash;</p>
+
+<div class="blockquot"><p>&#8220;That arrogant spirit of incredulity, which rejects facts without
+attempting to investigate them, is in some cases almost more injurious
+than an unquestioning credulity. Both are alike detrimental to the
+force of investigations.&#8221;<a name='fna_519' id='fna_519' href='#f_519'><small>[519]</small></a></p></div>
+
+<p>With reference to the precession of the equinoxes and the changes it
+produces in the position of the Pole Star, it is stated in a recent book
+on science that the entrance passage of the Great Pyramid of Ghizeh is
+inclined at an angle of 30&deg; to the horizon, and therefore points to the
+celestial pole. But this is quite incorrect. The Great Pyramid, it is
+true, is situated close to the latitude of 30&deg;. But the entrance passage
+does not point exactly to the pole. The inclination was measured by Col.
+Vyse, and found to be<span class="pagenum"><a name="Page_353" id="Page_353">[Pg 353]</a></span> 26&deg; 45&prime;. For six out of the nine pyramids of
+Ghizeh, Col. Vyse found an <i>average</i> inclination of 26&deg; 47&prime;, these
+inclinations ranging from 25&deg; 55&prime; (2nd, or pyramid of Mycerinus) to 28&deg; 0&prime;
+(9th pyramid).<a name='fna_520' id='fna_520' href='#f_520'><small>[520]</small></a> Sir John Herschel gives 3970 <span class="smcaplc">B.C.</span> as the probable date
+of the erection of the Great Pyramid.<a href='#f_520'><small>[520]</small></a> At that time the distance of
+&#945; Draconis (the Pole Star of that day) from the pole was 3&deg; 44&prime;
+25&Prime;, so that when on the meridian <i>below</i> the pole (its lower culmination
+as it is termed) its altitude was 30&deg; - 3&deg; 44&prime; 25&Prime; = 26&deg; 15&prime; 35&Prime;, which
+agrees fairly well with the inclination of the entrance passage. Letronne
+found a date of 3430 <span class="smcaplc">B.C.</span>; but the earlier date agrees better with the
+evidence derived from Egyptology.</p>
+
+<p>Emerson says&mdash;</p>
+
+<p class="poem">&#8220;I am brother to him who squared the pyramids<br />
+By the same stars I watch.&#8221;</p>
+
+<p>From February 6 to 15, 1908, all the bright planets were visible together
+at the same time. Mercury was visible above the western horizon after
+sunset, Venus very brilliant with Saturn a little above it, Mars higher
+still, all ranged along the ecliptic, and lastly Jupiter rising in the
+east.<a name='fna_521' id='fna_521' href='#f_521'><small>[521]</small></a> This simultaneous visibility of all the bright planets is
+rather a rare occurrence.</p>
+
+<p>With reference to the great improbability of<span class="pagenum"><a name="Page_354" id="Page_354">[Pg 354]</a></span> Laplace&#8217;s original Nebular
+Hypothesis being true, Dr. See says, &#8220;We may calculate from the
+preponderance of small bodies actually found in the solar system&mdash;eight
+principal planets, twenty-five satellites (besides our moon), and 625
+asteroids&mdash;that the chances of a nebula devoid of hydrostatic pressure
+producing small bodies is about 2<sup>658</sup> to 1, or a decillion decillion
+(10<sup>66</sup>)<sup>6</sup> to the sixth power, to unity. This figure is so very large
+that we shall content ourselves with illustrating a decillion decillion,
+and for this purpose we avail ourselves of a method employed by <span class="smcap">Archimedes</span>
+to illustrate his system of enumeration. Imagine sand so fine that 10,000
+grains will be contained in the space occupied by a poppy seed, itself
+about the size of a pin&#8217;s head; and then conceive a sphere described about
+our sun with a radius of 200,000 astronomical units<a name='fna_522' id='fna_522' href='#f_522'><small>[522]</small></a> (&#945;
+Centauri being at a distance of 275,000) entirely filled with this fine
+sand. The number of grains of sand in this sphere of the fixed stars would
+be a decillion decillion<a name='fna_523' id='fna_523' href='#f_523'><small>[523]</small></a> (10<sup>66</sup>)<sup>6</sup>. All these grains of sand
+against one is the probability that a nebula devoid of hydrostatical
+pressure, such as that which formed the planets and satellites, will lead
+to the genesis of such small bodies revolving about a greatly predominant<span class="pagenum"><a name="Page_355" id="Page_355">[Pg 355]</a></span>
+central mass.&#8221;<a name='fna_524' id='fna_524' href='#f_524'><small>[524]</small></a> In other words, it is practically certain that the
+solar system was <i>not</i> formed from a gaseous nebula in the manner
+originally proposed by Laplace. On the other hand, the evolution of the
+solar system from a rotating spiral nebula seems very probable.</p>
+
+<hr style="width: 25%;" />
+
+<p>Some one has said that &#8220;the world knows nothing of its greatest men.&#8221; The
+name of Mr. George W. Hill will probably be unknown to many of my readers.
+But the late Prof. Simon Newcomb said of him that he &#8220;will easily rank as
+the greatest master of mathematical astronomy during the last quarter of
+the nineteenth century.&#8221;<a name='fna_525' id='fna_525' href='#f_525'><small>[525]</small></a> Of Prof. Newcomb himself&mdash;also a great
+master in the same subject&mdash;Sir Robert Ball says he was &#8220;the most
+conspicuous figure among the brilliant band of contemporary American
+astronomers.&#8221;<a name='fna_526' id='fna_526' href='#f_526'><small>[526]</small></a></p>
+
+<p>An astronomer is supposed to say, with reference to unwelcome visitors to
+his observatory, &#8220;Who steals my purse steals trash; but he that filches
+from me my clear nights, robs me of that which not enriches him, and makes
+me poor indeed.&#8221;<a name='fna_527' id='fna_527' href='#f_527'><small>[527]</small></a></p>
+
+<p>Cicero said, &#8220;In the heavens there is nothing fortuitous, unadvised,
+inconstant, or variable; all there is order, truth, reason, and
+constancy&#8221;; and he adds, &#8220;The creation is as plain a signal<span class="pagenum"><a name="Page_356" id="Page_356">[Pg 356]</a></span> of the being
+of a God, as a globe, a clock, or other artificial machine, is of a
+man.&#8221;<a name='fna_528' id='fna_528' href='#f_528'><small>[528]</small></a></p>
+
+<p>&#8220;Of all the epigrams attributed rightly or wrongly to Plato, the most
+famous has been expanded by Shelley into the four glorious lines&mdash;</p>
+
+<p class="poem">&#8220;&#8216;Thou wert the morning star among the living<br />
+<span style="margin-left: 1em;">Ere thy pure light had fled,</span><br />
+Now having died, thou art as Hesperus, giving<br />
+<span style="margin-left: 1em;">New splendour to the dead.&#8217;&#8221;<a name='fna_529' id='fna_529' href='#f_529'><small>[529]</small></a></span></p>
+
+<p>Sir David Brewster has well said,<a name='fna_530' id='fna_530' href='#f_530'><small>[530]</small></a> &#8220;Isaiah furnishes us with a
+striking passage, in which the occupants of the earth and the heavens are
+separately described, &#8216;I have made the earth, and created man upon it: I,
+even My hands, have stretched out the heavens, and all <i>their</i> host have I
+commanded&#8217; (Isaiah xlv. 12). But in addition to these obvious references
+to life and things pertaining to life, we find in Isaiah the following
+remarkable passage: &#8216;For thus saith the Lord that created the heavens; God
+Himself that formed the earth and made it; He hath established it, <i>He
+created it not</i> <span class="smcaplc">IN VAIN</span>, He formed <i>it to be inhabited</i>&#8217; (Isaiah xlv. 18).
+Here we have a distinct declaration from the inspired prophet that the
+<i>earth would have been created</i> <span class="smcaplc">IN VAIN</span> <i>if it had not been formed to be
+inhabited</i>; and hence we draw the conclusion that as the Creator cannot be
+supposed to have made the worlds of<span class="pagenum"><a name="Page_357" id="Page_357">[Pg 357]</a></span> our system and those in the sidereal
+system in vain, they must have been formed to be inhabited.&#8221; This seems to
+the present writer to be a good and sufficient reply to Dr. Wallace&#8217;s
+theory that our earth is the only inhabited world in the Universe!<a name='fna_531' id='fna_531' href='#f_531'><small>[531]</small></a>
+Such a theory seems incredible.</p>
+
+<p>The recent discovery made by Prof. Kapteyn, and confirmed by Mr.
+Eddington, of two drifts of stars, indicating the existence of <i>two</i>
+universes, seems to render untenable Dr. Wallace&#8217;s hypothesis of the
+earth&#8217;s central position in a single universe.<a href='#f_531'><small>[531]</small></a></p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<div class="note">
+<p class="center"><span class="smcap">Note added in the Press.</span></p>
+
+<p>While these pages were in the Press, it was announced, by Dr. Max Wolf of
+Heidelberg, that he found Halley&#8217;s comet on a photograph taken on the
+early morning of September 12, 1909. The discovery has been confirmed at
+Greenwich Observatory. The comet was close to the position predicted by
+the calculations of Messrs. Cowell and Crommelin of Greenwich Observatory
+(<i>Nature</i>, September 16, 1908).</p></div>
+
+<p><span class="pagenum"><a name="Page_358" id="Page_358">[Pg 358]</a></span></p>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><span class="pagenum"><a name="Page_359" id="Page_359">[Pg 359]</a></span></p>
+<p class="title">INDEX</p>
+
+
+<p class="index">
+<span class="large">A</span><br />
+<br />
+Aboukir, <a href="#Page_287">287</a><br />
+<br />
+Aboul Hassan, <a href="#Page_221">221</a><br />
+<br />
+Abu Ali al Farisi, <a href="#Page_225">225</a><br />
+<br />
+Abu-Hanifa, <a href="#Page_233">233</a>, <a href="#Page_234">234</a><br />
+<br />
+Abul-fadl, <a href="#Page_236">236</a><br />
+<br />
+Accadians, <a href="#Page_250">250</a>, <a href="#Page_252">252</a><br />
+<br />
+Achernar, <a href="#Page_275">275</a><br />
+<br />
+Aclian, <a href="#Page_282">282</a><br />
+<br />
+Adam, <a href="#Page_96">96</a>, <a href="#Page_347">347</a><br />
+<br />
+Adhad-al-Davlat, <a href="#Page_225">225</a>, <a href="#Page_236">236</a><br />
+<br />
+Adonis, <a href="#Page_261">261</a><br />
+<br />
+Adreaansz, <a href="#Page_342">342</a><br />
+<br />
+Airy, Sir G. B., <a href="#Page_87">87</a>, <a href="#Page_140">140</a>, <a href="#Page_347">347</a>, <a href="#Page_357">357</a><br />
+<br />
+Aitken, <a href="#Page_160">160</a><br />
+<br />
+Al-Battani, <a href="#Page_232">232</a>, <a href="#Page_233">233</a><br />
+<br />
+Albrecht, <a href="#Page_173">173</a><br />
+<br />
+Albufaragius, <a href="#Page_283">283</a><br />
+<br />
+Alcor, <a href="#Page_241">241</a><br />
+<br />
+Alcyone, <a href="#Page_137">137</a><br />
+<br />
+Aldebaran, <a href="#Page_60">60</a>, <a href="#Page_156">156</a>, <a href="#Page_236">236</a>, <a href="#Page_252">252</a>, <a href="#Page_257">257</a>, <a href="#Page_310">310</a>, <a href="#Page_311">311</a><br />
+<br />
+Alfard, <a href="#Page_236">236</a>, <a href="#Page_289">289</a><br />
+<br />
+Alfargani, <a href="#Page_286">286</a><br />
+<br />
+Alfraganus, <a href="#Page_281">281</a><br />
+<br />
+Almagest, <a href="#Page_281">281</a><br />
+<br />
+Al-Sufi, <a href="#Page_47">47</a>, <a href="#Page_149">149</a>, <a href="#Page_179">179</a>, <a href="#Page_189">189</a>, <a href="#Page_221">221</a>, <a href="#Page_224">224</a>, <a href="#Page_225">225-238</a>, <a href="#Page_244">244</a>, <a href="#Page_246">246</a>, <a href="#Page_250">250</a>, <a href="#Page_251">251</a>, <a href="#Page_253">253</a>, <a href="#Page_254">254</a>, <a href="#Page_261">261</a>, <a href="#Page_263">263</a>, <a href="#Page_264">264</a>, <a href="#Page_266">266-270</a>, <a href="#Page_272">272</a>, <a href="#Page_274">274-278</a>, <a href="#Page_285">285</a>, <a href="#Page_287">287</a>, <a href="#Page_289">289</a>, <a href="#Page_290">290</a>, <a href="#Page_293">293</a>, <a href="#Page_298">298</a>, <a href="#Page_300">300-302</a>, <a href="#Page_304">304</a>, <a href="#Page_307">307</a><br />
+<br />
+Altair, <a href="#Page_246">246</a><br />
+<br />
+Ampelius, <a href="#Page_262">262</a><br />
+<br />
+Amphion, <a href="#Page_257">257</a><br />
+<br />
+Ancient eclipses, <a href="#Page_52">52</a>, <a href="#Page_53">53</a><br />
+<br />
+Anderson, <a href="#Page_120">120</a>, <a href="#Page_277">277</a><br />
+<br />
+Andromeda nebula, <a href="#Page_198">198-206</a>, <a href="#Page_231">231</a><br />
+<br />
+Annals of Ulster, <a href="#Page_332">332</a><br />
+<br />
+Antares, <a href="#Page_60">60</a>, <a href="#Page_179">179</a>, <a href="#Page_310">310</a>, <a href="#Page_311">311</a><br />
+<br />
+Anthelm, <a href="#Page_300">300</a><br />
+<br />
+Antinous, <a href="#Page_248">248</a><br />
+<br />
+Antlia, <a href="#Page_302">302</a><br />
+<br />
+Apollo, <a href="#Page_257">257</a><br />
+<br />
+Apparent diameter of moon, <a href="#Page_49">49</a><br />
+<br />
+Apple, <a href="#Page_79">79</a><br />
+<br />
+&#8220;Apples, golden,&#8221; <a href="#Page_258">258</a><br />
+<br />
+Apus, <a href="#Page_306">306</a><br />
+<br />
+Aquarius, <a href="#Page_268">268</a><br />
+<br />
+Aquila, <a href="#Page_246">246</a><br />
+<br />
+Aquillus, <a href="#Page_220">220</a><br />
+<br />
+Ara <a href="#Page_295">295</a><br />
+<br />
+Arago, <a href="#Page_26">26</a>, <a href="#Page_30">30</a>, <a href="#Page_57">57</a>, <a href="#Page_116">116</a>, <a href="#Page_193">193</a>, <a href="#Page_331">331</a><br />
+<br />
+Aratus, <a href="#Page_219">219</a>, <a href="#Page_242">242</a>, <a href="#Page_245">245</a>, <a href="#Page_250">250</a>, <a href="#Page_255">255</a>, <a href="#Page_256">256</a>, <a href="#Page_261">261</a>, <a href="#Page_263">263</a>, <a href="#Page_272">272</a><br />
+<br />
+Archimedes, <a href="#Page_346">346</a>, <a href="#Page_354">354</a><br />
+<br />
+Arcturus, <a href="#Page_148">148</a>, <a href="#Page_188">188</a>, <a href="#Page_244">244</a><br />
+<br />
+Argelander, <a href="#Page_29">29</a>, <a href="#Page_227">227</a>, <a href="#Page_229">229</a>, <a href="#Page_230">230</a>, <a href="#Page_240">240</a><br />
+<br />
+Argo, <a href="#Page_285">285-288</a>, <a href="#Page_305">305</a><br />
+<br />
+Argon in sun, <a href="#Page_4">4</a><br />
+<br />
+Argonauts, <a href="#Page_243">243</a>, <a href="#Page_250">250</a><br />
+<br />
+Aries, <a href="#Page_250">250</a><br />
+<br />
+Aristotle, <a href="#Page_49">49</a>, <a href="#Page_67">67</a><br />
+<br />
+Arrhenius, <a href="#Page_4">4</a>, <a href="#Page_8">8</a>, <a href="#Page_22">22</a>, <a href="#Page_45">45</a>, <a href="#Page_66">66</a><br />
+<br />
+<span class="pagenum"><a name="Page_360" id="Page_360">[Pg 360]</a></span>Ashtoreth, <a href="#Page_260">260</a><br />
+<br />
+<i>Astra Borbonia</i>, <a href="#Page_4">4</a><br />
+<br />
+Astr&aelig;a, <a href="#Page_263">263</a><br />
+<br />
+Astronomy, Laplace on, <a href="#Page_44">44</a><br />
+<br />
+<i>Astro Theology</i>, <a href="#Page_23">23</a><br />
+<br />
+Atarid, <a href="#Page_232">232</a>, <a href="#Page_233">233</a><br />
+<br />
+Atmosphere, height of, <a href="#Page_33">33</a><br />
+<br />
+Augean stables, <a href="#Page_269">269</a><br />
+<br />
+Augustus, <a href="#Page_262">262</a><br />
+<br />
+Auriga, <a href="#Page_245">245</a><br />
+<br />
+Aurora, <a href="#Page_33">33</a>, <a href="#Page_41">41</a>, <a href="#Page_42">42</a><br />
+<br />
+Auwers, <a href="#Page_206">206</a><br />
+<br />
+Axis of Mars, <a href="#Page_59">59</a><br />
+<br />
+<br />
+<span class="large">B</span><br />
+<br />
+Babilu, <a href="#Page_267">267</a><br />
+<br />
+Baily, <a href="#Page_137">137</a>, <a href="#Page_144">144</a><br />
+<br />
+Baker, <a href="#Page_183">183</a><br />
+<br />
+Ball, Sir Robert, <a href="#Page_6">6</a>, <a href="#Page_355">355</a><br />
+<br />
+Barnard, Prof., <a href="#Page_29">29</a>, <a href="#Page_54">54</a>, <a href="#Page_57">57</a>, <a href="#Page_79">79</a>, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>, <a href="#Page_85">85</a>, <a href="#Page_86">86</a>, <a href="#Page_91">91</a>, <a href="#Page_93">93</a>, <a href="#Page_103">103</a>, <a href="#Page_104">104</a>, <a href="#Page_114">114</a>, <a href="#Page_130">130</a>, <a href="#Page_132">132</a>, <a href="#Page_139">139</a>, <a href="#Page_192">192</a>, <a href="#Page_213">213</a>, <a href="#Page_316">316</a>, <a href="#Page_317">317</a>, <a href="#Page_350">350</a><br />
+<br />
+Barnes, <a href="#Page_78">78</a>, <a href="#Page_79">79</a><br />
+<br />
+Bartlett, <a href="#Page_35">35</a>, <a href="#Page_36">36</a><br />
+<br />
+Bartschius, <a href="#Page_296">296</a>, <a href="#Page_298">298</a><br />
+<br />
+Bauschingen, <a href="#Page_69">69</a>, <a href="#Page_70">70</a><br />
+<br />
+Bayer, <a href="#Page_179">179</a>, <a href="#Page_221">221</a>, <a href="#Page_272">272</a>, <a href="#Page_284">284</a>, <a href="#Page_309">309</a>, <a href="#Page_310">310</a><br />
+<br />
+Bayeux Tapestry, <a href="#Page_105">105</a><br />
+<br />
+Becquerel, <a href="#Page_8">8</a><br />
+<br />
+&#8220;Beehive,&#8221; <a href="#Page_259">259</a><br />
+<br />
+Beer, <a href="#Page_20">20</a><br />
+<br />
+Bel, <a href="#Page_250">250</a><br />
+<br />
+Bellatrix, <a href="#Page_253">253</a><br />
+<br />
+Benoit, <a href="#Page_22">22</a><br />
+<br />
+Berenice, <a href="#Page_297">297</a><br />
+<br />
+Berry, <a href="#Page_25">25</a><br />
+<br />
+Bessel, <a href="#Page_339">339</a><br />
+<br />
+Betelgeuse, <a href="#Page_179">179</a>, <a href="#Page_222">222</a>, <a href="#Page_264">264</a><br />
+<br />
+Bianchini, <a href="#Page_21">21</a>, <a href="#Page_22">22</a>, <a href="#Page_77">77</a><br />
+<br />
+Biela&#8217;s comet, <a href="#Page_99">99</a><br />
+<br />
+Bifornis, <a href="#Page_268">268</a><br />
+<br />
+Binary stars, <a href="#Page_162">162</a><br />
+<br />
+Birmingham, <a href="#Page_5">5</a>, <a href="#Page_114">114</a><br />
+<br />
+&#8220;Black body,&#8221; <a href="#Page_3">3</a><br />
+<br />
+&#8220;Blackness&#8221; of sun-spots, <a href="#Page_6">6</a><br />
+<br />
+&#8220;Blaze star,&#8221; <a href="#Page_180">180</a>, <a href="#Page_184">184</a><br />
+<br />
+Bode, <a href="#Page_276">276</a><br />
+<br />
+Bohlin, <a href="#Page_199">199</a>, <a href="#Page_200">200</a><br />
+<br />
+Bond, <a href="#Page_85">85</a><br />
+<br />
+Bond (Jun.), <a href="#Page_74">74</a><br />
+<br />
+<i>Book of the Dead</i>, <a href="#Page_264">264</a>, <a href="#Page_274">274</a><br />
+<br />
+Borelly, <a href="#Page_103">103</a><br />
+<br />
+Boserup, <a href="#Page_28">28</a><br />
+<br />
+Boss, <a href="#Page_152">152</a><br />
+<br />
+Brah&eacute;, Tycho. <i>See</i> <a href="#tycho">Tycho Brah&eacute;</a><br />
+<br />
+Brauner, <a href="#Page_211">211</a><br />
+<br />
+Bravais, <a href="#Page_42">42</a><br />
+<br />
+Bredikhin, <a href="#Page_76">76</a><br />
+<br />
+Bremiker, <a href="#Page_94">94</a><br />
+<br />
+Brenner, L&eacute;o, <a href="#Page_13">13</a>, <a href="#Page_22">22</a>, <a href="#Page_87">87</a>, <a href="#Page_91">91</a>, <a href="#Page_133">133</a><br />
+<br />
+Brewster, <a href="#Page_356">356</a><br />
+<br />
+Brightness of Mercury, <a href="#Page_10">10-12</a><br />
+<br />
+<span style="margin-left: 2em;">"</span><span style="margin-left: 1.75em;">of nebul&aelig;, <a href="#Page_193">193</a></span><br />
+<br />
+<span style="margin-left: 2em;">"</span><span style="margin-left: 1.75em;">of sun, <a href="#Page_1">1</a>, <a href="#Page_2">2</a>, <a href="#Page_3">3</a></span><br />
+<br />
+<span style="margin-left: 2em;">"</span><span style="margin-left: 1.75em;">of Venus, <a href="#Page_14">14</a>, <a href="#Page_17">17</a>, <a href="#Page_19">19</a>, <a href="#Page_31">31</a></span><br />
+<br />
+Bright clouds, <a href="#Page_33">33</a>, <a href="#Page_34">34</a><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1.25em;">night, <a href="#Page_45">45</a></span><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1.25em;">stars, <a href="#Page_278">278</a></span><br />
+<br />
+Brooks, <a href="#Page_118">118</a><br />
+<br />
+Brown, <a href="#Page_218">218</a>, <a href="#Page_219">219</a>, <a href="#Page_248">248</a>, <a href="#Page_255">255</a>, <a href="#Page_260">260</a>, <a href="#Page_267">267</a>, <a href="#Page_272">272</a>, <a href="#Page_279">279</a>, <a href="#Page_281">281</a>, <a href="#Page_291">291</a>, <a href="#Page_295">295</a><br />
+<br />
+Browning, <a href="#Page_25">25</a><br />
+<br />
+Brugsch, <a href="#Page_127">127</a><br />
+<br />
+Buddha, <a href="#Page_256">256</a><br />
+<br />
+Bull, Pope&#8217;s, <a href="#Page_107">107</a><br />
+<br />
+&#8220;Bull&#8217;s foot,&#8221; <a href="#Page_253">253</a><br />
+<br />
+Buonaparte, <a href="#Page_30">30</a><br />
+<br />
+Burnham, <a href="#Page_160">160</a>, <a href="#Page_165">165-167</a>, <a href="#Page_180">180</a>, <a href="#Page_184">184</a>, <a href="#Page_260">260</a>, <a href="#Page_350">350</a>, <a href="#Page_351">351</a><br />
+<br />
+Burns, <a href="#Page_130">130</a><br />
+<br />
+Buss, <a href="#Page_4">4</a><br />
+<br />
+<br />
+<span class="large">C</span><br />
+<br />
+Caaba, <a href="#Page_125">125</a><br />
+<br />
+Cacciatore, <a href="#Page_72">72</a><br />
+<br />
+C&aelig;lum, <a href="#Page_302">302</a><br />
+<br />
+Callimachus, <a href="#Page_297">297</a><br />
+<br />
+<span class="pagenum"><a name="Page_361" id="Page_361">[Pg 361]</a></span>Callixtus III., <a href="#Page_107">107</a><br />
+<br />
+Calvisius, <a href="#Page_53">53</a><br />
+<br />
+Camelopardalis, <a href="#Page_296">296</a><br />
+<br />
+Cameron, <a href="#Page_18">18</a><br />
+<br />
+Campbell, <a href="#Page_85">85</a>, <a href="#Page_153">153</a>, <a href="#Page_159">159</a>, <a href="#Page_178">178</a><br />
+<br />
+&#8220;Canals&#8221; on Mars, <a href="#Page_61">61-63</a><br />
+<br />
+Cancer, <a href="#Page_258">258</a>, <a href="#Page_259">259</a><br />
+<br />
+Canes Venatici, <a href="#Page_296">296</a><br />
+<br />
+Canicula, <a href="#Page_280">280</a><br />
+<br />
+Canis Major, <a href="#Page_279">279</a><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1em;">Minor, <a href="#Page_284">284</a></span><br />
+<br />
+Canopus, <a href="#Page_157">157</a>, <a href="#Page_286">286</a>, <a href="#Page_344">344</a><br />
+<br />
+Capella, <a href="#Page_156">156</a>, <a href="#Page_164">164</a>, <a href="#Page_189">189</a>, <a href="#Page_236">236</a>, <a href="#Page_245">245</a>, <a href="#Page_246">246</a><br />
+<br />
+Capricornus, <a href="#Page_267">267</a>, <a href="#Page_268">268</a><br />
+<br />
+&#8220;Capture&#8221; of satellites, <a href="#Page_58">58</a><br />
+<br />
+Carbonic acid, <a href="#Page_66">66</a><br />
+<br />
+Cassini, <a href="#Page_20">20</a>, <a href="#Page_22">22</a>, <a href="#Page_74">74</a>, <a href="#Page_78">78</a>, <a href="#Page_358">358</a><br />
+<br />
+Cassiopeia&#8217;s Chair, <a href="#Page_244">244</a><br />
+<br />
+Castor, <a href="#Page_160">160</a>, <a href="#Page_257">257</a><br />
+<br />
+Caswell, <a href="#Page_52">52</a><br />
+<br />
+Catullus, <a href="#Page_297">297</a><br />
+<br />
+Caussin, <a href="#Page_225">225</a><br />
+<br />
+Cecrops, <a href="#Page_268">268</a><br />
+<br />
+&#8220;Celestial Rivers,&#8221; <a href="#Page_308">308</a><br />
+<br />
+Celoria, <a href="#Page_324">324</a>, <a href="#Page_326">326</a><br />
+<br />
+Centaurus, <a href="#Page_292">292</a>, <a href="#Page_293">293</a><br />
+<br />
+Centre of gravity, <a href="#Page_8">8</a><br />
+<br />
+Cephalus, <a href="#Page_279">279</a><br />
+<br />
+Cepheid variables, <a href="#Page_187">187</a><br />
+<br />
+Ceraski, <a href="#Page_2">2</a>, <a href="#Page_176">176</a><br />
+<br />
+Cerberus, <a href="#Page_243">243</a>, <a href="#Page_257">257</a><br />
+<br />
+Ceres, <a href="#Page_260">260</a><br />
+<br />
+Cerulli, <a href="#Page_22">22</a>, <a href="#Page_62">62</a><br />
+<br />
+Cetus, <a href="#Page_272">272</a><br />
+<br />
+Chacornac, <a href="#Page_18">18</a>, <a href="#Page_84">84</a><br />
+<br />
+Cham&aelig;lion, <a href="#Page_305">305</a><br />
+<br />
+Chamberlin, <a href="#Page_194">194</a><br />
+<br />
+Chambers, <a href="#Page_72">72</a><br />
+<br />
+&#8220;Charles&#8217; Wain,&#8221; <a href="#Page_240">240</a><br />
+<br />
+Chinese Annals, <a href="#Page_19">19</a>, <a href="#Page_30">30</a>, <a href="#Page_105">105</a>, <a href="#Page_186">186</a>, <a href="#Page_223">223</a>, <a href="#Page_267">267</a>, <a href="#Page_330">330</a><br />
+<br />
+Childrey, <a href="#Page_128">128</a><br />
+<br />
+Chiron, <a href="#Page_295">295</a><br />
+<br />
+Christmann, <a href="#Page_281">281</a><br />
+<br />
+Chromosphere, sun&#8217;s, <a href="#Page_4">4</a><br />
+<br />
+Cicero, <a href="#Page_49">49</a>, <a href="#Page_262">262</a>, <a href="#Page_280">280</a>, <a href="#Page_355">355</a><br />
+<br />
+Circinus, <a href="#Page_307">307</a><br />
+<br />
+Clavius, <a href="#Page_334">334</a><br />
+<br />
+Climate, <a href="#Page_45">45</a><br />
+<br />
+&#8220;Coal Sack,&#8221; <a href="#Page_293">293</a>, <a href="#Page_320">320</a><br />
+<br />
+Cobham, <a href="#Page_88">88</a>, <a href="#Page_102">102</a><br />
+<br />
+Colbert, <a href="#Page_175">175</a><br />
+<br />
+Colours of stars, <a href="#Page_140">140</a>, <a href="#Page_141">141</a>, <a href="#Page_188">188-190</a><br />
+<br />
+Coma Berenices, <a href="#Page_297">297</a>, <a href="#Page_298">298</a><br />
+<br />
+Comets, number of, <a href="#Page_98">98</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.75em;">tails of, <a href="#Page_115">115</a>, <a href="#Page_116">116</a></span><br />
+<br />
+Comet years, <a href="#Page_104">104</a><br />
+<br />
+Comiers, <a href="#Page_99">99</a><br />
+<br />
+Comstock, <a href="#Page_90">90</a>, <a href="#Page_146">146</a><br />
+<br />
+Condamine, <a href="#Page_257">257</a><br />
+<br />
+Conon, <a href="#Page_297">297</a><br />
+<br />
+Coon Butte mountain, <a href="#Page_120">120</a>, <a href="#Page_121">121</a><br />
+<br />
+Cooper, <a href="#Page_3">3</a><br />
+<br />
+Copeland, <a href="#Page_76">76</a>, <a href="#Page_157">157</a><br />
+<br />
+Corona, sun&#8217;s, <a href="#Page_1">1</a>, <a href="#Page_334">334</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.75em;">round moon, <a href="#Page_35">35</a>, <a href="#Page_36">36</a></span><br />
+<br />
+Corona Australis, <a href="#Page_295">295</a><br />
+<br />
+Corvinus, <a href="#Page_292">292</a><br />
+<br />
+Corvus, <a href="#Page_292">292</a><br />
+<br />
+Cotsworth, <a href="#Page_46">46</a><br />
+<br />
+Cowell, <a href="#Page_105">105</a><br />
+<br />
+Crabtree, <a href="#Page_337">337</a><br />
+<br />
+Crater, <a href="#Page_291">291</a><br />
+<br />
+Craters on moon, <a href="#Page_55">55</a>, <a href="#Page_56">56</a><br />
+<br />
+Crawford, <a href="#Page_348">348</a><br />
+<br />
+Crecy, Battle of, <a href="#Page_333">333</a><br />
+<br />
+Crescent of Venus, <a href="#Page_19">19</a>, <a href="#Page_20">20</a><br />
+<br />
+Crommelin, <a href="#Page_105">105</a>, <a href="#Page_111">111</a><br />
+<br />
+Crucifixion, <a href="#Page_18">18</a><br />
+<br />
+Curtis, <a href="#Page_344">344</a><br />
+<br />
+Cusps of Venus, <a href="#Page_20">20</a><br />
+<br />
+Cygnus, (61), <a href="#Page_155">155</a><br />
+<br />
+Cynocephalus, <a href="#Page_222">222</a><br />
+<br />
+<br />
+<span class="large">D</span><br />
+<br />
+Dante, <a href="#Page_156">156</a>, <a href="#Page_258">258</a>, <a href="#Page_265">265</a><br />
+<br />
+Dark shade on moon, <a href="#Page_333">333</a><br />
+<br />
+D&#8217;Arrest, <a href="#Page_94">94</a><br />
+<br />
+Darwin, Sir George, <a href="#Page_158">158</a>, <a href="#Page_319">319</a><br />
+<br />
+&#8220;David&#8217;s Chariot,&#8221; <a href="#Page_241">241</a><br />
+<br />
+Davis, <a href="#Page_155">155</a><br />
+<br />
+Dawes, <a href="#Page_168">168</a><br />
+<br />
+<span class="pagenum"><a name="Page_362" id="Page_362">[Pg 362]</a></span>&#8220;Dawn proclaimer,&#8221; <a href="#Page_251">251</a><br />
+<br />
+Delambre, <a href="#Page_185">185</a><br />
+<br />
+Delauney, <a href="#Page_347">347</a><br />
+<br />
+Dembowski, <a href="#Page_190">190</a><br />
+<br />
+Demetrius, <a href="#Page_111">111</a><br />
+<br />
+Denning, <a href="#Page_11">11</a>, <a href="#Page_74">74</a>, <a href="#Page_77">77</a>, <a href="#Page_84">84</a>, <a href="#Page_86">86</a>, <a href="#Page_87">87</a>, <a href="#Page_89">89</a>, <a href="#Page_99">99</a>, <a href="#Page_118">118</a>, <a href="#Page_340">340</a><br />
+<br />
+Derham, <a href="#Page_21">21</a>, <a href="#Page_23">23</a><br />
+<br />
+Deucalion, <a href="#Page_268">268</a><br />
+<br />
+De Vico, <a href="#Page_21">21</a>, <a href="#Page_22">22</a><br />
+<br />
+Diamonds in meteorites, <a href="#Page_127">127</a><br />
+<br />
+Dilkur, <a href="#Page_251">251</a><br />
+<br />
+Diodorus Siculus, <a href="#Page_127">127</a><br />
+<br />
+Diogenes Laertius, <a href="#Page_41">41</a><br />
+<br />
+Diomed, <a href="#Page_272">272</a><br />
+<br />
+Dione, <a href="#Page_89">89</a><br />
+<br />
+&#8220;Dipper,&#8221; <a href="#Page_241">241</a><br />
+<br />
+Doberck, <a href="#Page_160">160</a><br />
+<br />
+Dollond, <a href="#Page_24">24</a><br />
+<br />
+Domitian, <a href="#Page_334">334</a><br />
+<br />
+Donati&#8217;s comet, <a href="#Page_100">100</a><br />
+<br />
+Dorado, <a href="#Page_304">304</a><br />
+<br />
+Dordona, <a href="#Page_256">256</a><br />
+<br />
+Dorn, <a href="#Page_245">245</a><br />
+<br />
+Douglass, <a href="#Page_81">81</a><br />
+<br />
+Dragon, <a href="#Page_242">242</a><br />
+<br />
+Draper, <a href="#Page_75">75</a><br />
+<br />
+Drayton, <a href="#Page_156">156</a><br />
+<br />
+Dreyer, <a href="#Page_115">115</a><br />
+<br />
+Drifting stars, <a href="#Page_152">152</a><br />
+<br />
+Dryden, <a href="#Page_242">242</a><br />
+<br />
+Duncan, <a href="#Page_187">187</a><br />
+<br />
+Dunlop, <a href="#Page_264">264</a><br />
+<br />
+Dupret, <a href="#Page_83">83</a><br />
+<br />
+Dupuis, <a href="#Page_245">245</a>, <a href="#Page_252">252</a>, <a href="#Page_257">257</a>, <a href="#Page_258">258</a>, <a href="#Page_259">259</a>, <a href="#Page_266">266</a>, <a href="#Page_267">267</a>, <a href="#Page_268">268</a><br />
+<br />
+&#8220;Dusky star,&#8221; <a href="#Page_272">272</a><br />
+<br />
+<br />
+<span class="large">E</span><br />
+<br />
+&#8220;Earthen jar,&#8221; <a href="#Page_247">247</a><br />
+<br />
+Earth&#8217;s attraction on moon, <a href="#Page_55">55</a><br />
+<br />
+Earth&#8217;s motions, <a href="#Page_39">39</a><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1.75em;">rotation, <a href="#Page_46">46</a></span><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1.75em;">surface, <a href="#Page_32">32</a></span><br />
+<br />
+&#8220;Earthshine&#8221; on moon, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_56">56</a>, <a href="#Page_57">57</a><br />
+<br />
+Eastmann, <a href="#Page_316">316</a><br />
+<br />
+Easton, <a href="#Page_323">323</a>, <a href="#Page_324">324</a>, <a href="#Page_325">325</a><br />
+<br />
+Eclipses, ancient, <a href="#Page_52">52</a>, <a href="#Page_53">53</a>, <a href="#Page_57">57</a>, <a href="#Page_58">58</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.75em;">dark, of moon, <a href="#Page_53">53</a>, <a href="#Page_57">57</a>, <a href="#Page_58">58</a></span><br />
+<br />
+Ecliptic, obliquity of, <a href="#Page_47">47</a><br />
+<br />
+Eddington, <a href="#Page_357">357</a><br />
+<br />
+Electra, <a href="#Page_19">19</a><br />
+<br />
+Elster, <a href="#Page_39">39</a><br />
+<br />
+Emerson, <a href="#Page_353">353</a><br />
+<br />
+Enceladus, <a href="#Page_89">89</a><br />
+<br />
+Encke, <a href="#Page_113">113</a>, <a href="#Page_116">116</a>, <a href="#Page_240">240</a><br />
+<br />
+Ennis, <a href="#Page_189">189</a><br />
+<br />
+Eratosthenes, <a href="#Page_250">250</a>, <a href="#Page_297">297</a>, <a href="#Page_345">345</a><br />
+<br />
+Eridanus, <a href="#Page_274">274-278</a><br />
+<br />
+Eros, <a href="#Page_69">69</a>, <a href="#Page_70">70</a>, <a href="#Page_71">71</a><br />
+<br />
+Eta Argus, <a href="#Page_177">177</a>, <a href="#Page_287">287</a><br />
+<br />
+Eudemus, <a href="#Page_47">47</a><br />
+<br />
+Eudoxus, <a href="#Page_218">218</a>, <a href="#Page_219">219</a>, <a href="#Page_223">223</a><br />
+<br />
+Euler, <a href="#Page_56">56</a><br />
+<br />
+Eunomia, <a href="#Page_71">71</a><br />
+<br />
+Europa, <a href="#Page_252">252</a><br />
+<br />
+<br />
+<span class="large">F</span><br />
+<br />
+Fabritius, <a href="#Page_4">4</a>, <a href="#Page_101">101</a><br />
+<br />
+Fabry, <a href="#Page_1">1</a><br />
+<br />
+Faint stars in telescope, <a href="#Page_176">176</a><br />
+<br />
+&#8220;False Cross,&#8221; <a href="#Page_156">156</a><br />
+<br />
+&#8220;Famous stars,&#8221; <a href="#Page_246">246</a><br />
+<br />
+Fath, <a href="#Page_130">130</a>, <a href="#Page_213">213</a><br />
+<br />
+Faye, <a href="#Page_100">100</a><br />
+<br />
+February, Five Sundays in, <a href="#Page_36">36</a><br />
+<br />
+Fergani, <a href="#Page_189">189</a><br />
+<br />
+&#8220;Fisher Stars,&#8221; <a href="#Page_256">256</a><br />
+<br />
+&#8220;Fishes in Andromeda,&#8221; <a href="#Page_249">249</a><br />
+<br />
+Fitzgerald, <a href="#Page_127">127</a><br />
+<br />
+Flammarion, <a href="#Page_22">22</a>, <a href="#Page_26">26</a>, <a href="#Page_50">50</a>, <a href="#Page_138">138</a>, <a href="#Page_255">255</a>, <a href="#Page_265">265</a>, <a href="#Page_276">276</a><br />
+<br />
+Flamsteed, <a href="#Page_348">348</a><br />
+<br />
+&#8220;Flat earth&#8221; theory, <a href="#Page_32">32</a><br />
+<br />
+Fomalhaut, <a href="#Page_271">271</a>, <a href="#Page_309">309</a>, <a href="#Page_310">310</a><br />
+<br />
+Fontana, <a href="#Page_20">20</a><br />
+<br />
+Fontenelle, <a href="#Page_357">357</a><br />
+<br />
+Forbes, <a href="#Page_82">82</a>, <a href="#Page_95">95</a>, <a href="#Page_96">96</a><br />
+<br />
+Fornax, <a href="#Page_301">301</a><br />
+<br />
+<span class="pagenum"><a name="Page_363" id="Page_363">[Pg 363]</a></span>Fournier, <a href="#Page_87">87</a><br />
+<br />
+Fovea, <a href="#Page_284">284</a><br />
+<br />
+Freeman, <a href="#Page_88">88</a><br />
+<br />
+Fr&eacute;ret, <a href="#Page_222">222</a><br />
+<br />
+Frisby, <a href="#Page_101">101</a><br />
+<br />
+Fritsch, <a href="#Page_21">21</a><br />
+<br />
+Furner, <a href="#Page_163">163</a><br />
+<br />
+<br />
+<span class="large">G</span><br />
+<br />
+Gale, <a href="#Page_78">78</a><br />
+<br />
+Galileo, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>, <a href="#Page_80">80</a>, <a href="#Page_82">82</a><br />
+<br />
+Galle, <a href="#Page_94">94</a>, <a href="#Page_341">341</a><br />
+<br />
+Ganymede, <a href="#Page_268">268</a><br />
+<br />
+Gaseous nebula, spectra of, <a href="#Page_195">195-198</a>, <a href="#Page_212">212</a><br />
+<br />
+Gassendi, <a href="#Page_14">14</a>, <a href="#Page_139">139</a><br />
+<br />
+Gathman, <a href="#Page_118">118</a><br />
+<br />
+Gaubil, <a href="#Page_99">99</a><br />
+<br />
+Gauthier, <a href="#Page_103">103</a><br />
+<br />
+Gegenschein, <a href="#Page_131">131</a><br />
+<br />
+Gemini, <a href="#Page_257">257</a>, <a href="#Page_258">258</a><br />
+<br />
+Geminid variables, <a href="#Page_187">187</a><br />
+<br />
+Gentil, Le, <a href="#Page_338">338</a>, <a href="#Page_339">339</a><br />
+<br />
+Gertel, <a href="#Page_39">39</a><br />
+<br />
+Ghizeh, Pyramids of, <a href="#Page_353">353</a><br />
+<br />
+Gibbous phase of Jupiter, <a href="#Page_75">75</a><br />
+<br />
+Gill, Sir David, <a href="#Page_118">118</a>, <a href="#Page_215">215</a>, <a href="#Page_216">216</a>, <a href="#Page_346">346</a><br />
+<br />
+Glacial epoch, <a href="#Page_42">42</a><br />
+<br />
+Gledhill, <a href="#Page_76">76</a><br />
+<br />
+Globular clusters, <a href="#Page_214">214</a>, <a href="#Page_215">215</a><br />
+<br />
+Goad, <a href="#Page_12">12</a><br />
+<br />
+Goatcher, <a href="#Page_179">179</a><br />
+<br />
+&#8220;Golden apples,&#8221; <a href="#Page_258">258</a><br />
+<br />
+Golius, <a href="#Page_281">281</a><br />
+<br />
+Gould, <a href="#Page_229">229</a>, <a href="#Page_278">278</a>, <a href="#Page_301">301</a>, <a href="#Page_304">304</a>, <a href="#Page_309">309</a>, <a href="#Page_310">310</a>, <a href="#Page_326">326</a><br />
+<br />
+Grant, <a href="#Page_82">82</a>, <a href="#Page_96">96</a>, <a href="#Page_345">345</a><br />
+<br />
+Gravitation, Law of, <a href="#Page_15">15</a>, <a href="#Page_40">40</a><br />
+<br />
+Greely, <a href="#Page_186">186</a><br />
+<br />
+Greisbach, <a href="#Page_80">80</a><br />
+<br />
+Groombridge 1830, <a href="#Page_159">159</a><br />
+<br />
+Grubb, Sir Howard, <a href="#Page_164">164</a><br />
+<br />
+Gruithuisen, <a href="#Page_21">21</a>, <a href="#Page_25">25</a>, <a href="#Page_26">26</a>, <a href="#Page_28">28</a><br />
+<br />
+Gruson, <a href="#Page_127">127</a><br />
+<br />
+Guillaume, <a href="#Page_331">331</a><br />
+<br />
+Guthrie, <a href="#Page_25">25</a><br />
+<br />
+<br />
+<span class="large">H</span><br />
+<br />
+Habitability of Mars, <a href="#Page_63">63-66</a><br />
+<br />
+<span style="margin-left: 2em;">"</span><span style="margin-left: 2.25em;">of planets, <a href="#Page_40">40</a></span><br />
+<br />
+Hadrian, <a href="#Page_248">248</a><br />
+<br />
+Halbert, <a href="#Page_78">78</a><br />
+<br />
+Hale, <a href="#Page_148">148</a>, <a href="#Page_150">150</a><br />
+<br />
+Hall, <a href="#Page_15">15</a>, <a href="#Page_131">131</a><br />
+<br />
+Halley, <a href="#Page_14">14</a>, <a href="#Page_17">17</a>, <a href="#Page_99">99</a>, <a href="#Page_105">105</a>, <a href="#Page_106">106</a>, <a href="#Page_108">108</a>, <a href="#Page_109">109</a>, <a href="#Page_116">116</a>, <a href="#Page_143">143</a>, <a href="#Page_145">145</a>, <a href="#Page_276">276</a><br />
+<br />
+Halm, <a href="#Page_122">122</a><br />
+<br />
+Halo, <a href="#Page_35">35</a>, <a href="#Page_36">36</a><br />
+<br />
+Hanouman, <a href="#Page_284">284</a><br />
+<br />
+Hansen, <a href="#Page_351">351</a><br />
+<br />
+Hansky, <a href="#Page_27">27</a><br />
+<br />
+Harding, <a href="#Page_25">25</a>, <a href="#Page_26">26</a>, <a href="#Page_94">94</a><br />
+<br />
+&#8220;Harris, Mrs.,&#8221; <a href="#Page_90">90</a><br />
+<br />
+Hartwig, <a href="#Page_88">88</a>, <a href="#Page_173">173</a><br />
+<br />
+Harvests, <a href="#Page_104">104</a><br />
+<br />
+Heat of sun, <a href="#Page_2">2</a>, <a href="#Page_3">3</a>, <a href="#Page_7">7</a><br />
+<br />
+Height of atmosphere, <a href="#Page_33">33</a><br />
+<br />
+Heis, <a href="#Page_132">132</a>, <a href="#Page_175">175</a>, <a href="#Page_189">189</a>, <a href="#Page_227">227</a>, <a href="#Page_229">229</a>, <a href="#Page_344">344</a><br />
+<br />
+Helium, <a href="#Page_4">4</a><br />
+<br />
+Hepidanus, <a href="#Page_267">267</a>, <a href="#Page_348">348</a><br />
+<br />
+Hercules, <a href="#Page_243">243</a>, <a href="#Page_259">259</a>, <a href="#Page_268">268</a><br />
+<br />
+Herod, <a href="#Page_18">18</a>, <a href="#Page_53">53</a><br />
+<br />
+Herschel, Miss Caroline, <a href="#Page_193">193</a>, <a href="#Page_194">194</a>, <a href="#Page_324">324</a>, <a href="#Page_357">357</a><br />
+<br />
+Herschel, Sir John, <a href="#Page_112">112</a>, <a href="#Page_177">177</a>, <a href="#Page_190">190</a>, <a href="#Page_207">207</a>, <a href="#Page_209">209</a>, <a href="#Page_210">210</a>, <a href="#Page_215">215</a>, <a href="#Page_289">289</a>, <a href="#Page_314">314</a>, <a href="#Page_346">346</a>, <a href="#Page_353">353</a><br />
+<br />
+Herschel, Sir Wm., <a href="#Page_3">3</a>, <a href="#Page_24">24</a>, <a href="#Page_80">80</a>, <a href="#Page_112">112</a>, <a href="#Page_114">114</a>, <a href="#Page_115">115</a>, <a href="#Page_116">116</a>, <a href="#Page_171">171</a>, <a href="#Page_178">178</a>, <a href="#Page_179">179</a>, <a href="#Page_190">190</a>, <a href="#Page_324">324</a>, <a href="#Page_325">325</a><br />
+<br />
+Hesiod, <a href="#Page_17">17</a>, <a href="#Page_220">220</a><br />
+<br />
+Hesperus, <a href="#Page_256">256</a><br />
+<br />
+Hevelius, <a href="#Page_99">99</a>, <a href="#Page_116">116</a>, <a href="#Page_221">221</a>, <a href="#Page_296">296</a>, <a href="#Page_299">299</a>, <a href="#Page_300">300</a><br />
+<br />
+Hill, <a href="#Page_87">87</a>, <a href="#Page_355">355</a><br />
+<br />
+Hind, <a href="#Page_19">19</a>, <a href="#Page_30">30</a>, <a href="#Page_54">54</a>, <a href="#Page_105">105</a>, <a href="#Page_111">111</a>, <a href="#Page_180">180</a><br />
+<br />
+Hipparchus, <a href="#Page_135">135</a>, <a href="#Page_221">221-223</a>, <a href="#Page_226">226</a>, <a href="#Page_250">250</a>, <a href="#Page_278">278</a>, <a href="#Page_281">281</a>, <a href="#Page_293">293</a>, <a href="#Page_329">329</a><br />
+<br />
+Hippocrates, <a href="#Page_258">258</a><br />
+<br />
+Hirst, <a href="#Page_333">333</a><br />
+<br />
+Holetschak, <a href="#Page_108">108</a><br />
+<br />
+Homer, <a href="#Page_17">17</a><br />
+<br />
+<span class="pagenum"><a name="Page_364" id="Page_364">[Pg 364]</a></span>Honorat, <a href="#Page_84">84</a><br />
+<br />
+Hooke, <a href="#Page_74">74</a>, <a href="#Page_128">128</a><br />
+<br />
+Horace, <a href="#Page_280">280</a><br />
+<br />
+Horologium, <a href="#Page_303">303</a><br />
+<br />
+Horus, <a href="#Page_145">145</a>, <a href="#Page_258">258</a><br />
+<br />
+Horrebow, <a href="#Page_29">29</a><br />
+<br />
+Horrocks, <a href="#Page_337">337</a><br />
+<br />
+Hortensus, Martinus, <a href="#Page_139">139</a><br />
+<br />
+Hough, <a href="#Page_76">76</a><br />
+<br />
+Houzeau, <a href="#Page_227">227</a>, <a href="#Page_229">229</a>, <a href="#Page_262">262</a>, <a href="#Page_274">274</a>, <a href="#Page_344">344</a><br />
+<br />
+Hovedin, Roger de, <a href="#Page_53">53</a><br />
+<br />
+Hubbard, <a href="#Page_100">100</a><br />
+<br />
+Huggins, Sir Wm., <a href="#Page_91">91</a>, <a href="#Page_148">148</a>, <a href="#Page_180">180</a><br />
+<br />
+Humboldt, <a href="#Page_30">30</a>, <a href="#Page_82">82</a>, <a href="#Page_83">83</a>, <a href="#Page_124">124</a>, <a href="#Page_128">128</a>, <a href="#Page_134">134</a>, <a href="#Page_154">154</a>, <a href="#Page_157">157</a>, <a href="#Page_342">342</a>, <a href="#Page_352">352</a>, <a href="#Page_357">357</a><br />
+<br />
+Hussey, <a href="#Page_88">88</a><br />
+<br />
+Hyades, <a href="#Page_157">157</a>, <a href="#Page_252">252</a>, <a href="#Page_253">253</a>, <a href="#Page_257">257</a><br />
+<br />
+Hydra, <a href="#Page_288">288</a><br />
+<br />
+Hydrus, <a href="#Page_303">303</a><br />
+<br />
+Hyperion, <a href="#Page_88">88</a>, <a href="#Page_90">90</a><br />
+<br />
+<br />
+<span class="large">I</span><br />
+<br />
+Ibn al-Aalam, <a href="#Page_225">225</a><br />
+<br />
+Ibn Alraqqa, <a href="#Page_281">281</a><br />
+<br />
+Icarus, <a href="#Page_284">284</a><br />
+<br />
+Indus, <a href="#Page_307">307</a><br />
+<br />
+Inhabited worlds, <a href="#Page_328">328</a>, <a href="#Page_357">357</a><br />
+<br />
+Innes, <a href="#Page_78">78</a>, <a href="#Page_168">168</a><br />
+<br />
+Intra-Mercurial planet, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_29">29</a><br />
+<br />
+Invention of telescope, <a href="#Page_342">342</a><br />
+<br />
+Io, <a href="#Page_252">252</a><br />
+<br />
+Ions, <a href="#Page_27">27</a><br />
+<br />
+Iris, <a href="#Page_71">71</a><br />
+<br />
+Isaiah, <a href="#Page_17">17</a>, <a href="#Page_356">356</a><br />
+<br />
+Isis, <a href="#Page_252">252</a>, <a href="#Page_261">261</a>, <a href="#Page_282">282</a>, <a href="#Page_283">283</a><br />
+<br />
+Istar, <a href="#Page_260">260</a><br />
+<br />
+<br />
+<span class="large">J</span><br />
+<br />
+Jansen, <a href="#Page_342">342</a><br />
+<br />
+Japetus, <a href="#Page_89">89</a>, <a href="#Page_90">90</a><br />
+<br />
+Jason, <a href="#Page_257">257</a>, <a href="#Page_285">285</a><br />
+<br />
+Johnson, Rev. S. J., <a href="#Page_19">19</a><br />
+<br />
+Jonckheere, <a href="#Page_15">15</a><br />
+<br />
+Jones, <a href="#Page_129">129</a><br />
+<br />
+Jordan, <a href="#Page_174">174</a><br />
+<br />
+Jupiter, <a href="#CHAPTER_VIII">chap. viii.</a><br />
+<br />
+<span style="margin-left: 1.25em;">"</span><span style="margin-left: 1.5em;">gibbous form of, <a href="#Page_75">75</a></span><br />
+<br />
+<span style="margin-left: 1.25em;">"</span><span style="margin-left: 1.5em;">and sun, <a href="#Page_8">8</a></span><br />
+<br />
+<br />
+<span class="large">K</span><br />
+<br />
+Kalevala, <a href="#Page_240">240</a><br />
+<br />
+Kapteyn, <a href="#Page_314">314</a>, <a href="#Page_316">316</a>, <a href="#Page_321">321</a>, <a href="#Page_322">322</a>, <a href="#Page_326">326</a>, <a href="#Page_357">357</a><br />
+<br />
+Kazemerski, <a href="#Page_244">244</a><br />
+<br />
+Keeler, <a href="#Page_86">86</a>, <a href="#Page_215">215</a><br />
+<br />
+Kelvin, Lord, <a href="#Page_206">206</a>, <a href="#Page_315">315</a>, <a href="#Page_316">316</a><br />
+<br />
+Kempf, <a href="#Page_174">174</a><br />
+<br />
+Kepler, <a href="#Page_52">52</a>, <a href="#Page_57">57</a>, <a href="#Page_298">298</a>, <a href="#Page_340">340</a>, <a href="#Page_341">341</a>, <a href="#Page_351">351</a><br />
+<br />
+Khayyam, Omar, <a href="#Page_127">127</a><br />
+<br />
+Kimah, <a href="#Page_255">255</a><br />
+<br />
+Kimball, <a href="#Page_51">51</a><br />
+<br />
+Kimta, <a href="#Page_255">255</a><br />
+<br />
+Kirch, <a href="#Page_23">23</a>, <a href="#Page_115">115</a><br />
+<br />
+Kirkwood, <a href="#Page_6">6</a><br />
+<br />
+Kleiber, <a href="#Page_123">123</a><br />
+<br />
+Klein, <a href="#Page_114">114</a>, <a href="#Page_183">183</a><br />
+<br />
+Knobel, <a href="#Page_238">238</a>, <a href="#Page_263">263</a><br />
+<br />
+Konkoly, <a href="#Page_183">183</a><br />
+<br />
+Koran, <a href="#Page_127">127</a>, <a href="#Page_270">270</a><br />
+<br />
+Kreusler, <a href="#Page_4">4</a><br />
+<br />
+Kreutz, <a href="#Page_101">101</a>, <a href="#Page_112">112</a><br />
+<br />
+<br />
+<span class="large">L</span><br />
+<br />
+Lacaille, <a href="#Page_294">294</a>, <a href="#Page_301">301</a>, <a href="#Page_302">302</a><br />
+<br />
+Lacerta, <a href="#Page_300">300</a><br />
+<br />
+Lagrange, <a href="#Page_345">345</a><br />
+<br />
+La Hire, <a href="#Page_20">20</a>, <a href="#Page_21">21</a><br />
+<br />
+Lalande, <a href="#Page_143">143</a>, <a href="#Page_144">144</a>, <a href="#Page_284">284</a><br />
+<br />
+Landerer, <a href="#Page_52">52</a><br />
+<br />
+Langdon, <a href="#Page_25">25</a><br />
+<br />
+Langley, Prof., <a href="#Page_3">3</a><br />
+<br />
+Laplace, <a href="#Page_43">43</a>, <a href="#Page_44">44</a>, <a href="#Page_98">98</a>, <a href="#Page_346">346</a>, <a href="#Page_351">351</a>, <a href="#Page_354">354</a><br />
+<br />
+Larkin, <a href="#Page_65">65</a><br />
+<br />
+Lassell, <a href="#Page_77">77</a>, <a href="#Page_128">128</a><br />
+<br />
+&#8220;Last in the River,&#8221; <a href="#Page_275">275-298</a><br />
+<br />
+Last year of century, <a href="#Page_37">37</a><br />
+<span class="pagenum"><a name="Page_365" id="Page_365">[Pg 365]</a></span><br />
+Lau, <a href="#Page_178">178</a>, <a href="#Page_183">183</a><br />
+<br />
+Leo, <a href="#Page_259">259</a><br />
+<br />
+Leo Minor, <a href="#Page_298">298</a><br />
+<br />
+Lepus, <a href="#Page_278">278</a>, <a href="#Page_279">279</a><br />
+<br />
+Lern&aelig;an marsh, <a href="#Page_258">258</a><br />
+<br />
+Leverrier, <a href="#Page_44">44</a>, <a href="#Page_347">347</a>, <a href="#Page_351">351</a><br />
+<br />
+Lewis, <a href="#Page_156">156</a>, <a href="#Page_162">162</a><br />
+<br />
+Lewis, Sir G. C., <a href="#Page_17">17</a><br />
+<br />
+Lexell&#8217;s comet, <a href="#Page_98">98</a><br />
+<br />
+Libra, <a href="#Page_262">262</a><br />
+<br />
+Life, possible, in Mars, <a href="#Page_63">63-65</a><br />
+<br />
+Light of full moon, <a href="#Page_1">1</a>, <a href="#Page_51">51</a><br />
+<br />
+Lippershey, <a href="#Page_342">342</a><br />
+<br />
+Littrow, <a href="#Page_339">339</a><br />
+<br />
+Lockyer, Sir Norman, <a href="#Page_144">144</a>, <a href="#Page_147">147</a><br />
+<br />
+Lodge, Sir Oliver, <a href="#Page_55">55</a><br />
+<br />
+Long, <a href="#Page_343">343</a>, <a href="#Page_357">357</a><br />
+<br />
+Longfellow, <a href="#Page_156">156</a>, <a href="#Page_273">273</a><br />
+<br />
+Lottin, <a href="#Page_42">42</a><br />
+<br />
+Lowell, <a href="#Page_22">22</a>, <a href="#Page_43">43</a>, <a href="#Page_59">59</a>, <a href="#Page_61">61</a>, <a href="#Page_64">64</a>, <a href="#Page_88">88</a><br />
+<br />
+Lucifer, <a href="#Page_17">17</a><br />
+<br />
+Lucretius, <a href="#Page_320">320</a><br />
+<br />
+&#8220;Luminous clouds,&#8221; <a href="#Page_33">33</a>, <a href="#Page_34">34</a><br />
+<br />
+Lunar craters, <a href="#Page_55">55</a>, <a href="#Page_56">56</a><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1em;">&#8220;mansions,&#8221; <a href="#Page_251">251</a></span><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1em;">mountains, <a href="#Page_58">58</a></span><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1em;">theory, <a href="#Page_56">56</a></span><br />
+<br />
+Lunt, <a href="#Page_179">179</a><br />
+<br />
+Lupus, <a href="#Page_294">294</a><br />
+<br />
+Lyman, <a href="#Page_25">25</a><br />
+<br />
+Lynn, <a href="#Page_37">37</a>, <a href="#Page_38">38</a>, <a href="#Page_96">96</a>, <a href="#Page_106">106</a>, <a href="#Page_179">179</a>, <a href="#Page_243">243</a>, <a href="#Page_244">244</a>, <a href="#Page_310">310</a><br />
+<br />
+Lynx, <a href="#Page_296">296</a><br />
+<br />
+Lyra, <a href="#Page_243">243</a>, <a href="#Page_244">244</a>, <a href="#Page_266">266</a><br />
+<br />
+<br />
+<span class="large">M</span><br />
+<br />
+Maclear, <a href="#Page_77">77</a><br />
+<br />
+M&auml;dler, <a href="#Page_20">20</a>, <a href="#Page_22">22</a><br />
+<br />
+M&aelig;stlin, <a href="#Page_341">341</a><br />
+<br />
+Magi, star of, <a href="#Page_1">1</a>, <a href="#Page_18">18</a>, <a href="#Page_145">145</a><br />
+<br />
+Magnitudes, star, <a href="#Page_311">311</a><br />
+<br />
+Maia, <a href="#Page_19">19</a>, <a href="#Page_256">256</a><br />
+<br />
+Mairan, <a href="#Page_357">357</a><br />
+<br />
+&#8220;Manger,&#8221; <a href="#Page_259">259</a><br />
+<br />
+Manilius, <a href="#Page_250">250</a>, <a href="#Page_259">259</a>, <a href="#Page_272">272</a><br />
+<br />
+Marius, Simon, <a href="#Page_82">82</a>, <a href="#Page_83">83</a>, <a href="#Page_231">231</a><br />
+<br />
+Markree Castle, <a href="#Page_3">3</a><br />
+<br />
+Marmol, <a href="#Page_76">76</a><br />
+<br />
+Mars, <a href="#CHAPTER_VI">chap. vi.</a>;<br />
+<span style="margin-left: 1em;">axis of <a href="#Page_59">59</a>;</span><br />
+<span style="margin-left: 1em;">red colour of, <a href="#Page_60">60</a>;</span><br />
+<span style="margin-left: 1em;">water vapour in, <a href="#Page_60">60</a>;</span><br />
+<span style="margin-left: 1em;">clouds in, <a href="#Page_61">61</a>;</span><br />
+<span style="margin-left: 1em;">&#8220;canals&#8221; in, <a href="#Page_61">61</a></span><br />
+<br />
+Martial, <a href="#Page_17">17</a><br />
+<br />
+Mascari, <a href="#Page_22">22</a><br />
+<br />
+Ma-tuan-lin, <a href="#Page_186">186</a>, <a href="#Page_267">267</a><br />
+<br />
+Mayer, <a href="#Page_24">24</a><br />
+<br />
+May transits of Mercury, <a href="#Page_15">15</a><br />
+<br />
+Maxwell, Clerk, <a href="#Page_86">86</a><br />
+<br />
+McHarg, <a href="#Page_16">16</a><br />
+<br />
+McKay, <a href="#Page_286">286</a><br />
+<br />
+Medusa, <a href="#Page_244">244</a><br />
+<br />
+Mee, <a href="#Page_88">88</a><br />
+<br />
+Melotte, <a href="#Page_82">82</a><br />
+<br />
+Mendelief, <a href="#Page_212">212</a><br />
+<br />
+Mensa, <a href="#Page_304">304</a><br />
+<br />
+Mercury, <a href="#CHAPTER_II">chap, ii.</a>, <a href="#Page_258">258</a><br />
+<br />
+Merrill, <a href="#Page_121">121</a><br />
+<br />
+Messier, <a href="#Page_114">114</a><br />
+<br />
+Meteoric stones, <a href="#Page_119">119</a><br />
+<br />
+Meteors, <a href="#Page_33">33</a><br />
+<br />
+Metius, <a href="#Page_342">342</a><br />
+<br />
+Microscopium, <a href="#Page_302">302</a><br />
+<br />
+Milky Way, <a href="#Page_320">320</a>, <a href="#Page_323">323</a>, <a href="#Page_325">325</a>, <a href="#Page_326">326</a>, <a href="#Page_328">328</a><br />
+<br />
+Milton, <a href="#Page_263">263</a><br />
+<br />
+Mimas, <a href="#Page_88">88</a>, <a href="#Page_89">89</a><br />
+<br />
+Minor planets, <a href="#CHAPTER_VII">chap. vii.</a><br />
+<br />
+Mira Ceti, <a href="#Page_178">178</a>, <a href="#Page_186">186</a>, <a href="#Page_272">272</a>, <a href="#Page_273">273</a><br />
+<br />
+Mitchell, <a href="#Page_4">4</a><br />
+<br />
+Mithridates, <a href="#Page_111">111</a><br />
+<br />
+Mitra, <a href="#Page_145">145</a><br />
+<br />
+Molyneux, <a href="#Page_80">80</a><br />
+<br />
+Monck, <a href="#Page_156">156</a>, <a href="#Page_181">181</a><br />
+<br />
+Monoceros, <a href="#Page_298">298</a><br />
+<br />
+Montanari, <a href="#Page_170">170</a>, <a href="#Page_171">171</a><br />
+<br />
+Montigny, <a href="#Page_34">34</a><br />
+<br />
+Moon, light of, <a href="#Page_1">1</a>, <a href="#Page_51">51</a><br />
+<br />
+<span style="margin-left: 1em;">"</span><span style="margin-left: 1.5em;">as seen through a telescope, <a href="#Page_50">50</a></span><br />
+<br />
+&#8220;Moon maiden,&#8221; <a href="#Page_52">52</a><br />
+<br />
+Moon mountains, <a href="#Page_58">58</a><br />
+<br />
+Morehouse, <a href="#Page_103">103</a>, <a href="#Page_110">110</a><br />
+<span class="pagenum"><a name="Page_366" id="Page_366">[Pg 366]</a></span><br />
+Motions of stars in line of sight, <a href="#Page_141">141</a>, <a href="#Page_142">142</a><br />
+<br />
+Moulton, <a href="#Page_133">133</a>, <a href="#Page_318">318</a><br />
+<br />
+Mountains, lunar, <a href="#Page_58">58</a><br />
+<br />
+M&uuml;ller, <a href="#Page_174">174</a><br />
+<br />
+Musca, <a href="#Page_305">305</a><br />
+<br />
+Mycerinus, Pyramid of, <a href="#Page_353">353</a><br />
+<br />
+<br />
+<span class="large">N</span><br />
+<br />
+Nasmyth, <a href="#Page_11">11</a><br />
+<br />
+Nath, <a href="#Page_253">253</a><br />
+<br />
+Nautical Almanac, <a href="#Page_349">349</a><br />
+<br />
+Nebula in Andromeda, <a href="#Page_198">198-206</a>, <a href="#Page_231">231</a><br />
+<br />
+Nebul&aelig;, gaseous, <a href="#Page_195">195-198</a>, <a href="#Page_212">212</a>, <a href="#Page_213">213</a><br />
+<br />
+Nebul&aelig;, spiral, <a href="#Page_213">213</a><br />
+<br />
+Nebular hypothesis, <a href="#Page_354">354</a><br />
+<br />
+Nem&aelig;lian lion, <a href="#Page_259">259</a><br />
+<br />
+Nem&aelig;us, <a href="#Page_259">259</a><br />
+<br />
+Neon in sun, <a href="#Page_4">4</a><br />
+<br />
+Nepthys, <a href="#Page_271">271</a><br />
+<br />
+Neptune, <a href="#Page_341">341</a><br />
+<br />
+Newcomb, <a href="#Page_13">13</a>, <a href="#Page_15">15</a>, <a href="#Page_33">33</a>, <a href="#Page_50">50</a>, <a href="#Page_65">65</a>, <a href="#Page_70">70</a>, <a href="#Page_129">129</a>, <a href="#Page_130">130</a>, <a href="#Page_153">153</a>, <a href="#Page_191">191</a>, <a href="#Page_203">203</a>, <a href="#Page_282">282</a>, <a href="#Page_339">339</a>, <a href="#Page_347">347</a>, <a href="#Page_349">349</a>, <a href="#Page_350">350</a>, <a href="#Page_355">355</a><br />
+<br />
+Newton, <a href="#Page_15">15</a>, <a href="#Page_351">351</a><br />
+<br />
+Nicephorus, <a href="#Page_127">127</a><br />
+<br />
+Nicholls, <a href="#Page_148">148</a>, <a href="#Page_154">154</a><br />
+<br />
+Nineveh tablets, <a href="#Page_17">17</a><br />
+<br />
+Noble, <a href="#Page_25">25</a><br />
+<br />
+Norma, <a href="#Page_302">302</a><br />
+<br />
+Nov&aelig;, <a href="#Page_180">180-182</a>, <a href="#Page_265">265</a>, <a href="#Page_267">267</a>, <a href="#Page_343">343</a><br />
+<br />
+Nova Persei, <a href="#Page_190">190</a><br />
+<br />
+November transits of Mercury, <a href="#Page_15">15</a><br />
+<br />
+Number of nebul&aelig;, <a href="#Page_191">191</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.5em;">of stars, <a href="#Page_135">135</a>, <a href="#Page_136">136</a>, <a href="#Page_236">236</a>, <a href="#Page_237">237</a></span><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.5em;">of variable stars, <a href="#Page_182">182</a>, <a href="#Page_183">183</a></span><br />
+<br />
+<br />
+<span class="large">O</span><br />
+<br />
+Obliquity of ecliptic, <a href="#Page_47">47</a><br />
+<br />
+Occupations, <a href="#Page_14">14</a>, <a href="#Page_15">15</a>, <a href="#Page_54">54</a>, <a href="#Page_67">67</a>, <a href="#Page_80">80</a>, <a href="#Page_84">84</a>, <a href="#Page_85">85</a>, <a href="#Page_259">259</a>, <a href="#Page_340">340</a>, <a href="#Page_341">341</a><br />
+<br />
+Octans, <a href="#Page_303">303</a><br />
+<br />
+Odling, <a href="#Page_122">122</a><br />
+<br />
+Oeltzen, <a href="#Page_72">72</a><br />
+<br />
+Olbers, <a href="#Page_104">104</a>, <a href="#Page_124">124</a><br />
+<br />
+Old, <a href="#Page_340">340</a><br />
+<br />
+Orion, <a href="#Page_49">49</a>, <a href="#Page_146">146</a>, <a href="#Page_273">273</a>, <a href="#Page_274">274</a><br />
+<br />
+Osiris, <a href="#Page_145">145</a>, <a href="#Page_259">259</a>, <a href="#Page_261">261</a>, <a href="#Page_283">283</a><br />
+<br />
+&#8220;Ostriches,&#8221; <a href="#Page_266">266</a><br />
+<br />
+Otawa, <a href="#Page_240">240</a><br />
+<br />
+Ovid, <a href="#Page_242">242</a>, <a href="#Page_250">250</a>, <a href="#Page_255">255</a>, <a href="#Page_265">265</a>, <a href="#Page_288">288</a>, <a href="#Page_291">291</a>, <a href="#Page_322">322</a><br />
+<br />
+<br />
+<span class="large">P</span><br />
+<br />
+Palisa, <a href="#Page_71">71</a><br />
+<br />
+Palmer, <a href="#Page_182">182</a><br />
+<br />
+Parker, <a href="#Page_19">19</a><br />
+<br />
+Parkhurst, <a href="#Page_174">174</a><br />
+<br />
+Paschen, <a href="#Page_2">2</a><br />
+<br />
+Pastorff, <a href="#Page_25">25</a><br />
+<br />
+Pavo, <a href="#Page_307">307</a><br />
+<br />
+Payne, <a href="#Page_139">139</a><br />
+<br />
+Pearson, <a href="#Page_77">77</a><br />
+<br />
+Peary, <a href="#Page_119">119</a><br />
+<br />
+Peck, <a href="#Page_176">176</a><br />
+<br />
+Pegasus, <a href="#Page_248">248</a><br />
+<br />
+Pelion, <a href="#Page_282">282</a><br />
+<br />
+Peritheus, <a href="#Page_258">258</a><br />
+<br />
+Perrine, <a href="#Page_15">15</a>, <a href="#Page_76">76</a>, <a href="#Page_191">191</a>, <a href="#Page_192">192</a>, <a href="#Page_214">214</a><br />
+<br />
+Perrotin, <a href="#Page_351">351</a><br />
+<br />
+Perseus, <a href="#Page_244">244</a><br />
+<br />
+Petosiris, <a href="#Page_222">222</a><br />
+<br />
+Philostratus, <a href="#Page_334">334</a><br />
+<br />
+Phlegon, <a href="#Page_332">332</a><br />
+<br />
+Ph&oelig;be, <a href="#Page_90">90</a><br />
+<br />
+Ph&oelig;nix, <a href="#Page_301">301</a><br />
+<br />
+Phosphorus, <a href="#Page_17">17</a><br />
+<br />
+Photographic nebula, <a href="#Page_192">192</a><br />
+<br />
+Pickering, E. C., <a href="#Page_125">125</a>, <a href="#Page_140">140</a>, <a href="#Page_144">144</a>, <a href="#Page_177">177</a><br />
+<br />
+Pickering, W. H., <a href="#Page_1">1</a>, <a href="#Page_12">12</a>, <a href="#Page_51">51</a>, <a href="#Page_61">61</a>, <a href="#Page_95">95</a>, <a href="#Page_102">102</a><br />
+<br />
+Pictor, <a href="#Page_304">304</a><br />
+<br />
+Pierce, <a href="#Page_228">228</a><br />
+<br />
+&#8220;Pilgrim Star,&#8221; <a href="#Page_180">180</a>, <a href="#Page_185">185</a>, <a href="#Page_186">186</a><br />
+<br />
+Pingr&eacute;, <a href="#Page_54">54</a><br />
+<br />
+Pinzon, <a href="#Page_294">294</a><br />
+<span class="pagenum"><a name="Page_367" id="Page_367">[Pg 367]</a></span><br />
+Pisces, <a href="#Page_271">271</a><br />
+<br />
+Piscis Australis, <a href="#Page_295">295</a>, <a href="#Page_296">296</a><br />
+<br />
+Planetary nebul&aelig;, <a href="#Page_213">213</a><br />
+<br />
+Platina, <a href="#Page_107">107</a><br />
+<br />
+Pleiades, <a href="#Page_19">19</a>, <a href="#Page_52">52</a>, <a href="#Page_137">137</a>, <a href="#Page_154">154</a>, <a href="#Page_157">157</a>, <a href="#Page_235">235</a>, <a href="#Page_254">254-257</a><br />
+<br />
+Pliny, <a href="#Page_17">17</a>, <a href="#Page_265">265</a>, <a href="#Page_280">280</a><br />
+<br />
+Plummer, W. E., <a href="#Page_180">180</a><br />
+<br />
+Plurality of worlds, <a href="#Page_328">328</a>, <a href="#Page_356">356</a>, <a href="#Page_357">357</a><br />
+<br />
+Pococke, <a href="#Page_271">271</a><br />
+<br />
+Pogson, <a href="#Page_317">317</a><br />
+<br />
+Polarization of moon&#8217;s surface, <a href="#Page_52">52</a><br />
+<br />
+Polarization on Mars, <a href="#Page_61">61</a><br />
+<br />
+Pole of cold, <a href="#Page_33">33</a><br />
+<br />
+<span style="margin-left: .75em;">"</span><span style="margin-left: 1em;">star, <a href="#Page_138">138</a>, <a href="#Page_239">239</a>, <a href="#Page_240">240</a></span><br />
+<br />
+Pollux, <a href="#Page_257">257</a><br />
+<br />
+Polydectus, <a href="#Page_244">244</a><br />
+<br />
+Poor, <a href="#Page_15">15</a> (footnote)<br />
+<br />
+Poynting, <a href="#Page_130">130</a><br />
+<br />
+Pr&aelig;sape, <a href="#Page_259">259</a><br />
+<br />
+Prince, <a href="#Page_25">25</a><br />
+<br />
+Proclus, <a href="#Page_221">221</a><br />
+<br />
+Proctor, <a href="#Page_7">7</a>, <a href="#Page_49">49</a>, <a href="#Page_59">59</a>, <a href="#Page_123">123</a>, <a href="#Page_285">285</a>, <a href="#Page_308">308</a>, <a href="#Page_323">323</a>, <a href="#Page_352">352</a><br />
+<br />
+Procyon, <a href="#Page_156">156</a>, <a href="#Page_157">157</a>, <a href="#Page_236">236</a>, <a href="#Page_284">284</a><br />
+<br />
+Ptolemy, <a href="#Page_189">189</a>, <a href="#Page_221">221-223</a>, <a href="#Page_224">224</a>, <a href="#Page_227">227</a>, <a href="#Page_230">230</a>, <a href="#Page_231">231</a>, <a href="#Page_234">234</a>, <a href="#Page_238">238</a>, <a href="#Page_244">244</a>, <a href="#Page_252">252</a>, <a href="#Page_253">253</a>, <a href="#Page_260">260</a>, <a href="#Page_263">263</a>, <a href="#Page_264">264</a>, <a href="#Page_267">267</a>, <a href="#Page_269">269</a>, <a href="#Page_275">275</a>, <a href="#Page_278">278</a>, <a href="#Page_281">281</a>, <a href="#Page_284">284</a>, <a href="#Page_293">293</a>, <a href="#Page_302">302</a>, <a href="#Page_330">330</a><br />
+<br />
+Pyramid, Great, <a href="#Page_46">46</a>, <a href="#Page_47">47</a>, <a href="#Page_308">308</a>, <a href="#Page_353">353</a><br />
+<br />
+Pytheas, <a href="#Page_46">46</a><br />
+<br />
+<br />
+<span class="large">Q</span><br />
+<br />
+Quadruple system, <a href="#Page_168">168</a><br />
+<br />
+Qu&eacute;nisset, <a href="#Page_21">21</a>, <a href="#Page_133">133</a><br />
+<br />
+<br />
+<span class="large">R</span><br />
+<br />
+Rabourdin, <a href="#Page_103">103</a><br />
+<br />
+Radium, <a href="#Page_7">7</a>, <a href="#Page_8">8</a>, <a href="#Page_38">38</a><br />
+<br />
+R&acirc;hu, <a href="#Page_93">93</a><br />
+<br />
+Rama, <a href="#Page_284">284</a>, <a href="#Page_340">340</a><br />
+<br />
+<i>Rational Almanac</i>, <a href="#Page_46">46</a><br />
+<br />
+&#8220;Red Bird,&#8221; <a href="#Page_290">290</a><br />
+<br />
+Red star, <a href="#Page_279">279</a>, <a href="#Page_292">292</a><br />
+<br />
+Regulus, <a href="#Page_30">30</a>, <a href="#Page_156">156</a>, <a href="#Page_235">235</a>, <a href="#Page_236">236</a>, <a href="#Page_260">260</a>, <a href="#Page_310">310</a>, <a href="#Page_340">340</a><br />
+<br />
+Remote galaxies, <a href="#Page_193">193</a>, <a href="#Page_204">204</a>, <a href="#Page_205">205</a><br />
+<br />
+Reticulum, <a href="#Page_304">304</a><br />
+<br />
+Rhea, <a href="#Page_89">89</a><br />
+<br />
+Rheita, De, <a href="#Page_144">144</a><br />
+<br />
+Riccioli, <a href="#Page_189">189</a><br />
+<br />
+Ricco, <a href="#Page_32">32</a><br />
+<br />
+Rigel, <a href="#Page_156">156</a>, <a href="#Page_157">157</a>, <a href="#Page_222">222</a><br />
+<br />
+Rigge, <a href="#Page_107">107</a><br />
+<br />
+Ring nebula in Lyra, <a href="#Page_211">211</a><br />
+<br />
+Rings of Saturn, <a href="#Page_85">85</a><br />
+<br />
+Rishis, <a href="#Page_240">240</a><br />
+<br />
+Ritter, <a href="#Page_76">76</a>, <a href="#Page_147">147</a><br />
+<br />
+&#8220;Rivers, celestial,&#8221; <a href="#Page_308">308</a><br />
+<br />
+Roberts, Dr. A. W., <a href="#Page_172">172</a>, <a href="#Page_173">173</a><br />
+<br />
+Roberts, Dr. I., <a href="#Page_95">95</a>, <a href="#Page_154">154</a>, <a href="#Page_200">200</a>, <a href="#Page_201">201</a>, <a href="#Page_203">203</a>, <a href="#Page_317">317</a><br />
+<br />
+Roberts, C., <a href="#Page_84">84</a><br />
+<br />
+Robigalia, <a href="#Page_280">280</a><br />
+<br />
+Robinson, <a href="#Page_342">342</a>, <a href="#Page_357">357</a><br />
+<br />
+R&oelig;deck&oelig;r, <a href="#Page_28">28</a><br />
+<br />
+Rogovsky, <a href="#Page_42">42</a>, <a href="#Page_43">43</a>, <a href="#Page_44">44</a>, <a href="#Page_75">75</a><br />
+<br />
+Rosse, Lord, <a href="#Page_76">76</a><br />
+<br />
+Roszel, <a href="#Page_70">70</a><br />
+<br />
+Rotation of Mercury, <a href="#Page_16">16</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.5em;">of Uranus, <a href="#Page_91">91</a></span><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.5em;">of Venus, <a href="#Page_22">22</a></span><br />
+<br />
+Rub&aacute;iy&aacute;t, <a href="#Page_127">127</a><br />
+<br />
+Rudaux, <a href="#Page_80">80</a>, <a href="#Page_89">89</a><br />
+<br />
+Russell, H. C., <a href="#Page_21">21</a><br />
+<br />
+Russell, H. N., <a href="#Page_146">146</a><br />
+<br />
+Russell, J. C., <a href="#Page_333">333</a><br />
+<br />
+Rutherford, <a href="#Page_38">38</a><br />
+<br />
+<br />
+<span class="large">S</span><br />
+<br />
+Sadler, <a href="#Page_78">78</a>, <a href="#Page_299">299</a><br />
+<br />
+Safarik, <a href="#Page_24">24</a>, <a href="#Page_25">25</a><br />
+<br />
+Sagittarius, <a href="#Page_265">265-267</a><br />
+<span class="pagenum"><a name="Page_368" id="Page_368">[Pg 368]</a></span><br />
+<i>Sahu</i>, <a href="#Page_274">274</a><br />
+<br />
+Santini, <a href="#Page_357">357</a><br />
+<br />
+Satellite, eighth, of Jupiter, <a href="#Page_82">82</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.75em;">possible lunar, <a href="#Page_54">54</a></span><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.75em;">of Venus, <a href="#Page_28">28</a>, <a href="#Page_29">29</a></span><br />
+<br />
+Sawyer, <a href="#Page_186">186</a><br />
+<br />
+Sayce, <a href="#Page_218">218</a>, <a href="#Page_261">261</a><br />
+<br />
+Scaliger, <a href="#Page_299">299</a><br />
+<br />
+Schaeberle, <a href="#Page_93">93</a><br />
+<br />
+Schaer, <a href="#Page_88">88</a><br />
+<br />
+Scheiner, <a href="#Page_4">4</a>, <a href="#Page_150">150</a>, <a href="#Page_188">188</a>, <a href="#Page_195">195</a><br />
+<br />
+Scheuter, <a href="#Page_30">30</a><br />
+<br />
+Schiaparelli, <a href="#Page_22">22</a>, <a href="#Page_326">326</a><br />
+<br />
+Schjellerup, <a href="#Page_226">226</a>, <a href="#Page_228">228</a>, <a href="#Page_230">230</a>, <a href="#Page_231">231</a>, <a href="#Page_264">264</a>, <a href="#Page_277">277</a>, <a href="#Page_281">281</a>, <a href="#Page_340">340</a><br />
+<br />
+Schlesinger, <a href="#Page_183">183</a><br />
+<br />
+Sch&ouml;nfeld, <a href="#Page_287">287</a><br />
+<br />
+Schiraz, <a href="#Page_47">47</a><br />
+<br />
+Schmidt, <a href="#Page_51">51</a>, <a href="#Page_188">188</a>, <a href="#Page_220">220</a>, <a href="#Page_271">271</a><br />
+<br />
+Scholl, <a href="#Page_79">79</a><br />
+<br />
+Schr&ouml;ter, <a href="#Page_13">13</a>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a>, <a href="#Page_22">22</a>, <a href="#Page_24">24</a>, <a href="#Page_26">26</a>, <a href="#Page_48">48</a><br />
+<br />
+Schuster, <a href="#Page_2">2</a>, <a href="#Page_148">148</a>, <a href="#Page_149">149</a>, <a href="#Page_150">150</a><br />
+<br />
+Schwabe, <a href="#Page_5">5</a><br />
+<br />
+Scorpio, <a href="#Page_263">263-265</a><br />
+<br />
+Sculptor, <a href="#Page_301">301</a><br />
+<br />
+Scutum, <a href="#Page_299">299</a><br />
+<br />
+Searle, <a href="#Page_132">132</a><br />
+<br />
+&#8220;Secondary light&#8221; of Venus, <a href="#Page_23">23-28</a><br />
+<br />
+See, Dr., <a href="#Page_12">12</a>, <a href="#Page_13">13</a>, <a href="#Page_33">33</a>, <a href="#Page_58">58</a>, <a href="#Page_96">96</a>, <a href="#Page_161">161</a>, <a href="#Page_164">164</a>, <a href="#Page_165">165</a>, <a href="#Page_210">210</a>, <a href="#Page_211">211</a>, <a href="#Page_281">281</a>, <a href="#Page_282">282</a>, <a href="#Page_354">354</a><br />
+<br />
+Seeliger, <a href="#Page_181">181</a>, <a href="#Page_206">206</a><br />
+<br />
+Seneca, <a href="#Page_218">218</a>, <a href="#Page_220">220</a><br />
+<br />
+Serapis, <a href="#Page_145">145</a><br />
+<br />
+Sestini, <a href="#Page_190">190</a><br />
+<br />
+&#8220;Seven Perfect Ones,&#8221; <a href="#Page_256">256</a><br />
+<br />
+Sextans, <a href="#Page_298">298</a><br />
+<br />
+Shaler, <a href="#Page_48">48</a><br />
+<br />
+Sharpe, <a href="#Page_357">357</a><br />
+<br />
+Shelley, <a href="#Page_356">356</a><br />
+<br />
+Shicor, <a href="#Page_274">274</a><br />
+<br />
+&#8220;Ship,&#8221; <a href="#Page_285">285</a><br />
+<br />
+&#8220;Sickle,&#8221; <a href="#Page_259">259</a><br />
+<br />
+Signalling to Mars, <a href="#Page_65">65</a><br />
+<br />
+Sihor, <a href="#Page_280">280</a><br />
+<br />
+Silkit, <a href="#Page_264">264</a><br />
+<br />
+Silvestria, <a href="#Page_124">124</a><br />
+<br />
+Simeon of Durham, <a href="#Page_53">53</a><br />
+<br />
+Simonides, <a href="#Page_255">255</a><br />
+<br />
+&#8220;Singing Maidens,&#8221; <a href="#Page_256">256</a><br />
+<br />
+Sirius, <a href="#Page_138">138</a>, <a href="#Page_156">156</a>, <a href="#Page_157">157</a>, <a href="#Page_160">160</a>, <a href="#Page_163">163</a>, <a href="#Page_236">236</a>, <a href="#Page_274">274</a>, <a href="#Page_280">280</a>, <a href="#Page_282">282</a>, <a href="#Page_283">283</a><br />
+<br />
+Slipher, <a href="#Page_60">60</a>, <a href="#Page_87">87</a>, <a href="#Page_161">161</a>, <a href="#Page_178">178</a><br />
+<br />
+Smart, <a href="#Page_109">109</a><br />
+<br />
+Smyth, Admiral, <a href="#Page_12">12</a>, <a href="#Page_72">72</a>, <a href="#Page_77">77</a>, <a href="#Page_107">107</a>, <a href="#Page_136">136</a>, <a href="#Page_140">140</a>, <a href="#Page_145">145</a>, <a href="#Page_170">170</a>, <a href="#Page_176">176</a>, <a href="#Page_190">190</a>, <a href="#Page_194">194</a>, <a href="#Page_253">253</a>, <a href="#Page_259">259</a>, <a href="#Page_351">351</a><br />
+<br />
+Snyder, Carl, <a href="#Page_8">8</a>, <a href="#Page_345">345</a><br />
+<br />
+Sobieski, <a href="#Page_299">299</a><br />
+<br />
+Sola, Comas, <a href="#Page_81">81</a>, <a href="#Page_87">87</a><br />
+<br />
+Somerville, Mrs., <a href="#Page_357">357</a><br />
+<br />
+Sothis, <a href="#Page_286">286</a><br />
+<br />
+Southern Cross, <a href="#Page_293">293</a>, <a href="#Page_344">344</a><br />
+<br />
+Spectra of double stars, <a href="#Page_162">162</a><br />
+<br />
+Spectrum of gaseous nebul&aelig;, <a href="#Page_195">195-198</a>, <a href="#Page_212">212</a><br />
+<br />
+Spectrum of sun&#8217;s chromosphere, <a href="#Page_4">4</a><br />
+<br />
+Spencer, Herbert, <a href="#Page_193">193</a><br />
+<br />
+Sphinx, <a href="#Page_261">261</a><br />
+<br />
+Spica, <a href="#Page_156">156</a>, <a href="#Page_236">236</a><br />
+<br />
+Spiral nebul&aelig;, <a href="#Page_213">213</a><br />
+<br />
+Star magnitudes, <a href="#Page_311">311</a><br />
+<br />
+&#8220;Star of Bethlehem,&#8221; <a href="#Page_17">17</a>, <a href="#Page_18">18</a><br />
+<br />
+Stars in daytime, <a href="#Page_158">158</a><br />
+<br />
+Stebbins, <a href="#Page_51">51</a><br />
+<br />
+Stockwell, <a href="#Page_18">18</a>, <a href="#Page_331">331</a><br />
+<br />
+&#8220;Stones from heaven,&#8221; <a href="#Page_125">125</a>, <a href="#Page_126">126</a><br />
+<br />
+Stoney, <a href="#Page_133">133</a><br />
+<br />
+Strabo, <a href="#Page_127">127</a><br />
+<br />
+Stratonoff, <a href="#Page_151">151</a>, <a href="#Page_320">320</a>, <a href="#Page_321">321</a><br />
+<br />
+Stromgen, <a href="#Page_88">88</a><br />
+<br />
+Strutt, <a href="#Page_7">7</a><br />
+<br />
+Struve, <a href="#Page_113">113</a>, <a href="#Page_240">240</a><br />
+<br />
+Struyck, <a href="#Page_54">54</a><br />
+<br />
+Succul&aelig;, <a href="#Page_253">253</a><br />
+<br />
+Suhail, <a href="#Page_283">283</a>, <a href="#Page_286">286</a><br />
+<br />
+Sun darkenings, <a href="#Page_5">5</a>, <a href="#Page_335">335</a>, <a href="#Page_336">336</a><br />
+<br />
+Sun&#8217;s heat, <a href="#Page_7">7</a><br />
+<br />
+Sunlight, <a href="#Page_1">1</a>, <a href="#Page_2">2</a><br />
+<br />
+Sun-spots, <a href="#Page_5">5</a>, <a href="#Page_6">6</a><br />
+<br />
+Swift, <a href="#Page_102">102</a><br />
+<br />
+<i>Sydera Austricea</i>, <a href="#Page_5">5</a><br />
+<span class="pagenum"><a name="Page_369" id="Page_369">[Pg 369]</a></span><br />
+<br />
+<span class="large">T</span><br />
+<br />
+Tacchini, <a href="#Page_22">22</a><br />
+<br />
+Tamerlane, <a href="#Page_238">238</a><br />
+<br />
+Tammuz, <a href="#Page_261">261</a><br />
+<br />
+Tard&eacute;, <a href="#Page_4">4</a><br />
+<br />
+Taurus, <a href="#Page_251">251</a><br />
+<br />
+Taylor, <a href="#Page_40">40</a><br />
+<br />
+T Coron&aelig;, <a href="#Page_184">184</a><br />
+<br />
+Tebbutt, <a href="#Page_183">183</a>, <a href="#Page_278">278</a><br />
+<br />
+Telescopium, <a href="#Page_302">302</a><br />
+<br />
+Temporary stars, <a href="#Page_180">180-182</a>, <a href="#Page_265">265</a>, <a href="#Page_267">267</a>, <a href="#Page_343">343</a><br />
+<br />
+Tennyson, <a href="#Page_40">40</a><br />
+<br />
+Terby, <a href="#Page_88">88</a><br />
+<br />
+Tethys, <a href="#Page_89">89</a><br />
+<br />
+Thales, <a href="#Page_357">357</a><br />
+<br />
+Thebes, <a href="#Page_271">271</a><br />
+<br />
+Themis, <a href="#Page_88">88-90</a><br />
+<br />
+Theogirus, <a href="#Page_279">279</a><br />
+<br />
+Theon, <a href="#Page_245">245</a><br />
+<br />
+Theseus, <a href="#Page_257">257</a><br />
+<br />
+Thome, <a href="#Page_101">101</a><br />
+<br />
+Thucydides, <a href="#Page_331">331</a><br />
+<br />
+Tibertinus, <a href="#Page_281">281</a><br />
+<br />
+Tibullus, <a href="#Page_282">282</a><br />
+<br />
+Tides, <a href="#Page_40">40</a><br />
+<br />
+Timocharis, <a href="#Page_340">340</a><br />
+<br />
+Tin, <a href="#Page_179">179</a><br />
+<br />
+Titan, <a href="#Page_85">85</a>, <a href="#Page_88">88</a>, <a href="#Page_89">89</a><br />
+<br />
+Titanium, <a href="#Page_179">179</a><br />
+<br />
+Toucan, <a href="#Page_308">308</a><br />
+<br />
+Transits of Mercury, <a href="#Page_14">14</a>, <a href="#Page_15">15</a><br />
+<br />
+<span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.5em;">of Venus, <a href="#Page_337">337</a>, <a href="#Page_338">338</a>, <a href="#Page_339">339</a></span><br />
+<br />
+Triangulum, <a href="#Page_271">271</a><br />
+<br />
+<span style="margin-left: 2em;">"</span><span style="margin-left: 1.75em;">Australis, <a href="#Page_306">306</a></span><br />
+<br />
+Trio, <a href="#Page_220">220</a><br />
+<br />
+Triptolemus, <a href="#Page_257">257</a><br />
+<br />
+Triton, <a href="#Page_93">93</a><br />
+<br />
+Trouvelot, <a href="#Page_21">21</a>, <a href="#Page_22">22</a>, <a href="#Page_78">78</a>, <a href="#Page_211">211</a><br />
+<br />
+Tumlirz, <a href="#Page_46">46</a><br />
+<br />
+Turrinus, <a href="#Page_220">220</a><br />
+<br /><a name="tycho" id="tycho"></a>
+Tycho Brah&eacute;, <a href="#Page_10">10</a>, <a href="#Page_30">30</a>, <a href="#Page_99">99</a>, <a href="#Page_145">145</a>, <a href="#Page_179">179</a>, <a href="#Page_298">298</a><br />
+<br />
+Typhon, <a href="#Page_263">263</a>, <a href="#Page_272">272</a><br />
+<br />
+<br />
+<span class="large">U</span><br />
+<br />
+Ulugh Beigh, <a href="#Page_238">238</a>, <a href="#Page_276">276</a>, <a href="#Page_278">278</a><br />
+<br />
+Underwood, <a href="#Page_85">85</a><br />
+<br />
+Uranus, <a href="#CHAPTER_X">chap. x.</a>;<br />
+<span style="margin-left: 1em;">spectrum of, <a href="#Page_91">91</a>, <a href="#Page_92">92</a></span><br />
+<br />
+Urda, <a href="#Page_71">71</a><br />
+<br />
+<br />
+<span class="large">V</span><br />
+<br />
+Valz <a href="#Page_72">72</a><br />
+<br />
+&#8220;Vanishing star,&#8221; <a href="#Page_59">59</a><br />
+<br />
+Varvadjah, <a href="#Page_236">236</a><br />
+<br />
+Vega, <a href="#Page_148">148</a>, <a href="#Page_156">156</a>, <a href="#Page_244">244</a><br />
+<br />
+Vencontre, <a href="#Page_220">220</a><br />
+<br />
+Venus, <a href="#CHAPTER_III">chap. iii.</a>;<br />
+<span style="margin-left: 1em;">apparent motion of, <a href="#Page_28">28</a>;</span><br />
+<span style="margin-left: 1em;">supposed satellite of, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>;</span><br />
+<span style="margin-left: 1em;">transit of, <a href="#Page_337">337-339</a></span><br />
+<br />
+Veronica, S, <a href="#Page_145">145</a><br />
+<br />
+Vesta, <a href="#Page_70">70</a><br />
+<br />
+Virgil, <a href="#Page_17">17</a>, <a href="#Page_218">218</a>, <a href="#Page_242">242</a>, <a href="#Page_262">262</a>, <a href="#Page_309">309</a><br />
+<br />
+Virgo, <a href="#Page_260">260</a><br />
+<br />
+Vogel, <a href="#Page_180">180</a><br />
+<br />
+Vogt, <a href="#Page_122">122</a><br />
+<br />
+Volans, <a href="#Page_304">304</a><br />
+<br />
+Voltaire, <a href="#Page_15">15</a><br />
+<br />
+Von Hahn, <a href="#Page_24">24</a><br />
+<br />
+Vulpecula, <a href="#Page_300">300</a><br />
+<br />
+<br />
+<span class="large">W</span><br />
+<br />
+Wallace, Dr., <a href="#Page_212">212</a>, <a href="#Page_357">357</a><br />
+<br />
+Wallis, <a href="#Page_80">80</a><br />
+<br />
+Ward, <a href="#Page_88">88</a><br />
+<br />
+Wargentin, <a href="#Page_178">178</a><br />
+<br />
+Watson, <a href="#Page_339">339</a><br />
+<br />
+Webb, <a href="#Page_24">24</a>, <a href="#Page_25">25</a>, <a href="#Page_77">77</a>, <a href="#Page_190">190</a>, <a href="#Page_286">286</a><br />
+<br />
+Weber, <a href="#Page_183">183</a><br />
+<br />
+Weinhand, <a href="#Page_122">122</a><br />
+<br />
+Wendell, <a href="#Page_71">71</a>, <a href="#Page_103">103</a>, <a href="#Page_109">109</a><br />
+<br />
+Werchojansk, <a href="#Page_33">33</a><br />
+<br />
+White spots on Jupiter&#8217;s satellites, <a href="#Page_81">81</a><br />
+<br />
+White spots on Venus, <a href="#Page_21">21</a><br />
+<br />
+Whitmell, <a href="#Page_50">50</a>, <a href="#Page_86">86</a><br />
+<br />
+Wiggins, <a href="#Page_333">333</a><br />
+<span class="pagenum"><a name="Page_370" id="Page_370">[Pg 370]</a></span><br />
+Wilczyniski, <a href="#Page_195">195</a><br />
+<br />
+Williams, Stanley, <a href="#Page_22">22</a>, <a href="#Page_277">277</a>, <a href="#Page_302">302</a><br />
+<br />
+Wilsing, <a href="#Page_155">155</a><br />
+<br />
+Wilson, H. C., <a href="#Page_137">137</a>, <a href="#Page_139">139</a><br />
+<br />
+Wilson, Dr. W. E., <a href="#Page_3">3</a>, <a href="#Page_148">148</a><br />
+<br />
+Winnecke, <a href="#Page_26">26</a>, <a href="#Page_188">188</a><br />
+<br />
+Winterhalter, <a href="#Page_351">351</a><br />
+<br />
+Wolf, Dr. Max, <a href="#Page_71">71</a>, <a href="#Page_72">72</a>, <a href="#Page_191">191</a>, <a href="#Page_211">211</a>, Note p. 537<br />
+<br />
+Wrangel, <a href="#Page_240">240</a><br />
+<br />
+<br />
+<span class="large">Y</span><br />
+<br />
+Young, Prof., <a href="#Page_4">4</a>, <a href="#Page_7">7</a>, <a href="#Page_9">9</a><br />
+<br />
+Young, Miss Anne S., <a href="#Page_79">79</a><br />
+<br />
+Yunis, Ibn, <a href="#Page_30">30</a><br />
+<br />
+<br />
+<span class="large">Z</span><br />
+<br />
+Zach, <a href="#Page_331">331</a><br />
+<br />
+Zenophon, <a href="#Page_127">127</a><br />
+<br />
+Zethas, <a href="#Page_257">257</a><br />
+<br />
+Z&ouml;llner, <a href="#Page_27">27</a><br />
+</p>
+
+
+<p>&nbsp;</p>
+<p class="center">THE END</p>
+<p>&nbsp;</p>
+<p class="center">PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLES.</p>
+
+<p>&nbsp;</p>
+<div class="figcenter"><img src="images/img3.jpg" alt="" /></div>
+
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><strong>Footnotes:</strong></p>
+
+<p><a name='f_1' id='f_1' href='#fna_1'>[1]</a> <i>Comptes Rendus</i>, 1903, December 7.</p>
+
+<p><a name='f_2' id='f_2' href='#fna_2'>[2]</a> <i>Nature</i>, April 11, 1907.</p>
+
+<p><a name='f_3' id='f_3' href='#fna_3'>[3]</a> <i>Astrophysical Journal</i>, vol. 19 (1904), p. 39.</p>
+
+<p><a name='f_4' id='f_4' href='#fna_4'>[4]</a> <i>Astrophysical Journal</i>, vol. 21 (1905), p. 260.</p>
+
+<p><a name='f_5' id='f_5' href='#fna_5'>[5]</a> <i>Knowledge</i>, July, 1902, p. 132.</p>
+
+<p><a name='f_6' id='f_6' href='#fna_6'>[6]</a> <i>Nature</i>, April 30, 1903.</p>
+
+<p><a name='f_7' id='f_7' href='#fna_7'>[7]</a> <i>Ibid.</i>, May 18, 1905.</p>
+
+<p><a name='f_8' id='f_8' href='#fna_8'>[8]</a> <i>Ibid.</i>, May 18, 1905.</p>
+
+<p><a name='f_9' id='f_9' href='#fna_9'>[9]</a> <i>Nature</i>, June 29, 1871.</p>
+
+<p><a name='f_10' id='f_10' href='#fna_10'>[10]</a> <i>Nature</i>, October 15, 1903.</p>
+
+<p><a name='f_11' id='f_11' href='#fna_11'>[11]</a> <i>The Life of the Universe</i> (1909), vol. ii. p. 209.</p>
+
+<p><a name='f_12' id='f_12' href='#fna_12'>[12]</a> <i>The World Machine</i>, p. 234.</p>
+
+<p><a name='f_13' id='f_13' href='#fna_13'>[13]</a> Quoted in <i>The Observatory</i>, March 1908, p. 125.</p>
+
+<p><a name='f_14' id='f_14' href='#fna_14'>[14]</a> <i>The Observatory</i>, September, 1906.</p>
+
+<p><a name='f_15' id='f_15' href='#fna_15'>[15]</a> <i>Nature</i>, March 1, 1900.</p>
+
+<p><a name='f_16' id='f_16' href='#fna_16'>[16]</a> <i>Cycle of Celestial Objects</i>, p. 96.</p>
+
+<p><a name='f_17' id='f_17' href='#fna_17'>[17]</a> <i>Ast. Nach.</i> No. 3737.</p>
+
+<p><a name='f_18' id='f_18' href='#fna_18'>[18]</a> <i>Observatory</i>, September, 1906.</p>
+
+<p><a name='f_19' id='f_19' href='#fna_19'>[19]</a> <i>Nature</i>, November 29 and December 20, 1894.</p>
+
+<p><a name='f_20' id='f_20' href='#fna_20'>[20]</a> <i>Bulletin, Ast. Soc. de France</i>, July, 1898.</p>
+
+<p><a name='f_21' id='f_21' href='#fna_21'>[21]</a> <i>Observatory</i>, vol. 8 (1885), pp. 306-7.</p>
+
+<p><a name='f_22' id='f_22' href='#fna_22'>[22]</a> <i>Nature</i>, October 30, 1902.</p>
+
+<p><a name='f_23' id='f_23' href='#fna_23'>[23]</a> Charles Lane Poor, <i>The Solar System</i>, p. 170.</p>
+
+<p><a name='f_24' id='f_24' href='#fna_24'>[24]</a> Smyth, <i>Celestial Cycle</i>, p. 60.</p>
+
+<p><a name='f_25' id='f_25' href='#fna_25'>[25]</a> Denning, <i>Telescopic Work for Starlight Evenings</i>, p. 225.</p>
+
+<p><a name='f_26' id='f_26' href='#fna_26'>[26]</a> <i>The Observatory</i>, 1894, p. 395.</p>
+
+<p><a name='f_27' id='f_27' href='#fna_27'>[27]</a> <i>Ast. Nach.</i> 4333, quoted in <i>Nature</i>, July 1, 1909, p. 20.</p>
+
+<p><a name='f_28' id='f_28' href='#fna_28'>[28]</a> <i>English Mechanic</i>, July 23, 1909.</p>
+
+<p><a name='f_29' id='f_29' href='#fna_29'>[29]</a> <i>Nature</i>, December 22, 1892.</p>
+
+<p><a name='f_30' id='f_30' href='#fna_30'>[30]</a> <i>Celestial Objects</i>, vol. i. p. 52, footnote.</p>
+
+<p><a name='f_31' id='f_31' href='#fna_31'>[31]</a> <i>Ibid.</i>, p. 54.</p>
+
+<p><a name='f_32' id='f_32' href='#fna_32'>[32]</a> <i>Astronomy and Astrophysics</i>, 1892, p. 618.</p>
+
+<p><a name='f_33' id='f_33' href='#fna_33'>[33]</a> <i>Nature</i>, August 7, 1879.</p>
+
+<p><a name='f_34' id='f_34' href='#fna_34'>[34]</a> <i>The World of Space</i>, p. 56.</p>
+
+<p><a name='f_35' id='f_35' href='#fna_35'>[35]</a> <i>Nature</i>, September 15, 1892.</p>
+
+<p><a name='f_36' id='f_36' href='#fna_36'>[36]</a> <i>Observatory</i>, 1880, p. 574.</p>
+
+<p><a name='f_37' id='f_37' href='#fna_37'>[37]</a> <i>Knowledge</i>, November 1, 1897, pp. 260, 261.</p>
+
+<p><a name='f_38' id='f_38' href='#fna_38'>[38]</a> <i>Worlds in the Making</i>, p. 61.</p>
+
+<p><a name='f_39' id='f_39' href='#fna_39'>[39]</a> <i>Ibid.</i>, p. 48.</p>
+
+<p><a name='f_40' id='f_40' href='#fna_40'>[40]</a> <i>Nature</i>, June 1, 1876.</p>
+
+<p><a name='f_41' id='f_41' href='#fna_41'>[41]</a> <i>Cel. Objects</i>, vol. i. p. 66 (5th Edition).</p>
+
+<p><a name='f_42' id='f_42' href='#fna_42'>[42]</a> <i>Celestial Objects</i>, vol. i. p. 65 (5th Edition).</p>
+
+<p><a name='f_43' id='f_43' href='#fna_43'>[43]</a> <i>Ast. Nach.</i> No. 1863.</p>
+
+<p><a name='f_44' id='f_44' href='#fna_44'>[44]</a> <i>Nature</i>, June 1, 1876.</p>
+
+<p><a name='f_45' id='f_45' href='#fna_45'>[45]</a> <i>Ibid.</i>, June 8, 1876.</p>
+
+<p><a name='f_46' id='f_46' href='#fna_46'>[46]</a> <i>Nature</i>, October 17, 1895.</p>
+
+<p><a name='f_47' id='f_47' href='#fna_47'>[47]</a> <i>Ibid.</i>, July 27, 1905.</p>
+
+<p><a name='f_48' id='f_48'>[48]</a> <i>Celestial Cycle</i>, p. 107.</p>
+
+<p><a name='f_49' id='f_49' href='#fna_49'>[49]</a> <i>Nature</i>, October 6, 1887.</p>
+
+<p><a name='f_50' id='f_50' href='#fna_50'>[50]</a> <i>Ast. Nach.</i>, No. 4106.</p>
+
+<p><a name='f_51' id='f_51' href='#fna_51'>[51]</a> <i>Copernicus</i>, vol. ii. p. 168.</p>
+
+<p><a name='f_52' id='f_52' href='#fna_52'>[52]</a> <i>Cosmos</i>, vol. iv. p. 476, footnote.</p>
+
+<p><a name='f_53' id='f_53' href='#fna_53'>[53]</a> Denning, <i>Telescopic Work for Starlight Evenings</i>, p. 153.</p>
+
+<p><a name='f_54' id='f_54' href='#fna_54'>[54]</a> <i>Ibid.</i>, p. 154.</p>
+
+<p><a name='f_55' id='f_55' href='#fna_55'>[55]</a> <i>Nature</i>, July 13, 1876.</p>
+
+<p><a name='f_56' id='f_56' href='#fna_56'>[56]</a> P. M. Ryves in <i>Knowledge</i>, June 1, 1897, p. 144.</p>
+
+<p><a name='f_57' id='f_57' href='#fna_57'>[57]</a> <i>Bulletin, Ast. Soc. de France</i>, August, 1905.</p>
+
+<p><a name='f_58' id='f_58' href='#fna_58'>[58]</a> <i>Nature</i>, April 5, 1894.</p>
+
+<p><a name='f_59' id='f_59' href='#fna_59'>[59]</a> <i>Nature</i>, May 14, 1896. Some have attributed these &#8220;luminous clouds&#8221;
+to light reflected from the dust of the Krakatoa eruption (1883).</p>
+
+<p><a name='f_60' id='f_60' href='#fna_60'>[60]</a> <i>The Observatory</i>, 1877, p. 90.</p>
+
+<p><a name='f_61' id='f_61' href='#fna_61'>[61]</a> <i>Popular Astronomy</i>, vol. 11 (1903), p. 293.</p>
+
+<p><a name='f_62' id='f_62' href='#fna_62'>[62]</a> <i>Popular Astronomy</i>, vol. 13 (1905), p. 226.</p>
+
+<p><a name='f_63' id='f_63' href='#fna_63'>[63]</a> <i>Nature</i>, July 25, 1901 (from Flammarion).</p>
+
+<p><a name='f_64' id='f_64' href='#fna_64'>[64]</a> <i>Popular Astronomy</i>, vol. 11 (1903), p. 496.</p>
+
+<p><a name='f_65' id='f_65' href='#fna_65'>[65]</a> <i>Kinetic Theories of Gravitation</i>, Washington, 1877.</p>
+
+<p><a name='f_66' id='f_66' href='#fna_66'>[66]</a> <i>The Observatory</i>, June, 1894, p. 208.</p>
+
+<p><a name='f_67' id='f_67' href='#fna_67'>[67]</a> <i>Nature</i>, June 8, 1899.</p>
+
+<p><a name='f_68' id='f_68' href='#fna_68'>[68]</a> <i>Astrophysical Journal</i>, vol. 14 (1901), p. 238, footnote.</p>
+
+<p><a name='f_69' id='f_69' href='#fna_69'>[69]</a> <i>Mars as the Abode of Life</i>, p. 52.</p>
+
+<p><a name='f_70' id='f_70' href='#fna_70'>[70]</a> Second Book of the Maccabees v. 1-4 (Revised Edition).</p>
+
+<p><a name='f_71' id='f_71' href='#fna_71'>[71]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. i. p. 169 (Ott&eacute;&#8217;s translation).</p>
+
+<p><a name='f_72' id='f_72' href='#fna_72'>[72]</a> Quoted by Grant in <i>History of Physical Astronomy</i>, p. 71.</p>
+
+<p><a name='f_73' id='f_73' href='#fna_73'>[73]</a> <i>Ibid.</i>, pp. 100, 101.</p>
+
+<p><a name='f_74' id='f_74' href='#fna_74'>[74]</a> <i>Exposition du Syst&egrave;me du Monde</i>, quoted by Carl Snyder in <i>The World
+Machine</i>, p. 226.</p>
+
+<p><a name='f_75' id='f_75' href='#fna_75'>[75]</a> <i>Worlds in the Making</i>, p. 63.</p>
+
+<p><a name='f_76' id='f_76' href='#fna_76'>[76]</a> <i>Cosmos</i>, vol. i. p. 131.</p>
+
+<p><a name='f_77' id='f_77' href='#fna_77'>[77]</a> <i>The Observatory</i>, June, 1909, p. 261.</p>
+
+<p><a name='f_78' id='f_78' href='#fna_78'>[78]</a> <i>Astronomical Essays</i>, pp. 61, 62.</p>
+
+<p><a name='f_79' id='f_79' href='#fna_79'>[79]</a> <i>Encyclop&aelig;dia Britannica</i> (<i>Schiraz</i>).</p>
+
+<p><a name='f_80' id='f_80' href='#fna_80'>[80]</a> <i>Monthly Notices</i>, R.A.S., February, 1905.</p>
+
+<p><a name='f_81' id='f_81' href='#fna_81'>[81]</a> <i>Nature</i>, March 3, 1870.</p>
+
+<p><a name='f_82' id='f_82' href='#fna_82'>[82]</a> <i>Ibid.</i>, March 31, 1870, p. 557.</p>
+
+<p><a name='f_83' id='f_83' href='#fna_83'>[83]</a> Prof. W. H. Pickering found 12 times (see p. 1).</p>
+
+<p><a name='f_84' id='f_84' href='#fna_84'>[84]</a> <i>Nature</i>, January 30, 1908.</p>
+
+<p><a name='f_85' id='f_85' href='#fna_85'>[85]</a> <i>Nature</i>, September 5, 1901.</p>
+
+<p><a name='f_86' id='f_86' href='#fna_86'>[86]</a> <i>Ibid.</i>, July 31, 1890.</p>
+
+<p><a name='f_87' id='f_87' href='#fna_87'>[87]</a> <i>Nature</i>, October 16, 1884.</p>
+
+<p><a name='f_88' id='f_88' href='#fna_88'>[88]</a> <i>Nature</i>, February 19, 1885.</p>
+
+<p><a name='f_89' id='f_89' href='#fna_89'>[89]</a> <i>Nature</i>, January 14, 1909, p. 323.</p>
+
+<p><a name='f_90' id='f_90' href='#fna_90'>[90]</a> <i>Photographic Atlas of the Moon, Annals of Harvard Observatory</i>, vol.
+li. pp. 14, 15.</p>
+
+<p><a name='f_91' id='f_91' href='#fna_91'>[91]</a> <i>Nature</i>, January 18, 1906.</p>
+
+<p><a name='f_92' id='f_92' href='#fna_92'>[92]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. iv. p. 481.</p>
+
+<p><a name='f_93' id='f_93' href='#fna_93'>[93]</a> <i>Ibid.</i>, p. 482.</p>
+
+<p><a name='f_94' id='f_94' href='#fna_94'>[94]</a> <i>Monthly Notices</i>, R.A.S., June, 1895.</p>
+
+<p><a name='f_95' id='f_95' href='#fna_95'>[95]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. iv. p. 483 (Ott&eacute;&#8217;s translation).</p>
+
+<p><a name='f_96' id='f_96' href='#fna_96'>[96]</a> Grant, <i>History of Physical Astronomy</i>, p. 229.</p>
+
+<p><a name='f_97' id='f_97' href='#fna_97'>[97]</a> <i>Popular Astronomy</i>, vol. xvii. No. 6, p. 387 (June-July, 1909).</p>
+
+<p><a name='f_98' id='f_98' href='#fna_98'>[98]</a> <i>Nature</i>, October 7, 1875.</p>
+
+<p><a name='f_99' id='f_99' href='#fna_99'>[99]</a> <i>Mars as an Abode of Life</i> (1908), p. 281.</p>
+
+<p><a name='f_100' id='f_100' href='#fna_100'>[100]</a> <i>Knowledge</i>, May 2, 1886.</p>
+
+<p><a name='f_101' id='f_101' href='#fna_101'>[101]</a> <i>Nature</i>, March 12, 1908.</p>
+
+<p><a name='f_102' id='f_102' href='#fna_102'>[102]</a> <i>Bulletin, Ast. Soc. de France</i>, April, 1899.</p>
+
+<p><a name='f_103' id='f_103' href='#fna_103'>[103]</a> <i>Astronomy and Astrophysics</i> (1894), p. 649.</p>
+
+<p><a name='f_104' id='f_104' href='#fna_104'>[104]</a> <i>Nature</i>, April 20, 1905.</p>
+
+<p><a name='f_105' id='f_105' href='#fna_105'>[105]</a> <i>Astrophysical Journal</i>, vol. 14 (1901), p. 258.</p>
+
+<p><a name='f_106' id='f_106' href='#fna_106'>[106]</a> <i>Nature</i>, August 22, 1907.</p>
+
+<p><a name='f_107' id='f_107' href='#fna_107'>[107]</a> <i>Popular Astronomy</i>, vol. 12 (1904), p. 679.</p>
+
+<p><a name='f_108' id='f_108' href='#fna_108'>[108]</a> <i>Mars as an Abode of Life</i>, p. 69.</p>
+
+<p><a name='f_109' id='f_109' href='#fna_109'>[109]</a> <i>Ibid.</i>, p. 146.</p>
+
+<p><a name='f_110' id='f_110' href='#fna_110'>[110]</a> <i>Worlds in the Making</i>, p. 49.</p>
+
+<p><a name='f_111' id='f_111' href='#fna_111'>[111]</a> <i>Worlds in the Making</i>, p. 53.</p>
+
+<p><a name='f_112' id='f_112' href='#fna_112'>[112]</a> Denning, <i>Telescopic Work for Starlight Evenings</i>, p. 158.</p>
+
+<p><a name='f_113' id='f_113' href='#fna_113'>[113]</a> <i>Ibid.</i>, p. 166.</p>
+
+<p><a name='f_114' id='f_114' href='#fna_114'>[114]</a> <i>Nature</i>, July 13, 1876.</p>
+
+<p><a name='f_115' id='f_115' href='#fna_115'>[115]</a> <i>Nature</i>, May 2, 1907.</p>
+
+<p><a name='f_116' id='f_116' href='#fna_116'>[116]</a> <i>Nature</i>, May 30, 1907.</p>
+
+<p><a name='f_117' id='f_117' href='#fna_117'>[117]</a> <i>Publications of the Astronomical Society of the Pacific</i>, August,
+1908.</p>
+
+<p><a name='f_118' id='f_118' href='#fna_118'>[118]</a> <i>Monthly Notices</i>, R.A.S., 1902, p. 291.</p>
+
+<p><a name='f_119' id='f_119' href='#fna_119'>[119]</a> <i>Monthly Notices</i>, R.A.S., February, 1902, p. 291.</p>
+
+<p><a name='f_120' id='f_120' href='#fna_120'>[120]</a> <i>Nature</i>, May 24, 1894.</p>
+
+<p><a name='f_121' id='f_121' href='#fna_121'>[121]</a> <i>Ibid.</i>, February 14, 1895.</p>
+
+<p><a name='f_122' id='f_122' href='#fna_122'>[122]</a> <i>Ibid.</i>, September 14, 1905.</p>
+
+<p><a name='f_123' id='f_123' href='#fna_123'>[123]</a> <i>Ibid.</i>, September 21, 1905.</p>
+
+<p><a name='f_124' id='f_124' href='#fna_124'>[124]</a> <i>Ibid.</i>, September 28, 1905.</p>
+
+<p><a name='f_125' id='f_125' href='#fna_125'>[125]</a> <i>Ibid.</i>, July 13, 1905.</p>
+
+<p><a name='f_126' id='f_126' href='#fna_126'>[126]</a> <i>Nature</i>, November 3, 1898.</p>
+
+<p><a name='f_127' id='f_127' href='#fna_127'>[127]</a> <i>Ibid.</i>, July 14, 1881, p. 235.</p>
+
+<p><a name='f_128' id='f_128' href='#fna_128'>[128]</a> Quoted in <i>The Observatory</i>, February, 1896, p. 104, from <i>Ast.
+Nach.</i>, No. 3319.</p>
+
+<p><a name='f_129' id='f_129' href='#fna_129'>[129]</a> <i>Monthly Notices</i>, R.A.S., February, 1909.</p>
+
+<p><a name='f_130' id='f_130' href='#fna_130'>[130]</a> <i>Celestial Objects</i>, vol. i. p. 163.</p>
+
+<p><a name='f_131' id='f_131' href='#fna_131'>[131]</a> <i>Nature</i>, December 29, 1898.</p>
+
+<p><a name='f_132' id='f_132' href='#fna_132'>[132]</a> <i>Celestial Objects</i>, vol. i. p. 166.</p>
+
+<p><a name='f_133' id='f_133' href='#fna_133'>[133]</a> <i>Astrophysical Journal</i>, vol. 14 (1901), pp. 248-9.</p>
+
+<p><a name='f_134' id='f_134' href='#fna_134'>[134]</a> <i>Nature</i>, August 27, 1908.</p>
+
+<p><a name='f_135' id='f_135' href='#fna_135'>[135]</a> Webb&#8217;s <i>Celestial Objects</i>, vol. i. p. 177.</p>
+
+<p><a name='f_136' id='f_136' href='#fna_136'>[136]</a> <i>Ibid.</i>, vol. i. p. 187.</p>
+
+<p><a name='f_137' id='f_137' href='#fna_137'>[137]</a> <i>Celestial Objects</i>, vol. i. p. 186.</p>
+
+<p><a name='f_138' id='f_138' href='#fna_138'>[138]</a> <i>Astronomy and Astrophysics</i>, 1892, p. 87.</p>
+
+<p><a name='f_139' id='f_139' href='#fna_139'>[139]</a> <i>Ibid.</i>, 1892, pp. 94-5.</p>
+
+<p><a name='f_140' id='f_140' href='#fna_140'>[140]</a> <i>Observatory</i>, December, 1891.</p>
+
+<p><a name='f_141' id='f_141' href='#fna_141'>[141]</a> <i>Popular Astronomy</i>, vol. 11 (1903), p. 574.</p>
+
+<p><a name='f_142' id='f_142' href='#fna_142'>[142]</a> <i>Ibid.</i>, October, 1908.</p>
+
+<p><a name='f_143' id='f_143' href='#fna_143'>[143]</a> <i>Bulletin, Ast. Soc. de France</i>, August, 1907.</p>
+
+<p><a name='f_144' id='f_144' href='#fna_144'>[144]</a> <i>Nature</i>, August, 29 1907.</p>
+
+<p><a name='f_145' id='f_145' href='#fna_145'>[145]</a> <i>Ibid.</i>, March 7, 1907.</p>
+
+<p><a name='f_146' id='f_146' href='#fna_146'>[146]</a> <i>Bulletin, Ast. Soc. de France</i>, June, 1904.</p>
+
+<p><a name='f_147' id='f_147' href='#fna_147'>[147]</a> <i>The Observatory</i>, October, 1903, p. 392.</p>
+
+<p><a name='f_148' id='f_148' href='#fna_148'>[148]</a> <i>Astronomy and Astrophysics</i>, 1894, p. 277.</p>
+
+<p><a name='f_149' id='f_149' href='#fna_149'>[149]</a> <i>Nature</i>, November 18, 1897.</p>
+
+<p><a name='f_150' id='f_150' href='#fna_150'>[150]</a> <i>Journal</i>, B.A.A., January, 1907.</p>
+
+<p><a name='f_151' id='f_151' href='#fna_151'>[151]</a> <i>Journal</i>, B.A.A., February, 1909, p. 161.</p>
+
+<p><a name='f_152' id='f_152' href='#fna_152'>[152]</a> <i>Cosmos</i>, vol. ii. p. 703.</p>
+
+<p><a name='f_153' id='f_153' href='#fna_153'>[153]</a> <i>Ibid.</i></p>
+
+<p><a name='f_154' id='f_154' href='#fna_154'>[154]</a> Denning, <i>Telescopic Work for Starlight Evenings</i>, p. 349.</p>
+
+<p><a name='f_155' id='f_155' href='#fna_155'>[155]</a> <i>Cosmos</i>, vol. iii. p. 75.</p>
+
+<p><a name='f_156' id='f_156' href='#fna_156'>[156]</a> <i>Journal</i>, B.A.A., June, 1896.</p>
+
+<p><a name='f_157' id='f_157' href='#fna_157'>[157]</a> <i>Celestial Objects</i>, vol. i. p. 191.</p>
+
+<p><a name='f_158' id='f_158' href='#fna_158'>[158]</a> <i>Nature</i>, May 30, 1901.</p>
+
+<p><a name='f_159' id='f_159' href='#fna_159'>[159]</a> <i>Bulletin, Ast. Soc. de France</i>, August, 1900.</p>
+
+<p><a name='f_160' id='f_160' href='#fna_160'>[160]</a> <i>Astronomy and Astrophysics</i>, 1892.</p>
+
+<p><a name='f_161' id='f_161' href='#fna_161'>[161]</a> <i>Astrophysical Journal</i>, January, 1908, p. 35.</p>
+
+<p><a name='f_162' id='f_162' href='#fna_162'>[162]</a> <i>Nature</i>, May 22, 1902.</p>
+
+<p><a name='f_163' id='f_163' href='#fna_163'>[163]</a> <i>Ibid.</i>, July 9, 1903.</p>
+
+<p><a name='f_164' id='f_164' href='#fna_164'>[164]</a> <i>Ibid.</i>, July 16, 1903.</p>
+
+<p><a name='f_165' id='f_165' href='#fna_165'>[165]</a> <i>Nature</i>, September 24, 1903.</p>
+
+<p><a name='f_166' id='f_166' href='#fna_166'>[166]</a> <i>Ibid.</i>, October 8, 1903.</p>
+
+<p><a name='f_167' id='f_167' href='#fna_167'>[167]</a> <i>Astrophysical Journal</i>, vol. 26 (1907), p. 60.</p>
+
+<p><a name='f_168' id='f_168' href='#fna_168'>[168]</a> <i>Nature</i>, January 30, 1908.</p>
+
+<p><a name='f_169' id='f_169' href='#fna_169'>[169]</a> <i>Ibid.</i>, October 15, 1908.</p>
+
+<p><a name='f_170' id='f_170' href='#fna_170'>[170]</a> <i>Ibid.</i>, October 29, 1908.</p>
+
+<p><a name='f_171' id='f_171' href='#fna_171'>[171]</a> <i>Journal</i>, B.A.A., March, 1908, and June 22, 1908.</p>
+
+<p><a name='f_172' id='f_172' href='#fna_172'>[172]</a> <i>Nature</i>, June 25, 1903.</p>
+
+<p><a name='f_173' id='f_173' href='#fna_173'>[173]</a> <i>Bulletin, Ast. Soc. de France</i>, June, 1904.</p>
+
+<p><a name='f_174' id='f_174' href='#fna_174'>[174]</a> <i>Pop. Ast.</i>, vol. 12, pp. 408-9.</p>
+
+<p><a name='f_175' id='f_175' href='#fna_175'>[175]</a> <i>Nature</i>, August 29, 1889.</p>
+
+<p><a name='f_176' id='f_176' href='#fna_176'>[176]</a> <i>Astrophysical Journal</i>, vol. 26 (1907), p. 62.</p>
+
+<p><a name='f_177' id='f_177' href='#fna_177'>[177]</a> <i>Bulletin, Ast. Soc. de France</i>, January, 1904.</p>
+
+<p><a name='f_178' id='f_178' href='#fna_178'>[178]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. iv. p. 532.</p>
+
+<p><a name='f_179' id='f_179' href='#fna_179'>[179]</a> <i>Copernicus</i>, vol. ii. p. 64.</p>
+
+<p><a name='f_180' id='f_180' href='#fna_180'>[180]</a> <i>Knowledge</i>, May, 1909.</p>
+
+<p><a name='f_181' id='f_181' href='#fna_181'>[181]</a> <i>Journal</i>, British Astronomical Association, January, 1909, p. 132.</p>
+
+<p><a name='f_182' id='f_182' href='#fna_182'>[182]</a> <i>Ast. Nach.</i>, No. 4308.</p>
+
+<p><a name='f_183' id='f_183' href='#fna_183'>[183]</a> <i>History of Physical Astronomy</i>, p. 204.</p>
+
+<p><a name='f_184' id='f_184' href='#fna_184'>[184]</a> Smyth&#8217;s <i>Celestial Cycle</i>, pp. 210, 211.</p>
+
+<p><a name='f_185' id='f_185' href='#fna_185'>[185]</a> Poor, <i>The Solar System</i>, p. 274.</p>
+
+<p><a name='f_186' id='f_186' href='#fna_186'>[186]</a> <i>Celestial Cycle</i>, p. 246.</p>
+
+<p><a name='f_187' id='f_187' href='#fna_187'>[187]</a> <i>Nature</i>, October 2, 1879.</p>
+
+<p><a name='f_188' id='f_188' href='#fna_188'>[188]</a> <i>Ibid.</i>, May 6, 1880.</p>
+
+<p><a name='f_189' id='f_189' href='#fna_189'>[189]</a> <i>Ibid.</i>, February 19, 1880.</p>
+
+<p><a name='f_190' id='f_190' href='#fna_190'>[190]</a> <i>Nature</i>, September 30, 1897.</p>
+
+<p><a name='f_191' id='f_191' href='#fna_191'>[191]</a> <i>Nature</i>, August 5, 1875.</p>
+
+<p><a name='f_192' id='f_192' href='#fna_192'>[192]</a> <i>Ibid.</i>, October 12, 1882, and <i>Copernicus</i>, vol. iii. p. 85.</p>
+
+<p><a name='f_193' id='f_193' href='#fna_193'>[193]</a> <i>Nature</i>, May 8, 1884.</p>
+
+<p><a name='f_194' id='f_194' href='#fna_194'>[194]</a> <i>Ibid.</i>, June 16, 1887.</p>
+
+<p><a name='f_195' id='f_195' href='#fna_195'>[195]</a> <i>Journal</i>, B.A.A., December 13, 1901.</p>
+
+<p><a name='f_196' id='f_196' href='#fna_196'>[196]</a> <i>Nature</i>, September 20, 1900.</p>
+
+<p><a name='f_197' id='f_197' href='#fna_197'>[197]</a> <i>Ast. Nach.</i>, No. 3868, and <i>Nature</i>, March 12, 1903.</p>
+
+<p><a name='f_198' id='f_198' href='#fna_198'>[198]</a> <i>Nature</i>, November 13, 1908.</p>
+
+<p><a name='f_199' id='f_199' href='#fna_199'>[199]</a> <i>Nature</i>, December 7, 1905.</p>
+
+<p><a name='f_200' id='f_200' href='#fna_200'>[200]</a> <i>Celestial Cycle</i>, p. 259.</p>
+
+<p><a name='f_201' id='f_201' href='#fna_201'>[201]</a> <i>Celestial Cycle</i>, p. 260.</p>
+
+<p><a name='f_202' id='f_202' href='#fna_202'>[202]</a> <i>Journal</i>, B.A.A., April, 1907.</p>
+
+<p><a name='f_203' id='f_203' href='#fna_203'>[203]</a> <i>Monthly Notices</i>, R.A.S., March, 1908.</p>
+
+<p><a name='f_204' id='f_204' href='#fna_204'>[204]</a> <i>Celestial Cycle</i>, p. 231.</p>
+
+<p><a name='f_205' id='f_205' href='#fna_205'>[205]</a> <i>Journal</i>, B.A.A., July, 1908.</p>
+
+<p><a name='f_206' id='f_206' href='#fna_206'>[206]</a> <i>Popular Astronomy</i>, October, 1908.</p>
+
+<p><a name='f_207' id='f_207' href='#fna_207'>[207]</a> <i>Cape Obs.</i>, p. 401.</p>
+
+<p><a name='f_208' id='f_208' href='#fna_208'>[208]</a> <i>Nature</i>, July 2, 1908.</p>
+
+<p><a name='f_209' id='f_209' href='#fna_209'>[209]</a> <i>Journal</i>, B.A.A., January 20, 1909, pp. 123-4.</p>
+
+<p><a name='f_210' id='f_210' href='#fna_210'>[210]</a> Chambers&#8217; <i>Handbook of Astronomy</i>, Catalogue of Comets.</p>
+
+<p><a name='f_211' id='f_211' href='#fna_211'>[211]</a> Seneca, quoted by Chambers, <i>Handbook</i>, vol. i. p. 554 (Fourth
+Edition).</p>
+
+<p><a name='f_212' id='f_212' href='#fna_212'>[212]</a> <i>Ibid.</i></p>
+
+<p><a name='f_213' id='f_213' href='#fna_213'>[213]</a> <i>Ibid.</i></p>
+
+<p><a name='f_214' id='f_214' href='#fna_214'>[214]</a> <i>Ibid.</i>, p. 534.</p>
+
+<p><a name='f_215' id='f_215' href='#fna_215'>[215]</a> <i>Ibid.</i></p>
+
+<p><a name='f_216' id='f_216' href='#fna_216'>[216]</a> Ma-tuoan-lin, quoted by Chambers, <i>Handbook</i>, p. 570.</p>
+
+<p><a name='f_217' id='f_217' href='#fna_217'>[217]</a> <i>Astronomy and Astrophysics</i>, 1893, p. 798.</p>
+
+<p><a name='f_218' id='f_218' href='#fna_218'>[218]</a> <i>The Observatory</i>, October, 1898.</p>
+
+<p><a name='f_219' id='f_219' href='#fna_219'>[219]</a> Grant&#8217;s <i>History of Physical Astronomy</i>, p. 293.</p>
+
+<p><a name='f_220' id='f_220' href='#fna_220'>[220]</a> <i>Ibid.</i>, p. 294.</p>
+
+<p><a name='f_221' id='f_221' href='#fna_221'>[221]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. i. pp. 89, 90 (Ott&eacute;&#8217;s translation).</p>
+
+<p><a name='f_222' id='f_222' href='#fna_222'>[222]</a> <i>Celestial Objects</i>, vol. i. p. 211, footnote.</p>
+
+<p><a name='f_223' id='f_223' href='#fna_223'>[223]</a> Denning, <i>Telescopic Work for Starlight Evenings</i>, p. 248.</p>
+
+<p><a name='f_224' id='f_224' href='#fna_224'>[224]</a> <i>Ibid.</i>, p. 248.</p>
+
+<p><a name='f_225' id='f_225' href='#fna_225'>[225]</a> <i>Ibid.</i>, p. 250.</p>
+
+<p><a name='f_226' id='f_226' href='#fna_226'>[226]</a> <i>Ibid.</i>, p. 231.</p>
+
+<p><a name='f_227' id='f_227' href='#fna_227'>[227]</a> Vol. iii. p. 106.</p>
+
+<p><a name='f_228' id='f_228' href='#fna_228'>[228]</a> Grant&#8217;s <i>History of Physical Astronomy</i>, p. 298.</p>
+
+<p><a name='f_229' id='f_229' href='#fna_229'>[229]</a> <i>Ibid.</i>, p. 305.</p>
+
+<p><a name='f_230' id='f_230' href='#fna_230'>[230]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. i. p. 95.</p>
+
+<p><a name='f_231' id='f_231' href='#fna_231'>[231]</a> <i>Nature</i>, April 30, 1908.</p>
+
+<p><a name='f_232' id='f_232' href='#fna_232'>[232]</a> <i>Bulletin, Ast. Soc. de France</i>, May, 1906.</p>
+
+<p><a name='f_233' id='f_233' href='#fna_233'>[233]</a> <i>Nature</i>, November 24, 1904.</p>
+
+<p><a name='f_234' id='f_234' href='#fna_234'>[234]</a> <i>Ibid.</i>, September 10, 1896.</p>
+
+<p><a name='f_235' id='f_235' href='#fna_235'>[235]</a> <i>Ibid.</i>, June 29, 1893.</p>
+
+<p><a name='f_236' id='f_236' href='#fna_236'>[236]</a> <i>Journal</i>, B.A.A., May 22, 1903.</p>
+
+<p><a name='f_237' id='f_237' href='#fna_237'>[237]</a> <i>Nature</i>, December 13, 1906, p. 159.</p>
+
+<p><a name='f_238' id='f_238' href='#fna_238'>[238]</a> <i>Nature</i>, September 13, 1906.</p>
+
+<p><a name='f_239' id='f_239' href='#fna_239'>[239]</a> <i>Nature</i>, October 12, 1905, p. 596.</p>
+
+<p><a name='f_240' id='f_240' href='#fna_240'>[240]</a> <i>Knowledge</i>, January 13, 1882.</p>
+
+<p><a name='f_241' id='f_241' href='#fna_241'>[241]</a> <i>Ibid.</i>, January 20, 1882.</p>
+
+<p><a name='f_242' id='f_242' href='#fna_242'>[242]</a> <i>Popular Astronomy</i>, June-July, 1908, p. 345.</p>
+
+<p><a name='f_243' id='f_243' href='#fna_243'>[243]</a> <i>The Observatory</i>, March, 1896, p. 135.</p>
+
+<p><a name='f_244' id='f_244' href='#fna_244'>[244]</a> <i>The Observatory</i>, February, 1900, pp. 106-7.</p>
+
+<p><a name='f_245' id='f_245' href='#fna_245'>[245]</a> <i>Knowledge</i>, March, 1893, p. 51.</p>
+
+<p><a name='f_246' id='f_246' href='#fna_246'>[246]</a> <i>Ibid.</i>, July 3, 1885, p. 11.</p>
+
+<p><a name='f_247' id='f_247' href='#fna_247'>[247]</a> <i>Cosmos</i>, vol. i. p. 108 (Ott&eacute;&#8217;s translation).</p>
+
+<p><a name='f_248' id='f_248' href='#fna_248'>[248]</a> <i>Ibid.</i>, vol. i. p. 124.</p>
+
+<p><a name='f_249' id='f_249' href='#fna_249'>[249]</a> <i>Ibid.</i>, vol. i. p. 119, footnote.</p>
+
+<p><a name='f_250' id='f_250' href='#fna_250'>[250]</a> <i>Copernicus</i>, vol. i. p. 72.</p>
+
+<p><a name='f_251' id='f_251' href='#fna_251'>[251]</a> <i>Ibid.</i></p>
+
+<p><a name='f_252' id='f_252' href='#fna_252'>[252]</a> <i>Astrophysical Journal</i>, June, 1909, pp. 378-9.</p>
+
+<p><a name='f_253' id='f_253' href='#fna_253'>[253]</a> <i>Knowledge</i>, July, 1909, p. 264.</p>
+
+<p><a name='f_254' id='f_254' href='#fna_254'>[254]</a> Quoted by Miss Irene E. T. Warner in <i>Knowledge</i>, July, 1909, p.
+264.</p>
+
+<p><a name='f_255' id='f_255' href='#fna_255'>[255]</a> <i>The Observatory</i>, November, 1900.</p>
+
+<p><a name='f_256' id='f_256' href='#fna_256'>[256]</a> Or, &#8220;Before the phantom of false morning died&#8221; (4th edition); <i>The
+Observatory</i>, September, 1905, p. 356.</p>
+
+<p><a name='f_257' id='f_257' href='#fna_257'>[257]</a> <i>The Observatory</i>, July, 1896, p. 274.</p>
+
+<p><a name='f_258' id='f_258' href='#fna_258'>[258]</a> <i>Journal</i>, B.A.A., January 24, 1906.</p>
+
+<p><a name='f_259' id='f_259' href='#fna_259'>[259]</a> <i>Ast. Soc. of the Pacific</i>, December, 1908, p. 280.</p>
+
+<p><a name='f_260' id='f_260' href='#fna_260'>[260]</a> <i>Nature</i>, November 1, 1906.</p>
+
+<p><a name='f_261' id='f_261' href='#fna_261'>[261]</a> <i>Ibid.</i>, November 22, 1906, p. 93.</p>
+
+<p><a name='f_262' id='f_262' href='#fna_262'>[262]</a> <i>Nature</i>, August 30, 1906.</p>
+
+<p><a name='f_263' id='f_263' href='#fna_263'>[263]</a> <i>Cosmos</i>, vol. i. p. 131, footnote.</p>
+
+<p><a name='f_264' id='f_264' href='#fna_264'>[264]</a> <i>Nature</i>, December 16, 1875.</p>
+
+<p><a name='f_265' id='f_265' href='#fna_265'>[265]</a> <i>Ibid.</i>, July 23, 1891.</p>
+
+<p><a name='f_266' id='f_266' href='#fna_266'>[266]</a> <i>Bulletin, Ast. Soc. de France</i>, April, 1903.</p>
+
+<p><a name='f_267' id='f_267' href='#fna_267'>[267]</a> <i>Bulletin, Ast. Soc. de France</i>, April, 1903.</p>
+
+<p><a name='f_268' id='f_268' href='#fna_268'>[268]</a> <i>The Observatory</i>, May, 1896. The italics are Brenner&#8217;s.</p>
+
+<p><a name='f_269' id='f_269' href='#fna_269'>[269]</a> <i>Cosmos</i>, vol. iv. p. 563.</p>
+
+<p><a name='f_270' id='f_270' href='#fna_270'>[270]</a> For details of this enumeration, see <i>Astronomical Essays</i>, p. 222.</p>
+
+<p><a name='f_271' id='f_271' href='#fna_271'>[271]</a> <i>Nature</i>, June 11, 1908.</p>
+
+<p><a name='f_272' id='f_272' href='#fna_272'>[272]</a> <i>Popular Astronomy</i>, vol. 14 (1906), p. 510.</p>
+
+<p><a name='f_273' id='f_273' href='#fna_273'>[273]</a> <i>Bedford Catalogue</i>, p. 532.</p>
+
+<p><a name='f_274' id='f_274' href='#fna_274'>[274]</a> <i>Popular Astronomy</i>, vol. 15 (1907), p. 194.</p>
+
+<p><a name='f_275' id='f_275' href='#fna_275'>[275]</a> <i>Popular Astronomy</i>, vol. 15 (1907), p. 195.</p>
+
+<p><a name='f_276' id='f_276' href='#fna_276'>[276]</a> <i>Bulletin, Ast. Soc. de France</i>, February, 1903.</p>
+
+<p><a name='f_277' id='f_277' href='#fna_277'>[277]</a> Here &#967; is probably 17 Cygni, &#967; being the famous
+variable near it.</p>
+
+<p><a name='f_278' id='f_278' href='#fna_278'>[278]</a> <i>Popular Astronomy</i>, vol. 13 (1904), p. 509.</p>
+
+<p><a name='f_279' id='f_279' href='#fna_279'>[279]</a> <i>Astrophysical Journal</i>, December, 1895.</p>
+
+<p><a name='f_280' id='f_280' href='#fna_280'>[280]</a> <i>The Observatory</i>, July, 1895, p. 290.</p>
+
+<p><a name='f_281' id='f_281' href='#fna_281'>[281]</a> <i>Celestial Cycle</i>, p. 302.</p>
+
+<p><a name='f_282' id='f_282' href='#fna_282'>[282]</a> <i>Nature</i>, December 13, 1894.</p>
+
+<p><a name='f_283' id='f_283' href='#fna_283'>[283]</a> <i>Histoire Celeste</i>, p. 211.</p>
+
+<p><a name='f_284' id='f_284' href='#fna_284'>[284]</a> <i>Nature</i>, October, 1887.</p>
+
+<p><a name='f_285' id='f_285' href='#fna_285'>[285]</a> <i>Ibid.</i>, August 29, 1889.</p>
+
+<p><a name='f_286' id='f_286' href='#fna_286'>[286]</a> <i>Science Abstracts</i>, February 25, 1908, pp. 82, 83.</p>
+
+<p><a name='f_287' id='f_287' href='#fna_287'>[287]</a> <i>Bedford Catalogue</i>, pp. 227-8.</p>
+
+<p><a name='f_288' id='f_288' href='#fna_288'>[288]</a> <i>Knowledge</i>, February 1, 1888.</p>
+
+<p><a name='f_289' id='f_289' href='#fna_289'>[289]</a> <i>Celestial Cycle</i>, p. 280.</p>
+
+<p><a name='f_290' id='f_290' href='#fna_290'>[290]</a> <i>Popular Astronomy</i>, February, 1904.</p>
+
+<p><a name='f_291' id='f_291' href='#fna_291'>[291]</a> <i>Ibid.</i>, vol. 15 (1907), p. 444.</p>
+
+<p><a name='f_292' id='f_292' href='#fna_292'>[292]</a> <i>Journal</i>, B.A.A., June, 1899.</p>
+
+<p><a name='f_293' id='f_293' href='#fna_293'>[293]</a> <i>Astrophysical Journal</i>, vol. 8 (1898), p. 314.</p>
+
+<p><a name='f_294' id='f_294' href='#fna_294'>[294]</a> <i>Astrophysical Journal</i>, vol. 8, p. 213.</p>
+
+<p><a name='f_295' id='f_295' href='#fna_295'>[295]</a> <i>Ibid.</i>, vol. 17, January to June, 1902.</p>
+
+<p><a name='f_296' id='f_296' href='#fna_296'>[296]</a> <i>Astronomy and Astrophysics</i>, 1894, pp. 569-70.</p>
+
+<p><a name='f_297' id='f_297' href='#fna_297'>[297]</a> <i>The Study of Stellar Evolution</i> (1908), p. 171.</p>
+
+<p><a name='f_298' id='f_298' href='#fna_298'>[298]</a> <i>Astrophysical Journal</i>, January, 1905.</p>
+
+<p><a name='f_299' id='f_299' href='#fna_299'>[299]</a> <i>Journal</i>, B.A.A., June, 1901.</p>
+
+<p><a name='f_300' id='f_300' href='#fna_300'>[300]</a> <i>Ast. Soc. of the Pacific</i>, December, 1908.</p>
+
+<p><a name='f_301' id='f_301' href='#fna_301'>[301]</a> <i>The Observatory</i>, November, 1902, p. 391.</p>
+
+<p><a name='f_302' id='f_302' href='#fna_302'>[302]</a> <i>Cosmos</i>, vol. iv. p. 567 (Ott&eacute;&#8217;s translation).</p>
+
+<p><a name='f_303' id='f_303' href='#fna_303'>[303]</a> <i>Journal</i>, B.A.A., February, 1898.</p>
+
+<p><a name='f_304' id='f_304' href='#fna_304'>[304]</a> <i>The Observatory</i>, April, 1887.</p>
+
+<p><a name='f_305' id='f_305' href='#fna_305'>[305]</a> <i>Evangeline</i>, Part the Second, III.</p>
+
+<p><a name='f_306' id='f_306' href='#fna_306'>[306]</a> <i>Legend of Robert, Duke of Normandy.</i></p>
+
+<p><a name='f_307' id='f_307' href='#fna_307'>[307]</a> <i>Copernicus</i>, vol. iii. p. 231.</p>
+
+<p><a name='f_308' id='f_308' href='#fna_308'>[308]</a> <i>Ibid.</i>, p. 61.</p>
+
+<p><a name='f_309' id='f_309' href='#fna_309'>[309]</a> <i>Cosmos</i>, vol. i. p. 142.</p>
+
+<p><a name='f_310' id='f_310' href='#fna_310'>[310]</a> These apertures are computed from the formula, minimum visible = 9 +
+5 log. aperture.</p>
+
+<p><a name='f_311' id='f_311' href='#fna_311'>[311]</a> <i>Cosmos</i>, vol. iii. p. 73.</p>
+
+<p><a name='f_312' id='f_312' href='#fna_312'>[312]</a> <i>Darwin and Modern Science</i>, p. 563.</p>
+
+<p><a name='f_313' id='f_313' href='#fna_313'>[313]</a> <i>Journal</i>, B.A.A., October, 1895.</p>
+
+<p><a name='f_314' id='f_314' href='#fna_314'>[314]</a> Burnham&#8217;s <i>General Catalogue of Double Stars</i>, p. 494.</p>
+
+<p><a name='f_315' id='f_315' href='#fna_315'>[315]</a> <i>Journal</i>, B.A.A., November 18, 1896.</p>
+
+<p><a name='f_316' id='f_316' href='#fna_316'>[316]</a> <i>Ibid.</i>, B.A.A., January, 1907.</p>
+
+<p><a name='f_317' id='f_317' href='#fna_317'>[317]</a> <i>Studies in Astronomy</i>, p. 185.</p>
+
+<p><a name='f_318' id='f_318' href='#fna_318'>[318]</a> <i>Knowledge</i>, June, 1891.</p>
+
+<p><a name='f_319' id='f_319' href='#fna_319'>[319]</a> Seen by Drs. Ludendorff and Eberhard, <i>The Observatory</i>, April,
+1906, p. 166, quoted from <i>Ast. Nach.</i>, No. 4067.</p>
+
+<p><a name='f_320' id='f_320' href='#fna_320'>[320]</a> <i>The Observatory</i>, January, 1907, p. 61.</p>
+
+<p><a name='f_321' id='f_321' href='#fna_321'>[321]</a> <i>Astronomy and Astrophysics</i>, 1894.</p>
+
+<p><a name='f_322' id='f_322' href='#fna_322'>[322]</a> Smyth&#8217;s <i>Celestial Cycle</i>, p. 223.</p>
+
+<p><a name='f_323' id='f_323' href='#fna_323'>[323]</a> <i>Nature</i>, February 7, 1907.</p>
+
+<p><a name='f_324' id='f_324' href='#fna_324'>[324]</a> <i>Ibid.</i>, March 19, 1908.</p>
+
+<p><a name='f_325' id='f_325' href='#fna_325'>[325]</a> <i>Popular Astronomy</i>, vol. 15 (1907), p. 9.</p>
+
+<p><a name='f_326' id='f_326' href='#fna_326'>[326]</a> <i>Astrophysical Journal</i>, June, 1907, p. 330.</p>
+
+<p><a name='f_327' id='f_327' href='#fna_327'>[327]</a> <i>Ibid.</i>, vol. 22, p. 172.</p>
+
+<p><a name='f_328' id='f_328' href='#fna_328'>[328]</a> <i>Nature</i>, November 18, 1886.</p>
+
+<p><a name='f_329' id='f_329' href='#fna_329'>[329]</a> <i>Astrophysical Journal</i>, vol. 17 (1903), p. 282.</p>
+
+<p><a name='f_330' id='f_330' href='#fna_330'>[330]</a> <i>Astrophysical Journal</i>, vol. 12 (1900), p. 54.</p>
+
+<p><a name='f_331' id='f_331' href='#fna_331'>[331]</a> <i>Nature</i>, March 21, 1878.</p>
+
+<p><a name='f_332' id='f_332' href='#fna_332'>[332]</a> <i>Bulletin, Ast. Soc. de France</i>, June, 1904.</p>
+
+<p><a name='f_333' id='f_333' href='#fna_333'>[333]</a> <i>Journal</i>, B.A.A., vol. 17 (1903), p. 282.</p>
+
+<p><a name='f_334' id='f_334' href='#fna_334'>[334]</a> <i>Nature</i>, June 20, 1909.</p>
+
+<p><a name='f_335' id='f_335' href='#fna_335'>[335]</a> <i>The Observatory</i>, vol. 7 (1884), p. 17.</p>
+
+<p><a name='f_336' id='f_336' href='#fna_336'>[336]</a> <i>The Observatory</i>, vol. 14 (1891), p. 69.</p>
+
+<p><a name='f_337' id='f_337' href='#fna_337'>[337]</a> <i>Astronomy and Astrophysics</i>, 1896, p. 54</p>
+
+<p><a name='f_338' id='f_338' href='#fna_338'>[338]</a> <i>Nature</i>, August 28, 1902.</p>
+
+<p><a name='f_339' id='f_339' href='#fna_339'>[339]</a> <i>Astrophysical Journal</i>, October, 1903.</p>
+
+<p><a name='f_340' id='f_340' href='#fna_340'>[340]</a> <i>Nature</i>, May 30, 1907.</p>
+
+<p><a name='f_341' id='f_341' href='#fna_341'>[341]</a> <i>Popular Astronomy</i>, February, 1909, p. 125.</p>
+
+<p><a name='f_342' id='f_342' href='#fna_342'>[342]</a> <i>The Observatory</i>, May, 1907, p. 216.</p>
+
+<p><a name='f_343' id='f_343' href='#fna_343'>[343]</a> <i>Astrophysical Journal</i>, May, 1907.</p>
+
+<p><a name='f_344' id='f_344' href='#fna_344'>[344]</a> <i>Histoire de l&#8217;Astronomie Moderne</i>, vol. i. pp. 185-6.</p>
+
+<p><a name='f_345' id='f_345' href='#fna_345'>[345]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. iii. p. 210 (Ott&eacute;&#8217;s translation).</p>
+
+<p><a name='f_346' id='f_346' href='#fna_346'>[346]</a> <i>Ibid.</i>, vol. iii. pp. 213-14.</p>
+
+<p><a name='f_347' id='f_347' href='#fna_347'>[347]</a> J. C. Duncan, <i>Lick Observatory Bulletin</i>, No. 151.</p>
+
+<p><a name='f_348' id='f_348' href='#fna_348'>[348]</a> <i>Astrophysical Journal</i>, vol. 17, p. 283.</p>
+
+<p><a name='f_349' id='f_349' href='#fna_349'>[349]</a> <i>The Origin of the Stars</i>, p. 143.</p>
+
+<p><a name='f_350' id='f_350' href='#fna_350'>[350]</a> <i>Ibid.</i>, p. 135.</p>
+
+<p><a name='f_351' id='f_351' href='#fna_351'>[351]</a> Quoted by Ennis in <i>The Origin of the Stars</i>, p. 133.</p>
+
+<p><a name='f_352' id='f_352' href='#fna_352'>[352]</a> <i>Astrophysical Journal</i>, vol. 20 (1904), p. 357.</p>
+
+<p><a name='f_353' id='f_353' href='#fna_353'>[353]</a> <i>Nature</i>, March 8, 1906.</p>
+
+<p><a name='f_354' id='f_354' href='#fna_354'>[354]</a> <i>Astronomical Society of the Pacific</i>, August, 1908.</p>
+
+<p><a name='f_355' id='f_355' href='#fna_355'>[355]</a> <i>Astronomy and Astrophysics</i>, 1894, p. 812.</p>
+
+<p><a name='f_356' id='f_356' href='#fna_356'>[356]</a> <i>The Observatory</i>, May, 1905.</p>
+
+<p><a name='f_357' id='f_357' href='#fna_357'>[357]</a> This is a misquotation. See my <i>Astronomical Essays</i>, p. 135.</p>
+
+<p><a name='f_358' id='f_358' href='#fna_358'>[358]</a> <i>Nature</i>, February 3, 1870.</p>
+
+<p><a name='f_359' id='f_359' href='#fna_359'>[359]</a> <i>Bedford Catalogue</i>, p. 14.</p>
+
+<p><a name='f_360' id='f_360' href='#fna_360'>[360]</a> <i>Ibid.</i>, p. 307.</p>
+
+<p><a name='f_361' id='f_361' href='#fna_361'>[361]</a> <i>Astrophysical Journal</i>, vol. 14, p. 37.</p>
+
+<p><a name='f_362' id='f_362' href='#fna_362'>[362]</a> <i>Ibid.</i>, vol. 9, p. 149.</p>
+
+<p><a name='f_363' id='f_363' href='#fna_363'>[363]</a> <i>Nature</i>, July 20, 1899.</p>
+
+<p><a name='f_364' id='f_364' href='#fna_364'>[364]</a> <i>Ast. Nach.</i>, No. 3476.</p>
+
+<p><a name='f_365' id='f_365' href='#fna_365'>[365]</a> <i>Astronomische Nachrichten</i>, No. 4213.</p>
+
+<p><a name='f_366' id='f_366' href='#fna_366'>[366]</a> <i>Astrophysical Journal</i>, vol. 9, p. 149.</p>
+
+<p><a name='f_367' id='f_367' href='#fna_367'>[367]</a> <i>Cape Observations</i>, p. 61.</p>
+
+<p><a name='f_368' id='f_368' href='#fna_368'>[368]</a> <i>Ibid.</i>, p. 85.</p>
+
+<p><a name='f_369' id='f_369' href='#fna_369'>[369]</a> <i>Cape Observations</i>, p. 98.</p>
+
+<p><a name='f_370' id='f_370' href='#fna_370'>[370]</a> <i>Transactions</i>, Royal Dublin Society, vol. 2.</p>
+
+<p><a name='f_371' id='f_371' href='#fna_371'>[371]</a> <i>Ast. Nach.</i>, 3628, quoted in <i>The Observatory</i>, April, 1900.</p>
+
+<p><a name='f_372' id='f_372' href='#fna_372'>[372]</a> <i>Nature</i>, April 8, 1909.</p>
+
+<p><a name='f_373' id='f_373' href='#fna_373'>[373]</a> <i>Problems in Astrophysics</i>, p. 477.</p>
+
+<p><a name='f_374' id='f_374' href='#fna_374'>[374]</a> <i>Ibid.</i>, p. 499.</p>
+
+<p><a name='f_375' id='f_375' href='#fna_375'>[375]</a> <i>Copernicus</i>, vol. iii. p. 55.</p>
+
+<p><a name='f_376' id='f_376' href='#fna_376'>[376]</a> <i>Lick Observatory Bulletin</i>, No. 149.</p>
+
+<p><a name='f_377' id='f_377' href='#fna_377'>[377]</a> <i>Ibid.</i></p>
+
+<p><a name='f_378' id='f_378' href='#fna_378'>[378]</a> <i>Ibid.</i></p>
+
+<p><a name='f_379' id='f_379' href='#fna_379'>[379]</a> <i>Monthly Notices</i>, R.A.S., April, 1908, pp. 465-481.</p>
+
+<p><a name='f_380' id='f_380' href='#fna_380'>[380]</a> <i>Lick Observatory Bulletin</i>, No. 155 (February, 1909).</p>
+
+<p><a name='f_381' id='f_381' href='#fna_381'>[381]</a> <i>Outlines of Astronomy</i>, par. 870 (Edition of 1875).</p>
+
+<p><a name='f_382' id='f_382' href='#fna_382'>[382]</a> <i>Georgics</i>, i. II. 217-18.</p>
+
+<p><a name='f_383' id='f_383' href='#fna_383'>[383]</a> See paper by Mr. and Mrs. Maunder in <i>Monthly Notices</i>, R.A.S.,
+March, 1904, p. 506.</p>
+
+<p><a name='f_384' id='f_384' href='#fna_384'>[384]</a> <i>Primitive Constellations</i>, vol. ii. p. 143.</p>
+
+<p><a name='f_385' id='f_385' href='#fna_385'>[385]</a> <i>Recherches sur l&#8217;Histoire de l&#8217;Astronomie Ancienne</i>, by Paul
+Tannery (1893), p. 298.</p>
+
+<p><a name='f_386' id='f_386' href='#fna_386'>[386]</a> <i>Primitive Constellations</i>, vol. ii. p. 225.</p>
+
+<p><a name='f_387' id='f_387' href='#fna_387'>[387]</a> <i>Nature</i>, October 2, 1890.</p>
+
+<p><a name='f_388' id='f_388' href='#fna_388'>[388]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. pp. 243-4.</p>
+
+<p><a name='f_389' id='f_389' href='#fna_389'>[389]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. pp. 242-3.</p>
+
+<p><a name='f_390' id='f_390' href='#fna_390'>[390]</a> There are three copies of Al-Sufi&#8217;s work in the Imperial Library at
+Paris, but these are inaccurate. There is also one in the British Museum
+Library, and another in the India Office Library; but these are imperfect,
+considerable portions of the original work being missing.</p>
+
+<p><a name='f_391' id='f_391' href='#fna_391'>[391]</a> <i>Harvard Annals</i>, vol. ix. p. 51.</p>
+
+<p><a name='f_392' id='f_392' href='#fna_392'>[392]</a> The science of the risings and settings of the stars was called <i>ilm
+el-anwa</i> (Caussin, <i>Notices et Extraits des Manuscrits de la Biblioth&egrave;que
+due Roi</i>, tome xii. p. 237).</p>
+
+<p><a name='f_393' id='f_393' href='#fna_393'>[393]</a> See Mr. E. B. Knobel&#8217;s papers on this subject in the <i>Monthly
+Notices</i>, R.A.S., for 1879 and 1884.</p>
+
+<p><a name='f_394' id='f_394' href='#fna_394'>[394]</a> In reading this chapter the reader is recommended to have a Star
+Atlas beside him for reference; Proctor&#8217;s smaller Star Atlas will be found
+very convenient for this purpose. On the title-page of this useful work
+the author quotes Carlyle&#8217;s words, &#8220;Why did not somebody teach me the
+constellations and make me at home in the starry heavens which are always
+overhead, and which I don&#8217;t half know to this day?&#8221;</p>
+
+<p><a name='f_395' id='f_395' href='#fna_395'>[395]</a> <i>Bedford Catalogue</i>, p. 29.</p>
+
+<p><a name='f_396' id='f_396' href='#fna_396'>[396]</a> <i>Cosmos</i>, vol. iii. p. 87.</p>
+
+<p><a name='f_397' id='f_397' href='#fna_397'>[397]</a> <i>Heavenly Display</i>, 579-85.</p>
+
+<p><a name='f_398' id='f_398' href='#fna_398'>[398]</a> <i>Bedford Catalogue</i>, p. 385.</p>
+
+<p><a name='f_399' id='f_399' href='#fna_399'>[399]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 529.</p>
+
+<p><a name='f_400' id='f_400' href='#fna_400'>[400]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. pp. 268-9.</p>
+
+<p><a name='f_401' id='f_401' href='#fna_401'>[401]</a> <i>Primitive Constellations</i>, vol. i. p. 48.</p>
+
+<p><a name='f_402' id='f_402' href='#fna_402'>[402]</a> <i>Bedford Catalogue</i>, pp. 27, 28.</p>
+
+<p><a name='f_403' id='f_403' href='#fna_403'>[403]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 492.</p>
+
+<p><a name='f_404' id='f_404' href='#fna_404'>[404]</a> <i>Bedford Catalogue</i>, p. 120.</p>
+
+<p><a name='f_405' id='f_405' href='#fna_405'>[405]</a> <i>Primitive Constellations</i>, vol. i. p. 143.</p>
+
+<p><a name='f_406' id='f_406' href='#fna_406'>[406]</a> Perseus.</p>
+
+<p><a name='f_407' id='f_407' href='#fna_407'>[407]</a> <i>Heavenly Display</i>, 254-8, 261-5, quoted by Brown in <i>Primitive
+Constellations</i>, vol. i. p. 274.</p>
+
+<p><a name='f_408' id='f_408' href='#fna_408'>[408]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 493.</p>
+
+<p><a name='f_409' id='f_409' href='#fna_409'>[409]</a> <i>Primitive Constellations</i>, vol. i. p. 292.</p>
+
+<p><a name='f_410' id='f_410' href='#fna_410'>[410]</a> <i>Paradiso</i>, xxii. 111.</p>
+
+<p><a name='f_411' id='f_411' href='#fna_411'>[411]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 493.</p>
+
+<p><a name='f_412' id='f_412' href='#fna_412'>[412]</a> <i>Bedford Catalogue</i>, p. 225.</p>
+
+<p><a name='f_413' id='f_413' href='#fna_413'>[413]</a> <i>Nature</i>, April 6, 1882.</p>
+
+<p><a name='f_414' id='f_414' href='#fna_414'>[414]</a> <i>Primitive Constellations</i>, vol. i. p. 68.</p>
+
+<p><a name='f_415' id='f_415' href='#fna_415'>[415]</a> <i>Ibid.</i>, vol. i. p. 71.</p>
+
+<p><a name='f_416' id='f_416' href='#fna_416'>[416]</a> <i>Bibliographie G&egrave;n&egrave;rale de l&#8217;Astronomie</i>, vol. i. Introduction, pp.
+131, 132.</p>
+
+<p><a name='f_417' id='f_417' href='#fna_417'>[417]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. p. 296.</p>
+
+<p><a name='f_418' id='f_418' href='#fna_418'>[418]</a> <i>Primitive Constellations</i>, vol. i. p. 74.</p>
+
+<p><a name='f_419' id='f_419' href='#fna_419'>[419]</a> <i>Cape Observations</i>, p. 116.</p>
+
+<p><a name='f_420' id='f_420' href='#fna_420'>[420]</a> <i>Metamorphoses</i>, xv. 371.</p>
+
+<p><a name='f_421' id='f_421' href='#fna_421'>[421]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 487.</p>
+
+<p><a name='f_422' id='f_422' href='#fna_422'>[422]</a> <i>Monthly Notices</i>, R.A.S., April 14, 1848.</p>
+
+<p><a name='f_423' id='f_423' href='#fna_423'>[423]</a> <i>Prim. Const.</i>, vol. ii. p. 45.</p>
+
+<p><a name='f_424' id='f_424' href='#fna_424'>[424]</a> Lalande&#8217;s <i>Astronomie</i>, pp. 472-3.</p>
+
+<p><a name='f_425' id='f_425' href='#fna_425'>[425]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 485.</p>
+
+<p><a name='f_426' id='f_426' href='#fna_426'>[426]</a> This star is not shown in Proctor&#8217;s small Atlas, but it lies between
+&#956; and &#957;, nearer to &#956;.</p>
+
+<p><a name='f_427' id='f_427' href='#fna_427'>[427]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. p. 247.</p>
+
+<p><a name='f_428' id='f_428' href='#fna_428'>[428]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 489.</p>
+
+<p><a name='f_429' id='f_429' href='#fna_429'>[429]</a> <i>Primitive Constellations</i>, vol. i. p. 91.</p>
+
+<p><a name='f_430' id='f_430' href='#fna_430'>[430]</a> <i>Memoirs</i>, R.A.S., vol. xiii. 61.</p>
+
+<p><a name='f_431' id='f_431' href='#fna_431'>[431]</a> <i>Monthly Notices</i>, R.A.S., June, 1895.</p>
+
+<p><a name='f_432' id='f_432' href='#fna_432'>[432]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. p. 274.</p>
+
+<p><a name='f_433' id='f_433' href='#fna_433'>[433]</a> <i>Primitive Constellations</i>, vol. i. p. 143.</p>
+
+<p><a name='f_434' id='f_434' href='#fna_434'>[434]</a> <i>Primitive Constellations</i>, vol. i. p. 278.</p>
+
+<p><a name='f_435' id='f_435' href='#fna_435'>[435]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv. p. 468.</p>
+
+<p><a name='f_436' id='f_436' href='#fna_436'>[436]</a> <i>Qu&aelig;st. Nat.</i>, Lib. 1, Cap. I. &sect; 6; quoted by Dr. See. &#8220;Canicula&#8221; is
+Sirius, and &#8220;Nartis,&#8221; Mars.</p>
+
+<p><a name='f_437' id='f_437' href='#fna_437'>[437]</a> <i>Astronomy and Astrophysics</i>, vol. 11, 1892.</p>
+
+<p><a name='f_438' id='f_438' href='#fna_438'>[438]</a> <i>The Observatory</i>, April, 1906, p. 175.</p>
+
+<p><a name='f_439' id='f_439' href='#fna_439'>[439]</a> Houzeau, <i>Bibliographie G&egrave;n&egrave;rale de l&#8217;Astronomie</i>, vol. i.,
+Introduction, p. 129.</p>
+
+<p><a name='f_440' id='f_440' href='#fna_440'>[440]</a> <i>English Mechanic</i>, March 25, 1904, p. 145.</p>
+
+<p><a name='f_441' id='f_441' href='#fna_441'>[441]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. iii. p. 185, footnote (Ott&eacute;&#8217;s
+translation).</p>
+
+<p><a name='f_442' id='f_442' href='#fna_442'>[442]</a> Lalande&#8217;s <i>Astronomie</i>, vol, i. p. 277.</p>
+
+<p><a name='f_443' id='f_443' href='#fna_443'>[443]</a> This was pointed out by Flammarion in his work <i>Les &Eacute;toiles</i>, page
+532; but his identifications do not agree exactly with mine.</p>
+
+<p><a name='f_444' id='f_444' href='#fna_444'>[444]</a> See Proctor&#8217;s Map 7, now x.</p>
+
+<p><a name='f_445' id='f_445' href='#fna_445'>[445]</a> <i>Primitive Constellations</i>, vol. i. p. 106.</p>
+
+<p><a name='f_446' id='f_446' href='#fna_446'>[446]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i. p. 278.</p>
+
+<p><a name='f_447' id='f_447' href='#fna_447'>[447]</a> Lalande&#8217;s <i>Astronomie</i>, vol. iv.</p>
+
+<p><a name='f_448' id='f_448'>[448]</a> <i>Primitive Constellations</i>, vol. i. p. 112.</p>
+
+<p><a name='f_449' id='f_449' href='#fna_449'>[449]</a> <i>Ibid.</i>, vol. i. p. 113.</p>
+
+<p><a name='f_450' id='f_450' href='#fna_450'>[450]</a> Lalande&#8217;s <i>Astronomie</i>, vol. i.</p>
+
+<p><a name='f_451' id='f_451' href='#fna_451'>[451]</a> W. T. Lynn in <i>The Observatory</i>, vol. 22, p. 236.</p>
+
+<p><a name='f_452' id='f_452' href='#fna_452'>[452]</a> <i>Knowledge</i>, May 1, 1889. Sir John Herschel, however, gives 3970
+<span class="smcaplc">B.C.</span></p>
+
+<p><a name='f_453' id='f_453' href='#fna_453'>[453]</a> <i>The Observatory</i>, November 1907, p. 412.</p>
+
+<p><a name='f_454' id='f_454' href='#fna_454'>[454]</a> This is not, however, <i>invariably</i> the case, as pointed out by Mr.
+Denning in <i>The Observatory</i>, 1885, p. 340.</p>
+
+<p><a name='f_455' id='f_455' href='#fna_455'>[455]</a> <i>The Observatory</i>, vol. 8 (1885), pp. 246-7.</p>
+
+<p><a name='f_456' id='f_456' href='#fna_456'>[456]</a> <i>Harvard College Observatory Annals</i>, vol. xlviii. No. 5.</p>
+
+<p><a name='f_457' id='f_457' href='#fna_457'>[457]</a> <i>Popular Astronomy</i>, vol. 15 (1907), p. 529.</p>
+
+<p><a name='f_458' id='f_458' href='#fna_458'>[458]</a> <i>Cape Observations</i>, p. 77.</p>
+
+<p><a name='f_459' id='f_459' href='#fna_459'>[459]</a> <i>Monthly Notices</i>, R.A.S., March, 1899.</p>
+
+<p><a name='f_460' id='f_460' href='#fna_460'>[460]</a> <i>Nature</i>, February 13, 1890.</p>
+
+<p><a name='f_461' id='f_461' href='#fna_461'>[461]</a> <i>Popular Astronomy</i>, vol. 15 (1907), p. 530.</p>
+
+<p><a name='f_462' id='f_462' href='#fna_462'>[462]</a> <i>Photographs of Star-Clusters and Nebul&aelig;</i>, vol. ii. p. 17.</p>
+
+<p><a name='f_463' id='f_463' href='#fna_463'>[463]</a> <i>Monthly Notices</i>, R.A.S., May 9, 1856.</p>
+
+<p><a name='f_464' id='f_464' href='#fna_464'>[464]</a> <i>Astrophysical Journal</i>, vol. 25 (1907), p. 219.</p>
+
+<p><a name='f_465' id='f_465' href='#fna_465'>[465]</a> <i>Popular Astronomy</i>, vol. 11 (1903), p. 293.</p>
+
+<p><a name='f_466' id='f_466' href='#fna_466'>[466]</a> Translated by W. H. Mallock, <i>Nature</i>, February 8, 1900, p. 352.</p>
+
+<p><a name='f_467' id='f_467' href='#fna_467'>[467]</a> Howard Payn, <i>Nature</i>, May 16, 1901, p. 56.</p>
+
+<p><a name='f_468' id='f_468' href='#fna_468'>[468]</a> Howard Payn, <i>Nature</i>, May 16, 1901, p. 56.</p>
+
+<p><a name='f_469' id='f_469' href='#fna_469'>[469]</a> <i>Contributions from the Mount Wilson Solar Observatory</i>, No. 31.</p>
+
+<p><a name='f_470' id='f_470' href='#fna_470'>[470]</a> Quoted by Denning in <i>Telescopic Work for Starlight Evenings</i>, p.
+297.</p>
+
+<p><a name='f_471' id='f_471' href='#fna_471'>[471]</a> <i>Astrophysical Journal</i>, March, 1895.</p>
+
+<p><a name='f_472' id='f_472' href='#fna_472'>[472]</a> <i>Outlines of Astronomy</i>, Tenth Edition, p. 571.</p>
+
+<p><a name='f_473' id='f_473' href='#fna_473'>[473]</a> <i>Astrophysical Journal</i>, vol. 12, p. 136.</p>
+
+<p><a name='f_474' id='f_474' href='#fna_474'>[474]</a> <i>De Placitis.</i> Quoted by Carl Snyder in <i>The World Machine</i> p. 354.</p>
+
+<p><a name='f_475' id='f_475' href='#fna_475'>[475]</a> <i>Popular Astronomy</i>, vol. 14 (1906), p. 638.</p>
+
+<p><a name='f_476' id='f_476' href='#fna_476'>[476]</a> Article on &#8220;The Greek Anthology,&#8221; <i>Nineteenth Century</i>, April, 1907,
+quoted in <i>The Observatory</i>, May, 1907.</p>
+
+<p><a name='f_477' id='f_477' href='#fna_477'>[477]</a> <i>Popular Astronomy</i>, vol. 13 (1905), p. 346.</p>
+
+<p><a name='f_478' id='f_478' href='#fna_478'>[478]</a> <i>Bulletin de la Soc. Ast. de France</i>, April, 1908.</p>
+
+<p><a name='f_479' id='f_479' href='#fna_479'>[479]</a> <i>The Observatory</i>, vol. 11, p. 375.</p>
+
+<p><a name='f_480' id='f_480' href='#fna_480'>[480]</a> Grant, <i>History of Physical Astronomy</i>, p. 364.</p>
+
+<p><a name='f_481' id='f_481' href='#fna_481'>[481]</a> <i>Ibid.</i>, p. 377.</p>
+
+<p><a name='f_482' id='f_482' href='#fna_482'>[482]</a> <i>Ibid.</i>, p. 366.</p>
+
+<p><a name='f_483' id='f_483' href='#fna_483'>[483]</a> <i>Ibid.</i>, p. 367.</p>
+
+<p><a name='f_484' id='f_484' href='#fna_484'>[484]</a> Grant, <i>History of Physical Astronomy</i>, p. 370.</p>
+
+<p><a name='f_485' id='f_485' href='#fna_485'>[485]</a> <i>Nature</i>, July 25, 1889.</p>
+
+<p><a name='f_486' id='f_486' href='#fna_486'>[486]</a> <i>Cosmos</i>, vol. iv. p. 381.</p>
+
+<p><a name='f_487' id='f_487' href='#fna_487'>[487]</a> <i>Cosmos</i>, vol. iv. pp. 381-6.</p>
+
+<p><a name='f_488' id='f_488' href='#fna_488'>[488]</a> <i>Ibid.</i>, vol. i. p. 121.</p>
+
+<p><a name='f_489' id='f_489' href='#fna_489'>[489]</a> <i>The Observatory</i>, vol. 6 (1883), pp. 327-8.</p>
+
+<p><a name='f_490' id='f_490' href='#fna_490'>[490]</a> <i>Nature</i>, June 25, 1874.</p>
+
+<p><a name='f_491' id='f_491' href='#fna_491'>[491]</a> <i>Popular Astronomy</i>, May, 1895, &#8220;Reflectors or Refractors.&#8221;</p>
+
+<p><a name='f_492' id='f_492' href='#fna_492'>[492]</a> Denning, <i>Telescopic Work for Starlight Evenings</i>, p. 225.</p>
+
+<p><a name='f_493' id='f_493' href='#fna_493'>[493]</a> <i>Nature</i>, November 2, 1893.</p>
+
+<p><a name='f_494' id='f_494' href='#fna_494'>[494]</a> <i>Telescopic Work</i>, p. 226.</p>
+
+<p><a name='f_495' id='f_495' href='#fna_495'>[495]</a> <i>Copernicus</i>, vol. i. p. 229.</p>
+
+<p><a name='f_496' id='f_496' href='#fna_496'>[496]</a> Grant, <i>History of Physical Astronomy</i>, p. 433.</p>
+
+<p><a name='f_497' id='f_497' href='#fna_497'>[497]</a> <i>Cosmos</i>, vol. ii. p. 699.</p>
+
+<p><a name='f_498' id='f_498' href='#fna_498'>[498]</a> Grant, <i>History of Physical Astronomy</i>, p. 536, footnote.</p>
+
+<p><a name='f_499' id='f_499' href='#fna_499'>[499]</a> <i>Bedford Catalogue</i>, p. 179.</p>
+
+<p><a name='f_500' id='f_500' href='#fna_500'>[500]</a> <i>The Observatory</i>, July, 1891.</p>
+
+<p><a name='f_501' id='f_501' href='#fna_501'>[501]</a> <i>Nature</i>, September 3, 1903.</p>
+
+<p><a name='f_502' id='f_502' href='#fna_502'>[502]</a> <i>Cosmos</i>, vol. ii. p. 669.</p>
+
+<p><a name='f_503' id='f_503' href='#fna_503'>[503]</a> <i>The World Machine</i>, p. 80.</p>
+
+<p><a name='f_504' id='f_504' href='#fna_504'>[504]</a> <i>Ibid.</i>, p. 89.</p>
+
+<p><a name='f_505' id='f_505' href='#fna_505'>[505]</a> Grant, <i>History of Physical Astronomy</i>, p. 107.</p>
+
+<p><a name='f_506' id='f_506' href='#fna_506'>[506]</a> Grant, <i>History of Physical Astronomy</i>, p. 113.</p>
+
+<p><a name='f_507' id='f_507' href='#fna_507'>[507]</a> <i>Nature</i>, August 11, 1898.</p>
+
+<p><a name='f_508' id='f_508' href='#fna_508'>[508]</a> <i>Ibid.</i>, August 18, 1898.</p>
+
+<p><a name='f_509' id='f_509' href='#fna_509'>[509]</a> <i>Ibid.</i>, October 20, 1898.</p>
+
+<p><a name='f_510' id='f_510' href='#fna_510'>[510]</a> <i>The Observatory</i>, vol. iv. (1881), p. 234.</p>
+
+<p><a name='f_511' id='f_511' href='#fna_511'>[511]</a> W. T. Lynn, <i>The Observatory</i>, July, 1909, p. 291.</p>
+
+<p><a name='f_512' id='f_512' href='#fna_512'>[512]</a> Quoted in <i>The Observatory</i>, July, 1902, p. 281.</p>
+
+<p><a name='f_513' id='f_513' href='#fna_513'>[513]</a> <i>Astrophysical Journal</i>, vol. 6, 1897, p. 304.</p>
+
+<p><a name='f_514' id='f_514' href='#fna_514'>[514]</a> <i>Celestial Cycle</i>, p. 367.</p>
+
+<p><a name='f_515' id='f_515' href='#fna_515'>[515]</a> <i>The Observatory</i>, vol. 5 (1882), p. 251.</p>
+
+<p><a name='f_516' id='f_516' href='#fna_516'>[516]</a> Quoted by Humboldt in <i>Cosmos</i>, vol. ii. p. 696, footnote.</p>
+
+<p><a name='f_517' id='f_517' href='#fna_517'>[517]</a> Quoted by Denning in <i>Telescopic Work</i>, p. 347.</p>
+
+<p><a name='f_518' id='f_518' href='#fna_518'>[518]</a> <i>Knowledge</i>, February 20, 1885, p. 149.</p>
+
+<p><a name='f_519' id='f_519' href='#fna_519'>[519]</a> Humboldt&#8217;s <i>Cosmos</i>, vol. i. p. 123.</p>
+
+<p><a name='f_520' id='f_520' href='#fna_520'>[520]</a> <i>Outlines of Astronomy</i>, par. 319; edition of 1875.</p>
+
+<p><a name='f_521' id='f_521' href='#fna_521'>[521]</a> <i>Bulletin de la Soc. Ast. de France</i>, March, 1908, p. 146.</p>
+
+<p><a name='f_522' id='f_522' href='#fna_522'>[522]</a> An &#8220;astronomical unit&#8221; is the sun&#8217;s mean distance from the earth.</p>
+
+<p><a name='f_523' id='f_523' href='#fna_523'>[523]</a> This is on the American and French system of notation, but on the
+English system, 10<sup>66</sup> = 10<sup>60</sup> &times; 10<sup>6</sup> would be a million decillion.</p>
+
+<p><a name='f_524' id='f_524' href='#fna_524'>[524]</a> <i>Astronomical Society of the Pacific</i>, April, 1909 (No. 125), and
+<i>Popular Astronomy</i>, May, 1909.</p>
+
+<p><a name='f_525' id='f_525' href='#fna_525'>[525]</a> <i>Nature</i>, July 22, 1909.</p>
+
+<p><a name='f_526' id='f_526' href='#fna_526'>[526]</a> <i>Ibid.</i></p>
+
+<p><a name='f_527' id='f_527' href='#fna_527'>[527]</a> <i>The Observatory</i>, vol. 9 (December, 1886), p. 389.</p>
+
+<p><a name='f_528' id='f_528' href='#fna_528'>[528]</a> <i>De Nat. Deorum</i>, quoted in Smyth&#8217;s <i>Cycle</i>, p. 19.</p>
+
+<p><a name='f_529' id='f_529' href='#fna_529'>[529]</a> <i>The Observatory</i>, May, 1907.</p>
+
+<p><a name='f_530' id='f_530' href='#fna_530'>[530]</a> <i>More Worlds than Ours</i>, p. 17.</p>
+
+<p><a name='f_531' id='f_531' href='#fna_531'>[531]</a> <i>Man&#8217;s Place in Nature.</i></p>
+
+
+<p>&nbsp;</p><p>&nbsp;</p>
+<hr style="width: 50%;" />
+<p><strong>Transcriber&#8217;s Notes:</strong></p>
+
+<p>Foonote <a href='#f_48'>48</a> appears on <a href="#Page_28">page 28</a> of the text, but there is no corresponding marker on the page.</p>
+
+<p>Foonote <a href='#f_448'>448</a> appears on <a href="#Page_295">page 295</a> of the text, but there is no corresponding marker on the page.</p>
+
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of Project Gutenberg's Astronomical Curiosities, by J. Ellard Gore
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+The Project Gutenberg EBook of Astronomical Curiosities, by J. Ellard Gore
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org/license
+
+
+Title: Astronomical Curiosities
+       Facts and Fallacies
+
+Author: J. Ellard Gore
+
+Release Date: March 25, 2012 [EBook #39263]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ASTRONOMICAL CURIOSITIES ***
+
+
+
+
+Produced by The Online Distributed Proofreading Team at
+http://www.pgdp.net (This file was produced from images
+generously made available by The Internet Archive.)
+
+
+
+
+
+
+
+
+
+  ASTRONOMICAL CURIOSITIES
+
+  FACTS AND FALLACIES
+
+
+
+
+  ASTRONOMICAL CURIOSITIES
+
+  FACTS AND FALLACIES
+
+
+  BY J. ELLARD GORE
+
+  MEMBER OF THE ROYAL IRISH ACADEMY FELLOW OF THE
+  ROYAL ASTRONOMICAL SOCIETY CORRESPONDING MEMBER
+  OF THE ROYAL ASTRONOMICAL SOCIETY OF CANADA ETC.
+  AUTHOR OF "ASTRONOMICAL ESSAYS," "STUDIES IN
+  ASTRONOMY," "THE VISIBLE UNIVERSE," ETC.
+
+
+  LONDON
+  CHATTO & WINDUS
+  1909
+
+
+
+
+  PRINTED BY
+  WILLIAM CLOWES AND SONS, LIMITED
+  LONDON AND BECCLES
+
+  _All rights reserved_
+
+
+
+
+PREFACE
+
+
+The curious facts, fallacies, and paradoxes contained in the following
+pages have been collected from various sources. Most of the information
+given will not, I think, be found in popular works on astronomy, and will,
+it is hoped, prove of interest to the general reader.
+
+J. E. G.
+
+_September, 1909._
+
+
+
+
+CONTENTS
+
+
+                                                PAGE
+
+  CHAPTER
+
+      I. THE SUN                                   1
+
+     II. MERCURY                                  10
+
+    III. VENUS                                    17
+
+     IV. THE EARTH                                32
+
+      V. THE MOON                                 48
+
+     VI. MARS                                     59
+
+    VII. THE MINOR PLANETS                        68
+
+   VIII. JUPITER                                  74
+
+     IX. SATURN                                   84
+
+      X. URANUS AND NEPTUNE                       91
+
+     XI. COMETS                                   97
+
+    XII. METEORS                                 117
+
+   XIII. THE ZODIACAL LIGHT AND GEGENSCHEIN      127
+
+    XIV. THE STARS                               135
+
+     XV. DOUBLE AND BINARY STARS                 160
+
+    XVI. VARIABLE STARS                          170
+
+   XVII. NEBULAE AND CLUSTERS                     191
+
+  XVIII. HISTORICAL                              217
+
+    XIX. THE CONSTELLATIONS                      239
+
+     XX. THE VISIBLE UNIVERSE                    313
+
+    XXI. GENERAL                                 329
+
+         INDEX                                   359
+
+
+
+
+ILLUSTRATIONS
+
+
+                                                PAGE
+
+  AL-SUFI'S "EARTHEN JAR"                        247
+
+  AL-SUFI'S "FISHES" IN ANDROMEDA                249
+
+
+
+
+ASTRONOMICAL CURIOSITIES
+
+
+
+
+CHAPTER I
+
+The Sun
+
+
+Some observations recently made by Prof. W. H. Pickering in Jamaica, make
+the value of sunlight 540,000 times that of moonlight. This makes the
+sun's "stellar magnitude" minus 26.83, and that of moonlight minus 12.5.
+Prof. Pickering finds that the light of the full moon is equal to 100,000
+stars of zero magnitude. He finds that the moon's "albedo" is about
+0.0909; or in other words, the moon reflects about one-tenth of the light
+which falls on it from the sun. He also finds that the light of the full
+moon is about twelve times the light of the half moon: a curious and
+rather unexpected result.
+
+M. C. Fabry found that during the total eclipse of the sun on August 30,
+1905, the light of the corona at a distance of five minutes of arc from
+the sun's limit, and in the vicinity of the sun's equator, was about 720
+candle-power. Comparing this with the intrinsic light of the full moon
+(2600 candle-power) we have the ratio of 0.28 to 1. He finds that the
+light of the sun in the zenith, and at its mean distance from the earth,
+is 100,000 times greater than the light of a "decimal candle" placed at a
+distance of one metre from the eye.[1] He also finds that sunlight is
+equal to 60,000 million times the light of Vega. This would make the sun's
+"stellar magnitude" minus 26.7, which does not differ much from Prof.
+Pickering's result, given above, and is probably not far from the truth.
+
+From experiments made in 1906 at Moscow, Prof. Ceraski found that the
+light of the sun's limb is only 31.4 to 38.4 times brighter than the
+illumination of the earth's atmosphere very near the limb. This is a very
+unexpected result; and considering the comparative faintness of the sun's
+corona during a total eclipse, it is not surprising that all attempts to
+photograph it without an eclipse have hitherto failed.[2]
+
+From Paschen's investigations on the heat of the sun's surface, he finds a
+result of 5961 deg. (absolute), "assuming that the sun is a perfectly black
+body."[3] Schuster finds that "There is a stratum near the sun's surface
+having an average temperature of approximately 5500 deg. C., to which about
+0.3 of the sun's radiation is due. The remaining portion of the radiation
+has an intensity equal to that due to a black body having a temperature of
+about 6700 deg. C." The above results agree fairly well with those found by
+the late Dr. W. E. Wilson.[4] The assumption of the sun being "a black
+body" seems a curious paradox; but the simple meaning of the statement is
+that the sun is assumed to act as a radiator as _if it were a perfectly
+black body heated to the high temperature given above_.
+
+According to Prof. Langley, the sun's photosphere is 5000 times brighter
+than the molten metal in a "Bessemer convertor."[5]
+
+Observations of the sun even with small telescopes and protected by dark
+glasses are very dangerous to the eyesight. Galileo blinded himself in
+this way; Sir William Herschel lost one of his eyes; and some modern
+observers have also suffered. The present writer had a narrow escape from
+permanent injury while observing the transit of Venus, in 1874, in India,
+the dark screen before the eyepiece of a 3-inch telescope having
+blistered--that is, partially fused during the observation. Mr. Cooper,
+Markree Castle, Ireland, in observing the sun, used a "drum" of alum water
+and dark spectacles, and found this sufficient protection against the
+glare in using his large refracting telescope of 13.3-inches aperture.
+
+Prof. Mitchell, of Columbia University (U.S.A.), finds that lines due to
+the recently discovered atmospherical gases argon and neon are present in
+the spectrum of the sun's chromosphere. The evidence for the existence of
+krypton and xenon is, however, inconclusive. Prof. Mitchell suggests that
+these gases may possibly have reached the earth's atmosphere from the sun.
+This would agree with the theory advanced by Arrhenius that "ionised
+particles are constantly being repulsed by the pressure of light, and thus
+journey from one sun to another."[6]
+
+Prof. Young in 1870, and Dr. Kreusler in June, 1904, observed the helium
+line D_{3} as a _dark_ line "in the spectrum of the region about a
+sun-spot."[7] This famous line, from which helium was originally
+discovered in the sun, and by which it was long afterwards detected in
+terrestrial minerals, usually appears as a _bright_ line in the spectrum
+of the solar chromosphere and "prominences." It has also been seen _dark_
+by Mr. Buss in sun-spot regions.[8]
+
+The discovery of sun-spots was claimed by Hariotte, in 1610, and by
+Galileo, Fabricius, and Scheiner, in 1611. The latter wrote 800 pages on
+them, and thought they were small planets revolving round the sun! This
+idea was also held by Tarde, who called them _Astra Borbonia_, and by C.
+Malapert, who termed them _Sydera Austricea_. But they seem to have been
+noticed by the ancients.
+
+Although in modern times there has been no extraordinary development of
+sun-spots at the epoch of maximum, it is not altogether impossible that in
+former times these spots may have occasionally increased to such an
+extent, both in number and size, as to have perceptibly darkened the sun's
+light. A more probable explanation of recorded sun-darkenings seems,
+however, to be the passing of a meteoric or nebulous cloud between the sun
+and the earth. A remarkable instance of sun-darkening recorded in Europe
+occurred on May 22, 1870, when the sun's light was observed to be
+considerably reduced in a cloudless sky in the west of Ireland, by the
+late John Birmingham; at Greenwich on the 23rd; and on the same date, but
+at a later hour, in North-Eastern France--"a progressive manifestation,"
+Mr. Birmingham says, "that seems to accord well with the hypothesis of
+moving nebulous matter." A similar phenomenon was observed in New England
+(U.S.A.), on September 6, 1881.
+
+One of the largest spots ever seen on the sun was observed in June, 1843.
+It remained visible for seven or eight days. According to Schwabe--the
+discoverer of the sun-spot period--its diameter was 74,000 miles, so that
+its area was many times that of the earth's surface. The most curious
+thing about this spot was that it appeared near a _minimum_ of the
+sun-spot cycle! and was therefore rather an anomalous phenomenon. It was
+suggested by the late Daniel Kirkwood that this great spot was caused by
+the fall of meteoric matter into the sun; and that it had possibly some
+connection with the great comet of 1843, which approached the sun nearer
+than any other recorded comet, its distance from the sun at perihelion
+being about 65,000 miles, or less than one-third of the moon's distance
+from the earth. This near approach of the comet to the sun occurred about
+three months before the appearance of the great sun-spot; and it seems
+probable that the spot was caused by the downfall of a large meteorite
+travelling in the wake of the comet.[9] The connection between comets and
+meteors is well known.
+
+The so-called blackness of sun-spots is merely relative. They are really
+very bright. The most brilliant light which can be produced artificially
+looks like a black spot when projected on the sun's disc.
+
+According to Sir Robert Ball a pound of coal striking a body with a
+velocity of five miles a second would develop as much heat as it would
+produce by its combustion. A body falling into the sun from infinity would
+have a velocity of 450 miles a second when it reached the sun's surface.
+Now as the momentum varies as the square of the velocity we have a pound
+of coal developing 90{2} (=450/5){2}, or 8,100 times as much heat as would
+be produced by its combustion. If the sun were formed of coal it would be
+consumed in about 3000 years. Hence it follows that the contraction of the
+sun's substance from infinity would produce a supply of heat for 3000 x
+8100, or 24,300,000 years.
+
+The late Mr. Proctor and Prof. Young believed "that the contraction theory
+of the sun's heat is the true and only available theory." The theory is,
+of course, a sound one; but it may now be supplemented by supposing the
+sun to contain a certain small amount of radium. This would bring physics
+and geology into harmony. Proctor thought the "sun's real globe is very
+much smaller than the globe we see. In other words the process of
+contraction has gone on further than, judging from the sun's apparent
+size, we should suppose it to have done, and therefore represents more sun
+work" done in past ages.
+
+With reference to the suggestion, recently made, that a portion, at least,
+of the sun's heat may be due to radium, and the experiments which have
+been made with negative results, Mr. R. T. Strutt--the eminent
+physicist--has made some calculations on the subject and says, "even if
+all the sun's heat were due to radium, there does not appear to be the
+smallest possibility that the Becquerel radiation from it could ever be
+detected at the earth's surface."[10]
+
+The eminent Swedish physicist Arrhenius, while admitting that a large
+proportion of the sun's heat is due to contraction, considers that it is
+probably the chemical processes going on in the sun, and not the
+contraction which constitute the _chief_ source of the solar heat.[11]
+
+As the centre of gravity of the sun and Jupiter lies at a distance of
+about 460,000 miles from the sun's centre, and the sun's radius is only
+433,000 miles, it follows that the centre of gravity of the sun and planet
+is about 27,000 miles _outside_ the sun's surface. The attractions of the
+other planets perpetually change the position of the centre of gravity of
+the solar system; but in some books on astronomy it is erroneously stated
+that the centre of gravity of the system is _always_ within the sun's
+surface. If _all_ the planets lay on the same side of the sun at the same
+time (as might possibly happen), then the centre of gravity of the whole
+system would lie considerably more than 27,000 miles outside the sun's
+surface.
+
+With reference to the sun's great size, Carl Snyder has well said, "It was
+as if in Vulcan's smithy the gods had moulded one giant ball, and the
+planets were but bits and small shot which had spattered off as the
+glowing ingot was cast and set in space. Little man on a little part of a
+little earth--a minor planet, a million of which might be tumbled into the
+shell of the central sun--was growing very small; his wars, the
+convulsions of a state, were losing consequence. Human endeavour, human
+ambitions could now scarce possess the significance they had when men
+could regard the earth as the central fact of the universe."[12]
+
+With reference to the late Prof. C. A. Young (U.S.A.)--a great authority
+on the sun--an American writer has written the following lines:--
+
+  "The destined course of whirling worlds to trace,
+  To plot the highways of the universe,
+  And hear the morning stars their song rehearse,
+  And find the wandering comet in his place;
+  This is the triumph written in his face,
+  And in the gleaming eye that read the sun
+  Like open book, and from the spectrum won
+  The secrets of immeasurable space."[13]
+
+
+
+
+CHAPTER II
+
+Mercury
+
+
+As the elongation of Mercury from the sun seldom exceeds 18 deg., it is a
+difficult object, at least in this country, to see without a telescope. As
+the poet says, the planet--
+
+  "Can scarce be caught by philosophic eye
+  Lost in the near effulgence of its blaze."
+
+Tycho Brahe, however, records several observations of Mercury with the
+unaided vision in Denmark.
+
+It can be occasionally caught with the naked eye in this country after
+sunset, when it is favourably placed for observation, and I have so seen
+it several times in Ireland. On February 19, 1888, I found it very visible
+in strong twilight near the western horizon, and apparently brighter than
+an average star of the first magnitude would be in the same position. In
+the clear air of the Punjab sky I observed Mercury on November 24-29,
+1872, near the western horizon after sunset. Its appearance was that of a
+reddish star of the first magnitude. On November 29 I compared its
+brilliancy with that of Saturn, which was some distance above it, and
+making allowance for the glare near the horizon in which Mercury was
+immersed, its brightness appeared to me to be quite equal to that of
+Saturn. In June, 1874, I found it equal to Aldebaran, and of very much the
+same colour. Mr. W. F. Denning, the famous observer of meteors, states
+that he observed Mercury with the naked eye about 150 times during the
+years 1868 to 1905.[14]
+
+He found that the duration of visibility after sunset is about 1{h} 40{m}
+when seen in March, 1{h} 30{m} in April, and 1{h} 20{m} in May. He thinks
+that the planet is, at its brightest, "certainly much brighter than a
+first magnitude star."[15] In February, 1868, he found that its brightness
+rivalled that of Jupiter, then only 2 deg. or 3 deg. distant. In November, 1882,
+it seemed brighter than Sirius. In 1876 it was more striking than Mars,
+but the latter was then "faint and at a considerable distance from the
+earth."
+
+In 1878, when Mercury and Venus were in the same field of view of a
+telescope, Nasmyth found that the surface brightness (or "intrinsic
+brightness," as it is called) of Venus was at least twice as great as that
+of Mercury; and Zoellner found that from a photometric point of view the
+surface of Mercury is comparable with that of the moon.
+
+With reference to the difficulty of seeing Mercury, owing to its proximity
+to the sun, Admiral Smyth says, "Although Mercury is never in _opposition_
+to the earth, he was, when in the house of Mars, always viewed by
+astrologers as a most malignant planet, and one full of evil influences.
+The sages stigmatized him as a false deceitful star (_sidus dolosum_), the
+eternal torment of astronomers, eluding them as much as terrestrial
+mercury did the alchemists; and Goad, who in 1686 published a whole folio
+volume full of astro-meteorological aphorisms, unveiling the choicest
+secrets of nature, contemptuously calls Mercury a 'squinting lacquey of
+the sun, who seldom shows his head in these parts, as if he was in debt.'
+His extreme mobility is so striking that chemists adopted his symbol to
+denote quicksilver."[16]
+
+Prof. W. H. Pickering thinks that the shortness of the cusps (or "horns")
+of Mercury's disc indicates that the planet's atmosphere is of small
+density--even rarer than that of Mars.
+
+The diameter of Mercury is usually stated at about 3000 miles; but a long
+series of measures made by Prof. See in the year 1901 make the real
+diameter about 2702 miles. This would make the planet smaller than some of
+the satellites of the large planets, probably smaller than satellites III.
+and IV. of Jupiter, less than Saturn's satellite Titan, and possibly
+inferior in size to the satellite of Neptune. Prof. Pickering thinks that
+the density of Mercury is about 3 (water = 1). Dr. See's observations show
+"no noticeable falling off in the brightness of Mercury near the limb."
+There is therefore no evidence of any kind of atmospheric absorption in
+Mercury, and the observer "gets the impression that the physical condition
+of the planet is very similar to that of our moon."[17]
+
+Schroeter (1780-1815) observed markings on Mercury, from which he inferred
+that the planet's surface was mountainous, and one of these mountains he
+estimated at about 11 miles in height![18] But this seems very doubtful.
+
+To account for the observed irregularities in the motion of Mercury in its
+orbit, Prof. Newcomb thinks it possible that there may exist a ring or
+zone of "asteroids" a little "outside the orbit of Mercury" and having a
+combined mass of "one-fiftieth to one-three-hundredth of the mass of
+Venus, according to its distance from Mercury." Prof. Newcomb, however,
+considers that the existence of such a ring is extremely improbable, and
+regards it "more as a curiosity than a reality."[19]
+
+M. Leo Brenner thinks that he has seen the dark side of Mercury, in the
+same way that the dark side of Venus has been seen by many observers. In
+the case of Mercury the dark side appeared _darker_ than the background of
+the sky. Perhaps this may be due to its being projected on the zodiacal
+light, or outer envelope of the sun.[20]
+
+Mercury is said to have been occulted by Venus in the year 1737.[21] But
+whether this was an actual occultation, or merely a near approach does not
+seem to be certain.
+
+The first transit of Mercury across the sun's disc was observed by
+Gassendi on November 6, 1631, and Halley observed one on November 7, 1677,
+when in the island of St. Helena.
+
+Seen from Mercury, Venus would appear brighter than even we see it, and as
+it would be at its brightest when in opposition to the sun, and seen on a
+dark sky with a full face, it must present a magnificent appearance in the
+midnight sky of Mercury. The earth will also form a brilliant object, and
+the moon would be distinctly visible. The other planets would appear very
+much as they do to us, but with somewhat less brilliancy owing to their
+greater distance.
+
+As the existence of an intra-Mercurial planet (that is a planet revolving
+round the sun within the orbit of Mercury) seems now to be very
+improbable, Prof. Perrine suggests that possibly "the finely divided
+matter which produces the zodiacal light when considered in the aggregate
+may be sufficient to cause the perturbations in the orbit of Mercury."[22]
+Prof. Newcomb, however, questions the exact accuracy of Newton's law, and
+seems to adopt Hall's hypothesis that gravity does not act _exactly_ as
+the inverse square of the distance, and that the exponent of the distance
+is not 2, but 2.0000001574.[23]
+
+Voltaire said, "If Newton had been in Portugal, and any Dominican had
+discovered a heresy in his inverse ratio of the squares of the distances,
+he would without hesitation have been clothed in a _san benito_, and burnt
+as a sacrifice to God at an _auto da fe_."[24]
+
+An occultation of Mercury by Venus was observed with a telescope on May
+17, 1737.[25]
+
+May transits of Mercury across the sun's disc will occur in the years
+1924, 1957, and 1970; and November transits in the years 1914, 1927, and
+1940.[26]
+
+From measurements of the disc of Mercury during the last transit, M. R.
+Jonckheere concludes that the _polar_ diameter of the planet is greater
+than the _equatorial_! His result, which is very curious, if true, seems
+to be supported by the observations of other observers.[27]
+
+The rotation period of Mercury, or the length of its day, seems to be
+still in doubt. From a series of observations made in the years 1896 to
+1909, Mr. John McHarg finds a period of 1.0121162 day, or 1{d} 0{h} 17{m}
+26{s}.8. He thinks that "the planet possesses a considerable atmosphere
+not so clear as that of Mars"; that "its axis is very considerably
+tilted"; and that it "has fairly large sheets of water."[28]
+
+
+
+
+CHAPTER III
+
+Venus
+
+
+Venus was naturally--owing to its brightness--the first of the planets
+known to the ancients. It is mentioned by Hesiod, Homer, Virgil, Martial,
+and Pliny; and Isaiah's remark about "Lucifer, son of the morning" (Isaiah
+xiv. 12) probably refers to Venus as a "morning star." An observation of
+Venus is found on the Nineveh tablets of date B.C. 684. It was observed in
+daylight by Halley in July, 1716.
+
+In _very_ ancient times Venus, when a morning star, was called Phosphorus
+or Lucifer, and when an evening star Hesperus; but, according to Sir G. C.
+Lewis, the identity of the two objects was known so far back as 540 B.C.
+
+When Venus is at its greatest brilliancy, and appears as a morning star
+about Christmas time (which occurred in 1887, and again in 1889), it has
+been mistaken by the public for a return of the "Star of Bethlehem."[29]
+But whatever "the star of the Magi" was it certainly was _not_ Venus. It,
+seems, indeed absurd to suppose that "the wise men" of the East should
+have mistaken a familiar object like Venus for a strange apparition. There
+seems to be nothing whatever in the Bible to lead us to expect that the
+star of Bethlehem will reappear.
+
+Mr. J. H. Stockwell has suggested that the "Star of Bethlehem" may perhaps
+be explained by a conjunction of the planets Venus and Jupiter which
+occurred on May 8, B.C. 6, which was two years before the death of Herod.
+From this it would follow that the Crucifixion took place on April 3, A.D.
+33. But it seems very doubtful that the phenomenon recorded in the Bible
+refers to any conjunction of planets.
+
+Chacornac found the intrinsic brightness of Venus to be ten times greater
+than the most luminous parts of the moon.[30] But this estimate is
+probably too high.
+
+When at its brightest, the planet is visible in broad daylight to good
+eyesight, if its exact position in the sky is known. In the clear air of
+Cambridge (U.S.A.) it is said to be possible to see it in this way in all
+parts of its orbit, except when the planet is within 10 deg. of the sun.[31]
+Mr. A. Cameron, of Yarmouth, Nova Scotia, has, however, seen Venus with
+the naked eye three days before conjunction when the planet was only
+6-1/4 deg. from the sun.[32] This seems a remarkable observation, and shows
+that the observer's eyesight must have been very keen. In a private letter
+dated October 22, 1888, the late Rev. S. J. Johnson informed the present
+writer that he saw Venus with the naked eye only four days before
+conjunction with the sun in February, 1878, and February, 1886.
+
+The crescent shape of Venus is said to have been seen with the naked eye
+by Theodore Parker in America when he was only 12 years old. Other
+observers have stated the same thing; but the possibility of such an
+observation has been much disputed in recent years.
+
+In the Chinese Annals some records are given of Venus having been seen in
+the Pleiades. On March 16, A.D. 845, it is said that "Venus eclipsed the
+Pleiades." This means, of course, that the cluster was apparently effaced
+by the brilliant light of the planet. Computing backwards for the above
+date, Hind found that on the evening of March 16, 845, Venus was situated
+near the star Electra; and on the following evening the planet passed
+close to Maia; thus showing the accuracy of the Chinese record. Another
+"eclipse" of the Pleiades by Venus is recorded in the same annals as
+having occurred on March 10, A.D. 1002.[33]
+
+When Venus is in the crescent phase, that is near "Inferior conjunction"
+with the sun, it will be noticed, even by a casual observer, that the
+crescent is not of the same shape as that of the crescent moon. The horns
+or "cusps" of the planetary crescent are more prolonged than in the case
+of the moon, and extend beyond the hemisphere. This appearance is caused
+by refraction of the sun's light through the planetary atmosphere, and is,
+in fact, a certain proof that Venus has an atmosphere similar to that of
+the earth. Observations further show that this atmosphere is denser than
+ours.
+
+Seen from Venus, the earth and moon, when in opposition, must present a
+splendid spectacle. I find that the earth would shine as a star about half
+as bright again as Venus at her brightest appears to us, and the moon
+about equal in brightness to Sirius! the two forming a superb "naked eye
+double star"--perhaps the finest sight of its kind in the solar
+system.[34]
+
+Some of the earlier observers, such as La Hire, Fontana, Cassini, and
+Schroeter, thought they saw evidence of mountains on Venus. Schroeter
+estimated some of these to be 27 or 28 miles in height! but this seems
+very doubtful. Sir William Herschel severely attacked these supposed
+discoveries. Schroeter defended himself, and was supported by Beer and
+Maedler, the famous lunar observers. Several modern observers seem to
+confirm Schroeter's conclusions; but very little is really known about the
+topography of Venus.
+
+The well-known French astronomer Trouvelot--a most excellent observer--saw
+white spots on Venus similar to those on Mars. These were well seen and
+quite brilliant in July and August, 1876, and in February and November,
+1877. The observations seem to show that these spots do not (unlike Mars)
+increase and decrease with the planet's seasons. These white spots had
+been previously noticed by former observers, including Bianchini, Derham,
+Gruithuisen, and La Hire; but these early observers do not seem to have
+considered them as snow caps, like those of Mars. Trouvelot was led by his
+own observations to conclude that the period of rotation of Venus is
+short, and the best result he obtained was 23{h} 49{m} 28{s}. This does
+not differ much from the results previously found by De Vico, Fritsch, and
+Schroeter.[35]
+
+A white spot near the planet's south pole was seen on several occasions by
+H. C. Russell in May and June, 1876.[36]
+
+Photographs of Venus taken on March 18 and April 29, 1908, by M. Quenisset
+at the Observatory of Juvissy, France, show a white polar spot. The spot
+was also seen at the same observatory by M. A. Benoit on May 20, 1903.
+
+The controversy on the period of rotation of Venus, or the length of its
+day, is a very curious one and has not yet been decided. Many good
+observers assert confidently that it is short (about 24 hours); while
+others affirm with equal confidence that it is long (about 225 days, the
+period of the planet's revolution round the sun). Among the observers who
+favour the short period of rotation are: D. Cassini (1667), J. Cassini
+(1730), Schroeter (1788-93), Maedler (1836), De Vico (1840?) Trouvelot
+(1871-79), Flammarion, Leo Brenner, Stanley Williams, and J. McHarg; and
+among those who support the long period are: Bianchini (1727),
+Schiaparelli, Cerulli, Tacchini, Mascari, and Lowell. Some recent
+spectroscopic observations seem to favour the short period.
+
+Flammarion thinks that "nothing certain can be descried upon the surface
+of Venus, and that whatever has hitherto been written regarding its period
+of rotation must be considered null and void"; and again he says, "Nothing
+can be affirmed regarding the rotation of Venus, inasmuch as the
+absorption of its immense atmosphere certainly prevents any detail on its
+surface from being perceived."[37]
+
+The eminent Swedish physicist Arrhenius thinks, however, that the dense
+atmosphere and clouds of Venus are in favour of a rapid rotation on its
+axis.[38] He thinks that the mean temperature of Venus may "not differ
+much from the calculated temperature 104 deg. F." "Under these circumstances
+the assumption would appear plausible that a very considerable portion of
+the surface of Venus, and particularly the districts about the poles,
+would be favourable to organic life."[39]
+
+The "secondary light of Venus," or the visibility of the dark side, seems
+to have been first mentioned by Derham in his _Astro Theology_ published
+in 1715. He speaks of the visibility of the dark part of the planet's disc
+"by the aid of a light of a somewhat dull and ruddy colour." The date of
+Derham's observation is not given, but it seems to have been previous to
+the year 1714. The light seems to have been also seen by a friend of
+Derham. We next find observations by Christfried Kirch, assistant
+astronomer to the Berlin Academy of Sciences, on June 7, 1721, and March
+8, 1726. These observations are found in his original papers, and were
+printed in the _Astronomische Nachrichten_, No. 1586. On the first date
+the telescopic image of the planet was "rather tremulous," but in 1726 he
+noticed that the dark part of the circle seemed to belong to a smaller
+circle than the illuminated portion of the disc.[40] The same effect was
+also noted by Webb.[41] A similar illusion is seen in the case of the
+crescent moon, and this has given rise to the saying, "the old moon in the
+new moon's arms."
+
+We next come, in order of date, to an observation made by Andreas Mayer,
+Professor of Mathematics at Griefswald in Prussia. The observation was
+made on October 20, 1759, and the dark part of Venus was seen distinctly
+by Mayer. As the planet's altitude at the time was not more than 14 deg. above
+the horizon, and its apparent distance from the sun only 10 deg., the
+phenomenon--as Professor Safarik has pointed out--"must have had a most
+unusual intensity."
+
+Sir William Herschel makes no mention of having ever seen the "secondary
+light" of Venus, although he noticed the extension of the horns beyond a
+semicircle.
+
+In the spring and summer of the year 1793, Von Hahn of Remplin in
+Mecklenburg, using excellent telescopes made by Dollond and Herschel, saw
+the dark part of Venus on several occasions, and describes the light as
+"grey verging upon brown."
+
+Schroeter of Lilienthal--the famous observer of the moon--saw the horns of
+the crescent of Venus extended many degrees beyond the semicircle on
+several occasions in 1784 and 1795, and the border of the dark part
+faintly lit up by a dusky grey light. On February 14, 1806, at 7 P.M. he
+saw the whole of the dark part visible with an ash-coloured light, and he
+was satisfied that there was no illusion. On January 24 of the same year,
+1806, Harding at Goettingen, using a reflector of 9 inches aperture and
+power 84, saw the dark side of Venus "shining with a pale ash-coloured
+light," and very visible against the dark background of the sky. The
+appearance was seen with various magnifying powers, and he thought that
+there could be no illusion. In fact the phenomenon was as evident as in
+the case of the moon. Harding again saw it on February 28 of the same
+year, the illumination being of a reddish grey colour, "like that of the
+moon in a total eclipse."
+
+The "secondary light" was also seen by Pastorff in 1822, and by
+Gruithuisen in 1825. Since 1824 observations of the "light" were made by
+Berry, Browning, Guthrie, Langdon, Noble, Prince, Webb, and others. Webb
+saw it with powers of 90 and 212 on a 9.38-inch mirror, and found it
+"equally visible when the bright crescent was hidden by a field bar."[42]
+
+Captain Noble's observation was rather unique. He found that the dark side
+was "always distinctly and positively _darker_ than the background upon
+which it is projected."
+
+The "light" was also seen by Lyman in America in 1867, and by Safarik at
+Prague. In 1871 the whole disc of Venus was seen by Professor
+Winnecke.[43] On the other hand, Winnecke stated that he only saw it twice
+in 24 years; and the great observers Dawes and Maedler never saw it at
+all![44]
+
+Various attempts have been made to explain the visibility--at times--of
+the "dark side" of Venus. The following may be mentioned[45]:--(1)
+Reflected earth-light, analogous to the dark side of the crescent moon.
+This explanation was advocated by Harding, Schroeter, and others. But,
+although the earth is undoubtedly a bright object in the sky of Venus, the
+explanation is evidently quite inadequate. (2) Phosphorescence of the
+planet's atmosphere. This has been suggested by some observers. (3)
+Visibility by contrast, a theory advanced by the great French astronomer
+Arago. (4) Illumination of the planet's surface by an aurora borealis.
+This also seems rather inadequate, but would account for the light being
+sometimes visible and sometimes not. (5) Luminosity of the oceans--if
+there be any--on Venus. But this also seems inadequate. (6) A planetary
+surface glowing with intense heat. But this seems improbable. (7) The
+Kunstliche Feuer (artificial fire) of Gruithuisen, a very fanciful theory.
+Flammarion thinks that the visibility of the dark side may perhaps be
+explained by its projection on a somewhat lighter background, such as the
+zodiacal light, or an extended solar envelope.[46]
+
+It will be seen that none of these explanations are entirely satisfactory,
+and the phenomenon, if real, remains a sort of astronomical enigma. The
+fact that the "light" is visible on some occasions and not on others would
+render some of the explanations improbable or even inadmissible. But the
+condition of the earth's atmosphere at times might account for its
+invisibility on many occasions.
+
+A curious suggestion was made by Zoellner, namely, that if the secondary
+light of Venus could be observed with the spectroscope it would show
+bright lines! But such an observation would be one of extreme difficulty.
+
+M. Hansky finds that the visibility of the "light" is greater during
+periods of maximum solar activity--that is, at the maxima of sun spots.
+This he explains by the theory of Arrhenius, in which electrified "ions
+emitted by the sun cause the phenomena of terrestrial magnetic storms and
+auroras." "In the same way the dense atmosphere of Venus is rendered more
+phosphorescent, and therefore more easily visible by the increased solar
+activity."[47] This seems a very plausible hypothesis.
+
+On the whole the occasional illumination of the night side of Venus by a
+very brilliant aurora (explanation (4) above) seems to the present writer
+to be the most probable explanation. Gruithuisen's hypothesis (7) seems
+utterly improbable.
+
+There is a curious apparent anomaly about the motion of Venus in the sky.
+Although the planet's period of revolution round the sun is 224.7 days, it
+remains on the same side of the sun, as seen from the earth, for 290 days.
+The reason of this is that the earth is going at the same time round the
+sun in the same direction, though at a slower pace; and Venus must
+continue to appear on the same side of the sun until the excess of her
+daily motion above that of the earth amounts to 179 deg., and this at the
+daily rate of 37' will be about 290 days.
+
+Several observations have been recorded of a supposed satellite of Venus.
+But the existence of such a body has never been verified. In the year
+1887, M. Stroobant investigated the various accounts, and came to the
+conclusion that in several at least of the recorded observations the
+object seen was certainly a star. Thus, in the observation made by
+Roedickoer and Boserup on August 4, 1761, a satellite and star are
+recorded as having been seen near the planet. M. Stroobant finds that the
+supposed "satellite" was the star [Greek: ch]_{4} Orionis, and the "star"
+[Greek: ch]_{3} Orionis. A supposed observation of a satellite made by
+Horrebow on January 3, 1768, was undoubtedly [Greek: th] Librae. M.
+Stroobant found that the supposed motion of the "satellite" as seen by
+Horrebow is accurately represented by the motion of Venus itself during
+the time of observation. In most of the other supposed observations of a
+satellite a satisfactory identification has also been found. M. Stroobant
+finds that with a telescope of 6 inches aperture, a star of the 8th or
+even the 9th magnitude can be well seen when close to Venus.[49]
+
+On the night of August 13, 1892, Professor Barnard, while examining Venus
+with the great 36-inch telescope of the Lick Observatory, saw a star of
+the 7th magnitude in the same field with the planet. He carefully
+determined the exact position of this star, and found that it is not in
+Argelander's great catalogue, the _Durchmusterung_. Prof. Barnard finds
+that owing to elongation of Venus from the sun at the time of observation
+the star could not possibly be an intra-Mercurial planet (that is, a
+planet revolving round the sun inside the orbit of Mercury); but that
+possibly it might be a planet revolving between the orbits of Venus and
+Mercury. As the brightest of the minor planets--Ceres, Pallas, Juno, and
+Vesta--were not at the time near the position of the observed object, the
+observation remains unexplained. It might possibly have been a _nova_, or
+temporary star.[50]
+
+Scheuten is said to have seen a supposed satellite of Venus following the
+planet across the sun at the end of the transit of June 6, 1761.[51]
+
+Humboldt speaks of the supposed satellite of Venus as among "the
+astronomical myths of an uncritical age."[52]
+
+An occultation of Venus by the moon is mentioned in the Chinese Annals as
+having occurred on March 19, 361 A.D., and Tycho Brahe observed another on
+May 23, 1587.[53]
+
+A close conjunction of Venus and Regulus ([Greek: a] Leonis) is recorded
+by the Arabian astronomer, Ibn Yunis, as having occurred on September 9,
+885 A.D. Calculations by Hind show that the planet and star were within 2'
+of arc on that night, and consequently would have appeared as a single
+star to the naked eye. The telescope had not then been invented.[54]
+
+Seen from Venus, the maximum apparent distance between the earth and moon
+would vary from about 5' to 31'.[55]
+
+It is related by Arago that Buonaparte, when going to the Luxembourg in
+Paris, where the Directory were giving a fete in his honour, was very
+much surprised to find the crowd assembled in the Rue de Touracour "pay
+more attention to a region of the heavens situated above the palace than
+to his person or the brilliant staff that accompanied him. He inquired the
+cause and learned that these curious persons were observing with
+astonishment, although it was noon, a star, which they supposed to be that
+of the conqueror of Italy--an allusion to which the illustrious general
+did not seem indifferent, when he himself, with his piercing eyes,
+remarked the radiant body." The "star" in question was Venus.[56]
+
+
+
+
+CHAPTER IV
+
+The Earth
+
+
+The earth being our place of abode is, of course, to us the most important
+planet in the solar system. It is a curious paradox that the moon's
+surface (at least the visible portion) is better known to us than the
+surface of the earth. Every spot on the moon's visible surface equal in
+size to say Liverpool or Glasgow is well known to lunar observers, whereas
+there are thousands of square miles on the earth's surface--for example,
+near the poles and in the centre of Australia--which are wholly unknown to
+the earth's inhabitants; and are perhaps likely to remain so.
+
+Many attempts have been made by "paradoxers" to show that the earth is a
+flat plane and not a sphere. But M. Ricco has found by actual experiment
+that the reflected image of the setting sun from a smooth sea is an
+elongated ellipse. This proves mathematically beyond all doubt that the
+surface of the sea is spherical; for the reflection from a plane surface
+would be necessarily _circular_. The theory of a "flat earth" is
+therefore proved to be quite untenable, and all the arguments (?) of the
+"earth flatteners" have now been--like the French Revolution--"blown into
+space."
+
+The pole of minimum temperature in the northern hemisphere, or "the pole
+of cold," as it has been termed, is supposed to lie near Werchojansk in
+Siberia, where a temperature of nearly -70 deg. has been observed.
+
+From a series of observations made at Annapolis (U.S.A.) on the gradual
+disappearance of the blue of the sky after sunset, Dr. See finds that the
+extreme height of the earth's atmosphere is about 130 miles. Prof. Newcomb
+finds that meteors first appear at a mean height of about 74 miles.[57]
+
+An aurora seen in Canada on July 15, 1893, was observed from stations 110
+miles apart, and from these observations the aurora was found to lie at a
+height of 166 miles above the earth's surface. It was computed that if the
+auroral "arch maintained an equal height above the earth its ends were
+1150 miles away, so that the magnificent sight was presented of an auroral
+belt in the sky with 2300 miles between its two extremities."[58]
+
+"Luminous clouds" are bright clouds sometimes seen at night near the end
+of June and beginning of July. They appear above the northern horizon
+over the sun's place about midnight, and evidently lie at a great height
+above the earth's surface. Observations made in Germany by Dr. Jesse, and
+in England by Mr. Backhouse, in the years 1885-91, show that the height of
+these clouds is nearly constant at about 51 miles.[59] The present writer
+has seen these remarkable clouds on one or two occasions in County Sligo,
+Ireland, during the period above mentioned.
+
+M. Montigny has shown that "the approach of violent cyclones or other
+storms is heralded by an increase of scintillation" (or twinkling of the
+stars). The effect is also very evident when such storms pass at a
+considerable distance. He has also made some interesting observations
+(especially on the star Capella), which show that, not only does
+scintillation increase in rainy weather, but that "it is very evident, at
+such times, in stars situated at an altitude at which on other occasions
+it would not be perceptible at all; thus confirming the remark of
+Humboldt's with regard to the advent of the wet season in tropical
+countries."[60]
+
+In a paper on the subject of "Optical Illusions" in _Popular Astronomy_,
+February, 1906, Mr. Arthur K. Bartlett, of Batter Creek, Michigan
+(U.S.A.), makes the following interesting remarks:--
+
+    "The lunar halo which by many persons is regarded as a remarkable and
+    unexplained luminosity associated with the moon, is to meteorological
+    students neither a mysterious nor an anomalous occurrence. It has been
+    frequently observed and for many years thoroughly understood, and at
+    the present time admits of an easy scientific explanation. It is an
+    atmospheric exhibition due to the refraction and dispersion of the
+    moon's light through very minute ice crystals floating at great
+    elevations above the earth, and it is explained by the science of
+    meteorology, to which it properly belongs; for it is not of cosmical
+    origin, and in no way pertains to astronomy, as most persons suppose,
+    except as it depends on the moon, whose light passing through the
+    atmosphere, produces the luminous halo, which as will be seen, is
+    simply an optical illusion, originating, not in the vicinity of the
+    moon--two hundred and forty thousand miles away--but just above the
+    earth's surface, and within the aqueous envelope that surrounds it on
+    all sides.... A halo may form round the sun as well as the moon ...
+    but a halo is more frequently noticed round the moon for the reason
+    that we are too much dazzled by the sun's light to distinguish faint
+    colours surrounding its disc, and to see them it is necessary to look
+    through smoked glass, or view the sun by reflection from the surface
+    of still water, by which its brilliancy is very much reduced."...
+
+"A 'corona' is an appearance of faintly coloured rings often seen around
+the sun and moon when a light fleecy cloud passes over them, and should
+not be mistaken for a halo, which is much larger and more complicated in
+its structure. These two phenomena are frequently confounded by
+inexperienced observers." With these remarks the present writer fully
+concurs.
+
+Mr. Bartlett adds--
+
+    "As a halo is never seen except when the sky is hazy, it indicates
+    that moisture is accumulating in the atmosphere which will form
+    clouds, and usually result in a storm. But the popular notion that the
+    number of bright stars visible within the circle indicates the number
+    of days before the storm will occur, is without any foundation
+    whatever, and the belief is almost too absurd to be refuted. In
+    whatever part of the sky a lunar halo is seen, one or more bright
+    stars are always sure to be noticed inside the luminous ring, and the
+    number visible depends entirely upon the position of the moon.
+    Moreover, when the sky within the circle is examined with even a small
+    telescope, hundreds of stars are visible where only one, or perhaps
+    two or three, are perceived with the naked eye."
+
+It is possible to have five Sundays in February (the year must of course
+be a "leap year"). This occurred in the year 1880, Sunday falling on
+February 1, 8, 15, 22, and 29. But this will not happen again till the
+year 1920. No century year (such as 1900, 2000, etc.) could possibly have
+five Sundays in February, and the Rev. Richard Campbell, who investigated
+this matter, finds the following sequence of years in which five Sundays
+occur in February: 1604, 1632, 1660, 1688, 1728, 1756, 1784, 1824, 1852,
+1880, 1920, 1948, 1976.[61]
+
+In an article on "The Last Day and Year of the Century: Remarks on Time
+Reckoning," in _Nature_, September 10, 1896, Mr. W. T. Lynn, the eminent
+astronomer, says, "The late Astronomer Royal, Sir George Airy, once
+received a letter requesting him to settle a dispute which had arisen in
+some local debating society, as to which would be the first day of the
+next century. His reply was, 'A very little consideration will suffice to
+show that the first day of the twentieth century will be January 1, 1901.'
+Simple as the matter seems, the fact that it is occasionally brought into
+question shows that there is some little difficulty connected with it.
+Probably, however, this is in a great measure due to the circumstance that
+the actual figures are changed on January 1, 1900, the day preceding being
+December 31, 1899. A century is a very definite word for an interval
+respecting which there is no possible room for mistake or difference of
+opinion. But the date of its ending depends upon that of its beginning.
+Our double system of backward and forward reckoning leads to a good deal
+of inconvenience. Our reckoning supposes (what we know was not the case,
+but as an era the date does equally well) that Christ was born at the end
+of B.C. 1. At the end of A.D. 1, therefore, one year had elapsed from the
+event, at the end of A.D. 100, one century, and at the end of 1900,
+nineteen centuries.... It is clear, then, that the year, as we call it, is
+an ordinal number, and that 1900 years from the birth of Christ (reckoning
+as we do from B.C. 1) will not be completed until the end of December 31
+in that year, the twentieth century beginning with January 1, 1901, that
+is (to be exact) at the previous midnight, when the day commences by civil
+reckoning." With these remarks of Mr. Lynn I fully concur, and, so far as
+I know, all astronomers agree with him. As the discussion will probably
+again arise at the end of the twentieth century, I would like to put on
+record here what the scientific opinion was at the close of the nineteenth
+century.
+
+Prof. E. Rutherford, the well-known authority on radium, suggests that
+possibly radium is a source of heat from within the earth. Traces of
+radium have been detected in many rocks and soils, and even in sea water.
+Calculation shows that the total amount distributed through the earth's
+crust is enormously large, although relatively small "compared with the
+annual output of coal for the world." The amount of radium necessary to
+compensate for the present loss of heat from the earth "corresponds to
+only five parts in one hundred million millions per unit mass," and the
+"observations of Elster and Gertel show that the radio-activity observed
+in soils corresponds to the presence of about this proportion of
+radium."[62]
+
+The earth has 12 different motions. These are as follows:--
+
+1. Rotation on its axis, having a period of 24 hours.
+
+2. Revolution round the sun; period 365-1/4 days.
+
+3. Precession; period of about 25,765 years.
+
+4. Semi-lunar gravitation; period 28 days.
+
+5. Nutation; period 18-1/2 years.
+
+6. Variation in obliquity of the ecliptic; about 47" in 100 years.
+
+7. Variation of eccentricity of orbit.
+
+8. Change of line of apsides; period about 21,000 years.
+
+9. Planetary perturbations.
+
+10. Change of centre of gravity of whole solar system.
+
+11. General motion of solar system in space.
+
+12. Variation of latitude with several degrees of periodicity.[63]
+
+    "An amusing story has been told which affords a good illustration of
+    the ignorance and popular notions regarding the tides prevailing even
+    among persons of average intelligence. 'Tell me,' said a man to an
+    eminent living English astronomer not long ago, 'is it still
+    considered probable that the tides are caused by the moon?' The man of
+    science replied that to the best of his belief it was, and then asked
+    in turn whether the inquirer had any serious reason for questioning
+    the relationship. 'Well, I don't know,' was the answer; 'sometimes
+    when there is no moon there seems to be a tide all the same.'"![64]
+
+With reference to the force of gravitation, on the earth and other bodies
+in the universe, Mr. William B. Taylor has well said, "With each revolving
+year new demonstrations of its absolute precision and of its universal
+domination serves only to fill the mind with added wonder and with added
+confidence in the stability and the supremacy of the power in which has
+been found no variableness neither shadow of turning, but which--the same
+yesterday, to-day and for ever--
+
+  "Lives through all life, extends through all extent,
+  Spreads undivided, operates unspent."[65]
+
+With reference to the habitability of other planets, Tennyson has
+beautifully said--
+
+  "Venus near her! smiling downwards at this earthlier earth of ours,
+  Closer on the sun, perhaps a world of never fading flowers.
+  Hesper, whom the poets call'd the Bringer home of all good things;
+  All good things may move in Hesper; perfect people, perfect kings.
+  Hesper--Venus--were we native to that splendour, or in Mars,
+  We should see the globe we groan in fairest of their evening stars.
+  Could we dream of war and carnage, craft and madness, lust and spite,
+  Roaring London, raving Paris, in that spot of peaceful light?
+  Might we not in glancing heavenward on a star so silver fair,
+  Yearn and clasp the hands, and murmur, 'Would to God that we were
+      there!'"
+
+The ancient Greek writer, Diogenes Laertius, states that Anaximander
+(610-547 B.C.) believed that the earth was a sphere. The Greek words are:
+[Greek: misen te ten gen keisthai, kentry taxin epechousan ousan
+sphairoeide].[66]
+
+With reference to the Aurora Borealis, the exact nature of which is not
+accurately known, "a good story used to be told some years ago of a
+candidate who, undergoing the torture of a _viva voce_ examination, was
+unable to reply satisfactorily to any of the questions asked. 'Come, sir,'
+said the examiner, with the air of a man asking the simplest question,
+'explain to me the cause of the aurora borealis.' 'Sir,' said the unhappy
+aspirant for physical honours, 'I could have explained it perfectly
+yesterday, but nervousness has, I think, made me lose my memory.' 'This is
+very unfortunate,' said the examiner; 'you are the only man who could have
+explained this mystery, and you have forgotten it.'"[67] This was written
+in the year 1899, and probably the phenomenon of the aurora remains
+nearly as great a mystery to-day. In 1839, MM. Bravais and Lottin made
+observations on the aurora in Norway in about N. latitude 70 deg.. Bravais
+found the height to be between 62 and 93 miles above the earth's surface.
+
+The cause of the so-called Glacial Epoch in the earth's history has been
+much discussed. The Russian physicist, Rogovsky, has advanced the
+following theory--
+
+    "If we suppose that the temperature of the sun at the present time is
+    still increasing, or at least has been increasing until now, the
+    glacial epoch can be easily accounted for. Formerly the earth had a
+    high temperature of its own, but received a lesser quantity of heat
+    from the sun than now; on cooling gradually, the earth's surface
+    attained such a temperature as caused a great part of the surface of
+    the northern and southern hemispheres to be covered with ice; but the
+    sun's radiation increasing, the glaciers melted, and the climatic
+    conditions became as they are now. In a word, the temperature of the
+    earth's surface is a function of two quantities: one decreasing (the
+    earth's own heat), and the other increasing (the sun's radiation), and
+    consequently there may be a minimum, and this minimum was the glacial
+    epoch, which, as shown by recent investigations, those of Luigi de
+    Marchi (Report of _G. Schiaparelli, Meteorolog. Zeitschr._, 30,
+    130-136, 1895), are not local, but general for the whole earth" (see
+    also M. Neumahr, _Erdegeschicht_).[68]
+
+Prof. Percival Lowell thinks that the life of geological palaeozoic times
+was supported by the earth's internal heat, which maintained the ocean at
+a comparatively warm temperature.[69]
+
+The following passage in the Book of the Maccabees may possibly refer to
+an aurora--
+
+    "Now about this time Antiochus made his second inroad into Egypt. And
+    it _so_ befell that throughout all the city, for the space of almost
+    forty days, there appeared in the midst of the sky horsemen in swift
+    motion, wearing robes inwrought with gold and _carrying_ spears,
+    equipped in troops for battle; and drawing of swords; and _on the
+    other side_ squadrons of horse in array; and encounters and pursuits
+    of both armies; and shaking of shields, and multitudes of lances, and
+    casting of darts, and flashing of golden trappings, and girding on of
+    all sorts of armour. Wherefore all men besought that the vision might
+    have been given for food."[70]
+
+According to Laplace "the decrease of the mean heat of the earth during a
+period of 2000 years has not, taking the extremist limits, diminished as
+much as 1/300th of a degree Fahrenheit."[71]
+
+From his researches on the cause of the Precession of the Equinoxes,
+Laplace concluded that "the motion of the earth's axis is the same as if
+the whole sea formed a solid mass adhering to its surface."[72]
+
+Laplace found that the major (or longer) axis of the earth's orbit
+coincided with the line of Equinoxes in the year 4107 B.C. The earth's
+perigee then coincided with the autumnal equinox. The epoch at which the
+major axis was perpendicular to the line of equinoxes fell in the year
+1250 A.D.[73]
+
+Leverrier has found the minimum eccentricity of the earth's orbit round
+the sun to be 0.0047; so that the orbit will never become absolutely
+circular, as some have imagined.
+
+Laplace says--
+
+    "Astronomy considered in its entirety is the finest monument of the
+    human mind, the noblest essay of its intelligence. Seduced by the
+    illusions of the senses and of self-pride, for a long time man
+    considered himself as the centre of the movement of the stars; his
+    vain-glory has been punished by the terrors which his own ideas have
+    inspired. At last the efforts of several centuries brushed aside the
+    veil which concealed the system of the world. We discover ourselves
+    upon a planet, itself almost imperceptible in the vast extent of the
+    solar system, which in its turn is only an insensible point in the
+    immensity of space. The sublime results to which this discovery has
+    led should suffice to console us for our extreme littleness, and the
+    rank which it assigns to the earth. Let us treasure with solicitude,
+    let us add to as we may, this store of higher knowledge, the most
+    exquisite treasure of thinking beings."[74]
+
+With reference to probable future changes in climate, the great physicist,
+Arrhenius, says--
+
+    "We often hear lamentation that the coal stored up in the earth is
+    wasted by the present generation without any thought of the future,
+    and we are terrified by the awful destruction of life and property
+    which has followed the volcanic eruptions of our days. We may find a
+    kind of consolation in the consideration that here, as in every other
+    case, there is good mixed with evil. By the influence of the
+    increasing percentage of carbonic acid in the atmosphere, we may hope
+    to enjoy ages with more equable and better climates, especially as
+    regards the colder regions of the earth, ages when the earth will
+    bring forth much more abundant crops than at present, for the benefit
+    of rapidly propagating mankind."[75]
+
+The night of July 1, 1908, was unusually bright. This was noticed in
+various parts of England and Ireland, and by the present writer in Dublin.
+Humboldt states that "at the time of the new moon at midnight in 1743, the
+phosphorescence was so intense that objects could be distinctly recognized
+at a distance of more than 600 feet."[76]
+
+An interesting proof of the earth's rotation on its axis has recently been
+found.
+
+    "In a paper in the _Proceedings_ of the Vienna Academy (June, 1908) by
+    Herr Tumlirz, it is shown mathematically that if a liquid is flowing
+    outwards between two horizontal discs, the lines of flow will be
+    strictly straight only if the discs and vessel be at rest, and will
+    assume certain curves if that vessel and the discs are in rotation,
+    as, for example, due to the earth's rotation. An experimental
+    arrangement was set up with all precautions, and the stream lines were
+    marked with coloured liquids and photographed. These were in general
+    accord with the predictions of theory and the supposition that the
+    earth is rotating about an axis."[77]
+
+In a book published in 1905 entitled _The Rational Almanac_, by Moses B.
+Cotsworth, of York, the author states that (p. 397), "The explanation is
+apparent from the Great Pyramid's Slope, which conclusively proves that
+when it was built the latitude of that region was 7 deg..1 more than at
+present. Egyptian Memphis now near Cairo was then in latitude 37 deg..1, where
+Asia Minor now ranges, whilst Syria would then be where the Caucasus
+regions now experience those rigorous winters formerly experienced in
+Syria." But the reality of this comparatively great change of latitude in
+the position of the Great Pyramid can be easily disproved. Pytheas of
+Marseilles--who lived in the time of Alexander the Great, about 330
+B.C.--measured the latitude of Marseilles by means of a gnomon, and found
+it to be about 42 deg. 56'-1/2. As the present latitude of Marseilles is 43 deg.
+17' 50", no great change in the latitude could have taken place in over
+2000 years.[78] From this we may conclude that the latitude of the Great
+Pyramid has _not_ changed by 7 deg..1 since its construction. There is, it is
+true, a slow diminution going on in the obliquity of the ecliptic (or
+inclination of the earth's axis), but modern observations show that this
+would not amount to as much as one degree in 6000 years. Eudemus of
+Rhodes--a disciple of Aristotle (who died in 322 B.C.)--found the
+obliquity of the ecliptic to be 24 deg., which differs but little from its
+present value, 23 deg. 27'. Al-Sufi in the tenth century measured the latitude
+of Schiraz in Persia, and found it 29 deg. 36'. Its present latitude is 29 deg.
+36' 30",[79] so that evidently there has been no change in the latitude in
+900 years.
+
+
+
+
+CHAPTER V
+
+The Moon
+
+
+The total area of the moon's surface is about equal to that of North and
+South America. The actual surface visible at any one time is about equal
+to North America.
+
+The famous lunar observer, Schroeter, thought that the moon had an
+atmosphere, but estimated its height at only a little over a mile. Its
+density he supposed to be less than that of the vacuum in an air-pump.
+Recent investigations, however, seem to show that owing to its small mass
+and attractive force the moon could not retain an atmosphere like that of
+the earth.
+
+Prof. N. S. Shaler, of Harvard (U.S.A.), finds from a study of the moon
+(from a geological point of view) with the 15-inch refractor of the
+Harvard Observatory, that our satellite has no atmosphere nor any form of
+organic life, and he believes that its surface "was brought to its present
+condition before the earth had even a solid crust."[80]
+
+There is a curious illusion with reference to the moon's apparent
+diameter referred to by Proctor.[81] If, when the moon is absent in the
+winter months, we ask a person whether the moon's diameter is greater or
+less than the distance between the stars [Greek: d] and [Greek: e], and
+[Greek: e] and [Greek: z] Orionis, the three well-known stars in the "belt
+of Orion," the answer will probably be that the moon's apparent diameter
+is about equal to each of these distances. But in reality the apparent
+distance between [Greek: d] and [Greek: e] Orionis (or between [Greek: e]
+and [Greek: z], which is about the same) is more than double the moon's
+apparent diameter. This seems at first sight a startling statement; but
+its truth is, of course, beyond all doubt and is not open to argument.
+Proctor points out that if a person estimates the moon as a foot in
+diameter, as its apparent diameter is about half a degree, this would
+imply that the observer estimates the circumference of the star sphere as
+about 720 feet (360 deg. x 2), and hence the radius (or the moon's distance
+from the earth) about 115 feet. But in reality all such estimates have no
+scientific (that is, accurate) meaning. Some of the ancients, such as
+Aristotle, Cicero, and Heraclitus, seem to have estimated the moon's
+apparent diameter at about a foot.[82] This shows that even great minds
+may make serious mistakes.
+
+It has been stated by some writer that the moon as seen with the highest
+powers of the great Yerkes telescope (40 inches aperture) appears "just
+as it would be seen with the naked eye if it were suspended 60 miles over
+our heads." But this statement is quite erroneous. The moon as seen with
+the naked eye or with a telescope shows us nearly a whole hemisphere of
+its surface. But if the eye were placed only 60 miles from the moon's
+surface, we should see only a small portion of its surface. In fact, it is
+a curious paradox that the nearer the eye is to a sphere the less we see
+of its surface! The truth of this will be evident from the fact that on a
+level plain an eye placed at a height, say 5 feet, sees a very small
+portion indeed of the earth's surface, and the higher we ascend the more
+of the surface we see. I find that at a distance of 60 miles from the
+moon's surface we should only see a small portion of its visible
+hemisphere (about 1/90th). The lunar features would also appear under a
+different aspect. The view would be more of a landscape than that seen in
+any telescope. This view of the matter is not new. It has been previously
+pointed out, especially by M. Flammarion and Mr. Whitmell, but its truth
+is not, I think, generally recognized. Prof. Newcomb doubts whether with
+any telescope the moon has ever been seen so well as it would be if
+brought within 500 miles of the earth.
+
+A relief map of the moon 19 feet in diameter was added, in 1898, to the
+Field Columbian Museum (U.S.A.). It was prepared with great care from the
+lunar charts of Beer and Maedler, and Dr. Schmidt of the Athens
+Observatory, and it shows the lunar features very accurately. Its
+construction took five years.
+
+On a photograph of a part of the moon's surface near the crater
+Eratosthenes, Prof. William H. Pickering finds markings which very much
+resemble the so-called "canals" of Mars. The photograph was taken in
+Jamaica, and a copy of it is given in Prof. Pickering's book on the Moon,
+and in _Popular Astronomy_, February, 1904.
+
+Experiments made in America by Messrs. Stebbins and F. C. Brown, by means
+of selenium cells, show that the light of the full moon is about nine
+times that of the half moon;[83] and that "the moon is brighter between
+the first quarter and full than in the corresponding phase after full
+moon." They also find that the light of the full moon is equal to "0.23
+candle power,"[83] that is, according to the method of measurement used in
+America, its light is equal to 0.23 of a standard candle placed at a
+distance of one metre (39.37 inches) from the eye.[84]
+
+Mr. H. H. Kimball finds that no less than 52 per cent. of the observed
+changes in intensity of the "earth-shine" visible on the moon when at or
+near the crescent phase is due to the eccentricity of the lunar orbit,
+and "this is probably much greater than could be expected from any
+increase or diminution in the average cloudiness over the hemisphere of
+the earth reflecting light to the moon."[85]
+
+The "moon maiden" is a term applied to a fancied resemblance of a portion
+of the Sinus Iridum to a female head. It forms the "promontory" known as
+Cape Heraclides, and may be looked for when the moon's "age" is about 11
+days. Mr. C. J. Caswell, who observed it on September 29, 1895, describes
+it as resembling "a beautiful silver statuette of a graceful female figure
+with flowing hair."
+
+M. Landerer finds that the angle of polarization of the moon's
+surface--about 33 deg.--agrees well with the polarizing angle for many
+specimens of igneous rocks (30 deg. 51' to 33 deg. 46'). The polarizing angle for
+ice is more than 37 deg., and this fact is opposed to the theories of lunar
+glaciation advanced by some observers.[86]
+
+Kepler states in his _Somnium_ that he saw the moon in the crescent phase
+on the morning and evening of the _same_ day (that is, before and after
+conjunction with the sun). Kepler could see 14 stars in the Pleiades with
+the naked eye, so his eyesight must have been exceptionally keen.
+
+Investigations on ancient eclipses of the moon show that the eclipse
+mentioned by Josephus as having occurred before the death of Herod is
+probably that which took place on September 15, B.C. 5. This occurred
+about 9.45 p.m.; and probably about six months before the death of Herod
+(St. Matthew ii. 15).
+
+The total lunar eclipse which occurred on October 4, 1884, was remarkable
+for the almost total disappearance of the moon during totality. One
+observer says that "in the open air, if one had not known exactly where to
+look for it, one might have searched for some time without discovering it.
+I speak of course of the naked eye appearance."[87] On the other hand the
+same observer, speaking of the total eclipse of the moon on August 23,
+1877, which was a bright one, says--
+
+    "The moon even in the middle of the total phase was a conspicuous
+    object in the sky, and the ruddy colour was well marked. In the very
+    middle of the eclipse the degree of illumination was as nearly as
+    possible equal all round the edge of the moon, the central parts being
+    darker than those near the edge."
+
+In Roger de Hovedin's _Chronicle_ (A.D. 756) an account is given of the
+occultation of "a bright star," by the moon during a total eclipse. This
+is confirmed by Simeon of Durham, who also dates the eclipse A.D. 756.
+This is, however, a mistake, the eclipse having occurred on the evening of
+November 23, A.D. 755. Calvisius supposed that the occulted "star" might
+have been Aldebaran. Pingre, however, showed that this was impossible, and
+Struyck, in 1740, showed that the planet Jupiter was the "star" referred
+to by the early observer. Further calculations by Hind (1885) show
+conclusively that Struyck was quite correct, and that the phenomenon
+described in the old chronicles was the occultation of Jupiter by a
+totally eclipsed moon--a rather unique phenomenon.[88]
+
+An occultation of Mars by the moon is recorded by the Chinese, on February
+14, B.C. 69, and one of Venus, on March 30, A.D. 361. These have also been
+verified by Hind, and his calculations show the accuracy of these old
+Chinese records.
+
+It has been suggested that the moon may possibly have a satellite
+revolving round it, as the moon itself revolves round the earth. This
+would, of course, form an object of great interest. During the total lunar
+eclipses of March 10 and September 3, 1895, a careful photographic search
+was made by Prof. Barnard for a possible lunar satellite. The eclipse of
+March 10 was not very suitable for the purpose owing to a hazy sky, but
+that of September 3 was "entirely satisfactory," as the sky was very
+clear, and the duration of totality was very long. On the latter occasion
+"six splendid" photographs were obtained of the total phase with a 6-inch
+Willard lens. The result was that none of these photographs "show
+anything which might be taken for a lunar satellite," at least any
+satellite as bright as the 10th or 12th magnitude. It is, of course, just
+possible that the supposed satellite might have been behind the moon
+during the totality.
+
+With reference to the attraction between the earth and moon, Sir Oliver
+Lodge says--
+
+    "The force with which the moon is held in its orbit would be great
+    enough to tear asunder a steel rod 400 miles thick, with a tenacity of
+    30 tons to the square inch, so that if the moon and earth were
+    connected by steel instead of gravity, a forest of pillars would be
+    necessary to whirl the system once a month round their common centre
+    of gravity. Such a force necessarily implies enormous tensure or
+    pressure in the medium. Maxwell calculates that the gravitational
+    stress near the earth, which we must suppose to exist in the invisible
+    medium, is 3000 times greater than what the strongest steel can stand,
+    and near the sun it should be 2500 times as great as that."[89]
+
+With reference to the names given to "craters" on the moon, Prof. W. H.
+Pickering says,[90] "The system of nomenclature is, I think, unfortunate.
+The names of the chief craters are generally those of men who have done
+little or nothing for selenography, or even for astronomy, while the men
+who should be really commemorated are represented in general by small and
+unimportant craters," and again--
+
+    "A serious objection to the whole system of nomenclature lies in the
+    fact that it has apparently been used by some selenographers, from the
+    earliest times up to the present, as a means of satisfying their spite
+    against some of their contemporaries. Under the guise of pretending to
+    honour them by placing their names in perpetuity upon the moon, they
+    have used their names merely to designate the smallest objects that
+    their telescopes were capable of showing. An interesting illustration
+    of this point is found in the craters of Galileo and Riccioli, which
+    lie close together on the moon. It will be remembered that Galileo was
+    the discoverer of the craters on the moon. Both names were given by
+    Riccioli, and the relative size and importance of the craters
+    [Riccioli large, and Galileo very small] probably indicates to us the
+    relative importance that he assigned to the two men themselves. Other
+    examples might be quoted of craters named in the same spirit after men
+    still living.... With the exception of Maedler, one might almost say,
+    the more prominent the selenographer the more insignificant the
+    crater."
+
+The mathematical treatment of the lunar theory is a problem of great
+difficulty. The famous mathematician, Euler, described it as _incredibile
+stadium atque indefessus labor_.[91]
+
+With reference to the "earth-shine" on the moon when in the crescent
+phase, Humboldt says, "Lambert made the remarkable observation (14th of
+February, 1774) of a change of the ash-coloured moonlight into an
+olive-green colour, bordering upon yellow. The moon, which then stood
+vertically over the Atlantic Ocean, received upon its night side the green
+terrestrial light, which is reflected towards her when the sky is clear by
+the forest districts of South America."[92] Arago said, "Il n'est donc pas
+impossible, malgre tout ce qu'un pareil resultat exciterait de surprise au
+premier coup d'oeil qu'un jour les meteorologistes aillent puiser dans
+l'aspect de la Lune des notions precieuses sur _l'etat moyen_ de
+diaphanite de l'atmosphere terrestre, dans les hemispheres qui
+successivement concurrent a la production de la lumiere cendree."[93]
+
+The "earth-shine" on the new moon was successfully photographed in
+February, 1895, by Prof. Barnard at the Lick Observatory, with a 6-inch
+Willard portrait lens. He says--
+
+    "The earth-lit globe stands out beautifully round, encircled by the
+    slender crescent. All the 'seas' are conspicuously visible, as are
+    also the other prominent features, especially the region about
+    _Tycho_. _Aristarchus_ and _Copernicus_ appear as bright specks, and
+    the light streams from _Tycho_ are very distinct."[94]
+
+Kepler found that the moon completely disappeared during the total eclipse
+of December 9, 1601, and Hevelius observed the same phenomenon during the
+eclipse of April 25, 1642, when "not a vestige of the moon could be
+seen."[95] In the total lunar eclipse of June 10, 1816, the moon during
+totality was not visible in London, even with a telescope![95]
+
+The lunar mountains are _relatively_ much higher than those on the earth.
+Beer and Maedler found the following heights: Doerfel, 23,174 feet; Newton,
+22,141; Casatus, 21,102; Curtius, 20,632; Callippus, 18,946; and Tycho,
+18,748 feet.[96]
+
+Taking the earth's diameter at 7912 miles, the moon's diameter, 2163
+miles, and the height of Mount Everest as 29,000 feet, I find that
+
+      Everest          1            Doerfel        1
+  ---------------- = ----, and --------------- = ---
+  Earth's diameter   1440      moon's diameter   492
+
+From which it follows that the lunar mountains are _proportionately_ about
+three times higher than those on the earth.
+
+According to an hypothesis recently advanced by Dr. See, all the
+satellites of the solar system, including our moon, were "captured" by
+their primaries. He thinks, therefore, that the "moon came to earth from
+heavenly space."[97]
+
+
+
+
+CHAPTER VI
+
+Mars
+
+
+Mars was called by the ancients "the vanishing star," owing to the long
+periods during which it is practically invisible from the earth.[98] It
+was also called [Greek: puroeis] and Hercules.
+
+I have seen it stated in a book on the "Solar System" by a well-known
+astronomer that the _axis_ of Mars "is inclined to the plane of the orbit"
+at an angle of 24 deg. 50'! But this is quite erroneous. The angle given is
+the angle between _the plane of the planet's equator_ and the plane of its
+orbit, which is quite a different thing. This angle, which may be called
+the obliquity of Mars' ecliptic, does not differ much from that of the
+earth. Lowell finds it 23 deg. 13' from observations in 1907.[99]
+
+The late Mr. Proctor thought that Mars is "far the reddest star in the
+heavens; Aldebaran and Antares are pale beside him."[100] But this does
+not agree with my experience. Antares is to my eye quite as red as Mars.
+Its name is derived from two Greek words implying "redder than Mars." The
+colour of Aldebaran is, I think, quite comparable with that of the "ruddy
+planet." In the telescope the colour of Mars is, I believe, more yellow
+than red, but I have not seen the planet very often in a telescope. Sir
+John Herschel suggested that the reddish colour of Mars may possibly be
+due to red rocks, like those of the Old Red Sandstone, and the red soil
+often associated with such rocks, as I have myself noticed near Torquay
+and other places in Devonshire.
+
+The ruddy colour of Mars was formerly thought to be due to the great
+density of its atmosphere. But modern observations seem to show that the
+planet's atmosphere is, on the contrary, much rarer than that of the
+earth. The persistent visibility of the markings on its surface shows that
+its atmosphere cannot be cloud-laden like ours; and the spectroscope shows
+that the water vapour present is--although perceptible--less than that of
+our terrestrial envelope.
+
+The existence of water vapour is clearly shown by photographs of the
+planet's spectrum taken by Mr. Slipher at the Lowell Observatory in 1908.
+These show that the water vapour bands _a_ and near D are stronger in the
+spectrum of Mars than in that of the moon at the same altitude.[101]
+
+The dark markings on Mars were formerly supposed to represent water and
+the light parts land. But this idea has now been abandoned. Light
+reflected from a water surface is polarized at certain angles. Prof. W. H.
+Pickering, in his observations on Mars, finds no trace of polarization in
+the light reflected from the dark parts of the planet. But under the same
+conditions he finds that the bluish-black ring surrounding the white polar
+cap shows a well-marked polarization of light, thus indicating that this
+dark ring is probably water.[102]
+
+Projections on the limb of the planet have frequently been observed in
+America. These are known _not_ to be mountains, as they do not reappear
+under similar conditions. They are supposed to be clouds, and one seen in
+December, 1900, has been explained as a cloud lying at a height of some 13
+miles above the planet's surface and drifting at the rate of about 27
+miles an hour. If there are any mountains on Mars they have not yet been
+discovered.
+
+The existence of the so-called "canals" of Mars is supposed to be
+confirmed by Lowell's photographs of the planet. But what these "canals"
+really represent, that is the question. They have certainly an artificial
+look about them, and they form one of the most curious and interesting
+problems in the heavens. Prof. Lowell says--
+
+    "Most suggestive of all Martian phenomena are the canals. Were they
+    more generally observable the world would have been spared much
+    scepticism and more theory. They may of course not be artificial, but
+    observations here [Flagstaff] indicate that they are; as will, I
+    think, appear from the drawings. For it is one thing to see two or
+    three canals and quite another to have the planet's disc mapped with
+    them on a most elaborate system of triangulation. In the first place
+    they are this season (August, 1894) bluish-green, of the same colour
+    as the seas into which the longer ones all eventually debouch. In the
+    next place they are almost without exception geodetically straight,
+    supernaturally so, and this in spite of their leading in every
+    possible direction. Then they are of apparently nearly uniform width
+    throughout their length. What they are is another matter. Their mere
+    aspect, however, is enough to cause all theories about glaciation
+    fissures or surface cracks to die an instant and natural death."[103]
+
+Some of the observed colour-changes on Mars are very curious. In April,
+1905, Mr. Lowell observed that the marking known as Mare Erythraeum, just
+above Syrtis, had "changed from a blue-green to a chocolate-brown colour."
+The season on Mars corresponded with our February.
+
+Signor V. Cerulli says that, having observed Mars regularly for ten years,
+he has come to the conclusion that the actual existence of the "canals" is
+as much a subject for physiological as for astronomical investigation. He
+states that "the phenomena observed are so near the limit of the range of
+the human eye that in observing them one really experiences an effect
+accompanying the 'birth of vision.' That is to say, the eye sees more and
+more as it becomes accustomed, or strained, to the delicate markings, and
+thus the joining up of spots to form 'canals' and the gemination of the
+latter follow as a physiological effect, and need not necessarily be
+subjective phenomena seen by the unaccustomed eye."[104]
+
+The possibility of life on Mars has been recently much discussed; some
+denying, others asserting. M. E. Rogovsky says--
+
+    "As free oxygen and carbonic dioxide may exist in the atmosphere of
+    _Mars_, vegetable and animal life is quite possible. If the
+    temperature which prevails upon _Mars_ is nearer to -36 deg. C. than to
+    -73 deg. C., the existence of living beings like ourselves is possible. In
+    fact, the ice of some Greenland and Alpine glaciers is covered by red
+    algae (_Sphaerella nivalis_); we find there also different species of
+    rotaloria, variegated spiders, and other animals on the snow fields
+    illuminated by the sun; at the edges of glacier snows in the Tyrol we
+    see violet bells of _Soldanella pusilla_, the stalks of which make
+    their way through the snow by producing heat which melts it round
+    about them. Finally the Siberian town Verkhociansk, near Yakutsk,
+    exists, though the temperature there falls to -69 deg..8 C. and the mean
+    temperature of January to -51 deg..2, and the mean pressure of the vapour
+    of water is less than 0.05mm. It is possible, therefore, that living
+    beings have become adapted to the conditions now prevailing upon
+    _Mars_ after the lapse of many ages, and live at an even lower
+    temperature than upon the earth, developing the necessary heat
+    themselves."
+
+M. Rogovsky adds, "Water in organisms is mainly a liquid or solvent, and
+many other liquids may be the same. We have no reason to believe that life
+is possible only under the same conditions and with the same chemical
+composition of organisms as upon the earth, although indeed we cannot
+affirm that they actually exist on Mars."[105] With the above views the
+present writer fully concurs.
+
+Prof. Lowell thinks that the polar regions of Mars, both north and south,
+are actually warmer than the corresponding regions of the earth, although
+the mean temperature of the planet is probably twelve degrees lower than
+the earth's mean temperature.[106]
+
+A writer in _Astronomy and Astrophysics_ (1892, p. 748) says--
+
+    "Whether the planet Mars is inhabited or not seems to be the
+    all-absorbing question with the ordinary reader. With the astronomer
+    this query is almost the last thing about the planet that he would
+    think of when he has an opportunity to study its surface markings ...
+    no astronomer claims to know whether the planet is inhabited or not."
+
+Several suggestions have been made with reference to the possibility of
+signalling to Mars. But, as Mr. Larkin of Mount Lowe (U.S.A.) points out,
+all writers on this subject seem to forget the fact that the night side of
+two planets are never turned towards each other. "When the sun is between
+them it is day on the side of Mars which is towards us, and also day on
+the side of the earth which is towards Mars. When they are on the same
+side of the sun, it is day on Mars when night on the earth, and for this
+reason they could never see our signals. This should make it apparent that
+the task of signalling to Mars is a more difficult one than the most
+hopeful theorist has probably considered. All this is under the
+supposition that the Martians (if there are such) are beings like
+ourselves. If they are not like us, we cannot guess what they are
+like."[107] These views seem to me to be undoubtedly correct, and show the
+futility of visual signals. Electricity might, however, be conceivably
+used for the purpose; but even this seems highly improbable.
+
+Prof. Newcomb, in his work _Astronomy for Everybody_, says with reference
+to this question, "The reader will excuse me from saying nothing in this
+chapter about the possible inhabitants of Mars. He knows just as much
+about the subject as I do, and that is nothing at all."
+
+It is, however, quite possible that life _in some form_ may exist on Mars.
+As Lowell well says, "Life but waits in the wings of existence for its cue
+to enter the scene the moment the stage is set."[108] With reference to
+the "canals" he says--
+
+    "It is certainly no exaggeration to say that they are the most
+    astonishing objects to be viewed in the heavens. There are celestial
+    sights more dazzling, spectacles that inspire more awe, but to the
+    thoughtful observer who is privileged to see them well, there is
+    nothing in the sky so profoundly impressive as these canals of
+    Mars."[109]
+
+The eminent Swedish physicist Arrhenius thinks that the mean annual
+temperature on Mars may possibly be as high as 50 deg. F. He says, "Sometimes
+the snow-caps on the poles of Mars disappear entirely during the Mars
+summer; this never happens on our terrestrial poles. The mean temperature
+of Mars must therefore be above zero, probably about +10 deg. [Centigrade =
+50 deg. Fahrenheit]. Organic life may very probably thrive, therefore, on
+Mars."[110] He thinks that this excess of mean temperature above the
+calculated temperature may be due to an increased amount of carbonic acid
+in the planet's atmosphere, and says "any doubling of the percentage of
+carbon dioxide in the air would raise the temperature of the earth's
+surface by 4 deg.; and if the carbon dioxide were increased fourfold, the
+temperature would rise by 8 deg.."[111]
+
+Denning says,--[112]
+
+    "A few years ago, when christening celestial formations was more in
+    fashion than it is now, a man simply had to use a telescope for an
+    evening or two on Mars or the moon, and spice the relation of his
+    seeings with something in the way of novelty, when his name would be
+    pretty certainly attached to an object and hung in the heavens for all
+    time! A writer in the _Astronomical Register_ for January, 1879,
+    humorously suggested that 'the matter should be put into the hands of
+    an advertising agent,' and 'made the means of raising a revenue for
+    astronomical purposes.' Some men would not object to pay handsomely
+    for the distinction of having their names applied to the seas and
+    continents of Mars or the craters of the moon."
+
+An occultation of Mars by the moon is recorded by Aristotle as having
+occurred on April 4, 357 B.C.[113]
+
+Seen from Mars the maximum apparent distance between the earth and moon
+would vary from 3-1/2' to nearly 17'.[114]
+
+
+
+
+CHAPTER VII
+
+The Minor Planets
+
+
+Up to 1908 the number of minor planets (or asteroids) certainly known
+amounted to over 650.
+
+From an examination of the distribution of the first 512 of these small
+bodies, Dr. P. Stroobant finds that a decided maximum in number occurs
+between the limits of distance of 2.55 and 2.85 (earth's mean distance
+from sun = 1), "199 of the asteroids considered revolving in this
+annulus." He finds that nearly all the asteroidal matter is concentrated
+near to the middle of the ring in the neighbourhood of the mean distance
+of 2.7, and the smallest asteroids are relatively less numerous in the
+richest zones.[115]
+
+There are some "striking similarities" in the orbits of some of the
+asteroids. Thus, in the small planets Sophia (No. 251 in order of
+discovery) and Magdalena (No. 318) we have the mean distance of Sophia
+3.10, and that of Magdalena 3.19 (earth's mean distance = 1). The
+eccentricities of the orbits are 0.09 and 0.07; and the inclinations of
+the orbits to the plane of the ecliptic 10 deg. 29' and 10 deg. 33'
+respectively.[116] This similarity may be--and probably is--merely
+accidental, but it is none the less curious and interesting.
+
+Some very interesting discoveries have recently been made among the minor
+planets. The orbit of Eros intersects the orbit of Mars; and the following
+have nearly the same mean distance from the sun as Jupiter:--
+
+  Achilles (1906 TG), No. 588,
+  Patrocles (1906 XY), No. 617,
+  Hector (1907 XM), No. 624,
+
+and another (No. 659) has been recently found. Each of these small planets
+"moves approximately in a vertex of an equilateral triangle that it forms
+with Jupiter and the sun."[117] The minor planet known provisionally as HN
+is remarkable for the large eccentricity of its orbit (0.38), and its
+small perihelion distance (1.6). When discovered it had a very high South
+Declination (61-1/2 deg.), showing that the inclination of the plane of its
+orbit to the plane of the ecliptic is considerable.[118]
+
+Dr. Bauschinger has made a study of the minor planets discovered up to the
+end of 1900. He finds that the ascending nodes of the orbits show a
+marked tendency to cluster near the ascending node of Jupiter's orbit, a
+fact which agrees well with Prof. Newcomb's theoretical results. There
+seems to be a slight tendency for large inclinations and great
+eccentricities to go together; but there appears to be no connection
+between the eccentricity and the mean distance from the sun. The
+longitudes of the perihelia of these small planets "show a well-marked
+maximum near the longitude of _Jupiter's_ perihelion, and equally
+well-marked minimum near the longitude of his aphelion," which is again in
+good agreement with Newcomb's calculations.[119] Dr. Bauschinger's
+diameter for Eros is 20 miles. He finds that the whole group, including
+those remaining to be discovered, would probably form a sphere of about
+830 miles in diameter.
+
+The total mass of the minor planets has been frequently estimated, but
+generally much too high. Mr. B. M. Roszel of the John Hopkins University
+(U.S.A.) has made a calculation of the probable mass from the known
+diameter of Vesta (319 miles, Pickering), and finds the volume of the
+first 216 asteroids discovered. From this calculation it appears that it
+would take 310 asteroids of the 6th magnitude, or 1200 of the 7th to equal
+the moon in volume. Mr. Roszel concludes that the probable mass of the
+whole asteroidal belt is between 1/50th and 1/100th of that of the
+moon.[120] Subsequently Mr. Roszel extended his study to the mass of 311
+asteroids,[121] and found a combined mass of about 1/40th of the moon's
+mass.
+
+Dr. Palisa finds that the recently discovered minor planet (1905 QY)
+varies in light to a considerable extent.[122] This planet was discovered
+by Dr. Max Wolf on August 23, 1905; but it was subsequently found that it
+is identical with one previously known, (167) Urda.[123] The light
+variation is said to be from the 11th to the 13th magnitude.[124]
+Variation in some of the other minor planets has also been suspected.
+Prof. Wendell found a variation of about half a magnitude in the planet
+Eunomia (No. 15). He also found that Iris (No. 7) varies about a quarter
+of a magnitude in a period of about 6{h} 12{m}.[125] But these variations
+are small, and perhaps doubtful. The variability of Eros is well known.
+
+The planet Eros is a very interesting one. The perihelion portion of its
+orbit lies between the orbits of Mars and the earth, and the aphelion part
+is outside the orbit of Mars. Owing to the great variation in its distance
+from the earth the brightness of Eros varies from the 6th to the 12th
+magnitude. That is, when brightest, it is 250 times brighter than when it
+is faintest.[126] This variation of light, is of course, merely due to the
+variation of distance; but some actual variation in the brightness of the
+planet has been observed.
+
+It has been shown by Oeltzen and Valz that Cacciatore's supposed distant
+comet, mentioned by Admiral Smyth in his _Bedford Catalogue_, must have
+been a minor planet.[127]
+
+Dr. Max Wolf discovered 36 new minor planets by photography in the years
+1892-95. Up to the latter year he had never seen one of these through a
+telescope! His words are, "Ich selsbt habe noch nie einen meinen kleinen
+Planeten am Himmel gesehen."[128]
+
+These small bodies have now become so numerous that it is a matter of much
+difficulty to follow them. At the meeting of the Royal Astronomical
+Society on January 8, 1909, Mr. G. F. Chambers made the following
+facetious remarks--
+
+    "I would like to make a suggestion that has been in my mind for
+    several years past--that it should be made an offence punishable by
+    fine or imprisonment to discover any more minor planets. They seem to
+    be an intolerable nuisance, and are a great burden upon the literary
+    gentlemen who have to keep pace with them and record them. I have
+    never seen, during the last few years at any rate, any good come from
+    them, or likely to come, and I should like to see the supply stopped,
+    and the energies of the German gentlemen who find so many turned into
+    more promising channels."
+
+Among the minor planets numbered 1 to 500, about 40 "have not been seen
+since the year of their discovery, and must be regarded as lost."[129]
+
+
+
+
+CHAPTER VIII
+
+Jupiter
+
+
+This brilliant planet--only inferior to Venus in brightness--was often
+seen by Bond (Jun.) with the naked eye in "high and clear sunshine"; also
+by Denning, who has very keen eyesight. Its brightness on such occasions
+is so great, that--like Venus--it casts a distinct shadow in a dark
+room.[130]
+
+The great "red spot" on Jupiter seems to have been originally discovered
+by Robert Hooke on May 9, 1664, with a telescope of 2 inches aperture and
+12 feet focus. It seems to have existed ever since; at least the evidence
+is, according to Denning, in favour of the identity of Hooke's spot with
+the red spot visible in recent years. The spot was also observed by
+Cassini in the years 1665-72, and is sometimes called "Cassini's spot."
+But the real discoverer was Hooke.[131]
+
+The orbit of Jupiter is so far outside the earth's orbit that there can
+be little visible in the way of "phase"--as in the case of Mars, where the
+"gibbous" phase is sometimes very perceptible. Some books on astronomy
+state that Jupiter shows no phase. But this is incorrect. A distinct,
+although very slight, gibbous appearance is visible when the planet is
+near quadrature. Webb thought it more conspicuous in twilight than in a
+dark sky. With large telescopes, Jupiter's satellites II. and III. have
+been seen--in consequence of Jupiter's phase--to emerge from occultation
+"at a sensible distance from the limb."[132]
+
+According to M. E. Rogovsky, the high "albedo of Jupiter, the appearance
+of the clear (red) and dark spots on its surface and their continual
+variation, the different velocity of rotation of the equatorial and other
+zones of its surface, and particularly its small density (1.33, water as
+unity), all these facts afford irrefragable proofs of the high temperature
+of this planet. The dense and opaque atmosphere hides its glowing surface
+from our view, and we see therefore only the external surface of its
+clouds. The objective existence of this atmosphere is proved by the bands
+and lines of absorption in its spectrum. The interesting photograph
+obtained by Draper, September 27, 1879, in which the blue and green parts
+are more brilliant for the equatorial zone than for the adjacent parts of
+the surface, appears to show that _Jupiter_ emits its proper light. It is
+possible that the constant red spot noticed on its surface by several
+observers, as Gledhill, Lord Rosse, and Copeland (1873), Russel and
+Bredikhin (1876), is the summit of a high glowing mountain. G. W. Hough
+considers Jupiter to be gaseous, and A. Ritter inferred from his formulae
+that in this case the temperature at the centre would be 600,000 deg. C."[133]
+
+The four brighter satellites of Jupiter are usually known by numbers I.,
+II., III., and IV.; I. being the nearest to the planet, and IV. the
+farthest. III. is usually the brightest, and IV. the faintest, but
+exceptions to this rule have been noticed.
+
+With reference to the recently discovered sixth and seventh satellites of
+Jupiter, Prof. Perrine has suggested that the large inclination of their
+orbits to the plane of the planet's equator seems to indicate that neither
+of these bodies was originally a member of Jupiter's family, but has been
+"captured by the planet." This seems possible as the orbits of some of the
+minor planets lie near the orbit of Jupiter (see "Minor Planets"). A
+similar suggestion has been made by Prof. del Marmol.[134]
+
+Many curious observations have been recorded with reference to Jupiter's
+satellites; some very difficult of explanation. In 1711 Bianchini saw
+satellite IV. so faint for more than an hour that it was hardly visible! A
+similar observation was made by Lassell with a more powerful telescope on
+June 13, 1849. Key, T. T. Smyth, and Denning have also recorded unusual
+faintness.[135] A very remarkable phenomenon was seen by Admiral Smyth,
+Maclear, and Pearson on June 26, 1828. Satellite II., "having fairly
+entered on Jupiter, was found 12 or 13 minutes afterwards _outside the
+limb_, where it remained visible for at least 4 minutes, and then suddenly
+vanished." As Webb says, "Explanation is here set at defiance;
+demonstrably neither in the atmosphere of the earth, nor Jupiter, where
+and what could have been the cause? At present we can get no answer."[136]
+When Jupiter is in opposition to the sun--that is, on the meridian at
+midnight--satellite I. has been seen projected on its own shadow, the
+shadow appearing as a dark ring round the satellite.
+
+On January 28, 1848, at Cambridge (U.S.A.) satellite III. was seen in
+transit lying between the shadows of I. and II. and so black that it could
+not be distinguished from the shadows, "except by the place it occupied."
+This seems to suggest inherent light in the planet's surface, as the
+satellite was at the time illuminated by full sunshine; its apparent
+blackness being due to the effect of contrast. Cassini on one occasion
+failed to find the shadow of satellite I. when it should have been on the
+planet's disc,[137] an observation which again points to the glowing light
+of Jupiter's surface. Sadler and Trouvelot saw the shadow of satellite I.
+double! an observation difficult to explain--but the same phenomenon was
+again seen on the evening of September 19, 1891, by Mr. H. S. Halbert of
+Detroit, Michigan (U.S.A.). He says that the satellite "was in transit
+nearing egress, and it appeared as a white disc against the dark southern
+equatorial belt; following it was the usual shadow, and at an equal
+distance from this was a second shadow, smaller and not so dark as the
+true one, and surrounded by a faint penumbra."[138]
+
+A dark transit of satellite III. was again seen on the evening of December
+19, 1891, by two observers in America. One observer noted that the
+satellite, when on the disc of the planet, was intensely black. To the
+other observer (Willis L. Barnes) it appeared as an ill-defined _dark_
+image.[139] A similar observation was made on October 9 of the same year
+by Messrs. Gale and Innes.[140]
+
+A "black transit" of satellite IV. was seen by several observers in 1873,
+and by Prof. Barnard on May 4, 1886. The same phenomenon was observed on
+October 30, 1903, in America, by Miss Anne S. Young and Willis S. Barnes.
+Miss Young says--
+
+    "The ingress of the satellite took place at 8{h} 50{m} (E. standard
+    time) when it became invisible upon the background of the planet. An
+    hour later it was plainly visible as a dark round spot upon the
+    planet. It was decidedly darker than the equatorial belt."[141]
+
+The rather rare phenomenon of an occultation of one of Jupiter's
+satellites by another was observed by Mr. Apple, director of the Daniel
+Scholl Observatory, Franklin and Marshall College, Lancaster, Pa.
+(U.S.A.), on the evening of March 16, 1908. The satellites in question
+were I. and II., and they were so close that they could not be separated
+with the 11.5-inch telescope of the Observatory.[142] One of the present
+writer's first observations with a telescope is dated May 17, 1873, and is
+as follows: "Observed one of Jupiter's satellites occulted (or very nearly
+so) by another. Appeared as one with power 133" (on 3-inch refractor in
+the Punjab). These satellites were probably I. and II.
+
+Jupiter has been seen on several occasions apparently without his
+satellites; some being behind the disc, some eclipsed in his shadow, and
+some in transit across the disc. This phenomenon was seen by Galileo,
+March 15, 1611; by Molyneux, on November 12, 1681; by Sir William
+Herschel, May 23, 1802; by Wallis, April 15, 1826; by Greisbach, September
+27, 1843; and by several observers on four occasions in the years
+1867-1895.[143] The phenomenon again occurred on October 3, 1907, No. 1
+being eclipsed and occulted, No. 2 in transit, No. 3 eclipsed, and No. 4
+occulted.[144] It was not, however, visible in Europe, but could have been
+seen in Asia and Oceania.[144] The phenomenon will occur again on October
+22, 1913.[145]
+
+On the night of September 19, 1903, a star of magnitude 6-1/2 was occulted
+by the disc of Jupiter. This curious and rare phenomenon was photographed
+by M. Lucien Rudaux at the Observatory of Donville, France.[146] The star
+was Lalande 45698 (= BAC 8129).[147]
+
+Prof. Barnard, using telescopes with apertures from 5 inches up to 36
+inches (Lick), has failed to see a satellite through the planet's limb (an
+observation which has been claimed by other astronomers). He says, "To my
+mind this has been due to either poor seeing, a poor telescope, or an
+excited observer."[148] He adds--
+
+    "I think it is high time that the astronomers reject the idea that the
+    satellites of Jupiter can be seen through his limb at occultation.
+    When the seeing is bad there is a spurious limb to Jupiter that well
+    might give the appearance of transparency at the occultation of a
+    satellite. But under first-class conditions the limb of Jupiter is
+    perfectly opaque. It is quibbling and begging the question altogether
+    to say the phenomenon of transparency may be a rare one and so have
+    escaped my observations. Has any one said that the moon was
+    transparent when a star has been seen projected on it when it ought to
+    have been behind it?"
+
+Prof. Barnard and Mr. Douglass have seen white polar caps on the third and
+fourth satellites of Jupiter. The former says they are "exactly like those
+on Mars." "Both caps of the fourth satellite have been clearly
+distinguished, that at the north being sometimes exceptionally large,
+covering a surface equal to one-quarter or one-third of the diameter of
+the satellite."[149] This was confirmed on November 23, 1906, when Signor
+J. Comas Sola observed a brilliant white spot surrounded by a dark marking
+in the north polar region of the third satellite. There were other dark
+markings visible, and the satellite presented the appearance of a
+miniature of Mars.[150]
+
+An eighth satellite of Jupiter has recently been discovered by Mr. Melotte
+at the Greenwich Observatory by means of photography. It moves in a
+retrograde direction round Jupiter in an orbit inclined about 30 deg. to that
+of the planet. The period of revolution is about two years. The orbit is
+very eccentric, the eccentricity being about one-third, or greater than
+that of any other satellite of the solar system. When nearest to Jupiter
+it is about 9 millions of miles from the planet, and when farthest about
+20 millions.[151] It has been suggested by Mr. George Forbes that this
+satellite may possibly be identical with the lost comet of Lexell which at
+its return in the year 1779 became entangled in Jupiter's system, and has
+not been seen since. If this be the case, we should have the curious
+phenomenon of a comet revolving round a planet!
+
+According to Humboldt the four bright satellites of Jupiter were seen
+almost simultaneously and quite independently by Simon Marius at Ausbach
+on December 29, 1609, and by Galileo at Padua on January 7, 1610.[152] The
+actual priority, therefore, seems to rest with Simon Marius, but the
+publication of the discovery was first made by Galileo in his _Nuncius
+Siderius_ (1610).[153] Grant, however, in his _History of Physical
+Astronomy_, calls Simon Marius an "impudent pretender"! (p. 79).
+
+M. Dupret at Algiers saw Jupiter with the naked eye on September 26, 1890,
+twenty minutes before sunset.[154]
+
+Humboldt states that he saw Jupiter with the naked eye when the sun was
+from 18 deg. to 20 deg. above the horizon.[155] This was in the plains of South
+America near the sea-level.
+
+
+
+
+CHAPTER IX
+
+Saturn
+
+
+To show the advantages of large telescopes over small ones, Mr. C. Roberts
+says that "with the 25-inch refractor of the Cambridge Observatory the
+view of the planet Saturn is indescribably glorious; everything I had ever
+seen before was visible at a glance, and an enormous amount of detail that
+I had never even glimpsed before, after a few minutes' observation."[156]
+
+Chacornac found that the illumination of Saturn's disc is the reverse of
+that of Jupiter, the edges of Saturn being brighter than the centre of the
+disc, while in the case of Jupiter--as in that of the sun--the edges are
+fainter than the centre.[157] According to Mr. Denning, Saturn bears
+satisfactorily "greater magnifying power than either Mars or
+Jupiter."[158]
+
+At an occultation of Saturn by the moon, which occurred on June 13, 1900,
+M. M. Honorat noticed the great contrast between the slightly yellowish
+colour of the moon and the greenish tint of the planet.[159]
+
+In the year 1892, when the rings of Saturn had nearly disappeared, Prof.
+L. W. Underwood, of the Underwood Observatory, Appleton, Wisconsin
+(U.S.A.), saw one of Saturn's satellites (Titan) apparently moving along
+the needlelike appendage to the planet presented by the rings. "The
+apparent diameter of the satellite so far exceeded the apparent thickness
+of the ring that it gave the appearance of a beautiful golden bead moving
+very slowly along a fine golden thread."[160]
+
+In 1907, when the rings of Saturn became invisible in ordinary telescopes,
+Professor Campbell, observing with the great Lick telescope, noticed
+"prominent bright knots, visible ... in Saturn's rings. The knots were
+symmetrically placed, two being to the east and two to the west." This was
+confirmed by Mr. Lowell, who says, "Condensations in Saturn's rings
+confirmed here and measured repeatedly. Symmetric and permanent." This
+phenomenon was previously seen by Bond in the years 1847-56. Measures of
+these light spots made by Prof. Barnard with the 40-inch Yerkes telescope
+show that the outer one corresponded in position with the outer edge of
+the middle ring close to the Cassini division, and the inner condensation,
+curious to say, seemed to coincide in position with the "crape ring."
+Prof. Barnard thinks that the thickness of the rings "must be greatly
+under 100 miles, and probably less than 50 miles," and he says--
+
+    "The important fact clearly brought out at this apparition of _Saturn_
+    is that the bright rings are not opaque to the light of the sun--and
+    this is really what we should expect from the nature of their
+    constitution as shown by the theory of Clerk Maxwell, and the
+    spectroscopic results of Keeler."[161]
+
+Under certain conditions it would be theoretically possible, according to
+Mr. Whitmell, to see the globe of Saturn through the Cassini division in
+the ring. But the observation would be one of great difficulty and
+delicacy. The effect would be that, of the arc of the division which
+crosses the planet's disc, "a small portion will appear bright instead of
+dark, and may almost disappear."[162]
+
+A remarkable white spot was seen on Saturn on June 23, 1903, by Prof.
+Barnard, and afterwards by Mr. Denning.[163] Another white spot was seen
+by Denning on July 9 of the same year.[164] From numerous observations of
+these spots, Denning found a rotation period for the planet of about
+10{h} 39{m} 21{s}.[165] From observations of the same spots Signor Comas
+Sola found a period 10{h} 38{m}.4, a close agreement with Denning's
+result. For Saturn's equator, Prof. Hill found a rotation period of 10{h}
+14{m} 23{s}.8, so that--as in the case of Jupiter--the rotation is faster
+at the equator than in the northern latitudes of the planet. A similar
+phenomenon is observed in the sun. Mr. Denning's results were fully
+confirmed by Herr Leo Brenner, and other German astronomers.[166]
+
+Photographs taken by Prof. V. M. Slipher in America show that the spectrum
+of Saturn is similar to that of Jupiter. None of the bands observed in the
+planet's spectrum are visible in the spectrum of the rings. This shows
+that if the rings possess an atmosphere at all, it must be much rarer than
+that surrounding the ball of the planet. Prof. Slipher says that "none of
+the absorption bands in the spectrum of _Saturn_ can be identified with
+those bands due to absorption in the earth's atmosphere," and there is no
+trace of aqueous vapour.[167]
+
+In September, 1907, M. G. Fournier suspected the existence of a "faint
+transparent and luminous ring" outside the principal rings of Saturn. He
+thinks that it may possibly be subject to periodical fluctuations of
+brightness, sometimes being visible and sometimes not.[168] This dusky
+ring was again suspected at the Geneva Observatory in October, 1908.[169]
+M. Schaer found it a difficult object with a 16-inch Cassegrain reflector.
+Prof. Stromgen at Copenhagen, and Prof. Hartwig at Bamberg, however,
+failed to see any trace of the supposed ring.[170] It was seen at
+Greenwich in October, 1908.
+
+A "dark transit" of Saturn's satellite Titan across the disc of the planet
+has been observed on several occasions. It was seen by Mr. Isaac W. Ward,
+of Belfast, on March 27, 1892, with a 4.3-inch Wray refractor. The
+satellite appeared smaller than its shadow. The phenomenon was also seen
+on March 12 of the same year by the Rev. A. Freeman, Mr. Mee, and M. F.
+Terby; and again on November 6, 1907, by Mr. Paul Chauleur and Mr. A. B.
+Cobham.[171]
+
+The recently discovered tenth satellite of Saturn, Themis, was discovered
+by photography, and has never been seen by the eye even with the largest
+telescopes! But its existence is beyond all doubt, and its orbit round the
+planet has been calculated.
+
+Prof. Hussey of the Lick Observatory finds that Saturn's satellite Mimas
+is probably larger than Hyperion. He also finds from careful measurements
+that the diameter of Titan is certainly overestimated, and that its
+probable diameter is about 2500 miles.[172]
+
+The French astronomer, M. Lucien Rudaux, finds the following variation in
+the light of the satellites of Saturn:--
+
+  Japetus from 9th magnitude to 12th
+  Rhea     "   9       "        10.6
+  Dione    "   9.5     "        10.5
+  Tethys   "   9.8     "        10.5
+  Titan    "   8       "         8.6
+
+The variation of light is, he thinks, due to the fact that the period of
+rotation of each satellite is equal to that of their revolution round the
+planet; as in the case of our moon.[173]
+
+The names of the satellites of Saturn are derived from the ancient heathen
+mythology. They are given in order of distance from the planet, the
+nearest being Mimas and the farthest Themis.
+
+1. Mimas was a Trojan born at the same time as Paris.
+
+2. Enceladus was son of Tartarus and Ge.
+
+3. Tethys was wife of Oceanus, god of ocean currents. She became mother of
+all the chief rivers in the universe, as also the Oceanides or sea nymphs.
+
+4. Dione was one of the wives of Zeus.
+
+5. Rhea was a daughter of Uranus. She married Saturn, and became the
+mother of Vesta, Ceres, Juno, and Pluto.
+
+6. Titan was the eldest son of Uranus.
+
+7. Hyperion was the god of day, and the father of sun and moon.
+
+8. Japetus was the fifth son of Uranus, and father of Atlas and
+Prometheus.[174]
+
+9. Phoebe was daughter of Uranus and Ge.
+
+10. Themis was daughter of Uranus and Ge, and, therefore, sister of
+Phoebe.
+
+In a review of Prof. Comstock's _Text Book of Astronomy_ in _The
+Observatory_, November, 1901, the remark occurs, "We are astonished to see
+that Mr. Comstock alludes with apparent seriousness to the _nine_
+satellites of Saturn. As regards the ninth satellite, we thought that all
+astronomers held with Mrs. Betsy Prig on the subject of this astronomical
+Mrs. Harris." This reads curiously now (1909) when the existence of the
+ninth satellite (Phoebe) has been fully confirmed, and a tenth satellite
+discovered.
+
+
+
+
+CHAPTER X
+
+Uranus and Neptune
+
+
+From observations of Uranus made in 1896, M. Leo Brenner concluded that
+the planet rotates on its axis in about 8-1/2 hours (probably 8{h} 27{m}).
+This is a short period, but considering the short periods of Jupiter and
+Saturn there seems to be nothing improbable about it.
+
+Prof. Barnard finds that the two inner satellites of Uranus are difficult
+objects even with the great 36-inch telescope of the Lick Observatory!
+They have, however, been photographed at Cambridge (U.S.A.) with a 13-inch
+lens, although they are "among the most difficult objects known."[175]
+
+Sir William Huggins in 1871 found strong absorption lines (six strong
+lines) in the spectrum of Uranus. One of these lines indicated the
+presence of hydrogen, a gas which does not exist in our atmosphere. Three
+of the other lines seen were situated near lines in the spectrum of
+atmospheric air. Neither carbonic acid nor sodium showed any indications
+of their presence in the planet's spectrum. A photograph by Prof. Slipher
+of Neptune's spectrum "shows the spectrum of this planet to contain many
+strong absorption bands. These bands are so pronounced in the part of the
+spectrum between the Fraunhofer lines F and D, as to leave the solar
+spectrum unrecognizable.... Neptune's spectrum is strikingly different
+from that of _Uranus_, the bands in the latter planet all being reinforced
+in _Neptune_. In this planet there are also new bands which have not been
+observed in any of the other planets. The F line of hydrogen is remarkably
+dark ... this band is of more than solar strength in the spectrum of
+Uranus also. Thus free hydrogen seems to be present in the atmosphere of
+both these planets. This and the other dark bands in these planets bear
+evidence of an enveloping atmosphere of gases which is quite unlike that
+which surrounds the earth."[176]
+
+With the 18-inch equatorial telescope of the Strasburgh Observatory, M.
+Wirtz measured the diameter of Neptune, and found from forty-nine measures
+made between December 9, 1902, and March 28, 1903, a value of 2".303 at a
+distance of 30.1093 (earth's distance from sun = 1). This gives a diameter
+of 50,251 kilometres, or about 31,225 miles,[177] and a mean density of
+1.54 (water = 1; earth's mean density = 5.53). Prof. Barnard's measures
+gave a diameter of 32,900 miles, a fairly close agreement, considering the
+difficulty of measuring so small a disc as that shown by Neptune.
+
+The satellite of Neptune was photographed at the Pulkown Observatory in
+the year 1899. The name Triton has been suggested for it. In the old Greek
+mythology Triton was a son of Neptune, so the name would be an appropriate
+one.
+
+The existence of a second satellite of Neptune is suspected by Prof.
+Schaeberle, who thinks he once saw it with the 36-inch telescope of the
+Lick Observatory "on an exceptionally fine night" in 1895.[178] But this
+supposed discovery has not yet been confirmed. Lassell also thought he had
+discovered a second satellite, but this supposed discovery was never
+confirmed.[178]
+
+The ancient Burmese mention eight planets, the sun, the moon, Mercury,
+Venus, Mars, Jupiter, Saturn, and another named Rahu, which is invisible.
+It has been surmised that "Rahu" is Uranus, which is just visible to the
+naked eye, and may possibly have been discovered by keen eyesight in
+ancient times. The present writer has seen it several times without
+optical aid in the West of Ireland, and with a binocular field-glass of 2
+inches aperture he found it quite a conspicuous object.
+
+When Neptune was _visually_ discovered by Galle, at Berlin, he was
+assisted in his observation by Prof. d'Arrest. The incident is thus
+described by Dr. Dreyer, "On the night of June 14, 1874, while observing
+Coggia's comet together, I reminded Prof. d'Arrest how he had once said in
+the course of a lecture, that he had been present at the finding of
+Neptune, and that 'he might say it would not have been found without him.'
+He then told me (and I wrote it down the next day), how he had suggested
+the use of Bremiker's map (as first mentioned by Dr. Galle in 1877) and
+continued, 'We then went back to the dome, where there was a kind of desk,
+at which I placed myself with the map, while Galle, looking through the
+refractor, described the configurations of the stars he saw. I followed
+them on the map one by one, until he said: "And then there is a star of
+the 8th magnitude, in such and such a position," whereupon I immediately
+exclaimed: "That star is not on the map."'"[179] This was the planet. But
+it seems to the present writer that if Galle or d'Arrest had access to
+Harding's Atlas (as they probably had) they might easily have found the
+planet with a good binocular field-glass. As a matter of fact Neptune is
+shown in Harding's Atlas (1822) as a star of the 8th magnitude, having
+been mistaken for a star by Lalande on May 8 and 10, 1795; and the present
+writer has found Harding's 8th magnitude stars quite easy objects with a
+binocular field-glass having object-glasses of two inches diameter, and a
+power of about six diameters.
+
+SUPPOSED PLANET BEYOND NEPTUNE.--The possible existence of a planet beyond
+Neptune has been frequently suggested. From considerations on the aphelia
+of certain comets, Prof. Forbes in 1880 computed the probable position of
+such a body. He thought this hypothetical planet would be considerably
+larger than Jupiter, and probably revolve round the sun at a distance of
+about 100 times the earth's mean distance from the sun. The place
+indicated was between R.A. 11{h} 24{m} and 12{h} 12{m}, and declination 0 deg.
+0' to 6 deg. 0' north. With a view to its discovery, the late Dr. Roberts took
+a series of eighteen photographs covering the region indicated. The result
+of an examination of these photographs showed, Dr. Roberts says, that "no
+planet of greater brightness than a star of the 15th magnitude exists on
+the sky area herein indicated." Prof. W. H. Pickering has recently revived
+the question, and has arrived at the following results: Mean distance of
+the planet from the sun, 51.9 (earth's mean distance = 1); period of
+revolution, 373-1/2 years; mass about twice the earth's mass; probable
+position for 1909 about R.A. 7{h} 47{m}, north declination 21 deg., or about
+5 deg. south-east of the star [Greek: k] Geminorum. The supposed planet would
+be faint, its brightness being from 11-1/2 to 13-1/2, according to the
+"albedo" (or reflecting power) it may have.[180]
+
+Prof. Forbes has again attacked the question of a possible ultra-Neptunian
+planet, and from a consideration of the comets of 1556, 1843 I, 1880 I,
+and 1882 II, finds a mean distance of 105.4, with an inclination of the
+orbit of 52 deg. to the plane of the ecliptic. This high inclination implies
+that "during the greatest part of its revolution it is beyond the zodiac,"
+and this, Mr. W. T. Lynn thinks, "may partly account for its not having
+hitherto been found by observation."[181]
+
+From a consideration of the approximately circular shape of the orbits of
+all the large planets of the solar system, Dr. See suggests the existence
+of three planets outside Neptune, with approximate distances from the sun
+of 42, 56, and 72 respectively (earth's distance = 1), and recommends a
+photographic search for them. He says, "To suppose the planetary system to
+terminate with an orbit so round as that of Neptune is as absurd as to
+suppose that Jupiter's system terminates with the orbit of the fourth
+satellite."[182]
+
+According to Grant, even twenty years before the discovery of Neptune the
+error of Prof. Adams' first approximation amounted to little more than
+10 deg..[183]
+
+
+
+
+CHAPTER XI
+
+Comets
+
+
+We learn from Pliny that comets were classified in ancient times,
+according to their peculiar forms, into twelve classes, of which the
+principal were: _Pogonias_, bearded; _Lampadias_, torch-like; _Xiphias_,
+sword-like; _Pitheus_, tun-like; _Acontias_, javelin-like; _Ceratias_,
+horn-like; _Disceus_, quoit-like; and _Hippias_, horse-mane-like.[184]
+
+Of the numerous comets mentioned in astronomical records, comparatively
+few have been visible to the naked eye. Before the invention of the
+telescope (1610) only those which were so visible _could_, of course, be
+recorded. These number about 400. Of the 400 observed since then, some 70
+or 80 only have been visible by unaided vision; and most of these now
+recorded could never have been seen without a telescope. During the last
+century, out of 300 comets discovered, only 13 were very visible to the
+naked eye. Hence, when we read in the newspapers that a comet has been
+discovered the chances are greatly against it becoming visible to the
+naked eye.[185]
+
+Although comparatively few comets can be seen without a telescope, they
+are sometimes bright enough to be visible in daylight! Such were those of
+B.C. 43, A.D. 1106, 1402, 1532, 1577, 1744, 1843, and the "great September
+comet" of 1882.
+
+If we except the great comet of 1861, through the tail of which the earth
+is supposed to have passed, the comet which came nearest to the earth was
+that of 1770, known as Lexell's, which approached us within two millions
+of miles, moving nearly in the plane of the ecliptic. It produced,
+however, no effect on the tides, nor on the moon's motion, which shows
+that its mass must have been very small. It was computed by Laplace that
+if its mass had equalled that of the earth, the length of our year would
+have been shortened by 2 hours 47 minutes, and as there was no perceptible
+change Laplace concluded that the comet's mass did not exceed 1/5000th of
+the earth's mass. This is the comet which passed so near to Jupiter that
+its period was reduced to 5-1/2 years. Owing to another near approach in
+1779 it became invisible from the earth, and is now lost.[186] Its
+identity with the recently discovered eighth satellite of Jupiter has been
+suggested by Mr. George Forbes (see under "Jupiter"). At the near approach
+of Lexell's comet to the earth in 1770, Messier, "the comet ferret,"
+found that its head had an apparent diameter of 2-1/2 deg., or nearly five
+times that of the moon!
+
+Another case of near approach to the earth was that of Biela's comet at
+its appearance in 1805. On the evening of December 9 of that year, the
+comet approached the earth within 3,380,000 miles.[187]
+
+The comet of A.D. 1106 is stated to have been seen in daylight close to
+the sun. This was on February 4 of that year. On February 10 it had a tail
+of 60 deg. in length, according to Gaubil.[188]
+
+The comet of 1577 seems to have been one of the brightest on record.
+According to Tycho Brahe, it was visible in broad daylight. He describes
+the head as "round, bright, and of a yellowish light," with a curved tail
+of a reddish colour.[189]
+
+The comet of 1652 was observed for about three weeks only, and Hevelius
+and Comiers state that it was equal to the moon in apparent size! This
+would indicate a near approach to the earth. An orbit computed by Halley
+shows that the least distance was about 12 millions of miles, and the
+diameter of the comet's head rather less than 110,000 miles, or about 14
+times the earth's diameter.
+
+According to Mr. Denning, "most of the periodical comets at perihelion are
+outside the earth's orbit, and hence it follows that they escape
+observation unless the earth is on the same side of the sun as the
+comet."[190]
+
+It was computed by M. Faye that the _volume_ of the famous Donati's comet
+(1858) was about 500 times that of the sun! On the other hand, he
+calculated that its _mass_ (or quantity of matter it contained) was only a
+fraction of the earth's mass. This shows how almost inconceivably tenuous
+the material forming the comet must have been--much more rarefied, indeed,
+than the most perfect vacuum which can be produced in an air-pump. This
+tenuity is shown by the fact that stars were seen through the tail "as if
+the tail did not exist." A mist of a few hundred yards in thickness is
+sufficient to hide the stars from our view, while a thickness of thousands
+of miles of cometary matter does not suffice even to dim their brilliancy!
+
+At the time of the appearance of the great comet of 1843, it was doubtful
+whether the comet had transited the sun's disc. But it is now known, from
+careful calculations by Prof. Hubbard, that a transit really took place
+between 11{h} 28{m} and 12{h} 29{m} on February 27, 1843, and might have
+been observed in the southern hemisphere. The distance of this remarkable
+comet from the sun at its perihelion passage was less than that of any
+known comet. A little before 10 p.m. on February 27, the comet passed
+within 81,500 miles of the sun's surface with the enormous velocity of
+348 miles a second! It remained less than 2-1/4 hours north of the
+ecliptic, passing from the ascending to the descending node of its orbit
+in 2{h} 13{m}.4.[191] The great comet of 1882 transited the sun's disc on
+Sunday, September 17, of that year, the ingress taking place at 4{h} 50{m}
+58{s}, Cape mean time. When on the sun the comet was absolutely invisible,
+showing that there was nothing solid about it. It was visible near the sun
+with the naked eye a little before the transit took place.[192] This great
+comet was found by several computors to have been travelling in an
+elliptic orbit with a period of about eight centuries. Morrison found 712
+years; Frisby, 794; Fabritius, 823; and Kreutz, 843 years.[193]
+
+The great southern comet of 1887 may be described as a comet without a
+head! The popular idea of a comet is a star with a tail. But in this case
+there was no head visible--to the naked eye at least. Dr. Thome of the
+Cordoba Observatory--its discoverer--describes it as "a beautiful
+object--a narrow, straight, sharply defined, graceful tail, over 40 deg. long,
+shining with a soft starry light against a dark sky, beginning apparently
+without a head, and gradually widening and fading as it extended
+upwards."[194]
+
+The great southern comet of 1901 had five tails on May 6 of that year. Two
+were fairly bright, and the remaining three rather faint. Mr. Gale saw a
+number of faint stars through the tails. The light of these seem to have
+been "undimmed." Mr. Cobham noticed that the stars Rigel and [Greek: b]
+Eridani shone through one of the faint tails, and "showed no perceptible
+difference."[195]
+
+Prof. W. H. Pickering says that "the head of a comet, as far as our
+present knowledge is concerned, seems therefore to be merely a meteor
+swarm containing so much gaseous material that when electrified by its
+approach to the sun it will be rendered luminous" (_Harvard Annual_, vol.
+xxxii. part ii. p. 295) "... if the meteors and their atmospheres are
+sufficiently widely separated from one another, the comet may be brilliant
+and yet transparent at the same time."
+
+In the case of Swift's comet of 1892 some periodical differences of
+appearance were due, according to Prof. W. H. Pickering, to a rotation of
+the comet round an axis passing longitudinally through the tail, and he
+estimated the period of rotation at about 94 to 97 hours. He computed that
+in this comet the repulsive force exerted by the sun on the comet's tail
+was "about 39.5 times the gravitational force."[196]
+
+The comet known as 1902_b_ approached the planet Mercury within two
+millions of miles on November 29 of that year. Prof. O. C. Wendell, of
+Harvard Observatory, made some observations on the transparency of this
+comet. He found with the aid of a photometer and the 15-inch telescope of
+the observatory that in the case of two faint stars over which the comet
+passed on October 14, 1902, the absorption of light by the comet was
+insensible, and possibly did not exceed one or two hundredths of a
+magnitude,[197] an amount quite imperceptible to the naked eye, and shows
+conclusively how almost inconceivably rarefied the substance of this comet
+must be.
+
+The comet known as Morehouse (1908_c_) showed some curious and wonderful
+changes. Mr. Borelly found that five tails are visible on a photographic
+plate taken on October 3, 1908, and the trail of an occulted star
+indicates a slight absorption effect. According to M. L. Rabourdin, great
+changes took place from day to day, and even during the course of an hour!
+Similar changes were recorded by G. M. Gauthier; and Prof. Barnard, who
+photographed the comet on 30 nights from September 2 to October 13, states
+that the photographs of September 30 "are unique, whilst the
+transformation which took place between the taking of these and the taking
+of the next one on October 1 was very wonderful."[198] The spectrum
+showed the lines of cyanogen instead of the hydrocarbon spectrum shown by
+most comets.
+
+Prof. Barnard has suggested that all the phenomena of comets' tails cannot
+be explained by a repulsive force from the sun. Short tails issuing from
+the comet's nucleus at considerable angles with the main tail point to
+eruptive action in the comet itself. The rapid changes and distortions
+frequently observed in the tails of some comets suggest motion through a
+resisting medium; and the sudden increase of light also occasionally
+observed points in the same direction.[199]
+
+It was computed by Olbers that if a comet having a mass of 1/2000th of the
+earth's mass--which would form a globe of about 520 miles in diameter and
+of the density of granite--collided with the earth, with a velocity of 40
+miles a second, our globe would be shattered into fragments.[200] But that
+any comet has a solid nucleus of this size seems very doubtful; and we may
+further say that the collision of the earth with _any_ comet is highly
+improbable.
+
+It seems to be a common idea that harvests are affected by comets, and
+even "comet wines" are sometimes spoken of. But we know that the earth
+receives practically no heat from the brightest comet. Even in the case of
+the brilliant comet of 1811, one of the finest on record, it was found
+that "all the efforts to concentrate its rays did not produce the
+slightest effect on the blackened bulb of the most sensitive thermometer."
+Arago found that the year 1808, in which several comets were visible, was
+a cold year, "and 1831, in which there was no comet, enjoyed a much higher
+temperature than 1819, when there were three comets, one of which was very
+brilliant."[201] We may, therefore, safely conclude that even a large
+comet has no effect whatever on the weather.
+
+From calculations on the orbit of Halley's comet, the next return of which
+is due in 1910, Messrs. Cowell and Crommelin find that the identity of the
+comet shown on the Bayeux Tapestry with Halley's comet is now "fully
+established." They find that the date of perihelion passage was March 25,
+1066, which differs by only 4 days from the date found by Hind. The
+imposing aspect of the comet in 1066 described in European chronicles of
+that time is confirmed by the Chinese Annals. In the latter records the
+brightness is compared to that of Venus, and even with that of the moon!
+The comparison with the moon was probably an exaggeration, but the comet
+doubtless made a very brilliant show. In the Bayeux Tapestry the
+inscription on the wall behind the spectators reads: "_isti mirant
+stella_." Now, this is bad Latin, and Mr. W. T. Lynn has made the
+interesting suggestion that some of the letters are hidden by the
+buildings in front and that the real sentence is "_isti mirantur
+stellam_."[202] The present writer has examined the copy of the Bayeux
+Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn's
+suggestion seems very plausible. But the last letter of _stellam_ is
+apparently hidden by the comet's tail, which does not seem very probable!
+
+The conditions under which the comet will appear in 1910 are not unlike
+those of 1066 and 1145. "In each year the comet was discovered as a
+morning star, then lost in the sun's rays; on its emergence it was near
+the earth and moved with great rapidity, finally becoming stationary in
+the neighbourhood of Hydra, where it was lost to view."[203] In 1910 it
+will probably be an evening star before March 17, and after May 11, making
+a near approach to the earth about May 12. About this time its apparent
+motion in the sky will be very rapid. As, however, periodical comets--such
+as Halley's--seem to become fainter at each return, great expectations
+with reference to its appearance in 1910 should not be indulged in.
+
+The appearance of Halley's comet in A.D. 1222 is thus described by
+Pingre--a great authority on comets--(quoting from an ancient writer)--
+
+    "In autumn, that is to say in the months of August and September, a
+    star of the first magnitude was seen, very red, and accompanied by a
+    great tail which extended towards the top of the sky in the form of a
+    cone extremely pointed. It appeared to be very near the earth. It was
+    observed (at first?) near the place of the setting sun in the month of
+    December."
+
+With reference to its appearance in the year 1456, when it was of "vivid
+brightness," and had a tail of 60 deg. in length, Admiral Smyth says,[204] "To
+its malign influence were imputed the rapid successes of Mahomet II.,
+which then threatened all Christendom. The general alarm was greatly
+aggravated by the conduct of Pope Callixtus III., who, though otherwise a
+man of abilities, was a poor astronomer; for that pontiff daily ordered
+the church bells to be rung at noon-tide, extra _Ave-Marias_ to be
+repeated, and a special protest and excommunication was composed,
+exorcising equally the Devil, the Turks, and the comet." With reference to
+this story, Mr. G. F. Chambers points out[205] that it is probably based
+on a passage in Platina's _Vitae Pontificum_. But in this passage there is
+no mention made of excommunication or exorcism, so that the story, which
+has long been current, is probably mythical. In confirmation of this view,
+the Rev. W. F. Rigge has shown conclusively[206] that no bull was ever
+issued by Pope Callixtus III. containing a reference to _any_ comet. The
+story would therefore seem to be absolutely without foundation, and should
+be consigned to the limbo of all such baseless myths.
+
+With reference to the appearance of Halley's comet, at his last return in
+1835, Sir John Herschel, who observed it at the Cape of Good Hope, says--
+
+    "Among the innumerable stars of all magnitudes, from the ninth
+    downwards, which at various times were seen through it, and some
+    extremely near to the nucleus (though not _exactly on it_) there never
+    appeared the least ground for presuming any extinction of their light
+    in traversing it. Very minute stars indeed, on entering its brightest
+    portions, were obliterated, as they would have been by an equal
+    illumination of the field of view; but stars which before their entry
+    appeared bright enough to bear that degree of illumination, were in no
+    case, so far as I could judge, affected to a greater extent than they
+    would have been by so much lamp-light artificially introduced."[207]
+
+It is computed by Prof. J. Holetschak that, early in October, 1909,
+Halley's comet should have the brightness of a star of about 14-1/2
+magnitude.[208] It should then--if not detected before--be discoverable
+with some of the large telescopes now available.
+
+According to the computations of Messrs. Cowell and Crommelin, the comet
+should enter Pisces from Aries in January, 1910. "Travelling westward
+towards the star [Greek: g] Piscium until the beginning of May, and then
+turning eastward again, it will travel back through the constellations
+Cetus, Orion, Monoceros, Hydra, and Sextans." From this it seems that
+observers in the southern hemisphere will have a better view of the comet
+than those in northern latitudes. The computed brightness varies from 1 on
+January 2, 1910, to 1112 on May 10. But the actual brightness of a comet
+does not always agree with theory. It is sometimes brighter than
+calculation would indicate.
+
+According to Prof. O. C. Wendell, Halley's comet will, on May 12, 1910,
+approach the earth's orbit within 4.6 millions of miles; and he thinks
+that possibly the earth may "encounter some meteors," which are presumably
+connected with the comet. He has computed the "radiant point" of these
+meteors (that is, the point from which they appear to come), and finds its
+position to be R.A. 22{h} 42{m}.9, Decl. N. 1 deg. 18'. This point lies a
+little south-west of the star [Greek: b] Piscium.
+
+According to Dr. Smart, the comet will, on June 2, "cross the Equator
+thirteen degrees south of Regulus, and will then move slowly in the
+direction of [Greek: ph] Leonis. The comet will be at its descending node
+on the ecliptic in the morning of May 16, and the earth will pass through
+the node on the comet's orbit about two and a half days later. The
+comet's orbit at the node is about 13 million miles within that of the
+earth. Matter repelled from the comet's nucleus by the sun with a velocity
+of about 216,000 miles per hour, would just meet the earth when crossing
+the comet's orbit plane. Matter expelled with a velocity of 80,000 miles
+per hour, as in the case of Comet Morehouse, would require seven days for
+the journey. Cometary matter is said to have acquired greater velocities
+than this, for (according to Webb, who quotes Chacornac) Comet II., 1862,
+shot luminous matter towards the sun, with a velocity of nearly 2200 miles
+per second. It is therefore possible that matter thrown off by the comet
+at the node may enter our atmosphere, in which case we must hope that
+cyanogen, which so often appears in cometary spectra, may not be
+inconveniently in evidence."[209]
+
+Cyanogen is, of course, a poisonous gas, but cometary matter is so
+rarefied that injurious effects on the earth need not be feared.
+
+If we can believe the accounts which have been handed down to us, some
+very wonderful comets were visible in ancient times. The following may be
+mentioned:--
+
+B.C. 165. The sun is said to have been "seen for several hours in the
+night." If this was a comet it must have been one of extraordinary
+brilliancy.[210]
+
+B.C. 146. "After the death of Demetrius, king of Syria, the father of
+Demetrius and Antiochus, a little before the war in Achaia, there appeared
+a comet as large as the sun. Its disc was first red, and like fire,
+spreading sufficient light to dissipate the darkness of night; after a
+little while its size diminished, its brilliancy became weakened, and at
+length it entirely disappeared."[211]
+
+B.C. 134. It is recorded that at the birth of Mithridates a great comet
+appeared which "occupied the fourth part of the sky, and its brilliancy
+was superior to that of the sun." (?)[212]
+
+B.C. 75. A comet is described as equal in size to the moon, and giving as
+much light as the sun on a cloudy day. (!)[213]
+
+A.D. 531. In this year a great comet was observed in Europe and China. It
+is described as "a very large and fearful comet," and was visible in the
+west for three weeks. Hind thinks that this was an appearance of Halley's
+comet,[214] and this has been confirmed by Mr. Crommelin.
+
+A.D. 813, August 4. A comet is said to have appeared on this date, of
+which the following curious description is given: "It resembled two moons
+joined together; they separated, and having taken different forms, at
+length appeared like a man without a head." (!)[215]
+
+A.D. 893. A great comet is said to have appeared in this year with a tail
+100 deg. in length, which afterwards increased to 200 deg.![216]
+
+A.D. 1402. A comet appeared in February of this year, which was visible in
+daylight for eight days. "On Palm Sunday, March 19, its size was
+prodigious." Another comet, visible in the daytime, was seen from June to
+September of the same year.
+
+When the orbit of the comet known as 1889 V was computed, it was found
+that it had passed through Jupiter's system in 1886 (July 18-21). The
+calculations show that it must have passed within a distance of 112,300
+miles of the planet itself--or less than half the moon's distance from the
+earth--and "its centre may possibly have grazed the surface of
+Jupiter."[217]
+
+Sir John Herschel thought that the great comet of 1861 was by far the
+brightest comet he had ever seen, those of 1811 and 1858 (Donati's) not
+excepted.[218] Prof. Kreutz found its period of revolution round the sun
+to be about 409 years, with the plane of the orbit nearly at right angles
+to the plane of the ecliptic.
+
+       *       *       *       *       *
+
+On November 9, 1795, Sir William Herschel saw the comet of that year pass
+centrally over a small double star of the 11th and 12th magnitudes, and
+the fainter of the two components remained distinctly visible during the
+comet's transit over the star. This comet was an appearance of the comet
+now known as Encke's.[219] Struve saw a star of the 10th magnitude through
+nearly the brightest part of Encke's comet on November 7, 1828, but the
+star's light was not dimmed by the comet.
+
+Sir John Herschel saw a cluster of stars of the 16th or 17th magnitude
+through Biela's comet, although the interposed cometary matter must have
+been at least 50,000 miles in thickness.[220]
+
+Bessel found that on September 29, 1835, a star of the 10th magnitude
+shone with undimmed lustre through the tail of Halley's comet within 8
+seconds of arc of the central point of the head. At Dorpat (Russia) Struve
+saw the same star "in conjunction only 2".2 from the brightest point of
+the comet. The star remained continuously visible, and its light was not
+perceptibly diminished whilst the nucleus of the comet seemed to be almost
+extinguished before the radiance of the small star of the 9th or 10th
+magnitude."[221]
+
+Webb says--
+
+    "Donati saw a 7 mg. star enlarged so as to show a sensible disc, when
+    the nucleus of comet III., 1860, passed very near it. Stars are said
+    to have started, or become tremulous, during occultations by comets.
+    Birmingham observed the comet of Encke illuminated by a star over
+    which it passed, August 23, 1868; and Klein, in 1861, remarked an
+    exceptional twinkling in 5 mg. stars involved in the tail."[222]
+
+The comet of 1729 had the greatest perihelion distance of any known
+comet;[223] that is, when nearest to the sun, it did not approach the
+central luminary within four times the earth's distance from the sun!
+
+Barnard's comet, 1889 I., although it never became visible to the naked
+eye, was visible with a telescope from September 2, 1888, to August 18,
+1890, or 715 days--the longest period of visibility of any comet on
+record. When last seen it was 6-1/4 times the earth's distance from the
+sun, or about 580 millions of miles,[224] or beyond the orbit of Jupiter!
+
+Messier, who was called "the comet ferret," discovered "all his comets
+with a small 2-foot telescope of 2-1/4 inches aperture, magnifying 5
+times, and with a field of 4 deg.."[225]
+
+It is a very curious fact that Sir William Herschel, "during all his
+star-gaugings and sweeps for nebulae, never discovered a comet;"[226] that
+is an object which was afterwards _proved_ to be a comet. Possibly,
+however, some of his nebulae which are now missing, may have been really
+comets.
+
+Sir William Herschel found the diameter of the head of the great comet of
+1811 to be 127,000 miles. The surrounding envelope he estimated to be at
+least 643,000 miles, or about three-fourths of the sun's diameter.
+
+On a drawing of the tails of the great comet of 1744 given in a little
+book printed in Berlin in that year, no less than 12 tails are shown!
+These vary in length and brightness. A copy of this drawing is given in
+_Copernicus_.[227] The observations were made by "einen geschichten
+Frauenzimmer," who Dr. Dreyer identifies with Christian Kirch, or one of
+her two sisters, daughters of the famous Gottfried and Maria Margaretta
+Kirch (_Idem_, p. 107). Dr. Dreyer thinks that the drawing "seems to have
+been carefully made, and not to be a mere rough sketch as I had at first
+supposed" (_Idem_, p. 185).
+
+The tails of some comets were of immense length. That of the comet of 1769
+had an absolute length of 38 millions of miles. That of 1680, 96 million
+of miles, or more than the sun's distance from the earth. According to Sir
+William Herschel, the tail of the great comet of 1811 was over 100
+millions of miles in length. That of the great comet of 1843--one of the
+finest in history--is supposed to have reached a length of 150 millions of
+miles![228]
+
+In width the tails of comets were in some cases enormous. According to Sir
+William Herschel, the tail of the comet of 1811 had a diameter of 15
+millions of miles! Its volume was, therefore, far greater than that of the
+sun![228]
+
+According to Hevelius the comet of 1652 was of such a magnitude that it
+"resembled the moon when half full; only it shone with a pale and dismal
+light."[229]
+
+Halley's comet at its next appearance will be examined with the
+spectroscope for the first time in its history. At its last return in
+1835, the spectroscope had not been invented.
+
+For the great comet of 1811, Arago computed a period of 3065 years; and
+Encke found a period of 8800 years for the great comet of 1680.[230]
+
+The variation in the orbital velocity of some comets is enormous. The
+velocity of the comet of 1680 when passing round the sun (perihelion) was
+about 212 miles a second! Whereas at its greatest distance from the sun
+(aphelion) the velocity is reduced to about 10 feet a second!
+
+
+
+
+CHAPTER XII
+
+Meteors
+
+
+Mr. Denning thinks that the meteor shower of the month of May, known as
+the Aquarids, is probably connected with Halley's comet. The meteors
+should be looked for after 1 a.m. during the first week in May, and may
+possibly show an enhanced display in May, 1910, when Halley's comet will
+be near the sun and earth.[231]
+
+On November 29, 1905, Sir David Gill observed a fireball with an apparent
+diameter equal to that of the moon, which remained visible for 5 minutes
+and disappeared in a hazy sky. Observed from another place, Mr. Fuller
+found that the meteor was visible 2 hours later! Sir David Gill stated
+that he does not know of any similar phenomenon.[232]
+
+Mr. Denning finds that swiftly moving meteors become visible at a greater
+height above the earth's surface than the slower ones. Thus, for the
+Leonids and Perseids, which are both swift, it has been found that the
+Leonids appear at an average height of 84 miles, and disappear at a height
+of 56 miles; and the Perseids at 80 and 54 miles respectively. "On the
+other hand, the mean height of the very slow meteors average about 65
+miles at the beginning and 38 miles at the end of their appearance."[233]
+
+During the night of July 21-22, 1896, Mr. William Brooks, the well-known
+astronomer, and director of the Smith Observatory at Geneva (New York),
+saw a round dark body pass slowly across the moon's bright disc, the moon
+being nearly full at the time. The apparent diameter of the object was
+about one minute of arc, and the duration of the transit 3 or 4 seconds,
+the direction of motion being from east to west. On August 22 of the same
+year, Mr. Gathman (an American observer) saw a meteor crossing the _sun's_
+disc, the transit lasting about 8 seconds.[234]
+
+A meteor which appeared in Italy on July 7, 1892, was shown by Prof. von
+Niessl to have had an _ascending_ path towards the latter end of its
+course! The length of its path was computed to be 683 miles. When first
+seen, its height above the earth was about 42 miles, and when it
+disappeared its height had increased to about 98 miles, showing that its
+motion was directed upwards![235]
+
+In the case of the fall of meteoric stones, which occasionally occur, it
+has sometimes been noticed that the sound caused by the explosion of the
+meteorite, or its passage through the air, is heard before the meteorite
+is seen to fall. This has been explained by the fact that owing to the
+resistance of the air to a body moving at first with a high velocity its
+speed is so reduced that it strikes the earth with a velocity less than
+that of sound. Hence the sound reaches the earth before the body strikes
+the ground.[236]
+
+The largest meteoric stone preserved in a museum is that known as the
+Anighita, which weighs 36-1/2 tons, and was found at Cape York in
+Greenland. It was brought to the American Museum of Natural History by
+Commander R. E. Peary, the Arctic explorer.
+
+The second largest known is that of Bacubirito in Mexico, the weight of
+which is estimated at 27-1/2 tons.
+
+The third largest is that known as the Williamette, which was found in
+1902 near the town of that name in Western Oregon (U.S.A.). It is composed
+of metallic nickel-iron, and weighs about 13-1/2 tons. It is now in the
+American Museum of Natural History.
+
+A large meteorite was actually seen, from the deck of the steamer _African
+Prince_, to fall into the Atlantic Ocean, on October 7, 1906! The captain
+of the vessel, Captain Anderson, describes it as having a train of light
+resembling "an immense broad electric-coloured band, gradually turning to
+orange, and then to the colour of molten metal. When the meteor came into
+the denser atmosphere close to the earth, it appeared, as nearly as is
+possible to describe it, like a molten mass of metal being poured out. It
+entered the water with a hissing noise close to the ship."[237] This was a
+very curious and perhaps unique phenomenon, and it would seem that the
+vessel had a narrow escape from destruction.
+
+In Central Arizona (U.S.A.) there is a hill called Coon Butte, or Coon
+Mountain. This so-called "mountain" rises to a height of only 130 to 160
+feet above the surrounding plain, and has on its top a crater of 530 to
+560 feet deep; the bottom of the crater--which is dry--being thus 400 feet
+below the level of the surrounding country. This so-called "crater" is
+almost circular and nearly three-quarters of a mile in diameter. It has
+been suggested that this "crater" was formed by the fall of an enormous
+iron meteorite, or small asteroid. The "crater" has been carefully
+examined by a geologist and a physicist. From the evidence and facts
+found, the geologist (Mr. Barringer) states that "they do not leave, in my
+mind, a scintilla of doubt that this mountain and its crater were produced
+by the impact of a huge meteorite or small asteroid." The physicist (Mr.
+Tilghmann) says that he "is justified, under due reserve as to
+subsequently developed facts, in announcing that the formation at this
+locality is due to the impact of a meteor of enormous and unprecedented
+size." There are numerous masses of meteoric iron in the vicinity of the
+"crater." The so-called Canyon Diabolo meteorite was found in a canyon of
+that name about 2-1/2 miles from the Coon Mountain. The investigators
+estimate that the great meteoric fall took place "not more than 5000 years
+ago, perhaps much less." Cedar trees about 700 years old are now growing
+on the rim of the mountain. From the results of artillery experiments, Mr.
+Gilbert finds that "a spherical projectile striking solid limestone with a
+velocity of 1800 feet a second will penetrate to a depth of something less
+than two diameters," and from this Mr. L. Fletcher concludes "that a
+meteorite of large size would not be prevented by the earth's atmosphere
+from having a penetration effect sufficient for the production of such a
+crater."[238]
+
+The meteoric origin of this remarkable "crater" is strongly favoured by
+Mr. G. P. Merrill, Head Curator of Geology, U.S. National Museum.
+
+The Canyon Diabolo meteorite above referred to was found to contain
+diamonds! some black, others transparent. So some have said that "the
+diamond is a gift from Heaven," conveyed to earth in meteoric
+showers.[239] But diamond-bearing meteorites would seem to be rather a
+freak of nature. It does not follow that _all_ diamonds had their origin
+in meteoric stones. The mineral known as periodot is frequently found in
+meteoric stones, but it is also a constituent of terrestrial rocks.
+
+In the year 1882 it was stated by Dr. Halm and Dr. Weinhand that they had
+found fossil sponges, corals, and crinoids in meteoric stones! Dr.
+Weinhand thought he had actually determined three genera![240] But this
+startling result was flatly contradicted by Carl Vogt, who stated that the
+supposed fossils are merely crystalline conformations.[241]
+
+Some meteorites contain a large quantity of occluded gases, hydrogen,
+helium, and carbon oxides. It is stated that Dr. Odling once "lighted up
+the theatre of the Royal Institution with gas brought down from
+interstellar space by meteorites"![242]
+
+On February 10, 1896, a large meteorite burst over Madrid with a loud
+report. The concussion was so great that many windows in the city were
+broken, and some partitions in houses were shaken down![243]
+
+A very brilliant meteor or fireball was seen in daylight on June 9, 1900,
+at 2{h} 55{m} p.m. from various places in Surrey, Sussex, and near London.
+Calculations showed that "the meteor began 59 miles in height over a point
+10 miles east of Valognes, near Cherbourg, France. Meteor ended 23 miles
+in height, over Calais, France. Length of path 175 miles. Radiant point,
+280 deg., 12 deg.."[244]
+
+It was decided some years ago "in the American Supreme Court that a
+meteorite, though a stone fallen from heaven, belongs to the owner of the
+freehold interest in the land on which it falls, and not to the
+tenant."[245]
+
+With reference to the fall of meteoric matter on the earth, Mr. Proctor
+says, "It is calculated by Dr. Kleiber of St. Petersburgh that 4250 lbs.
+of meteoric dust fall on the earth every hour--that is, 59 tons a day, and
+more than 11,435 tons a year. I believe this to be considerably short of
+the truth. It sounds like a large annual growth, and the downfall of such
+an enormous mass of meteoric matter seems suggestive of some degree of
+danger. But in reality, Dr. Kleiber's estimate gives only about 25
+millions of pounds annually, which is less than 2 ounces annually to each
+square mile of the earth's surface,"[246] a quantity which is, of course,
+quite insignificant.
+
+According to Humboldt, Chladni states that a Franciscan monk was killed by
+the fall of an aerolite at Milan in the year 1660.[247] Humboldt also
+mentions the death by meteoric stones of a monk at Crema on September 4,
+1511, and two Swedish sailors on board ship in 1674.[248]
+
+It is a curious fact that, according to Olbers, "no fossil meteoric
+stones" have ever been discovered.[249] Considering the number which are
+supposed to have fallen to the earth in the course of ages, this fact
+seems a remarkable one.
+
+On May 10, 1879, a shower of meteorites fell at Eitherville, Iowa
+(U.S.A.). Some of the fragments found weighed 437, 170, 92-1/2, 28,
+10-1/2, 4 and 2 lbs. in weight. In the following year (1880) when the
+prairie grass had been consumed by a fire, about "5000 pieces were found
+from the size of a pin to a pound in weight."[250]
+
+According to Prof. Silvestria of Catania, a shower of meteoric dust mixed
+with rain fell on the night of March 29, 1880. The dust contained a large
+proportion of iron in the metallic state. In size the particles varied
+from a tenth to a hundredth of a millimetre.[251]
+
+It is sometimes stated that the average mass of a "shooting star" is only
+a few grains. But from comparisons with an electric arc light, Prof. W.
+H. Pickering concludes that a meteor as bright as a third magnitude star,
+composed of iron or stone, would probably have a diameter of 6 or 7
+inches. An average bright fireball would perhaps measure 5 or 6 feet in
+diameter.[252]
+
+In the Book of Joshua we are told "that the LORD cast down great stones
+from heaven upon them unto Azekah, and they died" (Joshua x. 11). In the
+latter portion of the verse "hailstones" are mentioned, but as the
+original Hebrew word means stones in general (not hailstones), it seems
+very probable that the stones referred to were aerolites.[253]
+
+The stone mentioned in the Acts of the Apostles, from which was found "the
+_image_ which fell down from Jupiter" (Acts xix. 35), was evidently a
+meteoric stone.[253]
+
+The famous stone in the Caaba at Mecca, is probably a stone of meteoric
+origin.[253]
+
+  I
+
+  "Stones from Heaven! Can you wonder,
+    You who scrutinize the Earth,
+  At the love and veneration
+    They received before the birth
+  Of our scientific methods?
+
+
+  II
+
+  "Stones from Heaven! we can handle
+    Fragments fallen from realms of Space;
+  Oh! the marvel and the mystery,
+    Could we understand their place
+  In the scheme of things created!
+
+
+  III
+
+  "Stones from Heaven! With a mighty
+    Comet whirling formed they part?
+  Fell they from their lofty station
+    Like a brilliant fiery dart,
+  Hurl'd from starry fields of Night?"[254]
+
+
+
+
+CHAPTER XIII
+
+The Zodiacal Light and Gegenschein
+
+
+According to Gruson and Brugsch, the Zodiacal Light was known in ancient
+times, and was even worshipped by the Egyptians. Strabo does not mention
+it; but Diodorus Siculus seems to refer to it (B.C. 373), and he probably
+obtained his information from some Greek writers before his time, possibly
+from Zenophon, who lived in the sixth century B.C.[255] Coming to the
+Christian era, it was noticed by Nicephorus, about 410 B.C. In the Koran,
+it is called the "false Aurora"; and it is supposed to be referred to in
+the "Rubaiyat" of Omar Khayyam, the Persian astronomical poet, in the
+second stanza of that poem (Edward Fitzgerald's translation)--
+
+  "Dreaming when Dawn's Left Hand was in the Sky,[256]
+  I heard a voice within the Tavern cry,
+  Awake, my Little ones, and fill the Cup,
+  Before Life's Liquor in its Cup be dry."
+
+It was observed by Cassini in 1668,[257] and by Hooke in 1705. A short
+description of its appearance will be found in Childrey's _Britannia
+Baconica_ (1661), p. 183.
+
+The finest displays of this curious light seem to occur between the middle
+of January and the middle of February. In February, 1856, Secchi found it
+brighter than he had ever seen it before. It was yellowish towards the
+axis of the cone, and it seemed to be brighter than the Milky Way in
+Cygnus. He described it as "un grande spectacle." In the middle of
+February, 1866, Mr. Lassell, during his last residence in Malta, saw a
+remarkable display of the Zodiacal Light. He found it at least twice as
+bright as the brightest part of the Milky Way, and much brighter than he
+had previously seen it. He found that the character of its light differed
+considerably from that of the Milky Way. It was of a much redder hue than
+the Galaxy. In 1874 very remarkable displays were seen in the
+neighbourhood of London in January and February of that year; and in 1875
+on January 24, 25, and 30. On January 24 it was noticed that the "light"
+was distinctly reddish and much excelled in brightness any portion of the
+Milky Way.
+
+Humboldt, who observed it from Andes (at a height of 13,000 to 15,000
+feet), from Venezuela and from Cumana, tells us that he has seen the
+Zodiacal Light equal in brightness to the Milky Way in Sagittarius.
+
+As probably many people have never seen the "light," a caution may be
+given to those who care to look for it. It is defined by the Rev. George
+Jones, Chaplain to the "United States' Japan Expedition" (1853-55), as "a
+brightness that appears in the western sky after sunset, and in the east
+before sunrise; following nearly or quite the line of the ecliptic in the
+heavens, and stretching upwards to various elevations according to the
+season of the year." From the description some might suppose that the
+light is visible _immediately_ after sunset. But this is not so; it never
+appears until twilight is over and "the night has fully set in."
+
+The "light" is usually seen after sunset or before sunrise. But attempts
+have recently been made by Prof. Simon Newcomb to observe it north of the
+sun. To avoid the effects of twilight the sun must be only slightly more
+than 18 deg. below the horizon (that is, a little before or after the longest
+day). This condition limits the place of observation to latitudes not much
+south of 46 deg.; and to reduce atmospheric absorption the observing station
+should be as high as possible above the level of the sea. Prof. Newcomb,
+observing from the Brienzer Rothorn in Switzerland (latitude 46 deg. 47' N.,
+longitude 8 deg. 3' E.), succeeded in tracing the "light" to a distance of 35 deg.
+north of the sun. It would seem, therefore, that the Zodiacal Light
+envelops the sun on all sides, but has a greater extension in the
+direction of the ecliptic.[258] From observations at the Lick Observatory,
+Mr. E. A. Fath found an extension of 46 deg. north of the sun.[259]
+
+From observations of the "light" made by Prof. Barnard at the Yerkes
+Observatory during the summer of 1906, he finds that it extends to at
+least 65 deg. north of the sun, a considerably higher value than that found by
+Prof. Newcomb.[260] The difference may perhaps be explained by actual
+variation of the meteoric matter producing the light. Prof. J. H. Poynting
+thinks that possibly the Zodiacal Light is due to the "dust of long dead
+comets."[261]
+
+From careful observations of the "light," Mr. Gavin J. Burns finds that
+its luminosity is "some 40 or 50 per cent. brighter than the background of
+the sky. Prof. Newcomb has made a precisely similar remark about the
+luminosity of the Milky Way, viz. that it is surprisingly small." This
+agrees with my own observations during many years. It is only on the
+finest and clearest nights that the Milky Way forms a conspicuous object
+in the night sky. And this only in the country. The lights of a city
+almost entirely obliterate it. Mr. Burns finds that the Zodiacal Light
+appears "to be of a yellowish tint; or if we call it white, then the Milky
+Way is comparatively of a bluish tint." During my residence in the Punjab
+the Zodiacal Light seemed to me constantly visible in the evening sky in
+the spring months. In the west of Ireland I have seen it nearly as bright
+as the brightest portions of the Milky Way visible in this country
+(February 20, 1890). The "meteoric theory" of the "light" seems to be the
+one now generally accepted by astronomers, and in this opinion I fully
+concur.
+
+From observations made in Jamaica in the years 1899 and 1901, Mr. Maxwell
+Hall arrived at the conclusion that "the Zodiacal Light is caused by
+reflection of sunlight from masses of meteoric matter still contained in
+the invariable plane, which may be considered the original plane of the
+solar system."[262] According to Humboldt, Cassini believed that the
+Zodiacal Light "consisted of innumerably small planetary bodies revolving
+round the sun."[263]
+
+THE GEGENSCHEIN, or COUNTER-GLOW.--This is a faint patch of light seen
+opposite the sun's place in the sky, that is on the meridian at midnight.
+It is usually elliptical in shape, with its longer axis lying nearly in
+the plane of the ecliptic. It seems to have been first detected by Brorsen
+(the discoverer of the short-period comet of 1846) about the middle of
+the nineteenth century. But it is not easy to see, for the famous Heis of
+Muenster, who had very keen eyesight, did not succeed in seeing it for
+several years after Brorsen's announcement.[264] It was afterwards
+independently discovered by Backhouse, and Barnard.
+
+Prof. Barnard's earlier observations seemed to show that the Gegenschein
+does not lie exactly opposite to the sun, but very nearly so. He found its
+longitude is within one degree of 180 deg., and its latitude about 1 deg..3 north
+of the ecliptic.[265] But from subsequent observations he came to the
+conclusion that the differences in longitude and apparent latitude are due
+to atmospheric absorption, and that the object really lies in the ecliptic
+and _exactly_ opposite to the sun.[266]
+
+Barnard finds that the Gegenschein is not so faint as is generally
+supposed. He says "it is best seen by averted vision, the face being
+turned 60 deg. or 70 deg. to the right or left, and the eyes alone turned towards
+it." It is invisible in June and December, while in September it is round,
+with a diameter of 20 deg., and very distinct. No satisfactory theory has yet
+been advanced to account for this curious phenomenon. Prof. Arthur Searle
+of Harvard attributes it to a number of asteroids too small to be seen
+individually. When in "opposition" to the sun these would be fully
+illuminated and nearest to the earth. Its distance from the earth probably
+exceeds that of the moon. Dr. Johnson Stoney thinks that the Gegenschein
+may possibly be due to a "tail" of hydrogen and helium gases repelled from
+the earth by solar action; this "tail" being visible to us by reflected
+sunlight.
+
+It was observed under favourable circumstances in January and February,
+1903, by the French astronomer, M. F. Quenisset. He found that it was
+better seen when the atmosphere was less clear, contrary to his experience
+of the Zodiacal Light. Prof. Barnard's experience confirms this. M.
+Quenisset notes that--as in the case of the Zodiacal Light--the southern
+border of the Gegenschein is sharper than the northern. He found that its
+brightness is less than that of the Milky Way between Betelgeuse and
+[Greek: g] Geminorum; and thinks that it is merely a strengthening of the
+Zodiacal Light.[267]
+
+A meteoritic theory of the Gegenschein has been advanced by Prof. F. R.
+Moulton, which explains it by light reflected from a swarm of meteorites
+revolving round the sun at a distance of 930,240 miles outside the earth's
+orbit.
+
+Both the Zodiacal Light and Gegenschein were observed by Herr Leo Brenner
+on the evening of March 4, 1896. He found the Zodiacal Light on this
+evening to be "_perhaps eight times brighter_ than the Milky Way in
+Perseus." The "_Gegenschein distinctly visible_ as a round, bright,
+cloud-like nebula below Leo (Virgo), and about twice the brightness of the
+Milky Way in Monoceros between Canis Major and Canis Minor."[268]
+
+Humboldt thought that the fluctuations in the brilliancy of the Zodiacal
+Light were probably due to a real variation in the intensity of the
+phenomenon rather than to the elevated position of the observer.[269] He
+says that he was "astonished in the tropical climates of South America, to
+observe the variable intensity of the light."
+
+
+
+
+CHAPTER XIV
+
+The Stars
+
+
+Pliny says that Hipparchus "ventured to count the stars, a work arduous
+even for the Deity." But this was quite a mistaken idea. Those visible to
+the naked eye are comparatively few in number, and the enumeration of
+those visible in an opera-glass--which of course far exceed those which
+can be seen by unaided vision--is a matter of no great difficulty. Those
+visible in a small telescope of 2-3/4 inches aperture have all been
+observed and catalogued; and even those shown on photographs taken with
+large telescopes can be easily counted. The present writer has made an
+attempt in this direction, and taking an average of a large number of
+counts in various parts of the sky, as shown on stellar photographs, he
+finds a total of about 64 millions for the whole sky in both
+hemispheres.[270] Probably the total number will not exceed 100 millions.
+But this is a comparatively small number, even when compared with the
+human population of our little globe.
+
+With reference to the charts made by photography in the International
+scheme commenced some years ago, it has now been estimated that the charts
+will probably contain a total of about 9,854,000 stars down to about the
+14th magnitude (13.7). The "catalogue plates" (taken with a shorter
+exposure) will, it is expected, include about 2,676,500 stars down to
+11-1/2 magnitude. These numbers may, however, be somewhat increased when
+the work has been completed.[271] If this estimate proves to be correct,
+the number of stars visible down to the 14th magnitude will be
+considerably less than former estimates have made it.
+
+Prof. E. C. Pickering estimates that the total number of stars visible on
+photographs down to the 16th magnitude (about the faintest visible in the
+great Lick telescope) will be about 50 millions.[272] In the present
+writer's enumeration, above referred to, many stars fainter than the 16th
+magnitude were included.
+
+Admiral Smyth says, with reference to Sir William Herschel--perhaps the
+greatest observer that ever lived--"As to Sir William himself, he could
+unhesitatingly call every star down to the 6th magnitude, by its name,
+letter, or number."[273] This shows great powers of observation, and a
+wonderful memory.
+
+On a photographic plate of the Pleiades taken with the Bruce telescope and
+an exposure of 6 hours, Prof. Bailey of Harvard has counted "3972 stars
+within an area 2 deg. square, having Alcyone at its centre."[274] This would
+give a total of about 41 millions for the whole sky, if of the same
+richness.
+
+With an exposure of 16 hours, Prof. H. C. Wilson finds on an area of less
+that 110' square a total of 4621 stars. He thinks, "That all of these
+stars belong to the Pleiades group is not at all probable. The great
+majority of them probably lie at immense distances beyond the group, and
+simply appear in it by projection."[274] He adds, "It has been found,
+however, by very careful measurements made during the last 75 years at the
+Koenigsbergh and Yale Observatories, that of the sixty-nine brighter stars,
+including those down to the 9th magnitude, only eight show any certain
+movement with reference to Alcyone. Since Alcyone has a proper motion or
+drift of 6" per century, this means that all the brightest stars except
+the eight mentioned are drifting with Alcyone and so form a true cluster,
+at approximately the same distance from the earth. Six of the eight stars
+which show relative drift are moving in the opposite direction to the
+movement of Alcyone, and at nearly the same rate, so that their motion is
+only apparent. They are really stationary, while Alcyone and the rest of
+the cluster are moving past them."[275] This tends to show that the faint
+stars are really _behind_ the cluster, and are unconnected with it.
+
+It is a popular idea with some people that the Pole Star is the nearest of
+all the stars to the celestial pole. But photographs show that there are
+many faint stars nearer to the pole than the Pole Star. The Pole Star is
+at present at a distance of 1 deg. 13' from the real pole of the heavens, but
+it is slowly approaching it. The minimum distance will be reached in the
+year 2104. From photographs taken by M. Flammarion at the Juvisy
+Observatory, he finds that there are at least 128 stars nearer to the pole
+than the Pole Star! The nearest star to the pole was, in the year 1902, a
+small star of about 12-1/2 magnitude, which was distant about 4 minutes of
+arc from the pole.[276] The estimated magnitude shows that the Pole Star
+is nearly 10,000 times brighter than this faint star!
+
+It has been found that Sirius is bright enough to cast a shadow under
+favourable conditions. On March 22, 1903, the distinguished French
+astronomer Touchet succeeded in photographing the shadow of a brooch cast
+by this brilliant star. The exposure was 1{h} 5{m}.
+
+Martinus Hortensius seems to have been the first to see stars in daylight,
+perhaps early in the seventeenth century. He mentions the fact in a letter
+to Gassendi dated October 12, 1636, but does not give the date of his
+observation. Schickard saw Arcturus in broad daylight early in 1632. Morin
+saw the same bright star half an hour after sunset in March, 1635.
+
+Some interesting observations were made by Professors Payne and H. C.
+Wilson, in the summer of 1904, at Midvale, Montana (U.S.A.), at a height
+of 4790 feet above sea-level. At this height they found the air very clear
+and transparent. "Many more stars were visible at a glance, and the
+familiar stars appeared more brilliant.... In the great bright cloud of
+the Milky Way, between [Greek: b] and [Greek: g] Cygni, one could count
+easily sixteen or seventeen stars, besides the bright ones [Greek: e] and
+[Greek: ch],[277] while at Northfield it is difficult to distinctly see
+eight or nine with the naked eye." Some nebulae and star fields were
+photographed with good results by the aid of a 2-1/2-inch Darlot lens and
+3 hours' exposure.[278]
+
+Prof. Barnard has taken some good stellar photographs with a lens of only
+1-1/2 inches in diameter, and 4 or 5 inches focus belonging to an
+ordinary "magic lantern"! He says that these "photographs with the small
+lens show us in the most striking manner how the most valuable and
+important information may be obtained with the simplest means."[279]
+
+With reference to the rising and setting of the stars due to the earth's
+rotation on its axis, the late Sir George B. Airy, Astronomer Royal of
+England, once said to a schoolmaster, "I should like to know how far your
+pupils go into the first practical points for which reading is scarcely
+necessary. Do they know that the stars rise and set? Very few people in
+England know it. I once had a correspondence with a literary man of the
+highest rank on a point of Greek astronomy, and found that he did not know
+it!"[280]
+
+Admiral Smyth says, "I have been struck with the beautiful blue tint of
+the smallest stars visible in my telescope. This, however, may be
+attributed to some optical peculiarity." This bluish colour of small stars
+agrees with the conclusion arrived at by Prof. Pickering in recent years,
+that the majority of faint stars in the Milky Way have spectra of the
+Sirian type and, like that brilliant star, are of a bluish white colour.
+Sir William Herschel saw many stars of a redder tinge than other observers
+have noticed. Admiral Smyth says, "This may be owing to the effect of his
+metallic mirror or to some peculiarity of vision, or perhaps both."[281]
+
+The ancient astronomers do not mention any coloured stars except white and
+red. Among the latter they only speak of Arcturus, Aldebaran, Pollux,
+Antares, and Betelgeuse as of a striking red colour. To these Al-Sufi adds
+Alphard ([Greek: a] Hydrae).
+
+Sir William Herschel remarked that no decidedly green or blue star "has
+ever been noticed unassociated with a companion brighter than itself." An
+exception to Herschel's rule seems to be found in the case of the star
+[Greek: b] Librae, which Admiral Smyth called "pale emerald." Mr. George
+Knott observed it on May 19, 1852, as "beautiful pale green" (3.7 inches
+achromatic, power 80), and on May 9, 1872, as "fine pale green" (5.5
+inches achromatic, power 65).
+
+The motion of stars in the line of sight, as shown by the
+spectroscope--should theoretically alter their brightness in the course of
+time; those approaching the earth becoming gradually brighter, while those
+receding should become fainter. But the distance of the stars is so
+enormous that even with very high velocities the change would not become
+perceptible for ages. Prof. Oudemans found that to change the brightness
+of a star by only one-tenth of a magnitude--a quantity barely perceptible
+to the eye-a number of years would be necessary, which is represented by
+the formula
+
+      5916 years
+  -----------------
+  parallax x motion
+
+for a star approaching the earth, and for a receding star
+
+  6195 years
+  ----------
+    p x m
+
+This is in geographical miles, 1 geographical mile being equal to 4.61
+English miles.
+
+Reducing the above to English miles, and taking an average for both
+approaching and receding stars, we have
+
+  27,660 years
+  ------------
+     p x m
+
+where p = parallax in seconds of arc, and m = radial velocity in English
+miles per second.
+
+Prof. Oudemans found that the only star which could have changed in
+brightness by one-tenth of a magnitude since the time of Hipparchus is
+Aldebaran. This is taking its parallax as 0".52. But assuming the more
+reliable parallax 0".12 found by Dr. Elkin, this period is 4-1/3 times
+longer. For Procyon, the period would be 5500 years.[282] The above
+calculation shows how absurd it is to suppose that any star could have
+gained or lost in brightness by motion in the line of sight during
+historical times. The "secular variation" of stars is quite another
+thing. This is due to physical changes in the stars themselves.
+
+The famous astronomer Halley, the second Astronomer Royal at Greenwich,
+says (_Phil. Trans._, 1796), "Supposing the number of 1st magnitude stars
+to be 13, at twice the distance from the sun there may be placed four
+times as many, or 52; which with the same allowance would nearly represent
+the star we find to be of the 2nd magnitude. So 9 x 13, or 117, for those
+at three times the distance; and at ten times the distance 100 x 13, or
+1300 stars; of which distance may probably diminish the light of any of
+the stars of the 1st magnitude to that of the 6th, it being but the
+hundredth part of what, at their present distance, they appear with." This
+agrees with the now generally accepted "light ratio" of 2.512 for each
+magnitude, which makes a first magnitude star 100 times the light of a 6th
+magnitude.
+
+On the 4th of March, 1796,[283] the famous French astronomer Lalande
+observed on the meridian a star of small 6th magnitude, the exact position
+of which he determined. On the 15th of the same month he again observed
+the star, and the places found for 1800 refer to numbers 16292-3 of the
+reduced catalogue. In the observation of March 4 he attached the curious
+remark, "Etoile singuliere" (the observation of March 15 is without
+note). This remark of Lalande has puzzled observers who failed to find any
+peculiarity about the star. Indeed, "the remark is a strange one for the
+observer of so many thousands of stars to attach unless there was really
+something singular in the star's aspect at the time." On the evening of
+April 18, 1887, the star was examined by the present writer, and the
+following is the record in his observing book, "Lalande's etoile
+singuliere (16292-3) about half a magnitude less than [Greek: e] Cancri.
+With the binocular I see two streams of small stars branching out from it,
+north preceding like the tails of comet." This may perhaps have something
+to do with Lalande's curious remark.
+
+The star numbered 1647 in Baily's _Flamsteed Catalogue_ is now known to
+have been an observation of the planet Uranus.[284]
+
+Prof. Pickering states that the fainter stars photographed with the 8-inch
+telescope at Cambridge (U.S.A.) are invisible to the eye in the 15-inch
+telescope.[285]
+
+Sir Norman Lockyer finds that the lines of sulphur are present in the
+spectrum of the bright star Rigel ([Greek: b] Orionis).[286]
+
+About 8-1/2 deg. south of the bright star Regulus ([Greek: a] Leonis) is a
+faint nebula (H I, 4 Sextantis). On or near this spot the Capuchin monk De
+Rheita fancied he saw, in the year 1643, a group of stars representing
+the napkin of S. Veronica--"sudarium Veronicae sive faciem Domini maxima
+similitudina in astris expressum." And he gave a picture of the napkin and
+star group. But all subsequent observers have failed to find any trace of
+the star group referred to by De Rheita![287]
+
+The Bible story of the star of the Magi is also told in connection with
+the birth of the sun-gods Osiris, Horus, Mithra, Serapis, etc.[288] The
+present writer has also heard it suggested that the phenomenon may have
+been an apparition of Halley's comet! But as this famous comet is known to
+have appeared in the year B.C. 11, and as the date of the Nativity was
+probably not earlier than B.C. 5, the hypothesis seems for this (and other
+reasons) to be inadmissible. It has also been suggested that the
+phenomenon might have been an appearance of Tycho Brahe's temporary star
+of 1572, known as the "Pilgrim star"; but there seems to be no real
+foundation for such an hypothesis. There is no reason to think that
+"temporary" or new stars ever appear a second time.
+
+Admiral Smyth has well said, "It checks one's pride to recollect that if
+our sun with the whole system of planets, asteroids, and moons, and comets
+were to be removed from the spectator to the distance of the nearest
+fixed star, not one of them would be visible, except the sun, which would
+then appear but as a star of perhaps the 2nd magnitude. Nay, more, were
+the whole system of which our globe forms an insignificant member, with
+its central luminary, suddenly annihilated, no effect would be produced on
+those unconnected and remote bodies; and the only annunciation of such a
+catastrophe in the Sidereal "Times" would be that a small star once seen
+in a distant quarter of the sky had ceased to shine."[289]
+
+Prof. George C. Comstock finds that the average parallax of 67 selected
+stars ranging in brightness between the 9th and the 12th magnitude, is of
+the value of 0".0051.[290] This gives a distance representing a journey
+for light of about 639 years!
+
+Mr. Henry Norris Russell thinks that nearly all the bright stars in the
+constellation of Orion are practically at the same distance from the
+earth. His reasons for this opinion are: (1) the stars are similar in
+their spectra and proper motions, (2) their proper motions are small,
+which suggests a small parallax, and therefore a great distance from the
+earth. Mr. Russell thinks that the average parallax of these stars may
+perhaps be 0".005, which gives a distance of about 650 "light
+years."[291]
+
+According to Sir Norman Lockyer's classification of the stars, the order
+of _increasing_ temperature is represented by the following, beginning
+with those in the earliest stage of stellar evolution:--Nebulae, Antares,
+Aldebaran, Polaris, [Greek: a] Cygni, Rigel, [Greek: e] Tauri, [Greek: b]
+Crucis. Then we have the hottest stars represented by [Greek: e] Puppis,
+[Greek: g] Argus, and Alnitam ([Greek: e] Orionis). _Decreasing_
+temperature is represented by (in order), Achernar, Algol, Markab, Sirius,
+Procyon, Arcturus, 19 Piscium, and the "Dark Stars."[292] But other
+astronomers do not agree with this classification. Antares and Aldebaran
+are by some authorities considered to be _cooling_ suns.
+
+According to Ritter's views of the Constitution of the Celestial Bodies,
+if we "divide the stars into three classes according to age corresponding
+to these three stages of development, we shall assign to the first class,
+A, those stars still in the nebular phase of development; to the second
+class, B, those in the transient stage of greatest brilliancy; and to the
+class C, those stars which have already entered into the long period of
+slow extinction. It should be noted in this classification that we refer
+to relative and not absolute age, since a star of slight mass passes
+through the successive phases of its development more rapidly than the
+star of greater mass."[293] Ritter comes to the conclusion that "the
+duration of the period in which the sun as a star had a greater brightness
+than at present was very short in comparison with the period in which it
+had and will continue to have a brightness differing only slightly from
+its present value."[294]
+
+In a valuable and interesting paper on "The Evolution of Solar
+Stars,"[295] Prof. Schuster says that "measurements by E. F. Nichols on
+the heat of Vega and Arcturus indicated a lower temperature for Arcturus,
+and confirms the conclusion arrived at on other grounds, that the hydrogen
+stars have a higher temperature than the solar stars." "An inspection of
+the ultraviolet region of the spectrum gives the same result. These
+different lines of argument, all leading to the same result, justify us in
+saying that the surface temperature of the hydrogen stars is higher than
+that of the solar stars. An extension of the same reasoning leads to the
+belief that the helium stars have a temperature which is higher still."
+Hence we have Schuster, Hale, and Sir William Huggins in agreement that
+the Sirian stars are hotter than the solar stars; and personally I agree
+with these high authorities. The late Dr. W. E. Wilson, however, held the
+opinion that the sun is hotter that Sirius!
+
+Schuster thinks that Lane's law does not apply to the temperature of the
+photosphere and the absorbing layers of the sun and stars, but only to the
+portions between the photosphere and the centre, which probably act like a
+perfect gas. On this view he says the interior might become "hotter and
+hotter until the condensation had reached a point at which the laws of
+gaseous condensation no longer hold."
+
+With reference to the stars having spectra of the 3rd and 4th type
+(usually orange and red in colour), Schuster says--
+
+    "The remaining types of spectra belong to lower temperature still, as
+    in place of metallic lines, or in addition to them, certain bands
+    appear which experiments show us invariably belong to lower
+    temperature than the lines of the same element.
+
+    "If an evolutionary process has been going on, which is similar for
+    all stars, there is little doubt that from the bright-line stars down
+    to the solar stars the order has been (1) helium or _Orion_ stars, (2)
+    hydrogen or Sirian stars, (3) calcium or Procyon stars, (4) solar or
+    Capellan stars."
+
+My investigations on "The Secular Variation of Starlight" (_Studies in
+Astronomy_, chap. 17, and _Astronomical Essays_, chap. 12) based on a
+comparison of Al-Sufi's star magnitudes (tenth century) with modern
+estimates and measures, tend strongly to confirm the above views.
+
+With regard to the 3rd-type stars, such as Betelgeuse and Mira Ceti,
+Schuster says, "It has been already mentioned that observers differ as to
+whether their position is anterior to the hydrogen or posterior to the
+solar stars, and there are valid arguments on both sides."
+
+Scheiner, however, shows, from the behaviour of the lines of magnesium,
+that stars of type I. (Sirian) are the hottest, and type III. the coolest,
+and he says, we have "for the first time a direct proof of the correctness
+of the physical interpretation of Vogel's spectral classes, according to
+which class II. is developed by cooling from I., and III. by a further
+process of cooling from II."[296]
+
+Prof. Hale says that "the resemblance between the spectra of sun-spots and
+of 3rd-type stars is so close as to indicate that the same cause is
+controlling the relative intensities of many lines in both instances. This
+cause, as the laboratory work indicates, is to be regarded as reduced
+temperature."[297]
+
+According to Prof. Schuster, "a spectrum of bright lines may be given by a
+mass of luminous gas, even if the gas is of great thickness. There is,
+therefore, no difficulty in explaining the existence of stars giving
+bright lines." He thinks that the difference between "bright line" stars
+and those showing dark lines depends upon the rate of increase of the
+temperature from the surface towards the centre. If this rate is slow,
+bright lines will be seen. If the rate of increase is rapid, the
+dark-line spectrum shown by the majority of the stars will appear. This
+rate, he thinks, is regulated by the gravitational force. So that in the
+early stages of condensation bright lines are more likely to occur. "If
+the light is not fully absorbed," both bright and dark lines of the same
+element may be visible in the same star. Schuster considers it quite
+possible that if we could remove the outer layers of the Sun's atmosphere,
+we should obtain a spectrum of bright lines.[298]
+
+M. Stratonoff finds that stars having spectra of the Orion and Sirian
+types--supposed to represent an early stage in stellar evolution--tend to
+congregate in or near the Milky Way. Star clusters in general show a
+similar tendency, "but to this law the globular clusters form an
+exception."[299] We may add that the spiral nebulae--which seem to be
+scattered indifferently over all parts of the sky--also seem to form an
+exception; for the spectra of these wonderful objects seem to show that
+they are really star clusters, in which the components are probably
+relatively small; that is, small in comparison with our sun.
+
+If we accept the hypothesis that suns and systems were evolved from
+nebulae, and if we consider the comparatively small number of nebulae
+hitherto discovered in the largest telescopes--about half a million; and
+if we further consider the very small number of red stars, or those having
+spectra of the third and fourth types--usually considered to be dying-out
+suns--we seem led to the conclusion that our sidereal system is now at
+about the zenith of its life-history; comparatively few nebulae being left
+to consolidate into stars, and comparatively few stars having gone far on
+the road to the final extinction of their light.
+
+Prof. Boss of Albany (U.S.A.) finds that about forty stars of magnitudes
+from 3-1/2 to 7 in the constellation Taurus are apparently drifting
+together towards one point. These stars are included between about R.A.
+3{h} 47{m} to 5{h} 4{m}, and Declination + 5 deg. to + 23 deg. (that is, in the
+region surrounding the Hyades). These motions apparently converge to a
+point near R.A. 6{h}, Declination + 7 deg. (near Betelgeuse). Prof. Boss has
+computed the velocity of the stars in this group to be 45.6 kilometres
+(about 28 miles) a second towards the "vanishing point," and he estimated
+the average parallax of the group to be 0".025--about 130 years' journey
+for light. Although the motions are apparently converging to a point, it
+does not follow that the stars in question will, in the course of ages,
+meet at the "vanishing point." On the contrary, the observed motions show
+that the stars are moving in parallel lines through space. About 15
+kilometres of the observed speed is due to the sun's motion through space
+in the opposite direction. Prof. Campbell finds from spectroscopic
+measures that of these forty stars, nine are receding from the earth with
+velocities varying from 12 to 60 kilometres a second, and twenty-three
+others with less velocities than 38 kilometres.[300] It will be obvious
+that, as there is a "vanishing point," the motion in the line of sight
+must be one of _recession_ from the earth.
+
+It has been found that on an average the parallax of a star is about
+one-seventh of its "proper motion."[301]
+
+Adopting Prof. Newcomb's parallax of 0".14 for the famous star 1830
+Groombridge, the velocity perpendicular to the line of sight is about 150
+miles a second. The velocity _in_ the line of sight--as shown by the
+spectroscope--is 59 miles a second approaching the earth. Compounding
+these two velocities we find a velocity through space of about 161 miles a
+second!
+
+An eminent American writer puts into the mouth of one of his characters, a
+young astronomer, the following:--
+
+                          "I read the page
+  Where every letter is a glittering sun."
+
+From an examination of the heat radiated by some bright stars, made by
+Dr. E. F. Nicholls in America with a very sensitive radiometer of his own
+construction, he finds that "we do not receive from Arcturus more heat
+than we should from a candle at a distance of 5 or 6 miles."
+
+With reference to the progressive motion of light, and the different times
+taken by light to reach the earth from different stars, Humboldt says,
+"The aspect of the starry heavens presents to us objects of _unequal
+date_. Much has long ceased to exist before the knowledge of its presence
+reaches us; much has been otherwise arranged."[302]
+
+The photographic method of charting the stars, although a great
+improvement on the old system, seems to have its disadvantages. One of
+these is that the star images are liable to disappear from the plates in
+the course of time. The reduction of stellar photograph plates should,
+therefore, be carried out as soon as possible after they are taken. The
+late Dr. Roberts found that on a plate originally containing 364 stars, no
+less than 130 had completely disappeared in 9-1/4 years!
+
+It has been assumed by some writers on astronomy that the faint stars
+visible on photographs of the Pleiades are at practically the same
+distance from the earth as the brighter stars of the cluster, and that
+consequently there must be an enormous difference in actual size between
+the brighter and fainter stars. But there is really no warrant for any
+such assumption. Photographs of the vicinity show that the sky all round
+the Pleiades is equally rich in faint stars. It seems, therefore, more
+reasonable to suppose that most of the faint stars visible in the Pleiades
+are really far behind the cluster in space. For if _all_ the faint stars
+visible on photographs belonged to the cluster, then if we imagine the
+cluster removed, a "hole" would be left in the sky, which is of course
+utterly improbable, and indeed absurd. An examination of the proper
+motions tends to confirm this view of the matter, and indicates that the
+Pleiades cluster is a comparatively small one and simply projected on a
+background of fainter stars.
+
+It has long been suspected that the famous star 61 Cygni, which is a
+double star, forms a binary system--that is, that the two stars composing
+it revolve round their common centre of gravity and move together through
+space. But measures of parallax made by Herman S. Davis and Wilsing seem
+to show a difference of parallax between the two components of about 0.08
+of a second of arc. This difference of parallax implies a distance of
+about 2-1/4 "light years" between the two stars, and "if this is correct,
+the stars are too remote to form a binary system. The proper motions of
+5".21 and 5".15 seem to show that they are moving in nearly parallel
+directions; but are probably slowly separating." Mr. Lewis, however,
+thinks that a physical connection probably exists.[303]
+
+Dante speaks of the four bright stars of the Southern Cross as
+emblematical of the four cardinal virtues, Justice, Temperance, Fortitude,
+and Prudence; and he seems to refer to the stars Canopus, Achernar, and
+Foomalhaut under the symbols of Faith, Hope, and Charity. The so-called
+"False Cross" is said to be formed by the stars [Greek: k], [Greek: d],
+[Greek: e], and [Greek: i] of the constellation Argo Navis. But it seems
+to me that a better (although larger) cross is formed by the stars [Greek:
+a] Centauri and [Greek: a], [Greek: b], and [Greek: g] of Triangulum
+Australis.
+
+Mr. Monck has pointed out that the names of the brightest stars seem to be
+arranged alphabetically in order of colour, beginning with red and ending
+with blue. Thus we have Aldebaran, Arcturus, Betelgeuse, Capella, Procyon,
+Regulus, Rigel, Sirius, Spica and Vega. But as the origin of these names
+is different, this must be merely a curious coincidence.[304] And, to my
+eye at least, Betelgeuse is redder than Arcturus.
+
+The poet Longfellow speaks of the--
+
+  "Stars, the thoughts of God in the heavens,"[305]
+
+and Drayton says--
+
+  "The stars to me an everlasting book
+  In that eternal register, the sky."[306]
+
+Observing at a height of 12,540 feet on the Andes, the late Dr. Copeland
+saw Sirius with the naked eye less than 10 minutes before sunset.[307] He
+also saw Jupiter 3{m} 47{s} before sunset; and the following bright
+stars--Canopus, 0{m} 52{s} before sunset; Rigel ([Greek: b] Orionis) 16{m}
+32{s} after sunset; and Procyon 11{m} 28{s} after sunset. From a height of
+12,050 feet at La Paz, Bolivia, he saw with the naked eye in February,
+1883, ten stars in the Pleiades in full moonlight, and seventeen stars in
+the Hyades. He also saw [Greek: s] Tauri double.[308]
+
+Humboldt says, "In whatever point the vault of heaven has been pierced by
+powerful and far-penetrating telescopic instruments, stars or luminous
+nebulae are everywhere discoverable, the former in some cases not exceeding
+the 20th or 24th degree of telescopic magnitude."[309] But this is a
+mistake. No star of even the 20th magnitude has ever been seen by any
+telescope. Even on the best photographic plates it is doubtful that any
+stars much below the 18th magnitude are visible. To show a star of the
+20th magnitude--if such stars exist--would require a telescope of 144
+inches or 12 feet in aperture. To show a star of the 24th magnitude--if
+such there be--an aperture of 33 feet would be necessary![310]
+
+It is a popular idea that stars may be seen in the daytime from the bottom
+of a deep pit or high chimney. But this has often been denied. Humboldt
+says, "While practically engaged in mining operations, I was in the habit,
+during many years, of passing a great portion of the day in mines where I
+could see the sky through deep shafts, yet I never was able to observe a
+star."[311]
+
+Stars may, however, be seen in the daytime with even small telescopes. It
+is said that a telescope of 1 inch aperture will show stars of the 2nd
+magnitude; 2 inches, stars of the 3rd magnitude; and 4 inches, stars of
+the 4th magnitude. But I cannot confirm this from personal observation. It
+may be so, but I have not tried the experiment.
+
+Sir George Darwin says--
+
+    "Human life is too short to permit us to watch the leisurely procedure
+    of cosmical evolution, but the celestial museum contains so many
+    exhibits that it may become possible, by the aid of theory, to piece
+    together, bit by bit, the processes through which stars pass in the
+    course of their evolutions."[312]
+
+The so-called "telluric lines" seen in the solar spectrum, are due to
+water vapour in the earth's atmosphere. As the light of the stars also
+passes through the atmosphere, it is evident that these lines should also
+be visible in the spectra of the stars. This is found to be the case by
+Prof. Campbell, Director of the Lick Observatory, who has observed all the
+principal bands in the spectrum of every star he has examined.[313]
+
+The largest "proper motion" now known is that of a star of the 8-1/2
+magnitude in the southern hemisphere, known as Cordoba Zone V. No. 243.
+Its proper motion is 8.07 seconds of arc per annum, thus exceeding that of
+the famous "runaway star," 1830 Groombridge, which has a proper motion of
+7.05 seconds per annum. This greater motion is, however, only apparent.
+Measures of parallax show that the southern "runaway" is much nearer to us
+than its northern rival, its parallax being 0".32, while that of
+Groombridge 1830 is only 0".14. With these data the actual velocity across
+the line of sight can be easily computed. That of the southern star comes
+out 80 miles a second, while that of Groombridge 1830 is 148 miles a
+second. The actual velocity of Arcturus is probably still greater.
+
+The poet Barton has well said--
+
+  "The stars! the stars! go forth at night,
+    Lift up thine eyes on high,
+  And view the countless orbs of light,
+    Which gem the midnight sky.
+  Go forth in silence and alone,
+    This glorious sight to scan,
+  And bid the humbled spirit own
+    The littleness of man."
+
+
+
+
+CHAPTER XV
+
+Double and Binary Stars
+
+
+Prof. R. G. Aitken, the eminent American observer of double stars, finds
+that of all the stars down to the 9th magnitude--about the faintest
+visible in a powerful binocular field-glass--1 in 18, or 1 in 20, on the
+average, are double, with the component stars less than 5 seconds of arc
+apart. This proportion of double stars is not, however, the same for all
+parts of the sky; while in some regions double stars are very scarce, in
+other places the proportion rises to 1 in 8.
+
+For the well-known binary star Castor ([Greek: a] Geminorum), several
+orbits have been computed with periods ranging from 232 years (Maedler) to
+1001 years (Doberck). But Burnham finds that "the orbit is absolutely
+indeterminate at this time, and likely to remain so for another century or
+longer."[314] Both components are spectroscopic binaries, and the system
+is a most interesting one.
+
+The well-known companion of Sirius became invisible in all telescopes in
+the year 1890, owing to its near approach to its brilliant primary. It
+remained invisible until August 20, 1896, when it was again seen by Dr.
+See at the Lowell Observatory.[315] Since then its distance has been
+increasing, and it has been regularly measured. The maximum distance will
+be attained about the year 1922.
+
+The star [Greek: b] Cephei has recently been discovered to be a
+spectroscopic binary with the wonderfully short period of 4{h} 34{m}
+11{s}. The orbital velocity is about 10-1/2 miles a second, and as this
+velocity is not very great, the distance between the components must be
+very small, and possibly the two component bodies are revolving in actual
+contact. The spectrum is of the "Orion type."[316]
+
+According to Slipher the spectroscopic binary [Greek: g] Geminorum has the
+comparatively long period (for a spectroscopic binary) of about 3-1/2
+years. This period is comparable with that of the telescopic binary
+system, [Greek: d] Equulei (period about 5.7 years). The orbit is quite
+eccentric. I have shown elsewhere[317] that [Greek: g] Geminorum has
+probably increased in brightness since the time of Al-Sufi (tenth
+century). Possibly its spectroscopic duplicity may have something to do
+with the variation in its light.
+
+With reference to the spectra of double stars, Mr. Maunder suggests that
+the fact of the companion of a binary star showing a Sirian spectrum while
+the brighter star has a solar spectrum may be explained by supposing that,
+on the theory of fission, "the smaller body when thrown off consisted of
+the lighter elements, the heavier remaining in the principal star. In
+other words, in these cases spectral type depends upon original chemical
+constitution, and not upon the stage of stellar development
+attained."[318]
+
+A curious paradox with reference to binary stars has recently come to
+light. For many years it was almost taken for granted that the brighter
+star of a pair had a larger mass than the fainter component. This was a
+natural conclusion, as both stars are practically at the same distance
+from the earth. But it has been recently found that in some binary stars
+the fainter component has actually the larger mass! Thus, in the binary
+star [Greek: e] Hydrae, the "magnitude" of the component stars are 3 and 6,
+indicating that the brighter star is about 16 times brighter than the
+fainter component. Yet calculations by Lewis show that the fainter star
+has 6 times the mass of the brighter, that is, contains 6 times the
+quantity of matter! In the well-known binary 70 Ophiuchi, Prey finds that
+the fainter star has about 4 times the mass of the brighter! In 85
+Pegasi, the brighter star is about 40 times brighter than its companion,
+while Furner finds that the mass of the fainter star is about 4 times that
+of the brighter! And there are other similar cases. In fact, in these
+remarkable combinations of suns the fainter star is really the "primary,"
+and is, so far as mass is concerned, "the predominant partner." This is a
+curious anomaly, and cannot be well explained in the present state of our
+knowledge of stellar systems. In the case of [Greek: a] Centauri the
+masses of the components are about equal, while the primary star is about
+3 times brighter than the other. But here the discrepancy is
+satisfactorily explained by the difference in character of the spectra,
+the brighter component having a spectrum of the solar type, while the
+fainter seems further advanced on the downward road of evolution, that is,
+more consolidated and having, perhaps, less intrinsic brightness of
+surface.
+
+In the case of Sirius and its faint attendant, the mass of the bright star
+is about twice the mass of the satellite, while its light is about 40,000
+times greater! Here the satellite is either a cooled-down sun or perhaps a
+gaseous nebula. There seems to be no other explanation of this curious
+paradox. The same remark applies to Procyon, where the bright star is
+about 100,000 times brighter than its faint companion, although its mass
+is only 5 times greater.
+
+The bright star Capella forms a curious anomaly or paradox. Spectroscopic
+observations show that it is a very close binary pair. It has been seen
+"elongated" at the Greenwich Observatory with the great 28-inch
+refractor--the work of Sir Howard Grubb--and the spectroscopic and visual
+measurements agree in indicating that its mass is about 18 times the mass
+of the sun. But its parallax (about 0".08) shows that it is about 128
+times brighter than the sun! This great brilliancy is inconsistent with
+the star's computed mass, which would indicate a much smaller brightness.
+The sun placed at the distance of Capella would, I find, shine as a star
+of about 5-1/2 magnitude, while Capella is one of the brightest stars in
+the sky. As the spectrum of Capella's light closely resembles the solar
+spectrum, we seem justified in assuming that the two bodies have pretty
+much the same physical composition. The discrepancy between the computed
+and actual brightness of the star cannot be explained satisfactorily, and
+the star remains an astronomical enigma.
+
+Three remarkable double-star systems have been discovered by Dr. See in
+the southern hemisphere. The first of these is the bright star [Greek: a]
+Phoenicis, of which the magnitude is 2.4, or only very slightly fainter
+than the Pole Star. It is attended by a faint star of the 13th magnitude
+at a distance of less than 10 seconds (1897). The bright star is of a
+deep orange or reddish colour, and the great difference in brightness
+between the component stars "renders the system both striking and
+difficult." The second is [Greek: m] Velorum, a star of the 3rd magnitude,
+which has a companion of the 11th magnitude, and only 2-1/2" from its
+bright primary (1897). Dr. See describes this pair as "one of the most
+extraordinary in the heavens." The third is [Greek: e] Centauri, of 2-1/2
+magnitude, with a companion of 13-1/2 magnitude at a distance of 5".65
+(1897); colours yellow and purple. This pair is "extremely difficult,
+requiring a powerful telescope to see it." Dr. See thinks that these three
+objects "may be regarded as amongst the most splendid in the heavens."
+
+The following notes are from Burnham's recently published _General
+Catalogue of Double Stars_.
+
+The Pole Star has a well-known companion of about the 9th magnitude, which
+is a favourite object for small telescopes. Burnham finds that the bright
+star and its faint companion are "relatively fixed," and are probably only
+an "optical pair." Some other companions have been suspected by amateur
+observers, but Burnham finds that "there is nothing nearer" than the known
+companion within the reach of the great 36-inch telescope of the Lick
+Observatory (_Cat._, p. 299).
+
+The well-known companion to the bright star Rigel ([Greek: b] Orionis)
+has been suspected for many years to be a close double star. Burnham
+concludes that it is really a binary star, and its "period may be shorter
+than that of any known pair" (_Cat._, p. 411).
+
+Burnham finds that the four brighter stars in the trapezium in the great
+Orion nebula (in the "sword") are relatively fixed (_Cat._, p. 426).
+
+[Greek: g] Leonis. This double star was for many years considered to be a
+binary, but Burnham has shown that all the measures may be satisfactorily
+represented by a straight line, and that consequently the pair merely
+forms an "optical double."
+
+42 Comae Berenices. This is a binary star of which the orbit plane passes
+nearly through the earth. The period is about 25-1/2 years, and Burnham
+says the orbit "is as accurately known as that of any known binary."
+
+[Greek: s] Coronae Borealis. Burnham says that the orbits hitherto
+computed--with periods ranging from 195 years (Jacob) to 846 years
+(Doberck) are "mere guess work," and it will require the measures of at
+least another century, and perhaps a much longer time, to give an
+approximate period (_Cat._, p. 209). So here is some work left for
+posterity to do in this field.
+
+70 Ophiuchi. With reference to this well-known binary star, Burnham says,
+"the elements of the orbit are very accurately known." The periods
+computed range from 86.66 years (Doolittle) to 98.15 years (Powell). The
+present writer found a period of 87.84 years, which cannot be far from the
+truth. Burnham found 87.75 years (_Cat._, p. 774). In this case there is
+not much left for posterity to accomplish.
+
+61 Cygni. With reference to this famous star Burnham says, "So far the
+relative motion is practically rectilinear. If the companion is moving in
+a curved path, it will require the measures of at least another
+half-century to make this certain. The deviation of the measured positions
+during the last 70 years from a right line are less than the average
+errors of the observations."
+
+Burnham once saw a faint companion to Sirius of the 16th magnitude, and
+measured its position with reference to the bright star (280 deg..6: 40".25:
+1899.86). But he afterwards found that it was "not a real object but a
+reflection from Sirius" (in the eye-piece). Such false images are called
+"ghosts."
+
+With reference to the well-known double (or rather quadruple) star [Greek:
+e] Lyrae, near Vega, and supposed faint stars near it, Burnham says, "From
+time to time various small stars in the vicinity have been mapped, and
+much time wasted in looking for and speculating about objects which only
+exist in the imagination of the observer." He believes that many of these
+faint stars, supposed to have been seen by various observers, are merely
+"ghosts produced by reflection."
+
+The binary star [Greek: z] Booetis, which has long been suspected of small
+and irregular variation of light, showed remarkable spectral changes in
+the year 1905,[319] somewhat similar to those of a _nova_, or temporary
+star. It is curious that such changes should occur in a star having an
+ordinary Sirian type of spectrum!
+
+A curious quadruple system has been discovered by Mr. R. T. A. Innes in
+the southern hemisphere. The star [Greek: k] Toucani is a binary star with
+components of magnitudes 5 and 7.7, and a period of revolution of perhaps
+about 1000 years. Within 6' of this pair is another star (Lacaille 353),
+which is also a binary, with a period of perhaps 72 years. Both pairs have
+the same proper motion through space, and evidently form a vast quadruple
+system; for which Mr. Innes finds a possible period of 300,000 years.[320]
+
+It is a curious fact that the performance of a really good refracting
+telescope actually exceeds what theory would indicate! at least so far as
+double stars are concerned. For example, the famous double-star observer
+Dawes found that the distance between the components of a double star
+which can just be divided, is found by dividing 4".56 by the aperture of
+the object-glass in inches. Now theory gives 5".52 divided by the
+aperture. "The actual telescope--if a really good one--thus exceeds its
+theoretical requirements. The difference between theory and practice in
+this case seems to be due to the fact that in the 'spurious' star disc
+shown by good telescopes, the illumination at the edges of the star disc
+is very feeble, so that its full size is not seen except in the case of a
+very bright star."[321]
+
+
+
+
+CHAPTER XVI
+
+Variable Stars
+
+
+In that interesting work _A Cycle of Celestial Objects_, Admiral Smyth
+says (p. 275), "Geminiano Montanari, as far back as 1670, was so struck
+with the celestial changes, that he projected a work to be intituled the
+_Instabilities of the Firmament_, hoping to show such alterations as would
+be sufficient to make even Aristotle--were he alive--reverse his opinion
+on the incorruptibility of the spangled sky: 'There are now wanting in the
+heavens,' said he, 'two stars of the 2nd magnitude in the stem and yard of
+the ship Argo. I and others observed them in the year 1664, upon occasion
+of the comet that appeared in that year. When they first disappeared I
+know not; only I am sure that on April 10, 1668, there was not the least
+glimpse of them to be seen.'" Smyth adds, "Startling as this account
+is--and I am even disposed to question the fact--it must be recollected
+that Montanari was a man of integrity, and well versed in the theory and
+practice of astronomy; and his account of the wonder will be found--in
+good set Latin--in page 2202 of the _Philosophical Transactions_ for
+1671."
+
+There must be, I think--as Smyth suggests--some mistake in Montanari's
+observations, for it is quite certain that of the stars mentioned by
+Ptolemy (second century A.D.) there is no star of the 2nd magnitude now
+missing. It is true that Al-Sufi (tenth century) mentions a star of the
+_third_ magnitude mentioned by Ptolemy in the constellation of the Centaur
+(about 2 deg. east of the star [Greek: e] Centauri) which he could not find.
+But this has nothing to do with Montanari's stars. Montanari's words are
+very clear. He says, "_Desunt in Coelo duae stellae_ Secundae Magnitudinis
+_in_ Puppi Navis _ejusve Transtris_ Bayero [Greek: b] et [Greek: g],
+_prope_ Canem Majoris, _a me et aliis, occasione praesertim Cometae_ A. 1664
+_observatae et recognitae. Earum Disparitionem_ cui Anno debeam, non novi;
+_hoc indubium, quod a die_ 10 April, 1668, _ne_ vestigium quidem _illarum
+adesse amplius observe; caeteris circa eas etium quartae et quintae
+magnitudinis, immotis._" So the puzzle remains unsolved.
+
+Sir William Herschel thought that "of all stars which are singly visible,
+about one in thirty are undergoing an observable change."[322] Now taking
+the number of stars visible to the naked eye at 6000, this would give
+about 200 variable stars visible at maximum to the unaided vision. But
+this estimate seems too high. Taking all the stars visible in the largest
+telescopes--possibly about 100 millions--the proportion of variable stars
+will probably be much smaller still.
+
+The theory that the variation of light in the variable stars of the Algol
+type is due to a partial eclipse by a companion star (not necessarily a
+dark body) is now well established by the spectroscope, and is accepted by
+all astronomers. The late Miss Clarke has well said "to argue this point
+would be _enforcer une porte ouverte_."
+
+According to Dr. A. W. Roberts, the components of the following "Algol
+variables" "revolve in contact": V Puppis, X Carinae, [Greek: b] Lyrae, and
+[Greek: u] Pegasi. Of those V Puppis and [Greek: b] Lyrae are known
+spectroscopic binaries. The others are beyond the reach of the
+spectroscope, owing to their faintness.
+
+A very curious variable star of the Algol type is that known as R R
+Draconis. Its normal magnitude is 10, but at minimum it becomes invisible
+in a 7-1/2-inch refracting telescope. The variation must, therefore, be
+over 3 magnitudes, that is, at minimum its light must be reduced to about
+one-sixteenth of its normal brightness. The period of variation from
+maximum to minimum is about 2.83 days. The variation of light near minimum
+is extraordinarily rapid, the light decreasing by about 1 magnitude in
+half an hour.[323]
+
+A very remarkable variable star has been recently discovered in the
+constellation Auriga. Prof. Hartwig found it of the 9th magnitude on March
+6, 1908, the star "having increased four magnitudes in one day, whilst
+within eight days it was less than the 14th magnitude."[324] In other
+words its light increased at least one-hundredfold in eight days!
+
+The period of the well-known variable star [Greek: b] Lyrae seems to be
+slowly increasing. This Dr. Roberts (of South Africa) considers to be due
+to the component stars slowly receding from each other. He finds that "a
+very slight increase of one-thousandth part of the radius of the orbit
+would account for the augmentation in time, 30{m} in a century." According
+to the theory of stellar evolution the lengthening of the period of
+revolution of a binary star would be due to the "drag" caused by the tides
+formed by each component on the other.[325]
+
+M. Sebastian Albrecht finds that in the short-period variable star known
+as T Vulpeculae (and other variables of this class, such as Y Ophiuchi),
+there can be no eclipse to explain the variation of light (as in the case
+of Algol). The star is a spectroscopic binary, it is true, but the
+maximum of light coincides with the greatest velocity of _approach_ in
+the line of sight, and the minimum with the greatest velocity of
+_recession_. Thus the light curve and the spectroscopic velocity curve are
+very similar in shape, but one is like the other turned upside down. "That
+is, the two curves have a very close correspondence in phase in addition
+to correspondence of shape and period."[326]
+
+The star now known as W Ursae Majoris (the variability of which was
+discovered by Mueller and Kempf in 1902), and which lies between the stars
+[Greek: th] and [Greek: u] of that constellation, has the marvellously
+short period of 4 hours (from maximum to maximum). Messrs. Jordan and
+Parkhurst (U.S.A.), find from photographic plates that the star varies
+from 7.24 to 8.17 magnitude.[327] The light at maximum is, therefore, more
+than double the light at minimum. A sun which loses more than half its
+light and recovers it again in the short period of 4 hours is certainly a
+curious and wonderful object.
+
+In contrast with the above, the same astronomers have discovered a star in
+Perseus which seems to vary from about the 6th to the 7th magnitude in the
+very long period of 7-1/2 years! It is now known as X Persei, and its
+position for 1900 is R.A. 3{h} 49{m} 8{s}, Dec. N. 30 deg. 46', or about one
+degree south-east of the star [Greek: z] Persei. It seems to be a
+variable of the Algol type, as the star remained constant in light at
+about the 6th magnitude from 1887 to 1891. It then began to fade, and on
+December 1, 1897, it was reduced to about the 7th magnitude.
+
+On the night of August 20, 1886, Prof. Colbert, of Chicago, noticed that
+the star [Greek: z] Cassiopeiae increased in brightness "by quite half a
+magnitude, and about half an hour afterwards began to return to its normal
+magnitude."[328] This curious outburst of light in a star usually constant
+in brightness is (if true) a very unusual phenomenon. But a somewhat
+similar fluctuation of light is recorded by the famous German astronomer
+Heis. On September 26, 1850, he noted that the star "[Greek: z] Lyrae
+became, for a moment, _very bright_, and then again faint." (The words in
+his original observing book are: "[Greek: z] Lyrae wurde einen _Moment sehr
+hell_ und hierauf wieder dunkel.") As Heis was a remarkably accurate
+observer of star brightness, the above remark deserves the highest
+confidence.[329]
+
+The variable star known as the V Delphini was found to be invisible in the
+great 40-inch telescope of the Yerkes Observatory on July 20, 1900. Its
+magnitude was, therefore, below the 17th. At its maximum brightness it is
+about 7-1/2, or easily visible in an ordinary opera-glass, so that its
+range of variation is nearly, or quite, ten magnitudes. That is, its light
+at maximum is about 10,000 times its light at minimum. That a sun should
+vary in light to this enormous extent is certainly a wonderful fact. A
+variable discovered by Ceraski (and numbered 7579 in Chandlers' Catalogue)
+"had passed below the limit of the 40-inch in June, 1900, and was,
+therefore, not brighter than 17 mag."[330]
+
+The late Sir C. E. Peck and his assistant, Mr. Grover, made many valuable
+observations of variable stars at the Rousden Observatory during many
+years past. Among other interesting things noted, Peck sometimes saw faint
+stars in the field of view of his telescope which were at other times
+invisible for many months, and he suggested that these are faint variable
+stars with a range of brightness from the 13th to the 20th magnitude. He
+adds, "Here there is a practically unemployed field for the largest
+telescopes." Considering the enormous number of faint stars visible on
+stellar photographs the number of undiscovered variable stars must be very
+large.
+
+Admiral Smyth describes a small star near [Greek: b] Leonis, about 5'
+distant, of about 8th magnitude, and dull red. In 1864 Mr. Knott measured
+a faint star close to Smyth's position, but estimated it only 11.6
+magnitude. The Admiral's star would thereupon seem to be variable.[331]
+
+The famous variable star [Greek: e] Argus, which Sir John Herschel, when
+at the Cape of Good Hope in 1838, saw involved in dense nebulosity, was in
+April, 1869, "seen on the bare sky," with the great Melbourne telescope,
+"the nebula having disappeared for some distance round it." Other changes
+were noticed in this remarkable nebula. The Melbourne observers saw "three
+times as many stars as were seen by Herschel." But of course their
+telescope is much larger--48 inches aperture, compared with Herschel's 20
+inches.
+
+Prof. E. C. Pickering thinks that the fluctuations of light of the
+well-known variable star R Coronae (in the Northern Crown), "are unlike
+those of any known variable." This very curious object--one of the most
+curious in the heavens--sometimes remains for many months almost constant
+in brightness (just visible to the naked eye), and then rapidly fades in
+light by several magnitudes! Thus its changes of light in April and May,
+1905, were as follows:--
+
+  1905, April 1   6.0 magnitude
+          "  11   7.3     "
+          "  12   8.4     "
+         May  1  11.4     "
+          "   7  12.5     "
+
+Thus between April 1 and May 1, its light was reduced by over 5
+magnitudes. In other words, the light of the star on May 1 was reduced to
+less than one-hundredth of its light on April 1. If our sun were to
+behave in this way nearly all life would soon be destroyed on the face of
+the earth.
+
+M. H. E. Lau finds that the short-period variable star [Greek: d] Cephei
+varies slightly in colour as well as in light, and that the colour curve
+is parallel to the light curve. Near the minimum of light the colour is
+reddish yellow, almost as red as [Greek: z] Cephei; a day later it is pure
+yellow, and of about the same colour as the neighbouring [Greek: e]
+Cephei.[332] But it would not be easy to fully establish such slight
+variations of tint.
+
+A remarkably bright maximum of the famous variable Mira Ceti occurred in
+1906. In December of that year it was fully 2nd magnitude. The present
+writer estimated it 1.8, or nearly equal to the brightest on record--1.7
+observed by Sir William Herschel and Wargentin in the year 1779. From
+photographs of the spectrum taken by Mr. Slipher at the Lowell Observatory
+in 1907, he finds strong indications of the presence of the rather rare
+element vanadium in the star's surroundings. Prof. Campbell finds with the
+Mills spectrograph attached to the great 36-inch telescope of the Lick
+Observatory that Mira is receding from the earth at the apparently
+constant velocity of about 38 miles a second.[333] This, of course, has
+nothing to do with the variation in the star's light. Prof. Campbell
+failed to see any trace of the green line of hydrogen in the star's
+spectrum, while two other lines of the hydrogen series "glowed with
+singular intensity."
+
+Mr. Newall has found evidence of the element titanium in the spectrum of
+Betelgeuse ([Greek: a] Orionis); Mr. Goatcher and Mr. Lunt (of the Cape
+Observatory) find tin in Antares (and Scorpii). If the latter observation
+is confirmed it will be the first time this metal has been found in a
+star's atmosphere.[334]
+
+It is a curious fact that Al-Sufi (tenth century) does not mention the
+star [Greek: e] Aquilae, which lies closely north-west of [Greek: z]
+Aquilae, as it is now quite conspicuous to the naked eye. It was suspected
+of variation by Sir William Herschel. It was first recorded by Tycho Brahe
+about 1590, and he called it 3rd magnitude. Bayer also rated it 3, and
+since his time it has been variously estimated from 3-1/2 to 4. If it was
+anything like its present brightness (4.21 Harvard) in the tenth century
+it seems difficult to explain how it could have escaped Al-Sufi's careful
+scrutiny of the heavens, unless it is variable. Its colour seems reddish
+to me.
+
+Mr. W. T. Lynn has shown--and I think conclusively--that the so-called
+"new star" of A.D. 389 (which is said to have appeared near Altair in the
+Eagle) was really a comet.[335]
+
+Near the place of Tycho Brahe's great new star of 1572 (the "Pilgrim
+Star"), Hind and W. E. Plummer observed a small star (No. 129 of
+d'Arrest's catalogue of the region) which seemed to show small
+fluctuations of light, which "scarcely include a whole magnitude." This
+may possibly be identical with Tycho Brahe's wonderful star, and should be
+watched by observers. The place of this small star is (for 1865) R.A. 0{h}
+17{m} 18{s}, N.P.D. 26 deg. 37'.1. The region was examined by Prof. Burnham in
+1890 with the 36-inch telescope of the Lick Observatory. "None of the
+faint stars near the place presented any peculiarity worthy of remark, but
+three double stars were found."[336]
+
+With reference to the famous Nova (T) Coronae--the "Blaze Star" of
+1866--Prof. Barnard finds from careful comparisons with small stars in its
+vicinity that "the Nova is now essentially of the same brightness it was
+before the outburst of 1866 ... there seems to be no indication of motion
+in the _Nova_."
+
+With reference to the cause of "temporary" stars, or _novae_, as they are
+now called by astronomers--the late Prof. H. C. Vogel said--
+
+    "A direct collision of two celestial bodies is not regarded by Huggins
+    as an admissible explanation of the Nova; a partial collision has
+    little probability, and the most that can be admitted is perhaps the
+    mutual penetration and admixture of the outer gaseous envelopes of
+    the two bodies at the time of their closest approach. A more probable
+    explanation is given by an hypothesis which we owe to Klinkerfues, and
+    which has more recently been further developed by Wilsing, viz. that
+    by the very close passage of two celestial bodies enormous tidal
+    disturbances are produced and thereby changes in the brightness of the
+    bodies. In the case of the two bodies which form the Nova, it must be
+    assumed that these phenomena are displayed in the highest degree of
+    development, and that changes of pressure have been produced which
+    have caused enormous eruptions from the heated interior of the bodies;
+    the eruptions are perhaps accompanied by electrical actions, and are
+    comparable with the outbursts in our own sun, although they are on a
+    much larger scale."[337]
+
+It will be noticed that this hypothesis agrees with the fundamental
+assumption of the "Planetesimal Hypothesis" advocated by Professors
+Chamberlin and Moulton (see my _Astronomical Essays_, p. 324).
+
+The rush of a comparatively small body through a mass of gaseous matter
+seems also a very plausible hypothesis. This idea was originally advanced
+by Prof. Seeliger, and independently by Mr. Monck.
+
+With reference to the nebula which was observed round the great new star
+of 1901--Nova Persei--Prof. Lewis Bell supports the theory of Seeliger,
+which accounts for the apparent movements of the brightest portions of the
+nebula by supposing that the various parts of the highly tenuous matter
+were successively lighted up by the effects of a travelling
+electro-magnetic wavefront, and he shows that this theory agrees well with
+the observed phenomenon.[338] The "collision theory" which explained the
+sudden outburst of light by the meeting of two dark bodies in space, seems
+to be now abandoned by the best astronomers. The rapid cooling down of the
+supposed bodies indicated by the rapid decrease of light is quite
+inconsistent with this hypothesis.
+
+The rapid diminution in the light of some of these "new stars" is very
+remarkable. Thus the new star which suddenly blazed out near the nucleus
+of the great nebula in Andromeda in August, 1885, faded down in 5 months
+from "the limit of visibility to the naked eye to that of a 26-inch
+telescope"! A _large_ body could not cool in this way.
+
+Mr. Harold K. Palmer thinks that the "complete and astonishingly rapid
+changes of spectral type observed in the case of _Nova Cygni_ and _Nova
+Aurigae_, and likewise those observed in _Nova Normae_, _Nova Sagittarii_
+and _Nova Persei_, leave little doubt that the masses of these objects are
+small."[339]
+
+No less than 3748 variable stars had been discovered up to May, 1907. Of
+these 2909 were found at Harvard Observatory (U.S.A.) chiefly by means of
+photography.[340]
+
+The star 14. 1904 Cygni has a period of only 3 hours 14 minutes, which is
+the shortest period known for a variable star.
+
+A very interesting discovery has recently been made with reference to the
+star [Greek: m] Herculis. It has been long suspected of variable light
+with a period of 35 or 40 days, or perhaps irregular. Frost and Adams now
+find it to be a spectroscopic binary, and further observations at Harvard
+Observatory show that it is a variable of the Algol (or perhaps [Greek: b]
+Lyrae) type. The Algol variation of light was suggested by MM. Baker and
+Schlesinger. The period seems to be about 2.05 days.[341]
+
+The northern of the two "pointers" in the Plough (so called because they
+nearly point to the Pole Star) is about the 2nd magnitude, as Al-Sufi
+rated it. It was thought to be variable in colour by Klein, Konkoly, and
+Weber; and M. Lau has recently found a period of 50 days with a maximum of
+"jaune rougeatre" on April 2, 1902.
+
+The famous variable star [Greek: e] Argus did "not exceed the 8th
+magnitude" in February, 1907, according to Mr. Tebbutt.[342] This is the
+faintest ever recorded for this wonderful star.
+
+It is stated in _Knowledge_ (vol. 5, p. 3, January 4, 1884) that the
+temporary star of 1876 (in the constellation of Cygnus) "had long been
+known and catalogued as a telescopic star of the 9th magnitude with
+nothing to distinguish it from the common herd." But this is quite
+erroneous. The star was quite unknown before it was discovered by Schmidt
+at Athens on November 24 of that year. The remark apparently refers to the
+"Blaze Star" of 1866 in Corona Borealis, which _was_ known previously as a
+star of about the 9th magnitude before its sudden outburst on May 12 of
+that year.
+
+This "new star" of 1866--T Coronae, as it is now called--was, with the
+possible exception of Nova Persei (1901), the only example of a _nova_
+which was known to astronomers as a small star previous to the great
+outburst of light. It is the brightest of the _novae_ still visible. It was
+the first of these interesting objects to be examined with the
+spectroscope. It was observed by Burnham in the years 1904-1906 with the
+great 40-inch telescope of the Yerkes Observatory (U.S.A.). He found its
+colour white, or only slightly tinged with yellow. In August and
+September, 1906, he estimated its magnitude at about 9.3, and "it would
+seem therefore that the Nova is now essentially of the same brightness it
+was before the outburst in 1866." It shows no indication of motion.
+Burnham found no peculiarity about its telescopic image. A small and very
+faint nebula was found by Burnham a little following (that is east of) the
+_nova_.[343]
+
+The following details of the great new star of 1572--the "Pilgrim Star" of
+Tycho Brahe--are given by Delambre.[344] In November, 1572, it was
+brighter than Sirius, Vega, and Jupiter, and almost equal to Venus at its
+brightest. During December it resembled Jupiter in brightness. In January,
+1573, it was fainter and only a little brighter than stars of the 1st
+magnitude. In February and March it was equal to 1st magnitude stars, and
+in April and May was reduced to the 2nd magnitude. In June and July it was
+3rd magnitude; in September of the 4th, and at the end of 1573 it was
+reduced to the 5th magnitude. In February, 1574, it was 6th magnitude, and
+in March of the same year it became invisible to the naked eye.
+
+From this account it will be seen that the decrease in light of this
+curious object was much slower than that of Nova Persei (1901) ("the new
+star of the new century"). This would suggest that it was a much larger
+body.
+
+There were also changes in its colour. When it was of the brightness of
+Venus or Jupiter it shone with a white light. It then became golden, and
+afterwards reddish like Mars, Aldebaran, or Betelgeuse. It afterwards
+became of a livid white colour like Saturn, and this it retained as long
+as it was visible. Tycho Brahe thought that its apparent diameter might
+have been about 3-1/2 minutes of arc, and that it was possibly 361 times
+smaller than the earth(!) But we now know that these estimates were
+probably quite erroneous.
+
+Temporary stars were called by the ancient Chinese "Ke-sing," or guest
+stars.[345]
+
+A temporary star recorded by Ma-tuan-lin (Chinese Annals) in February,
+1578, is described as "a star as large as the sun." But its position is
+not given.[346]
+
+About the middle of September, 1878, Mr. Greely, of Boston (U.S.A.),
+reported to Mr. E. F. Sawyer (the eminent observer of variable stars)
+that, about the middle of August of that year, he had seen the famous
+variable star Mira Ceti of about the 2nd magnitude, although the star did
+not attain its usual maximum until early in October, 1878. Mr. Greely
+stated that several nights after he first saw Mira it had faded to the 4th
+or 5th magnitude. If there was no mistake in this observation (and Sawyer
+could find none) it was quite an unique phenomenon, as nothing of the sort
+has been observed before or since in the history of this famous star. It
+looks as if Mr. Greely had observed a new or "temporary" star near the
+place of Mira Ceti; but as the spot is far from the Milky Way, which is
+the usual seat of such phenomena, this hypothesis seems improbable.
+
+In the so-called Cepheid and Geminid variables of short period, the
+principal characteristics of the light variation are as follows:--
+
+    "1. The light varies without pause.
+
+    "2. The amount of their light variation is usually about 1 magnitude.
+
+    "3. Their periods are short--a few days only.
+
+    "4. They are of a spectral type approximately solar; no Orion, Sirian
+    or Arcturian stars having been found among them.
+
+    "5. They seem to be found in greater numbers in certain parts of the
+    sky, notably in the Milky Way, but exhibit no tendency to form
+    clusters.
+
+    "6. All those stars whose radial velocities have been studied have
+    been found to be binaries whose period of orbital revolution coincides
+    with that of their light change.
+
+    "7. The orbits, so far as determined, are all small, _a_ sin _i_ being
+    2,000,000 kilometres or less.
+
+    "8. Their maximum light synchronizes with their maximum velocity of
+    approach, and minimum light with maximum velocity of recession.
+
+    "9. No case has been found in which the spectrum of more than one
+    component has been bright enough to be recorded in the
+    spectrograms."[347]
+
+It is very difficult to find an hypothesis which will explain
+satisfactorily _all_ these characteristics, and attempts in this direction
+have not proved very successful. Mr. J. C. Duncan suggests the action of
+an absorbing atmosphere surrounding the component stars.
+
+On March 30, 1612, Scheiner saw a star near Jupiter. It was at first equal
+in brightness to Jupiter's satellites. It gradually faded, and on April 8
+of the same year it was only seen with much difficulty in a very clear
+sky. "After that date it was never seen again, although carefully looked
+for under favourable conditions."
+
+An attempted identification of Scheiner's star was made in recent years by
+Winnecke. He found that its position, as indicated by Scheiner, agrees
+with that of the Bonn _Durchmusterung_ star 15 deg., 2083 (8-1/2 magnitude).
+This star is not a known variable. Winnecke watched it for 17 years, but
+found no variation of light. From Scheiner's recorded observations his
+star seems to have reached the 6th magnitude, which is considerably
+brighter than the _Durchmusterung_ star watched by Winnecke.[348]
+
+With reference to the colours of the stars, the supposed change of colour
+in Sirius from red to white is well known, and will be considered in the
+chapter on the Constellations. The bright star Arcturus has also been
+suspected of variation in colour. About the middle of the nineteenth
+century Dr. Julius Schmidt, of Athens, the well-known observer of variable
+stars, thought it one of the reddest stars in the sky, especially in the
+year 1841, when he found its colour comparable with that of the planet
+Mars.[349] In 1852, however, he was surprised to find it yellow and devoid
+of any reddish tinge; in colour it was lighter than that of Capella. In
+1863, Mr. Jacob Ennis found it "decidedly orange." Ptolemy and Al-Sufi
+called it red.
+
+Mr. Ennis speaks of Capella as "blue" (classing it with Rigel), and
+comparing its colour with that of Vega![350] But the present writer has
+never seen it of this colour. To his eye it seems yellowish or orange. It
+was called red by Ptolemy, El Fergani, and Riccioli; but Al-Sufi says
+nothing about its colour.
+
+Of [Greek: b] Ursae Minoris, Heis, the eminent German astronomer said, "I
+have had frequent opportunities of convincing myself that the colour of
+this star is not always equally red; at times it is more or less yellow,
+at others most decidedly red."[351]
+
+Among double stars there are many cases in which variation of colour has
+been suspected. In some of these the difference in the recorded colour may
+possibly be due to "colour blindness" in some of the observers; but in
+others there seems to be good evidence in favour of a change. The
+following may be mentioned:--
+
+[Greek: e] Cassiopeiae. Magnitudes of the components about 4 and 7-1/2.
+Recorded as red and green by Sir John Herschel and South; but yellow and
+orange by Sestini.
+
+[Greek: i] Trianguli. Magnitudes 5-1/2 and 7. Secchi estimated them as
+white or yellow and blue; but Webb called them yellow and green (1862).
+
+[Greek: g] Leonis, 2 and 3-1/2. Sir William Herschel noted them white and
+reddish white; but Webb, light orange and greenish yellow.
+
+12 Canum Venaticorum, 2-1/2 and 6-1/2. White and red, Sir William
+Herschel; but Sir John Herschel says in 1830, "With all attention I could
+perceive no contrast of colours in the two stars." Struve found them both
+white in 1830, thus agreeing with Sir John Herschel. Sestini saw them
+yellow and blue in 1844; Smyth, in 1855, pale reddish white and lilac;
+Dembowski, in 1856, white and pale olive blue; and Webb, in 1862, flushed
+white and pale lilac.
+
+On October 13, 1907, Nova Persei, the great new star of 1901, was
+estimated to be only 11.44 magnitude, or about 11-1/2. When at its
+brightest this famous star was about zero magnitude; so that it has in
+about 6 years faded about 11-1/2 magnitudes in brightness; in other words,
+it has been reduced to 1/40000 of its greatest brilliancy!
+
+
+
+
+CHAPTER XVII
+
+Nebulae and Clusters
+
+
+In his interesting and valuable work on "The Stars," the late Prof.
+Newcomb said--
+
+    "Great numbers of the nebulae are therefore thousands of times the
+    dimensions of the earth's orbit, and most of them are thousands of
+    times the dimensions of the whole solar system. That they should be
+    completely transparent through such enormous dimensions shows their
+    extreme tenuity. Were our solar system placed in the midst of one of
+    them it is probable that we should not be able to find any evidence of
+    its existence"!
+
+Prof. Perrine thinks that the total number of the nebulae will ultimately
+be found to exceed a million.[352]
+
+Dr. Max Wolf has discovered a number of small nebulae in the regions near
+Algol and Nova Persei (the great "new star" of 1901). He says, "They
+mostly lie in two bands," and are especially numerous where the two bands
+meet, a region of 12 minutes of arc square containing no less than 148 of
+them. They are usually "round with central condensation," and form of
+Andromeda nebula.[353]
+
+Some small nebulae have been found in the vicinity of the globular
+clusters. They are described by Prof. Perrine as very small and like an
+"out of focus" image of a small star. "They appear to be most numerous
+about clusters which are farthest from the galaxy." Prof. Perrine says,
+"Practically all the small nebulae about the globular clusters are
+elliptical or circular. Those large enough to show structure are spirals.
+Doubtless the majority of these are spirals."[354] This seems further
+evidence in favour of the "spiral nebular hypothesis" of Chamberlin and
+Moulton.
+
+A great photographic nebula in Orion was discovered by Prof. Barnard in
+1894. In a drawing he gives of the nebula,[355] it forms a long streak
+beginning a little south of [Greek: g] Orionis (Bellatrix), passing
+through the star 38 Orionis north of 51 and south of 56 and 60 Orionis.
+Then turning south it sweeps round a little north of [Greek: k] Orionis;
+then over 29 Orionis, and ends a little to the west of [Greek: e] Orionis.
+There is an outside patch west of Rigel. Barnard thinks that the whole
+forms a vast spiral structure; probably connected with the "great nebula"
+in the "sword of Orion," which it surrounds.
+
+From calculations of the brightness of surface ("intrinsic brightness") of
+several "planetary" nebulae made by the present writer in the year 1905, he
+finds that the luminosity is very small compared with that of the moon.
+The brightest of those examined (_h_ 3365, in the southern hemisphere,
+near the Southern Cross) has a surface luminosity of only 1/400 of that of
+the moon.[356] The great nebulae in Orion and Andromeda seem to have "still
+smaller intrinsic brightness."
+
+Arago says--
+
+    "The spaces which precede or which follow simple nebulae, and _a
+    fortiori_ groups of nebulae, contain generally few stars. Herschel
+    found this rule to be invariable. Thus every time that, during a short
+    interval, no star appeared, in virtue of the diurnal motion, to place
+    itself in the field of his motionless telescope, he was accustomed to
+    say to the secretary who assisted him (Miss Caroline Herschel),
+    'Prepare to write; nebulae are about to arrive.'"[357]
+
+Commenting on this remark of Arago, the late Herbert Spencer says--
+
+    "How does this fact consist with the hypothesis that nebulae are remote
+    galaxies? If there were but one nebula, it would be a curious
+    coincidence were this one nebula so placed in the distant regions of
+    space as to agree in direction with a starless spot in our sidereal
+    system! If there were but two nebulae, and both were so placed, the
+    coincidence would be excessively strange. What shall we say on
+    finding that they are habitually so placed? (the last five words
+    replace some that are possibly a little too strong).... When to the
+    fact that the general mass of nebulae are antithetical in position to
+    the general mass of the stars, we add the fact that local regions of
+    nebulae are regions where stars are scarce, and the further fact that
+    single nebulae are habitually found in comparatively starless spots,
+    does not the proof of a physical connection become overwhelming?"[358]
+
+With reference to the small elongated nebula discovered by Miss Caroline
+Herschel in 1783 near the great nebula in Andromeda, Admiral Smyth says,
+"It lies between two sets of stars, consisting of four each, and each
+disposed like the figure 7, the preceding group being the smallest."[359]
+
+Speaking of the "nebula" Messier 3--a globular cluster in Canes
+Venatici--Admiral Smyth says, "This mass is one of those balls of compact
+and wedged stars whose laws of aggregation it is so impossible to assign;
+but the rotundity of the figure gives full indication of some general
+attractive bond of union."[360] The terms "compact and wedged" are,
+however, too strong, for we know that in the globular clusters the
+component stars must be separated from each other by millions of miles!
+
+Prof. Chamberlin suggests that the secondary nebula (as it is called) in
+the great spiral in Canes Venatici (Messier 51) may possibly represent
+the body which collided with the other (the chief nucleus) in a grazing
+collision, and is now escaping. He considers this secondary body to have
+been "a dead sun"--that is, a dark body.[361] This would be very
+interesting if it could be proved. But it seems to me more probable that
+the secondary nucleus is simply a larger portion of the ejected matter,
+which is now being gradually detached from the parent mass.
+
+Scheiner says "the previous suspicion that the spiral nebulae are star
+clusters is now raised to a certainty," and that the spectrum of the
+Andromeda nebula is very similar to that of the sun. He says there is "a
+surprising agreement of the two, even in respect to the relative intensity
+of the separate spectral regions."[362]
+
+In the dynamical theory of spiral nebulae, Dr. E. J. Wilczynski thinks that
+the age of a spiral nebula may be indicated by the number of its coils;
+those having the largest number of coils being the oldest, from the point
+of view of evolution.[363] This seems to be very probable.
+
+In the spectrum of the gaseous nebulae, the F line of hydrogen (H[Greek:
+b]) is visible, but not the C line (H[Greek: a]). The invisibility of the
+C line is explained by Scheiner as due to a physiological cause, "the eye
+being less sensitive to that part of the spectrum in which the line
+appears than to the part containing the F line."[364]
+
+An apparent paradox is found in the case of the gaseous nebulae. The
+undefined outlines of these objects render any attempt at measuring their
+parallax very difficult, if not impossible. Their distance from the earth
+is therefore unknown, and perhaps likely to remain so for many years to
+come. It is possible that they may not be farther from us than some of the
+stars visible in their vicinity. On the other hand, they may lie far
+beyond them in space. But whatever their distance from the earth may be,
+it may be easily shown that their attraction on the sun is directly
+proportioned to their distance--that is, the greater their distance, the
+greater the attraction! This is evidently a paradox, and rather a
+startling one too. But it is nevertheless mathematically true, and can be
+easily proved. For, _their distance being unknown_, they may be of any
+dimensions. They might be comparatively small bodies relatively near the
+earth, or they may be immense masses at a vast distance from us. The
+latter is, of course, the more probable. In either case the _apparent_
+size would be the same. Take the case of any round gaseous nebula.
+Assuming it to be of a globular form, its _real_ diameter will depend on
+its distance from the earth--the greater the distance, the greater the
+diameter. Now, as the volumes of spheres vary as the cubes of their
+diameters, it follows that the volume of the nebula will vary as the cube
+of its distance from the earth. As the mass of an attracting body depends
+on its volume and density, its real mass will depend on the cube of its
+distance, the density (although unknown) being a fixed quantity. If at a
+certain distance its mass is _m_, at double the distance (the _apparent_
+diameter being the same) it would have a mass of eight times _m_ (8 being
+the cube of 2), and at treble the distance its mass would be 27 _m_, and
+so on, its _apparent_ size being known, but not its _real_ size. This is
+obvious. Now, the attractive power of a body varies directly as its
+mass--the greater the mass, the greater the attraction. Again, the
+attraction varies _inversely_ as the square of the distance, according to
+the well-known law of Newton. Hence if _d_ be the unknown distance of the
+nebula, we have its attractive power varying as _d_{3} divided by _d_{2},
+or directly as the distance _d_. We have then the curious paradox that for
+a nebula whose distance from the earth is unknown, its attractive power on
+the sun (or earth) will vary directly as the distance--the greater the
+distance the greater the attraction, and, of course, conversely, the
+smaller the distance the less the attractive power. This result seems at
+first sight absurd and incredible, but a little consideration will show
+that it is quite correct. Consider a small wisp of cloud in our
+atmosphere. Its mass is almost infinitesimal and its attractive power on
+the earth practically _nil_. But a gaseous nebula having the same
+_apparent size_ would have an enormous volume, and, although probably
+formed of very tenuous gas, its mass would be very great, and its
+attractive power considerable. The large apparent size of the Orion nebula
+shows that its volume is probably enormous, and as its attraction on the
+sun is not appreciable, its density must be excessively small, less than
+the density of the air remaining in the receiver of the best air-pump
+after the air has been exhausted. How such a tenuous gas can shine as it
+does forms another paradox. Its light is possibly due to some
+phosphorescent or electrical action.
+
+The apparent size of "the great nebula in Andromeda" shows that it must be
+an object of vast dimensions. The nearest star to the earth, Alpha
+Centauri, although probably equal to our sun in volume, certainly does not
+exceed one-hundredth of a second in diameter as seen from the earth. But
+in the case of the Andromeda nebula we have an object of considerable
+apparent size, not measured by seconds of arc, but showing an area about
+three times greater than that of the full moon. The nebula certainly lies
+in the region of the stars--much farther off than Alpha Centauri--and its
+great apparent size shows that it must be of stupendous dimensions. A
+moment's consideration will show that whatever its distance may be, the
+farther it is from the earth the larger it must be in actual size. The sun
+is vastly larger than the moon, but its apparent size is about the same
+owing to its greater distance. Sir William Herschel thought the Andromeda
+nebula to be "undoubtedly the nearest of all the great nebulae," and he
+estimated its distance at 2000 times the distance of Sirius. This would
+not, however, indicate a relatively near object, as it would imply a
+"light journey" of over 17,000 years! (The distance of Sirius is about 88
+"light years.")
+
+It has been generally supposed that this great nebula lies at a vast
+distance from the earth, possibly far beyond most of the stars seen in the
+same region of the sky; but perhaps not quite so far as Herschel's
+estimate would imply. Recently, however, Prof. Bohlin of Stockholm has
+found from three series of measures made in recent years a parallax of
+0".17.[365]
+
+This indicates a distance of 1,213,330 times the sun's distance from the
+earth, and a "light journey" of about 19 years. This would make the
+distance of the nebula more than twice the distance of Sirius, about four
+times the distance of [Greek: a] Centauri, but less than that of Capella.
+
+Prof. Bohlin's result is rather unexpected, and will require confirmation
+before it can be accepted. But it will be interesting to inquire what this
+parallax implies as to the real dimensions and probable mass of this vast
+nebula. The extreme length of the nebula may be taken to represent its
+diameter considered as circular. For, although a circle seen obliquely is
+always foreshortened into an ellipse, still the longer axis of the ellipse
+will always represent the real diameter of the circle. This may be seen by
+holding a penny at various angles to the eye. Now, Dr. Roberts found that
+the apparent length of the Andromeda nebula is 2-1/3 degrees, or 8400
+seconds of arc. The diameter in seconds divided by the parallax will give
+the real diameter of the nebula in terms of the sun's distance from the
+earth taken as unity. Now, 8400 divided by 0".17 gives nearly 50,000, that
+is, the real diameter of the Andromeda nebula would be--on Bohlin's
+parallax--nearly 50,000 times the sun's distance from the earth. As light
+takes about 500 seconds to come from the sun to the earth, the above
+figures imply that light would take about 290 days, or over 9 months to
+cross the diameter of this vast nebula.
+
+Elementary geometrical considerations will show that if the Andromeda
+nebula lies at a greater distance from the earth than that indicated by
+Bohlin's parallax, its real diameter, and therefore its volume and mass,
+will be greater. If, therefore, we assume the parallax found by Bohlin,
+we shall probably find a _minimum_ value for the size and mass of this
+marvellous object.
+
+Among Dr. Roberts' photographs of spiral nebulae (and the Andromeda nebula
+is undoubtedly a spiral) there are some which are apparently seen nearly
+edgeways, and show that these nebulae are very thin in proportion to their
+diameter. From a consideration of these photographs we may, I think,
+assume a thickness of about one-hundredth of the diameter. This would give
+a thickness for the Andromeda nebulae of about 500 times the sun's distance
+from the earth. This great thickness will give some idea of the vast
+proportions of the object we are dealing with. The size of the whole solar
+system--large as it is--is small in comparison. The diameter and thickness
+found above can easily be converted into miles, and from these dimensions
+the actual volume of the nebula can be compared with that of the sun. It
+is merely a question of simple mensuration, and no problem of "high
+mathematics" is involved. Making the necessary calculations, I find that
+the volume of the Andromeda nebula would be about 2.32 trillion times
+(2.32 x 10{18}) the sun's volume! Now, assuming that the nebulous matter
+fills only one-half of the apparent volume of the nebula (allowing for
+spaces between the spiral branches), we have the volume = 1.16 x 10{18}.
+If the nebula had the same density as the sun, this would be its mass in
+terms of the sun's mass taken as unity, a mass probably exceeding the
+combined mass of all the _stars_ visible in the largest telescopes! But
+this assumption is, of course, inadmissible, as the sun is evidently quite
+opaque, whereas the nebula is, partially at least, more or less
+transparent. Let us suppose that the nebula has a _mean_ density equal to
+that of atmospheric air. As water is about 773 times heavier than air, and
+the sun's density is 1.4 (water = 1) we have the mass of the nebula equal
+to 1.16 x 10{18} divided by 773 x 1.4, or about 10{15} times the sun's
+mass, which is still much greater than the probable combined mass of all
+the _visible_ stars. As it seems unreasonable to suppose that the mass of
+an individual member of our sidereal system should exceed the combined
+mass of the remainder of the system, we seem compelled to further reduce
+the density of the Andromeda nebula. Let us assume a mean density of, say,
+a millionth of hydrogen gas (a sufficiently low estimate) which is about
+14.44 times lighter than air, and we obtain a mass of about 8 x 10{7} or
+80 million times the mass of the sun, which is still an enormous mass.
+
+As possibly I may have assumed too great a thickness for the nebula, let
+us take a thickness of one-tenth of that used above, or one thousandth of
+the length of the nebula. This gives a mass of 8 million times the sun's
+mass. This seems a more probable mass if the nebula is--as Bohlin's
+parallax implies--a member of our sidereal system.
+
+If we assume a parallax of say 0".01--or one-hundredth of a second of
+arc--which would still keep the nebula within the bounds of our sidereal
+system--we have the dimensions of the nebula increased 17 times, and hence
+its mass nearly 5000 times greater (17{3}) than that found above. The mass
+would then be 40,000 million times the sun's mass! This result seems
+highly improbable, for even this small parallax would imply a light
+journey of only 326 years, whereas the distance of the Milky Way has been
+estimated by Prof. Newcomb at about 3000 years' journey for light.
+
+In Dr. Roberts' photograph many small stars are seen scattered over the
+surface of the nebula; but these do not seem to be quite so numerous as in
+the surrounding sky. If the nebula lies nearer to us than the fainter
+stars visible on the photograph, some of them may be obscured by the
+denser portions of the nebula; some may be visible through the openings
+between the spiral branches; while others may be nearer to us and simply
+projected on the nebula.
+
+To add to the difficulty of solving this celestial problem, the
+spectroscope shows that the Andromeda nebula is not gaseous. The spectrum
+is, according to Scheiner, very similar to that of the sun, and "there is
+a surprising agreement of the two, even in respect to the relative
+intensities of the separate spectral regions."[366] He thinks that "the
+greater part of the stars comprising the nucleus of the nebula belong to
+the second spectral class" (solar), and that the nebula "is now in an
+advanced stage of development. No trace of bright nebular lines are
+present, so that the interstellar space in the Andromeda nebula, just as
+in our stellar system, is not appreciably occupied by gaseous
+matter."[366] He suggests that the inner part of the nebula [the
+"nucleus"] "corresponds to the complex of those stars which do not belong
+to the Milky Way, while the latter corresponds to the spirals of the
+Andromeda nebula."[366] On this view of the matter we may suppose that the
+component particles are small bodies widely separated, and in this way the
+_mean_ density of the Andromeda nebula may be very small indeed. They
+cannot be large bodies, as the largest telescopes have failed to resolve
+the nebula into stars, and photographs show no sign of resolution.
+
+It has often been suggested, and sometimes definitely stated, that the
+Andromeda nebula may possibly be an "external" universe, that is an
+universe entirely outside our sidereal system, and comparable with it in
+size. Let us examine the probability of such hypothesis. Assuming that the
+nebula has the same diameter as the Milky Way, or about 6000 "light
+years," as estimated by Prof. Newcomb, I find that its distance from the
+earth would be about 150,000 "light years." As this is about 8000 times
+the distance indicated by Bohlin's parallax, its dimensions would be 8000
+times as great, and hence its volume and mass would be 8000 cubed, or
+512,000,000,000 times greater than that found above. That is, about 4
+trillion (4 x 10{18}) times the sun's mass! As this appears an incredibly
+large mass to be compressed into a volume even so large as that of our
+sidereal system, we seem compelled to reject the hypothesis that the
+nebula represents an external universe. The sun placed at the distance
+corresponding to 150,000 light years would, I find, shine as a star of
+less than the 23rd magnitude, a magnitude which would be invisible in the
+largest telescope that man could ever construct. But the combined light of
+4 trillion of stars of even the 23rd magnitude would be equal to one of
+minus 23.5 magnitude, that is, 23-1/2 magnitude brighter than the zero
+magnitude, or not very much inferior to the sun in brightness. As the
+Andromeda nebula shines only as a star of about the 5th magnitude the
+hypothesis of an external universe seems to be untenable.
+
+It is evident, however, that the mass of the Andromeda nebula must be
+enormous; and if it belongs to our sidereal system, and if the other great
+nebulae have similar masses, it seems quite possible that the mass of the
+_visible_ universe may much exceed that of the _visible_ stars, and may be
+equal to 1000 million times the sun's mass--as supposed by the late Lord
+Kelvin--or even much more.
+
+With reference to the small star which suddenly blazed out near the
+nucleus of the Andromeda nebula in August, 1885, Prof. Seeliger has
+investigated the decrease in the light of the star on the hypothesis that
+it was a cooling body which had suddenly been raised to an intense heat by
+the shock of a collision, and finds a fair agreement between theory and
+observation. Prof. Auwers points out the similarity between this outburst
+and that of the "temporary star" of 1860, which appeared in the cluster 80
+Messier, and he thinks it very probable that both phenomena were due to
+physical changes in the nebulae in which they appeared.
+
+The appearance of this temporary star in the Andromeda nebula seems to
+afford further evidence against the hypothesis of the nebula being an
+external universe. For, as I have shown above, our sun, if placed at a
+distance of 150,000 light years, would shine only as a star of the 23rd
+magnitude, or over 15 magnitudes fainter than the temporary star. This
+would imply that the star shone with a brightness of over a million times
+that of the sun, and would therefore indicate a body of enormous size. But
+the rapid fading of its light would, on the contrary, imply a body of
+comparatively small dimensions. We must, therefore, conclude that the
+nebula, whatever it may be, is not an external universe, but forms a
+member of our own sidereal system.
+
+In Sir John Herschel's catalogue of Nebulae and Clusters of Stars,
+published in 1833, in the _Philosophical Transactions_ of the Royal
+Society, there are many curious objects mentioned. Of these I have
+selected the following:--
+
+No. 496 is described as "a superb cluster which fills the whole field;
+stars 9, 10 ... 13 magnitude and none below, but the whole ground of the
+sky on which it stands is singularly dotted over with infinitely minute
+points." This is No. 22 of Sir William Herschel's 6th class, and will be
+found about 3 degrees south and a little east of the triple star 29
+Monocerotis.
+
+No. 650. This object lies about 3 degrees north of the star [Greek: m]
+Leonis, the most northern of the bright stars in the well-known "Sickle,"
+and is thus described by Sir John Herschel: "A star 12th magnitude with an
+extremely faint nebulous atmosphere about 10" to 12". It is between a star
+8-9 magnitude north preceding, and one 10th magnitude south following,
+neither of which are so affected. A curious object."
+
+No. 1558. Messier 53. A little north-east of the star [Greek: a] Comae
+Berenices. Described as "a most beautiful highly compressed cluster.
+Stars very small, 12th ... 20th magnitude, with scattered stars to a
+considerable distance; irregularly round, but not globular. Comes up to a
+blaze in the centre; indicating a round mass of pretty equable density.
+Extremely compressed. A most beautiful object. A mass of close-wedged
+stars 5' in diameter; a few 12th magnitude, the rest of the smallest size
+and innumerable." Webb says, "Not very bright with 3-7/10 inches;
+beautiful with 9 inches." This should be a magnificent object with a very
+large telescope, like the Lick or Yerkes.
+
+No. 2018. "A more than usually condensed portion of the enormous cluster
+of the Milky Way. The field has 200 or 300 stars in it at once." This lies
+about 2 deg. south-west of the star 6 Aquilae, which is near the northern edge
+of the bright spot of Milky Way light in "Sobieski's Shield"--one of the
+brightest spots in the sky.
+
+No. 2093. "A most wonderful phenomenon. A very large space 20' or 30'
+broad in Polar Distance, and 1{m} or 2{m} in Right Ascension, full of
+nebula and stars mixed. The nebula is decidedly attached to the stars, and
+is as decidedly not stellar. It forms irregular lace-work marked out by
+stars, but some parts are decidedly nebulous, wherein no star can be
+seen." Sir John Herschel gives a figure of this curious spot, which he
+says represents its "general character, but not the minute details of
+this object, which would be extremely difficult to give with any degree of
+fidelity." It lies about 3 degrees west of the bright star [Greek: z]
+Cygni.
+
+Among the numerous curious objects observed by Sir John Herschel during
+his visit to the Cape of Good Hope, the following may be mentioned:--
+
+_h_ 2534 (H iv. 77). Near [Greek: t]{4} Eridani. Sir John Herschel says,
+"Attached cometically to a 9th magnitude star which forms its head. It is
+an exact resemblance to Halley's comet as seen in a night glass."... "A
+complete telescopic comet; a perfect miniature of Halley's comet, only the
+tail is rather broader in proportion."[367]
+
+_h_ 3075. Between [Greek: g] Monocerotis and [Greek: g] Canis Majoris. "A
+very singular nebula, and much like the profile of a bust (head, neck, and
+shoulders) or a silhouette portrait, very large, pretty well defined,
+light nearly uniform, about 12' diameter. In a crowded field of Milky Way
+stars, many of which are projected on it."[368]
+
+_h_ 3315 (Dunlop 323). In the Milky Way; about 3 deg. east of the Eta Argus
+nebula. Sir John Herschel says, "A glorious cluster of immense magnitude,
+being at least 2 fields in extent every way. The stars are 8, 9, 10, and
+11th magnitudes, but chiefly 10th magnitude, of which there must be at
+least 200. It is the most brilliant object of the kind I have ever seen"
+... "has several elegant double stars, and many orange-coloured
+stars."[369] This should form a fine object in even a comparatively small
+telescope, and may be recommended to observers in the southern hemisphere.
+A telescope of 3-inches aperture should show it well.
+
+Among astronomical curiosities may be counted "clusters within clusters."
+A cluster in Gemini (N.G.C. 2331) has a small group of "six or seven stars
+close together and well isolated from the rest."
+
+Lord Rosse describes No. 4511 of Sir John Herschel's General Catalogue of
+Nebulae and Clusters (_Phil. Trans._, 1864) as "a most gorgeous cluster,
+stars 12-15 magnitude, full of holes."[370] His sketch of this cluster
+shows 3 rings of stars in a line, each ring touching the next on the
+outside. Sir John Herschel described it as "Cluster; very large; very
+rich; stars 11-15 magnitude (Harding, 1827)," but says nothing about the
+rings. This cluster lies about 5 degrees south of [Greek: d] Cygni.
+
+Dr. See, observing with the large telescope of the Lowell Observatory,
+found that when the sky is clear, the moon absent, and the seeing perfect,
+"the sky appeared in patches to be of a brownish colour," and suggests
+that this colour owes its existence to immense cosmical clouds, which are
+shining by excessively feeble light! Dr. See found that these brown
+patches seem to cluster in certain regions of the Milky Way.[371]
+
+From a comparison of Trouvelot's drawing of the small elongated nebula
+near the great nebula in Andromeda with recent photographs, Mr. Easton
+infers that this small nebula has probably rotated through an angle of
+about 15 deg. in 25 years. An examination I have made of photographs taken in
+different years seems to me to confirm this suspicion, which, if true, is
+evidently a most interesting phenomenon.
+
+Dr. Max Wolf of Heidelberg finds, by spectrum photography, that the
+well-known "ring nebula" in Lyra consists of four rings composed of four
+different gases. Calling the inner ring A, the next B, the next C, and the
+outer D, he finds that A is the smallest ring, and is composed of an
+unknown gas; the next largest, B, is composed of hydrogen gas; the next,
+C, consists of helium gas; and the outer and largest ring, D, is
+composed--like A--of an unknown gas. As the molecular weight of hydrogen
+is 2.016, and that of helium is 3.96, Prof. Bohuslav Brauner suggests that
+the molecular weight of the gas composing the inner ring A is smaller than
+that of hydrogen, and the molecular weight of the gas forming the outer
+ring D is greater than that of helium. He also suggests that the gas of
+ring A may possibly be identical with the "coronium" of the solar corona,
+for which Mendelief found a hypothetical atomic and molecular weight of
+0.4.[372]
+
+With reference to the nebular hypothesis of Laplace, Dr. A. R. Wallace
+argues that "if there exists a sun in a state of expansion in which our
+sun was when it extended to the orbit of Neptune, it would, even with a
+parallax of 1/60th of a second, show a disc of half a second, which could
+be seen with the Lick telescope." My reply to this objection is, that with
+such an expansion there would probably be very little "intrinsic
+brightness," and if luminous enough to be visible the spectrum would be
+that of a gaseous nebula, and no known _star_ gives such a spectrum. But
+some planetary nebulae look like small stars, and with high powers on large
+telescopes would probably show a disc. On these considerations, Dr.
+Wallace's objection does not seem to be valid.
+
+It is usually stated in popular works on astronomy that the spectra of
+gaseous nebulae show only three or four bright lines on a faint continuous
+background. But this is quite incorrect. No less than forty bright lines
+have been seen and measured in the spectra of gaseous nebulae.[373] This
+includes 2 lines of "nebulium," 11 of hydrogen, 5 of helium, 1 of oxygen
+(?), 3 of nitrogen (?), 1 of silicon (?), and 17 of an unknown substance.
+In the great nebulae in Orion 30 bright lines have been photographed.[374]
+
+D'Arrest found that "gaseous nebulae are rarely met with outside the Milky
+Way, and never at a considerable distance from it."[375]
+
+Mr. A. E. Fath thinks that "no spiral nebula investigated has a truly
+continuous spectrum." He finds that so feeble is the intensity of the
+light of the spiral nebulae that, while a spectrogram of Arcturus can be
+secured with the Mills spectrograph "in less than two minutes," "an
+exposure of about 500 hours would be required for the great nebula in
+Andromeda, which is of the same spectral type."[376] Mr. Fath thinks that
+in the case of the Andromeda nebula, the "star cluster" theory "seems to
+be the only one that can at all adequately explain the spectrum
+obtained."[377]
+
+Prof. Barnard finds that the great cluster in Hercules (Messier 13) is
+"composed of stars of different spectral types." This result was confirmed
+by Mr. Fath.[378]
+
+From observations with the great 40-inch telescope of the Yerkes
+Observatory (U.S.A.), Prof. Barnard finds that the nucleus of the
+planetary nebula H. iv. 18 in Andromeda is variable to the extent of at
+least 3 magnitudes. At its brightest it is about the 12th magnitude; and
+the period seems to be about 28 days. Barnard says, "I think this is the
+first case in which the nucleus of a planetary or other nebula has been
+shown to be certainly variable." "The normal condition seems to be
+faint--the nucleus remaining bright for a few days only. In an ordinary
+telescope it looks like a small round disc of a bluish green colour." He
+estimated the brightness of the nebula as that of a star of 8.2
+magnitude.[379] Even in a telescope of 4 inches aperture, this would be a
+fairly bright object. It lies about 3-1/2 degrees south-west of the star
+[Greek: i] Andromedae.
+
+The so-called "globular clusters" usually include stars of different
+brightness; comparatively bright telescopic stars of the 10th to 13th
+magnitude with faint stars of the 15th to 17th magnitude. Prof. Perrine of
+the Lick Observatory finds that (_a_) "the division of the stars in
+globular clusters into groups, differing widely in brightness, is
+characteristic of these objects"; (_b_) "the globular clusters are devoid
+of true nebulosity"; and (_c_) "stars fainter than 15th magnitude
+predominate in the Milky Way and globular clusters, but elsewhere are
+relatively scarce." He found that "exposures of one hour or thereabouts
+showed as many stars as exposures four to six times as long; the only
+effect of the longer exposures being in the matter of density." This last
+result confirms the late Dr. Roberts' conclusions. Perrine finds that for
+clusters in the Milky Way, the faint stars (15th to 17th magnitude) "are
+about as numerous in proportion to the bright stars (10th to 13th
+magnitude) as in the globular clusters themselves." This is, however, not
+the case with globular clusters at a distance from the Milky Way. In these
+latter clusters he found that "in the regions outside the limits of the
+cluster there are usually very few faint stars, hardly more than
+one-fourth or one-tenth as many as there are bright stars"; and he thinks
+that "this paucity of faint stars" in the vicinity of these clusters
+"gives rise to the suspicion that all regions at a distance from the
+Galaxy may be almost devoid of these very faint stars." The late Prof.
+Keeler's series of nebular photographs "in or near the Milky Way" tend to
+confirm the above conclusions. Perrine finds the northernmost region of
+the Milky Way "to be almost, if not entirely, devoid of globular
+clusters."[380]
+
+According to Sir John Herschel, "the sublimity of the spectacle afforded"
+by Lord Rosse's great telescope of 6 feet in diameter of some of the
+"larger globular and other clusters" "is declared by all who have
+witnessed it, to be such that no words can express."[381]
+
+In his address to the British Association at Leicester in 1907, Sir David
+Gill said--
+
+    "Evidence upon evidence has accumulated to show that nebulae consist of
+    the matter out of which stars have been and are being evolved.... The
+    fact of such an evolution with the evidence before us, can hardly be
+    doubted. I most fully believe that, when the modifications of
+    terrestrial spectra under sufficiently varied conditions of
+    temperature, pressure, and environment, have been further studied,
+    this connection will be greatly strengthened."
+
+
+
+
+CHAPTER XVIII
+
+Historical
+
+
+The grouping of the stars into constellations is of great antiquity. The
+exact date of their formation is not exactly known, but an approximate
+result may be arrived at from the following considerations. On the
+celestial spheres, or "globes," used by the ancient astronomers, a portion
+of the southern heavens of a roughly circular form surrounding the South
+Pole was left blank. This space presumably contained the stars in the
+southern hemisphere which they could not see from their northern stations.
+Now, the centre of this circular blank space most probably coincided with
+the South Pole of the heavens at the time when the constellations were
+first formed. Owing to the "Precession of the Equinoxes" this centre has
+now moved away from the South Pole to a considerable distance. It can be
+easily computed at what period this centre coincided with the South Pole,
+and calculations show that this was the case about 2700 B.C. The position
+of this circle also indicates that the constellations were formed at a
+place between 36 deg. and 40 deg. north latitude, and therefore probably somewhere
+in Asia Minor north of Mesopotamia. Again, the most ancient observations
+refer to Taurus as the equinoxial constellation. Virgil says--
+
+  "Candidus auratis aperit cum cornibus annum Taurus."[382]
+
+This would indicate a date about 3000 B.C. There is no tradition, however,
+that the constellation Gemini was ever _seen_ to occupy this position, so
+that 3000 B.C. seems to be the earliest date admissible.[383]
+
+Prof. Sayce thinks that the "signs of the Zodiac" had their origin in the
+plains of Mesopotamia in the twentieth or twenty-third century B.C., and
+Brown gives the probable date as 2084 B.C.[384]
+
+According to Seneca, the study of astronomy among the Greeks dates back to
+about 1400 B.C.; and the ancient constellations were already classical in
+the time of Eudoxus in the fourth century B.C. Eudoxus (408-355 B.C.)
+observed the positions of forty-seven stars visible in Greece, thus
+forming the most ancient star catalogue which has been preserved. He was a
+son of Eschinus, and a pupil of Archytas and probably Plato.
+
+The work of Eudoxus was put into verse by the poet Aratus (third century
+B.C.). This poem describes all the old constellations now known, except
+Libra, the Balance, which was at that time included in the Claws of the
+Scorpion. About B.C. 50, the Romans changed the Claws, or Chelae, into
+Libra. Curious to say, Aratus states that the constellation Lyra contained
+no bright star![385] Whereas its principal star, Vega, is now one of the
+brightest stars in the heavens!
+
+With reference to the origin of the constellations, Aratus says--
+
+                    "Some men of yore
+  A nomenclature thought of and devised
+  And forms sufficient found."
+
+This shows that even in the time of Aratus the constellations were of
+great antiquity.
+
+Brown says--
+
+    "Writers have often told us, speaking only from the depths of their
+    ignorance, how 'Chaldean' shepherds were wont to gaze at the brilliant
+    nocturnal sky, and to _imagine_ that such and such stars resemble this
+    or that figure. But all this is merely the old effort to make capital
+    out of nescience, and the stars are before our eyes to prove the
+    contrary. Having already certain fixed ideas and figures in his mind,
+    the constellation-former, when he came to his task, applied his
+    figures to the stars and the stars to his figures as harmoniously as
+    possible."[386] "Thus _e.g._ he arranged the stars of _Andromeda_ into
+    the representation of a chained lady, not because they naturally
+    reminded him (or anybody else) of such a figure, but because he
+    desired to express that idea."
+
+A coin of Manius Aquillus, B.C. 94, shows four stars in Aquila, and seems
+to be the oldest representation extant of a star group. On a coin of B.C.
+43, Dr. Vencontre found five stars, one of which was much larger than the
+others, and concludes that it represents the Hyades (in Taurus). He
+attributes the coin to P. Clodius Turrinus, who probably used the
+constellation Taurus or Taurinus as a phonetic reference to his surname. A
+coin struck by L. Lucretius Trio in 74 B.C., shows the seven stars of the
+Plough, or as the ancients called them Septem Triones. Here we have an
+allusion to the name of the magistrate Trio.[387]
+
+In a work published in Berne in 1760, Schmidt contends that the ancient
+Egyptians gave to the constellations of the Zodiac the names of their
+divinities, and expressed them by the signs which were used in their
+hieroglyphics.[388]
+
+Hesiod mentions Orion, the Pleiades, Sirius, Aldebaran, and Arcturus; and
+Homer refers to Orion, Arcturus, the Pleiades, the Hyades, the Great Bear
+(under the name of Amaxa, the Chariot), and the tail of the Little Bear,
+or "Cynosura."
+
+Hipparchus called the constellations Asterisms ([Greek: asterismos]),
+Aristotle and Hyginus [Greek: Somata] (bodies), and Ptolemy [Greek:
+Schemata] (figures). By some they were called [Greek: Morphoseis]
+(configurations), and by others [Greek: Meteore]. Proclus called those
+near the ecliptic [Greek: Zodia] (animals). Hence our modern name Zodiac.
+
+Hipparchus, Ptolemy, and Al-Sufi referred the positions of the stars to
+the ecliptic. They are now referred to the equator. Aboul Hassan in the
+thirteenth century (1282) was the first to use Right Ascensions and
+Declinations instead of Longitudes and Latitudes. The ancient writers
+described the stars by their positions in the ancient figures. Thus they
+spoke of "the star in the head of Hercules," "the bright star in the left
+foot of Orion" (Rigel); but Bayer in 1603 introduced the Greek letters to
+designate the brighter stars, and these are now universally used by
+astronomers. These letters being sometimes insufficient, Hevelius added
+numbers, but the numbers in _Flamsteed's Catalogue_ are now generally
+used.
+
+Ptolemy and all the ancient writers described the constellation figures as
+they are seen on globes, that is from the outside. Bayer in his Atlas,
+published in 1603, reversed the figures to show them as they would be seen
+from the _interior_ of a hollow globe and as, of course, they are seen in
+the sky. Hevelius again reversed Bayer's figures to make them correspond
+with those of Ptolemy. According to Bayer's arrangement, Betelgeuse
+([Greek: a] Orionis) would be on the left shoulder of Orion, instead of
+the right shoulder according to Ptolemy and Al-Sufi, and Rigel ([Greek: b]
+Orionis) on the right foot (Bayer) instead of the left foot (Ptolemy).
+This change of position has led to some confusion; but at present the
+positions of the stars are indicated by their Right Ascensions and
+Declinations, without any reference to their positions in the ancient
+figures.
+
+The classical constellations of Hipparchus and Ptolemy number forty-eight,
+and this is the number described by Al-Sufi in his "Description of the
+Fixed Stars" written in the tenth century A.D.
+
+Firminicus gives the names of several constellations not mentioned by
+Ptolemy. M. Freret thought that these were derived from the Egyptian
+sphere of Petosiris. Of these a Fox was placed north of the Scorpion; a
+constellation called Cynocephalus near the southern constellation of the
+Altar (Ara); and to the north of Pisces was placed a Stag. But all these
+have long since been discarded. Curious to say neither the Dragon nor
+Cepheus appears on the old Egyptian sphere.[389]
+
+Other small constellations have also been formed by various astronomers
+from time to time, but these have disappeared from our modern star maps.
+The total number of constellations now recognized in both hemispheres
+amounts to eighty-four.
+
+The first catalogue formed was nominally that of Eudoxus in the fourth
+century B.C. (about 370 B.C.). But this can hardly be dignified by the
+name of catalogue, as it contained only forty-seven stars, and it omits
+several of the brighter stars, notably Sirius! The first complete (or
+nearly complete) catalogue of stars visible to the naked eye was that of
+Hipparchus about 129 B.C. Ptolemy informs us that it was the sudden
+appearance of a bright new or "temporary star" in the year 134 B.C. in the
+constellation Scorpio which led Hipparchus to form his catalogue, and
+there seems to be no reason to doubt the accuracy of this statement, as
+the appearance of this star is recorded in the Chinese Annals. The
+Catalogue of Hipparchus contains only 1080 stars; but as many more are
+visible to the naked eye, Hipparchus must have omitted those which are not
+immediately connected with the old constellation figures of men and
+animals.
+
+Hipparchus' Catalogue was revised by Ptolemy in his famous work the
+_Almagest_. Ptolemy reduced the positions of the stars given by Hipparchus
+to the year 137 A.D.; but used a wrong value of the precession which only
+corresponded to about 50 A.D.; and he probably adopted the star magnitudes
+of Hipparchus without any revision. Indeed, it seems somewhat doubtful
+whether Ptolemy made any observations of the brightness of the stars
+himself. Ptolemy's catalogue contains 1022 stars.
+
+Prof. De Morgan speaks of Ptolemy as "a splendid mathematician and an
+indifferent observer"; and from my own examination of Al-Sufi's work on
+the Fixed Stars, which was based on Ptolemy's work, I think that De
+Morgan's criticism is quite justified.
+
+Al-Sufi's _Description of the Fixed Stars_ was written in the tenth
+century and contains 1018 stars. He seems to have adopted the _positions_
+of the stars given by Ptolemy, merely correcting them for the effects of
+precession; but he made a very careful revision of the star magnitudes of
+Ptolemy (or Hipparchus) from his own observations, and this renders his
+work the most valuable, from this point of view, of all the ancient
+catalogues.
+
+Very little is known about Al-Sufi's life, and the few details we have are
+chiefly derived from the works of the historians Abu'-l-faradji and
+Casiri, and the Oriental writers Hyde, Caussin, Sedillot, etc. Al-Sufi's
+complete name was Abd-al-Rahmaen Bin Umar Bin Muhammad Bin Sahl
+Abu'l-husain al-Sufi al-Razi. The name Sufi indicates that he belonged to
+the sect of Sufis (Dervishes), and the name Razi that he lived in the town
+of Rai in Persia, to the east of Teheran. He was born on December 7, 903
+A.D., and died on May 25, 986, so that, like many other astronomers, he
+lived to a good old age. According to ancient authorities, Al-Sufi--as he
+is usually called--was a very learned man, who lived at the courts of
+Schiraz and Baghdad under Adhad-al-Davlat--of the dynasty of the
+Buides--who was then the ruler of Persia. Al-Sufi was held in high esteem
+and great favour by this prince, who said of him, "Abd-al-Rahmaen al-Sufi
+taught me to know the names and positions of the fixed stars, Scharif Ibn
+al-Aalam the use of astronomical tables, and Abu Ali al-Farisi instructed
+me in the principles of grammar." Prince Adhad-al-Davlat died on March 26,
+983. According to Caussin, Al-Sufi also wrote a book on astrology, and a
+work entitled _Al-Ardjouze_, which seems to have been written in verse,
+but its subject is unknown. He also seems to have determined the exact
+length of the year, and to have undertaken geodetic measurements. The
+al-Aalam mentioned above was also an able astronomer, and in addition to
+numerous observations made at Baghdad, he determined with great care the
+precession of the equinoxes. He found the annual constant of precession to
+be 51".4, a value which differs but little from modern results.
+
+In the year 1874, the late M. Schjellerup, the eminent Danish astronomer,
+published a French translation of two Arabic manuscripts written by
+Al-Sufi and entitled "A Description of the Fixed Stars." One of these
+manuscripts is preserved in the Royal Library at Copenhagen, and the other
+in the Imperial Library at St. Petersburgh.[390]
+
+Al-Sufi seems to have been a most careful and accurate observer, and
+although, as a rule, his estimates of the relative brightness of stars are
+in fairly good agreement with modern estimates and photometric measures,
+there are many remarkable and interesting differences. Al-Sufi's
+observations have an important bearing on the supposed "secular variation"
+of the stars; that is, the slow variation in light which may have occurred
+in the course of ages in certain stars, apart from the periodical
+variation which is known to occur in the so-called variable stars. More
+than 900 years have now elapsed since the date of Al-Sufi's observations
+(about A.D. 964) and over 2000 years in the case of Hipparchus, and
+although these periods are of course very short in the life-history of any
+star, still _some_ changes may possibly have taken place in the brightness
+of some of them. There are several cases in which a star seems to have
+diminished in light since Al-Sufi's time. This change seems to have
+certainly occurred in the case of [Greek: th] Eridani, [Greek: b] Leonis,
+[Greek: z] Piscis Australis, and some others. On the other hand, some
+stars seem to have certainly increased in brightness, and the bearing of
+these changes on the question of "stellar evolution" will be obvious.
+
+In most cases Al-Sufi merely mentions the magnitude which he estimated a
+star to be; such as "third magnitude," "fourth," "small third magnitude,"
+"large fourth," etc. In some cases, however, he directly states that a
+certain star is a little brighter than another star near it. Such
+cases--unfortunately not numerous--are very valuable for comparison with
+modern estimates and measures, when variation is suspected in the light of
+a star. The estimates of Argelander, Heis, and Houzeau are based on the
+same scale as that used by Ptolemy and Al-Sufi. Al-Sufi's estimates are
+given in thirds of a magnitude. Thus, "small third magnitude" means 3-1/3,
+or 3.33 magnitude in modern measures; "large fourth," 3-2/3 or 3.66
+magnitude. These correspond with the estimates of magnitude given by
+Argelander, Heis, and Houzeau in their catalogues of stars visible to the
+naked eye, and so the estimates can be directly compared.
+
+I have made an independent identification of all the stars mentioned by
+Al-Sufi. In the majority of cases my identifications concur with those of
+Schjellerup; but in some cases I cannot agree with him. In a few cases I
+have found that Al-Sufi himself, although accurately describing the
+position of the stars observed by _him_, has apparently misidentified the
+star observed by Hipparchus and Ptolemy. This becomes evident when we plot
+Ptolemy's positions (as given by Al-Sufi) and compare them with Al-Sufi's
+descriptions of the stars observed by him. This I have done in all cases
+where there seemed to be any doubt; and in this way I have arrived at some
+interesting results which have escaped the notice of Schjellerup. This
+examination shows clearly, I think, that Al-Sufi did not himself measure
+the _positions_ of the stars he observed, but merely adopted those of
+Ptolemy, corrected for the effect of precession. The great value of his
+work, however, consists in his estimates of star magnitudes, which seem to
+have been most carefully made, and from this point of view, his work is
+invaluable. Prof. Pierce says, "The work which the learning of M.
+Schjellerup has brought to light is so important that the smallest errors
+of detail become interesting."[391]
+
+Although Al-Sufi's work is mentioned by the writers referred to above, no
+complete translation of his manuscript was made until the task was
+undertaken by Schjellerup, and even now Al-Sufi's name is not mentioned
+in some popular works on astronomy! But he was certainly the best of all
+the old observers, and his work is deserving of the most careful
+consideration.
+
+Al-Sufi's descriptions of the stars were, it is true, based on Ptolemy's
+catalogue, but his work is not a mere translation of that of his
+predecessor. It is, on the contrary, a careful and independent survey of
+the heavens, made from his own personal observations, each of Ptolemy's
+stars having been carefully examined as to its position and magnitude, and
+Ptolemy's mistakes corrected. In examining his descriptions, Schjellerup
+says, "We soon see the vast extent of his labours, his perseverance, and
+the minute accuracy and almost modern criticism with which he executed his
+work." In fact, Al-Sufi has given us a careful description of the starry
+sky as it appeared in his time, and one which deserves the greatest
+confidence. It far surpasses the work of Ptolemy, which had been without a
+rival for eight centuries previously, and it has only been equalled in
+modern times by the surveys of Argelander, Gould, Heis, and Houzeau. Plato
+remarked with reference to the catalogue of Hipparchus, _Coelam posteris
+in hereditatem relictum_, and the same may be said of Al-Sufi's work. In
+addition to his own estimates of star magnitudes, Al-Sufi adds the
+magnitudes given by Ptolemy whenever Ptolemy's estimate differs from his
+own; and this makes his work still more valuable, as Ptolemy's magnitudes
+given in all the editions of the _Almagest_ now extant are quite
+untrustworthy.
+
+In the preface to his translation of Al-Sufi's work, Schjellerup mentions
+some remarkable discrepancies between the magnitudes assigned to certain
+stars by Ptolemy and Argelander. This comparison is worthy of confidence
+as it is known that both Al-Sufi and Argelander adopted Ptolemy's (or
+Hipparchus') scale of magnitudes. For example, all these observers agree
+that [Greek: b] Ursae Minoris (Ptolemy's No. 6 of that constellation) is of
+the 2nd magnitude, while in the case of [Greek: g] Ursae Minoris (Ptolemy's
+No. 7), Ptolemy called it 2nd, and Argelander rated it 3rd; Argelander
+thus making [Greek: g] one magnitude fainter than Ptolemy's estimate. Now,
+Al-Sufi, observing over 900 years ago, rated [Greek: g] of the 3rd
+magnitude, thus correcting Ptolemy and agreeing with Argelander. Modern
+photometric measures confirm the estimates of Al-Sufi and Argelander. But
+it is, of course, possible that one or both stars may be variable in
+light, and [Greek: b] has actually been suspected of variation. Almost all
+the constellations afford examples of this sort. In the majority of cases,
+however, Al-Sufi agrees well with Argelander and Heis, but there are in
+some cases differences which suggest a change in relative brightness.
+
+Among other remarkable things contained in Al-Sufi's most interesting work
+may be mentioned the great nebula in Andromeda, which was first noticed in
+Europe as visible to the naked eye by Simon Marius in 1612. Al-Sufi,
+however, speaks of it as a familiar object in his time.
+
+Schjellerup says--
+
+    "For a long time many of the stars in Ptolemy's catalogue could not be
+    identified in the sky. Most of these discordances were certainly due
+    to mistakes in copying, either in longitude or latitude. Many of these
+    differences were, however, corrected by the help of new manuscripts.
+    For this purpose Al-Sufi's work is of great importance. By a direct
+    examination of the sky he succeeded in finding nearly all the stars
+    reported by Ptolemy (or Hipparchus). And even if his criticism may
+    sometimes seem inconclusive, his descriptions are not subject to
+    similar defects, his positions not depending solely on the places
+    given in Ptolemy's catalogue. For, in addition to the longitudes and
+    latitudes quoted from Ptolemy, he has described by alignment the
+    positions of the stars referred to. In going from the brightest and
+    best known stars of each constellation he indicates the others either
+    by describing some peculiarity in their position, or by giving their
+    mutual distance as so many cubits (_dzira_), or a span (_schibr_),
+    units of length which were used at that time to measure apparent
+    celestial distances. The term _dzira_ means literally the fore-arm
+    from the bone of the elbow to the tip of the middle finger, or an ell.
+    We should not, however, conclude from this that the Arabians were so
+    unscientific as to measure celestial distances by an ell, as this
+    would be quite in contradiction to their well-known knowledge of
+    Geometry and Trigonometry."
+
+With reference to the arc or angular distance indicated by the "cubit,"
+Al-Sufi states in his description of the constellation Auriga that the
+_dzira_ (or cubit) is equal to 2 deg. 20'. Three cubits, therefore, represent
+7 deg., and 4 cubits 9 deg. 20'.
+
+In Al-Sufi's own preface to his work, after first giving glory to God and
+blessings on "his elected messenger Muhammed and his family," he proceeds
+to state that he had often "met with many persons who wished to know the
+fixed stars, their positions on the celestial vault, and the
+constellations, and had found that these persons may be divided into two
+classes. One followed the method of astronomers and trust to spheres
+designed by artists, who not knowing, the stars themselves, take only the
+longitudes and latitudes which they find in the books, and thus place the
+stars on the sphere, without being able to distinguish truth from error.
+It then follows that those who really know the stars in the sky find on
+examining these spheres that many stars are otherwise than they are in the
+sky. Among these are Al-Battani, Atarid and others."
+
+Al-Sufi seems rather hard on Al-Battani (or Albategnius as he is usually
+called) for he is generally considered to have been the most
+distinguished of the Arabian astronomers. His real name was Mohammed Ibn
+Jaber Ibn Senan Abu Abdallah Al-Harrani. He was born about A.D. 850 at
+Battan, near Harran in Mesopotamia, and died about A.D. 929. He was the
+first to make use of sines instead of chords, and versed sines. The
+_Alphonsine Tables_ of the moon's motions were based on his observations.
+
+After some severe criticisms on the work of Al-Battani and Atarid, Al-Sufi
+goes on to say that the other class of amateurs who desire to know the
+fixed stars follow the method of the Arabians in the science of
+_Anva_[392] and the mansions of the moon and the books written on this
+subject. Al-Sufi found many books on the _anva_, the best being those of
+Abu Hanifa al-Dinavari. This work shows that the author knew the Arabic
+tradition better than any of the other writers on the subject. Al-Sufi,
+however, doubts that he had a good knowledge of the stars themselves, for
+if he had he would not have followed the errors of his predecessors.
+
+According to Al-Sufi, those who know one of these methods do not know the
+other. Among these is Abu-Hanifa, who states in his book that the names of
+the twelve signs (of the Zodiac) did not originate from the arrangement
+or configuration of the stars resembling the figure from which the name
+is derived. The stars, Abu-Hanifa said, "change their places, and although
+the names of the signs do not change, yet the arrangement of the stars
+ceases to be the same. This shows that he was not aware of the fact that
+the arrangement of the stars does not change, and their mutual distances
+and their latitudes, north and south of the ecliptic, are neither
+increased nor diminished." "The stars," Al-Sufi says, "do not change with
+regard to their configurations, because they are carried along together by
+a physical motion and by a motion round the poles of the ecliptic. This is
+why they are called fixed. Abu-Hanifa supposed that they are termed fixed
+because their motion is very slow in comparison with that of the planets."
+"These facts," he says, "can only be known to those who follow the method
+of the astronomers and are skilled in mathematics."
+
+Al-Sufi says that the stars of the Zodiac have a certain movement
+following the order of the signs, which according to Ptolemy and his
+predecessors is a degree in 100 years. But according to the authors of
+_al-mumtahan_ and those who have observed subsequently to Ptolemy, it is a
+degree in 66 years. According to modern measures, the precession is about
+50".35 per annum, or one degree in 71-1/2 years.
+
+Al-Sufi says that the Arabians did not make use of the figures of the
+Zodiac in their proper signification, because they divided the
+circumference of the sky by the number of days which the moon took to
+describe it--about 28 days--and they looked for conspicuous stars at
+intervals which, to the eye, the moon appeared to describe in a day and a
+night. They began with _al-scharatain_, "the two marks" ([Greek: a] and
+[Greek: b] Arietis) which were the first striking points following the
+point of the spring equinox. They then sought behind these two marks
+another point at a distance from them, equal to the space described by the
+moon in a day and a night. In this way they found _al-butain_ ([Greek: e],
+[Greek: d], and [Greek: r] Arietis); after that _al-tsuraija_, the
+Pleiades; then _al-dabaran_, the Hyades, and thus all the "mansions" of
+the moon. They paid no attention to the signs of the Zodiac, nor to the
+extent of the figures which composed them. This is why they reckoned among
+the "mansions" _al-haka_ ([Greek: l] Orionis) which forms no part of the
+signs of the Zodiac, since it belongs to the southern constellation of the
+Giant (Orion). And similarly for other stars near the Zodiac, of which
+Al-Sufi gives some details. He says that Regulus ([Greek: a] Leonis) was
+called by the Arabians _al-maliki_, the Royal Star, and that _al-anva_
+consists of five stars situated in the two wings of the Virgin. These
+stars seem to be [Greek: b], [Greek: e], [Greek: g], [Greek: d], and
+[Greek: e] Virginis, which form with Spica ([Greek: a] Virginis) a
+Y-shaped figure. Spica was called _simak al-azal_, the unarmed _simak_;
+the "armed _simak_" being Arcturus, _simak al-ramih_. These old Arabic
+names seem very fanciful.
+
+Al-Sufi relates that in the year 337 of the Hegira (about A.D. 948) he
+went to Ispahan with Prince Abul-fadhl, who introduced him to an
+inhabitant of that city, named Varvadjah, well known in that country, and
+famous for his astronomical acquirements. Al-Sufi asked him the names of
+the stars on an astrolabe which he had, and he named Aldebaran, the two
+bright stars in the Twins (Castor and Pollux), Regulus, Sirius, and
+Procyon, the two Simaks, etc. Al-Sufi also asked him in what part of the
+sky _Al-fard_ ([Greek: a] Hydrae) was, but he did not know! Afterwards, in
+the year 349, this same man was at the court of Prince Adhad-al-Davlat,
+and in the presence of the Prince, Al-Sufi asked him the name of a bright
+star--it was _al-nasr al-vaki_, the falling Vulture (Vega), and he
+replied, "That is _al-aijuk_" (Capella)! thus showing that he only knew
+the _names_ of the stars, but did not know them when he saw them in the
+sky. Al-Sufi adds that all the women "who spin in their houses" knew this
+star (Vega) by the name of _al-atsafi_, the Tripod. But this could not be
+said even of "educated women" at the present day.
+
+With reference to the number of stars which can be seen with the naked
+eye, Al-Sufi says, "Many people believe that the total number of fixed
+stars is 1025, but this is an evident error. The ancients only observed
+this number of stars, which they divided into six classes according to
+magnitude. They placed the brightest in the 1st magnitude; those which are
+a little smaller in the 2nd; those which are a little smaller again in the
+3rd; and so on to the 6th. As to those which are below the 6th magnitude,
+they found that their number was too great to count; and this is why they
+have omitted them. It is easy to convince one's self of this. If we
+attentively fix our gaze on a constellation of which the stars are well
+known and registered, we find in the spaces between them many other stars
+which have not been counted. Take, for example, the Hen [Cygnus]; it is
+composed of seventeen internal stars, the first on the beak, the brightest
+on the tail, the others on the wings, the neck and the breast; and below
+the left wing are two stars which do not come into the figure. Between
+these different stars, if you examine with attention, you will perceive a
+multitude of stars, so small and so crowded that we cannot determine their
+number. It is the same with all the other constellations." These remarks
+are so correct that they might have been written by a modern astronomer.
+It should be added, however, that _all_ the faint stars referred to by
+Al-Sufi--and thousands of others still fainter--have now been mapped down
+and their positions accurately determined.
+
+About the year 1437, Ulugh Beigh, son of Shah Rokh, and grandson of the
+Mogul Emperor Tamerlane, published a catalogue of stars in which he
+corrected Ptolemy's positions. But he seems to have accepted Al-Sufi's
+star magnitudes without any attempt at revision. This is unfortunate, for
+an _independent_ estimate of star magnitudes made in the fifteenth century
+would now be very valuable for comparison with Al-Sufi's work and with
+modern measures. Ulugh Beigh's catalogue contains 1018 stars, nearly the
+same number as given by Ali-Sufi.[393]
+
+
+
+
+CHAPTER XIX
+
+The Constellations[394]
+
+
+Curious to say, Al-Sufi rated the Pole Star as 3rd magnitude; for it is
+now only slightly less than the 2nd. At present it is about the same
+brightness as [Greek: b] of the same constellation (Ursa Minor) which
+Al-Sufi rated 2nd magnitude. It was, however, also rated 3rd magnitude by
+Ptolemy (or Hipparchus), and it may possibly have varied in brightness
+since ancient times. Admiral Smyth says that in his time (1830) it was
+"not even a very bright third size" (!)[395] Spectroscopic measures show
+that it is approaching the earth at the rate of 16 miles a second; but
+this would have no perceptible effect on its brightness in historical
+times. This may seem difficult to understand, and to some perhaps
+incredible; but the simple explanation is that its distance from the earth
+is so great that a journey of even 2000 years with the above velocity
+would make no _appreciable_ difference in its distance! This is
+undoubtedly true, as a simple calculation will show, and the fact will
+give some idea of the vast distance of the stars. The well-known 9th
+magnitude companion to the Pole Star was seen _by day_ in the Dorpat
+telescope by Struve and Wrangel; and "on one occasion by Encke and
+Argelander."[396]
+
+The star [Greek: b] Ursae Minoris was called by the Arabians _Kaukab
+al-shamali_, the North Star, as it was--owing to the precession of the
+Equinoxes--nearer to the Pole in ancient times than our present Pole Star
+was _then_.
+
+The "Plough" (or Great Bear) is supposed to represent a waggon and horses.
+"Charles' Wain" is a corruption of "churl's wain," or peasant's cart. The
+Arabians thought that the four stars in the quadrilateral represented a
+bier, and the three in the "tail" the children of the deceased following
+as mourners! In the Greek mythology, Ursa Major represented the nymph
+Callisto, a daughter of Lycaon, who was loved by Jupiter, and turned into
+a bear by the jealous Juno. Among the old Hindoos the seven stars
+represented the seven Rishis. It is the Otawa of the great Finnish epic,
+the "Kalevala." It was also called "David's Chariot," and in America it
+is known as "The Dipper."
+
+Closely north of the star [Greek: th] in Ursa Major is a small star known
+as Flamsteed 26. This is not mentioned by Al-Sufi, but is now, I find from
+personal observation, very visible, and indeed conspicuous, to the naked
+eye. I find, however, that owing to the large "proper motion" of the
+bright star (1".1 per annum) the two stars were much closer together in
+Al-Sufi's time than they are at present, and this probably accounts for
+Al-Sufi's omission. This is an interesting and curious fact, and shows the
+small changes which occur in the heavens during the course of ages.
+
+Close to the star [Greek: z], the middle star of the "tail" of Ursa Major
+(or handle of the "Plough"), is a small star known as Alcor, which is
+easily visible to good eyesight without optical aid. It is mentioned by
+Al-Sufi, who says the Arabians called it _al-suha_, "the little unnoticed
+one." He says that "Ptolemy does not mention it, and it is a star which
+seems to test the powers of the eyesight." He adds, however, an Arabian
+proverb, "I show him _al-suha_, and he shows me the moon," which seems to
+suggest that to some eyes, at least, it was no test of sight at all. It
+has, however, been suspected of variation in light. It was rated 5th
+magnitude by Argelander, Heis, and Houzeau, but was measured 4.02 at
+Harvard Observatory. It has recently been found to be a spectroscopic
+binary.
+
+The constellation of the Dragon (Draco) is probably referred to in Job
+(chap. xxvi. v. 13), where it is called "the crooked serpent." In the
+Greek mythology it is supposed to represent the dragon which guarded the
+golden apples in the Garden of the Hesperides. Some have suggested that it
+represented the serpent which tempted Eve. Dryden says, in his translation
+of Virgil--
+
+  "Around our Pole the spiry Dragon glides,
+  And like a wand'ring stream the Bears divides."
+
+The fact that the constellation Booetis rises quickly and sets slowly,
+owing to its lying horizontally when rising and vertically when setting,
+was noted by Aratus, who says--
+
+  "The Bearward now, past seen,
+  But more obscured, near the horizon lies;
+  For with the four Signs the Ploughman, as he sinks,
+  The deep receives; and when tired of day
+  At even lingers more than half the night,
+  When with the sinking sun he likewise sets
+  These nights from his late setting bear their name."[397]
+
+The cosmical setting of Booetis--that is, when he sets at sunset--is stated
+by Ovid to occur on March 5 of each year.
+
+With reference to the constellation Hercules, Admiral Smyth says--
+
+    "The kneeling posture has given rise to momentous discussion; and
+    whether it represents Lycaon lamenting his daughter's transformation,
+    or Prometheus sentenced, or Ixion ditto, or Thamyrus mourning his
+    broken fiddle, remains still uncertain. But in process of time, this
+    figure became a lion, and Hyginus mentions both the lion's skin and
+    the club; while the right foot's being just over the head of the
+    Dragon, satisfied the mythologists that he was crushing the Lernaean
+    hydra.... Some have considered the emblem as typifying the serpent
+    which infested the vicinity of Cape Taenarus, whence a sub-genus of
+    Ophidians still derives its name. At all events a poet, indignant at
+    the heathen exaltation of Hevelius, has said--
+
+        "'To Cerberus, too, a place is given--
+        His home of old was far from heaven.'"[398]
+
+Aratus speaks of Hercules as "the Phantom whose name none can tell."
+
+There were several heroes of the name of Hercules, but the most famous was
+Hercules the Theban, son of Jupiter and Alcmene wife of Amphitryon, King
+of Thebes, who is said to have lived some years before the siege of Troy,
+and went on the voyage of the Argonauts about 1300 B.C. According to some
+ancient writers, another Hercules lived about 2400 B.C., and was a
+contemporary of Atlas and Theseus. But according to Petau, Atlas lived
+about 1638 B.C., and Lalande thought that this chronology is the more
+probable.
+
+The small constellation Lyra, which contains the bright star Vega, is
+called by Al-Sufi the Lyre, the Goose, the Persian harp, and the Tortoise.
+In his translation of Al-Sufi's work, Schjellerup suggests that the name
+"Goose" may perhaps mean a plucked goose, which somewhat resembles a Greek
+lyre, and also a tortoise. The name of the bright star Vega is a
+corruption of the Arabic _vaki_. Ptolemy and Al-Sufi included all the very
+brightest stars in the "first magnitude," making no distinction between
+them, but it is evident at a glance that several of them, such as Arcturus
+and Vega, are brighter than an average star of the first magnitude, like
+Aldebaran.
+
+The constellation Perseus, which lies south-east of "Cassiopeia's Chair,"
+may be recognized by the festoon formed by some of its stars, the bright
+star [Greek: a] Persei being among them. It is called by Al-Sufi
+"_barschansch_, [Greek: Perseus], Perseus, who is _hamil ras al-gul_, the
+Bearer of the head of _al-gul_." According to Kazimirski, "_Gul_ was a
+kind of demon or ogre who bewilders travellers and devours them, beginning
+at the feet. In general any mischievous demon capable of taking all sorts
+of forms." In the Greek mythology Perseus was supposed to be the son of
+Jupiter and Danae. He is said to have been cast into the sea with his
+mother and saved by King Polydectus. He afterwards cut off the head of
+Medusa, one of the Gorgons, while she slept, and armed with this he
+delivered Andromeda from the sea-monster.
+
+The constellation Auriga lies east of Perseus and contains the bright star
+Capella, one of the three brightest stars in the northern hemisphere (the
+others being Arcturus and Vega). Theon, in his commentary on Aratus, says
+that Bellerophon invented the chariot, and that it is represented in the
+heavens by Auriga, the celestial coachman. According to Dupuis, Auriga
+represents Phaeton, who tried to drive the chariot of the sun, and losing
+his head fell into the river Eridanus. The setting of Eridanus precedes by
+a few minutes that of Auriga, which was called by some of the ancient
+writers Amnis Phai-tontis.[399] Auriga is called by Al-Sufi _numsick
+al-ainna_--He who holds the reins, the Coachman; also _al-inaz_, the
+She-goat. M. Dorn found in Ptolemy's work, the Greek name [Greek:
+Heniochoi], Auriga, written in Arabic characters. Al-Sufi says, "This
+constellation is represented by the figure of a standing man behind 'He
+who holds the head of _al-gul_' [Perseus], and between the Pleiades and
+the Great Bear."
+
+Capella is, Al-Sufi says, "the bright and great star of the first
+magnitude which is on the left shoulder [of the ancient figure] on the
+eastern edge of the Milky Way. It is that which is marked on the astrolabe
+as _al-aijuk_." The real meaning of this name is unknown. Schjellerup
+thought, contrary to what Ideler says, that the name is identical with
+the Greek word [Greek: Aix] (a goat). Capella was observed at Babylon
+about 2000 B.C., and was then known as Dilgan. The Assyrian name was
+_Icu_, and the Persian name _colca_. It was also called Capra Hircus,
+Cabrilla, Amalthea, and Olenia. In ancient times the rising of Capella was
+supposed to presage the approach of storms. Ovid says, "Olenia sidus
+pluviale Capellae."
+
+The constellation Aquila is called by Al-Sufi _al-ukab_, the Eagle, or
+_al-nasr al-tair_, the flying vulture. According to the ancient poets the
+eagle carried nectar to Jupiter when he was hidden in a cave in Crete.
+This eagle also assisted Jupiter in his victory over the Giants and
+contributed to his other pleasures. For these reasons the eagle was
+consecrated to Jupiter, and was placed in the sky. Al-Sufi says, "There
+are in this figure three famous stars [[Greek: g], [Greek: a], and [Greek:
+b] Aquilae], which are called _al-nasr al-tair_." Hence is derived the
+modern name Altair for the bright star [Greek: a] Aquilae. Al-Sufi says
+that the "common people" call "the three famous stars" _al-mizan_, the
+Balance, on account of the equality of the stars." This probably refers to
+the approximately equal distances between [Greek: g] and [Greek: a], and
+[Greek: a] and [Greek: b], and not to their relative brightness. He says
+"Between the bright one of the tail [[Greek: x] Aquilae] and the star in
+the beak of the Hen [[Greek: b] Cygni] in the thinnest part of the Milky
+Way, we see the figure of a little earthen jar, of which the stars begin
+at the bright one in the tail, and extend towards the north-west. [This
+seems to refer to [Greek: e] Aquilae and the small stars near it.] They
+then turn towards the east in the base of the jar, and then towards the
+south-east to a little cloud [4, 5, etc. Vulpeculae, a well-known group of
+small stars] which is found to the north of the two stars in the shaft of
+the Arrow [[Greek: a] and [Greek: b] Sagittae]. The cloud is on the eastern
+edge of the jar, and the bright one on the tail on the western edge; the
+orifice is turned towards the flying Vulture [Aquila], and the base
+towards the north. Among these are distinguished some of the fourth,
+fifth, and sixth magnitudes [including, probably, 110, 111, 112, 113
+Hercules, and 1 Vulpeculae] and Ptolemy says nothing of this figure, except
+the bright star in the tail of the Eagle" (see figure). The above is a
+good example of the minute accuracy of detail in Al-Sufi's description.
+
+[Illustration: AL-SUFI'S "EARTHEN JAR."]
+
+The southern portion of Aquila was formerly called Antinous, who was said
+to have been a young man of great beauty born at Claudiopolis in Bithynia,
+and drowned in the Nile. Others say that he sacrificed his life to save
+that of the Emperor Hadrian, who afterwards raised altars in his honour
+and placed his image on coins.[400]
+
+The constellation Pegasus, Al-Sufi says, "is represented by the figure of
+a horse, which has the head, legs, and forepart of the body to the end of
+the back, but it has neither hind quarters nor hind legs." According to
+Brown, Pegasus was the horse of Poseidon, the sea god. Half of it was
+supposed to be hidden in the sea, into which the river Eridanus
+flowed.[401] In the Greek mythology it was supposed to represent the
+winged horse produced by the blood which fell from the head of Medusa when
+she was killed by Perseus! Some think that it represents Bellerophon's
+horse, and others the horse of Nimrod. It was also called Sagmaria and
+Ephippiatus, and was sometimes represented with a saddle instead of wings.
+
+In describing the constellation Andromeda, Al-Sufi speaks of two series of
+stars which start from the great nebula in Andromeda; one series going
+through 32 Andromedae, [Greek: p, d], and [Greek: e] to [Greek: z] and
+[Greek: e]; and the other through [Greek: n, m, b] Andromedae into the
+constellation Pisces. He says they enclose a fish-shaped figure called by
+the Arabians _al-hut_, the Fish, _par excellence_. He speaks of two other
+series of stars which begin at [Greek: t] and [Greek: u], and diverging
+meet again at [Greek: ch] Persei, forming another "fish-like figure." The
+eastern stream starts from [Greek: t] and passes through 55, [Greek: g],
+60, 62, 64, and 65 Andromedae; and the western stream from [Greek: u]
+through [Greek: ch] 51, 54, and _g_ Persei up to [Greek: ch] Persei. The
+head of the first "fish," _al-hut_, is turned towards the north, and that
+of the second towards the south (see figure).
+
+[Illustration: AL-SUFI'S "FISHES" IN ANDROMEDA.]
+
+Al-Sufi says that the stars [Greek: a] Persei, [Greek: g, b, d], and
+[Greek: a] Andromedae, and [Greek: b] Pegasi form a curved line. This is
+quite correct, and this fine curve of bright stars may be seen at a glance
+on a clear night in September, when all the stars are high in the sky.
+
+The first constellation of the Zodiac, Aries, the Ram, was called,
+according to Aratus and Eratosthenes, [Greek: krios]. It is mentioned by
+Ovid under the name of Hellas. It was also called by the ancients the Ram
+with the golden horns. Manilius (fourth century B.C.) called it "The
+Prince." It is supposed to have represented the god Bel. Among the
+Accadians the sign meant "He who dwells on the altar of uprightness." It
+first appears on the Egyptian Zodiac; and it was sacred to Jupiter Ammon.
+In the Greek mythology it was supposed to represent the ram, the loss of
+whose fleece led to the voyage of the Argonauts. In the time of
+Hipparchus, about 2000 years ago, it was the first sign of the Zodiac, or
+that in which the sun is situated at the Vernal Equinox (about March 21 in
+each year). But owing to the precession of the equinoxes, this point has
+now moved back into Pisces.
+
+The brightest star of Aries ([Greek: a]) is sometimes called Hamal,
+derived from the Arabic _al-hamal_, a name given to the constellation
+itself by Al-Sufi. In the Accadian language it was called _Dilkur_, "the
+dawn proclaimer." Ali-Sufi says that close to [Greek: a], "as if it were
+attached to it," is a small star of the 6th magnitude, not mentioned by
+Ptolemy. This is clearly [Greek: k] Arietis. The fact of Al-Sufi having
+seen and noticed this small star, which modern measures show to be below
+the 5th magnitude, is good evidence of his keen eyesight and accuracy of
+observation.
+
+According to Al-Sufi, the stars [Greek: b] and [Greek: g] Arietis were
+called by the Arabians _al-scharatain_, "the two marks." They marked the
+"first mansion of the moon," and [Greek: e, d], and [Greek: r] the second
+mansion. With reference to these so-called "mansions of the moon," Admiral
+Smyth says--
+
+    "The famous _Manazil al-kamar_, i.e. Lunar mansions, constituted a
+    supposed broad circle in Oriental astronomy divided into twenty-eight
+    unequal parts, corresponding with the moon's course, and therefore
+    called the abodes of the moon. This was not a bad arrangement for a
+    certain class of gazers, since the luminary was observed to be in or
+    near one or other of these parts, or constellations every night.
+    Though tampered with by astrologers, these Lunar mansions are probably
+    the earliest step in ancient astronomy."[402]
+
+Taurus, the second constellation of the Zodiac, was in ancient times
+represented by the figure of a bull, the hinder part of which is turned
+towards the south-west, and the fore part towards the east. It had no hind
+legs, and the head was turned to one side, with the horns extended towards
+the east. Its most ancient name was _Te_, possibly a corruption of the
+Accadian _dimmena_, "a foundation-stone." The Greek name is [Greek: athor]
+([Greek: thoor], Eusebius). In the old Egyptian mythology Taurus
+represented the god Apis. According to Dupuis it also represented the 10th
+"labour of Hercules," namely, his victory over the cows of Geryon, King of
+Spain.[403] It was also supposed to represent the bull under the form of
+which Jupiter carried off Europa, daughter of Agenor, King of the
+Phoenicians. It may also refer to Io or Isis, who is supposed to have
+taught the ancient Egyptians the art of agriculture.
+
+Aldebaran is the well-known bright red star in the Hyades. It was called
+by Ptolemy _Fulgur succularum_. Ali-Sufi says it was marked on the old
+astrolabes as _al-dabaran_, "the Follower" (because it follows the Hyades
+in the diurnal motion), and also _ain al-tsaur_, the eye of the bull. It
+may be considered as a standard star of the 1st magnitude. Modern
+observations show that it has a parallax of 0".107. It is receding from
+the earth, according to Vogel, at the rate of about 30 miles a second;
+but even with this high velocity it will take thousands of years before
+its brightness is perceptibly diminished. It has a faint companion of
+about the 10th magnitude at the distance of 118", which forms a good
+"light test" for telescopes of 3 or 4 inches aperture. I saw it well with
+a 4-inch Wray in the Punjab sky. The Hyades were called _Succulae_ by the
+Romans, and in the Greek mythology were said to be children of Atlas.
+
+The star [Greek: b] Tauri, sometimes called Nath, from the Arabic
+_al-natih_, the butting, is a bright star between Capella and [Greek: g]
+Orionis (Bellatrix). It is on the tip of the horn in the ancient figure of
+Taurus, and "therefore" (says Admiral Smyth) "at the greatest distance
+from the hoof; can this have given rise to the otherwise pointless sarcasm
+of not knowing B from a bull's foot?"[404] Al-Sufi says that an imaginary
+line drawn from the star now known as A Tauri to [Greek: t] Tauri would
+pass between [Greek: u] and [Greek: k] Tauri, which is quite correct,
+another proof of the accuracy of his observations. He also says that the
+star [Greek: o] Tauri is exactly midway between A and [Greek: e], which is
+again correct. He points out that Ptolemy's position of [Greek: o] is
+incorrect. This is often the case with Ptolemy's positions, and tends to
+show that Ptolemy adopted the position given by Hipparchus without
+attempting to verify their position in the sky. Al-Sufi himself adopts
+the longitudes and latitudes of the stars as given by Ptolemy in the
+_Almagest_, but corrects the positions in his _descriptions_, when he
+found Ptolemy's places erroneous.
+
+The famous group of the Pleiades is well known; but there is great
+difficulty in understanding Al-Sufi's description of the cluster. He says,
+"The 29th star (of Taurus) is the more northern of the anterior side of
+the Pleiades themselves, and the 30th is the southern of the same side;
+the 31st is the following vertex of the Pleiades, and is in the more
+narrow part. The 32nd is situated outside the northern side. Among these
+stars, the 32nd is of the 4th magnitude, the others of the 5th." Now, it
+is very difficult or impossible to identify these stars with the stars in
+the Pleiades as they are at present. The brightest of all, Alcyone
+([Greek: e] Tauri), now about 3rd magnitude, does not seem to be mentioned
+at all by Al-Sufi! as he says distinctly that "the brightest star" (No 32
+of Taurus) is "outside" the Pleiades "on the northern side." It seems
+impossible to suppose that Al-Sufi could have overlooked Alcyone had it
+the same brightness it has now. The 32nd star seems to have disappeared,
+or at least diminished greatly in brightness, since the days of Al-Sufi.
+More than four stars were, however, seen by Al-Sufi, for he adds, "It is
+true that the stars of the Pleiades must exceed the four mentioned above,
+but I limit myself to these four because they are very near each other and
+the largest [that is, the brightest]; this is why I have mentioned them,
+neglecting the others." A full examination of the whole question is given
+by Flammarion in his interesting work _Les Etoiles_ (pp. 289-307), and I
+must refer my readers to this investigation for further details.
+
+According to Brown, Simonides of Keos (B.C. 556-467) says, "Atlas was the
+sire of seven daughters with violet locks, who are called the heavenly
+_Peleiades_."[405] The name is by some supposed to be derived from the
+Greek [Greek: pleion], full. The Old Testament word _Kimah_ (Job ix. 9 and
+xxviii. 31) and Amos (v. 8) is derived from the Assyrian _Kimta_, a
+"family." Aratus describes the Pleiades in the following lines:--
+
+  "Near his[406] left thigh together sweep along
+  The flock of Clusterers. Not a mighty span
+  Holds all, and they themselves are dim to see,
+  And seven paths aloft men say they take,
+  Yet six alone are viewed by mortal eye.
+  These seven are called by name Alkyoni
+  Kelaini, Meropi and Steropi
+  Taygeti, Elecktri, Maia queen.
+  They thus together small and faint roll on
+  Yet notable at morn and eve through Zeus."[407]
+
+The Pleiades are mentioned by Ovid. According to the ancient poets they
+were supposed to represent the children of Atlas and Hesperus, and on
+this account they were called Atlantids or Hesperides. From the
+resemblance in sound to the word [Greek: pleias], a pigeon, they were
+sometimes called "the doves," and for the same reason the word [Greek:
+plein], to navigate, led to their being called the "shipping stars." The
+word [Greek: pleias] was also applied to the priestesses of the god Zeus
+(Jupiter) at Dordona, in the groves of which temple there were a number of
+pigeons. This is, perhaps, what Aratus refers to in the last line of the
+extract quoted above. According to Neapolitan legends, the name of
+Virgil's mother was Maia. The mother of Buddha, the Hindoo _avatar_, was
+also named Maia. In Italy the Pleiades were called _Gallinata_, and in
+France _poussiniere_, both of which mean the hen and chickens, a term also
+given to them by Al-Sufi. The old Blackfoot Indians called them "The Seven
+Perfect Ones." The Crees and Ojibway Indians called them the "Fisher
+Stars." The Adipones of Brazil and some other nations claimed that they
+sprang from the Pleiades! The Wyandot Indians called them "The Singing
+Maidens."
+
+Photographs show that the brighter stars of the Pleiades are involved in
+nebulosity. That surrounding Maia seems to be of a spiral form. Now, there
+is a Sanscrit myth which represents Maia as "weaving the palpable
+universe," for which reason she was "typified as a spider." This seems
+very appropriate, considering the web of nebulous light which surrounds
+the stars of the group. Maia was also considered as a type of the
+universe, which again seems appropriate, as probably most of the stars
+were evolved from spiral nebulae.
+
+The name Hyades is supposed to be derived from the Greek word [Greek:
+hyein], to rain, because in ancient times they rose at the rainy season.
+
+In ancient Egypt, Aldebaran was called _ary_; and the Pleiades _chooa_, a
+word which means "thousands." The name Aldebaran seems to have been
+originally applied to the whole of the Hyades group. Aldebaran was also
+called by the Arabians _al-fanik_, the great Camel, and the Hyades
+_al-kilas_, the young Camels. The two close stars [Greek: u] and [Greek:
+k] Tauri were called _al-kalbain_, the dogs of Aldebaran. La Condamine
+states that the Indians of the Amazon saw in the Hyades the head of a
+bull.
+
+Gemini, the Twins, is the third constellation of the Zodiac. It was also
+called Gemelli, etc. According to Dupuis it represents the 11th "labour of
+Hercules"--his triumph over the dog Cerberus.[408] But some of Dupuis'
+ideas seem very fanciful. The Twins are usually called Castor and Pollux,
+but they were also called by the ancient writers Apollo and Hercules;
+Jason and Triptolemus; Amphion and Zethus; and Theseus and Peritheus. In
+Egypt they represented the deities Horus and Hippocrates. Brown thinks
+that the "Great Twins" were originally the sun and moon, "who live
+alternately. As one is born the other dies; as one rises the other
+sets."[409] This applies to the full moon, but does not seem applicable to
+the other lunar phases.
+
+Gemini was the constellation to which Dante supposed himself transported
+when he visited the stellar heavens.[410] He says he was born under the
+influence of this "sign."
+
+Cancer, the Crab, is the next sign of the Zodiac. In the Greek mythology
+it was supposed to have been placed in the sky by Juno to commemorate the
+crab which pinched the toes of Hercules in the Lernaean marsh. The Greek
+name was [Greek: tybi]. According to Dupuis it represents the 12th "labour
+of Hercules"--his capture of the golden apples in the Garden of the
+Hesperides, which were guarded by a Dragon. This Dragon is Draco, which
+was also called Custos Hesperidum.[411] But the connection between a crab
+and the myth of the golden apples is not obvious--unless some reference to
+"crab apples" is intended! Among the Romans, Cancer was consecrated to
+Mercury, and by the ancient Egyptians to their god Anubis.
+
+The well-known cluster in Cancer called the Praesape, Al-Sufi says, is "a
+little spot which resembles a cloud, and is surrounded by four stars, two
+to the west [[Greek: e] and [Greek: th] Cancri] and two to the east"
+[[Greek: g] and [Greek: d]]. This cluster is mentioned by Aratus, who
+calls it the "Manger." The word Praesape is often translated "Beehive," but
+there can be no doubt that it really means "Manger," referring to the
+stars [Greek: g] and [Greek: d] Cancri, which the ancients called Aselli,
+the ass's colts. These were supposed to represent the asses which in the
+war of Jupiter against the Giants helped his victory by their braying!
+
+Admiral Smyth says in his _Bedford Catalogue_ (p. 202) that he found
+[Greek: g] and [Greek: d] Cancri both of 4th magnitude; but the
+photometric measures show that [Greek: d] is now distinctly brighter than
+[Greek: g]. An occultation of [Greek: d] Cancri by the moon is recorded as
+having occurred on September 3, B.C. 240.
+
+The fine constellation Leo, the Lion, is the next "sign" of the Zodiac,
+and is marked by the well-known "Sickle." According to Dupuis, it
+represents the first "labour of Hercules"--the killing of the Nemaelian
+lion. Manilius called it Nemaeus. It was also called Janonus sidus, Bacchi
+sidus, etc. The Greek name was [Greek: mechir], [Greek: mecheir], or
+[Greek: mechos]. In ancient Egypt, Leo was sacred to Osiris, and many of
+the Egyptian monuments are ornamented with lions' heads. It is stated in
+the Horapolla that its appearance was supposed to announce the annual
+rising of the Nile.
+
+Regulus ([Greek: a] Leonis) is the brightest and most southern of the
+stars in the "Sickle." Al-Sufi says "it is situated in the heart and is of
+the 1st magnitude. It is that which is called _al-maliki_, the royal star.
+It is marked on the astrolabe as _kalb al-asad_, the Heart of the Lion"
+(whence the name Cor Leonis). Modern photometric measures make it about
+1.3 magnitude. It has an 8-1/2 magnitude companion at about 177" distance
+(Burnham) which is moving through space with the bright star, and is
+therefore at probably the same distance from the earth as its brilliant
+primary. This companion is double (8.5, 12.5: 3".05, Burnham). The
+spectroscope shows that Regulus is approaching the earth at the rate of
+5-1/2 miles a second. Its parallax is very small--about 0".022, according
+to Dr. Elkin--which indicates that it is at a vast distance from the
+earth; and its brightness shows that it must be a sun of enormous size.
+Ptolemy called it [Greek: basiliskos], whence its Latin name Regulus,
+first used by Copernicus as the diminutive of _rex_.[412]
+
+The next constellation of the Zodiac is Virgo, the Virgin. It was also
+called by the ancients Ceres, Isis, Erigone, Fortuna, Concorda, Astraea,
+and Themis. The Greek name was [Greek: phamenoth]. Ceres was the goddess
+of the harvest. Brown thinks that it probably represents the ancient
+goddess Istar, and also Ashtoreth. According to Prof. Sayce it is the
+same as the Accadian sign of "the errand of Istar, a name due to the
+belief that it was in August that the goddess Astarte descended into Hades
+in search of her betrothed, the sun god Tammuz, or Adonis, who had been
+slain by the boar's tusk."[413] The ear of corn (Spica) is found on the
+ancient Egyptian monuments, and is supposed to represent the fertility
+caused by the annual rising of the Nile. According to Aratus, the Virgin
+lived on earth during the golden age under the name of Justice, but that
+in the bronze age she left the earth and took up her abode in the heavens.
+
+  "Justice, loathing that race of men,
+  Winged her flight to heaven."
+
+The Sphinx near the Great Pyramid has the head of a virgin on the body of
+a lion, representing the goddess Isis (Virgo) and her husband Osiris
+(Leo).
+
+Al-Sufi's 5th star of Virgo is Flamsteed 63 Virginis. Al-Sufi says it is a
+double star of the 5th magnitude. In Al-Sufi's time it formed a "naked-eye
+double" with 61 Virginis, but owing to large proper motion, 61 has now
+moved about 26 minutes of arc towards the south, and no longer forms a
+double with 63. This interesting fact was first pointed out by Flammarion
+in his work _Les Etoiles_ (p. 373).
+
+Libra, the Balance, is one of the "signs" of the Zodiac, but originally
+formed the claws of the Scorpion. It was called Juguna by Cicero, and
+Mochos by Ampelius. The Greek name was [Greek: pharmouthe]. Virgil
+suggests that it represented the justice of the emperor Augustus, honoured
+by the name of a constellation; but probably this refers to the birth of
+Augustus under the sign of Libra, as Scaliger has pointed out. According
+to Brown, "the daily seizing of the dying western sun by the claws of the
+Scorpion of darkness is reduplicated annually at the Autumnal Equinox,
+when the feeble waning sun of shortening days falls ever earlier into his
+enemy's grasp;"[414] and he says, "The Balance or Scales (Libra), which it
+will be observed is in itself neither diurnal nor nocturnal, is the only
+one of the zodiacal signs not Euphratean in origin, having been imported
+from Egypt and representing originally the balance of the sun at the
+horizon between the upper and under worlds; and secondarily the equality
+of the days and nights at the equinox."[415]
+
+According to Houzeau, Libra was formed at the beginning of the second
+century B.C., and it does not appear in any writings before those of
+Geminus and Varron.[416]
+
+Milton says in _Paradise Lost_:--
+
+  "The Eternal to prevent such horrid fray,
+  Hung forth in heaven his golden scales, yet seen
+  Betwixt Astraea and the Scorpion's sign."
+
+(Here Astraea is Virgo.)
+
+It is worth noticing that both Ptolemy and Al-Sufi rated the star [Greek:
+k] Librae as two magnitudes brighter than [Greek: l] Librae. The two stars
+are now practically of equal brightness (5th magnitude), and it seems
+impossible to believe that this could have been the case in Al-Sufi's
+time. Surely a careful observer like Al-Sufi, who estimated the relative
+brightness of stars to a third of a magnitude, could not possibly have
+made an error of two magnitudes in the brightness of two stars near each
+other! It should be stated, however, that [Greek: k] Librae was rated 5th
+magnitude by Argelander and Heis, and [Greek: l], 6th magnitude by the
+same excellent observers.
+
+The next "sign" of the Zodiac, Scorpion, was consecrated by the Romans to
+Mars, and by the Egyptians to Typhon.[417] It was called _Nepa_ by Cicero,
+_Martis sidus_ by Manilius, and _Fera magna_ by Aratus. The Greek name was
+[Greek: pachon].
+
+Mr. E. B. Knobel has called attention to a curious remark of Ptolemy with
+reference to the bright star Antares ([Greek: a] Scorpii), "Media earum
+quae _tendit ad rapinam_ quae dicitur Cor Scorpionis"; and he made a similar
+remark with reference to Betelgeuse ([Greek: a] Orionis) and others. But
+Mr. Robert Brown[418] explains the remark by the fact that in ancient
+times these stars rose in the morning at a time when caravans were exposed
+to dangers from robbers. Thus the term had nothing to do with the aspect
+or colour of these stars, but was merely a reference to their supposed
+astrological influence on human affairs.
+
+In the Egyptian _Book of the Dead_, Silkit was a goddess who assumed the
+form of a scorpion in the sky. She was supposed to be the daughter of
+_Ra_.
+
+With reference to stars "outside" the ancient figure of Scorpio, the
+first, Al-Sufi says, "is a star which immediately follows _al-schaulat_"
+[[Greek: l]] and [Greek: k], "it is of small 4th magnitude; Ptolemy calls
+it [Greek: nepheloeides]" [nebulous]. Schjelerup, in his translation of
+Al-Sufi's work, does not identify this object; but it is very evidently
+[Greek: g] Telescopii, which lies exactly in the position described by
+Al-Sufi. Now, it is a very interesting and curious fact that Ptolemy
+called it nebulous, for in the same telescopic field with it is the nebula
+_h_ 3705 (= Dunlop 557). Dunlop describes it as a "small well-defined
+rather bright nebula, about 20" in diameter; a very small star precedes
+it, but is not involved; following [Greek: g] Telescopii." Sir John
+Herschel at the Cape found it fairly resolved into very faint stars, and
+adds, "The whole _ground_ of the heavens, for an immense extent is
+thickly sown with such stars. A beautiful object."[419] This perhaps
+accounts for the nebulous appearance of the star as seen by Ptolemy.
+
+Several _novae_ or temporary stars are recorded as having appeared in
+Scorpio. One in the year B.C. 134 is stated by Pliny to have induced
+Hipparchus to form his catalogue of stars. This star was also observed in
+China. Its exact position is unknown, but Flammarion thinks it may
+possibly have appeared about 4 deg. north of the star [Greek: b] Scorpii.
+Another new star is said to have appeared in A.D. 393, somewhere in the
+Scorpion's tail. One in A.D. 1203 and another in 1584 are also mentioned,
+the latter near [Greek: p] Scorpii.
+
+The constellation Scorpio seems to be referred to by Dante in his
+_Purgatorio_ (ix. 4-6) in the lines--
+
+  "De gemma la sua fronte era lucenta
+  Poste in figura del fredda animale
+  Che con la coda percota la genta,"
+
+perhaps suggested by Ovid's remark--
+
+  "Scorpius exhibit caudaque menabitur unca."[420]
+
+Next to Scorpio comes Sagittarius, the Archer. It is said to have been
+placed in the sky as a symbol of Hercules, a hero who was held in the
+greatest veneration by the ancient Egyptians. The horse, usually
+associated with this constellation, was a symbol of war. It was also
+called by the ancients Chiron, Arcitenens, Minotaurus, Croton, etc. The
+Greek name was [Greek: pauni], or [Greek: paoni]. Chiron was supposed to
+be the son of Saturn and Phillyra, and first taught men to ride on horses.
+The name is derived from the Greek [Greek: cheir], a hand. Some writers,
+however, think that Chiron is represented by the constellation of the
+Centaur, and others say that Sagittarius represents the Minotaur loved by
+Persephone. According to Dupuis, Sagittarius represents the 5th "labour of
+Hercules," which consisted in hunting the birds of the lake Stymphalus,
+which ravaged the neighbouring countries. These birds are perhaps
+represented by Cygnus, Altair, and the Vulture (Lyra). The Lyre probably
+represents the musical instrument which Hercules used to frighten the
+birds.[421]
+
+According to Al-Sufi, the Arabians called the stars [Greek: g, d, e], and
+[Greek: e] Sagittarii which form a quadrilateral figure, "the Ostrich
+which goes to the watering place," because they compared the Milky Way to
+a river. They compared the stars [Greek: s, ph, t], and [Greek: z]
+Sagittarii, which form another quadrilateral, to an ostrich which has
+drunk and returns from the "watering place." He says that the star [Greek:
+l] Sagittarii forms with these two "ostriches" a tent, and certainly the
+figure formed by [Greek: l, ph, z, e], and [Greek: d] is not unlike a
+tent. Al-Sufi says more about these "ostriches"; but the ideas of the old
+Arabians about the stars seem very fanciful.
+
+A "temporary star" is recorded in the Chinese Annals of Ma-touan-lin as
+having appeared in May, B.C. 48, about 4 deg. distant from [Greek: m]
+Sagittarii. Another in the year 1011 A.D. appeared near the quadrilateral
+figure formed by the stars [Greek: s, t, z], and [Greek: ph] Sagittarii.
+This may perhaps be identified with the object referred to by Hepidannus
+in the year 1012, which was of extraordinary brilliancy, and remained
+visible "in the southern part of the heavens during three months." Another
+is mentioned near the same place in A.D. 386 (April to July).[422] The
+number of "temporary stars" recorded in this part of the heavens is very
+remarkable.
+
+According to Brown, Sagittarius is depicted on a stone, cir. B.C. 1100,
+found at Babilu, and now in the British Museum.[423]
+
+       *       *       *       *       *
+
+The next of the "signs of the Zodiac" is Capricornus, the Goat. In the
+Arabo-Latin edition of Ptolemy's _Almagest_ it is called Alcaucurus. It is
+supposed to represent Amalthea, the goat which nursed Jupiter. According
+to Dupuis it represented the 6th "labour of Hercules," which was the
+cleaning out of the Augean stables.[424]
+
+[Greek: a]_{2} Capricorni is the northern of two stars of the 4th
+magnitude ([Greek: a] and [Greek: b] Capricorni). It really consists of
+two stars visible to the naked eye. The second of these two stars ([Greek:
+a]_{1}) is not mentioned by Al-Sufi, but I find that, owing to proper
+motion, they were nearer together in his time (tenth century), and were
+evidently seen by him as one star. [Greek: b] Capricorni (about 3rd
+magnitude) is a very wide double star (3-1/2, 6; 205"), which may be seen
+with any small telescope. The fainter star was found to be a close double
+by Burnham. At present [Greek: b] is brighter than [Greek: a], although
+rated of the same brightness by Al-Sufi.
+
+Aquarius is the next "sign of the Zodiac." It is supposed to represent a
+man pouring water out of an urn or bucket. Other names given to this
+constellation were Aristaeus, Ganymede, Cecrops, Amphora, Urna, and Aqua
+tyrannus. According to Dupuis it represents the 7th "labour of Hercules,"
+which was his victory over the famous bull which ravaged Crete.[425] But
+the connection between a bull and a bucket is not obvious. Aquarius is
+represented in several places on the Egyptian monuments. Some of the
+ancient poets supposed that it represented Deucalion (the Noah of the
+Greek story of the Deluge); others thought that it represented Cecrops,
+who came to Greece from Egypt, built Athens, and was also called Bifornis.
+Others say that he was Ganymede, the cup-bearer of the gods.
+
+There is some difficulty about the identification of some of Al-Sufi's
+stars in Aquarius. His sixth star (Fl. 7) is nearly 10 deg. south-west of
+[Greek: b] Aquarii, and is, Al-Sufi says, "the following of three stars in
+the left hand, and precedes the fourth [[Greek: b]] ... it is of the 6th
+magnitude. Ptolemy calls it third, but in reality it is very faint" [now
+about 6th magnitude]. The seventh [[Greek: m]] is the middle one of the
+three and about 4-1/2 magnitude, although Al-Sufi calls it "small fifth"
+[Ptolemy rated it 4]. The eighth star, [Greek: e], is the preceding of the
+three and about 3.8, agreeing closely with Al-Sufi's 4.3. Ptolemy rated it
+3. This star is mentioned under the name _nou_ in the time of
+_Tcheou-Kong_ in the twelfth century B.C. Al-Sufi says, "These three stars
+are followed by a star of the 5th magnitude which Ptolemy has not
+mentioned. It is brighter than the sixth star" [Fl. 7]. This is evidently
+[Greek: n] Aquarii. If, however, we plot Ptolemy's positions as given by
+Al-Sufi, it seems probable that _Ptolemy's_ sixth star was really [Greek:
+n], and that either [Greek: m] or Fl. 7 was not seen by him. As Ptolemy
+called his seventh star 4th magnitude, and his sixth and eighth stars 3rd
+magnitude, some considerable change of brightness seems to have taken
+place in these stars; as [Greek: n] is now only 4-1/2 and Fl. 7 only a
+bright sixth. Variation was suspected in Fl. 7[426] by Gould. I found it
+very reddish with binocular in October, 1892. Burnham found it to be a
+close double star, the companion being about 12th magnitude at a distance
+of only 2". It is probably a binary.
+
+According to Al-Sufi, the Arabians called the second and third stars of
+the figure ([Greek: a] and [Greek: o] Aquarii) _sad al-malik_ (_malk_ or
+_mulk_), "the Good Fortune of the king." They called the fourth and fifth
+stars ([Greek: b] and [Greek: x] Aquarii) with the twenty-eighth star of
+Capricornus (_c_) _sad al-sund_, "the Good Fortune of the Happy Events."
+"This is the 24th mansion of the moon." These stars rose at the time of
+year when the cold ends, and they set at the time the heat ends. Hence,
+Al-Sufi says, "when they rise the rains begin, and when they set the
+unhealthy winds cease, fertility abounds, and the dew falls." Hence
+probably the Arabic names. This, of course, applies to the climate of
+Persia and Arabia, and not to the British Isles. Al-Sufi says, "They call
+the 6th, 7th, and 8th stars _sad bula_, 'The Good Fortune which swallows
+up!' This is the 23rd mansion of the moon. They say that it is so called
+because that at the time of the Deluge it rose at the moment when God
+said, 'O earth! absorb the waters' (Koran, chap, xi., v. 46). They called
+the stars [Greek: g, p, z] and [Greek: e] Aquarii _sad al-achbija_, 'the
+the Good Fortune of the tents'; this is the 25th mansion of the moon, and
+they give them this name because of these four stars, three form a
+triangle, the fourth [[Greek: z]] being in the middle." The three were
+considered to form a tent.
+
+The Arabians called the bright star Fomalhaut "in the mouth of the
+southern fish _al-dhifda al-auval_, 'the first Frog,' as the bright one on
+the southern point of the tail of Kitus [Cetus] is called _al-dhifda
+al-tsani_ [[Greek: b] Ceti], 'the second Frog.'" Fomalhaut was also called
+_al-zhalim_, "the male ostrich."
+
+Al-Sufi says, "Some of the Arabians state that a ship is situated to the
+south of Aquarius." The stars in the Southern Fish (Piscis Australis) seem
+to be here referred to.
+
+The constellation Pisces, the Fishes, is the last of the "signs of the
+Zodiac." The Fishes appear on an ancient Greek obelisk described by
+Pococke. Among the Greeks this sign was consecrated to Venus; and in Egypt
+to Nepthys, wife of Typhon and goddess of the sea. Pisces is said to end
+the Zodiac as the Mediterranean Sea terminated Egypt. This idea was
+suggested by Schmidt, who also conjectured that the Ram (Aries) was placed
+at the beginning of the Zodiac because Thebes, a town sacred to Jupiter
+Ammon, was at the beginning of Egypt in ancient times; and he thought that
+the constellation Triangulum, the Triangle, represented the Nile Delta,
+Eridanus being the Nile.[427] The constellation was represented in ancient
+times by two fishes connected by a cord tied to their tails. The southern
+of these "fishes" lies south of the "Square of Pegasus," and the northern
+between Andromeda and Aries. According to Manilius, the origin of these
+fishes is as follows: Venus, seeing Typhon on the banks of the river
+Euphrates, cast herself with her son into the river and they were
+transformed into fishes!
+
+Some of the Arabians substituted a swallow for the northern of the two
+fishes--the one below Andromeda. The swallow was a symbol of Spring.
+According to Dupuis, Pisces represents the 8th "labour of Hercules," his
+triumph over the mares of Diomed which emitted fire from their
+nostrils.[428] But the connection between fishes and mares is not obvious,
+and some of Dupuis' ideas seem very fanciful. Here he seems to have found
+a "mare's nest."
+
+The constellation Cetus, the Whale, represents, according to ancient
+writers, the sea monster sent by Neptune to devour Andromeda when she was
+chained to the rock. Aratus calls Cetus the "dusky monster," and Brown
+remarks that "the 'Dusky Star' would be peculiarly appropriate to Mira
+(the wondrous [Greek: o] Ceti)."[429] Cetus was also called Canis
+Tritonis, or Dog of the Sea, Bayer in his Atlas (1603) shows a dragon
+instead of a whale, finding it so represented on some ancient spheres.
+Al-Sufi calls it Kitus or [Greek: ketos], the whale. He says, "it is
+represented by the figure of a marine animal, of which the fore part is
+turned towards the east, to the south of the Ram, and the hinder part
+towards the west behind the three 'extern' stars of Aquarius."
+
+Al-Sufi does not mention the variable star [Greek: o] Ceti, now called
+Mira, or the "wonderful," nor does he refer to any star in its immediate
+vicinity. We may, therefore, conclude that it was near a minimum of light
+at the time of his observation of the stars of Cetus.
+
+The constellation of Orion, one of the finest in the heavens, was called
+by Al-Sufi _al-djabbar_, "the Giant," and also _al-djauza_, "the Spouse."
+The poet Longfellow says--
+
+  "Sirius was rising in the east
+  And, slow ascending one by one,
+  The kindling constellations shone
+  Begirt with many a blazing star
+  Stood the great giant Al-gebar
+  Orion, hunter of the beast!
+  His sword hung gleaming at his side
+  And on his arm, the lion's hide--
+  Scattered across the midnight air
+  The golden radiance of its hair."
+
+Al-Sufi says it "is represented by the figure of a standing man, to the
+south of the sun's path. This constellation very much resembles a human
+figure with a head and two shoulders. It is called _al-djabbar_, 'the
+Giant,' because it has two thrones, holds a club in his hand, and is
+girded with a sword." Orion is supposed to have been a son of Neptune;
+but there are many stories of the origin of the name. It is also said to
+be derived from the Greek word [Greek: ora], because the constellation was
+used to mark the different times of the year. According to the ancient
+fable, Orion was killed by a scorpion, and was placed in the sky at the
+request of Diana. According to Houzeau, the name comes from _oriri_, to be
+born. Scorpio rises when Orion sets, and he thinks that the idea of the
+ancients was that the Scorpion in this way kills the giant Orion.
+
+In ancient Egypt Orion was called _Sahu_. This name occurs on the
+monuments of the Ptolemies, and also on those of the Pharaohs. It is also
+mentioned in the _Book of the Dead_. It seems to have been considered of
+great importance in ancient Egypt, as its heliacal rising announced that
+of Sirius, which heralded the annual rising of the Nile.
+
+The constellation Eridanus lies south of Taurus, east of Cetus, and west
+of Lepus. In ancient times it was supposed to represent the Nile or the
+Po. Ptolemy merely calls it [Greek: Potamou asterismos], or asterism of
+the river. It was called Eridanus by the Greeks, and Fluvius by the
+Romans. It appears to correspond with the Hebrew Shicor. Al-Sufi calls it
+_al-nahr_, "the River."
+
+One of the most interesting points in Al-Sufi's most interesting work is
+the identity of the bright star known to the ancient astronomers as
+_achir al-nahr_, "the End of the River," and called by Ptolemy [Greek:
+Eschatos tou potamou], "the Last in the River." Some astronomers have
+identified this star with [Greek: a] Eridani (Achernar), a bright southern
+star of the 1st magnitude, south of Eridanus. But Al-Sufi's description
+shows clearly that the star he refers to is really [Greek: th] Eridani;
+and the reader will find it interesting to follow his description with a
+star map before him. Describing Ptolemy's 34th star of Eridanus (the star
+in question), he says, "the 34th star is found before [that is west of]
+these three stars [the 31st, 32nd, and 33rd, which are [Greek: u]{2}, Du,
+and [Greek: u]' in Proctor's Atlas], the distance between it and that of
+the three which is nearest being about 4 cubits [9 deg. 20']. It is of the
+first magnitude; it is that which is marked on the southern astrolabe, and
+called _achir al-nahr_, 'the End of the River.' There are before this
+bright one two stars, one to the south, [[Greek: s] Eridani, not shown in
+Proctor's small Atlas], the other to the north [[Greek: i] Eridani];
+Ptolemy does not mention these. One of these stars is of the 4th
+magnitude, the other of the 5th. There is behind the same [that is, east
+of it] a star of the 4th magnitude distant from it two cubits [[Greek: e]
+Eridani]. To the south of the three stars which follow the bright one
+there are some stars of the 4th and 5th magnitudes, which he [Ptolemy] has
+not mentioned."
+
+Now, a glance at a star map of this region will show clearly that the
+bright star referred to by Al-Sufi is undoubtedly [Greek: th] Eridani,
+which is therefore the star known to the ancients as the "End of the
+River," or the "Last in the River."
+
+The position given by Ptolemy agrees fairly well with Al-Sufi's
+description, although the place is slightly erroneous, as is also the case
+with Fomalhaut and [Greek: b] Centauri. It is impossible to suppose that
+either Ptolemy or Al-Sufi could have seen [Greek: a] Eridani, as it is too
+far south to be visible from their stations, and, owing to the precession
+of the equinoxes, the star was still further south in ancient times.
+Al-Sufi says distinctly that the distance between Ptolemy's 33rd star
+(which is undoubtedly _h_ Eridani, or Proctor's [Greek: u]') and the 34th
+star was "4 cubits," or 9 deg. 20'. The actual distance is about 9 deg. 11', so
+that Al-Sufi's estimate was practically correct. Halley, in his _Catalogus
+Stellarium Australium_, identifies Ptolemy's star with [Greek: th]
+Eridani, and Baily agreed with him.[430] Ulugh Beigh also identifies the
+"Last in the River" with [Greek: th] Eridani. The Arabic observer Mohammed
+Ali Achsasi, who observed in the seventeenth century, called [Greek: th]
+Eridani _Achr al-nahr_, and rated it first magnitude.[431] To argue, as
+Bode and Flammarion have done, that Ptolemy and Al-Sufi may have heard of
+[Greek: a] Eridani from travellers in the southern hemisphere, is to beg
+the whole question at issue. This is especially true with reference to
+Al-Sufi, who says, in the preface to his work, that he has described the
+stars "as seen with my own eyes." [Greek: a] Eridani is over 11 "cubits"
+from _h_ Eridani instead of "4 cubits" as Al-Sufi says. This shows
+conclusively that the star seen by Al-Sufi was certainly _not_ [Greek: a]
+Eridani. The interest of the identification is that Al-Sufi rated [Greek:
+th] Eridani of the _first_ magnitude, whereas it is now only 3rd
+magnitude! It was measured 3.06 at Harvard and estimated 3.4 by Stanley
+Williams, so that it has evidently diminished greatly in brightness since
+Al-Sufi's time. There is an interesting paper on this subject by Dr.
+Anderson (the discoverer of Nova Aurigae and Nova Persei) in _Knowledge_
+for July, 1893, in which he states that the "Last in the River," according
+to the statements of Hipparchus and Ptolemy, _did_ rise above their
+horizon at a certain time of the year, which [Greek: a] Eridani could not
+possibly have done. This seems sufficient to settle the question in favour
+of [Greek: th] Eridani. Dr. Anderson says, "It is much to be regretted
+that Professor Schjellerup, the able and industrious translator of Sufi,
+has allowed this to escape his notice, and helped in the preface and note
+to his work to propagate the delusion that [Greek: a] Eridani is Ptolemy's
+'Last in the River'"; and in this opinion I fully concur. Al-Sufi's clear
+account places it beyond a doubt that the star known to Hipparchus,
+Ptolemy, Al-Sufi, and Ulugh Beigh as the "Last in the River" was [Greek:
+th] Eridani. [Greek: th] must have diminished greatly in brightness since
+Al-Sufi's time, for in ranking it as 1st magnitude he placed it in a very
+select list. He only rated thirteen stars in the whole heavens as being of
+the 1st magnitude. These are: Arcturus, Vega, Capella, Aldebaran, Regulus,
+[Greek: b] Leonis, Fomalhaut, Rigel, [Greek: th] Eridani, Sirius, Procyon,
+Canopus, and [Greek: a] Centauri. _All_ these stars were actually _seen_
+by Al-Sufi, _and described from his own observations_. He does not mention
+[Greek: a] Eridani, as it was not visible from his station in Persia.
+
+[Greek: th] Eridani is a splendid double star (3.40, 4.49: 8".38, 1902,
+Tebbutt). I found the components white and light yellow with 3-inch
+refractor in the Punjab. Dr. Gould thinks that one of the components is
+variable to some extent. This is interesting, considering the brilliancy
+of the star in Al-Sufi's time. The brighter component was found to be a
+spectroscopic binary by Wright, so that on the whole the star is a most
+interesting object.
+
+The small constellation Lepus, the Hare, lies south of Orion. Pliny calls
+it Dasypus, and Virgil Auritus. In ancient Egypt it was the symbol of
+vigilance, prudence, fear, solitude, and speed.[432] It may perhaps
+represent the hare hunted by Orion; but some say it was placed in the sky
+to commemorate a terrible plague of hares which occurred in Sicily in
+ancient times.
+
+A little north-west of the star [Greek: m] Leporis is Hind's "crimson
+star" (R.A. 4{h} 53{m}, S. 14 deg. 57', 1900) described by him as "of the most
+intense crimson, resembling a blood drop on the background of the sky; as
+regards depth of colour, no other star visible in these latitudes could be
+compared with it." It is variable from about the 6th to the 8th magnitude,
+with a period of about 436 days from maximum to maximum.
+
+The constellation Canis Major, the Great Dog, is remarkable for containing
+Sirius, the brightest star in the heavens. In the Greek mythology it was
+supposed to represent a dog given by Aurora to Cephalus as the swiftest of
+all dogs. Cephalus wished to match it against a fox which he thought
+surpassed all animals for speed. They both ran for so long a time, so the
+story goes, that Jupiter rewarded the dog by placing it among the stars.
+But probably the dog comes from Anubis, the dog-headed god of the ancient
+Egyptians. According to Brown, Theogirius (B.C. 544) refers to the
+constellation of the Dog.[433] He thinks that Canis Major is probably "a
+reduplication" of Orion; Sirius and [Greek: b] Canis Majoris corresponding
+to [Greek: a] and [Greek: g] Orionis; [Greek: d], 22, and [Greek: e] Canis
+Majoris to the stars in Orion's belt ([Greek: d, e], and [Greek: z]
+Orionis); and [Greek: e]; and [Greek: k] Canis Majoris with [Greek: k] and
+[Greek: b] Orionis.[434]
+
+The Arabic name of Sirius was _al-schira_, which might easily be corrupted
+into Sirius. The Hebrew name was Sihor. According to Plutarch, the
+Ethiopians paid regal honours to the Celestial Dog. The Romans used to
+sacrifice a dog in its honour at the fetes called Robigalia, which were
+held on the seventh day before the Calends of May, and nine days after the
+entry of the sun into Taurus. Pliny says, "Hoc tempus Varro determinat
+sole decimam partem Tauri obtinenti quod canis occidit, sidus per se
+vehemens," etc.[435]
+
+Owing to some remarks of Cicero, Horace, and Seneca, it has been supposed
+that in ancient times Sirius was of red colour. Seneca says, "Nec mirum
+est, si terra omnis generis et varia evaporatio est; quam in coelo
+quoque non unus appareat color rerum, sed acrior sit Caniculae rubor,
+Nartis remissior, Jovis nullus, in lucem puram nitore perducto."[436] It
+is now brilliantly white with a bluish tinge. But this change of colour is
+somewhat doubtful. The remarks of the ancient writers may possibly refer
+to its great brilliancy rather than its colour. Al-Sufi says nothing about
+its colour, and it was probably a white star in his time. If it were red
+in his day he would most probably have mentioned the fact, as he does in
+the case of several red stars. Brown, however, quotes the following from
+Ibn Alraqqa, an Arabian observer:--
+
+  "I recognize Sirius _shining red_, whilst the morning is becoming white.
+  The night fading away, has risen and left him,
+  The night is not afraid to lose him, since he follows her."
+
+Schjellerup thinks that it is very doubtful that Sirius was really red as
+seen by Hipparchus and Ptolemy. But in an exhaustive inquiry made by Dr.
+See on the supposed change of colour,[437] he comes to the conclusion that
+Sirius was really red in ancient times. Seneca states distinctly that it
+was redder than Mars (see extract above), and other ancient writers refer
+to its red colour. It has been generally supposed that the Arabian
+astronomer Alfraganus, in his translation of Ptolemy's _Almagest_, refers
+to only five red stars observed by Ptolemy, namely, Arcturus, Aldebaran,
+Betelgeuse, Antares, and Pollux. But Dr. See shows that this idea is due
+to a mistranslation of Alfraganus by Plato Tibertinus in 1537, and that
+Ptolemy did not speak of "five red stars," but five _nebulous_ stars, as
+stated by Christmann and Golius. Ptolemy described Sirius as [Greek:
+upokirros], "fiery red," the same word used with reference to the other
+stars mentioned above. The change of colour, if any, probably took place
+before Al-Sufi's time.
+
+Dr. See says--
+
+    "Prof. Newcomb rejects the former well-authenticated redness of
+    Sirius, because he cannot explain the fact. But the ink was scarcely
+    dry on his new book on the stars, in which he takes this position,
+    when Nova Persei blazed forth in 1901; and observers saw it change
+    colour from day to day and week to week. Could any one explain the
+    cause of these numerous and conspicuous changes of colour? Shall we,
+    then, deny the changes of colour in Nova Persei, some of which were
+    noticed when it was nearly as bright as Sirius?"[438]
+
+On the ceiling of the Memnonium at Thebes the heliacal rising of Sirius is
+represented under the form and name of Isis. The coincidence of this
+rising with the annual rising of the Nile is mentioned by Tibullus and
+Aclian. About 4000 B.C. the heliacal rising of Sirius coincided with the
+summer solstice (about June 21) and the beginning of the rising of the
+Nile. The festival in honour of this event was held by the Egyptians about
+July 20, and this marked the beginning of the sacred Egyptian year. On the
+summit of Mount Pelion in Thessaly there was a temple dedicated to Zeus,
+where sacrifices were offered at the rising of Sirius by men of rank who
+were chosen for the purpose by the priests and wore fresh sheepskins.
+
+Sirius seems to have been worshipped by the ancient Egyptians under the
+name of Sothis, and it was regarded as the star of Isis and Osiris. The
+last name without the initial O very much resembles our modern name.
+
+According to Al-Sufi, the Arabians called Sirius _al-schira al-abur_,
+"Sirius which has passed across," also _al-schira al Jamanija_, "the
+Sirius of Yemen." He says it is called _al-abur_, "because it has passed
+across the Milky Way into the southern region." He relates a mythological
+story why Sirius "fled towards the south" and passed across the Milky Way
+towards Suhail (Canopus). The same story is told by Albufaragius[439]
+(thirteenth century). (The story was probably derived from Al-Sufi.) Now,
+it seems to me a curious and interesting fact that the large proper motion
+of Sirius would have carried it across the Milky Way from the eastern to
+the western border in a period of 60,000 years. Possibly the Arabian story
+may be based on a tradition of Sirius having been seen on the opposite, or
+eastern, side of the Milky Way by the men of the early Stone Age. However
+this may be, we know from the amount and direction of the star's proper
+motion that it must have passed across the Milky Way from east to west
+within the period above stated. The Arabic name _al-abur_ is not,
+therefore, a merely fanciful one, but denotes an _actual fact_. The
+proper motion of Sirius could not possibly have been known to the
+ancients, as it was only revealed by accurate modern observations.
+
+The little constellation Canis Minor, the Little Dog, lies south of Gemini
+and Cancer. Small as it is, it was one of the original forty-eight
+constellations of Ptolemy. In the Greek mythology it was supposed to
+represent either one of Diana's hunting dogs, or one of Orion's hounds.
+Ovid calls it the dog of Icarus. Others say it was the dog of Helen, who
+was carried off by Paris. According to the old poets, Orion's dog, or the
+dog of Icarus, threw himself into a well after seeing his master perish.
+The name Fovea, given to the constellation by Bayer, signifies a pit where
+corn was deposited. This comes from the fact that the rising of the star
+Procyon ([Greek: a] Canis Minoris) indicated the season of abundance. But
+Lalande thought it more probable that the idea of a pit came from the
+Greek [Greek: seiros], which means a corn store, and that it was
+confounded with Sirius.
+
+The name of the bright star Procyon ([Greek: a] Canis Minoris) is derived
+from the Greek [Greek: prokuon], "the advanced day," because it appeared
+in the morning sky before Sirius. Procyon was called by the Hindoos
+Hanouman after their famous monkey god, from whose tail a bridge is said
+to have been formed to enable the army of Rama to pass from India to
+Ceylon. Al-Sufi says that the star was marked on the old astrolabes as
+_al-schira al-schamia_, "the Syrian Sirius." It was also called, he says,
+_al-schira al-gumaisa_, "the Sirius with blear eyes" (!) from weeping
+because Sirius had passed across the Milky Way, Procyon remaining on the
+eastern side. Here we have the same legend again. The proper motion of
+Procyon (about the same in amount and direction as that of Sirius) shows
+that the star has been on the eastern side of the Milky Way for many ages
+past. About 60,000 years hence, Procyon will be near the star [Greek: th]
+Canis Majoris, and will then--like Sirius--have passed across the Milky
+Way.
+
+Argo, the Ship, is a large constellation south of Hydra, Monoceros, and
+Canis Major. It is called by Al-Sufi _al-safina_, "the Ship." It is
+supposed to represent the first ship ever built. The name is derived from
+the builder Argo, or from the Greek word [Greek: Argos]. This ship is said
+to have been built in Thessaly by order of Minerva and Neptune, to go on
+the expedition for the conquest of the golden fleece. The date of this
+expedition, commanded by Jason, is usually fixed at 1300 or 1400 B.C. With
+reference to the position of this supposed ship in the sky, Proctor says,
+"It is noteworthy that when we make due correction for the effects of
+precession during the past 4000 years, the old constellation Argo is set
+on an even keel, instead of being tilted some 45 deg. to the horizon, as at
+present when due south." He connects Argo with Noah's Ark.
+
+The brightest star of Argo is Canopus, called Suhail by Al-Sufi. It is the
+second brightest star in the heavens; but it is not visible in northern
+latitudes. The Harvard photometric measures make it nearly one magnitude
+brighter than the zero magnitude, about two magnitudes brighter than
+Aldebaran, and about half the brightness of Sirius. This fine star has
+been suspected of variable light. Webb says, "It was thought (1861) in
+Chili brighter than Sirius." Observing it in the Punjab, the present
+writer found it on several occasions but little inferior to Sirius,
+although very low on the southern horizon. From recent observations by Mr.
+H. C. McKay in Australia, he believes that it is variable to the extent of
+at least half a magnitude.[440] But it is difficult to establish
+variations of light in very bright stars. The parallax of Canopus is
+_very_ small, so its distance from the earth is very great, and it must be
+a sun of gigantic size. According to Al-Fargani, Canopus was called the
+star of St. Catherine by the Christian pilgrims in the tenth century.[441]
+It was called Suhail by the old Arabians, a name apparently derived from
+the root _sahl_, "a plain"; and Schjellerup suggests that the name was
+probably applied to this and some other southern stars because they seem
+to move along a plain near the southern horizon. Al-Sufi says that he
+measured the latitude of Schiraz in Persia, where he observed, and found
+it to be 29 deg. 36'; and hence for that place Canopus, when on the meridian,
+had an altitude of about 9 deg.. Canopus was the ancient name of Aboukir in
+Egypt, and is said to have derived its name from the pilot of Menelaus,
+whose name was Kanobus, and who died there from the bite of a snake. The
+star is supposed to have been named after him, and it was worshipped by
+the ancient Egyptians.
+
+Al-Sufi does not mention the famous variable star [Greek: e] Argus, which,
+owing to the precession of the equinoxes, he might possibly have seen
+_close to the horizon_, if it had been a bright star in his day. It lies
+between [Greek: ph] Velorum and [Greek: a] Crucis. Both of these stars are
+mentioned by Al-Sufi, but he says nothing of any bright star (or indeed
+any star) between them. This negative evidence tends to show that [Greek:
+e] Argus was not visible to the naked eye in Al-Sufi's time. This
+extraordinary star has in modern times varied through all degrees of
+brightness from Sirius down to the 8th magnitude! Schoenfeld thought that a
+regular period is very improbable. It seems to be a sort of connecting
+link between the long period variables and the _novae_ or temporary stars.
+It is reddish in colour, and the spectrum of its light is very similar to
+that of the temporary stars. Whether it will ever become a brilliant
+object again, time alone can tell; but from the fact that it was
+presumably faint in Al-Sufi's time, and afterwards increased to the
+brightness of Sirius, it seems possible that its light may again revive.
+
+The long constellation Hydra lies south of Cancer, Leo, Crater, Corvus,
+Virgo, and Libra. It was also called Asina, Coluber, Anguis, Sublimatus,
+etc. In the Greek mythology it was supposed to represent the Lernaean
+serpent killed by Hercules. According to Ovid, who fixed its acronycal
+rising for February 14, it had a common origin with Corvus and Crater.
+Apollo, wishing to sacrifice to Jupiter, sent the Crow with a cup to fetch
+water. On his way to the well the Crow stopped at a fig tree and waited
+for the fruit to ripen! Afterwards, to excuse his delay, he said that a
+serpent had prevented him from drawing the water. But Apollo, to punish
+the Crow for his deception, changed his plumage from white to black, and
+ordered the serpent to prevent the Crow from drinking.[442] Hydra was
+called by Al-Sufi _al-schudja_, "the Serpent, or Hydra." He says that "it
+contains twenty-five stars in the figure and two 'outside', and its head
+is to the south of the southern scale of the Balance" ([Greek: a] Librae).
+But this is clearly a mistake (one of the very few errors to be found in
+Al-Sufi's work), for he goes on to say that the head is composed of four
+stars forming a figure like the head of a horse, and he adds, "This head
+is in the middle between _al-shira al-gumaisa_ [Procyon] and _Kalb
+al-asad_ [Regulus] the Heart, inclining from these two stars a little to
+the south." This clearly indicates the stars [Greek: d, e, e], and [Greek:
+s] Hydrae which, with [Greek: z] Hydrae, have always been considered as
+forming the Hydra's head. These stars lie south of [Greek: a] and [Greek:
+b] Cancri, not south of Libra as Al-Sufi says (doubtless by a slip of the
+pen).
+
+Ptolemy's 12th star of Hydra ([Greek: a] Hydrae) is, Al-Sufi says, "the
+bright red star which is found at the end of the neck where the back
+begins; it is of the 2nd magnitude. It is that which is marked on the
+astrolabe as _unk al-schudja_, 'the neck of the serpent,' also _al-fard_,
+'the solitary one.'" Al-Sufi's estimate of its brightness agrees well with
+modern measures; but it has been suspected of variable light. Sir John
+Herschel's estimates at the Cape of Good Hope varied from 1.75 to 2.58
+magnitude. He thought that its apparent variation might be due to its
+reddish colour, and compares it to the case of [Greek: a] Cassiopeiae. But
+as this latter star is now _known_ to be irregularly variable it seems
+probable that [Greek: a] Hydrae may be variable also. Gemmill found it
+remarkably bright on May 9, 1883, when he thought it nearly equal to
+Pollux (1.2 magnitude). On the other hand, Franks thought it nearer the
+3rd than the 2nd magnitude on March 2, 1878. On April 9, 1884, the
+present writer found it only slightly less than Regulus (1.3 magnitude).
+On April 6, 1886, how-ever, it was considerably less than Regulus, but
+half a magnitude brighter than [Greek: b] Canis Minoris, or about 2-1/2
+magnitude. In the Chinese Annals it is called the "Red Bird." In a list of
+thirty stars found on a tablet at Birs-Nimroud, it is called "The son of
+the supreme temple." Although to the naked eye deserving the name of
+Alphard or "the solitary one," it is by no means an isolated star when
+examined with a telescope. It has a faint and distant companion, observed
+by Admiral Smyth; and about 25' to the west of it Ward saw a small double
+star (8, 13: 90 deg.: 50"). With a 3-inch refractor in the Punjab, I saw a
+small star of about 8-1/2 magnitude to the south and a little east of the
+bright star, probably identical with Smyth's companion. Farther off in the
+same direction I saw a fainter star, and others at greater distances in
+the field. There is also a faint star a little to the north. I also saw
+Ward's double with the 3-inch telescope.
+
+There is some difficulty in identifying the stars numbered by Ptolemy 13,
+14, and 15 in Hydra. Having plotted a map from Ptolemy's positions (as
+given by Al-Sufi), I have come to the conclusion that Ptolemy's stars are
+13 = [Greek: k] Hydrae; 14 = [Greek: u]; and 15 = [Greek: l] Hydrae,
+probably. From the clear description given by Al-Sufi of the stars
+observed by _him_, I find that _his_ stars are 13 = [Greek: u]_{1}; 14 =
+[Greek: u]_{2}; and 15 = [Greek: l] Hydrae. We must, therefore, conclude
+that Ptolemy and Al-Sufi saw only three stars where now there are
+four,[443] and that [Greek: k] Hydrae was not seen, or at least is not
+mentioned by Al-Sufi. [Greek: k] is, therefore, probably variable. It was
+rated 4 by Tycho Brahe, Bayer, and Hevelius; it is at present about 5th
+magnitude. If Ptolemy did not see [Greek: u]_{2} it is probably variable
+also, and, indeed, it has been suspected of variable light.[444]
+
+The small constellation of Crater, the Cup, lies north of Hydra, and south
+of Leo and Virgo. Al-Sufi calls it _al-batija_, "the Jar, or Cup." He says
+the Arabians called it _al-malif_, "the Crib, or Manger." According to
+Brown, the stars of Crater exactly form a Bakhian [Greek: kantharos], with
+its two handles rising above the two extremities of the
+circumference.[445] An Asia Minor legend "connected Crater with the mixing
+of human blood with wine in a bowl." Crater is referred to by Ovid in the
+lines--
+
+  "Dixit et antiqui monumenta perennia facti
+  Anguis, Avis, Crater sidera, juncta micunt."
+
+The star [Greek: a] Crateris was rated 4th magnitude by Al-Sufi and all
+other observers, and the Harvard measures make it 4.20, a satisfactory
+agreement. It has three companions noted by Admiral Smyth. One of these he
+called "intense blood colour." This is R Crateris, now known to be
+variable from above the 8th magnitude to below the 9th. Sir John Herschel
+called it an "intense scarlet star, a curious colour." With 3-inch
+refractor in the Punjab I found it "full scarlet." It is one of an open
+pair, the further of the two from [Greek: a]. There is a third star about
+9th magnitude a little south of it. Ward saw a 13th magnitude star between
+[Greek: a] and R with a 2-7/8-inch (Wray) refractor. This I saw "readily"
+with my 3-inch. Smyth does not mention this faint star, although he used a
+much larger telescope.
+
+Corvus, the Crow, is a small constellation, north of Hydra. Aratus says
+"the Crow form seems to peck the fold of the water snake" (Hydra). The
+victory which Valerius Corvinus is said to have owed to a crow has given
+it the name of Pomptina, because the victory took place near the Pontine
+marshes.[446] A quadrilateral figure is formed by its four brightest
+stars, [Greek: g, d, b], and [Greek: e] Corvi. This figure has sometimes
+been mistaken for the Southern Cross by those who are not familiar with
+the heavens. But the stars of the Southern Cross are much brighter.
+
+The constellation Centaurus, the Centaur, lies south of Hydra and Libra,
+and north of the Southern Cross. According to Dupuis, Centaurus represents
+the 3rd "labour of Hercules," his triumph over the Centaurs.[447] The
+Centaurs were supposed to be a people living in the vicinity of Mount
+Ossa, who first rode on horses. The constellation was also called Semivir,
+Chiron, Phobos, Minotaurus, etc. Al-Sufi says it "is represented by the
+figure of an animal, of which the forepart is the upper part of a man from
+the head to end of the back, and its hinder part is the hinder part of a
+horse, from the beginning of the back to the tail. It is to the south of
+the Balance [Libra] turning its face towards the east, and the hinder part
+of the beast towards the west."
+
+Al-Sufi describes very clearly the four bright stars of the famous
+"Southern Cross." Owing to precession these stars were some 7 deg. further
+north in the tenth century than they are at present, and they could have
+been all seen by Al-Sufi, when on the meridian. In the time of Ptolemy and
+Hipparchus, they were still further north, and about 5000 years ago they
+were visible in the latitude of London. Dante speaks of these four stars
+as emblematical of the four cardinal virtues, Justice, Temperance,
+Fortitude, and Prudence.
+
+Closely south-east of [Greek: a] and [Greek: b] Crucis is the dark spot in
+the Milky Way known as the "Coal Sack," which forms such a conspicuous
+object near the Southern Cross. It was first described by Pinzon in 1499;
+and afterwards by Lacaille in 1755. Although to the naked eye apparently
+black, photographs show that it contains many faint stars, but, of course,
+much less numerous than in the surrounding regions. The dark effect is
+chiefly caused by contrast with the brilliancy of the Milky Way
+surrounding it.
+
+Al-Sufi also mentions the bright stars [Greek: a] and [Greek: b] Centauri
+which follow the Southern Cross. He says that the distance between them
+"is four cubits," that is about 9 deg. 20', but it is less than this now.
+[Greek: a] has a large "proper motion" of 3".67 per annum, and was farther
+from [Greek: b] in Al-Sufi's time than it is at present. This, however,
+would not _wholly_ account for the difference, and Al-Sufi's over-estimate
+is probably due to the well-known effect by which the distance between two
+stars is _apparently_ increased when they are near the horizon. Several of
+Al-Sufi's distances between southern stars are over-estimated, probably
+for the same reason.
+
+The constellation Lupus, the Wolf, is south of Libra and Scorpio. It lies
+along the western border of the Milky Way. According to ancient writers it
+represents Lycaon, King of Arcadia, a contemporary of Cecrops, who is said
+to have sacrificed human victims, and on account of his cruelty was
+changed into a wolf. Another fable is that it represents a wolf
+sacrificed by the Centaur Chiron. According to Brown, Lupus appears on the
+Euphratian planisphere discovered by George Smyth in the palace of
+Sennacherib. Al-Sufi called it _al-sabu_, "the Wild Beast." It was also
+called _al-fand_, "the Leopard," and _al-asada_, "the Lioness."
+
+Ara, the Altar, lies south of Scorpio. According to ancient writers it
+represents an altar built by Vulcan, when the gods made war against the
+Titans. It is called by Al-Sufi _al-midjman_, "the Scent Box," or "the
+Altar."
+
+The little constellation Corona Australis, the Southern Crown, lies south
+and west of Sagittarius, east of Scorpio, and west of Telescopium. Aratus
+refers to the stars in Corona Australis as--
+
+                          "Other few
+  Before the Archer under his forefeet
+  Led round in circle roll without a name."[449]
+
+But the constellation was known by the names Caduceus, Orbiculus, Corona
+Sagittarii, etc. The ancient poets relate that Bacchus placed this crown
+in the sky in honour of his mother Semele.[450] Others say that it
+represents the crown conferred on Corinne of Thebes, famous as a poet.
+
+The small constellation Piscis Australis, or the Southern Fish, lies
+south of Capricornus and Aquarius. In the most ancient maps it is
+represented as a fish drinking the water which flows from the urn of
+Aquarius.
+
+       *       *       *       *       *
+
+A good many constellations have been added to the heavens since the days
+of Al-Sufi, and notes on some of these may be of interest.
+
+CAMELOPARDALIS.--This constellation first appears on a celestial
+planisphere published by Bartschius in the year 1624. It was not formed by
+Bartschius himself, but by the navigators of the sixteenth century. It
+lies south of Ursa Minor, north of Perseus and Auriga, east of Draco, and
+west of Cassiopeia. It contains no star brighter than the 4th magnitude.
+
+LYNX.--This constellation is south of Camelopardalis and Ursa Major, and
+north of Gemini and Cancer. It was formed by Hevelius in 1660, and he
+called it the Lynx, because, he said, it contained only faint stars and
+"it was necessary to have the eyes of a lynx" to see them! Some of them
+were, however, observed by Ptolemy and Al-Sufi, and are mentioned by the
+latter under Ursa Major.
+
+CANES VENATICI, or the Hunting Dogs.--This was formed by Hevelius in 1660.
+It lies south of the Great Bear's tail, north of Coma Berenices, east of
+Ursa Major, and west of Booetis. Its brightest stars [Greek: a] (12) and
+[Greek: b] (8) were observed by Al-Sufi, and included by him in the
+"extern" stars of Ursa Major.
+
+COMA BERENICES.--This constellation lies between Canes Venatici and Virgo.
+Although it was not included among the old forty-eight constellations of
+Ptolemy, it is referred to by Al-Sufi as the Plat, or Tress of Hair, and
+he included its stars Flamsteed 12, 15, and 21 in the "extern" stars of
+Leo. It was originally formed by the poet Callimachus in the third century
+B.C., but was not generally accepted until reformed by Hevelius.
+Callimachus lived at Alexandria in the reigns of Ptolemy Philadelphus and
+Ptolemy Euergetes, and was chief librarian of the famous library of
+Alexandria from about B.C. 260 until his death in B.C. 240. Eratosthenes
+was one of his pupils. The history of the constellation is as follows:
+Berenice, wife of Ptolemy Euergetes, made a vow, when her husband was
+leaving her on a military expedition, that if he returned in safety she
+would cut off her hair and consecrate it in the temple of Mars. Her
+husband returned, and she fulfilled her vow. But on the next day the hair
+had disappeared--stolen from the temple--and Conon the mathematician
+showed Ptolemy seven stars near the constellation of the Lion which did
+not belong to any constellation. These were formed into a constellation
+and called Berenice's Hair. Conon is referred to by Catullus in the
+lines--
+
+  "Idem me ille Conon coeleste numine vidit
+  E. Berenico vertice Caesariem."
+
+Coma Berenices first occurs as a distinct constellation in the catalogue
+contained in the Rudolphine Tables formed by Kepler (epoch 1600) from the
+observations of Tycho Brahe.[451] Bayer substituted a sheaf of corn, an
+idea derived from an ancient manuscript.
+
+LEO MINOR.--This small constellation lies between Ursa Major and Leo, and
+east of the Lynx. It was formed by Halley about the year 1660; but is
+referred to by Al-Sufi, who includes one of its stars (Fl. 41) in the
+"extern" stars of Leo. There are, however, several brighter stars in the
+group. The brightest, Fl. 46, was measured 3.92 at Harvard. The star Fl.
+37 was called _praecipua_ (or brightest) by Tycho Brahe, and rated 3, but
+as it was measured only 4.77 at Harvard it may possibly have diminished in
+brightness.
+
+SEXTANS.--This constellation lies south of Leo, and north and east of
+Hydra. It was formed by Hevelius about the year 1680. According to the
+Harvard photometric measures its brightest star is Fl. 15 (4.50).
+
+MONOCEROS, or the Unicorn, lies south of Gemini and Canis Minor, north of
+Canis Major and Argo, east of Orion, and west of Hydra. It appears on the
+planisphere of Bartschius, published in 1624. According to Scaliger it is
+shown on an old Persian sphere. One of its stars, Fl. 22, is mentioned by
+Al-Sufi among the "extern" stars of Canis Major (No. 1). Another, Fl. 30,
+is given under Hydra ("Extern" No. 1) and Fl. 8, 13, and 15 are apparently
+referred to in Gemini. The star 15 Monocerotis is a little south of
+[Greek: x] Geminorum, and was measured 4.59 magnitude at Harvard. It was
+at one time supposed to be variable with a short period (about 3-1/2
+days), but this variation has not been confirmed. The spectrum is of the
+fifth type--with bright lines--a very rare type among naked-eye stars. It
+is a triple star (5, 8.8, 11.2: 2".9, 16".3) and should be seen with a
+4-inch telescope. It has several other small companions, one of which
+(139 deg..2: 75".7) has been suspected of variation in light. It was estimated
+8-1/2 by Main in 1863, but only 12 by Sadler in 1875. Observing it on
+March 28, 1889, with 3-inch refractor, I found it about one magnitude
+brighter than a star closely preceding, and estimated it 8 or 8-1/2
+magnitude. It is probably variable and should be watched.
+
+SCUTUM SOBIESKI.--This is, or was, a small constellation in the southern
+portion of Aquila, which was formed by Hevelius in 1660 in honour of the
+Polish hero Sobieski. Its principal stars, which lie south-west of [Greek:
+l] Aquilae, were mentioned by Al-Sufi and are referred to by him under that
+constellation. It contains a very bright spot of Milky Way light, which
+may be well seen in the month of July just below the star [Greek: l]
+Aquilae. Closely south of the star 6 Aquilae is a remarkable variable star R
+Scuti (R.A. 18{h} 42{m}.2, S. 5 deg. 49'). It varies from 4.8 to 7.8 with an
+irregular period. All the light changes can be observed with a good
+opera-glass.
+
+VULPECULA, the Fox.--This modern constellation lies south of Cygnus, north
+of Sagitta and Delphinus, east of Hercules, and west of Pegasus. It was
+formed by Hevelius in 1660. One of its stars, 6 Vulpeculae, is mentioned by
+Al-Sufi in describing the constellation Cygnus. Closely north-west of 32
+Vulpeculae is the short-period variable T Vulpeculae. It varies from 5.5 to
+6.2 magnitude, and its period is 4.436 days. This is an interesting
+object, and all the changes of light can be observed with an opera-glass.
+
+LACERTA.--This little constellation lies south of Cepheus and north of
+Pegasus. Its formation was first suggested by Roger and Anthelm in 1679,
+and it was called by them "The Sceptre and the Hand of Justice." It was
+named Lacerta by Hevelius in 1690, and this name it still retains. Al-Sufi
+seems to refer to its stars in his description of Andromeda, but does not
+mention any star in particular. It brightest star Fl. 7 ([Greek: a]
+Lacertae) is about the 4th magnitude. About one degree south-west of 7 is 5
+Lacertae, a deep orange star with a blue companion in a fine field.
+
+There are some constellations south of the Equator which, although above
+Al-Sufi's horizon when on the meridian, are not described by him, as they
+were formed since his time. These are as follows:--
+
+SCULPTOR.--This constellation lies south of Aquarius and Cetus, and north
+of Phoenix. Some of its stars are referred to by Al-Sufi under Eridanus
+as lying within the large triangle formed by [Greek: b] Ceti, Fomalhaut,
+and [Greek: a] Phoenicis. The brightest star is [Greek: a], about 12 deg.
+south of [Greek: b] Ceti (4.39 magnitude Harvard). About 7 deg. south-east of
+[Greek: a] is the red and variable star R Sculptoris; variable from 6.2 to
+8.8 magnitude, with a period of about 376 days. Gould describes it as
+"intense scarlet." It has a spectrum of the fourth type.
+
+PHOENIX.--This constellation lies south of Sculptor. Some of its stars
+are referred to by Al-Sufi, under Eridanus, as forming a boat-shaped
+figure. These are evidently [Greek: a, k, m, b, n], and [Greek: g].
+[Greek: a] is at the south-eastern angle of Al-Sufi's triangle referred to
+above (under "Sculptor"). (See Proctor's Atlas, No. 3.)
+
+FORNAX, the Furnace, lies south of Cetus, west of Eridanus, and east of
+Sculptor and Phoenix. It was formed by Lacaille, and is supposed to
+represent a chemical furnace with an alembic and receiver! Its brightest
+star, [Greek: a] Fornacis, is identical with 12 Eridani.
+
+CAELUM, the Sculptor's Tools, is a small constellation east of Columba, and
+west of Eridanus. It was formed by Lacaille. The brightest stars are
+[Greek: a] and [Greek: g], which are about 4-1/2 magnitude. [Greek: a] has
+a faint companion; and [Greek: g] is a wide double star to the naked eye.
+
+ANTLIA, the Air Pump, lies south of Hydra, east and north of Argo, and
+west of Centaurus. It was formed by Lacaille. It contains no star brighter
+than 4th magnitude. The brightest, [Greek: a], has been variously rated
+from 4 to 5, and Stanley Williams thinks its variability "highly
+probable."
+
+NORMA, the Rule, lies south of Scorpio. It contains no star brighter than
+the 4th magnitude.
+
+TELESCOPIUM.--This modern constellation lies south of Corona Australis,
+and north of Pavo. Its stars [Greek: a, d], and [Greek: z], which lie near
+the northern boundary of the constellation, are referred to by Al-Sufi in
+his description of Ara.
+
+MICROSCOPIUM.--This small constellation is south of Capricornus, and west
+of Piscis Australis. Its stars seem to be referred to by Al-Sufi as having
+been seen by Ptolemy, but he does not specify their exact positions. It
+contains no star brighter than 4-1/2 magnitude.
+
+       *       *       *       *       *
+
+South of Al-Sufi's horizon are a number of constellations surrounding the
+south pole, which, of course, he could not see. Most of these have been
+formed since his time, and these will now be considered; beginning with
+that immediately surrounding the South Pole (Octans), and then following
+the others as nearly as possible in order of Right Ascension.
+
+OCTANS.--This is the constellation surrounding the South Pole of the
+heavens. There is no bright star near the Pole, the nearest visible to the
+naked eye being [Greek: s] Octantis, which is within one degree of the
+pole. It was estimated 5.8 at Cordoba. The brightest star in the
+constellation is [Greek: n] Octantis ([Greek: a], Proctor), which lies
+about 12 degrees from the pole in the direction of Indus and Microscopium.
+The Harvard measure is 3.74 magnitude.
+
+HYDRUS, the Water-Snake, is north of Octans in the direction of Achernar
+([Greek: a] Eridani). The brightest star is [Greek: b], which lies close
+to [Greek: th] Octantis. The Harvard measure is 2.90. Gould says its
+colour is "clear yellow." It has a large proper motion of 2".28 per annum.
+Sir David Gill found a parallax of 0".134, and this combined with the
+proper motion gives a velocity of 50 miles a second at right angles to the
+line of sight. [Greek: g] Hydri is a comparatively bright star of about
+the 3rd magnitude, about 15-1/2 degrees from the South Pole. It is
+reddish, with a spectrum of the third type.
+
+HOROLOGIUM, the Clock, is north of Hydra, and south of Eridanus. Three of
+its stars, [Greek: a, d], and [Greek: ps], at the extreme northern end of
+the constellation, seem to be referred to by Al-Sufi in his description
+of Eridanus, but he does not give their exact positions. Most of the stars
+forming this constellation were below Al-Sufi's horizon.
+
+RETICULUM, the Net, is a small constellation to the east of Hydrus and
+Horologium. The brightest star of the constellation is [Greek: a] (3.36
+Harvard, 3.3 Cordoba, and "coloured").
+
+DORADO, the Sword Fish, lies east of Reticulum and west of Pictor. It
+contains only two stars brighter than the 4th magnitude. These are [Greek:
+a] (3.47 Harvard) and [Greek: b] (3.81 Harvard, but suspected of
+variation). About 3 deg. east of [Greek: a] Reticuli is the variable star R
+Doradus. It varies from 4.8 to 6.8, and its period is about 345 days.
+Gould calls it "excessively red." It may be followed through all its
+fluctuations of light with an opera-glass.
+
+MENSA, or Mons Mensa, the Table Mountain, lies between Dorado and the
+South Pole, and represents the Table Mountain of the Cape of Good Hope. It
+contains no star brighter than the 5th magnitude.
+
+PICTOR, the Painter's Easel, lies north of Doradus, and south of Columba.
+It contains no very bright stars, the brightest being [Greek: a] (3.30
+Harvard).
+
+VOLANS, the Flying Fish, is north of Mensa, and south and west of Argo.
+Its brighter stars, with the exception of [Greek: a] and [Greek: b], form
+an irregular six-sided figure. Its brightest star is [Greek: b] (3.65)
+according to the Harvard measures. The Cordoba estimates, however, range
+from 3.6 to 4.4, and Gould says its colour is "bright yellow." Williams
+rated it 3.8.
+
+CHAMAELION.--This small constellation lies south of Volans, and north of
+Mensa and Octans. None of its stars are brighter than the 4th magnitude,
+its brightest being [Greek: a] (4.08 Harvard) and [Greek: g] (4.10).
+
+ARGO.--This large constellation extends much further south than Al-Sufi
+could follow it. The most southern star he mentions is [Greek: e] Carinae,
+but south of this are several bright stars. [Greek: b] Carinae is 1.80
+according to the Harvard measures; [Greek: u] Carinae, 3.08; [Greek: th],
+3.03; [Greek: o], 3.56; and others. A little north-west of [Greek: i] is
+the long-period variable R Carinae (9{h} 29{m}.7, S. 62 deg. 21', 1900). It
+varies from 4.5 at maximum to 10 at minimum, and the period is about 309.7
+days. A little east of R Carinae is another remarkable variable star, _l_
+Carinae (R.A. 9{h} 42{m}.5, S. 62 deg. 3'). It varies from 3.6 to 5.0
+magnitude, with a period of 35-1/2 days from maximum to maximum. All the
+light changes can be observed with an opera-glass, or even with the naked
+eye. It was discovered at Cordoba. The spectrum is of the solar type (G).
+
+MUSCA, the Bee, is a small constellation south of the Southern Cross and
+Centaurus. Its brightest stars are [Greek: a] (2.84 Harvard) and [Greek:
+b] (3.26). These two stars form a fine pair south of [Greek: a] Crucis.
+Closely south-east of [Greek: a] is the short-period variable R Muscae. It
+varies from 6.5 to 7.6 magnitude, and its period is about 19 hours. All
+its changes of light may be observed with a good opera-glass.
+
+APUS, the Bird of Paradise, lies south-east of Musca, and north of Octans.
+Its brightest star is [Greek: a], about the 4th magnitude. Williams calls
+it "deep yellow." About 3 deg. north-west of [Greek: a], in the direction of
+the Southern Cross, is [Greek: th] Apodis, which was found to be variable
+at Cordoba from 5-1/2 to 6-1/2. The spectrum is of the third type, which
+includes so many variable stars.
+
+TRIANGULUM AUSTRALIS, the Southern Triangle, is a small constellation
+north of Apus, and south of Norma. A fine triangle, nearly isosceles, is
+formed by its three bright stars, [Greek: a, b, g], the brightest [Greek:
+a] being at the vertex. These three stars form with [Greek: a] Centauri an
+elongated cross. The stars [Greek: b] and [Greek: g] are about 3rd
+magnitude. [Greek: b] is reddish. [Greek: e] (4.11, Harvard) is also
+reddish, and is nearly midway between [Greek: b] and [Greek: g], and near
+the centre of the cross above referred to. [Greek: a] is a fine star (1.88
+Harvard) and is one of the brightest stars in the sky--No. 33 in a list of
+1500 highest stars given by Pickering. About 1 deg. 40' west of [Greek: e] is
+the short-period variable R Trianguli Australis (R.A. 15{h} 10{m}.8, S.
+66 deg. 8') discovered at Cordoba in 1871. It varies from 6.7 to 7.4, and the
+period is about 3{d} 7{h}.2. Although not visible to ordinary eyesight it
+is given here, as it is an interesting object and all its light changes
+may be well seen with an opera-glass. A little south-east of [Greek: b] is
+another short-period variable, S Trianguli Australis (R.A. 15{h} 52{m}.2,
+S. 63 deg. 30'), which varies from 6.4 to 7.4, with a period of 6.3 days; and
+all its fluctuations of light may also be observed with a good
+opera-glass.
+
+CIRCINUS, the Compass, is a very small constellation lying between
+Triangulum and Centaurus. Its brightest star, [Greek: a], is about 3-1/2
+magnitude, about 4 deg. south of [Greek: a] Centauri.
+
+PAVO, the Peacock, lies north of Octans and Apus, and south of
+Telescopium. Its brightest star is [Greek: a], which is a fine bright star
+(2.12 Harvard). [Greek: k] is a short-period variable. It varies from 3.8
+to 5.2, and the period is about 9 days. This is an interesting object, as
+all the fluctations of light can be observed by the naked eye or an
+opera-glass. [Greek: e] Pavonis was measured 4.10 at Harvard, but the
+Cordoba estimates vary from 3.6 to 4.2. Gould says "it is of a remarkably
+blue colour."
+
+INDUS.--This constellation lies north of Octans, and south of Sagittarius,
+Microscopium, and Grus. One of its stars, [Greek: a], is probably referred
+to by Al-Sufi in his description of Sagittarius; it lies nearly midway
+between [Greek: b] Sagittarii and [Greek: a] Gruis, and is the brightest
+star of the constellation. The star [Greek: e] Indi (4.74 Harvard) has a
+remarkably large proper motion of 4".68 per annum. Its parallax is about
+0".28, and the proper motion indicates a velocity of about 49 miles a
+second at right angles to the line of sight.
+
+TOUCAN.--This constellation lies north of Octans, and south of Phoenix
+and Grus, east of Indus, and west of Hydrus. Its brightest star is [Greek:
+a], of about the 3rd magnitude.
+
+       *       *       *       *       *
+
+There are seven "celestial rivers" alluded to by the ancient
+astronomers:--
+
+1. The Fish River, which flows from the urn of Aquarius.
+
+2. The "River of the Bird," or the Milky Way in Cygnus.
+
+3. The River of the Birds--2, including Aquila.
+
+4. The River of Orion--Eridanus.
+
+5. The River of the god Marduk--perhaps the Milky Way in Perseus.
+
+6. The River of Serpents (Serpens, or Hydra).
+
+7. The River of Gan-gal (The High Cloud)--probably the Milky Way as a
+whole.
+
+There are four serpents represented among the constellations. These are
+Hydra, Hydrus, Serpens, and Draco.
+
+According to the late Mr. Proctor the date of the building of the Great
+Pyramid was about 3400 B.C.[452] At this time the Spring Equinox was in
+Taurus, and this is referred to by Virgil. But this was not so in Virgil's
+time, when--on account of the precession of the equinoxes--the equinoctial
+point had already entered Pisces, in which constellation it still remains.
+At the date 3400 B.C. the celestial equator ran along the whole length of
+the constellation Hydra, nearly through Procyon, and a little north of the
+bright red star Antares.
+
+The star Fomalhaut ([Greek: a] Piscis Australis) is interesting as being
+the most southern 1st magnitude star visible in England, its meridian
+altitude at Greenwich being little more than eight degrees.[453]
+
+With reference to the Greek letters given to the brighter stars by Bayer
+(in his Atlas published in 1603), and now generally used by astronomers,
+Mr. Lynn has shown that although "Bayer did uniformly designate the
+brightest stars in each constellation by the letter [Greek: a],"[454] it
+is a mistake to suppose--as has often been stated in popular books on
+astronomy--that he added the other Greek letters _in order of brightness_.
+That this is an error clearly appears from Bayer's own "Explicatio" to his
+Atlas, and was long since pointed out by Argelander (1832), and by Dr.
+Gould in his _Uranometria Argentina_. Gould says, "For the stars of each
+order, the sequence of the letters in no manner represents that of their
+brightness, but depended upon the positions of the stars in the figure,
+beginning usually at the head, and following its course until all the
+stars of that order of magnitude were exhausted." Mr. Lynn says, "Perhaps
+one of the most remarkable instances in which the lettering is seen at a
+glance not to follow the order of the letters is that of the three
+brightest stars in Aquila [Al-Sufi's 'three famous stars'], [Greek: g]
+being evidently brighter than [Greek: b]. But there is no occasion to
+conjecture from this that any change of relative brightness has taken
+place. Bayer reckoned both of these two of the third magnitude, and
+appears to have arranged [Greek: b] before [Greek: g], according to his
+usual custom, simply because [Greek: b] is in the neck of the supposed
+eagle, and [Greek: g] at the root of one of the wings."[455] Another good
+example is found in the stars of the "Plough," in which the stars are
+evidently arranged in the order of the figure and not in the order of
+relative brightness. In fact, Bayer is no guide at all with reference to
+star magnitudes. How different Al-Sufi was in this respect!
+
+The stars Aldebaran, Regulus, Antares, and Fomalhaut were called royal
+stars by the ancients. The reason of this was that they lie roughly about
+90 deg. apart, that is 6 hours of Right Ascension. So, if through the north
+and south poles of the heavens and each of these stars we draw great
+circles of the sphere, these circles will divide the sphere into four
+nearly equal parts, and the ancients supposed that each of these stars
+ruled over a quarter of the sphere, an idea probably connected with
+astrology. As the position of Aldebaran is R.A. 4{h} 30{m}, Declination
+North 16 deg. 19', and that of Antares is R.A. 16{h} 15{m}, Declination South
+25 deg. 2', these two stars lie at nearly opposite points of the celestial
+sphere. From this it follows that our sun seen from Aldebaran would lie
+not very far from Antares, and seen from Antares it would appear not far
+from Aldebaran.
+
+The following may be considered as representative stars of different
+magnitudes. For those of first magnitude and fainter I have only given
+those for which all the best observers in ancient and modern times agree,
+and which have been confirmed by modern photometric measures. The Harvard
+measures are given:--
+
+  Brighter than "zero magnitude"    Sirius (-1.58); Canopus (-0.86)
+
+  Zero magnitude                    [Greek: a] Centauri (0.06)
+
+  0 to 0.4 magnitude                Vega (0.14); Capella (0.21);
+                                    Arcturus (0.24); Rigel (0.34)
+
+  0.5 magnitude                     Procyon (0.48)
+
+  1st     "                         Aldebaran (1.06)
+
+  2nd     "                         [Greek: a] Persei (1.90);
+                                    [Greek: b] Aurigae (2.07)
+
+  3rd     "                         [Greek: e] Booetis (3.08);
+                                    [Greek: z] Capricorni (2.98)
+
+  4th     "                         [Greek: r] Leonis (3.85);
+                                    [Greek: l] Scorpii (4.16);
+                                    [Greek: g] Crateris(4.14);
+                                    [Greek: r] Herculis (4.14)
+
+  5th     "                         [Greek: o] Pegasi (4.85);
+                                    [Greek: m] Capricorni (5.10)
+
+
+
+
+CHAPTER XX
+
+The Visible Universe
+
+
+Some researches on the distribution of stars in the sky have recently been
+made at the Harvard Observatory (U.S.A.). The principal results are:--(1)
+The number of stars on any "given area of the Milky Way is about twice as
+great as in an equal area of any other region." (2) This ratio does not
+increase for faint stars down to the 12th magnitude. (3) "The Milky Way
+covers about one-third of the sky and contains about half of the stars."
+(4) There are about 10,000 stars of magnitude 6.6 or brighter, 100,000
+down to magnitude 8.7, one million to magnitude 11, and two millions to
+magnitude 11.9. It is estimated that there are about 18 millions of stars
+down to the 15th magnitude visible in a telescope of 15 inches
+aperture.[456]
+
+According to Prof. Kapteyn's researches on stellar distribution, he finds
+that going out from the earth into space, the "star density"--that is,
+the number of stars per unit volume of space--is fairly constant until we
+reach a distance of about 200 "light years." From this point the density
+gradually diminishes out to a distance of 2500 "light years," at which
+distance it is reduced to about one-fifth of the density in the sun's
+vicinity.[457]
+
+In a letter to the late Mr. Proctor (_Knowledge_, November, 1885, p. 21),
+Sir John Herschel suggested that our Galaxy (or stellar system) "contained
+within itself miniatures of itself." This beautiful idea is probably true.
+In his account of the greater "Magellanic cloud," Sir John Herschel
+describes one of the numerous objects it contains as follows:--
+
+    "Very bright, very large; oval; very gradually pretty, much brighter
+    in the middle; a beautiful nebula; it has very much the resemblance to
+    the Nubecula Major itself as seen with the naked eye, but it is far
+    brighter and more impressive in its general aspect as if it were
+    doubled in intensity. Note--July 29, 1837. I well remember this
+    observation, it was the result of repeated comparisons between the
+    object seen in the telescope and the actual nubecula as seen high in
+    the sky on the meridian, and no vague estimate carelessly set down.
+    And who can say whether in this object, magnified and analysed by
+    telescopes infinitely superior to what we now possess, there may not
+    exist all the complexity of detail that the nubecula itself presents
+    to our examination?"[458]
+
+The late Lord Kelvin, in a remarkable address delivered before the
+Physical Science Section of the British Association at its meeting at
+Glasgow in 1901, considered the probable quantity of matter contained in
+our Visible Universe. He takes a sphere of radius represented by the
+distance of a star having a parallax of one-thousandth of a second (or
+about 3000 years' journey for light), and he supposes that uniformly
+distributed within this sphere there exists a mass of matter equal to 1000
+million times the sun's mass. With these data he finds that a body placed
+originally at the surface of the sphere would in 5 million years acquire
+by gravitational force a velocity of about 12-1/2 miles a second, and
+after 25 million of years a velocity of about 67 miles a second. As these
+velocities are of the same order as the observed velocities among the
+stars, Lord Kelvin concludes that there _is_ probably as much matter in
+our universe as would be represented by a thousand million suns. If we
+assumed a mass of ten thousand suns the velocities would be much too high.
+The most probable estimate of the total number of the visible stars is
+about 100 millions; so that if Lord Kelvin's calculations are correct we
+seem bound to assume that space contains a number of dark bodies. The
+nebulae, however, probably contain vast masses of matter, and this may
+perhaps account--partially, at least--for the large amount of matter
+estimated by Lord Kelvin. (See Chapter on "Nebulae.")
+
+In some notes on photographs of the Milky Way, Prof. Barnard says with
+reference to the great nebula near [Greek: r] Ophiuchi, "The peculiarity
+of this region has suggested to me the idea that the apparently small
+stars forming the ground work of the Milky Way here, are really very small
+bodies compared with our own sun"; and again, referring to the region near
+[Greek: b] Cygni, "One is specially struck with the apparent extreme
+smallness of the general mass of the stars in this region." Again, with
+reference to [Greek: ch] Cygni, he says, "The stars here also are
+remarkably uniform in size."[459]
+
+Eastman's results for parallax seem to show that "the fainter rather than
+the brighter stars are nearest to our system." But this apparent paradox
+is considered by Mr. Monck to be very misleading;[460] and the present
+writer holds the same opinion.
+
+Prof. Kapteyn finds "that stars whose proper motions exceed 0".05 are not
+more numerous in the Milky Way than in other parts of the sky; or, in
+other words, if only the stars having proper motions of 0".05 or upwards
+were mapped, there would be no aggregation of stars showing the existence
+of the Milky Way."[461]
+
+With reference to the number of stars visible on photographs, the late Dr.
+Isaac Roberts says--
+
+    "So far as I am able at present to judge, under the atmospheric
+    conditions prevalent in this country, the limit of the photographic
+    method of delineation will be reached at stellar, or nebular, light of
+    the feebleness of about 18th-magnitude stars. The reason for this
+    inference is that the general illumination of the atmosphere by
+    starlight concentrated upon a film by the instrument will mask the
+    light of objects that are fainter than about 18th-magnitude
+    stars."[462]
+
+With reference to blank spaces in the sky, the late Mr. Norman Pogson
+remarked--
+
+    "Near S Ophiuchi we find one of the most remarkable vacuities in this
+    hemisphere--an elliptic space of about 65' in length in the direction
+    of R.A., and 40' in width, in which there exists _no_ star larger than
+    the 13th magnitude ... it is impossible to turn a large telescope in
+    that direction and, if I may so express it, view such black darkness,
+    without a feeling that we are here searching into the remote regions
+    of space, far beyond the limits of our own sidereal system."[463]
+
+Prof. Barnard describes some regions in the constellation Taurus
+containing "dark lanes" in a groundwork of faint nebulosity. He gives two
+beautiful photographs of the regions referred to, and says that the dark
+holes and lanes are apparently darker than the sky in the immediate
+vicinity. He says, "A very singular feature in this connection is that the
+stars also are absent in general from the lanes." A close examination of
+these photographs has given the present writer the impression that the
+dark lanes and spots are _in_ the nebulosity, and that the nebulosity is
+mixed up with the stars. This would account for the fact that the stars
+are in general absent from the dark lanes. For if there is an intimate
+relation between the stars and the nebulosity, it would follow that where
+there is no nebulosity in this particular region there would be no stars.
+Prof. Barnard adds that the nebulosity is easily visible in a 12-inch
+telescope.[464]
+
+With reference to the life of the universe, Prof. F. R. Moulton well
+says--
+
+    "The lifetime of a man seems fairly long, and the epoch when Troy was
+    besieged, or when the Pharaohs piled up the pyramids in the valley of
+    the Nile, or when our ancestors separated on the high plateaux of
+    Asia, seems extremely remote, but these intervals are only moments
+    compared to the immense periods required for geological evolutions and
+    the enormously greater ones consumed in the developement of worlds
+    from widely extended nebulous masses. We recognize the existence of
+    only those forces whose immediate consequences are appreciable, and it
+    may be that those whose effects are yet unseen are really of the
+    highest importance. A little creature whose life extended over only
+    two or three hours of a summer's day might be led, if he were
+    sufficiently endowed with intelligence, to infer that passing clouds
+    were the chief influence at work in changing the climate instead of
+    perceiving that the sun's slow motion across the sky would bring on
+    the night and its southward motion the winter."[465]
+
+In a review of my book _Astronomical Essays_ in _The Observatory_,
+September, 1907, the following words occur. They seem to form a good and
+sufficient answer to people who ask, What is there beyond our visible
+universe? "If the stellar universe is contained in a sphere of say 1000
+stellar units radius, what is there beyond? To this the astronomer will
+reply that theories and hypotheses are put forward for the purpose of
+explaining observed facts; when there are no facts to be explained, no
+theory is required. As there are no observed facts as to what exists
+beyond the farthest stars, the mind of the astronomer is a complete blank
+on the subject. Popular imagination can fill up the blank as it pleases."
+With these remarks I fully concur.
+
+In his address to the British Association, Prof. G. H. Darwin (now Sir
+George Darwin) said--
+
+    "Man is but a microscopic being relatively to astronomical space, and
+    he lives on a puny planet circling round a star of inferior rank. Does
+    it not, then, seem futile to imagine that he can discover the origin
+    and tendency of the Universe as to expect a housefly to instruct us as
+    to the theory of the motions of the planets? And yet, so long as he
+    shall last, he will pursue his search, and will no doubt discover many
+    wonderful things which are still hidden. We may indeed be amazed at
+    all that man has been able to find out, but the immeasurable magnitude
+    of the undiscovered will throughout all time remain to humble his
+    pride. Our children's children will still be gazing and marvelling at
+    the starry heavens, but the riddle will never be read."
+
+The ancient philosopher Lucretius said--
+
+  "Globed from the atoms falling slow or swift
+  I see the suns, I see the systems lift
+  Their forms; and even the system and the suns
+  Shall go back slowly to the eternal drift."[466]
+
+But it has been well said that the structure of the universe "has a
+fascination of its own for most readers quite apart from any real progress
+which may be made towards its solution."[467]
+
+The Milky Way itself, Mr. Stratonoff considers to be an agglomeration of
+immense condensations, or stellar clouds, which are scattered round the
+region of the galactic equator. These clouds, or masses of stars,
+sometimes leave spaces between them, and sometimes they overlap, and in
+this way he accounts for the great rifts, like the Coal Sack, which allow
+us to see through this great circle of light. He finds other
+condensations of stars; the nearest is one of which our sun is a member,
+chiefly composed of stars of the higher magnitudes which "thin out rapidly
+as the Milky Way is approached." There are other condensations: one in
+stars of magnitudes 6.5 to 8.5; and a third, farther off, in stars of
+magnitudes 7.6 to 8. These may be called opera-glass, or field-glass
+stars.
+
+Stratonoff finds that stars with spectra of the first type (class A, B, C,
+and D of Harvard) which include the Sirian and Orion stars, are
+principally situated near the Milky Way, while those of type II. (which
+includes the solar stars) "are principally condensed in a region
+coinciding roughly with the terrestrial pole, and only show a slight
+increase, as compared with other stars, as the galaxy is approached."[468]
+
+Prof. Kapteyn thinks that "undoubtedly one of the greatest difficulties,
+if not the greatest of all, in the way of obtaining an understanding of
+the real distribution of the stars in space, lies in our uncertainty about
+the amount of loss suffered by the light of the stars on its way to the
+observer."[469] He says, "There can be little doubt in my opinion, about
+the existence of absorption in space, and I think that even a good guess
+as to the order of its amount can be made. For, first we know that space
+contains an enormous mass of meteoric matter. This matter must necessarily
+intercept some part of the star-light."
+
+This absorption, however, seems to be comparatively small. Kapteyn finds a
+value of 0.016 (about 1/60th) of a magnitude for a star at a distance
+corresponding to a parallax of one-tenth of a second (about 33 "light
+years"). This is a quantity almost imperceptible in the most delicate
+photometer. But for very great distances--such as 3000 "light years"--the
+absorption would evidently become very considerable, and would account
+satisfactorily for the gradual "thinning out" of the fainter stars. If
+this were fully proved, we should have to consider the fainter stars of
+the Milky Way to be in all probability fairly large suns, the light of
+which is reduced by absorption.
+
+That some of the ancients knew that the Milky Way is composed of stars is
+shown by the following lines translated from Ovid:--
+
+  "A way there is in heaven's extended plain
+  Which when the skies are clear is seen below
+  And mortals, by the name of Milky, know;
+  The groundwork is of stars, through which the road
+  Lies open to great Jupiter's abode."[470]
+
+From an examination of the distribution of the faint stars composing the
+Milky Way, and those shown in Argelander's charts of stars down to the
+9-1/2 magnitude, Easton finds that there is "a real connection between the
+distribution of 9th and 10th magnitude stars, and that of the faint stars
+of the Milky Way, and that consequently the faint or very faint stars of
+the galactic zone are at a distance which does not greatly exceed that of
+the 9th and 10th magnitude stars."[471] A similar conclusion was, I think,
+arrived at by Proctor many years ago. Now let us consider the meaning of
+this result. Taking stars of the 15th magnitude, if their faintness were
+merely due to greater distance, their actual brightness--if of the same
+size--would imply that they are at 10 times the distance of stars of the
+10th magnitude. But if at the same distance from us, a 10th magnitude star
+would be 100 times brighter than a 15th magnitude star, and if of the same
+density and "intrinsic brightness" (or luminosity of surface) the 10th
+magnitude would have 10 times the diameter of the fainter star, and hence
+its volume would be 1000 times greater (10{3}), and this great difference
+is not perhaps improbable.
+
+The constitution of the Milky Way is not the same in all its parts. The
+bright spot between [Greek: b] and [Greek: g] Cygni is due to relatively
+bright stars. Others equally dense but fainter regions in Auriga and
+Monoceros are only evident in stars of the 8th and 9th magnitude, and the
+light of the well-known luminous spot in "Sobieski's Shield," closely
+south of [Greek: l] Aquilae, is due to stars below magnitude 9-1/2.
+
+The correspondence in distribution between the stars of Argelander's
+charts and the fainter stars of the Milky Way shows, as Easton points out,
+that Herschel's hypothesis of a uniform distribution of stars of
+approximately equal size is quite untenable.
+
+It has been suggested that the Milky Way may perhaps form a ring of stars
+with the sun placed nearly, but not exactly, in the centre of the ring.
+But were it really a ring of uniform width with the sun eccentrically
+placed within it, we should expect to find the Milky Way wider at its
+nearest part, and gradually narrowing towards the opposite point. Now,
+Herschel's "gages" and Celoria's counts show that the Galaxy is wider in
+Aquila than in Monoceros. This is confirmed by Easton, who says, "_for the
+faint stars taken as a whole, the Milky Way is widest in its brightest
+part_" (the italics are Easton's). From this we should conclude that the
+Milky Way is nearer to us in the direction of Aquila than in that of
+Monoceros. Sir John Herschel suggested that the southern parts of the
+galactic zone are nearer to us on account of their greater _brightness_ in
+those regions.[472] But greater width is a safer test of distance than
+relative brightness. For it may be easily shown than the _intrinsic_
+brightness of an area containing a large number of stars would be the
+same for _all_ distances (neglecting the supposed absorption of light in
+space). For suppose any given area crowded with stars to be removed to a
+greater distance. The light of each star would be diminished inversely as
+the square of the distance. But the given area would also be diminished
+_directly_ as the square of the distance, so we should have a diminished
+amount of light on an equally diminished area, and hence the intrinsic
+brightness, or luminosity of the area per unit of surface, would remain
+unaltered. The increased brightness of the Milky Way in Aquila is
+accounted for by the fact that Herschel's "gages" show an increased number
+of stars, and hence the brightness in Aquila and Sagittarius does not
+necessarily imply that the Milky Way is nearer to us in those parts, but
+that it is richer in small stars than in other regions.
+
+Easton is of opinion that the annular hypothesis of the Milky Way is
+inconsistent with our present knowledge of the galactic phenomena, and he
+suggests that its actual constitution resembles more that of a spiral
+nebula.[473] On this hypothesis the increase in the number of stars in the
+regions above referred to may be due to our seeing one branch of the
+supposed "two-branched spiral" projected on another branch of the same
+spiral. This seems supported by Sir John Herschel's observations in the
+southern hemisphere, where he found in some places "a tissue as it were of
+large stars spread over another of very small ones, the immediate
+magnitudes being wanting." Again, portions of the spiral branches may be
+richer than others, as photographs of spiral nebulae seem to indicate.
+Celoria, rejecting the hypothesis of a single ring, suggests the existence
+of _two_ galactic rings inclined to each other at an angle of about 20 deg.,
+one of these including the brighter stars, and the other the fainter. But
+this seems to be a more artificial arrangement then the hypothesis of a
+spiral. Further, the complicated structure of the Milky Way cannot be well
+explained by Celoria's hypothesis of two distinct rings one inside the
+other. From analogy the spiral hypothesis seems much more probable.
+
+Considering the Milky Way to represent a colossal spiral nebula viewed
+from a point not far removed from the centre of the spiral branches,
+Easton suggests that the bright region between [Greek: b] and [Greek: g]
+Cygni, which is very rich in comparatively bright stars, may possibly
+represent the "_central accumulations of the Milky Way_," that is, the
+portion corresponding to the nucleus of a spiral nebula. If this be so,
+this portion of the Milky Way should be nearer to us than others. Easton
+also thinks that the so-called "solar cluster" of Gould, Kapteyn, and
+Schiaparelli may perhaps be "the expression of the central condensation
+of the galactic system itself, composed of the most part of suns
+comparable with our own, and which would thus embrace most of the bright
+stars to the 9th or 10th magnitude. The distance of the galactic streams
+and convolutions would thus be comparable with the distances of these
+stars." He thinks that the sun lies within a gigantic spiral, "in a
+comparatively sparse region between the central nucleus and Orion."
+
+Scheiner thinks that "the irregularities of the Milky Way, especially in
+streams, can be quite well accounted for, as Easton has attempted to do,
+if they are regarded as a system of spirals, and not as a ring system."
+
+Evidence in favour of the spiral hypothesis of the Milky Way, as advocated
+by Easton and Scheiner, may be found in Kapteyn's researches on the proper
+motions of the stars. This eminent astronomer finds that stars with
+measurable proper motions--and therefore in all probability relatively
+near the earth--have mostly spectra of the solar type, and seem to cluster
+round "a point adjacent to the sun, in total disregard to the position of
+the Milky Way," and that stars with little or no proper motion collect
+round the galactic plain. He is also of opinion that the Milky Way
+resembles the Andromeda nebula, "the globular nucleus representing the
+solar cluster, and the far spreading wings or whorls the compressed layer
+of stars enclosed by the rings of the remote Galaxy."
+
+With reference to the plurality of inhabited worlds, it has been well said
+by the ancient writer Metrodorus (third century B.C.), "The idea that
+there is but a single world in all infinitude would be as absurd as to
+suppose that a vast field had been formed to produce a single blade of
+wheat."[474] With this opinion the present writer fully concurs.
+
+
+
+
+CHAPTER XXI
+
+General
+
+
+The achievements of Hipparchus in astronomy were very remarkable,
+considering the age in which he lived. He found the amount of the apparent
+motion of the stars due to the precession of the equinoxes (of which he
+was the discoverer) to be 59" per annum. The correct amount is about 50".
+He measured the length of the year to within 9 minutes of its true value.
+He found the inclination of the ecliptic to the plane of the equator to be
+23 deg. 51'. It was then 23 deg. 46'--as we now know by modern calculations--so
+that Hipparchus' estimation was a wonderfully close approximation to the
+truth. He computed the moon's parallax to be 57', which is about its
+correct value. He found the eccentricity of the sun's apparent orbit round
+the earth to be one twenty-fourth, the real value being then about
+one-thirteenth. He determined other motions connected with the earth and
+moon; and formed a catalogue of 1080 stars. All this work has earned for
+him the well-merited title of "The Father of Astronomy."[475]
+
+The following is a translation of a Greek passage ascribed to Ptolemy: "I
+know that I am mortal and the creature of a day, but when I search out the
+many rolling circles of the stars, my feet touch the earth no longer, but
+with Zeus himself I take my fill of ambrosia, the food of the gods."[476]
+This was inscribed (in Greek) on a silver loving cup presented to the late
+Professor C. A. Young, the famous American astronomer.[477]
+
+Some curious and interesting phenomena are recorded in the old Chinese
+Annals, which go back to a great antiquity. In 687 B.C. "a night" is
+mentioned "without clouds and without stars" (!) This may perhaps refer to
+a total eclipse of the sun; but if so, the eclipse is not mentioned in the
+Chinese list of eclipses. In the year 141 B.C., it is stated that the sun
+and moon appeared of a deep red colour during 5 days, a phenomenon which
+caused great terror among the people. In 74 B.C., it is related that a
+star as large as the moon appeared, and was followed in its motion by
+several stars of ordinary size. This probably refers to an unusually large
+"bolide" or "fireball." In 38 B.C., a fall of meteoric stones is recorded
+"of the size of a walnut." In A.D. 88, another fall of stones is
+mentioned. In A.D. 321, sun-spots were visible to the naked eye.
+
+Homer speaks of a curious darkness which occurred during one of the great
+battles in the last year of the Trojan war. Mr. Stockwell identifies this
+with an eclipse of the sun which took place on August 28, 1184 B.C. An
+eclipse referred to by Thucydides as having occurred during the first year
+of the Peloponnesian War, when the darkness was so great that some stars
+were seen, is identified by Stockwell with a total eclipse of the sun,
+which took place on August 2, 430 B.C.
+
+A great eclipse of the sun is supposed to have occurred in the year 43 or
+44 B.C., soon after the death of Julius Caesar. Baron de Zach and Arago
+mention it as the first annular eclipse on record. But calculations show
+that no solar eclipse whatever, visible in Italy, occurred in either of
+these years. The phenomenon referred to must therefore have been of
+atmospherical origin, and indeed this is suggested by a passage in
+Suetonius, one of the authors quoted on the subject.
+
+M. Guillaume thinks that the ninth Egyptian plague, the thick "darkness"
+(Exodus x. 21-23), may perhaps be explained by a total eclipse of the sun
+which occurred in 1332 B.C. It is true that the account states that the
+darkness lasted "three days," but this, M. Guillaume thinks, may be due to
+an error in the translation.[478] This explanation, however, seems very
+improbable.
+
+According to Hind, the moon was eclipsed on the generally received date
+of the Crucifixion, A.D. 33, April 3. He says, "I find she had emerged
+from the earth's dark shadow a quarter of an hour before she rose at
+Jerusalem (6{h} 36{m} p.m.); but the penumbra continued upon her disc for
+an hour afterwards." An eclipse could not have had anything to do with the
+"darkness over all the land" during the Crucifixion. For this lasted for
+three hours, and the totality of a solar eclipse can only last a few
+minutes at the most. As a matter of fact the "eclipse of Phlegon," a
+partial one (A.D. 29, November 24) was "the only solar eclipse that could
+have been visible in Jerusalem during the period usually fixed for the
+ministry of Christ."
+
+It is mentioned in the Anglo-Saxon Chronicle that a total eclipse of the
+sun took place in the year after King Alfred's great battle with the
+Danes. Now, calculation shows that this eclipse occurred on October 29,
+878 A.D. King Alfred's victory over the Danes must, therefore, have taken
+place in 877 A.D., and his death probably occurred in 899 A.D. This solar
+eclipse is also mentioned in the Annals of Ulster. From this it will be
+seen that in some cases the dates of historical events can be accurately
+fixed by astronomical phenomena.
+
+It is stated by some historians that an eclipse of the sun took place on
+the morning of the battle of Crecy, August 26, 1346. But calculation
+shows that there was no eclipse of the sun visible in England in that
+year. At the time of the famous battle the moon had just entered on her
+first quarter, and she was partially eclipsed six days afterwards--that is
+on the 1st of September. The mistake seems to have arisen from a
+mistranslation of the old French word _esclistre_, which means lightning.
+This was mistaken for _esclipse_. The account seems to indicate that there
+was a heavy thunderstorm on the morning of the battle.
+
+A dark shade was seen on the waning moon by Messrs. Hirst and J. C.
+Russell on October 21, 1878, "as dark as the shadow during an eclipse of
+the moon."[479] If this observation is correct, it is certainly most
+difficult to explain. Another curious observation is recorded by Mr. E.
+Stone Wiggins, who says that a partial eclipse of the sun by a dark body
+was observed in the State of Michigan (U.S.A.) on May 16, 1884, at 7 p.m.
+The "moon at that moment was 12 degrees south of the equator and the sun
+as many degrees north of it." The existence of a dark satellite of the
+earth has been suggested, but this seems highly improbable.
+
+The sun's corona seems to have been first noticed in the total eclipse of
+the sun which occurred at the death of the Roman emperor Domitian, A.D.
+95. Philostratus in his _Life of Apollonius_ says, with reference to this
+eclipse, "In the heavens there appeared a prodigy of this nature: a
+certain _corona_ resembling the Iris surrounded the orb of the sun, and
+obscured its light."[480] In more modern times the corona seems to have
+been first noticed by Clavius during the total eclipse of April 9,
+1567.[481] Kepler proved that this eclipse was total, not annular, so that
+the ring seen by Clavius must have been the corona.
+
+With reference to the visibility of planets and stars during total
+eclipses of the sun; in the eclipse of May 12, 1706, Venus, Mercury, and
+Aldebaran, and several other stars were seen. During the totality of the
+eclipse of May 3, 1715, about twenty stars were seen with the naked
+eye.[482] At the eclipse of May 22, 1724, Venus and Mercury, and a few
+fixed stars were seen.[483] The corona was also noticed. At the eclipse of
+May 2, 1733, Jupiter, the stars of the "Plough," Capella, and other stars
+were visible to the naked eye; and the corona was again seen.[483]
+
+During the total eclipses of February 9, 1766, June 24, 1778, and June 16,
+1806, the corona was again noticed. But its true character was then
+unknown.
+
+At the eclipse of July 8, 1842, it was noticed by observers at Lipesk
+that the stars Aldebaran and Betelgeuse ([Greek: a] Orionis), which are
+usually red, "appeared quite white."[484]
+
+There will be seven eclipses in the years 1917, 1935, and 1985. In the
+year 1935 there will be five eclipses of the sun, a rare event; and in
+1985 there will be three total eclipses of the moon, a most unusual
+occurrence.[485]
+
+Among the ancient Hindoos, the common people believed that eclipses were
+caused by the interposition of a monstrous demon called Raha. This absurd
+idea, and others equally ridiculous, were based on declarations in their
+sacred books, and no pious Hindoo would think of denying it.
+
+The following cases of darkenings of the sun are given by Humboldt:--
+
+According to Plutarch the sun remained pale for a whole year at the death
+of Julius Caesar, and gave less than its usual heat.[486]
+
+A sun-darkening lasting for two hours is recorded on August 22, 358 A.D.,
+before the great earthquake of Nicomedia.
+
+In 360 A.D. there was a sun-darkening from early morn till noon. The
+description given by the historians of the time corresponds to an eclipse
+of the sun, but the duration of the obscurity is inexplicable.
+
+In 409 A.D., when Alaric lay siege to Rome, "there was so great a
+darkness that the stars were seen by day."
+
+In 536 A.D. the sun is said to have been darkened for a year and two
+months!
+
+In 626 A.D., according to Abul Farag, half the sun's disc was darkened for
+eight months!
+
+In 934 A.D. the sun lost its brightness for two months in Portugal.
+
+In 1090 A.D. the sun was darkened for three hours.
+
+In 1096, sun-spots were seen with the naked eye on March 3.
+
+In 1206 A.D. on the last day of February, "there was complete darkness for
+six hours, turning the day into night." This seems to have occurred in
+Spain.
+
+In 1241 the sun was so darkened that stars could be seen at 3 p.m. on
+Michaelmas day. This happened in Vienna.[487]
+
+The sun is said to have been so darkened in the year 1547 A.D. for three
+days that stars were visible at midday. This occurred about the time of
+the battle of Muehlbergh.[488]
+
+Some of these darkenings may possibly have been due to an enormous
+development of sun-spots; but in some cases the darkness is supposed by
+Chladni and Schnurrer to have been caused by "the passage of meteoric
+masses before the sun's disc."
+
+The first observer of a transit of Venus was Jeremiah Horrocks, who
+observed the transit of November 24 (O.S.), 1639. He had previously
+corrected Kepler's predicted time of the transit from 8{h} 8{m} a.m. at
+Manchester to 5{h} 57{m} p.m. At the end of 1875 a marble scroll was
+placed on the pedestal of the monument of John Conduitt (nephew of Sir
+Isaac Newton, and who adopted Horrocks' theory of lunar motions) at the
+west end of the nave of Westminster Abbey, bearing this inscription from
+the pen of Dean Stanley--
+
+  "Ad majora avocatus
+  quae ob haec parerga negligi non decuit"
+  IN MEMORY OF
+  JEREMIAH HORROCKS
+  Curate of Hoole in Lancashire
+  Who died on the 3{d} of January, 1641, in or near his
+  22{d} year
+  Having in so short a life
+  Detected the long inequality in the mean motion of
+  Jupiter and Saturn
+  Discovered the orbit of the Moon to be an ellipse;
+  Determined the motion of the lunar aspe,
+  Suggested the physical cause of its revolution;
+  And predicted from his own observations, the
+  Transit of Venus
+  Which was seen by himself and his friend
+  WILLIAM CRABTREE
+  On Sunday, the 24th November (O.S.) 1639;
+  This Tablet, facing the Monument of Newton
+  Was raised after the lapse of more than two centuries
+  December 9, 1874.[489]
+
+The transit of Venus which occurred in 1761 was observed on board ship(!)
+by the famous but unfortunate French astronomer Le Gentil. The ship was
+the frigate _Sylphide_, sent to the help of Pondicherry (India) which was
+then being besieged by the English. Owing to unfavourable winds the
+_Sylphide_ was tossed about from March 25, 1761, to May 24 of the same
+year. When, on the later date, off the coast of Malabar, the captain of
+the frigate learned that Pondicherry had been captured by the English, the
+vessel returned to the Isle of France, where it arrived on June 23, after
+touching at Point de Galle on May 30. It was between these two places that
+Le Gentil made his observations of the transit of Venus under such
+unfavourable conditions. He had an object-glass of 15 feet (French) focus,
+and this he mounted in a tube formed of "four pine planks." This rough
+instrument was fixed to a small mast set up on the quarter-deck and worked
+by ropes. The observations made under such curious conditions, were not,
+as may be imagined, very satisfactory. As another transit was to take
+place on June 3, 1769, Le Gentil made the heroic resolution of remaining
+in the southern hemisphere to observe it! This determination was duly
+carried out, but his devotion to astronomy was not rewarded; for on the
+day of the long waited for transit the sky at Pondicherry (where he had
+gone to observe it) was clouded over during the whole phenomenon,
+"although for many days previous the sky had been cloudless." To add to
+his feeling of disappointment he heard that at Manilla, where he had been
+staying some time previously, the sky was quite clear, and two of his
+friends there had seen the transit without any difficulty.[490] Truly the
+unfortunate Le Gentil was a martyr to science.
+
+The famous German astronomer Bessel once said "that a practical astronomer
+could make observations of value if he had only a cart-wheel and a gun
+barrel"; and Watson said that "the most important part of the instrument
+is the person at the small end."[491]
+
+With reference to Father Hell's supposed forgery of his observations of
+the transit of Venus in 1769, and Littrow's criticism of some of the
+entries in Hell's manuscript being corrected with a different coloured
+ink, Professor Newcomb ascertained from Weiss that Littrow was colour
+blind, and could not distinguish between the colour of Aldebaran and the
+whitest star. Newcomb adds, "For half a century the astronomical world had
+based an impression on the innocent but mistaken evidence of a
+colour-blind man respecting the tint of ink in a manuscript."
+
+It is recorded that on February 26, B.C. 2012, the moon, Mercury, Venus,
+Jupiter, and Saturn, were in the same constellation, and within 14
+degrees of each other. On September 14, 1186 A.D., the sun, moon, and all
+the planets then known, are said to have been situated in Libra.[492]
+
+In the Sanscrit epic poem, "The Ramaya," it is stated that at the birth of
+Rama, the moon was in Cancer, the sun in Aries, Mercury in Taurus, Venus
+in Pisces, Mars in Capricornus, Jupiter in Cancer, and Saturn in Libra.
+From these data, Mr. Walter R. Old has computed that Rama was born on
+February 10, 1761 B.C.[493]
+
+A close conjunction of Mars and Saturn was observed by Denning on
+September 29, 1889, the bright star Regulus ([Greek: a] Leonis) being at
+the time only 47' distant from the planets.[494]
+
+An occultation of the Pleiades by the moon was observed by Timocharis at
+Alexandria on January 29, 282 B.C. Calculations by Schjellerup show that
+Alcyone ([Greek: e] Tauri) was occulted; but the exact time of the day
+recorded by Timocharis differs very considerably from that computed by
+Schjellerup.[495] Another occultation of the Pleiades is recorded by
+Agrippa in the reign of Domitian. According to Schjellerup the phenomenon
+occurred on November 29, A.D. 92.
+
+"Kepler states that on the 9th of January, 1591, Maestlin and himself
+witnessed an occultation of Jupiter by Mars. The red colour of the latter
+on that occasion plainly indicated that it was the inferior planet."[496]
+That is, that Mars was nearer to the sun than Jupiter. But as the
+telescope had not then been invented, this may have been merely a near
+approach of the two planets.
+
+According to Kepler, Maestlin saw an occultation of Mars by Venus on
+October 3, 1590. But this may also have been merely a near approach.[496]
+
+A curious paradox is that one can discover an object without seeing it,
+and see an object without discovering it! The planet Neptune was
+discovered by Adams and Leverrier by calculation before it was seen in the
+telescope by Galle; and it was actually seen by Lalande on May 8 and 10,
+1795, but he took it for a _star_ and thus missed the discovery. In fact,
+he _saw_ the planet, but did not _discover_ it. It actually appears as a
+star of the 8th magnitude in Harding's Atlas (1822). The great "new star"
+of February, 1901, known as Nova Persei, was probably seen by some people
+before its discovery was announced; and it was actually noticed by a
+well-known American astronomer, who thought it was some bright star with
+which he was not familiar! But this did not amount to a discovery. Any one
+absolutely ignorant of astronomy might have made the same observation. An
+object must be _identified_ as a _new_ object before a discovery can be
+claimed. Some years ago a well-known Irish naturalist discovered a spider
+new to science, and after its discovery he found that it was common in
+nearly every house in Dublin! But this fact did not detract in the least
+from the merit of its scientific discovery.
+
+There is a story of an eminent astronomer who had been on several eclipse
+expeditions, and yet was heard to remark that he had never seen a total
+eclipse of the sun. "But your observations of several eclipses are on
+record," it was objected. "Certainly, I have on several occasions made
+observations, but I have always been too busy to look at the eclipse." He
+was probably in a dark tent taking photographs or using a spectroscope
+during the totality. This was observing an eclipse without seeing it!
+
+Humboldt gives the credit of the invention of the telescope to Hans
+Lippershey, a native of Wesel and a spectacle-maker at Middleburgh; to
+Jacob Adreaansz, surnamed Metius, who is also said to have made
+burning-glasses of ice; and to Zachariah Jansen.[497]
+
+With reference to the parabolic figure of the large mirrors of reflecting
+telescopes, Dr. Robinson remarked at the meeting of the British
+Association at Cork in 1843, "between the spherical and parabolic figures
+the extreme difference is so slight, even in the telescope of 6-feet
+aperture [Lord Rosse's] that if the two surfaces touched at their vertex,
+the distance at the edge would not amount to the 1/10000th of an inch, a
+space which few can measure, and none without a microscope."[498]
+
+In the year 1758, Roger Long, Lowndean Professor of Astronomy at
+Cambridge, constructed an "orrery" on a novel principle. It was a hollow
+metal sphere of about 18 feet in diameter with its fixed axis parallel to
+the earth's axis. It was rotated, by means of a winch and rackwork. It
+held about thirty persons in its interior, where astronomical lectures
+were delivered. The constellations were painted on the interior surface;
+and holes pierced through the shell and illuminated from the outside
+represented the stars according to their different magnitudes. This
+ingenious machine was much neglected for many years, but was still in
+existence in Admiral Smyth's time, 1844.[499]
+
+A "temporary star" is said to have been seen by Hepidanus in the
+constellation Aries in either 1006 or 1012 A.D. The late M. Schoenfeld, a
+great authority on variable stars, found from an Arabic and Syrian
+chronicle that 1012 is the correct year (396 of the Hegira), but that the
+word translated Aries would by a probable emendation mean Scorpio. The
+word in the Syrian record is not the word for Aries.[500]
+
+Mr. Heber D. Curtis finds that the faintest stars mentioned in Ptolemy's
+Catalogue are about 5.38 magnitude on the scale of the Harvard
+_Photometric Durchmustering_.[501] Heis and Houzeau saw stars of 6-7
+magnitude (about 6.4 on Harvard scale). The present writer found that he
+could see most of Heis' faintest stars in the west of Ireland (Co. Sligo)
+without optical aid (except short-sighted spectacles).
+
+With reference to the apparent changes in the stellar heavens produced by
+the precession of the equinoxes, Humboldt says--
+
+    "Canopus was fully 1 deg. 20' below the horizon of Toledo (39 deg. 54' north
+    latitude) in the time of Columbus; and now the same star is almost as
+    much above the horizon of Cadiz. While at Berlin, and in northern
+    latitudes, the stars of the Southern Cross, as well as [Greek: a] and
+    [Greek: b] Centauri, are receding more and more from view, the
+    Magellanic Clouds are slowly approaching our latitudes. Canopus was at
+    its greatest northern approximation during last century [eighteenth],
+    and is now moving nearer and nearer to the south, although very
+    slowly, owing to its vicinity to the south pole of the ecliptic. The
+    Southern Cross began to become invisible in 52 deg. 30' north latitude
+    2900 years before our era, since, according to Galle, this
+    constellation might previously have reached an altitude of more than
+    10 deg.. When it had disappeared from the horizon of the countries of the
+    Baltic, the great pyramid of Cheops had already been erected more than
+    five hundred years. The pastoral tribe of the Hyksos made their
+    incursion seven hundred years earlier. The past seems to be visibly
+    nearer to us when we connect its measurement with great and memorable
+    events."[502]
+
+With reference to the great Grecian philosopher and scientist Eratosthenes
+of Cyrene, keeper of the Alexandrian Library under Ptolemy Euergetes, Carl
+Snyder says, "Above all the Alexanders, Caesars, Tadema-Napoleons, I set
+the brain which first spanned the earth, over whose little patches these
+fought through their empty bootless lives. Why should we have no poet to
+celebrate so great a deed?"[503] And with reference to Aristarchus he
+says, "If grandeur of conceptions be a measure of the brain, or ingenuity
+of its powers, then we must rank Aristarchus as one of the three or four
+most acute intellects of the ancient world."[504]
+
+Lagrange, who often asserted Newton to be the greatest genius that ever
+existed, used to remark also--"and the most fortunate; we do not find more
+than once a system of the world to establish."[505]
+
+Grant says--
+
+    "Lagrange deserves to be ranked among the greatest mathematical
+    geniuses of ancient or modern times. In this respect he is worthy of a
+    place with Archimedes or Newton, although he was far from possessing
+    the sagacity in physical enquiries which distinguished these
+    illustrious sages. From the very outset of his career he assumed a
+    commanding position among the mathematicians of the age, and during
+    the course of nearly half a century previous to his death, he
+    continued to divide with Laplace the homage due to pre-eminence in the
+    exact sciences. His great rival survived him fourteen years, during
+    which he reigned alone as the prince of mathematicians and theoretical
+    astronomers."[506]
+
+A writer in _Nature_ (May 25, 1871) relates the following anecdote with
+reference to Sir John Herschel: "Some time after the death of Laplace, the
+writer of this notice, while travelling on the continent in company with
+the celebrated French _savant_ Biot, ventured to put to him the question,
+not altogether a wise one, 'And whom of all the philosophers of Europe do
+you regard as the most worthy successor of Laplace?' Probably no man was
+better able than Biot to form a correct conclusion, and the reply was more
+judicious than the question. It was this, 'If I did not love him so much I
+should unhesitatingly say, Sir John Herschel.'" Dr. Gill (now Sir David
+Gill), in an address at the Cape of Good Hope in June, 1898, spoke of Sir
+John Herschel as "the prose poet of science; his popular scientific works
+are models of clearness, and his presidential addresses teem with
+passages of surpassing beauty. His life was a pure and blameless one from
+first to last, full of the noblest effort and the noblest aim from the
+time when as a young Cambridge graduate he registered a vow 'to try to
+leave the world wiser than he found it'--a vow that his life amply
+fulfilled."[507]
+
+Prof. Newcomb said of Adams, the co-discoverer of Neptune with Leverrier,
+"Adams' intellect was one of the keenest I ever knew. The most difficult
+problem of mathematical astronomy and the most recondite principles that
+underlie the theory of the celestial motions were to him but child's
+play." Airy he regarded as "the most commanding figure in the astronomy of
+our time."[508] He spoke of Delaunay, the great French astronomer, as a
+most kindly and attractive man, and says, "His investigations of the
+moon's motion is one of the most extraordinary pieces of mathematical work
+ever turned out by a single person. It fills two quarto volumes, and the
+reader who attempts to go through any part of the calculations will wonder
+how one man could do the work in a lifetime."[509]
+
+Sir George B. Airy and Prof. J. C. Adams died in the same month. The
+former on January 2, 1892, and the latter on January 22 of the same year.
+
+It is known from the parish register of Burstow in Surrey that Flamsteed
+(Rev. John Flamsteed), the first Astronomer Royal at Greenwich, was buried
+in the church at that place on January 12, 1720; but a search for his
+grave made by Mr. J. Carpenter in 1866 and by Mr. Lynn in 1880 led to no
+result. In Mrs. Flamsteed's will a sum of twenty-five pounds was left for
+the purpose of erecting a monument to the memory of the great astronomer
+in Burstow Church; but it does not appear that any monument was ever
+erected. Flamsteed was Rector of the Parish of Burstow.[510] He was
+succeeded in 1720 by the Rev. James Pound, another well-known astronomer.
+Pound died in 1724.[511]
+
+Evelyn says in his Diary, 1676, September 10, "Dined with Mr. Flamsteed,
+the learned astrologer and mathematician, whom his Majesty had established
+in the new Observatory in Greenwich Park furnished with the choicest
+instruments. An honest sincere man."[512] This shows that in those days
+the term "astrologer" was synonymous with "astronomer."
+
+In an article on "Our Debt to Astronomy," by Prof. Russell Tracy Crawford
+(Berkeley Astronomical Department, California, U.S.A.), the following
+remarks occur:--
+
+    "Behind the artisan is a chemist, behind the chemist is a physicist,
+    behind the physicist is a mathematician, and behind the mathematician
+    is an astronomer." "Were it not for the data furnished by astronomers,
+    commerce by sea would practically stop. The sailing-master on the high
+    seas could not determine his position, nor in what direction to head
+    his ship in order to reach a desired harbour. Think what this means in
+    dollars and cents, and estimate it if you can. For this one service
+    alone the science of astronomy is worth more in dollars and cents to
+    the world in one week than has been expended upon it since the
+    beginning of civilization. Do you think that Great Britain, for
+    instance, would take in exchange an amount equal to its national debt
+    for what astronomy gives it? I answer for you most emphatically,
+    'No.'"
+
+In his interesting book, _Reminiscences of an Astronomer_, Prof. Simon
+Newcomb says with reference to the calculations for the _Nautical Almanac_
+(referred to in the above extract)--
+
+    "A more hopeless problem than this could not be presented to the
+    ordinary human intellect. There are tens of thousands of men who could
+    be successful in all the ordinary walks of life, hundreds who could
+    wield empires, thousands who could gain wealth, for one who could take
+    up this astronomical problem with any hope of success. The men who
+    have done it are, therefore, in intellect the select few of the human
+    race--an aristocracy ranking above all others in the scale of being.
+    The astronomical ephemeris is the last outcome of their productive
+    genius."
+
+In a paper on the "Aspects of American Astronomy," Prof. Newcomb says, "A
+great telescope is of no use without a man at the end of it, and what the
+telescope may do depends more upon this appendage than upon the instrument
+itself. The place which telescopes and observatories have taken in
+astronomical history are by no means proportional to their dimensions.
+Many a great instrument has been a mere toy in the hands of its owner.
+Many a small one has become famous. Twenty years ago there was here in
+your city [Chicago] a modest little instrument which, judged by its size,
+could not hold up its head with the great ones even of that day. It was
+the private property of a young man holding no scientific position and
+scarcely known to the public. And yet that little telescope is to-day
+among the famous ones of the world, having made memorable advances in the
+astronomy of double stars, and shown its owner to be a worthy successor of
+the Herschels and Struves in that line of work."[513] Here Prof. Newcomb
+evidently refers to Prof. Burnham, and the 6-inch telescope with which he
+made many of his remarkable discoveries of double stars. With reference to
+Burnham's work, Prof. Barnard says--
+
+    "It represents the labour of a struggling amateur, who during the day
+    led the drudging life of a stenographer in the United States court in
+    Chicago, and at night worked among the stars for the pure love of it.
+    Such work deserves an everlasting fame, and surely this has fallen to
+    Mr. Burnham."
+
+Admiral Smyth says--
+
+    "A man may prove a good astronomer without possessing a spacious
+    observatory: thus Kepler was wont to observe on the bridge at Prague;
+    Schroeter studied the moon, and Harding found a planet from a
+    _gloriette_; while Olbers discovered two new planets from an attic of
+    his house."[514]
+
+It is probably not generally known that "some of the greatest astronomers
+of modern times, such as Kepler, Newton, Hansen, Laplace, and Leverrier,
+scarcely ever looked through a telescope."[515]
+
+Kepler, who always signed himself Keppler in German, is usually supposed
+to have been born on December 21, 1571, in the imperial town of Weil, but
+according to Baron von Breitschwert,[516] he was really born on December
+27, 1571, in the village of Magstadt in Wurtemberg.
+
+According to Lieut. Winterhalter, M. Perrotin of the Nice Observatory
+declared "that two hours' work with a large instrument is as fatiguing as
+eight with a small one, the labour involved increasing in proportion to
+the cube of the aperture, the chances of seeing decreasing in the same
+ratio, while it can hardly be said that the advantages increase in like
+proportion."[517]
+
+The late Mr. Proctor has well said--
+
+    "It is well to remember that the hatred which many entertain against
+    the doctrine of development as applied to solar systems and stellar
+    galaxies is not in reality a sign, as they imagine, of humility, but
+    is an effort to avoid the recognition of the nothingness of man in the
+    presence of the infinities of space and time and vitality presented
+    within the universe of God."[518]
+
+Humboldt says--
+
+    "That arrogant spirit of incredulity, which rejects facts without
+    attempting to investigate them, is in some cases almost more injurious
+    than an unquestioning credulity. Both are alike detrimental to the
+    force of investigations."[519]
+
+With reference to the precession of the equinoxes and the changes it
+produces in the position of the Pole Star, it is stated in a recent book
+on science that the entrance passage of the Great Pyramid of Ghizeh is
+inclined at an angle of 30 deg. to the horizon, and therefore points to the
+celestial pole. But this is quite incorrect. The Great Pyramid, it is
+true, is situated close to the latitude of 30 deg.. But the entrance passage
+does not point exactly to the pole. The inclination was measured by Col.
+Vyse, and found to be 26 deg. 45'. For six out of the nine pyramids of
+Ghizeh, Col. Vyse found an _average_ inclination of 26 deg. 47', these
+inclinations ranging from 25 deg. 55' (2nd, or pyramid of Mycerinus) to 28 deg. 0'
+(9th pyramid).[520] Sir John Herschel gives 3970 B.C. as the probable date
+of the erection of the Great Pyramid.[520] At that time the distance of
+[Greek: a] Draconis (the Pole Star of that day) from the pole was 3 deg. 44'
+25", so that when on the meridian _below_ the pole (its lower culmination
+as it is termed) its altitude was 30 deg. - 3 deg. 44' 25" = 26 deg. 15' 35", which
+agrees fairly well with the inclination of the entrance passage. Letronne
+found a date of 3430 B.C.; but the earlier date agrees better with the
+evidence derived from Egyptology.
+
+Emerson says--
+
+  "I am brother to him who squared the pyramids
+  By the same stars I watch."
+
+From February 6 to 15, 1908, all the bright planets were visible together
+at the same time. Mercury was visible above the western horizon after
+sunset, Venus very brilliant with Saturn a little above it, Mars higher
+still, all ranged along the ecliptic, and lastly Jupiter rising in the
+east.[521] This simultaneous visibility of all the bright planets is
+rather a rare occurrence.
+
+With reference to the great improbability of Laplace's original Nebular
+Hypothesis being true, Dr. See says, "We may calculate from the
+preponderance of small bodies actually found in the solar system--eight
+principal planets, twenty-five satellites (besides our moon), and 625
+asteroids--that the chances of a nebula devoid of hydrostatic pressure
+producing small bodies is about 2{658} to 1, or a decillion decillion
+(10{66}){6} to the sixth power, to unity. This figure is so very large
+that we shall content ourselves with illustrating a decillion decillion,
+and for this purpose we avail ourselves of a method employed by ARCHIMEDES
+to illustrate his system of enumeration. Imagine sand so fine that 10,000
+grains will be contained in the space occupied by a poppy seed, itself
+about the size of a pin's head; and then conceive a sphere described about
+our sun with a radius of 200,000 astronomical units[522] ([Greek: a]
+Centauri being at a distance of 275,000) entirely filled with this fine
+sand. The number of grains of sand in this sphere of the fixed stars would
+be a decillion decillion[523] (10{66}){6}. All these grains of sand
+against one is the probability that a nebula devoid of hydrostatical
+pressure, such as that which formed the planets and satellites, will lead
+to the genesis of such small bodies revolving about a greatly predominant
+central mass."[524] In other words, it is practically certain that the
+solar system was _not_ formed from a gaseous nebula in the manner
+originally proposed by Laplace. On the other hand, the evolution of the
+solar system from a rotating spiral nebula seems very probable.
+
+       *       *       *       *       *
+
+Some one has said that "the world knows nothing of its greatest men." The
+name of Mr. George W. Hill will probably be unknown to many of my readers.
+But the late Prof. Simon Newcomb said of him that he "will easily rank as
+the greatest master of mathematical astronomy during the last quarter of
+the nineteenth century."[525] Of Prof. Newcomb himself--also a great
+master in the same subject--Sir Robert Ball says he was "the most
+conspicuous figure among the brilliant band of contemporary American
+astronomers."[526]
+
+An astronomer is supposed to say, with reference to unwelcome visitors to
+his observatory, "Who steals my purse steals trash; but he that filches
+from me my clear nights, robs me of that which not enriches him, and makes
+me poor indeed."[527]
+
+Cicero said, "In the heavens there is nothing fortuitous, unadvised,
+inconstant, or variable; all there is order, truth, reason, and
+constancy"; and he adds, "The creation is as plain a signal of the being
+of a God, as a globe, a clock, or other artificial machine, is of a
+man."[528]
+
+"Of all the epigrams attributed rightly or wrongly to Plato, the most
+famous has been expanded by Shelley into the four glorious lines--
+
+  "'Thou wert the morning star among the living
+    Ere thy pure light had fled,
+  Now having died, thou art as Hesperus, giving
+    New splendour to the dead.'"[529]
+
+Sir David Brewster has well said,[530] "Isaiah furnishes us with a
+striking passage, in which the occupants of the earth and the heavens are
+separately described, 'I have made the earth, and created man upon it: I,
+even My hands, have stretched out the heavens, and all _their_ host have I
+commanded' (Isaiah xlv. 12). But in addition to these obvious references
+to life and things pertaining to life, we find in Isaiah the following
+remarkable passage: 'For thus saith the Lord that created the heavens; God
+Himself that formed the earth and made it; He hath established it, _He
+created it not_ IN VAIN, He formed _it to be inhabited_' (Isaiah xlv. 18).
+Here we have a distinct declaration from the inspired prophet that the
+_earth would have been created_ IN VAIN _if it had not been formed to be
+inhabited_; and hence we draw the conclusion that as the Creator cannot be
+supposed to have made the worlds of our system and those in the sidereal
+system in vain, they must have been formed to be inhabited." This seems to
+the present writer to be a good and sufficient reply to Dr. Wallace's
+theory that our earth is the only inhabited world in the Universe![531]
+Such a theory seems incredible.
+
+The recent discovery made by Prof. Kapteyn, and confirmed by Mr.
+Eddington, of two drifts of stars, indicating the existence of _two_
+universes, seems to render untenable Dr. Wallace's hypothesis of the
+earth's central position in a single universe.[531]
+
+
+NOTE ADDED IN THE PRESS.
+
+While these pages were in the Press, it was announced, by Dr. Max Wolf of
+Heidelberg, that he found Halley's comet on a photograph taken on the
+early morning of September 12, 1909. The discovery has been confirmed at
+Greenwich Observatory. The comet was close to the position predicted by
+the calculations of Messrs. Cowell and Crommelin of Greenwich Observatory
+(_Nature_, September 16, 1908).
+
+
+
+
+INDEX
+
+
+  A
+
+  Aboukir, 287
+
+  Aboul Hassan, 221
+
+  Abu Ali al Farisi, 225
+
+  Abu-Hanifa, 233, 234
+
+  Abul-fadl, 236
+
+  Accadians, 250, 252
+
+  Achernar, 275
+
+  Aclian, 282
+
+  Adam, 96, 347
+
+  Adhad-al-Davlat, 225, 236
+
+  Adonis, 261
+
+  Adreaansz, 342
+
+  Airy, Sir G. B., 87, 140, 347, 357
+
+  Aitken, 160
+
+  Al-Battani, 232, 233
+
+  Albrecht, 173
+
+  Albufaragius, 283
+
+  Alcor, 241
+
+  Alcyone, 137
+
+  Aldebaran, 60, 156, 236, 252, 257, 310, 311
+
+  Alfard, 236, 289
+
+  Alfargani, 286
+
+  Alfraganus, 281
+
+  Almagest, 281
+
+  Al-Sufi, 47, 149, 179, 189, 221, 224, 225-238, 244, 246, 250, 251, 253,
+      254, 261, 263, 264, 266-270, 272, 274-278, 285, 287, 289, 290, 293,
+      298, 300-302, 304, 307
+
+  Altair, 246
+
+  Ampelius, 262
+
+  Amphion, 257
+
+  Ancient eclipses, 52, 53
+
+  Anderson, 120, 277
+
+  Andromeda nebula, 198-206, 231
+
+  Annals of Ulster, 332
+
+  Antares, 60, 179, 310, 311
+
+  Anthelm, 300
+
+  Antinous, 248
+
+  Antlia, 302
+
+  Apollo, 257
+
+  Apparent diameter of moon, 49
+
+  Apple, 79
+
+  "Apples, golden," 258
+
+  Apus, 306
+
+  Aquarius, 268
+
+  Aquila, 246
+
+  Aquillus, 220
+
+  Ara 295
+
+  Arago, 26, 30, 57, 116, 193, 331
+
+  Aratus, 219, 242, 245, 250, 255, 256, 261, 263, 272
+
+  Archimedes, 346, 354
+
+  Arcturus, 148, 188, 244
+
+  Argelander, 29, 227, 229, 230, 240
+
+  Argo, 285-288, 305
+
+  Argon in sun, 4
+
+  Argonauts, 243, 250
+
+  Aries, 250
+
+  Aristotle, 49, 67
+
+  Arrhenius, 4, 8, 22, 45, 66
+
+  Ashtoreth, 260
+
+  _Astra Borbonia_, 4
+
+  Astraea, 263
+
+  Astronomy, Laplace on, 44
+
+  _Astro Theology_, 23
+
+  Atarid, 232, 233
+
+  Atmosphere, height of, 33
+
+  Augean stables, 269
+
+  Augustus, 262
+
+  Auriga, 245
+
+  Aurora, 33, 41, 42
+
+  Auwers, 206
+
+  Axis of Mars, 59
+
+
+  B
+
+  Babilu, 267
+
+  Baily, 137, 144
+
+  Baker, 183
+
+  Ball, Sir Robert, 6, 355
+
+  Barnard, Prof., 29, 54, 57, 79, 80, 81, 85, 86, 91, 93, 103, 104, 114,
+      130, 132, 139, 192, 213, 316, 317, 350
+
+  Barnes, 78, 79
+
+  Bartlett, 35, 36
+
+  Bartschius, 296, 298
+
+  Bauschingen, 69, 70
+
+  Bayer, 179, 221, 272, 284, 309, 310
+
+  Bayeux Tapestry, 105
+
+  Becquerel, 8
+
+  "Beehive," 259
+
+  Beer, 20
+
+  Bel, 250
+
+  Bellatrix, 253
+
+  Benoit, 22
+
+  Berenice, 297
+
+  Berry, 25
+
+  Bessel, 339
+
+  Betelgeuse, 179, 222, 264
+
+  Bianchini, 21, 22, 77
+
+  Biela's comet, 99
+
+  Bifornis, 268
+
+  Binary stars, 162
+
+  Birmingham, 5, 114
+
+  "Black body," 3
+
+  "Blackness" of sun-spots, 6
+
+  "Blaze star," 180, 184
+
+  Bode, 276
+
+  Bohlin, 199, 200
+
+  Bond, 85
+
+  Bond (Jun.), 74
+
+  _Book of the Dead_, 264, 274
+
+  Borelly, 103
+
+  Boserup, 28
+
+  Boss, 152
+
+  Brahe, Tycho. _See_ Tycho Brahe
+
+  Brauner, 211
+
+  Bravais, 42
+
+  Bredikhin, 76
+
+  Bremiker, 94
+
+  Brenner, Leo, 13, 22, 87, 91, 133
+
+  Brewster, 356
+
+  Brightness of Mercury, 10-12
+
+      "      of nebulae, 193
+
+      "      of sun, 1, 2, 3
+
+      "      of Venus, 14, 17, 19, 31
+
+  Bright clouds, 33, 34
+
+    "    night, 45
+
+    "    stars, 278
+
+  Brooks, 118
+
+  Brown, 218, 219, 248, 255, 260, 267, 272, 279, 281, 291, 295
+
+  Browning, 25
+
+  Brugsch, 127
+
+  Buddha, 256
+
+  Bull, Pope's, 107
+
+  "Bull's foot," 253
+
+  Buonaparte, 30
+
+  Burnham, 160, 165-167, 180, 184, 260, 350, 351
+
+  Burns, 130
+
+  Buss, 4
+
+
+  C
+
+  Caaba, 125
+
+  Cacciatore, 72
+
+  Caelum, 302
+
+  Callimachus, 297
+
+  Callixtus III., 107
+
+  Calvisius, 53
+
+  Camelopardalis, 296
+
+  Cameron, 18
+
+  Campbell, 85, 153, 159, 178
+
+  "Canals" on Mars, 61-63
+
+  Cancer, 258, 259
+
+  Canes Venatici, 296
+
+  Canicula, 280
+
+  Canis Major, 279
+
+    "   Minor, 284
+
+  Canopus, 157, 286, 344
+
+  Capella, 156, 164, 189, 236, 245, 246
+
+  Capricornus, 267, 268
+
+  "Capture" of satellites, 58
+
+  Carbonic acid, 66
+
+  Cassini, 20, 22, 74, 78, 358
+
+  Cassiopeia's Chair, 244
+
+  Castor, 160, 257
+
+  Caswell, 52
+
+  Catullus, 297
+
+  Caussin, 225
+
+  Cecrops, 268
+
+  "Celestial Rivers," 308
+
+  Celoria, 324, 326
+
+  Centaurus, 292, 293
+
+  Centre of gravity, 8
+
+  Cephalus, 279
+
+  Cepheid variables, 187
+
+  Ceraski, 2, 176
+
+  Cerberus, 243, 257
+
+  Ceres, 260
+
+  Cerulli, 22, 62
+
+  Cetus, 272
+
+  Chacornac, 18, 84
+
+  Chamaelion, 305
+
+  Chamberlin, 194
+
+  Chambers, 72
+
+  "Charles' Wain," 240
+
+  Chinese Annals, 19, 30, 105, 186, 223, 267, 330
+
+  Childrey, 128
+
+  Chiron, 295
+
+  Christmann, 281
+
+  Chromosphere, sun's, 4
+
+  Cicero, 49, 262, 280, 355
+
+  Circinus, 307
+
+  Clavius, 334
+
+  Climate, 45
+
+  "Coal Sack," 293, 320
+
+  Cobham, 88, 102
+
+  Colbert, 175
+
+  Colours of stars, 140, 141, 188-190
+
+  Coma Berenices, 297, 298
+
+  Comets, number of, 98
+
+    "     tails of, 115, 116
+
+  Comet years, 104
+
+  Comiers, 99
+
+  Comstock, 90, 146
+
+  Condamine, 257
+
+  Conon, 297
+
+  Coon Butte mountain, 120, 121
+
+  Cooper, 3
+
+  Copeland, 76, 157
+
+  Corona, sun's, 1, 334
+
+    "     round moon, 35, 36
+
+  Corona Australis, 295
+
+  Corvinus, 292
+
+  Corvus, 292
+
+  Cotsworth, 46
+
+  Cowell, 105
+
+  Crabtree, 337
+
+  Crater, 291
+
+  Craters on moon, 55, 56
+
+  Crawford, 348
+
+  Crecy, Battle of, 333
+
+  Crescent of Venus, 19, 20
+
+  Crommelin, 105, 111
+
+  Crucifixion, 18
+
+  Curtis, 344
+
+  Cusps of Venus, 20
+
+  Cygnus, (61), 155
+
+  Cynocephalus, 222
+
+
+  D
+
+  Dante, 156, 258, 265
+
+  Dark shade on moon, 333
+
+  D'Arrest, 94
+
+  Darwin, Sir George, 158, 319
+
+  "David's Chariot," 241
+
+  Davis, 155
+
+  Dawes, 168
+
+  "Dawn proclaimer," 251
+
+  Delambre, 185
+
+  Delauney, 347
+
+  Dembowski, 190
+
+  Demetrius, 111
+
+  Denning, 11, 74, 77, 84, 86, 87, 89, 99, 118, 340
+
+  Derham, 21, 23
+
+  Deucalion, 268
+
+  De Vico, 21, 22
+
+  Diamonds in meteorites, 127
+
+  Dilkur, 251
+
+  Diodorus Siculus, 127
+
+  Diogenes Laertius, 41
+
+  Diomed, 272
+
+  Dione, 89
+
+  "Dipper," 241
+
+  Doberck, 160
+
+  Dollond, 24
+
+  Domitian, 334
+
+  Donati's comet, 100
+
+  Dorado, 304
+
+  Dordona, 256
+
+  Dorn, 245
+
+  Douglass, 81
+
+  Dragon, 242
+
+  Draper, 75
+
+  Drayton, 156
+
+  Dreyer, 115
+
+  Drifting stars, 152
+
+  Dryden, 242
+
+  Duncan, 187
+
+  Dunlop, 264
+
+  Dupret, 83
+
+  Dupuis, 245, 252, 257, 258, 259, 266, 267, 268
+
+  "Dusky star," 272
+
+
+  E
+
+  "Earthen jar," 247
+
+  Earth's attraction on moon, 55
+
+  Earth's motions, 39
+
+    "     rotation, 46
+
+    "     surface, 32
+
+  "Earthshine" on moon, 51, 52, 56, 57
+
+  Eastmann, 316
+
+  Easton, 323, 324, 325
+
+  Eclipses, ancient, 52, 53, 57, 58
+
+     "      dark, of moon, 53, 57, 58
+
+  Ecliptic, obliquity of, 47
+
+  Eddington, 357
+
+  Electra, 19
+
+  Elster, 39
+
+  Emerson, 353
+
+  Enceladus, 89
+
+  Encke, 113, 116, 240
+
+  Ennis, 189
+
+  Eratosthenes, 250, 297, 345
+
+  Eridanus, 274-278
+
+  Eros, 69, 70, 71
+
+  Eta Argus, 177, 287
+
+  Eudemus, 47
+
+  Eudoxus, 218, 219, 223
+
+  Euler, 56
+
+  Eunomia, 71
+
+  Europa, 252
+
+
+  F
+
+  Fabritius, 4, 101
+
+  Fabry, 1
+
+  Faint stars in telescope, 176
+
+  "False Cross," 156
+
+  "Famous stars," 246
+
+  Fath, 130, 213
+
+  Faye, 100
+
+  February, Five Sundays in, 36
+
+  Fergani, 189
+
+  "Fisher Stars," 256
+
+  "Fishes in Andromeda," 249
+
+  Fitzgerald, 127
+
+  Flammarion, 22, 26, 50, 138, 255, 265, 276
+
+  Flamsteed, 348
+
+  "Flat earth" theory, 32
+
+  Fomalhaut, 271, 309, 310
+
+  Fontana, 20
+
+  Fontenelle, 357
+
+  Forbes, 82, 95, 96
+
+  Fornax, 301
+
+  Fournier, 87
+
+  Fovea, 284
+
+  Freeman, 88
+
+  Freret, 222
+
+  Frisby, 101
+
+  Fritsch, 21
+
+  Furner, 163
+
+
+  G
+
+  Gale, 78
+
+  Galileo, 3, 4, 80, 82
+
+  Galle, 94, 341
+
+  Ganymede, 268
+
+  Gaseous nebula, spectra of, 195-198, 212
+
+  Gassendi, 14, 139
+
+  Gathman, 118
+
+  Gaubil, 99
+
+  Gauthier, 103
+
+  Gegenschein, 131
+
+  Gemini, 257, 258
+
+  Geminid variables, 187
+
+  Gentil, Le, 338, 339
+
+  Gertel, 39
+
+  Ghizeh, Pyramids of, 353
+
+  Gibbous phase of Jupiter, 75
+
+  Gill, Sir David, 118, 215, 216, 346
+
+  Glacial epoch, 42
+
+  Gledhill, 76
+
+  Globular clusters, 214, 215
+
+  Goad, 12
+
+  Goatcher, 179
+
+  "Golden apples," 258
+
+  Golius, 281
+
+  Gould, 229, 278, 301, 304, 309, 310, 326
+
+  Grant, 82, 96, 345
+
+  Gravitation, Law of, 15, 40
+
+  Greely, 186
+
+  Greisbach, 80
+
+  Groombridge 1830, 159
+
+  Grubb, Sir Howard, 164
+
+  Gruithuisen, 21, 25, 26, 28
+
+  Gruson, 127
+
+  Guillaume, 331
+
+  Guthrie, 25
+
+
+  H
+
+  Habitability of Mars, 63-66
+
+       "       of planets, 40
+
+  Hadrian, 248
+
+  Halbert, 78
+
+  Hale, 148, 150
+
+  Hall, 15, 131
+
+  Halley, 14, 17, 99, 105, 106, 108, 109, 116, 143, 145, 276
+
+  Halm, 122
+
+  Halo, 35, 36
+
+  Hanouman, 284
+
+  Hansen, 351
+
+  Hansky, 27
+
+  Harding, 25, 26, 94
+
+  "Harris, Mrs.," 90
+
+  Hartwig, 88, 173
+
+  Harvests, 104
+
+  Heat of sun, 2, 3, 7
+
+  Height of atmosphere, 33
+
+  Heis, 132, 175, 189, 227, 229, 344
+
+  Helium, 4
+
+  Hepidanus, 267, 348
+
+  Hercules, 243, 259, 268
+
+  Herod, 18, 53
+
+  Herschel, Miss Caroline, 193, 194, 324, 357
+
+  Herschel, Sir John, 112, 177, 190, 207, 209, 210, 215, 289, 314, 346,
+      353
+
+  Herschel, Sir Wm., 3, 24, 80, 112, 114, 115, 116, 171, 178, 179, 190,
+      324, 325
+
+  Hesiod, 17, 220
+
+  Hesperus, 256
+
+  Hevelius, 99, 116, 221, 296, 299, 300
+
+  Hill, 87, 355
+
+  Hind, 19, 30, 54, 105, 111, 180
+
+  Hipparchus, 135, 221-223, 226, 250, 278, 281, 293, 329
+
+  Hippocrates, 258
+
+  Hirst, 333
+
+  Holetschak, 108
+
+  Homer, 17
+
+  Honorat, 84
+
+  Hooke, 74, 128
+
+  Horace, 280
+
+  Horologium, 303
+
+  Horus, 145, 258
+
+  Horrebow, 29
+
+  Horrocks, 337
+
+  Hortensus, Martinus, 139
+
+  Hough, 76
+
+  Houzeau, 227, 229, 262, 274, 344
+
+  Hovedin, Roger de, 53
+
+  Hubbard, 100
+
+  Huggins, Sir Wm., 91, 148, 180
+
+  Humboldt, 30, 82, 83, 124, 128, 134, 154, 157, 342, 352, 357
+
+  Hussey, 88
+
+  Hyades, 157, 252, 253, 257
+
+  Hydra, 288
+
+  Hydrus, 303
+
+  Hyperion, 88, 90
+
+
+  I
+
+  Ibn al-Aalam, 225
+
+  Ibn Alraqqa, 281
+
+  Icarus, 284
+
+  Indus, 307
+
+  Inhabited worlds, 328, 357
+
+  Innes, 78, 168
+
+  Intra-Mercurial planet, 14, 15, 29
+
+  Invention of telescope, 342
+
+  Io, 252
+
+  Ions, 27
+
+  Iris, 71
+
+  Isaiah, 17, 356
+
+  Isis, 252, 261, 282, 283
+
+  Istar, 260
+
+
+  J
+
+  Jansen, 342
+
+  Japetus, 89, 90
+
+  Jason, 257, 285
+
+  Johnson, Rev. S. J., 19
+
+  Jonckheere, 15
+
+  Jones, 129
+
+  Jordan, 174
+
+  Jupiter, chap. viii.
+
+     "     gibbous form of, 75
+
+     "     and sun, 8
+
+
+  K
+
+  Kalevala, 240
+
+  Kapteyn, 314, 316, 321, 322, 326, 357
+
+  Kazemerski, 244
+
+  Keeler, 86, 215
+
+  Kelvin, Lord, 206, 315, 316
+
+  Kempf, 174
+
+  Kepler, 52, 57, 298, 340, 341, 351
+
+  Khayyam, Omar, 127
+
+  Kimah, 255
+
+  Kimball, 51
+
+  Kimta, 255
+
+  Kirch, 23, 115
+
+  Kirkwood, 6
+
+  Kleiber, 123
+
+  Klein, 114, 183
+
+  Knobel, 238, 263
+
+  Konkoly, 183
+
+  Koran, 127, 270
+
+  Kreusler, 4
+
+  Kreutz, 101, 112
+
+
+  L
+
+  Lacaille, 294, 301, 302
+
+  Lacerta, 300
+
+  Lagrange, 345
+
+  La Hire, 20, 21
+
+  Lalande, 143, 144, 284
+
+  Landerer, 52
+
+  Langdon, 25
+
+  Langley, Prof., 3
+
+  Laplace, 43, 44, 98, 346, 351, 354
+
+  Larkin, 65
+
+  Lassell, 77, 128
+
+  "Last in the River," 275-298
+
+  Last year of century, 37
+
+  Lau, 178, 183
+
+  Leo, 259
+
+  Leo Minor, 298
+
+  Lepus, 278, 279
+
+  Lernaean marsh, 258
+
+  Leverrier, 44, 347, 351
+
+  Lewis, 156, 162
+
+  Lewis, Sir G. C., 17
+
+  Lexell's comet, 98
+
+  Libra, 262
+
+  Life, possible, in Mars, 63-65
+
+  Light of full moon, 1, 51
+
+  Lippershey, 342
+
+  Littrow, 339
+
+  Lockyer, Sir Norman, 144, 147
+
+  Lodge, Sir Oliver, 55
+
+  Long, 343, 357
+
+  Longfellow, 156, 273
+
+  Lottin, 42
+
+  Lowell, 22, 43, 59, 61, 64, 88
+
+  Lucifer, 17
+
+  Lucretius, 320
+
+  "Luminous clouds," 33, 34
+
+  Lunar craters, 55, 56
+
+    "   "mansions," 251
+
+    "   mountains, 58
+
+    "   theory, 56
+
+  Lunt, 179
+
+  Lupus, 294
+
+  Lyman, 25
+
+  Lynn, 37, 38, 96, 106, 179, 243, 244, 310
+
+  Lynx, 296
+
+  Lyra, 243, 244, 266
+
+
+  M
+
+  Maclear, 77
+
+  Maedler, 20, 22
+
+  Maestlin, 341
+
+  Magi, star of, 1, 18, 145
+
+  Magnitudes, star, 311
+
+  Maia, 19, 256
+
+  Mairan, 357
+
+  "Manger," 259
+
+  Manilius, 250, 259, 272
+
+  Marius, Simon, 82, 83, 231
+
+  Markree Castle, 3
+
+  Marmol, 76
+
+  Mars, chap. vi.;
+    axis of 59;
+    red colour of, 60;
+    water vapour in, 60;
+    clouds in, 61;
+    "canals" in, 61
+
+  Martial, 17
+
+  Mascari, 22
+
+  Ma-tuan-lin, 186, 267
+
+  Mayer, 24
+
+  May transits of Mercury, 15
+
+  Maxwell, Clerk, 86
+
+  McHarg, 16
+
+  McKay, 286
+
+  Medusa, 244
+
+  Mee, 88
+
+  Melotte, 82
+
+  Mendelief, 212
+
+  Mensa, 304
+
+  Mercury, chap, ii., 258
+
+  Merrill, 121
+
+  Messier, 114
+
+  Meteoric stones, 119
+
+  Meteors, 33
+
+  Metius, 342
+
+  Microscopium, 302
+
+  Milky Way, 320, 323, 325, 326, 328
+
+  Milton, 263
+
+  Mimas, 88, 89
+
+  Minor planets, chap. vii.
+
+  Mira Ceti, 178, 186, 272, 273
+
+  Mitchell, 4
+
+  Mithridates, 111
+
+  Mitra, 145
+
+  Molyneux, 80
+
+  Monck, 156, 181
+
+  Monoceros, 298
+
+  Montanari, 170, 171
+
+  Montigny, 34
+
+  Moon, light of, 1, 51
+
+    "   as seen through a telescope, 50
+
+  "Moon maiden," 52
+
+  Moon mountains, 58
+
+  Morehouse, 103, 110
+
+  Motions of stars in line of sight, 141, 142
+
+  Moulton, 133, 318
+
+  Mountains, lunar, 58
+
+  Mueller, 174
+
+  Musca, 305
+
+  Mycerinus, Pyramid of, 353
+
+
+  N
+
+  Nasmyth, 11
+
+  Nath, 253
+
+  Nautical Almanac, 349
+
+  Nebula in Andromeda, 198-206, 231
+
+  Nebulae, gaseous, 195-198, 212, 213
+
+  Nebulae, spiral, 213
+
+  Nebular hypothesis, 354
+
+  Nemaelian lion, 259
+
+  Nemaeus, 259
+
+  Neon in sun, 4
+
+  Nepthys, 271
+
+  Neptune, 341
+
+  Newcomb, 13, 15, 33, 50, 65, 70, 129, 130, 153, 191, 203, 282, 339, 347,
+      349, 350, 355
+
+  Newton, 15, 351
+
+  Nicephorus, 127
+
+  Nicholls, 148, 154
+
+  Nineveh tablets, 17
+
+  Noble, 25
+
+  Norma, 302
+
+  Novae, 180-182, 265, 267, 343
+
+  Nova Persei, 190
+
+  November transits of Mercury, 15
+
+  Number of nebulae, 191
+
+    "    of stars, 135, 136, 236, 237
+
+    "    of variable stars, 182, 183
+
+
+  O
+
+  Obliquity of ecliptic, 47
+
+  Occupations, 14, 15, 54, 67, 80, 84, 85, 259, 340, 341
+
+  Octans, 303
+
+  Odling, 122
+
+  Oeltzen, 72
+
+  Olbers, 104, 124
+
+  Old, 340
+
+  Orion, 49, 146, 273, 274
+
+  Osiris, 145, 259, 261, 283
+
+  "Ostriches," 266
+
+  Otawa, 240
+
+  Ovid, 242, 250, 255, 265, 288, 291, 322
+
+
+  P
+
+  Palisa, 71
+
+  Palmer, 182
+
+  Parker, 19
+
+  Parkhurst, 174
+
+  Paschen, 2
+
+  Pastorff, 25
+
+  Pavo, 307
+
+  Payne, 139
+
+  Pearson, 77
+
+  Peary, 119
+
+  Peck, 176
+
+  Pegasus, 248
+
+  Pelion, 282
+
+  Peritheus, 258
+
+  Perrine, 15, 76, 191, 192, 214
+
+  Perrotin, 351
+
+  Perseus, 244
+
+  Petosiris, 222
+
+  Philostratus, 334
+
+  Phlegon, 332
+
+  Phoebe, 90
+
+  Phoenix, 301
+
+  Phosphorus, 17
+
+  Photographic nebula, 192
+
+  Pickering, E. C., 125, 140, 144, 177
+
+  Pickering, W. H., 1, 12, 51, 61, 95, 102
+
+  Pictor, 304
+
+  Pierce, 228
+
+  "Pilgrim Star," 180, 185, 186
+
+  Pingre, 54
+
+  Pinzon, 294
+
+  Pisces, 271
+
+  Piscis Australis, 295, 296
+
+  Planetary nebulae, 213
+
+  Platina, 107
+
+  Pleiades, 19, 52, 137, 154, 157, 235, 254-257
+
+  Pliny, 17, 265, 280
+
+  Plummer, W. E., 180
+
+  Plurality of worlds, 328, 356, 357
+
+  Pococke, 271
+
+  Pogson, 317
+
+  Polarization of moon's surface, 52
+
+  Polarization on Mars, 61
+
+  Pole of cold, 33
+
+    "  star, 138, 239, 240
+
+  Pollux, 257
+
+  Polydectus, 244
+
+  Poor, 15 (footnote)
+
+  Poynting, 130
+
+  Praesape, 259
+
+  Prince, 25
+
+  Proclus, 221
+
+  Proctor, 7, 49, 59, 123, 285, 308, 323, 352
+
+  Procyon, 156, 157, 236, 284
+
+  Ptolemy, 189, 221-223, 224, 227, 230, 231, 234, 238, 244, 252, 253, 260,
+      263, 264, 267, 269, 275, 278, 281, 284, 293, 302, 330
+
+  Pyramid, Great, 46, 47, 308, 353
+
+  Pytheas, 46
+
+
+  Q
+
+  Quadruple system, 168
+
+  Quenisset, 21, 133
+
+
+  R
+
+  Rabourdin, 103
+
+  Radium, 7, 8, 38
+
+  Rahu, 93
+
+  Rama, 284, 340
+
+  _Rational Almanac_, 46
+
+  "Red Bird," 290
+
+  Red star, 279, 292
+
+  Regulus, 30, 156, 235, 236, 260, 310, 340
+
+  Remote galaxies, 193, 204, 205
+
+  Reticulum, 304
+
+  Rhea, 89
+
+  Rheita, De, 144
+
+  Riccioli, 189
+
+  Ricco, 32
+
+  Rigel, 156, 157, 222
+
+  Rigge, 107
+
+  Ring nebula in Lyra, 211
+
+  Rings of Saturn, 85
+
+  Rishis, 240
+
+  Ritter, 76, 147
+
+  "Rivers, celestial," 308
+
+  Roberts, Dr. A. W., 172, 173
+
+  Roberts, Dr. I., 95, 154, 200, 201, 203, 317
+
+  Roberts, C., 84
+
+  Robigalia, 280
+
+  Robinson, 342, 357
+
+  Roedeckoer, 28
+
+  Rogovsky, 42, 43, 44, 75
+
+  Rosse, Lord, 76
+
+  Roszel, 70
+
+  Rotation of Mercury, 16
+
+     "     of Uranus, 91
+
+     "     of Venus, 22
+
+  Rubaiyat, 127
+
+  Rudaux, 80, 89
+
+  Russell, H. C., 21
+
+  Russell, H. N., 146
+
+  Russell, J. C., 333
+
+  Rutherford, 38
+
+
+  S
+
+  Sadler, 78, 299
+
+  Safarik, 24, 25
+
+  Sagittarius, 265-267
+
+  _Sahu_, 274
+
+  Santini, 357
+
+  Satellite, eighth, of Jupiter, 82
+
+      "      possible lunar, 54
+
+      "      of Venus, 28, 29
+
+  Sawyer, 186
+
+  Sayce, 218, 261
+
+  Scaliger, 299
+
+  Schaeberle, 93
+
+  Schaer, 88
+
+  Scheiner, 4, 150, 188, 195
+
+  Scheuter, 30
+
+  Schiaparelli, 22, 326
+
+  Schjellerup, 226, 228, 230, 231, 264, 277, 281, 340
+
+  Schlesinger, 183
+
+  Schoenfeld, 287
+
+  Schiraz, 47
+
+  Schmidt, 51, 188, 220, 271
+
+  Scholl, 79
+
+  Schroeter, 13, 20, 21, 22, 24, 26, 48
+
+  Schuster, 2, 148, 149, 150
+
+  Schwabe, 5
+
+  Scorpio, 263-265
+
+  Sculptor, 301
+
+  Scutum, 299
+
+  Searle, 132
+
+  "Secondary light" of Venus, 23-28
+
+  See, Dr., 12, 13, 33, 58, 96, 161, 164, 165, 210, 211, 281, 282, 354
+
+  Seeliger, 181, 206
+
+  Seneca, 218, 220
+
+  Serapis, 145
+
+  Sestini, 190
+
+  "Seven Perfect Ones," 256
+
+  Sextans, 298
+
+  Shaler, 48
+
+  Sharpe, 357
+
+  Shelley, 356
+
+  Shicor, 274
+
+  "Ship," 285
+
+  "Sickle," 259
+
+  Signalling to Mars, 65
+
+  Sihor, 280
+
+  Silkit, 264
+
+  Silvestria, 124
+
+  Simeon of Durham, 53
+
+  Simonides, 255
+
+  "Singing Maidens," 256
+
+  Sirius, 138, 156, 157, 160, 163, 236, 274, 280, 282, 283
+
+  Slipher, 60, 87, 161, 178
+
+  Smart, 109
+
+  Smyth, Admiral, 12, 72, 77, 107, 136, 140, 145, 170, 176, 190, 194, 253,
+      259, 351
+
+  Snyder, Carl, 8, 345
+
+  Sobieski, 299
+
+  Sola, Comas, 81, 87
+
+  Somerville, Mrs., 357
+
+  Sothis, 286
+
+  Southern Cross, 293, 344
+
+  Spectra of double stars, 162
+
+  Spectrum of gaseous nebulae, 195-198, 212
+
+  Spectrum of sun's chromosphere, 4
+
+  Spencer, Herbert, 193
+
+  Sphinx, 261
+
+  Spica, 156, 236
+
+  Spiral nebulae, 213
+
+  Star magnitudes, 311
+
+  "Star of Bethlehem," 17, 18
+
+  Stars in daytime, 158
+
+  Stebbins, 51
+
+  Stockwell, 18, 331
+
+  "Stones from heaven," 125, 126
+
+  Stoney, 133
+
+  Strabo, 127
+
+  Stratonoff, 151, 320, 321
+
+  Stromgen, 88
+
+  Strutt, 7
+
+  Struve, 113, 240
+
+  Struyck, 54
+
+  Succulae, 253
+
+  Suhail, 283, 286
+
+  Sun darkenings, 5, 335, 336
+
+  Sun's heat, 7
+
+  Sunlight, 1, 2
+
+  Sun-spots, 5, 6
+
+  Swift, 102
+
+  _Sydera Austricea_, 5
+
+
+  T
+
+  Tacchini, 22
+
+  Tamerlane, 238
+
+  Tammuz, 261
+
+  Tarde, 4
+
+  Taurus, 251
+
+  Taylor, 40
+
+  T Coronae, 184
+
+  Tebbutt, 183, 278
+
+  Telescopium, 302
+
+  Temporary stars, 180-182, 265, 267, 343
+
+  Tennyson, 40
+
+  Terby, 88
+
+  Tethys, 89
+
+  Thales, 357
+
+  Thebes, 271
+
+  Themis, 88-90
+
+  Theogirus, 279
+
+  Theon, 245
+
+  Theseus, 257
+
+  Thome, 101
+
+  Thucydides, 331
+
+  Tibertinus, 281
+
+  Tibullus, 282
+
+  Tides, 40
+
+  Timocharis, 340
+
+  Tin, 179
+
+  Titan, 85, 88, 89
+
+  Titanium, 179
+
+  Toucan, 308
+
+  Transits of Mercury, 14, 15
+
+     "     of Venus, 337, 338, 339
+
+  Triangulum, 271
+
+       "      Australis, 306
+
+  Trio, 220
+
+  Triptolemus, 257
+
+  Triton, 93
+
+  Trouvelot, 21, 22, 78, 211
+
+  Tumlirz, 46
+
+  Turrinus, 220
+
+  Tycho Brahe, 10, 30, 99, 145, 179, 298
+
+  Typhon, 263, 272
+
+
+  U
+
+  Ulugh Beigh, 238, 276, 278
+
+  Underwood, 85
+
+  Uranus, chap. x.;
+    spectrum of, 91, 92
+
+  Urda, 71
+
+
+  V
+
+  Valz 72
+
+  "Vanishing star," 59
+
+  Varvadjah, 236
+
+  Vega, 148, 156, 244
+
+  Vencontre, 220
+
+  Venus, chap. iii.;
+    apparent motion of, 28;
+    supposed satellite of, 28, 29;
+    transit of, 337-339
+
+  Veronica, S, 145
+
+  Vesta, 70
+
+  Virgil, 17, 218, 242, 262, 309
+
+  Virgo, 260
+
+  Vogel, 180
+
+  Vogt, 122
+
+  Volans, 304
+
+  Voltaire, 15
+
+  Von Hahn, 24
+
+  Vulpecula, 300
+
+
+  W
+
+  Wallace, Dr., 212, 357
+
+  Wallis, 80
+
+  Ward, 88
+
+  Wargentin, 178
+
+  Watson, 339
+
+  Webb, 24, 25, 77, 190, 286
+
+  Weber, 183
+
+  Weinhand, 122
+
+  Wendell, 71, 103, 109
+
+  Werchojansk, 33
+
+  White spots on Jupiter's satellites, 81
+
+  White spots on Venus, 21
+
+  Whitmell, 50, 86
+
+  Wiggins, 333
+
+  Wilczyniski, 195
+
+  Williams, Stanley, 22, 277, 302
+
+  Wilsing, 155
+
+  Wilson, H. C., 137, 139
+
+  Wilson, Dr. W. E., 3, 148
+
+  Winnecke, 26, 188
+
+  Winterhalter, 351
+
+  Wolf, Dr. Max, 71, 72, 191, 211, Note p. 537
+
+  Wrangel, 240
+
+
+  Y
+
+  Young, Prof., 4, 7, 9
+
+  Young, Miss Anne S., 79
+
+  Yunis, Ibn, 30
+
+
+  Z
+
+  Zach, 331
+
+  Zenophon, 127
+
+  Zethas, 257
+
+  Zoellner, 27
+
+
+THE END
+
+
+PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLES.
+
+
+[Illustration]
+
+
+
+
+FOOTNOTES:
+
+[1] _Comptes Rendus_, 1903, December 7.
+
+[2] _Nature_, April 11, 1907.
+
+[3] _Astrophysical Journal_, vol. 19 (1904), p. 39.
+
+[4] _Astrophysical Journal_, vol. 21 (1905), p. 260.
+
+[5] _Knowledge_, July, 1902, p. 132.
+
+[6] _Nature_, April 30, 1903.
+
+[7] _Ibid._, May 18, 1905.
+
+[8] _Ibid._, May 18, 1905.
+
+[9] _Nature_, June 29, 1871.
+
+[10] _Nature_, October 15, 1903.
+
+[11] _The Life of the Universe_ (1909), vol. ii. p. 209.
+
+[12] _The World Machine_, p. 234.
+
+[13] Quoted in _The Observatory_, March 1908, p. 125.
+
+[14] _The Observatory_, September, 1906.
+
+[15] _Nature_, March 1, 1900.
+
+[16] _Cycle of Celestial Objects_, p. 96.
+
+[17] _Ast. Nach._ No. 3737.
+
+[18] _Observatory_, September, 1906.
+
+[19] _Nature_, November 29 and December 20, 1894.
+
+[20] _Bulletin, Ast. Soc. de France_, July, 1898.
+
+[21] _Observatory_, vol. 8 (1885), pp. 306-7.
+
+[22] _Nature_, October 30, 1902.
+
+[23] Charles Lane Poor, _The Solar System_, p. 170.
+
+[24] Smyth, _Celestial Cycle_, p. 60.
+
+[25] Denning, _Telescopic Work for Starlight Evenings_, p. 225.
+
+[26] _The Observatory_, 1894, p. 395.
+
+[27] _Ast. Nach._ 4333, quoted in _Nature_, July 1, 1909, p. 20.
+
+[28] _English Mechanic_, July 23, 1909.
+
+[29] _Nature_, December 22, 1892.
+
+[30] _Celestial Objects_, vol. i. p. 52, footnote.
+
+[31] _Ibid._, p. 54.
+
+[32] _Astronomy and Astrophysics_, 1892, p. 618.
+
+[33] _Nature_, August 7, 1879.
+
+[34] _The World of Space_, p. 56.
+
+[35] _Nature_, September 15, 1892.
+
+[36] _Observatory_, 1880, p. 574.
+
+[37] _Knowledge_, November 1, 1897, pp. 260, 261.
+
+[38] _Worlds in the Making_, p. 61.
+
+[39] _Ibid._, p. 48.
+
+[40] _Nature_, June 1, 1876.
+
+[41] _Cel. Objects_, vol. i. p. 66 (5th Edition).
+
+[42] _Celestial Objects_, vol. i. p. 65 (5th Edition).
+
+[43] _Ast. Nach._ No. 1863.
+
+[44] _Nature_, June 1, 1876.
+
+[45] _Ibid._, June 8, 1876.
+
+[46] _Nature_, October 17, 1895.
+
+[47] _Ibid._, July 27, 1905.
+
+[48] _Celestial Cycle_, p. 107.
+
+[49] _Nature_, October 6, 1887.
+
+[50] _Ast. Nach._, No. 4106.
+
+[51] _Copernicus_, vol. ii. p. 168.
+
+[52] _Cosmos_, vol. iv. p. 476, footnote.
+
+[53] Denning, _Telescopic Work for Starlight Evenings_, p. 153.
+
+[54] _Ibid._, p. 154.
+
+[55] _Nature_, July 13, 1876.
+
+[56] P. M. Ryves in _Knowledge_, June 1, 1897, p. 144.
+
+[57] _Bulletin, Ast. Soc. de France_, August, 1905.
+
+[58] _Nature_, April 5, 1894.
+
+[59] _Nature_, May 14, 1896. Some have attributed these "luminous clouds"
+to light reflected from the dust of the Krakatoa eruption (1883).
+
+[60] _The Observatory_, 1877, p. 90.
+
+[61] _Popular Astronomy_, vol. 11 (1903), p. 293.
+
+[62] _Popular Astronomy_, vol. 13 (1905), p. 226.
+
+[63] _Nature_, July 25, 1901 (from Flammarion).
+
+[64] _Popular Astronomy_, vol. 11 (1903), p. 496.
+
+[65] _Kinetic Theories of Gravitation_, Washington, 1877.
+
+[66] _The Observatory_, June, 1894, p. 208.
+
+[67] _Nature_, June 8, 1899.
+
+[68] _Astrophysical Journal_, vol. 14 (1901), p. 238, footnote.
+
+[69] _Mars as the Abode of Life_, p. 52.
+
+[70] Second Book of the Maccabees v. 1-4 (Revised Edition).
+
+[71] Humboldt's _Cosmos_, vol. i. p. 169 (Otte's translation).
+
+[72] Quoted by Grant in _History of Physical Astronomy_, p. 71.
+
+[73] _Ibid._, pp. 100, 101.
+
+[74] _Exposition du Systeme du Monde_, quoted by Carl Snyder in _The World
+Machine_, p. 226.
+
+[75] _Worlds in the Making_, p. 63.
+
+[76] _Cosmos_, vol. i. p. 131.
+
+[77] _The Observatory_, June, 1909, p. 261.
+
+[78] _Astronomical Essays_, pp. 61, 62.
+
+[79] _Encyclopaedia Britannica_ (_Schiraz_).
+
+[80] _Monthly Notices_, R.A.S., February, 1905.
+
+[81] _Nature_, March 3, 1870.
+
+[82] _Ibid._, March 31, 1870, p. 557.
+
+[83] Prof. W. H. Pickering found 12 times (see p. 1).
+
+[84] _Nature_, January 30, 1908.
+
+[85] _Nature_, September 5, 1901.
+
+[86] _Ibid._, July 31, 1890.
+
+[87] _Nature_, October 16, 1884.
+
+[88] _Nature_, February 19, 1885.
+
+[89] _Nature_, January 14, 1909, p. 323.
+
+[90] _Photographic Atlas of the Moon, Annals of Harvard Observatory_, vol.
+li. pp. 14, 15.
+
+[91] _Nature_, January 18, 1906.
+
+[92] Humboldt's _Cosmos_, vol. iv. p. 481.
+
+[93] _Ibid._, p. 482.
+
+[94] _Monthly Notices_, R.A.S., June, 1895.
+
+[95] Humboldt's _Cosmos_, vol. iv. p. 483 (Otte's translation).
+
+[96] Grant, _History of Physical Astronomy_, p. 229.
+
+[97] _Popular Astronomy_, vol. xvii. No. 6, p. 387 (June-July, 1909).
+
+[98] _Nature_, October 7, 1875.
+
+[99] _Mars as an Abode of Life_ (1908), p. 281.
+
+[100] _Knowledge_, May 2, 1886.
+
+[101] _Nature_, March 12, 1908.
+
+[102] _Bulletin, Ast. Soc. de France_, April, 1899.
+
+[103] _Astronomy and Astrophysics_ (1894), p. 649.
+
+[104] _Nature_, April 20, 1905.
+
+[105] _Astrophysical Journal_, vol. 14 (1901), p. 258.
+
+[106] _Nature_, August 22, 1907.
+
+[107] _Popular Astronomy_, vol. 12 (1904), p. 679.
+
+[108] _Mars as an Abode of Life_, p. 69.
+
+[109] _Ibid._, p. 146.
+
+[110] _Worlds in the Making_, p. 49.
+
+[111] _Worlds in the Making_, p. 53.
+
+[112] Denning, _Telescopic Work for Starlight Evenings_, p. 158.
+
+[113] _Ibid._, p. 166.
+
+[114] _Nature_, July 13, 1876.
+
+[115] _Nature_, May 2, 1907.
+
+[116] _Nature_, May 30, 1907.
+
+[117] _Publications of the Astronomical Society of the Pacific_, August,
+1908.
+
+[118] _Monthly Notices_, R.A.S., 1902, p. 291.
+
+[119] _Monthly Notices_, R.A.S., February, 1902, p. 291.
+
+[120] _Nature_, May 24, 1894.
+
+[121] _Ibid._, February 14, 1895.
+
+[122] _Ibid._, September 14, 1905.
+
+[123] _Ibid._, September 21, 1905.
+
+[124] _Ibid._, September 28, 1905.
+
+[125] _Ibid._, July 13, 1905.
+
+[126] _Nature_, November 3, 1898.
+
+[127] _Ibid._, July 14, 1881, p. 235.
+
+[128] Quoted in _The Observatory_, February, 1896, p. 104, from _Ast.
+Nach._, No. 3319.
+
+[129] _Monthly Notices_, R.A.S., February, 1909.
+
+[130] _Celestial Objects_, vol. i. p. 163.
+
+[131] _Nature_, December 29, 1898.
+
+[132] _Celestial Objects_, vol. i. p. 166.
+
+[133] _Astrophysical Journal_, vol. 14 (1901), pp. 248-9.
+
+[134] _Nature_, August 27, 1908.
+
+[135] Webb's _Celestial Objects_, vol. i. p. 177.
+
+[136] _Ibid._, vol. i. p. 187.
+
+[137] _Celestial Objects_, vol. i. p. 186.
+
+[138] _Astronomy and Astrophysics_, 1892, p. 87.
+
+[139] _Ibid._, 1892, pp. 94-5.
+
+[140] _Observatory_, December, 1891.
+
+[141] _Popular Astronomy_, vol. 11 (1903), p. 574.
+
+[142] _Ibid._, October, 1908.
+
+[143] _Bulletin, Ast. Soc. de France_, August, 1907.
+
+[144] _Nature_, August, 29 1907.
+
+[145] _Ibid._, March 7, 1907.
+
+[146] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[147] _The Observatory_, October, 1903, p. 392.
+
+[148] _Astronomy and Astrophysics_, 1894, p. 277.
+
+[149] _Nature_, November 18, 1897.
+
+[150] _Journal_, B.A.A., January, 1907.
+
+[151] _Journal_, B.A.A., February, 1909, p. 161.
+
+[152] _Cosmos_, vol. ii. p. 703.
+
+[153] _Ibid._
+
+[154] Denning, _Telescopic Work for Starlight Evenings_, p. 349.
+
+[155] _Cosmos_, vol. iii. p. 75.
+
+[156] _Journal_, B.A.A., June, 1896.
+
+[157] _Celestial Objects_, vol. i. p. 191.
+
+[158] _Nature_, May 30, 1901.
+
+[159] _Bulletin, Ast. Soc. de France_, August, 1900.
+
+[160] _Astronomy and Astrophysics_, 1892.
+
+[161] _Astrophysical Journal_, January, 1908, p. 35.
+
+[162] _Nature_, May 22, 1902.
+
+[163] _Ibid._, July 9, 1903.
+
+[164] _Ibid._, July 16, 1903.
+
+[165] _Nature_, September 24, 1903.
+
+[166] _Ibid._, October 8, 1903.
+
+[167] _Astrophysical Journal_, vol. 26 (1907), p. 60.
+
+[168] _Nature_, January 30, 1908.
+
+[169] _Ibid._, October 15, 1908.
+
+[170] _Ibid._, October 29, 1908.
+
+[171] _Journal_, B.A.A., March, 1908, and June 22, 1908.
+
+[172] _Nature_, June 25, 1903.
+
+[173] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[174] _Pop. Ast._, vol. 12, pp. 408-9.
+
+[175] _Nature_, August 29, 1889.
+
+[176] _Astrophysical Journal_, vol. 26 (1907), p. 62.
+
+[177] _Bulletin, Ast. Soc. de France_, January, 1904.
+
+[178] Humboldt's _Cosmos_, vol. iv. p. 532.
+
+[179] _Copernicus_, vol. ii. p. 64.
+
+[180] _Knowledge_, May, 1909.
+
+[181] _Journal_, British Astronomical Association, January, 1909, p. 132.
+
+[182] _Ast. Nach._, No. 4308.
+
+[183] _History of Physical Astronomy_, p. 204.
+
+[184] Smyth's _Celestial Cycle_, pp. 210, 211.
+
+[185] Poor, _The Solar System_, p. 274.
+
+[186] _Celestial Cycle_, p. 246.
+
+[187] _Nature_, October 2, 1879.
+
+[188] _Ibid._, May 6, 1880.
+
+[189] _Ibid._, February 19, 1880.
+
+[190] _Nature_, September 30, 1897.
+
+[191] _Nature_, August 5, 1875.
+
+[192] _Ibid._, October 12, 1882, and _Copernicus_, vol. iii. p. 85.
+
+[193] _Nature_, May 8, 1884.
+
+[194] _Ibid._, June 16, 1887.
+
+[195] _Journal_, B.A.A., December 13, 1901.
+
+[196] _Nature_, September 20, 1900.
+
+[197] _Ast. Nach._, No. 3868, and _Nature_, March 12, 1903.
+
+[198] _Nature_, November 13, 1908.
+
+[199] _Nature_, December 7, 1905.
+
+[200] _Celestial Cycle_, p. 259.
+
+[201] _Celestial Cycle_, p. 260.
+
+[202] _Journal_, B.A.A., April, 1907.
+
+[203] _Monthly Notices_, R.A.S., March, 1908.
+
+[204] _Celestial Cycle_, p. 231.
+
+[205] _Journal_, B.A.A., July, 1908.
+
+[206] _Popular Astronomy_, October, 1908.
+
+[207] _Cape Obs._, p. 401.
+
+[208] _Nature_, July 2, 1908.
+
+[209] _Journal_, B.A.A., January 20, 1909, pp. 123-4.
+
+[210] Chambers' _Handbook of Astronomy_, Catalogue of Comets.
+
+[211] Seneca, quoted by Chambers, _Handbook_, vol. i. p. 554 (Fourth
+Edition).
+
+[212] _Ibid._
+
+[213] _Ibid._
+
+[214] _Ibid._, p. 534.
+
+[215] _Ibid._
+
+[216] Ma-tuoan-lin, quoted by Chambers, _Handbook_, p. 570.
+
+[217] _Astronomy and Astrophysics_, 1893, p. 798.
+
+[218] _The Observatory_, October, 1898.
+
+[219] Grant's _History of Physical Astronomy_, p. 293.
+
+[220] _Ibid._, p. 294.
+
+[221] Humboldt's _Cosmos_, vol. i. pp. 89, 90 (Otte's translation).
+
+[222] _Celestial Objects_, vol. i. p. 211, footnote.
+
+[223] Denning, _Telescopic Work for Starlight Evenings_, p. 248.
+
+[224] _Ibid._, p. 248.
+
+[225] _Ibid._, p. 250.
+
+[226] _Ibid._, p. 231.
+
+[227] Vol. iii. p. 106.
+
+[228] Grant's _History of Physical Astronomy_, p. 298.
+
+[229] _Ibid._, p. 305.
+
+[230] Humboldt's _Cosmos_, vol. i. p. 95.
+
+[231] _Nature_, April 30, 1908.
+
+[232] _Bulletin, Ast. Soc. de France_, May, 1906.
+
+[233] _Nature_, November 24, 1904.
+
+[234] _Ibid._, September 10, 1896.
+
+[235] _Ibid._, June 29, 1893.
+
+[236] _Journal_, B.A.A., May 22, 1903.
+
+[237] _Nature_, December 13, 1906, p. 159.
+
+[238] _Nature_, September 13, 1906.
+
+[239] _Nature_, October 12, 1905, p. 596.
+
+[240] _Knowledge_, January 13, 1882.
+
+[241] _Ibid._, January 20, 1882.
+
+[242] _Popular Astronomy_, June-July, 1908, p. 345.
+
+[243] _The Observatory_, March, 1896, p. 135.
+
+[244] _The Observatory_, February, 1900, pp. 106-7.
+
+[245] _Knowledge_, March, 1893, p. 51.
+
+[246] _Ibid._, July 3, 1885, p. 11.
+
+[247] _Cosmos_, vol. i. p. 108 (Otte's translation).
+
+[248] _Ibid._, vol. i. p. 124.
+
+[249] _Ibid._, vol. i. p. 119, footnote.
+
+[250] _Copernicus_, vol. i. p. 72.
+
+[251] _Ibid._
+
+[252] _Astrophysical Journal_, June, 1909, pp. 378-9.
+
+[253] _Knowledge_, July, 1909, p. 264.
+
+[254] Quoted by Miss Irene E. T. Warner in _Knowledge_, July, 1909, p.
+264.
+
+[255] _The Observatory_, November, 1900.
+
+[256] Or, "Before the phantom of false morning died" (4th edition); _The
+Observatory_, September, 1905, p. 356.
+
+[257] _The Observatory_, July, 1896, p. 274.
+
+[258] _Journal_, B.A.A., January 24, 1906.
+
+[259] _Ast. Soc. of the Pacific_, December, 1908, p. 280.
+
+[260] _Nature_, November 1, 1906.
+
+[261] _Ibid._, November 22, 1906, p. 93.
+
+[262] _Nature_, August 30, 1906.
+
+[263] _Cosmos_, vol. i. p. 131, footnote.
+
+[264] _Nature_, December 16, 1875.
+
+[265] _Ibid._, July 23, 1891.
+
+[266] _Bulletin, Ast. Soc. de France_, April, 1903.
+
+[267] _Bulletin, Ast. Soc. de France_, April, 1903.
+
+[268] _The Observatory_, May, 1896. The italics are Brenner's.
+
+[269] _Cosmos_, vol. iv. p. 563.
+
+[270] For details of this enumeration, see _Astronomical Essays_, p. 222.
+
+[271] _Nature_, June 11, 1908.
+
+[272] _Popular Astronomy_, vol. 14 (1906), p. 510.
+
+[273] _Bedford Catalogue_, p. 532.
+
+[274] _Popular Astronomy_, vol. 15 (1907), p. 194.
+
+[275] _Popular Astronomy_, vol. 15 (1907), p. 195.
+
+[276] _Bulletin, Ast. Soc. de France_, February, 1903.
+
+[277] Here [Greek: ch] is probably 17 Cygni, [Greek: ch] being the famous
+variable near it.
+
+[278] _Popular Astronomy_, vol. 13 (1904), p. 509.
+
+[279] _Astrophysical Journal_, December, 1895.
+
+[280] _The Observatory_, July, 1895, p. 290.
+
+[281] _Celestial Cycle_, p. 302.
+
+[282] _Nature_, December 13, 1894.
+
+[283] _Histoire Celeste_, p. 211.
+
+[284] _Nature_, October, 1887.
+
+[285] _Ibid._, August 29, 1889.
+
+[286] _Science Abstracts_, February 25, 1908, pp. 82, 83.
+
+[287] _Bedford Catalogue_, pp. 227-8.
+
+[288] _Knowledge_, February 1, 1888.
+
+[289] _Celestial Cycle_, p. 280.
+
+[290] _Popular Astronomy_, February, 1904.
+
+[291] _Ibid._, vol. 15 (1907), p. 444.
+
+[292] _Journal_, B.A.A., June, 1899.
+
+[293] _Astrophysical Journal_, vol. 8 (1898), p. 314.
+
+[294] _Astrophysical Journal_, vol. 8, p. 213.
+
+[295] _Ibid._, vol. 17, January to June, 1902.
+
+[296] _Astronomy and Astrophysics_, 1894, pp. 569-70.
+
+[297] _The Study of Stellar Evolution_ (1908), p. 171.
+
+[298] _Astrophysical Journal_, January, 1905.
+
+[299] _Journal_, B.A.A., June, 1901.
+
+[300] _Ast. Soc. of the Pacific_, December, 1908.
+
+[301] _The Observatory_, November, 1902, p. 391.
+
+[302] _Cosmos_, vol. iv. p. 567 (Otte's translation).
+
+[303] _Journal_, B.A.A., February, 1898.
+
+[304] _The Observatory_, April, 1887.
+
+[305] _Evangeline_, Part the Second, III.
+
+[306] _Legend of Robert, Duke of Normandy._
+
+[307] _Copernicus_, vol. iii. p. 231.
+
+[308] _Ibid._, p. 61.
+
+[309] _Cosmos_, vol. i. p. 142.
+
+[310] These apertures are computed from the formula, minimum visible = 9 +
+5 log. aperture.
+
+[311] _Cosmos_, vol. iii. p. 73.
+
+[312] _Darwin and Modern Science_, p. 563.
+
+[313] _Journal_, B.A.A., October, 1895.
+
+[314] Burnham's _General Catalogue of Double Stars_, p. 494.
+
+[315] _Journal_, B.A.A., November 18, 1896.
+
+[316] _Ibid._, B.A.A., January, 1907.
+
+[317] _Studies in Astronomy_, p. 185.
+
+[318] _Knowledge_, June, 1891.
+
+[319] Seen by Drs. Ludendorff and Eberhard, _The Observatory_, April,
+1906, p. 166, quoted from _Ast. Nach._, No. 4067.
+
+[320] _The Observatory_, January, 1907, p. 61.
+
+[321] _Astronomy and Astrophysics_, 1894.
+
+[322] Smyth's _Celestial Cycle_, p. 223.
+
+[323] _Nature_, February 7, 1907.
+
+[324] _Ibid._, March 19, 1908.
+
+[325] _Popular Astronomy_, vol. 15 (1907), p. 9.
+
+[326] _Astrophysical Journal_, June, 1907, p. 330.
+
+[327] _Ibid._, vol. 22, p. 172.
+
+[328] _Nature_, November 18, 1886.
+
+[329] _Astrophysical Journal_, vol. 17 (1903), p. 282.
+
+[330] _Astrophysical Journal_, vol. 12 (1900), p. 54.
+
+[331] _Nature_, March 21, 1878.
+
+[332] _Bulletin, Ast. Soc. de France_, June, 1904.
+
+[333] _Journal_, B.A.A., vol. 17 (1903), p. 282.
+
+[334] _Nature_, June 20, 1909.
+
+[335] _The Observatory_, vol. 7 (1884), p. 17.
+
+[336] _The Observatory_, vol. 14 (1891), p. 69.
+
+[337] _Astronomy and Astrophysics_, 1896, p. 54
+
+[338] _Nature_, August 28, 1902.
+
+[339] _Astrophysical Journal_, October, 1903.
+
+[340] _Nature_, May 30, 1907.
+
+[341] _Popular Astronomy_, February, 1909, p. 125.
+
+[342] _The Observatory_, May, 1907, p. 216.
+
+[343] _Astrophysical Journal_, May, 1907.
+
+[344] _Histoire de l'Astronomie Moderne_, vol. i. pp. 185-6.
+
+[345] Humboldt's _Cosmos_, vol. iii. p. 210 (Otte's translation).
+
+[346] _Ibid._, vol. iii. pp. 213-14.
+
+[347] J. C. Duncan, _Lick Observatory Bulletin_, No. 151.
+
+[348] _Astrophysical Journal_, vol. 17, p. 283.
+
+[349] _The Origin of the Stars_, p. 143.
+
+[350] _Ibid._, p. 135.
+
+[351] Quoted by Ennis in _The Origin of the Stars_, p. 133.
+
+[352] _Astrophysical Journal_, vol. 20 (1904), p. 357.
+
+[353] _Nature_, March 8, 1906.
+
+[354] _Astronomical Society of the Pacific_, August, 1908.
+
+[355] _Astronomy and Astrophysics_, 1894, p. 812.
+
+[356] _The Observatory_, May, 1905.
+
+[357] This is a misquotation. See my _Astronomical Essays_, p. 135.
+
+[358] _Nature_, February 3, 1870.
+
+[359] _Bedford Catalogue_, p. 14.
+
+[360] _Ibid._, p. 307.
+
+[361] _Astrophysical Journal_, vol. 14, p. 37.
+
+[362] _Ibid._, vol. 9, p. 149.
+
+[363] _Nature_, July 20, 1899.
+
+[364] _Ast. Nach._, No. 3476.
+
+[365] _Astronomische Nachrichten_, No. 4213.
+
+[366] _Astrophysical Journal_, vol. 9, p. 149.
+
+[367] _Cape Observations_, p. 61.
+
+[368] _Ibid._, p. 85.
+
+[369] _Cape Observations_, p. 98.
+
+[370] _Transactions_, Royal Dublin Society, vol. 2.
+
+[371] _Ast. Nach._, 3628, quoted in _The Observatory_, April, 1900.
+
+[372] _Nature_, April 8, 1909.
+
+[373] _Problems in Astrophysics_, p. 477.
+
+[374] _Ibid._, p. 499.
+
+[375] _Copernicus_, vol. iii. p. 55.
+
+[376] _Lick Observatory Bulletin_, No. 149.
+
+[377] _Ibid._
+
+[378] _Ibid._
+
+[379] _Monthly Notices_, R.A.S., April, 1908, pp. 465-481.
+
+[380] _Lick Observatory Bulletin_, No. 155 (February, 1909).
+
+[381] _Outlines of Astronomy_, par. 870 (Edition of 1875).
+
+[382] _Georgics_, i. II. 217-18.
+
+[383] See paper by Mr. and Mrs. Maunder in _Monthly Notices_, R.A.S.,
+March, 1904, p. 506.
+
+[384] _Primitive Constellations_, vol. ii. p. 143.
+
+[385] _Recherches sur l'Histoire de l'Astronomie Ancienne_, by Paul
+Tannery (1893), p. 298.
+
+[386] _Primitive Constellations_, vol. ii. p. 225.
+
+[387] _Nature_, October 2, 1890.
+
+[388] Lalande's _Astronomie_, vol. i. pp. 243-4.
+
+[389] Lalande's _Astronomie_, vol. i. pp. 242-3.
+
+[390] There are three copies of Al-Sufi's work in the Imperial Library at
+Paris, but these are inaccurate. There is also one in the British Museum
+Library, and another in the India Office Library; but these are imperfect,
+considerable portions of the original work being missing.
+
+[391] _Harvard Annals_, vol. ix. p. 51.
+
+[392] The science of the risings and settings of the stars was called _ilm
+el-anwa_ (Caussin, _Notices et Extraits des Manuscrits de la Bibliotheque
+due Roi_, tome xii. p. 237).
+
+[393] See Mr. E. B. Knobel's papers on this subject in the _Monthly
+Notices_, R.A.S., for 1879 and 1884.
+
+[394] In reading this chapter the reader is recommended to have a Star
+Atlas beside him for reference; Proctor's smaller Star Atlas will be found
+very convenient for this purpose. On the title-page of this useful work
+the author quotes Carlyle's words, "Why did not somebody teach me the
+constellations and make me at home in the starry heavens which are always
+overhead, and which I don't half know to this day?"
+
+[395] _Bedford Catalogue_, p. 29.
+
+[396] _Cosmos_, vol. iii. p. 87.
+
+[397] _Heavenly Display_, 579-85.
+
+[398] _Bedford Catalogue_, p. 385.
+
+[399] Lalande's _Astronomie_, vol. iv. p. 529.
+
+[400] Lalande's _Astronomie_, vol. i. pp. 268-9.
+
+[401] _Primitive Constellations_, vol. i. p. 48.
+
+[402] _Bedford Catalogue_, pp. 27, 28.
+
+[403] Lalande's _Astronomie_, vol. iv. p. 492.
+
+[404] _Bedford Catalogue_, p. 120.
+
+[405] _Primitive Constellations_, vol. i. p. 143.
+
+[406] Perseus.
+
+[407] _Heavenly Display_, 254-8, 261-5, quoted by Brown in _Primitive
+Constellations_, vol. i. p. 274.
+
+[408] Lalande's _Astronomie_, vol. iv. p. 493.
+
+[409] _Primitive Constellations_, vol. i. p. 292.
+
+[410] _Paradiso_, xxii. 111.
+
+[411] Lalande's _Astronomie_, vol. iv. p. 493.
+
+[412] _Bedford Catalogue_, p. 225.
+
+[413] _Nature_, April 6, 1882.
+
+[414] _Primitive Constellations_, vol. i. p. 68.
+
+[415] _Ibid._, vol. i. p. 71.
+
+[416] _Bibliographie Generale de l'Astronomie_, vol. i. Introduction, pp.
+131, 132.
+
+[417] Lalande's _Astronomie_, vol. i. p. 296.
+
+[418] _Primitive Constellations_, vol. i. p. 74.
+
+[419] _Cape Observations_, p. 116.
+
+[420] _Metamorphoses_, xv. 371.
+
+[421] Lalande's _Astronomie_, vol. iv. p. 487.
+
+[422] _Monthly Notices_, R.A.S., April 14, 1848.
+
+[423] _Prim. Const._, vol. ii. p. 45.
+
+[424] Lalande's _Astronomie_, pp. 472-3.
+
+[425] Lalande's _Astronomie_, vol. iv. p. 485.
+
+[426] This star is not shown in Proctor's small Atlas, but it lies between
+[Greek: m] and [Greek: n], nearer to [Greek: m].
+
+[427] Lalande's _Astronomie_, vol. i. p. 247.
+
+[428] Lalande's _Astronomie_, vol. iv. p. 489.
+
+[429] _Primitive Constellations_, vol. i. p. 91.
+
+[430] _Memoirs_, R.A.S., vol. xiii. 61.
+
+[431] _Monthly Notices_, R.A.S., June, 1895.
+
+[432] Lalande's _Astronomie_, vol. i. p. 274.
+
+[433] _Primitive Constellations_, vol. i. p. 143.
+
+[434] _Primitive Constellations_, vol. i. p. 278.
+
+[435] Lalande's _Astronomie_, vol. iv. p. 468.
+
+[436] _Quaest. Nat._, Lib. 1, Cap. I. Sec. 6; quoted by Dr. See. "Canicula" is
+Sirius, and "Nartis," Mars.
+
+[437] _Astronomy and Astrophysics_, vol. 11, 1892.
+
+[438] _The Observatory_, April, 1906, p. 175.
+
+[439] Houzeau, _Bibliographie Generale de l'Astronomie_, vol. i.,
+Introduction, p. 129.
+
+[440] _English Mechanic_, March 25, 1904, p. 145.
+
+[441] Humboldt's _Cosmos_, vol. iii. p. 185, footnote (Otte's
+translation).
+
+[442] Lalande's _Astronomie_, vol, i. p. 277.
+
+[443] This was pointed out by Flammarion in his work _Les Etoiles_, page
+532; but his identifications do not agree exactly with mine.
+
+[444] See Proctor's Map 7, now x.
+
+[445] _Primitive Constellations_, vol. i. p. 106.
+
+[446] Lalande's _Astronomie_, vol. i. p. 278.
+
+[447] Lalande's _Astronomie_, vol. iv.
+
+[448] _Primitive Constellations_, vol. i. p. 112.
+
+[449] _Ibid._, vol. i. p. 113.
+
+[450] Lalande's _Astronomie_, vol. i.
+
+[451] W. T. Lynn in _The Observatory_, vol. 22, p. 236.
+
+[452] _Knowledge_, May 1, 1889. Sir John Herschel, however, gives 3970
+B.C.
+
+[453] _The Observatory_, November 1907, p. 412.
+
+[454] This is not, however, _invariably_ the case, as pointed out by Mr.
+Denning in _The Observatory_, 1885, p. 340.
+
+[455] _The Observatory_, vol. 8 (1885), pp. 246-7.
+
+[456] _Harvard College Observatory Annals_, vol. xlviii. No. 5.
+
+[457] _Popular Astronomy_, vol. 15 (1907), p. 529.
+
+[458] _Cape Observations_, p. 77.
+
+[459] _Monthly Notices_, R.A.S., March, 1899.
+
+[460] _Nature_, February 13, 1890.
+
+[461] _Popular Astronomy_, vol. 15 (1907), p. 530.
+
+[462] _Photographs of Star-Clusters and Nebulae_, vol. ii. p. 17.
+
+[463] _Monthly Notices_, R.A.S., May 9, 1856.
+
+[464] _Astrophysical Journal_, vol. 25 (1907), p. 219.
+
+[465] _Popular Astronomy_, vol. 11 (1903), p. 293.
+
+[466] Translated by W. H. Mallock, _Nature_, February 8, 1900, p. 352.
+
+[467] Howard Payn, _Nature_, May 16, 1901, p. 56.
+
+[468] Howard Payn, _Nature_, May 16, 1901, p. 56.
+
+[469] _Contributions from the Mount Wilson Solar Observatory_, No. 31.
+
+[470] Quoted by Denning in _Telescopic Work for Starlight Evenings_, p.
+297.
+
+[471] _Astrophysical Journal_, March, 1895.
+
+[472] _Outlines of Astronomy_, Tenth Edition, p. 571.
+
+[473] _Astrophysical Journal_, vol. 12, p. 136.
+
+[474] _De Placitis._ Quoted by Carl Snyder in _The World Machine_ p. 354.
+
+[475] _Popular Astronomy_, vol. 14 (1906), p. 638.
+
+[476] Article on "The Greek Anthology," _Nineteenth Century_, April, 1907,
+quoted in _The Observatory_, May, 1907.
+
+[477] _Popular Astronomy_, vol. 13 (1905), p. 346.
+
+[478] _Bulletin de la Soc. Ast. de France_, April, 1908.
+
+[479] _The Observatory_, vol. 11, p. 375.
+
+[480] Grant, _History of Physical Astronomy_, p. 364.
+
+[481] _Ibid._, p. 377.
+
+[482] _Ibid._, p. 366.
+
+[483] _Ibid._, p. 367.
+
+[484] Grant, _History of Physical Astronomy_, p. 370.
+
+[485] _Nature_, July 25, 1889.
+
+[486] _Cosmos_, vol. iv. p. 381.
+
+[487] _Cosmos_, vol. iv. pp. 381-6.
+
+[488] _Ibid._, vol. i. p. 121.
+
+[489] _The Observatory_, vol. 6 (1883), pp. 327-8.
+
+[490] _Nature_, June 25, 1874.
+
+[491] _Popular Astronomy_, May, 1895, "Reflectors or Refractors."
+
+[492] Denning, _Telescopic Work for Starlight Evenings_, p. 225.
+
+[493] _Nature_, November 2, 1893.
+
+[494] _Telescopic Work_, p. 226.
+
+[495] _Copernicus_, vol. i. p. 229.
+
+[496] Grant, _History of Physical Astronomy_, p. 433.
+
+[497] _Cosmos_, vol. ii. p. 699.
+
+[498] Grant, _History of Physical Astronomy_, p. 536, footnote.
+
+[499] _Bedford Catalogue_, p. 179.
+
+[500] _The Observatory_, July, 1891.
+
+[501] _Nature_, September 3, 1903.
+
+[502] _Cosmos_, vol. ii. p. 669.
+
+[503] _The World Machine_, p. 80.
+
+[504] _Ibid._, p. 89.
+
+[505] Grant, _History of Physical Astronomy_, p. 107.
+
+[506] Grant, _History of Physical Astronomy_, p. 113.
+
+[507] _Nature_, August 11, 1898.
+
+[508] _Ibid._, August 18, 1898.
+
+[509] _Ibid._, October 20, 1898.
+
+[510] _The Observatory_, vol. iv. (1881), p. 234.
+
+[511] W. T. Lynn, _The Observatory_, July, 1909, p. 291.
+
+[512] Quoted in _The Observatory_, July, 1902, p. 281.
+
+[513] _Astrophysical Journal_, vol. 6, 1897, p. 304.
+
+[514] _Celestial Cycle_, p. 367.
+
+[515] _The Observatory_, vol. 5 (1882), p. 251.
+
+[516] Quoted by Humboldt in _Cosmos_, vol. ii. p. 696, footnote.
+
+[517] Quoted by Denning in _Telescopic Work_, p. 347.
+
+[518] _Knowledge_, February 20, 1885, p. 149.
+
+[519] Humboldt's _Cosmos_, vol. i. p. 123.
+
+[520] _Outlines of Astronomy_, par. 319; edition of 1875.
+
+[521] _Bulletin de la Soc. Ast. de France_, March, 1908, p. 146.
+
+[522] An "astronomical unit" is the sun's mean distance from the earth.
+
+[523] This is on the American and French system of notation, but on the
+English system, 10{66} = 10{60} x 10{6} would be a million decillion.
+
+[524] _Astronomical Society of the Pacific_, April, 1909 (No. 125), and
+_Popular Astronomy_, May, 1909.
+
+[525] _Nature_, July 22, 1909.
+
+[526] _Ibid._
+
+[527] _The Observatory_, vol. 9 (December, 1886), p. 389.
+
+[528] _De Nat. Deorum_, quoted in Smyth's _Cycle_, p. 19.
+
+[529] _The Observatory_, May, 1907.
+
+[530] _More Worlds than Ours_, p. 17.
+
+[531] _Man's Place in Nature._
+
+
+
+
+Transcriber's Notes:
+
+Passages in italics are indicated by _italics_.
+
+Superscripted characters are indicated by {superscript}.
+
+Subscripted characters are indicated by _{subscript}.
+
+The original text includes Greek characters. For this text version these
+letters have been replaced with transliterations.
+
+Foonote 48 appears on page 28 of the text, but there is no corresponding
+marker on the page.
+
+Foonote 448 appears on page 295 of the text, but there is no corresponding
+marker on the page.
+
+
+
+
+
+
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