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diff --git a/39263.txt b/39263.txt new file mode 100644 index 0000000..c1f660d --- /dev/null +++ b/39263.txt @@ -0,0 +1,11431 @@ +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. + + + + + + +End of Project Gutenberg's Astronomical Curiosities, by J. 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