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+Project Gutenberg Etext of A History of Science, V 3, by Williams
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+A History of Science, Volume 3
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+by Henry Smith Williams
+
+April, 1999  [Etext #1707]
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+A History of Science, Volume 3, by Henry Smith Williams
+
+Scanned by Charles Keller with OmniPage Professional OCR software
+
+
+
+
+
+A
+HISTORY OF SCIENCE
+BY
+HENRY SMITH WILLIAMS, M.D., LL.D.
+ASSISTED BY
+EDWARD H. WILLIAMS, M.D.
+
+IN FIVE VOLUMES
+VOLUME III.
+
+MODERN DEVELOPMENT OF THE
+PHYSICAL SCIENCES
+
+
+
+
+CONTENTS
+
+BOOK III
+
+CHAPTER I. THE SUCCESSORS OF NEWTON IN ASTRONOMY
+
+The work of Johannes Hevelius--Halley and Hevelius--Halley's
+observation of the transit of Mercury, and his method
+of determining the parallax of the planets--Halley's observation
+of meteors--His inability to explain these bodies--The important
+work of James Bradley--Lacaille's measurement of the arc of the
+meridian--The determination of the question as to the exact shape
+of the earth--D'Alembert and his influence upon science-
+-Delambre's History of Astronomy--The astronomical work of Euler.
+
+CHAPTER II. THE PROGRESS OF MODERN ASTRONOMY
+
+The work of William Herschel--His discovery of Uranus--His
+discovery that the stars are suns--His conception
+of the universe--His deduction that gravitation has caused
+the grouping of the heavenly bodies--The nebula, hypothesis,
+--Immanuel Kant's conception of the formation of the
+world--Defects in Kant's conception--Laplace's final solution of
+the problem--His explanation in detail--Change in the mental
+attitude of the world since Bruno--Asteroids and
+satellites--Discoveries of Olbers1--The mathematical calculations
+of Adams and Leverrier--The discovery of the inner ring of
+Saturn--Clerk Maxwell's paper on the stability of Saturn's
+rings--Helmholtz's conception of the action of tidal
+friction--Professor G. H. Darwin's estimate of the consequences
+of tidal action--Comets and meteors--Bredichin's cometary
+theory--The final solution of the structure of comets--Newcomb's
+estimate of the amount of cometary dust swept up daily by
+the earth--The fixed stars--John Herschel's studies
+of double stars--Fraunhofer's perfection of the refracting
+telescope--Bessel's measurement of the parallax of a
+star,--Henderson's measurements--Kirchhoff and Bunsen's
+perfection of the spectroscope--Wonderful revelations
+of the spectroscope--Lord Kelvin's estimate of the time that
+will be required for the earth to become completely cooled--
+Alvan Clark's discovery of the companion star of Sirius--
+The advent of the photographic film in astronomy--Dr.
+Huggins's studies of nebulae--Sir Norman Lockyer's "cosmogonic
+guess,"--Croll's pre-nebular theory.
+
+CHAPTER III. THE NEW SCIENCE OF PALEONTOLOGY
+
+William Smith and fossil shells--His discovery that fossil
+rocks are arranged in regular systems--Smith's inquiries
+taken up by Cuvier--His Ossements Fossiles containing the
+first description of hairy elephant--His contention that fossils
+represent extinct species only--Dr. Buckland's studies
+of English fossil-beds--Charles Lyell combats catastrophism,
+--Elaboration of his ideas with reference to the rotation of
+species--The establishment of the doctrine of uniformitarianism,
+--Darwin's Origin of Species--Fossil man--Dr. Falconer's visit to
+the fossil-beds in the valley of the Somme--Investigations of
+Prestwich and Sir John Evans--Discovery of the Neanderthal skull,
+--Cuvier's rejection of human fossils--The finding of prehistoric
+carving on ivory--The fossil-beds of America--Professor Marsh's
+paper on the fossil horses in America--The Warren mastodon,
+--The Java fossil, Pithecanthropus Erectus.
+
+CHAPTER IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY
+
+James Hutton and the study of the rocks--His theory of the
+earth--His belief in volcanic cataclysms in raising and forming
+the continents--His famous paper before the Royal Society of
+Edinburgh, 1781---His conclusions that all strata of
+the earth have their origin at the bottom of the sea---His
+deduction that heated and expanded matter caused the elevation
+of land above the sea-level--Indifference at first shown this
+remarkable paper--Neptunists versus Plutonists--
+Scrope's classical work on volcanoes--Final acceptance of
+Hutton's explanation of the origin of granites--Lyell and
+uniformitarianism--Observations on the gradual elevation
+of the coast-lines of Sweden and Patagonia--Observations
+on the enormous amount of land erosion constantly taking place,
+--Agassiz and the glacial theory--Perraudin the chamois-
+hunter, and his explanation of perched bowlders--De Charpentier's
+acceptance of Perraudin's explanation--Agassiz's
+paper on his Alpine studies--His conclusion that the Alps
+were once covered with an ice-sheet--Final acceptance of
+the glacial theory--The geological ages--The work
+of Murchison and Sedgwick--Formation of the American
+continents--Past, present, and future.
+
+CHAPTER V. THE NEW SCIENCE OF METEOROLOGY
+
+Biot's investigations of meteors--The observations of
+Brandes and Benzenberg on the velocity of falling stars--
+Professor Olmstead's observations on the meteoric shower of 1833-
+-Confirmation of Chladni's hypothesis of 1794--The
+aurora borealis--Franklin's suggestion that it is of electrical
+origin--Its close association with terrestrial
+magnetism--Evaporation, cloud-formation, and dew--Dalton's
+demonstration that water exists in the air as an independent
+gas--Hutton's theory of rain--Luke Howard's paper
+on clouds--Observations on dew, by Professor Wilson and
+Mr. Six--Dr. Wells's essay on dew--His observations
+on several appearances connected with dew--Isotherms
+and ocean currents--Humboldt and the-science of comparative
+climatology--His studies of ocean currents--
+Maury's theory that gravity is the cause of ocean currents--
+Dr. Croll on Climate and Time--Cyclones and anti-cyclones,
+--Dove's studies in climatology--Professor Ferrel's
+mathematical law of the deflection of winds--Tyndall's estimate
+of the amount of heat given off by the liberation of a pound
+of vapor--Meteorological observations and weather predictions.
+
+CHAPTER VI. MODERN THEORIES OF HEAT AND LIGHT
+
+Josiah Wedgwood and the clay pyrometer--Count Rumford
+and the vibratory theory of heat--His experiments with
+boring cannon to determine the nature of heat--Causing
+water to boil by the friction of the borer--His final
+determination that heat is a form of motion--Thomas Young
+and the wave theory of light--His paper on the theory of
+light and colors--His exposition of the colors of thin plates--Of
+the colors of thick plates, and of striated surfaces, --Arago and
+Fresnel champion the wave theory--opposition
+to the theory by Biot--The French Academy's tacit
+acceptance of the correctness of the theory by its admission of
+Fresnel as a member.
+
+CHAPTER VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM
+
+Galvani and the beginning of modern electricity--The construction
+of the voltaic pile--Nicholson's and Carlisle's discovery
+that the galvanic current decomposes water--Decomposition
+of various substances by Sir Humphry Davy--His construction of an
+arc-light--The deflection of the magnetic needle by electricity
+demonstrated by Oersted--Effect of this important
+discovery--Ampere creates the science of electro-dynamics--Joseph
+Henry's studies of electromagnets--Michael Faraday begins his
+studies of electromagnetic induction--His famous paper before the
+Royal Society, in 1831, in which he demonstrates electro-magnetic
+induction--His explanation of Arago's rotating disk--The
+search for a satisfactory method of storing electricity--
+Roentgen rays, or X-rays.
+
+CHAPTER VIII. THE CONSERVATION OF ENERGY
+
+Faraday narrowly misses the discovery of the doctrine of
+conservation--Carnot's belief that a definite quantity of work
+can be transformed into a definite quantity of heat--The work
+of James Prescott Joule--Investigations begun by Dr.
+Mayer--Mayer's paper of 1842--His statement of the law of the
+conservation of energy--Mayer and Helmholtz--Joule's paper of
+1843--Joule or Mayer--Lord Kelvin and the dissipation of
+energy-The final unification.
+
+
+CHAPTER IX. THE ETHER AND PONDERABLE MATTER
+
+James Clerk-Maxwell's conception of ether--Thomas Young
+and "Luminiferous ether,"--Young's and Fresnel's conception
+of transverse luminiferous undulations--Faraday's experiments
+pointing to the existence of ether--Professor
+Lodge's suggestion of two ethers--Lord Kelvin's calculation
+of the probable density of ether--The vortex theory of
+atoms--Helmholtz's calculations in vortex motions
+--Professor Tait's apparatus for creating vortex rings in the
+air---The ultimate constitution of matter as conceived by
+Boscovich--Davy's speculations as to the changes that occur in
+the substance of matter at different temperatures--Clausius's
+and Maxwell's investigations of the kinetic theory of gases--Lord
+Kelvin's estimate of the size of the molecule--
+Studies of the potential energy of molecules--Action of
+gases at low temperatures.
+
+APPENDIX
+
+
+
+
+A HISTORY OF SCIENCE
+
+BOOK III
+
+MODERN DEVELOPMENT OF THE PHYSICAL
+SCIENCES
+
+With the present book we enter the field of the
+distinctively modern. There is no precise date
+at which we take up each of the successive stories,
+but the main sweep of development has to do in each
+case with the nineteenth century. We shall see at
+once that this is a time both of rapid progress and of
+great differentiation. We have heard almost nothing
+hitherto of such sciences as paleontology, geology, and
+meteorology, each of which now demands full attention.
+Meantime, astronomy and what the workers of the
+elder day called natural philosophy become wonderfully
+diversified and present numerous phases that
+would have been startling enough to the star-gazers
+and philosophers of the earlier epoch.
+
+Thus, for example, in the field of astronomy, Herschel
+is able, thanks to his perfected telescope, to discover
+a new planet and then to reach out into the
+depths of space and gain such knowledge of stars and
+nebulae as hitherto no one had more than dreamed of.
+Then, in rapid sequence, a whole coterie of hitherto
+unsuspected minor planets is discovered, stellar distances
+are measured, some members of the starry
+galaxy are timed in their flight, the direction of movement
+of the solar system itself is investigated, the
+spectroscope reveals the chemical composition even of
+suns that are unthinkably distant, and a tangible
+theory is grasped of the universal cycle which includes
+the birth and death of worlds.
+
+Similarly the new studies of the earth's surface reveal
+secrets of planetary formation hitherto quite inscrutable.
+It becomes known that the strata of the
+earth's surface have been forming throughout untold
+ages, and that successive populations differing utterly
+from one another have peopled the earth in different
+geological epochs. The entire point of view of thoughtful
+men becomes changed in contemplating the history
+of the world in which we live--albeit the newest
+thought harks back to some extent to those days
+when the inspired thinkers of early Greece dreamed
+out the wonderful theories with which our earlier
+chapters have made our readers familiar.
+
+In the region of natural philosophy progress is no
+less pronounced and no less striking. It suffices here,
+however, by way of anticipation, simply to name the
+greatest generalization of the century in physical
+science--the doctrine of the conservation of energy.
+
+
+
+I
+
+THE SUCCESSORS OF NEWTON IN ASTRONOMY
+
+HEVELIUS AND HALLEY
+
+STRANGELY enough, the decade immediately following
+Newton was one of comparative barrenness
+in scientific progress, the early years of the eighteenth
+century not being as productive of great astronomers
+as the later years of the seventeenth, or, for
+that matter, as the later years of the eighteenth century
+itself. Several of the prominent astronomers of
+the later seventeenth century lived on into the opening
+years of the following century, however, and the
+younger generation soon developed a coterie of
+astronomers, among whom Euler, Lagrange, Laplace,
+and Herschel, as we shall see, were to accomplish great
+things in this field before the century closed.
+
+One of the great seventeenth-century astronomers,
+who died just before the close of the century, was
+Johannes Hevelius (1611-1687), of Dantzig, who advanced
+astronomy by his accurate description of the
+face and the spots of the moon. But he is remembered
+also for having retarded progress by his influence
+in refusing to use telescopic sights in his observations,
+preferring until his death the plain sights long
+before discarded by most other astronomers. The
+advantages of these telescope sights have been discussed
+under the article treating of Robert Hooke, but
+no such advantages were ever recognized by Hevelius.
+So great was Hevelius's reputation as an astronomer
+that his refusal to recognize the advantage of the telescope
+sights caused many astronomers to hesitate before
+accepting them as superior to the plain; and even
+the famous Halley, of whom we shall speak further in
+a moment, was sufficiently in doubt over the matter
+to pay the aged astronomer a visit to test his skill in
+using the old-style sights. Side by side, Hevelius and
+Halley made their observations, Hevelius with his old
+instrument and Halley with the new. The results
+showed slightly in the younger man's favor, but not
+enough to make it an entirely convincing demonstration.
+The explanation of this, however, did not lie in
+the lack of superiority of the telescopic instrument,
+but rather in the marvellous skill of the aged Hevelius,
+whose dexterity almost compensated for the defect of
+his instrument. What he might have accomplished
+could he have been induced to adopt the telescope can
+only be surmised.
+
+Halley himself was by no means a tyro in matters
+astronomical at that time. As the only son of a
+wealthy soap-boiler living near London, he had been
+given a liberal education, and even before leaving college
+made such novel scientific observations as that of
+the change in the variation of the compass. At nineteen
+years of age he discovered a new method of determining
+the elements of the planetary orbits which
+was a distinct improvement over the old. The year
+following he sailed for the Island of St, Helena to make
+observations of the heavens in the southern hemisphere.
+
+It was while in St. Helena that Halley made his
+famous observation of the transit of Mercury over the
+sun's disk, this observation being connected, indirectly
+at least, with his discovery of a method of determining
+the parallax of the planets. By parallax
+is meant the apparent change in the position of an object,
+due really to a change in the position of the observer.
+Thus, if we imagine two astronomers making
+observations of the sun from opposite sides of the
+earth at the same time, it is obvious that to these
+observers the sun will appear to be at two different
+points in the sky. Half the angle measuring this difference
+would be known as the sun's parallax. This
+would depend, then, upon the distance of the earth
+from the sun and the length of the earth's radius.
+Since the actual length of this radius has been determined,
+the parallax of any heavenly body enables
+the astronomer to determine its exact distance.
+
+The parallaxes can be determined equally well, however,
+if two observers are separated by exactly known
+distances, several hundreds or thousands of miles apart.
+In the case of a transit of Venus across the sun's disk,
+for example, an observer at New York notes the image
+of the planet moving across the sun's disk, and notes
+also the exact time of this observation. In the same
+manner an observer at London makes similar observations.
+Knowing the distance between New York
+and London, and the different time of the passage, it is
+thus possible to calculate the difference of the parallaxes
+of the sun and a planet crossing its disk. The
+idea of thus determining the parallax of the planets
+originated, or at least was developed, by Halley, and
+from this phenomenon he thought it possible to conclude
+the dimensions of all the planetary orbits. As
+we shall see further on, his views were found to be
+correct by later astronomers.
+
+In 1721 Halley succeeded Flamsteed as astronomer
+royal at the Greenwich Observatory. Although sixty-
+four years of age at that time his activity in astronomy
+continued unabated for another score of years. At
+Greenwich he undertook some tedious observations
+of the moon, and during those observations was first
+to detect the acceleration of mean motion. He was
+unable to explain this, however, and it remained for
+Laplace in the closing years of the century to do so,
+as we shall see later.
+
+Halley's book, the Synopsis Astronomiae Cometicae,
+is one of the most valuable additions to astronomical
+literature since the time of Kepler. He was first to
+attempt the calculation of the orbit of a comet, having
+revived the ancient opinion that comets belong to the
+solar system, moving in eccentric orbits round the sun,
+and his calculation of the orbit of the comet of 1682 led
+him to predict correctly the return of that comet in
+1758. Halley's Study of Meteors.
+
+Like other astronomers of his time be was greatly
+puzzled over the well-known phenomena of shooting-
+stars, or meteors, making many observations himself,
+and examining carefully the observations of other
+astronomers. In 1714 he gave his views as to the
+origin and composition of these mysterious visitors
+in the earth's atmosphere. As this subject will be
+again referred to in a later chapter, Halley's views,
+representing the most advanced views of his age, are
+of interest.
+
+"The theory of the air seemeth at present," he says,
+"to be perfectly well understood, and the differing
+densities thereof at all altitudes; for supposing the
+same air to occupy spaces reciprocally proportional to
+the quantity of the superior or incumbent air, I have
+elsewhere proved that at forty miles high the air is
+rarer than at the surface of the earth at three thousand
+times; and that the utmost height of the atmosphere,
+which reflects light in the Crepusculum, is not fully
+forty-five miles, notwithstanding which 'tis still
+manifest that some sort of vapors, and those in no
+small quantity, arise nearly to that height. An instance
+of this may be given in the great light the
+society had an account of (vide Transact. Sep., 1676)
+from Dr. Wallis, which was seen in very distant counties
+almost over all the south part of England. Of
+which though the doctor could not get so particular a
+relation as was requisite to determine the height thereof,
+yet from the distant places it was seen in, it could
+not but be very many miles high.
+
+"So likewise that meteor which was seen in 1708, on
+the 31st of July, between nine and ten o'clock at night,
+was evidently between forty and fifty miles perpendicularly
+high, and as near as I can gather, over Shereness
+and the buoy on the Nore. For it was seen at London
+moving horizontally from east by north to east by
+south at least fifty degrees high, and at Redgrove, in
+Suffolk, on the Yarmouth road, about twenty miles
+from the east coast of England, and at least forty miles
+to the eastward of London, it appeared a little to the
+westward of the south, suppose south by west, and
+was seen about thirty degrees high, sliding obliquely
+downward. I was shown in both places the situation
+thereof, which was as described, but could wish some
+person skilled in astronomical matters bad seen it,
+that we might pronounce concerning its height with
+more certainty. Yet, as it is, we may securely conclude
+that it was not many more miles westerly than Redgrove,
+which, as I said before, is about forty miles more
+easterly than London. Suppose it, therefore, where
+perpendicular, to have been thirty-five miles east from
+London, and by the altitude it appeared at in London--
+viz., fifty degrees, its tangent will be forty-two miles,
+for the height of the meteor above the surface of the
+earth; which also is rather of the least, because the
+altitude of the place shown me is rather more than
+less than fifty degrees; and the like may be concluded
+from the altitude it appeared in at Redgrove, near
+seventy miles distant. Though at this very great
+distance, it appeared to move with an incredible
+velocity, darting, in a very few seconds of time, for
+about twelve degrees of a great circle from north to
+south, being very bright at its first appearance; and
+it died away at the east of its course, leaving for some
+time a pale whiteness in the place, with some remains
+of it in the track where it had gone; but no hissing
+sound as it passed, or bounce of an explosion were
+heard.
+
+"It may deserve the honorable society's thoughts,
+how so great a quantity of vapor should be raised to
+the top of the atmosphere, and there collected, so
+as upon its ascension or otherwise illumination, to
+give a light to a circle of above one hundred miles
+diameter, not much inferior to the light of the moon;
+so as one might see to take a pin from the ground in
+the otherwise dark night. 'Tis hard to conceive what
+sort of exhalations should rise from the earth, either
+by the action of the sun or subterranean heat, so as to
+surmount the extreme cold and rareness of the air in
+those upper regions: but the fact is indisputable, and
+therefore requires a solution."
+
+From this much of the paper it appears that there
+was a general belief that this burning mass was
+heated vapor thrown off from the earth in some
+mysterious manner, yet this is unsatisfactory to Halley,
+for after citing various other meteors that
+have appeared within his knowledge, he goes on to
+say:
+
+"What sort of substance it must be, that could
+be so impelled and ignited at the same time; there
+being no Vulcano or other Spiraculum of subterraneous
+fire in the northeast parts of the world, that
+we ever yet heard of, from whence it might be projected.
+
+"I have much considered this appearance, and think
+it one of the hardest things to account for that I have
+yet met with in the phenomena of meteors, and I am
+induced to think that it must be some collection of
+matter formed in the aether, as it were, by some
+fortuitous concourse of atoms, and that the earth met
+with it as it passed along in its orb, then but newly
+formed, and before it had conceived any great impetus
+of descent towards the sun. For the direction of it
+was exactly opposite to that of the earth, which made
+an angle with the meridian at that time of sixty-seven
+gr., that is, its course was from west southwest to east
+northeast, wherefore the meteor seemed to move the
+contrary way. And besides falling into the power of
+the earth's gravity, and losing its motion from the
+opposition of the medium, it seems that it descended
+towards the earth, and was extinguished in the
+Tyrrhene Sea, to the west southwest of Leghorn. The
+great blow being heard upon its first immersion into
+the water, and the rattling like the driving of a cart
+over stones being what succeeded upon its quenching;
+something like this is always heard upon quenching a
+very hot iron in water. These facts being past dispute,
+I would be glad to have the opinion of the learned thereon,
+and what objection can be reasonably made against
+the above hypothesis, which I humbly submit to their
+censure."[1]
+
+These few paragraphs, coming as they do from a
+leading eighteenth-century astronomer, convey more
+clearly than any comment the actual state of the
+meteorological learning at that time. That this ball
+of fire, rushing "at a greater velocity than the swiftest
+cannon-ball," was simply a mass of heated rock passing
+through our atmosphere, did not occur to him, or at
+least was not credited. Nor is this surprising when we
+reflect that at that time universal gravitation had been
+but recently discovered; heat had not as yet been
+recognized as simply a form of motion; and thunder
+and lightning were unexplained mysteries, not to be
+explained for another three-quarters of a century.
+In the chapter on meteorology we shall see how the
+solution of this mystery that puzzled Halley and his
+associates all their lives was finally attained.
+
+
+BRADLEY AND THE ABERRATION OF LIGHT
+
+Halley was succeeded as astronomer royal by a man
+whose useful additions to the science were not to
+be recognized or appreciated fully until brought to
+light by the Prussian astronomer Bessel early in the
+nineteenth century. This was Dr. James Bradley, an
+ecclesiastic, who ranks as one of the most eminent
+astronomers of the eighteenth century. His most remarkable
+discovery was the explanation of a peculiar
+motion of the pole-star, first observed, but not explained,
+by Picard a century before. For many years a
+satisfactory explanation was sought unsuccessfully by
+Bradley and his fellow-astronomers, but at last he was
+able to demonstrate that the stary Draconis, on which
+he was making his observations, described, or appeared
+to describe, a small ellipse. If this observation was
+correct, it afforded a means of computing the aberration
+of any star at all times. The explanation of the
+physical cause of this aberration, as Bradley thought,
+and afterwards demonstrated, was the result of the
+combination of the motion of light with the annual
+motion of the earth. Bradley first formulated this
+theory in 1728, but it was not until 1748--twenty years
+of continuous struggle and observation by him--that he
+was prepared to communicate the results of his efforts
+to the Royal Society. This remarkable paper is
+thought by the Frenchman, Delambre, to entitle its
+author to a place in science beside such astronomers as
+Hipparcbus and Kepler.
+
+Bradley's studies led him to discover also the libratory
+motion of the earth's axis. "As this appearance
+of g Draconis. indicated a diminution of the
+inclination of the earth's axis to the plane of the
+ecliptic," he says; "and as several astronomers have
+supposed THAT inclination to diminish regularly; if this
+phenomenon depended upon such a cause, and amounted
+to 18" in nine years, the obliquity of the ecliptic
+would, at that rate, alter a whole minute in thirty
+years; which is much faster than any observations,
+before made, would allow. I had reason, therefore, to
+think that some part of this motion at the least, if not
+the whole, was owing to the moon's action upon the
+equatorial parts of the earth; which, I conceived, might
+cause a libratory motion of the earth's axis. But as I
+was unable to judge, from only nine years observations,
+whether the axis would entirely recover the same
+position that it had in the year 1727, I found it
+necessary to continue my observations through a
+whole period of the moon's nodes; at the end of
+which I had the satisfaction to see, that the stars,
+returned into the same position again; as if there had
+been no alteration at all in the inclination of the earth's
+axis; which fully convinced me that I had guessed
+rightly as to the cause of the phenomena. This circumstance
+proves likewise, that if there be a gradual
+diminution of the obliquity of the ecliptic, it does not
+arise only from an alteration in the position of the
+earth's axis, but rather from some change in the plane
+of the ecliptic itself; because the stars, at the end of the
+period of the moon's nodes, appeared in the same
+places, with respect to the equator, as they ought to
+have done, if the earth's axis had retained the same
+inclination to an invariable plane."[2]
+
+
+FRENCH ASTRONOMERS
+
+Meanwhile, astronomers across the channel were by
+no means idle. In France several successful observers
+were making many additions to the already long list
+of observations of the first astronomer of the Royal
+Observatory of Paris, Dominic Cassini (1625-1712),
+whose reputation among his contemporaries was
+much greater than among succeeding generations of
+astronomers. Perhaps the most deserving of these
+successors was Nicolas Louis de Lacaille (1713-1762),
+a theologian who had been educated at the expense
+of the Duke of Bourbon, and who, soon after completing
+his clerical studies, came under the patronage
+of Cassini, whose attention had been called to the
+young man's interest in the sciences. One of Lacaille's
+first under-takings was the remeasuring of the French
+are of the meridian, which had been incorrectly measured
+by his patron in 1684. This was begun in 1739,
+and occupied him for two years before successfully
+completed. As a reward, however, he was admitted
+to the academy and appointed mathematical professor
+in Mazarin College.
+
+In 1751 he went to the Cape of Good Hope for the
+purpose of determining the sun's parallax by observations
+of the parallaxes of Mars and Venus, and incidentally
+to make observations on the other southern
+hemisphere stars. The results of this undertaking
+were most successful, and were given in his Coelum
+australe stelligerum, etc., published in 1763. In this he
+shows that in the course of a single year he had observed
+some ten thousand stars, and computed the
+places of one thousand nine hundred and forty-two of
+them, measured a degree of the meridian, and made
+many observations of the moon--productive industry
+seldom equalled in a single year in any field. These
+observations were of great service to the astronomers,
+as they afforded the opportunity of comparing the stars
+of the southern hemisphere with those of the northern,
+which were being observed simultaneously by Lelande
+at Berlin.
+
+Lacaille's observations followed closely upon the
+determination of an absorbing question which occupied
+the attention of the astronomers in the
+early part of the century. This question was as
+to the shape of the earth--whether it was actually
+flattened at the poles. To settle this question once
+for all the Academy of Sciences decided to make the
+actual measurement of the length of two degrees, one
+as near the pole as possible, the other at the equator.
+Accordingly, three astronomers, Godin, Bouguer, and
+La Condamine, made the journey to a spot on the
+equator in Peru, while four astronomers, Camus,
+Clairaut, Maupertuis, and Lemonnier, made a voyage
+to a place selected in Lapland. The result of these
+expeditions was the determination that the globe is
+oblately spheroidal.
+
+A great contemporary and fellow-countryman of
+Lacaille was Jean Le Rond d'Alembert (1717-1783),
+who, although not primarily an astronomer, did so much
+with his mathematical calculations to aid that science
+that his name is closely connected with its progress
+during the eighteenth century. D'Alembert, who
+became one of the best-known men of science of
+his day, and whose services were eagerly sought
+by the rulers of Europe, began life as a foundling,
+having been exposed in one of the markets of
+Paris. The sickly infant was adopted and cared for
+in the family of a poor glazier, and treated as a member
+of the family. In later years, however, after the
+foundling had become famous throughout Europe, his
+mother, Madame Tencin, sent for him, and acknowledged
+her relationship. It is more than likely that
+the great philosopher believed her story, but if so he
+did not allow her the satisfaction of knowing his belief,
+declaring always that Madame Tencin could "not
+be nearer than a step-mother to him, since his mother
+was the wife of the glazier."
+
+D'Alembert did much for the cause of science by his
+example as well as by his discoveries. By living a
+plain but honest life, declining magnificent offers of
+positions from royal patrons, at the same time refusing
+to grovel before nobility, he set a worthy example to
+other philosophers whose cringing and pusillanimous
+attitude towards persons of wealth or position had
+hitherto earned them the contempt of the upper
+classes.
+
+His direct additions to astronomy are several, among
+others the determination of the mutation of the axis
+of the earth. He also determined the ratio of the attractive
+forces of the sun and moon, which he found
+to be about as seven to three. From this he reached
+the conclusion that the earth must be seventy times
+greater than the moon. The first two volumes of his
+Researches on the Systems of the World, published in
+1754, are largely devoted to mathematical and astronomical
+problems, many of them of little importance
+now, but of great interest to astronomers at that
+time.
+
+Another great contemporary of D'Alembert, whose
+name is closely associated and frequently confounded
+with his, was Jean Baptiste Joseph Delambre (1749-
+1822). More fortunate in birth as also in his educational
+advantages, Delambre as a youth began his
+studies under the celebrated poet Delille. Later he was
+obliged to struggle against poverty, supporting himself
+for a time by making translations from Latin, Greek,
+Italian, and English, and acting as tutor in private
+families. The turning-point of his fortune came when
+the attention of Lalande was called to the young man
+by his remarkable memory, and Lalande soon showed
+his admiration by giving Delambre certain difficult
+astronomical problems to solve. By performing these
+tasks successfully his future as an astronomer became
+assured. At that time the planet Uranus had
+just been discovered by Herschel, and the Academy
+of Sciences offered as the subject for one of
+its prizes the determination of the planet's orbit.
+Delambre made this determination and won the
+prize--a feat that brought him at once into prominence.
+
+By his writings he probably did as much towards
+perfecting modern astronomy as any one man. His
+History of Astronomy is not merely a narrative of progress
+of astronomy but a complete abstract of all the
+celebrated works written on the subject. Thus he
+became famous as an historian as well as an astronomer.
+
+
+LEONARD EULER
+
+Still another contemporary of D'Alembert and Delambre,
+and somewhat older than either of them, was
+Leonard Euler (1707-1783), of Basel, whose fame as a
+philosopher equals that of either of the great Frenchmen.
+He is of particular interest here in his capacity
+of astronomer, but astronomy was only one of the
+many fields of science in which he shone. Surely something
+out of the ordinary was to be expected of the
+man who could "repeat the AEneid of Virgil from the
+beginning to the end without hesitation, and indicate
+the first and last line of every page of the edition which
+he used." Something was expected, and he fulfilled
+these expectations.
+
+In early life he devoted himself to the study of
+theology and the Oriental languages, at the request of
+his father, but his love of mathematics proved too
+strong, and, with his father's consent, he finally gave
+up his classical studies and turned to his favorite
+study, geometry. In 1727 he was invited by Catharine
+I. to reside in St. Petersburg, and on accepting
+this invitation he was made an associate of the Academy
+of Sciences. A little later he was made professor
+of physics, and in 1733 professor of mathematics. In
+1735 he solved a problem in three days which some
+of the eminent mathematicians would not undertake
+under several months. In 1741 Frederick the Great
+invited him to Berlin, where he soon became a member
+of the Academy of Sciences and professor of mathematics; but in
+1766 he returned to St. Petersburg.
+Towards the close of his life be became virtually blind,
+being obliged to dictate his thoughts, sometimes to
+persons entirely ignorant of the subject in hand.
+Nevertheless, his remarkable memory, still further
+heightened by his blindness, enabled him to carry out
+the elaborate computations frequently involved.
+
+Euler's first memoir, transmitted to the Academy of
+Sciences of Paris in 1747, was on the planetary perturbations.
+This memoir carried off the prize that
+had been offered for the analytical theory of the motions
+of Jupiter and Saturn. Other memoirs followed,
+one in 1749 and another in 1750, with further expansions
+of the same subject. As some slight errors were
+found in these, such as a mistake in some of the formulae
+expressing the secular and periodic inequalities,
+the academy proposed the same subject for the prize
+of 1752. Euler again competed, and won this prize
+also. The contents of this memoir laid the foundation
+for the subsequent demonstration of the permanent
+stability of the planetary system by Laplace and
+Lagrange.
+
+It was Euler also who demonstrated that within
+certain fixed limits the eccentricities and places of the
+aphelia of Saturn and Jupiter are subject to constant
+variation, and he calculated that after a lapse of about
+thirty thousand years the elements of the orbits of
+these two planets recover their original values.
+
+
+
+II
+
+THE PROGRESS OF MODERN ASTRONOMY
+
+A NEW epoch in astronomy begins with the work
+of William Herschel, the Hanoverian, whom England
+made hers by adoption. He was a man with a
+positive genius for sidereal discovery. At first a mere
+amateur in astronomy, he snatched time from his
+duties as music-teacher to grind him a telescopic mirror,
+and began gazing at the stars. Not content with
+his first telescope, he made another and another, and
+he had such genius for the work that he soon possessed
+a better instrument than was ever made before. His
+patience in grinding the curved reflective surface was
+monumental. Sometimes for sixteen hours together
+he must walk steadily about the mirror, polishing it,
+without once removing his hands. Meantime his sister,
+always his chief lieutenant, cheered him with her presence,
+and from time to time put food into his mouth.
+The telescope completed, the astronomer turned night
+into day, and from sunset to sunrise, year in and year
+out, swept the heavens unceasingly, unless prevented
+by clouds or the brightness of the moon. His sister
+sat always at his side, recording his observations.
+They were in the open air, perched high at the mouth of
+the reflector, and sometimes it was so cold that the ink
+froze in the bottle in Caroline Herschel's hand; but the
+two enthusiasts hardly noticed a thing so common-place as
+terrestrial weather. They were living in distant worlds.
+
+The results? What could they be? Such enthusiasm
+would move mountains. But, after all, the moving
+of mountains seems a liliputian task compared
+with what Herschel really did with those wonderful
+telescopes. He moved worlds, stars, a universe--
+even, if you please, a galaxy of universes; at least he
+proved that they move, which seems scarcely less wonderful;
+and he expanded the cosmos, as man conceives
+it, to thousands of times the dimensions it had before.
+As a mere beginning, he doubled the diameter of the
+solar system by observing the great outlying planet
+which we now call Uranus, but which he christened
+Georgium Sidus, in honor of his sovereign, and which
+his French contemporaries, not relishing that name,
+preferred to call Herschel.
+
+This discovery was but a trifle compared with what
+Herschel did later on, but it gave him world-wide reputation
+none the less. Comets and moons aside, this
+was the first addition to the solar system that had been
+made within historic times, and it created a veritable
+furor of popular interest and enthusiasm. Incidentally
+King George was flattered at having a world named
+after him, and he smiled on the astronomer, and came
+with his court to have a look at his namesake. The
+inspection was highly satisfactory; and presently the
+royal favor enabled the astronomer to escape the
+thraldom of teaching music and to devote his entire
+time to the more congenial task of star-gazing.
+
+Thus relieved from the burden of mundane embarrassments,
+he turned with fresh enthusiasm to the skies, and his
+discoveries followed one another in bewildering
+profusion. He found various hitherto unseen
+moons of our sister planets; be made special
+studies of Saturn, and proved that this planet, with its
+rings, revolves on its axis; he scanned the spots on the
+sun, and suggested that they influence the weather of
+our earth; in short, he extended the entire field of solar
+astronomy. But very soon this field became too small
+for him, and his most important researches carried
+him out into the regions of space compared with which
+the span of our solar system is a mere point. With his
+perfected telescopes he entered abysmal vistas which
+no human eve ever penetrated before, which no human
+mind had hitherto more than vaguely imagined. He
+tells us that his forty-foot reflector will bring him light
+from a distance of "at least eleven and three-fourths
+millions of millions of millions of miles"--light which
+left its source two million years ago. The smallest
+stars visible to the unaided eye are those of the sixth
+magnitude; this telescope, he thinks, has power to
+reveal stars of the 1342d magnitude.
+
+But what did Herschel learn regarding these awful
+depths of space and the stars that people them? That
+was what the world wished to know. Copernicus,
+Galileo, Kepler, had given us a solar system, but the
+stars had been a mystery. What says the great
+reflector--are the stars points of light, as the ancients
+taught, and as more than one philosopher of the eighteenth
+century has still contended, or are they suns, as
+others hold? Herschel answers, they are suns, each
+and every one of all the millions--suns, many of them,
+larger than the one that is the centre of our tiny system.
+Not only so, but they are moving suns. Instead of
+being fixed in space, as has been thought, they are
+whirling in gigantic orbits about some common centre. Is
+our sun that centre? Far from it. Our sun is only a
+star like all the rest, circling on with its attendant
+satellites--our giant sun a star, no different from
+myriad other stars, not even so large as some; a mere
+insignificant spark of matter in an infinite shower of
+sparks.
+
+Nor is this all. Looking beyond the few thousand
+stars that are visible to the naked eye, Herschel sees
+series after series of more distant stars, marshalled in
+galaxies of millions; but at last he reaches a distance
+beyond which the galaxies no longer increase. And
+yet--so he thinks--he has not reached the limits of his
+vision. What then? He has come to the bounds of the
+sidereal system--seen to the confines of the universe.
+He believes that he can outline this system, this universe,
+and prove that it has the shape of an irregular
+globe, oblately flattened to almost disklike proportions,
+and divided at one edge--a bifurcation that is revealed
+even to the naked eye in the forking of the Milky Way.
+
+This, then, is our universe as Herschel conceives it--
+a vast galaxy of suns, held to one centre, revolving,
+poised in space. But even here those marvellous telescopes
+do not pause. Far, far out beyond the confines
+of our universe, so far that the awful span of our own
+system might serve as a unit of measure, are revealed
+other systems, other universes, like our own, each composed,
+as he thinks, of myriads of suns, clustered like
+our galaxy into an isolated system--mere islands of
+matter in an infinite ocean of space. So distant from
+our universe are these now universes of Herschel's discovery
+that their light reaches us only as a dim, nebulous
+glow, in most cases invisible to the unaided eye.
+About a hundred of these nebulae were known when
+Herschel began his studies. Before the close of the
+century he had discovered about two thousand more of
+them, and many of these had been resolved by his
+largest telescopes into clusters of stars. He believed
+that the farthest of these nebulae that he could see
+was at least three hundred thousand times as distant
+from us as the nearest fixed star. Yet that nearest
+star--so more recent studies prove--is so remote that
+its light, travelling one hundred and eighty thousand
+miles a second, requires three and one-half years to
+reach our planet.
+
+As if to give the finishing touches to this novel
+scheme of cosmology, Herschel, though in the main
+very little given to unsustained theorizing, allows himself
+the privilege of one belief that he cannot call upon
+his telescope to substantiate. He thinks that all the
+myriad suns of his numberless systems are instinct with
+life in the human sense. Giordano Bruno and a long
+line of his followers had held that some of our sister
+planets may be inhabited, but Herschel extends the
+thought to include the moon, the sun, the stars--all the
+heavenly bodies. He believes that he can demonstrate
+the habitability of our own sun, and, reasoning from
+analogy, he is firmly convinced that all the suns of all
+the systems are "well supplied with inhabitants." In
+this, as in some other inferences, Herschel is misled by
+the faulty physics of his time. Future generations,
+working with perfected instruments, may not sustain
+him all along the line of his observations, even, let alone
+his inferences. But how one's egotism shrivels and
+shrinks as one grasps the import of his sweeping
+thoughts!
+
+Continuing his observations of the innumerable nebulae,
+Herschel is led presently to another curious speculative
+inference. He notes that some star groups are
+much more thickly clustered than others, and he is led
+to infer that such varied clustering tells of varying
+ages of the different nebulae. He thinks that at first
+all space may have been evenly sprinkled with the
+stars and that the grouping has resulted from the
+action of gravitation.
+
+"That the Milky Way is a most extensive stratum of
+stars of various sizes admits no longer of lasting doubt,"
+he declares, "and that our sun is actually one of the
+heavenly bodies belonging to it is as evident. I have
+now viewed and gauged this shining zone in almost
+every direction and find it composed of stars whose
+number ... constantly increases and decreases in proportion
+to its apparent brightness to the naked eye.
+
+"Let us suppose numberless stars of various sizes,
+scattered over an indefinite portion of space in such
+a manner as to be almost equally distributed throughout
+the whole. The laws of attraction which no doubt
+extend to the remotest regions of the fixed stars will
+operate in such a manner as most probably to produce
+the following effects:
+
+"In the first case, since we have supposed the stars
+to be of various sizes, it will happen that a star, being
+considerably larger than its neighboring ones, will attract
+them more than they will be attracted by others
+that are immediately around them; by which means
+they will be, in time, as it were, condensed about a
+centre, or, in other words, form themselves into a cluster
+of stars of almost a globular figure, more or less
+regular according to the size and distance of the surrounding
+stars....
+
+"The next case, which will also happen almost as frequently
+as the former, is where a few stars, though not
+superior in size to the rest, may chance to be rather
+nearer one another than the surrounding ones,... and
+this construction admits of the utmost variety of
+shapes. . . .
+
+"From the composition and repeated conjunction of
+both the foregoing formations, a third may be derived
+when many large stars, or combined small ones, are
+spread in long, extended, regular, or crooked rows,
+streaks, or branches; for they will also draw the surrounding
+stars, so as to produce figures of condensed
+stars curiously similar to the former which gave rise to
+these condensations.
+
+"We may likewise admit still more extensive
+combinations; when, at the same time that a cluster of
+stars is forming at the one part of space, there may be
+another collection in a different but perhaps not far-
+distant quarter, which may occasion a mutual approach
+towards their own centre of gravity.
+
+"In the last place, as a natural conclusion of the
+former cases, there will be formed great cavities or
+vacancies by the retreating of the stars towards the
+various centres which attract them."[1]
+
+
+Looking forward, it appears that the time must come
+when all the suns of a system will be drawn together
+and destroyed by impact at a common centre. Already,
+it seems to Herschel, the thickest clusters have
+"outlived their usefulness" and are verging towards
+their doom.
+
+But again, other nebulae present an appearance suggestive
+of an opposite condition. They are not resolvable
+into stars, but present an almost uniform appearance
+throughout, and are hence believed to be
+composed of a shining fluid, which in some instances is
+seen to be condensed at the centre into a glowing mass.
+In such a nebula Herschel thinks he sees a sun in
+process of formation.
+
+
+THE NEBULAR HYPOTHESIS OF KANT
+
+Taken together, these two conceptions outline a majestic
+cycle of world formation and world destruction--
+a broad scheme of cosmogony, such as had been vaguely
+adumbrated two centuries before by Kepler and in
+more recent times by Wright and Swedenborg. This
+so-called "nebular hypothesis" assumes that in the
+beginning all space was uniformly filled with cosmic
+matter in a state of nebular or "fire-mist" diffusion,
+"formless and void." It pictures the condensation--
+coagulation, if you will--of portions of this mass to
+form segregated masses, and the ultimate development
+out of these masses of the sidereal bodies that we see.
+
+Perhaps the first elaborate exposition of this idea
+was that given by the great German philosopher Immanuel
+Kant (born at Konigsberg in 1724, died in
+1804), known to every one as the author of the Critique
+of Pure Reason. Let us learn from his own words how
+the imaginative philosopher conceived the world to
+have come into existence.
+
+"I assume," says Kant, "that all the material of
+which the globes belonging to our solar system--all
+the planets and comets--consist, at the beginning of
+all things was decomposed into its primary elements,
+and filled the whole space of the universe in which the
+bodies formed out of it now revolve. This state of
+nature, when viewed in and by itself without any reference
+to a system, seems to be the very simplest that
+can follow upon nothing. At that time nothing has
+yet been formed. The construction of heavenly bodies
+at a distance from one another, their distances regulated
+by their attraction, their form arising out of the
+equilibrium of their collected matter, exhibit a later
+state.... In a region of space filled in this manner, a
+universal repose could last only a moment. The elements
+have essential forces with which to put each
+other in motion, and thus are themselves a source of
+life. Matter immediately begins to strive to fashion
+itself. The scattered elements of a denser kind, by
+means of their attraction, gather from a sphere around
+them all the matter of less specific gravity; again, these
+elements themselves, together with the material which
+they have united with them, collect in those points
+where the particles of a still denser kind are found;
+these in like manner join still denser particles, and so
+on. If we follow in imagination this process by which
+nature fashions itself into form through the whole extent
+of chaos, we easily perceive that all the results of
+the process would consist in the formation of divers
+masses which, when their formation was complete,
+would by the equality of their attraction be at rest
+and be forever unmoved.
+
+"But nature has other forces in store which are
+specially exerted when matter is decomposed into fine
+particles. They are those forces by which these particles
+repel one another, and which, by their conflict
+with attractions, bring forth that movement which is,
+as it were, the lasting life of nature. This force of repulsion
+is manifested in the elasticity of vapors, the
+effluences of strong-smelling bodies, and the diffusion
+of all spirituous matters. This force is an uncontestable
+phenomenon of matter. It is by it that the elements,
+which may be falling to the point attracting
+them, are turned sideways promiscuously from their
+movement in a straight line; and their perpendicular
+fall thereby issues in circular movements, which encompass
+the centre towards which they were falling.
+In order to make the formation of the world more distinctly
+conceivable, we will limit our view by withdrawing
+it from the infinite universe of nature and directing
+it to a particular system, as the one which belongs to
+our sun. Having considered the generation of this
+system, we shall be able to advance to a similar consideration
+of the origin of the great world-systems, and
+thus to embrace the infinitude of the whole creation in
+one conception.
+
+"From what has been said, it will appear that if a
+point is situated in a very large space where the attraction
+of the elements there situated acts more strongly
+than elsewhere, then the matter of the elementary
+particles scattered throughout the whole region will fall
+to that point. The first effect of this general fall is
+the formation of a body at this centre of attraction,
+which, so to speak, grows from an infinitely small
+nucleus by rapid strides; and in the proportion in which
+this mass increases, it also draws with greater force
+the surrounding particles to unite with it. When the
+mass of this central body has grown so great that the
+velocity with which it draws the particles to itself with
+great distances is bent sideways by the feeble degree
+of repulsion with which they impede one another, and
+when it issues in lateral movements which are capable
+by means of the centrifugal force of encompassing the
+central body in an orbit, then there are produced
+whirls or vortices of particles, each of which by itself
+describes a curved line by the composition of the
+attracting force and the force of revolution that had been
+bent sideways. These kinds of orbits all intersect
+one another, for which their great dispersion in this
+space gives place. Yet these movements are in many
+ways in conflict with one another, and they naturally
+tend to bring one another to a uniformity--that is,
+into a state in which one movement is as little
+obstructive to the other as possible. This happens in
+two ways: first by the particles limiting one another's
+movement till they all advance in one direction; and,
+secondly, in this way, that the particles limit their
+vertical movements in virtue of which they are
+approaching the centre of attraction, till they all move
+horizontally--i. e., in parallel circles round the sun as
+their centre, no longer intercept one another, and by
+the centrifugal force becoming equal with the falling
+force they keep themselves constantly in free circular
+orbits at the distance at which they move. The result,
+finally, is that only those particles continue to move in
+this region of space which have acquired by their fall
+a velocity, and through the resistance of the other particles
+a direction, by which they can continue to maintain
+a FREE CIRCULAR MOVEMENT....
+
+"The view of the formation of the planets in this system
+has the advantage over every other possible theory
+in holding that the origin of the movements, and the
+position of the orbits in arising at that same point of
+time--nay, more, in showing that even the deviations
+from the greatest possible exactness in their determinations,
+as well as the accordances themselves, become
+clear at a glance. The planets are formed out of particles
+which, at the distance at which they move, have
+exact movements in circular orbits; and therefore the
+masses composed out of them will continue the same
+movements and at the same rate and in the same direction."[2]
+
+
+It must be admitted that this explanation leaves a
+good deal to be desired. It is the explanation of a
+metaphysician rather than that of an experimental
+scientist. Such phrases as "matter immediately begins
+to strive to fashion itself," for example, have no
+place in the reasoning of inductive science. Nevertheless,
+the hypothesis of Kant is a remarkable conception;
+it attempts to explain along rational lines
+something which hitherto had for the most part been
+considered altogether inexplicable.
+
+But there are various questions that at once suggest
+themselves which the Kantian theory leaves unanswered.
+How happens it, for example, that the cosmic
+mass which gave birth to our solar system was divided
+into several planetary bodies instead of remaining a
+single mass? Were the planets struck from the sun by
+the chance impact of comets, as Buffon has suggested?
+or thrown out by explosive volcanic action, in accordance
+with the theory of Dr. Darwin? or do they owe
+their origin to some unknown law? In any event, how
+chanced it that all were projected in nearly the same
+plane as we now find them?
+
+
+LAPLACE AND THE NEBULAR HYPOTHESIS
+
+It remained for a mathematical astronomer to solve
+these puzzles. The man of all others competent to
+take the subject in hand was the French astronomer
+Laplace. For a quarter of a century he had devoted
+his transcendent mathematical abilities to the solution
+of problems of motion of the heavenly bodies.
+Working in friendly rivalry with his countryman Lagrange,
+his only peer among the mathematicians of the
+age, he had taken up and solved one by one the problems
+that Newton left obscure. Largely through the
+efforts of these two men the last lingering doubts as to
+the solidarity of the Newtonian hypothesis of universal
+gravitation had been removed. The share of Lagrange
+was hardly less than that of his co-worker; but Laplace
+will longer be remembered, because he ultimately
+brought his completed labors into a system, and,
+incorporating with them the labors of his contemporaries,
+produced in the Mecanique Celeste the undisputed
+mathematical monument of the century, a fitting complement
+to the Principia of Newton, which it supplements
+and in a sense completes.
+
+In the closing years of the eighteenth century Laplace
+took up the nebular hypothesis of cosmogony, to
+which we have just referred, and gave it definite
+proportions; in fact, made it so thoroughly his own
+that posterity will always link it with his name.
+Discarding the crude notions of cometary impact
+and volcanic eruption, Laplace filled up the gaps in
+the hypothesis with the aid of well-known laws of
+gravitation and motion. He assumed that the primitive
+mass of cosmic matter which was destined to
+form our solar system was revolving on its axis
+even at a time when it was still nebular in character,
+and filled all space to a distance far beyond the
+present limits of the system. As this vaporous mass
+contracted through loss of heat, it revolved more
+and more swiftly, and from time to time, through balance
+of forces at its periphery, rings of its substance
+were whirled off and left revolving there, subsequently
+to become condensed into planets, and in their turn
+whirl off minor rings that became moons. The main
+body of the original mass remains in the present as the
+still contracting and rotating body which we call the
+sun.
+
+Let us allow Laplace to explain all this in detail:
+
+"In order to explain the prime movements of the
+planetary system," he says, "there are the five following
+phenomena: The movement of the planets in the
+same direction and very nearly in the same plane; the
+movement of the satellites in the same direction as
+that of the planets; the rotation of these different
+bodies and the sun in the same direction as their revolution,
+and in nearly the same plane; the slight eccentricity of the
+orbits of the planets and of the satellites;
+and, finally, the great eccentricity of the orbits of the
+comets, as if their inclinations had been left to chance.
+
+"Buffon is the only man I know who, since the discovery
+of the true system of the world, has endeavored
+to show the origin of the planets and their satellites.
+He supposes that a comet, in falling into the sun, drove
+from it a mass of matter which was reassembled at a
+distance in the form of various globes more or less
+large, and more or less removed from the sun, and that
+these globes, becoming opaque and solid, are now the
+planets and their satellites.
+
+"This hypothesis satisfies the first of the five preceding
+phenomena; for it is clear that all the bodies
+thus formed would move very nearly in the plane
+which passed through the centre of the sun, and in the
+direction of the torrent of matter which was produced;
+but the four other phenomena appear to be inexplicable
+to me by this means. Indeed, the absolute movement
+of the molecules of a planet ought then to be in
+the direction of the movement of its centre of gravity;
+but it does not at all follow that the motion of the rotation
+of the planets should be in the same direction.
+Thus the earth should rotate from east to west, but
+nevertheless the absolute movement of its molecules
+should be from east to west; and this ought also to
+apply to the movement of the revolution of the satellites,
+in which the direction, according to the hypothesis
+which he offers, is not necessarily the same as that
+of the progressive movement of the planets.
+
+"A phenomenon not only very difficult to explain
+under this hypothesis, but one which is even contrary
+to it, is the slight eccentricity of the planetary orbits.
+We know, by the theory of central forces, that if a body
+moves in a closed orbit around the sun and touches it,
+it also always comes back to that point at every revolution;
+whence it follows that if the planets were originally
+detached from the sun, they would touch it at
+each return towards it, and their orbits, far from being
+circular, would be very eccentric. It is true that a mass
+of matter driven from the sun cannot be exactly compared
+to a globe which touches its surface, for the impulse
+which the particles of this mass receive from one
+another and the reciprocal attractions which they exert
+among themselves, could, in changing the direction
+of their movements, remove their perihelions from the
+sun; but their orbits would be always most eccentric,
+or at least they would not have slight eccentricities
+except by the most extraordinary chance. Thus we
+cannot see, according to the hypothesis of Buffon,
+why the orbits of more than a hundred comets already
+observed are so elliptical. This hypothesis is therefore
+very far from satisfying the preceding phenomena.
+Let us see if it is possible to trace them back to their
+true cause.
+
+"Whatever may be its ultimate nature, seeing that it
+has caused or modified the movements of the planets,
+it is necessary that this cause should embrace every
+body, and, in view of the enormous distances which
+separate them, it could only have been a fluid of immense
+extent. In order to have given them an almost
+circular movement in the same direction around the
+sun, it is necessary that this fluid should have enveloped
+the sun as in an atmosphere. The consideration
+of the planetary movements leads us then to think
+that, on account of excessive heat, the atmosphere of
+the sun originally extended beyond the orbits of all
+the planets, and that it was successively contracted to
+its present limits.
+
+"In the primitive condition in which we suppose the
+sun to have been, it resembled a nebula such as the
+telescope shows is composed of a nucleus more or less
+brilliant, surrounded by a nebulosity which, on condensing
+itself towards the centre, forms a star. If it is
+conceived by analogy that all the stars were formed in
+this manner, it is possible to imagine their previous
+condition of nebulosity, itself preceded by other states
+in which the nebulous matter was still more diffused,
+the nucleus being less and less luminous. By going
+back as far as possible, we thus arrive at a nebulosity
+so diffused that its existence could hardly be suspected.
+
+"For a long time the peculiar disposition of certain
+stars, visible to the unaided eye, has struck philosophical
+observers. Mitchell has already remarked
+how little probable it is that the stars in the Pleiades,
+for example, could have been contracted into the small
+space which encloses them by the fortuity of chance
+alone, and he has concluded that this group of stars,
+and similar groups which the skies present to us, are
+the necessary result of the condensation of a nebula,
+with several nuclei, and it is evident that a nebula, by
+continually contracting, towards these various nuclei,
+at length would form a group of stars similar to the
+Pleiades. The condensation of a nebula with two
+nuclei would form a system of stars close together,
+turning one upon the other, such as those double stars
+of which we already know the respective movements.
+
+"But how did the solar atmosphere determine the
+movements of the rotation and revolution of the planets
+and satellites? If these bodies had penetrated very
+deeply into this atmosphere, its resistance would have
+caused them to fall into the sun. We can therefore
+conjecture that the planets were formed at their successive
+limits by the condensation of a zone of vapors
+which the sun, on cooling, left behind, in the plane of
+his equator.
+
+"Let us recall the results which we have given in
+a preceding chapter. The atmosphere of the sun could
+not have extended indefinitely. Its limit was the point
+where the centrifugal force due to its movement of
+rotation balanced its weight. But in proportion as
+the cooling contracted the atmosphere, and those molecules
+which were near to them condensed upon the
+surface of the body, the movement of the rotation increased;
+for, on account of the Law of Areas, the sum
+of the areas described by the vector of each molecule
+of the sun and its atmosphere and projected in the
+plane of the equator being always the same, the rotation
+should increase when these molecules approach the
+centre of the sun. The centrifugal force due to this
+movement becoming thus larger, the point where the
+weight is equal to it is nearer the sun. Supposing,
+then, as it is natural to admit, that the atmosphere
+extended at some period to its very limits, it should,
+on cooling, leave molecules behind at this limit and
+at limits successively occasioned by the increased
+rotation of the sun. The abandoned molecules would
+continue to revolve around this body, since their centrifugal
+force was balanced by their weight. But this
+equilibrium not arising in regard to the atmospheric
+molecules parallel to the solar equator, the latter, on
+account of their weight, approached the atmosphere
+as they condensed, and did not cease to belong to it
+until by this motion they came upon the equator.
+
+"Let us consider now the zones of vapor successively
+left behind. These zones ought, according to appearance,
+by the condensation and mutual attraction of
+their molecules, to form various concentric rings of
+vapor revolving around the sun. The mutual gravitational
+friction of each ring would accelerate some and
+retard others, until they had all acquired the same
+angular velocity. Thus the actual velocity of the
+molecules most removed from the sun would be the
+greatest. The following cause would also operate to
+bring about this difference of speed. The molecules
+farthest from the sun, and which by the effects of
+cooling and condensation approached one another to
+form the outer part of the ring, would have always
+described areas proportional to the time since the
+central force by which they were controlled has been
+constantly directed towards this body. But this constancy
+of areas necessitates an increase of velocity
+proportional to the distance. It is thus seen
+that the same cause would diminish the velocity
+of the molecules which form the inner part of the
+ring.
+
+"If all the molecules of the ring of vapor continued
+to condense without disuniting, they would at length
+form a ring either solid or fluid. But this formation
+would necessitate such a regularity in every part of
+the ring, and in its cooling, that this phenomenon is
+extremely rare; and the solar system affords us, indeed,
+but one example--namely, in the ring of Saturn.
+In nearly every case the ring of vapor was broken into
+several masses, each moving at similar velocities, and
+continuing to rotate at the same distance around the
+sun. These masses would take a spheroid form with a
+rotatory movement in the direction of the revolution,
+because their inner molecules had less velocity than
+the outer. Thus were formed so many planets in a
+condition of vapor. But if one of them were powerful
+enough to reunite successively by its attraction all the
+others around its centre of gravity, the ring of vapor
+would be thus transformed into a single spheroidical
+mass of vapor revolving around the sun with a rotation
+in the direction of its revolution. The latter case
+has been that which is the most common, but nevertheless
+the solar system affords us an instance of the
+first case in the four small planets which move between
+Jupiter and Mars; at least, if we do not suppose,
+as does M. Olbers, that they originally formed
+a single planet which a mighty explosion broke up
+into several portions each moving at different velocities.
+
+"According to our hypothesis, the comets are strangers
+to our planetary system. In considering them,
+as we have done, as minute nebulosities, wandering
+from solar system to solar system, and formed by
+the condensation of the nebulous matter everywhere
+existent in profusion in the universe, we see that when
+they come into that part of the heavens where the sun
+is all-powerful, he forces them to describe orbits either
+elliptical or hyperbolic, their paths being equally possible
+in all directions, and at all inclinations of the
+ecliptic, conformably to what has been observed. Thus
+the condensation of nebulous matter, by which we
+have at first explained the motions of the rotation and
+revolution of the planets and their satellites in the same
+direction, and in nearly approximate planes, explains
+also why the movements of the comets escape this
+general law."[3]
+
+
+The nebular hypothesis thus given detailed completion
+by Laplace is a worthy complement of the grand
+cosmologic scheme of Herschel. Whether true or false,
+the two conceptions stand as the final contributions of
+the eighteenth century to the history of man's ceaseless
+efforts to solve the mysteries of cosmic origin and cosmic
+structure. The world listened eagerly and without
+prejudice to the new doctrines; and that attitude tells
+of a marvellous intellectual growth of our race. Mark
+the transition. In the year 1600, Bruno was burned
+at the stake for teaching that our earth is not the centre
+of the universe. In 1700, Newton was pronounced
+"impious and heretical" by a large school of philosophers
+for declaring that the force which holds the planets
+in their orbits is universal gravitation. In 1800,
+Laplace and Herschel are honored for teaching that
+gravitation built up the system which it still controls;
+that our universe is but a minor nebula, our sun but
+a minor star, our earth a mere atom of matter, our
+race only one of myriad races peopling an infinity
+of worlds. Doctrines which but the span of two human
+lives before would have brought their enunciators
+to the stake were now pronounced not impious,
+but sublime.
+
+
+ASTEROIDS AND SATELLITES
+
+The first day of the nineteenth century was fittingly
+signalized by the discovery of a new world. On the
+evening of January 1, 1801, an Italian astronomer,
+Piazzi, observed an apparent star of about the eighth
+magnitude (hence, of course, quite invisible to the unaided
+eye), which later on was seen to have moved,
+and was thus shown to be vastly nearer the earth than
+any true star. He at first supposed, as Herschel had
+done when he first saw Uranus, that the unfamiliar
+body was a comet; but later observation proved it a
+tiny planet, occupying a position in space between
+Mars and Jupiter. It was christened Ceres, after the
+tutelary goddess of Sicily.
+
+Though unpremeditated, this discovery was not unexpected,
+for astronomers had long surmised the existence
+of a planet in the wide gap between Mars and Jupiter.
+Indeed, they were even preparing to make concerted
+search for it, despite the protests of philosophers,
+who argued that the planets could not possibly exceed
+the magic number seven, when Piazzi forestalled their
+efforts. But a surprise came with the sequel; for the
+very next year Dr. Olbers, the wonderful physician-
+astronomer of Bremen, while following up the course
+of Ceres, happened on another tiny moving star, similarly
+located, which soon revealed itself as planetary.
+Thus two planets were found where only one was expected.
+
+The existence of the supernumerary was a puzzle, but
+Olbers solved it for the moment by suggesting that
+Ceres and Pallas, as he called his captive, might be
+fragments of a quondam planet, shattered by internal
+explosion or by the impact of a comet. Other similar
+fragments, he ventured to predict, would be
+found when searched for. William Herschel sanctioned
+this theory, and suggested the name asteroids
+for the tiny planets. The explosion theory was supported
+by the discovery of another asteroid, by Harding,
+of Lilienthal, in 1804, and it seemed clinched
+when Olbers himself found a fourth in 1807. The
+new-comers were named Juno and Vesta respectively.
+
+There the case rested till 1845, when a Prussian
+amateur astronomer named Hencke found another
+asteroid, after long searching, and opened a new epoch
+of discovery. From then on the finding of asteroids
+became a commonplace. Latterly, with the aid of
+photography, the list has been extended to above four
+hundred, and as yet there seems no dearth in the supply,
+though doubtless all the larger members have been
+revealed. Even these are but a few hundreds of miles
+in diameter, while the smaller ones are too tiny for
+measurement. The combined bulk of these minor
+planets is believed to be but a fraction of that of the
+earth.
+
+Olbers's explosion theory, long accepted by astronomers,
+has been proven open to fatal objections. The
+minor planets are now believed to represent a ring of
+cosmical matter, cast off from the solar nebula like the
+rings that went to form the major planets, but prevented
+from becoming aggregated into a single body by the
+perturbing mass of Jupiter.
+
+
+The Discovery of Neptune
+
+As we have seen, the discovery of the first asteroid
+confirmed a conjecture; the other important planetary
+discovery of the nineteenth century fulfilled a prediction.
+Neptune was found through scientific prophecy.
+No one suspected the existence of a trans-Uranian
+planet till Uranus itself, by hair-breadth departures
+from its predicted orbit, gave out the secret. No one
+saw the disturbing planet till the pencil of the mathematician,
+with almost occult divination, had pointed
+out its place in the heavens. The general predication
+of a trans-Uranian planet was made by Bessel, the great
+Konigsberg astronomer, in 1840; the analysis that revealed
+its exact location was undertaken, half a decade
+later, by two independent workers--John Couch
+Adams, just graduated senior wrangler at Cambridge,
+England, and U. J. J. Leverrier, the leading French
+mathematician of his generation.
+
+Adams's calculation was first begun and first completed.
+But it had one radical defect--it was the work
+of a young and untried man. So it found lodgment in a
+pigeon-hole of the desk of England's Astronomer Royal,
+and an opportunity was lost which English astronomers
+have never ceased to mourn. Had the search
+been made, an actual planet would have been seen
+shining there, close to the spot where the pencil of the
+mathematician had placed its hypothetical counterpart.
+But the search was not made, and while the
+prophecy of Adams gathered dust in that regrettable
+pigeon-hole, Leverrier's calculation was coming on, his
+tentative results meeting full encouragement from
+Arago and other French savants. At last the laborious
+calculations proved satisfactory, and, confident of
+the result, Leverrier sent to the Berlin observatory,
+requesting that search be made for the disturber of
+Uranus in a particular spot of the heavens. Dr. Galle
+received the request September 23, 1846. That very
+night he turned his telescope to the indicated region,
+and there, within a single degree of the suggested spot,
+he saw a seeming star, invisible to the unaided eye,
+which proved to be the long-sought planet, henceforth
+to be known as Neptune. To the average mind, which
+finds something altogether mystifying about abstract
+mathematics, this was a feat savoring of the miraculous.
+
+Stimulated by this success, Leverrier calculated an
+orbit for an interior planet from perturbations of Mercury,
+but though prematurely christened Vulcan, this
+hypothetical nursling of the sun still haunts the realm
+of the undiscovered, along with certain equally hypothetical
+trans-Neptunian planets whose existence has
+been suggested by "residual perturbations" of Uranus,
+and by the movements of comets. No other veritable
+additions of the sun's planetary family have been made
+in our century, beyond the finding of seven small moons,
+which chiefly attest the advance in telescopic powers.
+Of these, the tiny attendants of our Martian neighbor,
+discovered by Professor Hall with the great Washington
+refractor, are of greatest interest, because of their
+small size and extremely rapid flight. One of them is
+poised only six thousand miles from Mars, and whirls
+about him almost four times as fast as he revolves,
+seeming thus, as viewed by the Martian, to rise in the
+west and set in the east, and making the month only
+one-fourth as long as the day.
+
+
+The Rings of Saturn
+
+The discovery of the inner or crape ring of Saturn,
+made simultaneously in 1850 by William C. Bond, at
+the Harvard observatory, in America, and the Rev.
+W. R. Dawes in England, was another interesting optical
+achievement; but our most important advances
+in knowledge of Saturn's unique system are due to the
+mathematician. Laplace, like his predecessors, supposed
+these rings to be solid, and explained their stability
+as due to certain irregularities of contour which
+Herschel bad pointed out. But about 1851 Professor
+Peirce, of Harvard, showed the untenability of this
+conclusion, proving that were the rings such as Laplace
+thought them they must fall of their own weight.
+Then Professor J. Clerk-Maxwell, of Cambridge, took
+the matter in hand, and his analysis reduced the puzzling
+rings to a cloud of meteoric particles--a "shower
+of brickbats"--each fragment of which circulates exactly
+as if it were an independent planet, though of
+course perturbed and jostled more or less by its fellows.
+Mutual perturbations, and the disturbing pulls
+of Saturn's orthodox satellites, as investigated by Maxwell,
+explain nearly all the phenomena of the rings in
+a manner highly satisfactory.
+
+After elaborate mathematical calculations covering
+many pages of his paper entitled "On the Stability
+of Saturn's Rings," he summarizes his deductions as
+follows:
+
+"Let us now gather together the conclusions we
+have been able to draw from the mathematical theory
+of various kinds of conceivable rings.
+
+"We found that the stability of the motion of a
+solid ring depended on so delicate an adjustment, and
+at the same time so unsymmetrical a distribution of
+mass, that even if the exact conditions were fulfilled, it
+could scarcely last long, and, if it did, the immense
+preponderance of one side of the ring would be easily
+observed, contrary to experience. These considerations,
+with others derived from the mechanical structure of
+so vast a body, compel us to abandon any theory of
+solid rings.
+
+"We next examined the motion of a ring of equal
+satellites, and found that if the mass of the planet is
+sufficient, any disturbances produced in the arrangement
+of the ring will be propagated around it in the
+form of waves, and will not introduce dangerous confusion.
+If the satellites are unequal, the propagations
+of the waves will no longer be regular, but disturbances
+of the ring will in this, as in the former case,
+produce only waves, and not growing confusion. Supposing
+the ring to consist, not of a single row of large
+satellites, but a cloud of evenly distributed unconnected
+particles, we found that such a cloud must
+have a very small density in order to be permanent,
+and that this is inconsistent with its outer and inner
+parts moving with the same angular velocity. Supposing
+the ring to be fluid and continuous, we found that
+it will be necessarily broken up into small portions.
+
+"We conclude, therefore, that the rings must consist
+of disconnected particles; these must be either
+solid or liquid, but they must be independent. The
+entire system of rings must, therefore, consist either
+of a series of many concentric rings each moving with
+its own velocity and having its own system of waves,
+or else of a confused multitude of revolving particles
+not arranged in rings and continually coming into
+collision with one another.
+
+"Taking the first case, we found that in an indefinite
+number of possible cases the mutual perturbations of
+two rings, stable in themselves, might mount up in
+time to a destructive magnitude, and that such cases
+must continually occur in an extensive system like
+that of Saturn, the only retarding cause being the irregularity
+of the rings.
+
+"The result of long-continued disturbance was found
+to be the spreading-out of the rings in breadth, the
+outer rings pressing outward, while the inner rings
+press inward.
+
+"The final result, therefore, of the mechanical
+theory is that the only system of rings which can
+exist is one composed of an indefinite number of
+unconnected particles, revolving around the planet with
+different velocities, according to their respective distances.
+These particles may be arranged in series of
+narrow rings, or they may move through one another
+irregularly. In the first case the destruction of the
+system will be very slow, in the second case it will be
+more rapid, but there may be a tendency towards arrangement
+in narrow rings which may retard the
+process.
+
+"We are not able to ascertain by observation the
+constitution of the two outer divisions of the system
+of rings, but the inner ring is certainly transparent,
+for the limb of Saturn has been observed through it.
+It is also certain that though the space occupied by
+the ring is transparent, it is not through the material
+parts of it that the limb of Saturn is seen, for his limb
+was observed without distortion; which shows that
+there was no refraction, and, therefore, that the rays
+did not pass through a medium at all, but between the
+solar or liquid particles of which the ring is composed.
+Here, then, we have an optical argument in favor of
+the theory of independent particles as the material of
+the rings. The two outer rings may be of the same
+nature, but not so exceedingly rare that a ray of light
+can pass through their whole thickness without encountering
+one of the particles.
+
+"Finally, the two outer rings have been observed for
+two hundred years, and it appears, from the careful
+analysis of all the observations of M. Struve, that the
+second ring is broader than when first observed, and
+that its inner edge is nearer the planet than formerly.
+The inner ring also is suspected to be approaching
+the planet ever since its discovery in 1850. These
+appearances seem to indicate the same slow progress of
+the rings towards separation which we found to be the
+result of theory, and the remark that the inner edge
+of the inner ring is more distinct seems to indicate that
+the approach towards the planet is less rapid near the
+edge, as we had reason to conjecture. As to the apparent
+unchangeableness of the exterior diameter of
+the outer ring, we must remember that the outer rings
+are certainly far more dense than the inner one, and
+that a small change in the outer rings must balance a
+great change in the inner one. It is possible, however,
+that some of the observed changes may be due
+to the existence of a resisting medium. If the changes
+already suspected should be confirmed by repeated
+observations with the same instruments, it will be
+worth while to investigate more carefully whether
+Saturn's rings are permanent or transitory elements
+of the solar system, and whether in that part of the
+heavens we see celestial immutability or terrestrial
+corruption and generation, and the old order giving
+place to the new before our eyes."[4]
+
+
+Studies of the Moon
+
+But perhaps the most interesting accomplishments
+of mathematical astronomy--from a mundane standpoint,
+at any rate--are those that refer to the earth's
+own satellite. That seemingly staid body was long
+ago discovered to have a propensity to gain a little on
+the earth, appearing at eclipses an infinitesimal moment
+ahead of time. Astronomers were sorely puzzled
+by this act of insubordination; but at last Laplace and
+Lagrange explained it as due to an oscillatory change
+in the earth's orbit, thus fully exonerating the moon,
+and seeming to demonstrate the absolute stability of
+our planetary system, which the moon's misbehavior
+had appeared to threaten.
+
+This highly satisfactory conclusion was an orthodox
+belief of celestial mechanics until 1853, when Professor
+Adams of Neptunian fame, with whom complex analyses
+were a pastime, reviewed Laplace's calculation,
+and discovered an error which, when corrected, left
+about half the moon's acceleration unaccounted for.
+This was a momentous discrepancy, which at first no
+one could explain. But presently Professor Helmholtz,
+the great German physicist, suggested that a key
+might be found in tidal friction, which, acting as a perpetual
+brake on the earth's rotation, and affecting not
+merely the waters but the entire substance of our
+planet, must in the long sweep of time have changed its
+rate of rotation. Thus the seeming acceleration of the
+moon might be accounted for as actual retardation of
+the earth's rotation--a lengthening of the day instead
+of a shortening of the month.
+
+Again the earth was shown to be at fault, but this
+time the moon could not be exonerated, while the
+estimated stability of our system, instead of being
+re-established, was quite upset. For the tidal retardation
+is not an oscillatory change which will presently
+correct itself, like the orbital wobble, but a
+perpetual change, acting always in one direction. Unless
+fully counteracted by some opposing reaction,
+therefore (as it seems not to be), the effect must be
+cumulative, the ultimate consequences disastrous.
+The exact character of these consequences was first
+estimated by Professor G. H. Darwin in 1879. He
+showed that tidal friction, in retarding the earth, must
+also push the moon out from the parent planet on a
+spiral orbit. Plainly, then, the moon must formerly
+have been nearer the earth than at present. At some
+very remote period it must have actually touched the
+earth; must, in other words, have been thrown off from
+the then plastic mass of the earth, as a polyp buds out
+from its parent polyp. At that time the earth was spinning
+about in a day of from two to four hours.
+
+Now the day has been lengthened to twenty-four
+hours, and the moon has been thrust out to a distance
+of a quarter-million miles; but the end is not yet. The
+same progress of events must continue, till, at some remote
+period in the future, the day has come to equal
+the month, lunar tidal action has ceased, and one face of
+the earth looks out always at the moon with that same
+fixed stare which even now the moon has been brought
+to assume towards her parent orb. Should we choose to
+take even greater liberties with the future, it may be
+made to appear (though some astronomers dissent
+from this prediction) that, as solar tidal action still
+continues, the day must finally exceed the month,
+and lengthen out little by little towards coincidence
+with the year; and that the moon meantime must
+pause in its outward flight, and come swinging back
+on a descending spiral, until finally, after the lapse
+of untold aeons, it ploughs and ricochets along the
+surface of the earth, and plunges to catastrophic destruction.
+
+But even though imagination pause far short of this
+direful culmination, it still is clear that modern calculations,
+based on inexorable tidal friction, suffice to
+revolutionize the views formerly current as to the stability
+of the planetary system. The eighteenth-century
+mathematician looked upon this system as a vast celestial
+machine which had been in existence about six
+thousand years, and which was destined to run on forever.
+The analyst of to-day computes both the past
+and the future of this system in millions instead of
+thousands of years, yet feels well assured that the solar
+system offers no contradiction to those laws of growth
+and decay which seem everywhere to represent the
+immutable order of nature.
+
+
+COMETS AND METEORS
+
+Until the mathematician ferreted out the secret, it
+surely never could have been suspected by any one that
+the earth's serene attendant,
+
+ "That orbed maiden, with white fire laden,
+ Whom mortals call the moon,"
+
+could be plotting injury to her parent orb. But there
+is another inhabitant of the skies whose purposes have
+not been similarly free from popular suspicion. Needless
+to say I refer to the black sheep of the sidereal
+family, that "celestial vagabond" the comet.
+
+Time out of mind these wanderers have been supposed
+to presage war, famine, pestilence, perhaps the
+destruction of the world. And little wonder. Here is
+a body which comes flashing out of boundless space into
+our system, shooting out a pyrotechnic tail some hundreds
+of millions of miles in length; whirling, perhaps,
+through the very atmosphere of the sun at a speed of
+three or four hundred miles a second; then darting off
+on a hyperbolic orbit that forbids it ever to return, or
+an elliptical one that cannot be closed for hundreds or
+thousands of years; the tail meantime pointing always
+away from the sun, and fading to nothingness as the
+weird voyager recedes into the spatial void whence it
+came. Not many times need the advent of such an apparition
+coincide with the outbreak of a pestilence or
+the death of a Caesar to stamp the race of comets as an
+ominous clan in the minds of all superstitious generations.
+
+It is true, a hard blow was struck at the prestige of
+these alleged supernatural agents when Newton proved
+that the great comet of 1680 obeyed Kepler's laws in its
+flight about the sun; and an even harder one when the
+same visitant came back in 1758, obedient to Halley's
+prediction, after its three-quarters of a century of voyaging
+but in the abyss of space. Proved thus to bow to
+natural law, the celestial messenger could no longer
+fully, sustain its role. But long-standing notoriety cannot
+be lived down in a day, and the comet, though
+proved a "natural" object, was still regarded as a very
+menacing one for another hundred years or so. It remained
+for the nineteenth century to completely unmask
+the pretender and show how egregiously our forebears
+had been deceived.
+
+The unmasking began early in the century, when Dr.
+Olbers, then the highest authority on the subject, expressed
+the opinion that the spectacular tail, which had
+all along been the comet's chief stock-in-trade as an
+earth-threatener, is in reality composed of the most
+filmy vapors, repelled from the cometary body by the
+sun, presumably through electrical action, with a velocity
+comparable to that of light. This luminous suggestion
+was held more or less in abeyance for half a
+century. Then it was elaborated by Zollner, and
+particularly by Bredichin, of the Moscow observatory, into
+what has since been regarded as the most plausible of
+cometary theories. It is held that comets and the sun
+are similarly electrified, and hence mutually repulsive.
+Gravitation vastly outmatches this repulsion in the
+body of the comet, but yields to it in the case of gases,
+because electrical force varies with the surface, while
+gravitation varies only with the mass. From study of
+atomic weights and estimates of the velocity of thrust
+of cometary tails, Bredichin concluded that the chief
+components of the various kinds of tails are hydrogen,
+hydrocarbons, and the vapor of iron; and spectroscopic
+analysis goes far towards sustaining these
+assumptions.
+
+But, theories aside, the unsubstantialness of the
+comet's tail has been put to a conclusive test. Twice
+during the nineteenth century the earth has actually
+plunged directly through one of these threatening
+appendages--in 1819, and again in 1861, once being immersed
+to a depth of some three hundred thousand
+miles in its substance. Yet nothing dreadful happened
+to us. There was a peculiar glow in the atmosphere,
+so the more imaginative observers thought, and
+that was all. After such fiascos the cometary train
+could never again pose as a world-destroyer.
+
+But the full measure of the comet's humiliation is not
+yet told. The pyrotechnic tail, composed as it is of portions
+of the comet's actual substance, is tribute paid the
+sun, and can never be recovered. Should the obeisance
+to the sun be many times repeated, the train-forming
+material will be exhausted, and the comet's chiefest
+glory will have departed. Such a fate has actually befallen
+a multitude of comets which Jupiter and the
+other outlying planets have dragged into our system
+and helped the sun to hold captive here. Many of
+these tailless comets were known to the eighteenth-
+century astronomers, but no one at that time suspected
+the true meaning of their condition. It was not even
+known how closely some of them are enchained until
+the German astronomer Encke, in 1822, showed that
+one which he had rediscovered, and which has since
+borne his name, was moving in an orbit so contracted
+that it must complete its circuit in about three and
+a half years. Shortly afterwards another comet, revolving
+in a period of about six years, was discovered
+by Biela, and given his name. Only two more of these
+short-period comets were discovered during the first half
+of last century, but latterly they have been shown to be
+a numerous family. Nearly twenty are known which
+the giant Jupiter holds so close that the utmost reach of
+their elliptical tether does not let them go beyond
+the orbit of Saturn. These aforetime wanderers have
+adapted themselves wonderfully to planetary customs,
+for all of them revolve in the same direction with the
+planets, and in planes not wide of the ecliptic.
+
+Checked in their proud hyperbolic sweep, made captive
+in a planetary net, deprived of their trains, these
+quondam free-lances of the heavens are now mere
+shadows of their former selves. Considered as to mere
+bulk, they are very substantial shadows, their extent
+being measured in hundreds of thousands of miles; but
+their actual mass is so slight that they are quite at the
+mercy of the gravitation pulls of their captors. And
+worse is in store for them. So persistently do sun and
+planets tug at them that they are doomed presently to
+be torn into shreds.
+
+Such a fate has already overtaken one of them, under
+the very eyes of the astronomers, within the relatively
+short period during which these ill-fated comets have.
+been observed. In 1832 Biela's comet passed quite
+near the earth, as astronomers measure distance, and in
+doing so created a panic on our planet. It did no
+greater harm than that, of course, and passed on its
+way as usual. The very next time it came within telescopic
+hail it was seen to have broken into two fragments.
+Six years later these fragments were separated
+by many millions of miles; and in 1852, when the comet
+was due again, astronomers looked for it in vain. It
+had been completely shattered.
+
+What had become of the fragments? At that time
+no one positively knew. But the question was to be
+answered presently. It chanced that just at this period
+astronomers were paying much attention to a class of
+bodies which they had hitherto somewhat neglected,
+the familiar shooting-stars, or meteors. The studies of
+Professor Newton, of Yale, and Professor Adams, of
+Cambridge, with particular reference to the great
+meteor-shower of November, 1866, which Professor Newton
+had predicted and shown to be recurrent at intervals
+of thirty-three years, showed that meteors are
+not mere sporadic swarms of matter flying at random,
+but exist in isolated swarms, and sweep about the sun
+in regular elliptical orbits.
+
+Presently it was shown by the Italian astronomer
+Schiaparelli that one of these meteor swarms moves
+in the orbit of a previously observed comet, and other
+coincidences of the kind were soon forthcoming. The
+conviction grew that meteor swarms are really the
+debris of comets; and this conviction became a practical
+certainty when, in November, 1872, the earth
+crossed the orbit of the ill-starred Biela, and a shower
+of meteors came whizzing into our atmosphere in lieu
+of the lost comet.
+
+And so at last the full secret was out. The awe-
+inspiring comet, instead of being the planetary body
+it had all along been regarded, is really nothing more
+nor less than a great aggregation of meteoric particles,
+which have become clustered together out in space
+somewhere, and which by jostling one another or
+through electrical action become luminous. So widely
+are the individual particles separated that the cometary
+body as a whole has been estimated to be thousands of
+times less dense than the earth's atmosphere at sea-
+level. Hence the ease with which the comet may be
+dismembered and its particles strung out into streaming
+swarms.
+
+So thickly is the space we traverse strewn with this
+cometary dust that the earth sweeps up, according to
+Professor Newcomb's estimate, a million tons of it each
+day. Each individual particle, perhaps no larger than
+a millet seed, becomes a shooting-star, or meteor, as it
+burns to vapor in the earth's upper atmosphere. And
+if one tiny planet sweeps up such masses of this cosmic
+matter, the amount of it in the entire stretch of our system
+must be beyond all estimate. What a story it tells
+of the myriads of cometary victims that have fallen
+prey to the sun since first he stretched his planetary net
+across the heavens!
+
+
+THE FIXED STARS
+
+When Biela's comet gave the inhabitants of the earth
+such a fright in 1832, it really did not come within
+fifty millions of miles of us. Even the great comet
+through whose filmy tail the earth passed in 1861 was
+itself fourteen millions of miles away. The ordinary
+mind, schooled to measure space by the tiny stretches
+of a pygmy planet, cannot grasp the import of such
+distances; yet these are mere units of measure compared
+with the vast stretches of sidereal space. Were
+the comet which hurtles past us at a speed of, say, a
+hundred miles a second to continue its mad flight unchecked
+straight into the void of space, it must fly on
+its frigid way eight thousand years before it could
+reach the very nearest of our neighbor stars; and even
+then it would have penetrated but a mere arm's-length
+into the vistas where lie the dozen or so of sidereal residents
+that are next beyond. Even to the trained mind
+such distances are only vaguely imaginable. Yet the
+astronomer of our century has reached out across this
+unthinkable void and brought back many a secret
+which our predecessors thought forever beyond human
+grasp.
+
+A tentative assault upon this stronghold of the stars
+was being made by Herschel at the beginning of the
+century. In 1802 that greatest of observing astronomers
+announced to the Royal Society his discovery that
+certain double stars had changed their relative positions
+towards one another since he first carefully charted
+them twenty years before. Hitherto it had been supposed
+that double stars were mere optical effects. Now
+it became clear that some of them, at any rate, are
+true "binary systems," linked together presumably by
+gravitation and revolving about one another. Halley
+had shown, three-quarters of a century before, that the
+stars have an actual or "proper" motion in space;
+Herschel himself had proved that the sun shares this
+motion with the other stars. Here was another shift
+of place, hitherto quite unsuspected, to be reckoned
+with by the astronomer in fathoming sidereal secrets.
+
+
+Double Stars
+
+When John Herschel, the only son and the worthy
+successor of the great astronomer, began star-gazing in
+earnest, after graduating senior wrangler at Cambridge,
+and making two or three tentative professional starts in
+other directions to which his versatile genius impelled
+him, his first extended work was the observation of his
+father's double stars. His studies, in which at first he
+had the collaboration of Mr. James South, brought to
+light scores of hitherto unrecognized pairs, and gave
+fresh data for the calculation of the orbits of those
+longer known. So also did the independent researches
+of F. G. W. Struve, the enthusiastic observer of the
+famous Russian observatory at the university of Dorpat,
+and subsequently at Pulkowa. Utilizing data
+gathered by these observers, M. Savary, of Paris,
+showed, in 1827, that the observed elliptical orbits of
+the double stars are explicable by the ordinary laws of
+gravitation, thus confirming the assumption that Newton's
+laws apply to these sidereal bodies. Henceforth
+there could be no reason to doubt that the same force
+which holds terrestrial objects on our globe pulls at
+each and every particle of matter throughout the visible
+universe.
+
+The pioneer explorers of the double stars early found
+that the systems into which the stars are linked are by
+no means confined to single pairs. Often three or four
+stars are found thus closely connected into gravitation
+systems; indeed, there are all gradations between binary
+systems and great clusters containing hundreds or
+even thousands of members. It is known, for example,
+that the familiar cluster of the Pleiades is not merely
+an optical grouping, as was formerly supposed, but an
+actual federation of associated stars, some two thousand
+five hundred in number, only a few of which are
+visible to the unaided eve. And the more carefully
+the motions of the stars are studied, the more evident
+it becomes that widely separated stars are linked together
+into infinitely complex systems, as yet but little
+understood. At the same time, all instrumental advances
+tend to resolve more and more seemingly single
+stars into close pairs and minor clusters. The two
+Herschels between them discovered some thousands
+of these close multiple systems; Struve and others increased
+the list to above ten thousand; and Mr. S. W.
+Burnham, of late years the most enthusiastic and successful
+of double-star pursuers, added a thousand new
+discoveries while he was still an amateur in astronomy,
+and by profession the stenographer of a Chicago court.
+Clearly the actual number of multiple stars is beyond
+all present estimate.
+
+The elder Herschel's early studies of double stars
+were undertaken in the hope that these objects might
+aid him in ascertaining the actual distance of a star,
+through measurement of its annual parallax--that is to
+say, of the angle which the diameter of the earth's
+orbit would subtend as seen from the star. The expectation
+was not fulfilled. The apparent shift of
+position of a star as viewed from opposite sides of the
+earth's orbit, from which the parallax might be estimated,
+is so extremely minute that it proved utterly
+inappreciable, even to the almost preternaturally acute
+vision of Herschel, with the aid of any instrumental
+means then at command. So the problem of star distance
+allured and eluded him to the end, and he died
+in 1822 without seeing it even in prospect of solution.
+His estimate of the minimum distance of the nearest
+star, based though it was on the fallacious test of apparent
+brilliancy, was a singularly sagacious one, but it
+was at best a scientific guess, not a scientific measurement.
+
+
+The Distance of the Stars
+
+Just about this time, however, a great optician came
+to the aid of the astronomers. Joseph Fraunhofer perfected
+the refracting telescope, as Herschel had perfected
+the reflector, and invented a wonderfully accurate
+"heliometer," or sun-measurer. With the aid of
+these instruments the old and almost infinitely difficult
+problem of star distance was solved. In 1838 Bessel
+announced from the Konigsberg observatory that he
+had succeeded, after months of effort, in detecting and
+measuring the parallax of a star. Similar claims had
+been made often enough before, always to prove fallacious
+when put to further test; but this time the announcement
+carried the authority of one of the greatest
+astronomers of the age, and scepticism was silenced.
+
+Nor did Bessel's achievement long await corroboration.
+Indeed, as so often happens in fields of discovery,
+two other workers had almost simultaneously
+solved the same problem--Struve at Pulkowa, where
+the great Russian observatory, which so long held the
+palm over all others, had now been established; and
+Thomas Henderson, then working at the Cape of Good
+Hope, but afterwards the Astronomer Royal of Scotland.
+Henderson's observations had actual precedence
+in point of time, but Bessel's measurements were so
+much more numerous and authoritative that he has
+been uniformly considered as deserving the chief credit
+of the discovery, which priority of publication secured
+him.
+
+By an odd chance, the star on which Henderson's observations
+were made, and consequently the first star
+the parallax of which was ever measured, is our nearest
+neighbor in sidereal space, being, indeed, some ten billions
+of miles nearer than the one next beyond. Yet
+even this nearest star is more than two hundred thousand
+times as remote from us as the sun. The sun's
+light flashes to the earth in eight minutes, and to Neptune
+in about three and a half hours, but it requires
+three and a half years to signal Alpha Centauri. And
+as for the great majority of the stars, had they been
+blotted out of existence before the Christian era, we of
+to-day should still receive their light and seem to see
+them just as we do. When we look up to the sky, we
+study ancient history; we do not see the stars as they
+ARE, but as they WERE years, centuries, even millennia
+ago.
+
+The information derived from the parallax of a star
+by no means halts with the disclosure of the distance of
+that body. Distance known, the proper motion of the
+star, hitherto only to be reckoned as so many seconds of
+arc, may readily be translated into actual speed of progress;
+relative brightness becomes absolute lustre, as
+compared with the sun; and in the case of the double
+stars the absolute mass of the components may be computed
+from the laws of gravitation. It is found that
+stars differ enormously among themselves in all these
+regards. As to speed, some, like our sun, barely creep
+through space--compassing ten or twenty miles a second,
+it is true, yet even at that rate only passing
+through the equivalent of their own diameter in a day.
+At the other extreme, among measured stars, is one
+that moves two hundred miles a second; yet even this
+"flying star," as seen from the earth, seems to change
+its place by only about three and a half lunar diameters
+in a thousand years. In brightness, some stars yield to
+the sun, while others surpass him as the arc-light surpasses
+a candle. Arcturus, the brightest measured star,
+shines like two hundred suns; and even this giant orb
+is dim beside those other stars which are so distant that
+their parallax cannot be measured, yet which greet our
+eyes at first magnitude. As to actual bulk, of which
+apparent lustre furnishes no adequate test, some stars
+are smaller than the sun, while others exceed him hundreds
+or perhaps thousands of times. Yet one and all,
+so distant are they, remain mere disklike points of light
+before the utmost powers of the modern telescope.
+
+
+Revelations of the Spectroscope
+
+All this seems wonderful enough, but even greater
+things were in store. In 1859 the spectroscope came
+upon the scene, perfected by Kirchhoff and Bunsen,
+along lines pointed out by Fraunhofer almost half a
+century before. That marvellous instrument, by
+revealing the telltale lines sprinkled across a prismatic
+spectrum, discloses the chemical nature and physical
+condition of any substance whose light is submitted to
+it, telling its story equally well, provided the light be
+strong enough, whether the luminous substance be near
+or far--in the same room or at the confines of space.
+Clearly such an instrument must prove a veritable
+magic wand in the hands of the astronomer.
+
+Very soon eager astronomers all over the world were
+putting the spectroscope to the test. Kirchhoff himself
+led the way, and Donati and Father Secchi in Italy,
+Huggins and Miller in England, and Rutherfurd in
+America, were the chief of his immediate followers.
+The results exceeded the dreams of the most visionary.
+At the very outset, in 1860, it was shown that such
+common terrestrial substances as sodium, iron, calcium,
+magnesium, nickel, barium, copper, and zinc exist
+in the form of glowing vapors in the sun, and very soon
+the stars gave up a corresponding secret. Since then
+the work of solar and sidereal analysis has gone on
+steadily in the hands of a multitude of workers (prominent
+among whom, in this country, are Professor
+Young of Princeton, Professor Langley of Washington,
+and Professor Pickering of Harvard), and more
+than half the known terrestrial elements have been
+definitely located in the sun, while fresh discoveries
+are in prospect.
+
+It is true the sun also contains some seeming elements
+that are unknown on the earth, but this is no
+matter for surprise. The modern chemist makes no
+claim for his elements except that they have thus far
+resisted all human efforts to dissociate them; it would
+be nothing strange if some of them, when subjected to
+the crucible of the sun, which is seen to vaporize iron,
+nickel, silicon, should fail to withstand the test. But
+again, chemistry has by no means exhausted the resources
+of the earth's supply of raw material, and the
+substance which sends its message from a star may
+exist undiscovered in the dust we tread or in the air
+we breathe. In the year 1895 two new terrestrial elements
+were discovered; but one of these had for years
+been known to the astronomer as a solar and suspected
+as a stellar element, and named helium because of its
+abundance in the sun. The spectroscope had reached
+out millions of miles into space and brought back this
+new element, and it took the chemist a score of years
+to discover that he had all along had samples of the
+same substance unrecognized in his sublunary laboratory.
+There is hardly a more picturesque fact than
+that in the entire history of science.
+
+But the identity in substance of earth and sun and
+stars was not more clearly shown than the diversity of
+their existing physical conditions. It was seen that sun
+and stars, far from being the cool, earthlike, habitable
+bodies that Herschel thought them (surrounded by
+glowing clouds, and protected from undue heat by other
+clouds), are in truth seething caldrons of fiery liquid, or
+gas made viscid by condensation, with lurid envelopes
+of belching flames. It was soon made clear, also,
+particularly by the studies of Rutherfurd and of Secchi,
+that stars differ among themselves in exact constitution
+or condition. There are white or Sirian stars, whose
+spectrum revels in the lines of hydrogen; yellow or
+solar stars (our sun being the type), showing various
+metallic vapors; and sundry red stars, with banded
+spectra indicative of carbon compounds; besides the
+purely gaseous stars of more recent discovery, which
+Professor Pickering had specially studied. Zollner's
+famous interpretation of these diversities, as indicative
+of varying stages of cooling, has been called in question
+as to the exact sequence it postulates, but the general
+proposition that stars exist under widely varying conditions
+of temperature is hardly in dispute.
+
+The assumption that different star types mark varying
+stages of cooling has the further support of modern
+physics, which has been unable to demonstrate any way
+in which the sun's radiated energy may be restored, or
+otherwise made perpetual, since meteoric impact has
+been shown to be--under existing conditions, at any
+rate--inadequate. In accordance with the theory of
+Helmholtz, the chief supply of solar energy is held to
+be contraction of the solar mass itself; and plainly this
+must have its limits. Therefore, unless some means as
+yet unrecognized is restoring the lost energy to the
+stellar bodies, each of them must gradually lose its lustre,
+and come to a condition of solidification, seeming
+sterility, and frigid darkness. In the case of our own
+particular star, according to the estimate of Lord
+Kelvin, such a culmination appears likely to occur
+within a period of five or six million years.
+
+
+The Astronomy of the Invisible
+
+But by far the strongest support of such a forecast as
+this is furnished by those stellar bodies which even now
+appear to have cooled to the final stage of star development
+and ceased to shine. Of this class examples in
+miniature are furnished by the earth and the smaller of
+its companion planets. But there are larger bodies of
+the same type out in stellar space--veritable "dark
+stars"--invisible, of course, yet nowadays clearly recognized.
+
+The opening up of this "astronomy of the invisible"
+is another of the great achievements of the nineteenth
+century, and again it is Bessel to whom the honor of
+discovery is due. While testing his stars for parallax;
+that astute observer was led to infer, from certain
+unexplained aberrations of motion, that various stars,
+Sirius himself among the number, are accompanied by
+invisible companions, and in 1840 he definitely predicated
+the existence of such "dark stars." The correctness
+of the inference was shown twenty years
+later, when Alvan Clark, Jr., the American optician,
+while testing a new lens, discovered the companion of
+Sirius, which proved thus to be faintly luminous.
+Since then the existence of other and quite invisible
+star companions has been proved incontestably, not
+merely by renewed telescopic observations, but by the
+curious testimony of the ubiquitous spectroscope.
+
+One of the most surprising accomplishments of that
+instrument is the power to record the flight of a luminous
+object directly in the line of vision. If the luminous
+body approaches swiftly, its Fraunhofer lines are
+shifted from their normal position towards the violet
+end of the spectrum; if it recedes, the lines shift in the
+opposite direction. The actual motion of stars whose
+distance is unknown may be measured in this way.
+But in certain cases the light lines are seen to oscillate
+on the spectrum at regular intervals. Obviously the
+star sending such light is alternately approaching and
+receding, and the inference that it is revolving about a
+companion is unavoidable. From this extraordinary
+test the orbital distance, relative mass, and actual
+speed of revolution of the absolutely invisible body
+may be determined. Thus the spectroscope, which
+deals only with light, makes paradoxical excursions
+into the realm of the invisible. What secrets may the
+stars hope to conceal when questioned by an instrument
+of such necromantic power?
+
+But the spectroscope is not alone in this audacious
+assault upon the strongholds of nature. It has a worthy
+companion and assistant in the photographic film,
+whose efficient aid has been invoked by the astronomer
+even more recently. Pioneer work in celestial
+photography was, indeed, done by Arago in France and
+by the elder Draper in America in 1839, but the results
+then achieved were only tentative, and it was not till
+forty years later that the method assumed really important
+proportions. In 1880, Dr. Henry Draper, at
+Hastings-on-the-Hudson, made the first successful
+photograph of a nebula. Soon after, Dr. David Gill,
+at the Cape observatory, made fine photographs of a
+comet, and the flecks of starlight on his plates first
+suggested the possibilities of this method in charting
+the heavens.
+
+Since then star-charting with the film has come virtually
+to supersede the old method. A concerted effort
+is being made by astronomers in various parts of the
+world to make a complete chart of the heavens, and
+before the close of our century this work will be accomplished,
+some fifty or sixty millions of visible stars being
+placed on record with a degree of accuracy hitherto
+unapproachable. Moreover, other millions of stars
+are brought to light by the negative, which are too distant
+or dim to be visible with any telescopic powers
+yet attained--a fact which wholly discredits all previous
+inferences as to the limits of our sidereal system.
+Hence, notwithstanding the wonderful instrumental
+advances of the nineteenth century, knowledge of the
+exact form and extent of our universe seems more
+unattainable than it seemed a century ago.
+
+
+The Structure of Nebulae
+
+Yet the new instruments, while leaving so much
+untold, have revealed some vastly important secrets of
+cosmic structure. In particular, they have set at rest
+the long-standing doubts as to the real structure and
+position of the mysterious nebulae--those lazy masses,
+only two or three of them visible to the unaided eye,
+which the telescope reveals in almost limitless abundance,
+scattered everywhere among the stars, but
+grouped in particular about the poles of the stellar
+stream or disk which we call the Milky Way.
+
+Herschel's later view, which held that some at least
+of the nebulae are composed of a "shining fluid," in
+process of condensation to form stars, was generally
+accepted for almost half a century. But in 1844, when
+Lord Rosse's great six-foot reflector--the largest telescope
+ever yet constructed--was turned on the nebulae,
+it made this hypothesis seem very doubtful. Just as
+Galileo's first lens had resolved the Milky Way into
+stars, just as Herschel had resolved nebulae that resisted
+all instruments but his own, so Lord Rosse's even
+greater reflector resolved others that would not yield to
+Herschel's largest mirror. It seemed a fair inference
+that with sufficient power, perhaps some day to be attained,
+all nebulae would yield, hence that all are in
+reality what Herschel had at first thought them--
+vastly distant "island universes," composed of aggregations
+of stars, comparable to our own galactic system.
+
+But the inference was wrong; for when the spectroscope
+was first applied to a nebula in 1864, by Dr. Huggins,
+it clearly showed the spectrum not of discrete
+stars, but of a great mass of glowing gases, hydrogen
+among others. More extended studies showed, it is
+true, that some nebulae give the continuous spectrum
+of solids or liquids, but the different types intermingle
+and grade into one another. Also, the closest affinity
+is shown between nebulae and stars. Some nebulae are
+found to contain stars, singly or in groups, in their
+actual midst; certain condensed "planetary" nebulae
+are scarcely to be distinguished from stars of the gaseous
+type; and recently the photographic film has
+shown the presence of nebulous matter about stars
+that to telescopic vision differ in no respect from the
+generality of their fellows in the galaxy. The familiar
+stars of the Pleiades cluster, for example, appear on the
+negative immersed in a hazy blur of light. All in all,
+the accumulated impressions of the photographic film
+reveal a prodigality of nebulous matter in the stellar
+system not hitherto even conjectured.
+
+And so, of course, all question of "island universes"
+vanishes, and the nebulae are relegated to their true position
+as component parts of the one stellar system--the
+one universe--that is open to present human inspection.
+And these vast clouds of world-stuff have been found
+by Professor Keeler, of the Lick observatory, to be
+floating through space at the starlike speed of from
+ten to thirty-eight miles per second.
+
+The linking of nebulae with stars, so clearly evidenced
+by all these modern observations, is, after all,
+only the scientific corroboration of what the elder Herschel's
+later theories affirmed. But the nebulae have
+other affinities not until recently suspected; for the
+spectra of some of them are practically identical with
+the spectra of certain comets. The conclusion seems
+warranted that comets are in point of fact minor nebulae
+that are drawn into our system; or, putting it otherwise,
+that the telescopic nebulae are simply gigantic
+distant comets.
+
+
+Lockyer's Meteoric Hypothesis
+
+Following up the surprising clews thus suggested,
+Sir Norman Lockyer, of London, has in recent years
+elaborated what is perhaps the most comprehensive
+cosmogonic guess that has ever been attempted. His
+theory, known as the "meteoric hypothesis," probably
+bears the same relation to the speculative thought of
+our time that the nebular hypothesis of Laplace bore
+to that of the eighteenth century. Outlined in a few
+words, it is an attempt to explain all the major phenomena
+of the universe as due, directly or indirectly, to
+the gravitational impact of such meteoric particles, or
+specks of cosmic dust, as comets are composed of. Nebulae
+are vast cometary clouds, with particles more or
+less widely separated, giving off gases through meteoric
+collisions, internal or external, and perhaps glowing also
+with electrical or phosphorescent light. Gravity eventually
+brings the nebular particles into closer aggregations,
+and increased collisions finally vaporize the entire
+mass, forming planetary nebulae and gaseous stars.
+Continued condensation may make the stellar mass
+hotter and more luminous for a time, but eventually
+leads to its liquefaction, and ultimate consolidation--
+the aforetime nebulae becoming in the end a dark or
+planetary star.
+
+The exact correlation which Lockyer attempts to
+point out between successive stages of meteoric condensation
+and the various types of observed stellar bodies
+does not meet with unanimous acceptance. Mr.
+Ranyard, for example, suggests that the visible nebulae
+may not be nascent stars, but emanations from stars,
+and that the true pre-stellar nebulae are invisible until
+condensed to stellar proportions. But such details
+aside, the broad general hypothesis that all the bodies
+of the universe are, so to speak, of a single species--
+that nebulae (including comets), stars of all types, and
+planets, are but varying stages in the life history of a
+single race or type of cosmic organisms--is accepted
+by the dominant thought of our time as having the
+highest warrant of scientific probability.
+
+All this, clearly, is but an amplification of that nebular
+hypothesis which, long before the spectroscope gave
+us warrant to accurately judge our sidereal neighbors,
+had boldly imagined the development of stars out of
+nebulae and of planets out of stars. But Lockyer's
+hypothesis does not stop with this. Having traced the
+developmental process from the nebular to the dark
+star, it sees no cause to abandon this dark star to its
+fate by assuming, as the original speculation assumed,
+that this is a culminating and final stage of cosmic existence.
+For the dark star, though its molecular activities
+have come to relative stability and impotence,
+still retains the enormous potentialities of molar motion;
+and clearly, where motion is, stasis is not. Sooner
+or later, in its ceaseless flight through space, the dark
+star must collide with some other stellar body, as Dr.
+Croll imagines of the dark bodies which his "pre-nebular
+theory" postulates. Such collision may be long
+delayed; the dark star may be drawn in comet-like circuit
+about thousands of other stellar masses, and be
+hurtled on thousands of diverse parabolic or elliptical
+orbits, before it chances to collide--but that matters
+not: "billions are the units in the arithmetic of eternity,"
+and sooner or later, we can hardly doubt, a collision
+must occur. Then without question the mutual
+impact must shatter both colliding bodies into vapor,
+or vapor combined with meteoric fragments; in short,
+into a veritable nebula, the matrix of future worlds.
+Thus the dark star, which is the last term of one series
+of cosmic changes, becomes the first term of another
+series--at once a post-nebular and a pre-nebular condition;
+and the nebular hypothesis, thus amplified,
+ceases to be a mere linear scale, and is rounded out to
+connote an unending series of cosmic cycles, more
+nearly satisfying the imagination.
+
+In this extended view, nebulae and luminous stars are
+but the infantile and adolescent stages of the life history
+of the cosmic individual; the dark star, its adult
+stage, or time of true virility. Or we may think of the
+shrunken dark star as the germ-cell, the pollen-grain, of
+the cosmic organism. Reduced in size, as becomes a
+germ-cell, to a mere fraction of the nebular body from
+which it sprang, it yet retains within its seemingly non-
+vital body all the potentialities of the original organism,
+and requires only to blend with a fellow-cell to
+bring a new generation into being. Thus may the
+cosmic race, whose aggregate census makes up the
+stellar universe, be perpetuated--individual solar systems,
+such as ours, being born, and growing old, and
+dying to live again in their descendants, while the universe
+as a whole maintains its unified integrity throughout
+all these internal mutations--passing on, it may be,
+by infinitesimal stages, to a culmination hopelessly beyond
+human comprehension.
+
+
+
+III. THE NEW SCIENCE OF PALEONTOLOGY
+
+WILLIAM SMITH AND FOSSIL SHELLS
+
+Ever since Leonardo da Vinci first recognized the
+true character of fossils, there had been here and
+there a man who realized that the earth's rocky crust
+is one gigantic mausoleum. Here and there a dilettante
+had filled his cabinets with relics from this monster
+crypt; here and there a philosopher had pondered
+over them--questioning whether perchance they had
+once been alive, or whether they were not mere
+abortive souvenirs of that time when the fertile matrix
+of the earth was supposed to have
+
+          "teemed at a birth
+ Innumerous living creatures, perfect forms,
+ Limbed and full grown."
+
+Some few of these philosophers--as Robert Hooke and
+Steno in the seventeenth century, and Moro, Leibnitz,
+Buffon, Whitehurst, Werner, Hutton, and others in the
+eighteenth--had vaguely conceived the importance of
+fossils as records of the earth's ancient history, but the
+wisest of them no more suspected the full import of the
+story written in the rocks than the average stroller in
+a modern museum suspects the meaning of the hieroglyphs
+on the case of a mummy.
+
+It was not that the rudiments of this story are so
+very hard to decipher--though in truth they are hard
+enough--but rather that the men who made the attempt
+had all along viewed the subject through an atmosphere
+of preconception, which gave a distorted
+image. Before this image could be corrected it was
+necessary that a man should appear who could see
+without prejudice, and apply sound common-sense to
+what he saw. And such a man did appear towards the
+close of the century, in the person of William Smith, the
+English surveyor. He was a self-taught man, and perhaps
+the more independent for that, and he had the
+gift, besides his sharp eyes and receptive mind, of a
+most tenacious memory. By exercising these faculties,
+rare as they are homely, he led the way to a
+science which was destined, in its later developments,
+to shake the structure of established thought to its
+foundations.
+
+Little enough did William Smith suspect, however,
+that any such dire consequences were to come of his act
+when he first began noticing the fossil shells that here
+and there are to be found in the stratified rocks and
+soils of the regions over which his surveyor's duties led
+him. Nor, indeed, was there anything of such apparent
+revolutionary character in the facts which he
+unearthed; yet in their implications these facts were
+the most disconcerting of any that had been revealed
+since the days of Copernicus and Galileo. In its bald
+essence, Smith's discovery was simply this: that the
+fossils in the rocks, instead of being scattered haphazard,
+are arranged in regular systems, so that any
+given stratum of rock is labelled by its fossil population;
+and that the order of succession of such groups of
+fossils is always the same in any vertical series of strata
+in which they occur. That is to say, if fossil A underlies
+fossil B in any given region, it never overlies it in
+any other series; though a kind of fossils found in one
+set of strata may be quite omitted in another. Moreover,
+a fossil once having disappeared never reappears
+in any later stratum.
+
+From these novel facts Smith drew the commonsense
+inference that the earth had had successive populations
+of creatures, each of which in its turn had become
+extinct. He partially verified this inference by
+comparing the fossil shells with existing species of similar
+orders, and found that such as occur in older
+strata of the rocks had no counterparts among living
+species. But, on the whole, being eminently a practical
+man, Smith troubled himself but little about the inferences
+that might be drawn from his facts. He was
+chiefly concerned in using the key he had discovered
+as an aid to the construction of the first geological map
+of England ever attempted, and he left to others the
+untangling of any snarls of thought that might seem
+to arise from his discovery of the succession of varying
+forms of life on the globe.
+
+He disseminated his views far and wide, however, in
+the course of his journeyings--quite disregarding the
+fact that peripatetics went out of fashion when the
+printing-press came in--and by the beginning of the
+nineteenth century he had begun to have a following
+among the geologists of England. It must not for a
+moment be supposed, however, that his contention regarding
+the succession of strata met with immediate
+or general acceptance. On the contrary, it was most
+bitterly antagonized. For a long generation after the
+discovery was made, the generality of men, prone as
+always to strain at gnats and swallow camels, preferred
+to believe that the fossils, instead of being deposited in
+successive ages, had been swept all at once into their
+present positions by the current of a mighty flood--and
+that flood, needless to say, the Noachian deluge. Just
+how the numberless successive strata could have been
+laid down in orderly sequence to the depth of several
+miles in one such fell cataclysm was indeed puzzling,
+especially after it came to be admitted that the heaviest
+fossils were not found always at the bottom; but to
+doubt that this had been done in some way was rank
+heresy in the early days of the nineteenth century.
+
+
+CUVIER AND FOSSIL VERTEBRATES
+
+But once discovered, William Smith's unique facts
+as to the succession of forms in the rocks would not
+down. There was one most vital point, however, regarding
+which the inferences that seem to follow from
+these facts needed verification--the question, namely,
+whether the disappearance of a fauna from the register
+in the rocks really implies the extinction of that fauna.
+Everything really depended upon the answer to that
+question, and none but an accomplished naturalist
+could answer it with authority. Fortunately, the most
+authoritative naturalist of the time, George Cuvier,
+took the question in hand--not, indeed, with the idea
+of verifying any suggestion of Smith's, but in the course
+of his own original studies--at the very beginning of
+the century, when Smith's views were attracting general
+attention.
+
+Cuvier and Smith were exact contemporaries, both
+men having been born in 1769, that "fertile year"
+which gave the world also Chateaubriand, Von Humboldt,
+Wellington, and Napoleon. But the French naturalist
+was of very different antecedents from the English
+surveyor. He was brilliantly educated, had early
+gained recognition as a scientist, and while yet a young
+man had come to be known as the foremost comparative
+anatomist of his time. It was the anatomical
+studies that led him into the realm of fossils. Some
+bones dug out of the rocks by workmen in a quarry
+were brought to his notice, and at once his trained eye
+told him that they were different from anything he had
+seen before. Hitherto such bones, when not entirely
+ignored, had been for the most part ascribed to giants
+of former days, or even to fallen angels. Cuvier soon
+showed that neither giants nor angels were in question,
+but elephants of an unrecognized species. Continuing
+his studies, particularly with material gathered from
+gypsum beds near Paris, he had accumulated, by the
+beginning of the nineteenth century, bones of about
+twenty-five species of animals that he believed to be
+different from any now living on the globe.
+
+The fame of these studies went abroad, and presently
+fossil bones poured in from all sides, and Cuvier's conviction
+that extinct forms of animals are represented
+among the fossils was sustained by the evidence of
+many strange and anomalous forms, some of them of
+gigantic size. In 1816 the famous Ossements Fossiles,
+describing these novel objects, was published, and vertebrate
+paleontology became a science. Among other
+things of great popular interest the book contained the
+first authoritative description of the hairy elephant,
+named by Cuvier the mammoth, the remains of which
+bad been found embedded in a mass of ice in Siberia in
+1802, so wonderfully preserved that the dogs of the
+Tungusian fishermen actually ate its flesh. Bones of
+the same species had been found in Siberia several
+years before by the naturalist Pallas, who had also
+found the carcass of a rhinoceros there, frozen in a
+mud-bank; but no one then suspected that these were
+members of an extinct population--they were supposed
+to be merely transported relics of the flood.
+
+Cuvier, on the other hand, asserted that these and the
+other creatures he described had lived and died in the
+region where their remains were found, and that most
+of them have no living representatives upon the globe.
+This, to be sure, was nothing more than William Smith
+had tried all along to establish regarding lower forms of
+life; but flesh and blood monsters appeal to the imagination
+in a way quite beyond the power of mere shells;
+so the announcement of Cuvier's discoveries aroused
+the interest of the entire world, and the Ossements
+Fossiles was accorded a popular reception seldom
+given a work of technical science--a reception in
+which the enthusiastic approval of progressive geologists
+was mingled with the bitter protests of the conservatives.
+
+
+"Naturalists certainly have neither explored all the
+continents," said Cuvier, "nor do they as yet even know
+all the quadrupeds of those parts which have been explored.
+New species of this class are discovered from
+time to time; and those who have not examined with
+attention all the circumstances belonging to these discoveries
+may allege also that the unknown quadrupeds,
+whose fossil bones have been found in the strata
+of the earth, have hitherto remained concealed in
+some islands not yet discovered by navigators, or in
+some of the vast deserts which occupy the middle of
+Africa, Asia, the two Americas, and New Holland.
+
+"But if we carefully attend to the kind of quadrupeds
+that have been recently discovered, and to the
+circumstances of their discovery, we shall easily perceive
+that there is very little chance indeed of our ever
+finding alive those which have only been seen in a
+fossil state.
+
+"Islands of moderate size, and at a considerable distance
+from the large continents, have very few quadrupeds.
+These must have been carried to them from
+other countries. Cook and Bougainville found no
+other quadrupeds besides hogs and dogs in the South
+Sea Islands; and the largest quadruped of the West
+India Islands, when first discovered, was the agouti, a
+species of the cavy, an animal apparently between the
+rat and the rabbit.
+
+"It is true that the great continents, as Asia, Africa,
+the two Americas, and New Holland, have large quadrupeds,
+and, generally speaking, contain species common
+to each; insomuch, that upon discovering countries
+which are isolated from the rest of the world, the
+animals they contain of the class of quadruped were
+found entirely different from those which existed in
+other countries. Thus, when the Spaniards first penetrated
+into South America, they did not find it to contain
+a single quadruped exactly the same with those of
+Europe, Asia, and Africa. The puma, the jaguar, the
+tapir, the capybara, the llama, or glama, and vicuna,
+and the whole tribe of sapajous, were to them entirely
+new animals, of which they had not the smallest
+idea....
+
+"If there still remained any great continent to be
+discovered, we might perhaps expect to be made acquainted
+with new species of large quadrupeds, among
+which some might be found more or less similar to those
+of which we find the exuviae in the bowels of the earth.
+But it is merely sufficient to glance the eye over the
+maps of the world and observe the innumerable directions
+in which navigators have traversed the ocean,
+in order to be satisfied that there does not remain any
+large land to be discovered, unless it may be situated
+towards the Antarctic Pole, where eternal ice necessarily
+forbids the existence of animal life."[1]
+
+Cuvier then points out that the ancients were well
+acquainted with practically all the animals on the
+continents of Europe, Asia, and Africa now known to
+scientists. He finds little grounds, therefore, for belief
+in the theory that at one time there were monstrous
+animals on the earth which it was necessary to destroy
+in order that the present fauna and men might flourish.
+After reviewing these theories and beliefs in detail, he
+takes up his Inquiry Respecting the Fabulous Animals
+of the Ancients. "It is easy," he says, "to reply to
+the foregoing objections, by examining the descriptions
+that are left us by the ancients of those unknown animals,
+and by inquiring into their origins. Now that
+the greater number of these animals have an origin,
+the descriptions given of them bear the most unequivocal
+marks; as in almost all of them we see merely the
+different parts of known animals united by an unbridled
+imagination, and in contradiction to every established
+law of nature."[2]
+
+Having shown how the fabulous monsters of ancient
+times and of foreign nations, such as the Chinese, were
+simply products of the imagination, having no prototypes
+in nature, Cuvier takes up the consideration of the
+difficulty of distinguishing the fossil bones of quadrupeds.
+
+We shall have occasion to revert to this part of Cuvier's
+paper in another connection. Here it suffices to
+pass at once to the final conclusion that the fossil bones
+in question are the remains of an extinct fauna, the like
+of which has no present-day representation on the
+earth. Whatever its implications, this conclusion now
+seemed to Cuvier to be fully established.
+
+In England the interest thus aroused was sent to
+fever-heat in 1821 by the discovery of abundant beds
+of fossil bones in the stalagmite-covered floor of a cave
+at Kirkdale, Yorkshire which went to show that England,
+too, had once had her share of gigantic beasts.
+Dr. Buckland, the incumbent of the chair of geology
+at Oxford, and the most authoritative English geologist
+of his day, took these finds in hand and showed that
+the bones belonged to a number of species, including
+such alien forms as elephants, rhinoceroses, hippopotami,
+and hyenas. He maintained that all of these
+creatures had actually lived in Britain, and that the
+caves in which their bones were found had been the
+dens of hyenas.
+
+The claim was hotly disputed, as a matter of course.
+As late as 1827 books were published denouncing Buckland,
+doctor of divinity though he was, as one who had
+joined in an "unhallowed cause," and reiterating the old
+cry that the fossils were only remains of tropical species
+washed thither by the deluge. That they were found
+in solid rocks or in caves offered no difficulty, at least
+not to the fertile imagination of Granville Penn, the
+leader of the conservatives, who clung to the old idea
+of Woodward and Cattcut that the deluge had dissolved
+the entire crust of the earth to a paste, into
+which the relics now called fossils had settled. The
+caves, said Mr. Penn, are merely the result of gases
+given off by the carcasses during decomposition--
+great air-bubbles, so to speak, in the pasty mass, becoming
+caverns when the waters receded and the paste
+hardened to rocky consistency.
+
+But these and such-like fanciful views were doomed
+even in the day of their utterance. Already in 1823
+other gigantic creatures, christened ichthyosaurus and
+plesiosaurus by Conybeare, had been found in deeper
+strata of British rocks; and these, as well as other
+monsters whose remains were unearthed in various parts
+of the world, bore such strange forms that even the
+most sceptical could scarcely hope to find their counterparts
+among living creatures. Cuvier's contention that
+all the larger vertebrates of the existing age are known
+to naturalists was borne out by recent explorations,
+and there seemed no refuge from the conclusion that
+the fossil records tell of populations actually extinct.
+But if this were admitted, then Smith's view that there
+have been successive rotations of population could no
+longer be denied. Nor could it be in doubt that the
+successive faunas, whose individual remains have been
+preserved in myriads, representing extinct species by
+thousands and tens of thousands, must have required
+vast periods of time for the production and growth of
+their countless generations.
+
+As these facts came to be generally known, and as it
+came to be understood in addition that the very matrix
+of the rock in which fossils are imbedded is in
+many cases one gigantic fossil, composed of the remains
+of microscopic forms of life, common-sense,
+which, after all, is the final tribunal, came to the aid of
+belabored science. It was conceded that the only
+tenable interpretation of the record in the rocks is that
+numerous populations of creatures, distinct from one
+another and from present forms, have risen and passed
+away; and that the geologic ages in which these creatures
+lived were of inconceivable length. The rank and
+file came thus, with the aid of fossil records, to realize
+the import of an idea which James Hutton, and here and
+there another thinker, had conceived with the swift intuition
+of genius long before the science of paleontology
+came into existence. The Huttonian proposition
+that time is long had been abundantly established,
+and by about the close of the first third of the last
+century geologists had begun to speak of "ages" and
+"untold aeons of time" with a familiarity which their
+predecessors had reserved for days and decades.
+
+
+CHARLES LYELL COMBATS CATASTROPHISM
+
+And now a new question pressed for solution. If the
+earth has been inhabited by successive populations of
+beings now extinct, how have all these creatures been
+destroyed? That question, however, seemed to present
+no difficulties. It was answered out of hand by the
+application of an old idea. All down the centuries,
+whatever their varying phases of cosmogonic thought,
+there had been ever present the idea that past times
+were not as recent times; that in remote epochs the
+earth had been the scene of awful catastrophes that
+have no parallel in "these degenerate days." Naturally
+enough, this thought, embalmed in every cosmogonic
+speculation of whatever origin, was appealed to in
+explanation of the destruction of these hitherto unimagined
+hosts, which now, thanks to science, rose from
+their abysmal slumber as incontestable, but also as
+silent and as thought-provocative, as Sphinx or pyramid.
+These ancient hosts, it was said, have been exterminated
+at intervals of odd millions of years by the recurrence
+of catastrophes of which the Mosaic deluge is
+the latest, but perhaps not the last.
+
+This explanation had fullest warrant of scientific authority.
+Cuvier had prefaced his classical work with
+a speculative disquisition whose very title (Discours
+sur les Revolutions du Globe) is ominous of
+catastrophism, and whose text fully sustains the augury.
+And Buckland, Cuvier's foremost follower across the
+Channel, had gone even beyond the master, naming
+the work in which he described the Kirkdale fossils,
+Reliquiae Diluvianae, or Proofs of a Universal Deluge.
+
+Both these authorities supposed the creatures whose
+remains they studied to have perished suddenly in the
+mighty flood whose awful current, as they supposed,
+gouged out the modern valleys and hurled great blocks
+of granite broadcast over the land. And they invoked
+similar floods for the extermination of previous populations.
+
+It is true these scientific citations had met with only
+qualified approval at the time of their utterance, because
+then the conservative majority of mankind did
+not concede that there had been a plurality of populations
+or revolutions; but now that the belief in past
+geologic ages had ceased to be a heresy, the recurring
+catastrophes of the great paleontologists were accepted
+with acclaim. For the moment science and tradition
+were at one, and there was a truce to controversy, except
+indeed in those outlying skirmish-lines of thought
+whither news from headquarters does not permeate till
+it has become ancient history at its source.
+
+The truce, however, was not for long. Hardly had
+contemporary thought begun to adjust itself to the
+conception of past ages of incomprehensible extent,
+each terminated by a catastrophe of the Noachian
+type, when a man appeared who made the utterly bewildering
+assertion that the geological record, instead
+of proving numerous catastrophic revolutions in the
+earth's past history, gives no warrant to the pretensions
+of any universal catastrophe whatever, near or
+remote.
+
+This iconoclast was Charles Lyell, the Scotchman,
+who was soon to be famous as the greatest geologist of
+his time. As a young man he had become imbued with
+the force of the Huttonian proposition, that present
+causes are one with those that produced the past
+changes of the globe, and he carried that idea to what
+he conceived to be its logical conclusion. To his mind
+this excluded the thought of catastrophic changes in
+either inorganic or organic worlds.
+
+But to deny catastrophism was to suggest a revolution
+in current thought. Needless to say, such revolution
+could not be effected without a long contest. For
+a score of years the matter was argued pro and con.,
+often with most unscientific ardor. A mere outline of
+the controversy would fill a volume; yet the essential
+facts with which Lyell at last established his proposition,
+in its bearings on the organic world, may be epitomized
+in a few words. The evidence which seems to tell
+of past revolutions is the apparently sudden change of
+fossils from one stratum to another of the rocks. But
+Lyell showed that this change is not always complete.
+Some species live on from one alleged epoch
+into the next. By no means all the contemporaries
+of the mammoth are extinct, and numerous marine
+forms vastly more ancient still have living representatives.
+
+Moreover, the blanks between strata in any particular
+vertical series are amply filled in with records in the
+form of thick strata in some geographically distant
+series. For example, in some regions Silurian rocks are
+directly overlaid by the coal measures; but elsewhere
+this sudden break is filled in with the Devonian rocks
+that tell of a great "age of fishes." So commonly are
+breaks in the strata in one region filled up in another
+that we are forced to conclude that the record shown
+by any single vertical series is of but local significance--
+telling, perhaps, of a time when that particular sea-bed
+oscillated above the water-line, and so ceased to receive
+sediment until some future age when it had oscillated
+back again. But if this be the real significance of the
+seemingly sudden change from stratum to stratum,
+then the whole case for catastrophism is hopelessly lost;
+for such breaks in the strata furnish the only suggestion
+geology can offer of sudden and catastrophic changes
+of wide extent.
+
+Let us see how Lyell elaborates these ideas, particularly
+with reference to the rotation of species.[2]
+
+"I have deduced as a corollary," he says, "that the
+species existing at any particular period must, in the
+course of ages, become extinct, one after the other.
+'They must die out,' to borrow an emphatic expression
+from Buffon, 'because Time fights against them.' If the
+views which I have taken are just, there will be no
+difficulty in explaining why the habitations of so many
+species are now restrained within exceeding narrow
+limits. Every local revolution tends to circumscribe
+the range of some species, while it enlarges that of
+others; and if we are led to infer that new species originate
+in one spot only, each must require time to diffuse
+itself over a wide area. It will follow, therefore, from
+the adoption of our hypothesis that the recent origin
+of some species and the high antiquity of others are
+equally consistent with the general fact of their limited
+distribution, some being local because they have not
+existed long enough to admit of their wide dissemination;
+others, because circumstances in the animate or
+inanimate world have occurred to restrict the range
+within which they may once have obtained. . . .
+
+"If the reader should infer, from the facts laid before
+him, that the successive extinction of animals and
+plants may be part of the constant and regular course
+of nature, he will naturally inquire whether there are
+any means provided for the repair of these losses? Is
+it possible as a part of the economy of our system that
+the habitable globe should to a certain extent become
+depopulated, both in the ocean and on the land, or
+that the variety of species should diminish until some
+new era arrives when a new and extraordinary effort
+of creative energy is to be displayed? Or is it possible
+that new species can be called into being from time to
+time, and yet that so astonishing a phenomenon can
+escape the naturalist?
+
+"In the first place, it is obviously more easy to prove
+that a species once numerously represented in a given
+district has ceased to be than that some other which
+did not pre-exist had made its appearance--assuming
+always, for reasons before stated, that single stocks
+only of each animal and plant are originally created,
+and that individuals of new species did not suddenly
+start up in many different places at once.
+
+"So imperfect has the science of natural history remained
+down to our own times that, within the memory
+of persons now living, the numbers of known animals
+and plants have doubled, or even quadrupled, in
+many classes. New and often conspicuous species are
+annually discovered in parts of the old continent long
+inhabited by the most civilized nations. Conscious,
+therefore, of the limited extent of our information, we
+always infer, when such discoveries are made, that the
+beings in question bad previously eluded our research,
+or had at least existed elsewhere, and only migrated at
+a recent period into the territories where we now find
+them.
+
+"What kind of proofs, therefore, could we reasonably
+expect to find of the origin at a particular period of a
+new species?
+
+"Perhaps, it may be said in reply, that within the
+last two or three centuries some forest tree or new
+quadruped might have been observed to appear suddenly
+in those parts of England or France which had
+been most thoroughly investigated--that naturalists
+might have been able to show that no such being inhabited
+any other region of the globe, and that there
+was no tradition of anything similar having been
+observed in the district where it had made its appearance.
+
+"Now, although this objection may seem plausible,
+yet its force will be found to depend entirely on the
+rate of fluctuation which we suppose to prevail in the
+animal world, and on the proportions which such conspicuous
+subjects of the animal and vegetable kingdoms
+bear to those which are less known and escape
+our observation. There are perhaps more than a million
+species of plants and animals, exclusive of the
+microscopic and infusory animalcules, now inhabiting
+the terraqueous globe, so that if only one of these were
+to become extinct annually, and one new one were to
+be every year called into being, much more than a
+million of years might be required to bring about a
+complete revolution of organic life.
+
+"I am not hazarding at present any hypothesis as to
+the probable rate of change, but none will deny that
+when the annual birth and the annual death of one
+species on the globe is proposed as a mere speculation,
+this, at least, is to imagine no slight degree of instability
+in the animate creation. If we divide the surface of
+the earth into twenty regions of equal area, one of
+these might comprehend a space of land and water
+about equal in dimensions to Europe, and might contain
+a twentieth part of the million of species which
+may be assumed to exist in the animal kingdom. In
+this region one species only could, according to the rate
+of mortality before assumed, perish in twenty years,
+or only five out of fifty thousand in the course of a
+century. But as a considerable portion of the whole
+world belongs to the aquatic classes, with which we
+have a very imperfect acquaintance, we must exclude
+them from our consideration, and, if they constitute
+half of the entire number, then one species only might
+be lost in forty years among the terrestrial tribes.
+Now the mammalia, whether terrestrial or aquatic,
+bear so small a proportion to other classes of animals,
+forming less, perhaps, than a thousandth part of a
+whole, that, if the longevity of species in the different
+orders were equal, a vast period must elapse before it
+would come to the turn of this conspicuous class to
+lose one of their number. If one species only of the
+whole animal kingdom died out in forty years, no
+more than one mammifer might disappear in forty
+thousand years, in a region of the dimensions of Europe.
+
+"It is easy, therefore, to see that in a small portion
+of such an area, in countries, for example, of the
+size of England and France, periods of much greater
+duration must elapse before it would be possible to
+authenticate the first appearance of one of the larger
+plants or animals, assuming the annual birth and death
+of one species to be the rate of vicissitude in the animal
+creation throughout the world."[3]
+
+
+In a word, then, said Lyell, it becomes clear that the
+numberless species that have been exterminated in the
+past have died out one by one, just as individuals of a
+species die, not in vast shoals; if whole populations
+have passed away, it has been not by instantaneous
+extermination, but by the elimination of a species now
+here, now there, much as one generation succeeds another
+in the life history of any single species. The
+causes which have brought about such gradual exterminations,
+and in the long lapse of ages have resulted
+in rotations of population, are the same natural
+causes that are still in operation. Species have died
+out in the past as they are dying out in the present,
+under influence of changed surroundings, such as altered
+climate, or the migration into their territory of
+more masterful species. Past and present causes are
+one--natural law is changeless and eternal.
+
+Such was the essence of the Huttonian doctrine,
+which Lyell adopted and extended, and with which his
+name will always be associated. Largely through his
+efforts, though of course not without the aid of many
+other workers after a time, this idea--the doctrine of
+uniformitarianism, it came to be called--became the
+accepted dogma of the geologic world not long after the
+middle of the nineteenth century. The catastrophists,
+after clinging madly to their phantom for a generation,
+at last capitulated without terms: the old heresy became
+the new orthodoxy, and the way was paved for a
+fresh controversy.
+
+
+THE ORIGIN OF SPECIES
+
+The fresh controversy followed quite as a matter of
+course. For the idea of catastrophism had not concerned
+the destruction of species merely, but their
+introduction as well. If whole faunas had been extirpated
+suddenly, new faunas had presumably been introduced
+with equal suddenness by special creation;
+but if species die out gradually, the introduction of new
+species may be presumed to be correspondingly gradual.
+Then may not the new species of a later geological
+epoch be the modified lineal descendants of the
+extinct population of an earlier epoch?
+
+The idea that such might be the case was not new.
+It had been suggested when fossils first began to attract
+conspicuous attention; and such sagacious thinkers as
+Buffon and Kant and Goethe and Erasmus Darwin had
+been disposed to accept it in the closing days of the
+eighteenth century. Then, in 1809, it had been contended
+for by one of the early workers in systematic
+paleontology--Jean Baptiste Lamarck, who had studied
+the fossil shells about Paris while Cuvier studied the
+vertebrates, and who had been led by these studies to
+conclude that there had been not merely a rotation but
+a progression of life on the globe. He found the fossil
+shells--the fossils of invertebrates, as he himself had
+christened them--in deeper strata than Cuvier's vertebrates;
+and he believed that there had been long ages
+when no higher forms than these were in existence, and
+that in successive ages fishes, and then reptiles, had
+been the highest of animate creatures, before mammals,
+including man, appeared. Looking beyond the pale of
+his bare facts, as genius sometimes will, he had insisted
+that these progressive populations had developed one
+from another, under influence of changed surroundings,
+in unbroken series.
+
+Of course such a thought as this was hopelessly misplaced
+in a generation that doubted the existence of extinct
+species, and hardly less so in the generation that
+accepted catastrophism; but it had been kept alive by
+here and there an advocate like Geoffrey Saint-Hilaire,
+and now the banishment of catastrophism opened the
+way for its more respectful consideration. Respectful
+consideration was given it by Lyell in each recurring
+edition of his Principles, but such consideration led to
+its unqualified rejection. In its place Lyell put forward
+a modified hypothesis of special creation. He assumed
+that from time to time, as the extirpation of a species
+had left room, so to speak, for a new species, such new
+species had been created de novo; and he supposed that
+such intermittent, spasmodic impulses of creation manifest
+themselves nowadays quite as frequently as at any
+time in the past. He did not say in so many words
+that no one need be surprised to-day were he to see a
+new species of deer, for example, come up out of the
+ground before him, "pawing to get free," like Milton's
+lion, but his theory implied as much. And that theory,
+let it be noted, was not the theory of Lyell alone, but
+of nearly all his associates in the geologic world. There
+is perhaps no other fact that will bring home to one so
+vividly the advance in thought of our own generation
+as the recollection that so crude, so almost unthinkable
+a conception could have been the current doctrine of
+science less than half a century ago.
+
+This theory of special creation, moreover, excluded
+the current doctrine of uniformitarianism as night excludes
+day, though most thinkers of the time did not
+seem to be aware of the incompatibility of the two
+ideas. It may be doubted whether even Lyell himself
+fully realized it. If he did, he saw no escape from the
+dilemma, for it seemed to him that the record in the
+rocks clearly disproved the alternative Lamarckian hypothesis.
+And almost with one accord the paleontologists
+of the time sustained the verdict. Owen, Agassiz,
+Falconer, Barrande, Pictet, Forbes, repudiated the idea
+as unqualifiedly as their great predecessor Cuvier had
+done in the earlier generation. Some of them did, indeed,
+come to believe that there is evidence of a progressive
+development of life in the successive ages, but
+no such graded series of fossils had been discovered as
+would give countenance to the idea that one species had
+ever been transformed into another. And to nearly
+every one this objection seemed insuperable.
+
+But in 1859 appeared a book which, though not
+dealing primarily with paleontology, yet contained a
+chapter that revealed the geological record in an
+altogether new light. The book was Charles Darwin's
+Origin of Species, the chapter that wonderful citation of
+the "Imperfections of the Geological Record." In this
+epoch-making chapter Darwin shows what conditions
+must prevail in any given place in order that fossils
+shall be formed, how unusual such conditions are, and
+how probable it is that fossils once imbedded in sediment
+of a sea-bed will be destroyed by metamorphosis
+of the rocks, or by denudation when the strata are
+raised above the water-level. Add to this the fact that
+only small territories of the earth have been explored
+geologically, he says, and it becomes clear that the
+paleontological record as we now possess it shows but a
+mere fragment of the past history of organisms on the
+earth. It is a history "imperfectly kept and written in
+a changing dialect. Of this history we possess the last
+volume alone, relating only to two or three countries.
+Of this volume only here and there a short chapter has
+been preserved, and of each page only here and there a
+few lines." For a paleontologist to dogmatize from
+such a record would be as rash, he thinks, as "for a
+naturalist to land for five minutes on a barren point of
+Australia and then discuss the number and range of its
+productions."
+
+This citation of observations, which when once pointed
+out seemed almost self-evident, came as a revelation
+to the geological world. In the clarified view now
+possible old facts took on a new meaning. It was recalled
+that Cuvier had been obliged to establish a new
+order for some of the first fossil creatures he examined,
+and that Buckland had noted that the nondescript
+forms were intermediate in structure between allied existing
+orders. More recently such intermediate forms
+had been discovered over and over; so that, to name
+but one example, Owen had been able, with the aid of
+extinct species, to "dissolve by gradations the apparently
+wide interval between the pig and the camel."
+Owen, moreover, had been led to speak repeatedly of
+the "generalized forms" of extinct animals, and Agassiz
+had called them "synthetic or prophetic types," these
+terms clearly implying "that such forms are in fact
+intermediate or connecting links." Darwin himself had
+shown some years before that the fossil animals of any
+continent are closely related to the existing animals
+of that continent--edentates predominating, for example,
+in South America, and marsupials in Australia.
+Many observers had noted that recent strata everywhere
+show a fossil fauna more nearly like the existing
+one than do more ancient strata; and that fossils from
+any two consecutive strata are far more closely related
+to each other than are the fossils of two remote formations,
+the fauna of each geological formation being,
+indeed, in a wide view, intermediate between preceding
+and succeeding faunas.
+
+So suggestive were all these observations that Lyell,
+the admitted leader of the geological world, after reading
+Darwin's citations, felt able to drop his own crass
+explanation of the introduction of species and adopt
+the transmutation hypothesis, thus rounding out the
+doctrine of uniformitarianism to the full proportions in
+which Lamarck had conceived it half a century before.
+Not all paleontologists could follow him at once, of
+course; the proof was not yet sufficiently demonstrative
+for that; but all were shaken in the seeming security
+of their former position, which is always a necessary
+stage in the progress of thought. And popular interest
+in the matter was raised to white heat in a twinkling.
+
+So, for the third time in this first century of its existence,
+paleontology was called upon to play a leading
+role in a controversy whose interest extended far beyond
+the bounds of staid truth-seeking science. And
+the controversy waged over the age of the earth had
+not been more bitter, that over catastrophism not more
+acrimonious, than that which now raged over the question
+of the transmutation of species. The question had
+implications far beyond the bounds of paleontology, of
+course. The main evidence yet presented had been
+drawn from quite other fields, but by common consent
+the record in the rocks might furnish a crucial test of
+the truth or falsity of the hypothesis. "He who rejects
+this view of the imperfections of the geological
+record," said Darwin, "will rightly reject the whole
+theory."
+
+With something more than mere scientific zeal, therefore,
+paleontologists turned anew to the records in the
+rocks, to inquire what evidence in proof or refutation
+might be found in unread pages of the "great stone
+book." And, as might have been expected, many
+minds being thus prepared to receive new evidence,
+such evidence was not long withheld.
+
+
+FOSSIL MAN
+
+Indeed, at the moment of Darwin's writing a new
+and very instructive chapter of the geologic record was
+being presented to the public--a chapter which for the
+first time brought man into the story. In 1859 Dr.
+Falconer, the distinguished British paleontologist,
+made a visit to Abbeville, in the valley of the Somme,
+incited by reports that for a decade before bad been
+sent out from there by M. Boucher de Perthes. These
+reports had to do with the alleged finding of flint implements,
+clearly the work of man, in undisturbed gravel-
+beds, in the midst of fossil remains of the mammoth
+and other extinct animals. What Falconer saw there
+and what came of his visit may best be told in his own
+words:
+
+"In September of 1856 I made the acquaintance
+of my distinguished friend M. Boucher de Perthes,"
+wrote Dr. Falconer, "on the introduction of M. Desnoyers
+at Paris, when he presented to me the earlier
+volume of his Antiquites celtiques, etc., with which I thus
+became acquainted for the first time. I was then fresh
+from the examination of the Indian fossil remains of
+the valley of the Jumna; and the antiquity of the human
+race being a subject of interest to both, we conversed
+freely about it, each from a different point of
+view. M. de Perthes invited me to visit Abbeville, in
+order to examine his antediluvian collection, fossil
+and geological, gleaned from the valley of the Somme.
+This I was unable to accomplish then, but I reserved
+it for a future occasion.
+
+"In October, 1856, having determined to proceed to
+Sicily, I arranged by correspondence with M. Boucher
+de Perthes to visit Abbeville on my journey through
+France. I was at the time in constant communication
+with Mr. Prestwich about the proofs of the antiquity
+of the human race yielded by the Broxham
+Cave, in which he took a lively interest; and I engaged
+to communicate to him the opinions at which I should
+arrive, after my examination of the Abbeville collection.
+M. de Perthes gave me the freest access to his
+materials, with unreserved explanations of all the facts
+of the case that had come under his observation; and
+having considered his Menchecourt Section, taken with
+such scrupulous care, and identified the molars of elephas
+primigenius, which he had exhumed with his own
+hands deep in that section, along with flint weapons,
+presenting the same character as some of those found
+in the Broxham Cave, I arrived at the conviction that
+they were of contemporaneous age, although I was not
+prepared to go along with M. de Perthes in all his inferences
+regarding the hieroglyphics and in an industrial
+interpretation of the various other objects which
+he had met with."[4]
+
+
+That Dr. Falconer was much impressed by the collection
+of M. de Perthes is shown in a communication
+which he sent at once to his friend Prestwich:
+
+"I have been richly rewarded," he exclaims. "His
+collection of wrought flint implements, and of the objects
+of every description associated with them, far
+exceeds everything I expected to have seen, especially
+from a single locality. He has made great additions,
+since the publication of his first volume, in the second,
+which I now have by me. He showed me flint hatchets
+which HE HAD DUG UP with his own hands, mixed INDISCRIMINATELY
+with molars of elephas primigenius. I examined
+and identified plates of the molars and the
+flint objects which were got along with them. Abbeville
+is an out-of-the-way place, very little visited; and
+the French savants who meet him in Paris laugh at
+Monsieur de Perthes and his researches. But after devoting
+the greater part of a day to his vast collection,
+I am perfectly satisfied that there is a great deal of fair
+presumptive evidence in favor of many of his speculations
+regarding the remote antiquity of these industrial
+objects and their association with animals now extinct.
+M. Boucher's hotel is, from the ground floor to garret, a
+continued museum, filled with pictures, mediaeval art,
+and Gaulish antiquities, including antediluvian flint-knives,
+fossil-bones, etc. If, during next summer,
+you should happen to be paying a visit to France, let
+me strongly recommend you to come to Abbeville. I
+am sure you would be richly rewarded."[5]
+
+
+This letter aroused the interest of the English geologists,
+and in the spring of 1859 Prestwich and Mr.
+(afterwards Sir John) Evans made a visit to Abbeville
+to see the specimens and examine at first hand the
+evidences as pointed out by Dr. Falconer. "The evidence
+yielded by the valley of the Somme," continues
+Falconer, in speaking of this visit, "was gone into with
+the scrupulous care and severe and exhaustive analysis
+which are characteristic of Mr. Prestwich's researches.
+The conclusions to which he was conducted were communicated
+to the Royal Society on May 12, 1859, in his
+celebrated memoir, read on May 26th and published
+in the Philosophical Transactions of 1860, which, in addition
+to researches made in the valley of the Somme,
+contained an account of similar phenomena presented
+by the valley of the Waveney, near Hoxne, in Suffolk.
+Mr. Evans communicated to the Society of Antiquaries
+a memoir on the character and geological position of
+the 'Flint Implements in the Drift,' which appeared in
+the Archaeologia for 1860. The results arrived at by
+Mr. Prestwich were expressed as follows:
+
+"First. That the flint implements are the result of
+design and the work of man.
+
+"Second. That they are found in beds of gravel, sand,
+and clay, which have never been artificially disturbed.
+
+"Third. That they occur associated with the remains
+of land, fresh-water, and marine testacea, of
+species now living, and most of them still common in
+the same neighborhood, and also with the remains of
+various mammalia--a few species now living, but more
+of extinct forms.
+
+"Fourth. That the period at which their entombment
+took place was subsequent to the bowlder-clay
+period, and to that extent post-glacial; and also that
+it was among the latest in geological time--one apparently
+anterior to the surface assuming its present
+form, so far as it regards some of the minor features."[6]
+
+
+These reports brought the subject of the very significant
+human fossils at Abbeville prominently before
+the public; whereas the publications of the original discoverer,
+Boucher de Perthes, bearing date of 1847, had
+been altogether ignored. A new aspect was thus given
+to the current controversy.
+
+As Dr. Falconer remarked, geology was now passing
+through the same ordeal that astronomy passed in the
+age of Galileo. But the times were changed since the
+day when the author of the Dialogues was humbled before
+the Congregation of the Index, and now no Index
+Librorum Prohibitorum could avail to hide from eager
+human eyes such pages of the geologic story as Nature
+herself had spared. Eager searchers were turning the
+leaves with renewed zeal everywhere, and with no small
+measure of success. In particular, interest attached
+just at this time to a human skull which Dr. Fuhlrott
+had discovered in a cave at Neanderthal two or three
+years before--a cranium which has ever since been
+famous as the Neanderthal skull, the type specimen of
+what modern zoologists are disposed to regard as a
+distinct species of man, Homo neanderthalensis. Like
+others of the same type since discovered at Spy, it is
+singularly simian in character--low-arched, with receding
+forehead and enormous, protuberant eyebrows.
+When it was first exhibited to the scientists at Berlin
+by Dr. Fuhlrott, in 1857, its human character was
+doubted by some of the witnesses; of that, however,
+there is no present question.
+
+This interesting find served to recall with fresh significance
+some observations that had been made in
+France and Belgium a long generation earlier, but
+whose bearings had hitherto been ignored. In 1826
+MM. Tournal and Christol had made independent discoveries
+of what they believed to be human fossils
+in the caves of the south of France; and in 1827
+Dr. Schmerling had found in the cave of Engis, in
+Westphalia, fossil bones of even greater significance.
+Schmerling's explorations had been made with the
+utmost care, and patience. At Engis he had found
+human bones, including skulls, intermingled with those
+of extinct mammals of the mammoth period in a way
+that left no doubt in his mind that all dated from
+the same geological epoch. He bad published a full
+account of his discoveries in an elaborate monograph
+issued in 1833.
+
+But at that time, as it chanced, human fossils were
+under a ban as effectual as any ever pronounced by
+canonical index, though of far different origin. The
+oracular voice of Cuvier had declared against the
+authenticity of all human fossils. Some of the bones
+brought him for examination the great anatomist had
+pettishly pitched out of the window, declaring them
+fit only for a cemetery, and that had settled the matter
+for a generation: the evidence gathered by lesser workers
+could avail nothing against the decision rendered
+at the Delphi of Science. But no ban, scientific or
+canonical, can longer resist the germinative power of a
+fact, and so now, after three decades of suppression,
+the truth which Cuvier had buried beneath the weight
+of his ridicule burst its bonds, and fossil man stood revealed,
+if not as a flesh-and-blood, at least as a skeletal
+entity.
+
+The reception now accorded our prehistoric ancestor
+by the progressive portion of the scientific world
+amounted to an ovation; but the unscientific masses,
+on the other hand, notwithstanding their usual fondness
+for tracing remote genealogies, still gave the men
+of Engis and Neanderthal the cold shoulder. Nor
+were all of the geologists quite agreed that the
+contemporaneity of these human fossils with the animals
+whose remains had been mingled with them had been
+fully established. The bare possibility that the bones
+of man and of animals that long preceded him had been
+swept together into the eaves in successive ages, and in
+some mysterious way intermingled there, was clung to
+by the conservatives as a last refuge. But even this
+small measure of security was soon to be denied them,
+for in 1865 two associated workers, M. Edouard Lartet
+and Mr. Henry Christy, in exploring the caves of Dordogne,
+unearthed a bit of evidence against which no
+such objection could be urged. This momentous exhibit
+was a bit of ivory, a fragment of the tusk of a
+mammoth, on which was scratched a rude but unmistakable
+outline portrait of the mammoth itself. If all
+the evidence as to man's antiquity before presented
+was suggestive merely, here at last was demonstration;
+for the cave-dwelling man could not well have drawn
+the picture of the mammoth unless he had seen that
+animal, and to admit that man and the mammoth had
+been contemporaries was to concede the entire case.
+So soon, therefore, as the full import of this most instructive
+work of art came to be realized, scepticism as
+to man's antiquity was silenced for all time to come.
+
+In the generation that has elapsed since the first
+drawing of the cave-dweller artist was discovered, evidences
+of the wide-spread existence of man in an early
+epoch have multiplied indefinitely, and to-day the
+paleontologist traces the history of our race back beyond
+the iron and bronze ages, through a neolithic or
+polished-stone age, to a paleolithic or rough-stone age,
+with confidence born of unequivocal knowledge. And
+he looks confidently to the future explorer of the earth's
+fossil records to extend the history back into vastly
+more remote epochs, for it is little doubted that paleolithic
+man, the most ancient of our recognized progenitors,
+is a modern compared to those generations that
+represented the real childhood of our race.
+
+
+THE FOSSIL-BEDS OF AMERICA
+
+Coincidently with the discovery of these highly suggestive
+pages of the geologic story, other still more instructive
+chapters were being brought to light in America.
+It was found that in the Rocky Mountain region,
+in strata found in ancient lake beds, records of the
+tertiary period, or age of mammals, had been made and
+preserved with fulness not approached in any other region
+hitherto geologically explored. These records were
+made known mainly by Professors Joseph Leidy, O. C.
+Marsh, and E. D. Cope, working independently, and
+more recently by numerous younger paleontologists.
+
+The profusion of vertebrate remains thus brought to
+light quite beggars all previous exhibits in point of mere
+numbers. Professor Marsh, for example, who was first
+in the field, found three hundred new tertiary species
+between the years 1870 and 1876. Meanwhile, in
+cretaceous strata, he unearthed remains of about two
+hundred birds with teeth, six hundred pterodactyls,
+or flying dragons, some with a spread of wings of twenty-
+five feet, and one thousand five hundred mosasaurs
+of the sea-serpent type, some of them sixty feet or more
+in length. In a single bed of Jurassic rock, not larger
+than a good-sized lecture-room, he found the remains
+of one hundred and sixty individuals of mammals, representing
+twenty species and nine genera; while beds
+of the same age have yielded three hundred reptiles,
+varying from the size of a rabbit to sixty or eighty feet
+in length.
+
+But the chief interest of these fossils from the West is
+not their number but their nature; for among them are
+numerous illustrations of just such intermediate types
+of organisms as must have existed in the past if the
+succession of life on the globe has been an unbroken
+lineal succession. Here are reptiles with bat-like wings,
+and others with bird-like pelves and legs adapted for
+bipedal locomotion. Here are birds with teeth, and
+other reptilian characters. In short, what with reptilian
+birds and birdlike reptiles, the gap between
+modern reptiles and birds is quite bridged over. In a
+similar way, various diverse mammalian forms, as the
+tapir, the rhinoceros, and the horse, are linked together
+by fossil progenitors. And, most important of all,
+Professor Marsh has discovered a series of mammalian
+remains, occurring in successive geological epochs,
+which are held to represent beyond cavil the actual line
+of descent of the modern horse; tracing the lineage of
+our one-toed species back through two and three toed
+forms, to an ancestor in the eocene or early tertiary
+that had four functional toes and the rudiment of a
+fifth. This discovery is too interesting and too important
+not to be detailed at length in the words of the
+discoverer.
+
+
+Marsh Describes the Fossil Horse
+
+"It is a well-known fact," says Professor Marsh,
+"that the Spanish discoverers of America discovered
+no horses on this continent, and that the modern horse
+(Equus caballus, Linn.) was subsequently introduced
+from the Old World. It is, however, not so generally
+known that these animals had formerly been abundant
+here, and that long before, in tertiary time, near
+relatives of the horse, and probably his ancestors, existed
+in the far West in countless numbers and in a
+marvellous variety of forms. The remains of equine
+mammals, now known from the tertiary and quaternary
+deposits of this country, already represent more than
+double the number of genera and species hitherto found
+in the strata of the eastern hemisphere, and hence afford
+most important aid in tracing out the genealogy
+of the horses still existing.
+
+"The animals of this group which lived in America
+during the three diversions of the tertiary period were
+especially numerous in the Rocky Mountain regions,
+and their remains are well preserved in the old lake
+basins which then covered so much of that country.
+The most ancient of these lakes--which extended over
+a considerable part of the present territories of Wyoming
+and Utah--remained so long in eocene times that
+the mud and sand, slowly deposited in it, accumulated
+to more than a mile in vertical thickness. In these
+deposits vast numbers of tropical animals were
+entombed, and here the oldest equine remains occur,
+four species of which have been described. These
+belong to the genus Orohippus (Marsh), and are all of a
+diminutive size, hardly bigger than a fox. The skeletons
+of these animals resemble that of the horse in
+many respects, much more indeed than any other
+existing species, but, instead of the single toe on each
+foot, so characteristic of all modern equines, the various
+species of Orohippus had four toes before and three
+behind, all of which reached the ground. The skull,
+too, was proportionately shorter, and the orbit was not
+enclosed behind by a bridge of bone. There were fifty
+four teeth in all, and the premolars were larger than
+the molars. The crowns of these teeth were very short.
+The canine teeth were developed in both sexes, and the
+incisors did not have the "mark" which indicates the
+age of the modern horse. The radius and ulna were
+separate, and the latter was entire through the whole
+length. The tibia and fibula were distinct. In the
+forefoot all the digits except the pollex, or first, were
+well developed. The third digit is the largest, and its
+close resemblance to that of the horse is clearly marked.
+The terminal phalanx, or coffin-bone, has a shallow
+median bone in front, as in many species of this group
+in the later tertiary. The fourth digit exceeds the
+second in size, and the second is much the shortest of
+all. Its metacarpal bone is considerably curved outward.
+In the hind-foot of this genus there are but
+three digits. The fourth metatarsal is much larger
+than the second.
+
+"The larger number of equine mammals now known
+from the tertiary deposits of this country, and their
+regular distributions through the subdivisions of this
+formation, afford a good opportunity to ascertain the
+probable descent of the modern horse. The American
+representative of the latter is the extinct Equus
+fraternus (Leidy), a species almost, if not wholly,
+identical with the Old World Equus caballus (Linnaeus),
+to which our recent horse belongs. Huxley
+has traced successfully the later genealogy of the horse
+through European extinct forms, but the line in America
+was probably a more direct one, and the record is
+more complete. Taking, then, as the extreme of a
+series, Orohippus agilis (Marsh), from the eocene, and
+Equus fraternus (Leidy), from the quaternary, intermediate
+forms may be intercalated with considerable certainty
+from thirty or more well-marked species that
+lived in the intervening periods. The natural line of
+descent would seem to be through the following genera:
+Orohippus, of the eocene; Miohippus and Anchitherium,
+of the miocene; Anchippus, Hipparion, Protohippus,
+Phohippus, of the pliocene; and Equus, quaternary
+and recent.
+
+The most marked changes undergone by the successive
+equine genera are as follows: First, increase in
+size; second, increase in speed, through concentration
+of limb bones; third, elongation of head and neck, and
+modifications of skull. The eocene Orohippus was the
+size of a fox. Miohippus and Anchitherium, from the
+miocene, were about as large as a sheep. Hipparion
+and Pliohippus, of the pliocene, equalled the ass in
+height; while the size of the quaternary Equus was
+fully up to that of a modern horse.
+
+"The increase of speed was equally well marked, and
+was a direct result of the gradual formation of the
+limbs. The latter were slowly concentrated by the
+reduction of their lateral elements and enlargement
+of the axial bone, until the force exerted by each
+limb came to act directly through its axis in the
+line of motion. This concentration is well seen--e.g.,
+in the fore-limb. There was, first, a change in the
+scapula and humerus, especially in the latter, which
+facilitated motion in one line only; second, an expansion
+of the radius and reduction of the ulna, until the
+former alone remained entire and effective; third, a
+shortening of all the carpal bones and enlargement of
+the median ones, insuring a firmer wrist; fourth, an increase
+of size of the third digit, at the expense of those
+of each side, until the former alone supported the
+limb.
+
+"Such is, in brief, a general outline of the more
+marked changes that seemed to have produced in
+America the highly specialized modern Equus from his
+diminutive four-toed predecessor, the eocene Orohippus.
+The line of descent appears to have been direct,
+and the remains now known supply every important
+intermediate form. It is, of course, impossible to say
+with certainty through which of the three-toed genera
+of the pliocene that lived together the succession came.
+It is not impossible that the latter species, which appear
+generically identical, are the descendants of more
+distinct pliocene types, as the persistent tendency in
+all the earlier forms was in the same direction.
+Considering the remarkable development of the group
+through the tertiary period, and its existence even
+later, it seems very strange that none of the species
+should have survived, and that we are indebted for our
+present horse to the Old World."[7]
+
+
+PALEONTOLOGY OF EVOLUTION
+
+These and such-like revelations have come to light in
+our own time--are, indeed, still being disclosed. Needless
+to say, no index of any sort now attempts to conceal
+them; yet something has been accomplished towards
+the same end by the publication of the discoveries
+in Smithsonian bulletins and in technical memoirs of
+government surveys. Fortunately, however, the results
+have been rescued from that partial oblivion by
+such interpreters as Professors Huxley and Cope, so
+the unscientific public has been allowed to gain at
+least an inkling of the wonderful progress of paleontology
+in our generation.
+
+The writings of Huxley in particular epitomize the
+record. In 1862 he admitted candidly that the paleontological
+record as then known, so far as it bears on the
+doctrine of progressive development, negatives that
+doctrine. In 1870 he was able to "soften somewhat
+the Brutus-like severity" of his former verdict, and to
+assert that the results of recent researches seem "to
+leave a clear balance in favor of the doctrine of the
+evolution of living forms one from another." Six
+years later, when reviewing the work of Marsh in
+America and of Gaudry in Pikermi, he declared that,
+"on the evidence of paleontology, the evolution of
+many existing forms of animal life from their predecessors
+is no longer an hypothesis, but an historical
+fact." In 1881 he asserted that the evidence gathered
+in the previous decade had been so unequivocal that,
+had the transmutation hypothesis not existed, "the
+paleontologist would have had to invent it."
+
+Since then the delvers after fossils have piled proof
+on proof in bewildering profusion. The fossil-beds in
+the "bad lands" of western America seem inexhaustible.
+And in the Connecticut River Valley near relatives
+of the great reptiles which Professor Marsh and
+others have found in such profusion in the West left
+their tracks on the mud-flats--since turned to sandstone;
+and a few skeletons also have been found. The
+bodies of a race of great reptiles that were the lords of
+creation of their day have been dissipated to their elements,
+while the chance indentations of their feet as
+they raced along the shores, mere footprints on the
+sands, have been preserved among the most imperishable
+of the memory-tablets of the world.
+
+Of the other vertebrate fossils that have been found
+in the eastern portions of America, among the most
+abundant and interesting are the skeletons of mastodons.
+Of these one of the largest and most complete is
+that which was unearthed in the bed of a drained lake
+near Newburg, New York, in 1845. This specimen was
+larger than the existing elephants, and had tusks eleven
+feet in length. It was mounted and described by Dr.
+John C. Warren, of Boston, and has been famous for
+half a century as the "Warren mastodon."
+
+But to the student of racial development as recorded
+by the fossils all these sporadic finds have but incidental
+interest as compared with the rich Western fossil-
+beds to which we have already referred. From records
+here unearthed, the racial evolution of many mammals
+has in the past few years been made out in greater or
+less detail. Professor Cope has traced the ancestry of
+the camels (which, like the rhinoceroses, hippopotami,
+and sundry other forms now spoken of as "Old World,"
+seem to have had their origin here) with much completeness.
+
+A lemuroid form of mammal, believed to be of the
+type from which man has descended, has also been
+found in these beds. It is thought that the descendants
+of this creature, and of the other "Old-World"
+forms above referred to, found their way to Asia, probably,
+as suggested by Professor Marsh, across a bridge
+at Bering Strait, to continue their evolution on the
+other hemisphere, becoming extinct in the land of their
+nativity. The ape-man fossil found in the tertiary
+strata of the island of Java in 1891 by the Dutch
+surgeon Dr. Eugene Dubois, and named Pithecanthropus
+erectus, may have been a direct descendant of the
+American tribe of primitive lemurs, though this is only
+a conjecture.
+
+Not all the strange beasts which have left their remains
+in our "bad lands" are represented by living descendants.
+The titanotheres, or brontotheridae, for example, a
+gigantic tribe, offshoots of the same stock
+which produced the horse and rhinoceros, represented
+the culmination of a line of descent. They developed
+rapidly in a geological sense, and flourished about the
+middle of the tertiary period; then, to use Agassiz's
+phrase," time fought against them." The story of their
+evolution has been worked out by Professors Leidy,
+Marsh, Cope, and H. F. Osborne.
+
+A recent bit of paleontological evidence bearing
+on the question of the introduction of species is that
+presented by Dr. J. L. Wortman in connection with the
+fossil lineage of the edentates. It was suggested by
+Marsh, in 1877, that these creatures, whose modern
+representatives are all South American, originated in
+North America long before the two continents had any
+land connection. The stages of degeneration by which
+these animals gradually lost the enamel from their teeth,
+coming finally to the unique condition of their modern
+descendants of the sloth tribe, are illustrated by strikingly
+graded specimens now preserved in the American
+Museum of Natural History, as shown by Dr. Wortman.
+
+All these and a multitude of other recent observations
+that cannot be even outlined here tell the same story.
+With one accord paleontologists of our time regard the
+question of the introduction of new species as solved.
+As Professor Marsh has said, "to doubt evolution today
+is to doubt science; and science is only another
+name for truth."
+
+Thus the third great battle over the meaning of the
+fossil records has come to a conclusion. Again there
+is a truce to controversy, and it may seem to the casual
+observer that the present stand of the science of fossils
+is final and impregnable. But does this really mean
+that a full synopsis of the story of paleontology has
+been told? Or do we only await the coming of the
+twentieth-century Lamarck or Darwin, who shall attack
+the fortified knowledge of to-day with the batteries
+of a new generalization?
+
+
+
+IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY
+
+JAMES HUTTON
+
+One might naturally suppose that the science of
+the earth which lies at man's feet would at least
+have kept pace with the science of the distant stars.
+But perhaps the very obviousness of the phenomena
+delayed the study of the crust of the earth. It is the
+unattainable that allures and mystifies and enchants
+the developing mind. The proverbial child spurns its
+toys and cries for the moon.
+
+So in those closing days of the eighteenth century,
+when astronomers had gone so far towards explaining
+the mysteries of the distant portions of the universe,
+we find a chaos of opinion regarding the structure and
+formation of the earth. Guesses were not wanting to
+explain the formation of the world, it is true, but, with
+one or two exceptions, these are bizarre indeed. One
+theory supposed the earth to have been at first a solid
+mass of ice, which became animated only after a comet
+had dashed against it. Other theories conceived the
+original globe as a mass of water, over which floated
+vapors containing the solid elements, which in due time
+were precipitated as a crust upon the waters. In a
+word, the various schemes supposed the original mass to
+have been ice, or water, or a conglomerate of water and
+solids, according to the random fancies of the theorists;
+and the final separation into land and water was conceived
+to have taken place in all the ways which fancy,
+quite unchecked by any tenable data, could invent.
+
+Whatever important changes in the general character
+of the surface of the globe were conceived to have taken
+place since its creation were generally associated with
+the Mosaic: deluge, and the theories which attempted to
+explain this catastrophe were quite on a par with those
+which dealt with a remoter period of the earth's history.
+Some speculators, holding that the interior
+of the globe is a great abyss of waters, conceived
+that the crust had dropped into this chasm and had
+thus been inundated. Others held that the earth had
+originally revolved on a vertical axis, and that the sudden
+change to its present position bad caused the catastrophic
+shifting of its oceans. But perhaps the favorite
+theory was that which supposed a comet to have wandered
+near the earth, and in whirling about it to have
+carried the waters, through gravitation, in a vast tide
+over the continents.
+
+Thus blindly groped the majority of eighteenth-century
+philosophers in their attempts to study what we
+now term geology. Deluded by the old deductive
+methods, they founded not a science, but the ghost of a
+science, as immaterial and as unlike anything in nature
+as any other phantom that could be conjured from the
+depths of the speculative imagination. And all the
+while the beckoning earth lay beneath the feet of these
+visionaries; but their eyes were fixed in air.
+
+At last, however, there came a man who had the
+penetration to see that the phantom science of geology
+needed before all else a body corporeal, and who took
+to himself the task of supplying it. This was Dr. James
+Hutton, of Edinburgh, physician, farmer, and manufacturing
+chemist--patient, enthusiastic, level-headed
+devotee of science. Inspired by his love of chemistry
+to study the character of rocks and soils, Hutton had
+not gone far before the earth stood revealed to him in
+a new light. He saw, what generations of predecessors
+had blindly refused to see, that the face of nature everywhere,
+instead of being rigid and immutable, is perennially
+plastic, and year by year is undergoing metamorphic
+changes. The solidest rocks are day by day
+disintegrated slowly, but none the less surely, by wind
+and rain and frost, by mechanical attrition and chemical
+decomposition, to form the pulverized earth and
+clay. This soil is being swept away by perennial showers,
+and carried off to the oceans. The oceans themselves
+beat on their shores, and eat insidiously into the
+structure of sands and rocks. Everywhere, slowly but
+surely, the surface of the land is being worn away; its
+substance is being carried to burial in the seas.
+
+Should this denudation continue long enough, thinks
+Hutton, the entire surface of the continents must be
+worn away. Should it be continued LONG ENOUGH! And
+with that thought there flashes on his mind an inspiring
+conception--the idea that solar time is long,
+indefinitely long. That seems a simple enough thought
+--almost a truism--to the twentieth-century mind;
+but it required genius to conceive it in the eighteenth.
+Hutton pondered it, grasped its full import, and made
+it the basis of his hypothesis, his "theory of the earth."
+
+
+MODERN GEOLOGY
+
+The hypothesis is this--that the observed changes
+of the surface of the earth, continued through indefinite
+lapses of time, must result in conveying all the land at
+last to the sea; in wearing continents away till the
+oceans overflow them. What then? Why, as the continents
+wear down, the oceans are filling up. Along
+their bottoms the detritus of wasted continents is deposited
+in strata, together with the bodies of marine
+animals and vegetables. Why might not this debris
+solidify to form layers of rocks--the basis of new continents?
+Why not, indeed?
+
+But have we any proof that such formation of rocks
+in an ocean-bed has, in fact, occurred? To be sure we
+have. It is furnished by every bed of limestone, every
+outcropping fragment of fossil-bearing rock, every
+stratified cliff. How else than through such formation
+in an ocean-bed came these rocks to be stratified?
+How else came they to contain the shells of once living
+organisms imbedded in their depths? The ancients,
+finding fossil shells imbedded in the rocks, explained
+them as mere freaks of "nature and the stars." Less
+superstitious generations had repudiated this explanation,
+but had failed to give a tenable solution of the
+mystery. To Hutton it is a mystery no longer. To
+him it seems clear that the basis of the present continents
+was laid in ancient sea-beds, formed of the detritus
+of continents yet more ancient.
+
+But two links are still wanting to complete the chain
+of Hutton's hypothesis. Through what agency has the
+ooze of the ocean-bed been transformed into solid rock?
+and through what agency has this rock been lifted
+above the surface of the water to form new continents?
+Hutton looks about him for a clew, and soon he finds
+it. Everywhere about us there are outcropping rocks
+that are not stratified, but which give evidence to the
+observant eye of having once been in a molten state.
+Different minerals are mixed together; pebbles are
+scattered through masses of rock like plums in a pudding;
+irregular crevices in otherwise solid masses of
+rock--so-called veinings--are seen to be filled with
+equally solid granite of a different variety, which can
+have gotten there in no conceivable way, so Hutton
+thinks, but by running in while molten, as liquid metal
+is run into the moulds of the founder. Even the
+stratified rocks, though they seemingly have not been
+melted, give evidence in some instances of having been
+subjected to the action of heat. Marble, for example,
+is clearly nothing but calcined limestone.
+
+With such evidence before him, Hutton is at no loss
+to complete his hypothesis. The agency which has
+solidified the ocean-beds, he says, is subterranean heat.
+The same agency, acting excessively, has produced
+volcanic cataclysms, upheaving ocean-beds to form
+continents. The rugged and uneven surfaces of mountains,
+the tilted and broken character of stratified rocks
+everywhere, are the standing witnesses of these gigantic
+upheavals.
+
+And with this the imagined cycle is complete. The
+continents, worn away and carried to the sea by the
+action of the elements, have been made over into rocks
+again in the ocean-beds, and then raised once more
+into continents. And this massive cycle, In Hutton's
+scheme, is supposed to have occurred not once only,
+but over and over again, times without number. In
+this unique view ours is indeed a world without beginning
+and without end; its continents have been
+making and unmaking in endless series since time
+began.
+
+Hutton formulated his hypothesis while yet a young
+man, not long after the middle of the century. He
+first gave it publicity in 1781, in a paper before the
+Royal Society of Edinburgh:
+
+"A solid body of land could not have answered the
+purpose of a habitable world," said Hutton, "for a soil
+is necessary to the growth of plants, and a soil is nothing
+but the material collected from the destruction of
+the solid land. Therefore the surface of this land inhabited
+by man, and covered by plants and animals, is
+made by nature to decay, in dissolving from that hard
+and compact state in which it is found; and this soil is
+necessarily washed away by the continual circulation
+of the water running from the summits of the mountains
+towards the general receptacle of that fluid.
+
+"The heights of our land are thus levelled with our
+shores, our fertile plains are formed from the ruins of
+the mountains; and those travelling materials are still
+pursued by the moving water, and propelled along the
+inclined surface of the earth. These movable materials,
+delivered into the sea, cannot, for a long continuance,
+rest upon the shore, for by the agitation of the winds,
+the tides, and the currents every movable thing is
+carried farther and farther along the shelving bottom
+of the sea, towards the unfathomable regions of the
+ocean.
+
+"If the vegetable soil is thus constantly removed
+from the surface of the land, and if its place is then to
+be supplied from the dissolution of the solid earth as
+here represented, we may perceive an end to this beautiful
+machine; an end arising from no error in its constitution
+as a world, but from that destructibility of
+its land which is so necessary in the system of the
+globe, in the economy of life and vegetation.
+
+"The immense time necessarily required for the
+total destruction of the land must not be opposed to
+that view of future events which is indicated by the
+surest facts and most approved principles. Time,
+which measures everything in our idea, and is often
+deficient to our schemes, is to nature endless and as
+nothing; it cannot limit that by which alone it has existence;
+and as the natural course of time, which to us
+seems infinite, cannot be bounded by any operation
+that may have an end, the progress of things upon this
+globe that in the course of nature cannot be limited by
+time must proceed in a continual succession. We are,
+therefore, to consider as inevitable the destruction of
+our land, so far as effected by those operations which
+are necessary in the purpose of the globe, considered
+as a habitable world, and so far as we have not examined
+any other part of the economy of nature, in
+which other operations and a different intention might
+appear.
+
+"We have now considered the globe of this earth as
+a machine, constructed upon chemical as well as mechanical
+principles, by which its different parts are all
+adapted, in form, in quality, and quantity, to a certain
+end--an end attained with certainty of success, and
+an end from which we may perceive wisdom in contemplating
+the means employed.
+
+"But is this world to be considered thus merely as a
+machine, to last no longer than its parts retain their
+present position, their proper forms and qualities?
+Or may it not be also considered as an organized body
+such as has a constitution, in which the necessary
+decay of the machine is naturally repaired in the exertion
+of those productive powers by which it has been
+formed?
+
+"This is the view in which we are now to examine
+the globe; to see if there be, in the constitution of the
+world, a reproductive operation by which a ruined
+constitution may be again repaired and a duration of
+stability thus procured to the machine considered as a
+world containing plants and animals.
+
+"If no such reproductive power, or reforming operation,
+after due inquiry, is to be found in the constitution
+of this world, we should have reason to conclude
+that the system of this earth has either been intentionally
+made imperfect or has not been the work of infinite
+power and wisdom."[1]
+
+
+This, then, was the important question to be
+answered--the question of the constitution of the globe.
+To accomplish this, it was necessary, first of all, to examine
+without prejudice the material already in hand,
+adding such new discoveries from time to time as
+might be made, but always applying to the whole
+unvarying scientific principles and inductive methods
+of reasoning.
+
+"If we are to take the written history of man for
+the rule by which we should judge of the time when the
+species first began," said Hutton, "that period would
+be but little removed from the present state of things.
+The Mosaic history places this beginning of man at no
+great distance; and there has not been found, in natural
+history, any document by which high antiquity might
+be attributed to the human race. But this is not the
+case with regard to the inferior species of animals,
+particularly those which inhabit the ocean and its
+shores. We find in natural history monuments which
+prove that those animals had long existed; and we
+thus procure a measure for the computation of a period
+of time extremely remote, though far from being precisely
+ascertained.
+
+"In examining things present, we have data from
+which to reason with regard to what has been; and
+from what actually has been we have data for concluding
+with regard to that which is to happen hereafter.
+Therefore, upon the supposition that the operations of
+nature are equable and steady, we find, in natural
+appearances, means for concluding a certain portion of
+time to have necessarily elapsed in the production of
+those events of which we see the effects.
+
+"It is thus that, in finding the relics of sea animals of
+every kind in the solid body of our earth, a natural
+history of those animals is formed, which includes a
+certain portion of time; and for the ascertaining this
+portion of time we must again have recourse to the
+regular operations of this world. We shall thus arrive
+at facts which indicate a period to which no other
+species of chronology is able to remount.
+
+"We find the marks of marine animals in the most
+solid parts of the earth, consequently those solid parts
+have been formed after the ocean was inhabited by
+those animals which are proper to that fluid medium.
+If, therefore, we knew the natural history of these
+solid parts, and could trace the operations of the globe
+by which they have been formed, we would have some
+means for computing the time through which those
+species of animals have continued to live. But how
+shall we describe a process which nobody has seen performed
+and of which no written history gives any account?
+This is only to be investigated, first, in examining
+the nature of those solid bodies the history of
+which we want to know; and, secondly, in examining
+the natural operations of the globe, in order to see if
+there now exist such operations as, from the nature
+of the solid bodies, appear to have been necessary for
+their formation.
+
+"There are few beds of marble or limestone in which
+may not be found some of those objects which indicate
+the marine object of the mass. If, for example, in a
+mass of marble taken from a quarry upon the top of
+the Alps or Andes there shall be found one cockle-shell
+or piece of coral, it must be concluded that this bed of
+stone has been originally formed at the bottom of the
+sea, as much as another bed which is evidently composed
+almost altogether of cockle-shells and coral. If
+one bed of limestone is thus found to have been of
+marine origin, every concomitant bed of the same
+kind must be also concluded to have been formed in the
+same manner.
+
+"In those calcareous strata, which are evidently of
+marine origin, there are many parts which are of
+sparry structure--that is to say, the original texture of
+those beds in such places has been dissolved, and a
+new structure has been assumed which is peculiar to
+a certain state of the calcareous earth. This change
+is produced by crystallization, in consequence of a previous
+state of fluidity, which has so disposed the concerting
+parts as to allow them to assume a regular
+shape and structure proper to that substance. A body
+whose external form has been modified by this process
+is called a CRYSTAL; one whose internal arrangement
+of parts is determined by it is said to be of a SPARRY
+STRUCTURE, and this is known from its fracture.
+
+"There are, in all the regions of the earth, huge
+masses of calcareous matter in that crystalline form or
+sparry state in which, perhaps, no vestige can be
+found of any organized body, nor any indication that
+such calcareous matter has belonged to animals; but
+as in other masses this sparry structure or crystalline
+state is evidently assumed by the marine calcareous
+substances in operations which are natural to the
+globe, and which are necessary to the consolidation of
+the strata, it does not appear that the sparry masses
+in which no figured body is formed have been originally
+different from other masses, which, being only
+crystallized in part, and in part still retaining their
+original form, have ample evidence of their marine
+origin.
+
+"We are led, in this manner, to conclude that all the
+strata of the earth, not only those consisting of such
+calcareous masses, but others superincumbent upon
+these, have had their origin at the bottom of the
+sea.
+
+"The general amount of our reasoning is this, that
+nine-tenths, perhaps, or ninety-nine-hundredths, of this
+earth, so far as we see, have been formed by natural operations
+of the globe in collecting loose materials and
+depositing them at the bottom of the sea; consolidating
+those collections in various degrees, and either elevating
+those consolidated masses above the level on
+which they were formed or lowering the level of that
+sea.
+
+"Let us now consider how far the other proposition
+of strata being elevated by the power of heat above the
+level of the sea may be confirmed from the examination
+of natural appearances. The strata formed at the bottom
+of the ocean are necessarily horizontal in their position,
+or nearly so, and continuous in their horizontal
+direction or extent. They may be changed and gradually
+assume the nature of each other, so far as concerns
+the materials of which they are formed, but there cannot
+be any sudden change, fracture, or displacement
+naturally in the body of a stratum. But if the strata
+are cemented by the heat of fusion, and erected with
+an expansive power acting below, we may expect to
+find every species of fracture, dislocation, and contortion
+in those bodies and every degree of departure from
+a horizontal towards a vertical position.
+
+"The strata of the globe are actually found in every
+possible position: for from horizontal they are frequently
+found vertical; from continuous they are broken
+and separated in every possible direction; and from a
+plane they are bent and doubled. It is impossible
+that they could have originally been formed, by the
+known laws of nature, in their present state and position;
+and the power that has been necessarily required
+for their change has not been inferior to that which
+might have been required for their elevation from the
+place in which they have been formed."[2]
+
+
+From all this, therefore, Hutton reached the conclusion
+that the elevation of the bodies of land above
+the water on the earth's surface had been effected by
+the same force which had acted in consolidating the
+strata and giving them stability. This force he
+conceived to be exerted by the expansion of heated
+matter.
+
+"We have," he said, "been now supposing that the
+beginning of our present earth had been laid in the bottom
+of the ocean, at the completion of the former land,
+but this was only for the sake of distinctness. The
+just view is this, that when the former land of the globe
+had been complete, so as to begin to waste and be
+impaired by the encroachment of the sea, the present
+land began to appear above the surface of the ocean.
+In this manner we suppose a due proportion to be always
+preserved of land and water upon the surface of
+the globe, for the purpose of a habitable world such as
+this which we possess. We thus also allow time and
+opportunity for the translation of animals and plants
+to occupy the earth.
+
+"But if the earth on which we live began to appear
+in the ocean at the time when the LAST began to be resolved,
+it could not be from the materials of the continent
+immediately preceding this which we examine
+that the present earth has been constructed; for the
+bottom of the ocean must have been filled with materials
+before land could be made to appear above its
+surface.
+
+"Let us suppose that the continent which is to succeed
+our land is at present beginning to appear above
+the water in the middle of the Pacific Ocean; it must
+be evident that the materials of this great body, which
+is formed and ready to be brought forth, must have
+been collected from the destruction of an earth which
+does not now appear. Consequently, in this true statement
+of the case there is necessarily required the destruction
+of an animal and vegetable earth prior to the
+former land; and the materials of that earth which is
+first in our account must have been collected at the
+bottom of the ocean, and begun to be concocted for
+the production of the present earth, when the land
+immediately preceding the present had arrived at its
+full extent.
+
+"We have now got to the end of our reasoning; we
+have no data further to conclude immediately from
+that which actually is; but we have got enough; we
+have the satisfaction to find that in nature there are
+wisdom, system, and consistency. For having in the
+natural history of the earth seen a succession of worlds,
+we may from this conclude that there is a system in
+nature; in like manner as, from seeing revolutions of
+the planets, it is concluded that there is a system by
+which they are intended to continue those revolutions.
+But if the succession of worlds is established in
+the system of nature, it is in vain to look for anything
+higher in the origin of the earth. The result, therefore,
+of our present inquiry is that we find no vestige of a
+beginning--no prospect of an end."
+
+
+Altogether remarkable as this paper seems in the
+light of later knowledge, neither friend nor foe deigned
+to notice it at the moment. It was not published in
+book form until the last decade of the century, when
+Hutton had lived with and worked over his theory for
+almost fifty years. Then it caught the eye of the
+world. A school of followers expounded the Huttonian
+doctrines; a rival school under Werner in Germany
+opposed some details of the hypothesis, and the educated
+world as a whole viewed the disputants askance.
+The very novelty of the new views forbade their immediate
+acceptance. Bitter attacks were made upon
+the "heresies," and that was meant to be a soberly
+tempered judgment which in 1800 pronounced Hutton's
+theories "not only hostile to sacred history, but equally
+hostile to the principles of probability, to the results
+of the ablest observations on the mineral kingdom,
+and to the dictates of rational philosophy." And all
+this because Hutton's theory presupposed the earth
+to have been in existence more than six thousand
+years.
+
+Thus it appears that though the thoughts of men had
+widened, in those closing days of the eighteenth century,
+to include the stars, they had not as yet expanded
+to receive the most patent records that are written
+everywhere on the surface of the earth. Before Hutton's
+views could be accepted, his pivotal conception
+that time is long must be established by convincing
+proofs. The evidence was being gathered by William
+Smith, Cuvier, and other devotees of the budding
+science of paleontology in the last days of the century,
+but their labors were not brought to completion till a
+subsequent epoch.
+
+
+NEPTUNISTS VERSUS PLUTONISTS
+
+In the mean time, James Hutton's theory that continents
+wear away and are replaced by volcanic upheaval
+gained comparatively few adherents. Even
+the lucid Illustrations of the Huttonian Theory, which
+Playfair, the pupil and friend of the great Scotchman,
+published in 1802, did not at once prove convincing.
+The world had become enamoured of the rival theory
+of Hutton's famous contemporary, Werner of Saxony
+--the theory which taught that "in the beginning" all
+the solids of the earth's present crust were dissolved
+in the heated waters of a universal sea. Werner affirmed
+that all rocks, of whatever character, had been
+formed by precipitation from this sea as the waters
+cooled; that even veins have originated in this way;
+and that mountains are gigantic crystals, not upheaved
+masses. In a word, he practically ignored volcanic
+action, and denied in toto the theory of metamorphosis
+of rocks through the agency of heat.
+
+The followers of Werner came to be known as Neptunists;
+the Huttonians as Plutonists. The history of
+geology during the first quarter of the nineteenth century
+is mainly a recital of the intemperate controversy
+between these opposing schools; though it should not
+be forgotten that, meantime, the members of the Geological
+Society of London were making an effort to hunt
+for facts and avoid compromising theories. Fact and
+theory, however, were too closely linked to be thus divorced.
+
+The brunt of the controversy settled about the unstratified
+rocks--granites and their allies--which the
+Plutonists claimed as of igneous origin. This contention
+had the theoretical support of the nebular hypothesis,
+then gaining ground, which supposed the
+earth to be a cooling globe. The Plutonists laid great
+stress, too, on the observed fact that the temperature
+of the earth increases at a pretty constant ratio as descent
+towards its centre is made in mines. But in particular
+they appealed to the phenomena of volcanoes.
+
+The evidence from this source was gathered and
+elaborated by Mr. G. Poulett Scrope, secretary of the
+Geological Society of England, who, in 1823, published
+a classical work on volcanoes in which he claimed that
+volcanic mountains, including some of the highest-
+known peaks, are merely accumulated masses of lava
+belched forth from a crevice in the earth's crust.
+
+"Supposing the globe to have had any irregular
+shape when detached from the sun," said Scrope, "the
+vaporization of its surface, and, of course, of its projecting
+angles, together with its rotatory motion on its
+axis and the liquefaction of its outer envelope, would
+necessarily occasion its actual figure of an oblate
+spheroid. As the process of expansion proceeded in
+depth, the original granitic beds were first partially
+disaggregated, next disintegrated, and more or less
+liquefied, the crystals being merged in the elastic vehicle
+produced by the vaporization of the water contained
+between the laminae.
+
+"Where this fluid was produced in abundance by
+great dilatation--that is, in the outer and highly
+disintegrated strata, the superior specific gravity of the
+crystals forced it to ooze upward, and thus a great quantity
+of aqueous vapor was produced on the surface of
+the globe. As this elastic fluid rose into outer space,
+its continually increasing expansion must have proportionately
+lowered its temperature; and, in consequence,
+a part was recondensed into water and sank back towards
+the more solid surface of the globe.
+
+"And in this manner, for a certain time, a violent
+reciprocation of atmospheric phenomena must have
+continued--torrents of vapor rising outwardly, while
+equally tremendous torrents of condensed vapor, or
+rain, fell towards the earth. The accumulation of the
+latter on the yet unstable and unconsolidated surface
+of the globe constituted the primeval ocean. The
+surface of this ocean was exposed to continued vaporization
+owing to intense heat; but this process, abstracting
+caloric from the stratum of the water below, by
+partially cooling it, tended to preserve the remainder
+in a liquid form. The ocean will have contained, both
+in solution and suspension, many of the matters carried
+upward from the granitic bed in which the vapors
+from whose condensation it proceeded were produced,
+and which they had traversed in their rise. The dissolved
+matters will have been silex, carbonates, and
+sulphates of lime, and those other mineral substances
+which water at an intense temperature and under such
+circumstances was enabled to hold in solution. The
+suspended substances will have been all the lighter and
+finer particles of the upper beds where the disintegration
+had been extreme; and particularly their mica,
+which, owing to the tenuity of its plate-shaped crystals,
+would be most readily carried up by the ascending
+fluid, and will have remained longest in suspension.
+
+"But as the torrents of vapor, holding these various
+matters in solution and suspension, were forced upward,
+the greater part of the disintegrated crystals
+by degrees subsided; those of felspar and quartz first,
+the mica being, as observed above, from the form of
+its plates, of peculiar buoyancy, and therefore held
+longest in suspension.
+
+"The crystals of felspar and quartz as they subsided,
+together with a small proportion of mica, would
+naturally arrange themselves so as to have their longest
+dimensions more or less parallel to the surface on
+which they rest; and this parallelism would be subsequently
+increased, as we shall see hereafter, by the
+pressure of these beds sustained between the weight
+of the supported column of matter and the expansive
+force beneath them. These beds I conceive, when
+consolidated, to constitute the gneiss formation.
+
+"The farther the process of expansion proceeded in
+depth, the more was the column of liquid matter
+lengthened, which, gravitating towards the centre of
+the globe, tended to check any further expansion.
+It is, therefore, obvious that after the globe settled
+into its actual orbit, and thenceforward lost little of
+its enveloping matter, the whole of which began from
+that moment to gravitate towards its centre, the progress
+of expansion inwardly would continually increase
+in rapidity; and a moment must have at length arrived
+hen the forces of expansion and repression had
+reached an equilibrium and the process was stopped
+from progressing farther inwardly by the great pressure
+of the gravitating column of liquid.
+
+This column may be considered as consisting of
+different strata, though the passage from one extremity
+of complete solidity to the other of complete expansion,
+in reality, must have been perfectly gradual.
+The lowest stratum, immediately above the extreme
+limit of expansion, will have been granite barely
+DISAGGREGATED, and rendered imperfectly liquid by the
+partial vaporization of its contained water.
+
+"The second stratum was granite DISINTEGRATED;
+aqueous vapor, having been produced in such abundance
+as to be enabled to rise upward, partially disintegrating
+the crystals of felspar and mica, and superficially
+dissolving those of quartz. This mass would
+reconsolidate into granite, though of a smaller grain
+than the preceding rock.
+
+"The third stratum was so disintegrated that a
+greater part of the mica had been carried up by the
+escaping vapor IN SUSPENSION, and that of quartz in
+solution; the felspar crystals, with the remaining
+quartz and mica, SUBSIDING by their specific gravity
+and arranging themselves in horizontal planes.
+
+"The consolidation of this stratum produced the
+gneiss formation.
+
+"The fourth zone will have been composed of the
+ocean of turbid and heated water, holding mica, etc.,
+in suspension, and quartz, carbonate of lime, etc., in
+solution, and continually traversed by reciprocating
+bodies of heated water rising from below, and of cold
+fluid sinking from the surface, by reason of their specific
+gravities.
+
+"The disturbance thus occasioned will have long
+retarded the deposition of the suspended particles.
+But this must by degrees have taken place, the quartz
+grains and the larger and coarser plates of mica subsiding
+first and the finest last.
+
+"But the fragments of quartz and mica were not
+deposited alone; a great proportion of the quartz held
+in SOLUTION must have been precipitated at the same
+time as the water cooled, and therefore by degrees lost
+its faculty of so much in solution. Thus was gradually
+produced the formation of mica-schist, the mica imperfectly
+recrystallizing or being merely aggregated
+together in horizontal plates, between which the quartz
+either spread itself generally in minute grains or unified
+into crystalline nuclei. On other spots, instead
+of silex, carbonate of lime was precipitated, together
+with more or less of the nucaceous sediment, and gave
+rise to saccharoidal limestones. At a later period,
+when the ocean was yet further cooled down, rock-salt
+and sulphate of lime were locally precipitated in a similar
+mode.
+
+"The fifth stratum was aeriform, and consisted in
+great part of aqueous vapors; the remainder being a
+compound of other elastic fluids (permanent gases)
+which had been formed probably from the volatilization
+of some of the substances contained in the primitive
+granite and carried upward with the aqueous
+vapor from below. These gases will have been either
+mixed together or otherwise disposed, according to
+their different specific gravities or chemical affinities,
+and this stratum constituted the atmosphere or aerial
+envelope of the globe.
+
+"When, in this manner, the general and positive expansion
+of the globe, occasioned by the sudden reduction
+of outward pressure, had ceased (in consequence
+of the REPRESSIVE FORCE, consisting of the weight of its
+fluid envelope, having reached an equilibrium with the
+EXPANSIVE FORCE, consisting of the caloric of the heated
+nucleus), the rapid superficial evaporation of the ocean
+continued; and, by gradually reducing its temperature,
+occasioned the precipitation of a proportionate quantity
+of the minerals it held in solution, particularly its
+silex. These substances falling to the bottom,
+accompanied by a large proportion of the matters held
+in solution, particularly the mica, in consequence of
+the greater comparative tranquillity of the ocean,
+agglomerated these into more or less compact beds of
+rock (the mica-schist formation), producing the first
+crust or solid envelope of the globe. Upon this, other
+stratified rocks, composed sometimes of a mixture,
+sometimes of an alternation of precipitations, sediments,
+and occasionally of conglomerates, were by
+degrees deposited, giving rise to the TRANSITION formations.
+
+"Beneath this crust a new process now commenced.
+The outer zones of crystalline matter having been suddenly
+refrigerated by the rapid vaporization and partial
+escape of the water they contained, abstracted
+caloric from the intensely heated nucleus of the globe.
+These crystalline zones were of unequal density, the
+expansion they had suffered diminishing from above
+downward.
+
+"Their expansive force was, however, equal at all
+points, their temperature everywhere bearing an inverse
+ratio to their density. But when by the accession
+of caloric from the inner and unliquefied nucleus
+the temperature, and consequently the expansive force of the
+lower strata of dilated crystalline
+matter, was augmented, it acted upon the upper and
+more liquefied strata. These being prevented from
+yielding OUTWARDLY by the tenacity and weight of the
+solid involucrum of precipitated and sedimental deposits
+which overspread them, sustained a pressure out
+of proportion to their expansive force, and were in
+consequence proportionately condensed, and by the
+continuance of the process, where the overlying strata
+were sufficiently resistant, finally consolidated.
+
+"This process of consolidation must have progressed
+from above downward, with the increase of the
+expansive force in the lower strata, commencing from
+the upper surface, which, its temperature being lowest,
+offered the least resistance to the force of compression.
+
+"By this process the upper zone of crystalline matter,
+which had intumesced so far as to allow of the escape
+of its aqueous vapor and of much of its mica and
+quartz, was resolidified, the component crystals
+arranging themselves in planes perpendicular to the
+direction of the pressure by which the mass was
+consolidated--that is, to the radius of the globe.
+The gneiss formation, as already observed, was the
+result.
+
+"The inferior zone of barely disintegrated granite,
+from which only a part of the steam and quartz and
+none of the mica had escaped, reconsolidated in a confused
+or granitoidal manner; but exhibits marks of the
+process it had undergone in its broken crystals of felspar
+and mica, its rounded and superficially dissolved
+grains of quartz, its imbedded fragments (broken from
+the more solid parts of the mass, as it rose, and enveloped
+by the softer parts), its concretionary nodules
+and new minerals, etc.
+
+"Beneath this, the granite which had been simply
+disintegrated was again solidified, and returned in all
+respects to its former condition. The temperature,
+however, and with it the expansive force of the inferior
+zone, was continually on the increase, the caloric
+of the interior of the globe still endeavoring to put itself
+in equilibrio by passing off towards the less-intensely
+heated crust.
+
+"This continually increasing expansive force must
+at length have overcome the resistance opposed by the
+tenacity and weight of the overlying consolidated
+strata. It is reasonable to suppose that this result
+took place contemporaneously, or nearly so, on many
+spots, wherever accidental circumstances in the texture
+or composition of the oceanic deposits led them to
+yield more readily; and in this manner were produced
+those original fissures in the primeval crust of the earth
+through some of which (fissures of elevation) were intruded
+portions of interior crystalline zones in a solid
+or nearly solid state, together with more or less of the
+intumescent granite, in the manner above described;
+while others (fissures of eruption) gave rise to extravasations
+of the heated crystalline matter, in the form
+of lavas--that is, still further liquefied by the greater
+comparative reduction of the pressure they endured."[3]
+
+
+The Neptunists stoutly contended for the aqueous
+origin of volcanic as of other mountains. But the
+facts were with Scrope, and as time went on it came
+to be admitted that not merely volcanoes, but many
+"trap" formations not taking the form of craters, had
+been made by the obtrusion of molten rock through
+fissures in overlying strata. Such, for example, to cite
+familiar illustrations, are Mount Holyoke, in Massachusetts,
+and the well-known formation of the Palisades
+along the Hudson.
+
+But to admit the "Plutonic" origin of such widespread
+formations was practically to abandon the Neptunian
+hypothesis. So gradually the Huttonian explanation
+of the origin of granites and other "igneous"
+rocks, whether massed or in veins, came to be accepted.
+Most geologists then came to think of the earth as a
+molten mass, on which the crust rests as a mere film.
+Some, indeed, with Lyell, preferred to believe that the
+molten areas exist only as lakes in a solid crust, heated
+to melting, perhaps, by electrical or chemical action, as
+Davy suggested. More recently a popular theory attempts
+to reconcile geological facts with the claim of
+the physicists, that the earth's entire mass is at least as
+rigid as steel, by supposing that a molten film rests between
+the observed solid crust and the alleged solid
+nucleus. But be that as it may, the theory that
+subterranean heat has been instrumental in determining
+the condition of "primary" rocks, and in producing
+many other phenomena of the earth's crust, has never
+been in dispute since the long controversy between
+the Neptunists and the Plutonists led to its establishment.
+
+
+LYELL AND UNIFORMITARIANISM
+
+If molten matter exists beneath the crust of the
+earth, it must contract in cooling, and in so doing it
+must disturb the level of the portion of the crust already
+solidified. So a plausible explanation of the
+upheaval of continents and mountains was supplied by
+the Plutonian theory, as Hutton had from the first
+alleged. But now an important difference of opinion
+arose as to the exact rationale of such upheavals.
+Hutton himself, and practically every one else who
+accepted his theory, had supposed that there are long
+periods of relative repose, during which the level of the
+crust is undisturbed, followed by short periods of active
+stress, when continents are thrown up with volcanic
+suddenness, as by the throes of a gigantic earthquake.
+But now came Charles Lyell with his famous extension
+of the "uniformitarian" doctrine, claiming that past
+changes of the earth's surface have been like present
+changes in degree as well as in kind. The making of
+continents and mountains, he said, is going on as rapidly
+to-day as at any time in the past. There have been
+no gigantic cataclysmic upheavals at any time, but all
+changes in level of the strata as a whole have been
+gradual, by slow oscillation, or at most by repeated
+earthquake shocks such as are still often experienced.
+
+In support of this very startling contention Lyell
+gathered a mass of evidence of the recent changes in
+level of continental areas. He corroborated by personal
+inspection the claim which had been made by Playfair
+in 1802, and by Von Buch in 1807, that the coast-line of
+Sweden is rising at the rate of from a few inches to
+several feet in a century. He cited Darwin's observations
+going to prove that Patagonia is similarly rising,
+and Pingel's claim that Greenland is slowly sinking.
+Proof as to sudden changes of level of several feet, over
+large areas, due to earthquakes, was brought forward in
+abundance. Cumulative evidence left it no longer open
+to question that such oscillatory changes of level, either
+upward or downward, are quite the rule, and it could
+not be denied that these observed changes, if continued
+long enough in one direction, would produce the highest
+elevations. The possibility that the making of even
+the highest ranges of mountains had been accomplished
+without exaggerated catastrophic action came
+to be freely admitted.
+
+It became clear that the supposedly stable-land surfaces
+are in reality much more variable than the surface
+of the "shifting sea"; that continental masses, seemingly
+so fixed, are really rising and falling in billows
+thousands of feet in height, ages instead of moments
+being consumed in the sweep between crest and hollow.
+
+These slow oscillations of land surfaces being understood,
+many geological enigmas were made clear--
+such as the alternation of marine and fresh-water formations
+in a vertical series, which Cuvier and Brongniart
+had observed near Paris; or the sandwiching of
+layers of coal, of subaerial formation, between layers
+of subaqueous clay or sandstone, which may be observed
+everywhere in the coal measures. In particular,
+the extreme thickness of the sedimentary strata as a
+whole, many times exceeding the depth of the deepest
+known sea, was for the first time explicable when it
+was understood that such strata had formed in slowly
+sinking ocean-beds.
+
+All doubt as to the mode of origin of stratified rocks
+being thus removed, the way was opened for a more
+favorable consideration of that other Huttonian doctrine of the
+extremely slow denudation of land surfaces.
+The enormous amount of land erosion will be patent to
+any one who uses his eyes intelligently in a mountain
+district. It will be evident in any region where the
+strata are tilted--as, for example, the Alleghanies--
+that great folds of strata which must once have risen
+miles in height have in many cases been worn entirely
+away, so that now a valley marks the location of the
+former eminence. Where the strata are level, as in
+the case of the mountains of Sicily, the Scotch Highlands,
+and the familiar Catskills, the evidence of denudation
+is, if possible, even more marked; for here it
+is clear that elevation and valley have been carved by
+the elements out of land that rose from the sea as level
+plateaus.
+
+But that this herculean labor of land-sculpturing
+could have been accomplished by the slow action of
+wind and frost and shower was an idea few men could
+grasp within the first half-century after Hutton propounded
+it; nor did it begin to gain general currency
+until Lyell's crusade against catastrophism, begun
+about 1830, had for a quarter of a century accustomed
+geologists to the thought of slow, continuous changes
+producing final results of colossal proportions. And
+even long after that it was combated by such men as
+Murchison, Director-General of the Geological Survey
+of Great Britain, then accounted the foremost
+field-geologist of his time, who continued to believe
+that the existing valleys owe their main features to
+subterranean forces of upheaval. Even Murchison,
+however, made some recession from the belief of the
+Continental authorities, Elie de Beaumont and
+Leopold von Buch, who contended that the mountains had
+sprung up like veritable jacks-in-the-box. Von Buch,
+whom his friend and fellow-pupil Von Humboldt considered
+the foremost geologist of the time, died in
+1853, still firm in his early faith that the erratic bowlders
+found high on the Jura had been hurled there, like
+cannon-balls, across the valley of Geneva by the sudden
+upheaval of a neighboring mountain-range.
+
+
+AGASSIZ AND THE GLACIAL THEORY
+
+The bowlders whose presence on the crags of the
+Jura the old Gerinan accounted for in a manner so
+theatrical had long been a source of contention among
+geologists. They are found not merely on the Jura, but
+on numberless other mountains in all north-temperate
+latitudes, and often far out in the open country, as
+many a farmer who has broken his plough against them
+might testify. The early geologists accounted for
+them, as for nearly everything else, with their supposititious
+Deluge. Brongniart and Cuvier and Buckland
+and their contemporaries appeared to have no
+difficulty in conceiving that masses of granite weighing
+hundreds of tons had been swept by this current
+scores or hundreds of miles from their source. But,
+of course, the uniformitarian faith permitted no such
+explanation, nor could it countenance the projection
+idea; so Lyell was bound to find some other means of
+transportation for the puzzling erratics.
+
+The only available medium was ice, but, fortunately,
+this one seemed quite sufficient. Icebergs, said Lyell,
+are observed to carry all manner of debris, and deposit
+it in the sea-bottoms. Present land surfaces have often
+been submerged beneath the sea. During the latest of
+these submergences icebergs deposited the bowlders
+now scattered here and there over the land. Nothing
+could be simpler or more clearly uniformitarian. And
+even the catastrophists, though they met Lyell amicably
+on almost no other theoretical ground, were inclined
+to admit the plausibility of his theory of erratics.
+Indeed, of all Lyell's nonconformist doctrines, this
+seemed the one most likely to meet with general acceptance.
+
+Yet, even as this iceberg theory loomed large and
+larger before the geological world, observations were
+making in a different field that were destined to show
+its fallacy. As early as 1815 a sharp-eyed chamois-
+hunter of the Alps, Perraudin by name, had noted the
+existence of the erratics, and, unlike most of his
+companion hunters, had puzzled his head as to how the
+bowlders got where he saw them. He knew nothing of
+submerged continents or of icebergs, still less of
+upheaving mountains; and though he doubtless had heard
+of the Flood, he had no experience of heavy rocks
+floating like corks in water. Moreover, he had never
+observed stones rolling uphill and perching themselves
+on mountain-tops, and he was a good enough uniformitarian
+(though he would have been puzzled indeed
+had any one told him so) to disbelieve that stones in
+past times had disported themselves differently in
+this regard from stones of the present. Yet there the
+stones are. How did they get there?
+
+The mountaineer thought that he could answer that
+question. He saw about him those gigantic serpent-
+like streams of ice called glaciers, "from their far
+fountains slow rolling on," carrying with them blocks of
+granite and other debris to form moraine deposits.
+If these glaciers had once been much more extensive
+than they now are, they might have carried the bowlders
+and left them where we find them. On the other
+hand, no other natural agency within the sphere of
+the chamois-hunter's knowledge could have accomplished
+this, ergo the glaciers must once have been
+more extensive. Perraudin would probably have said
+that common-sense drove him to this conclusion; but
+be that as it may, he had conceived one of the few truly
+original and novel ideas of which the nineteenth century
+can boast.
+
+Perraudin announced his idea to the greatest scientist
+in his little world--Jean de Charpentier, director
+of the mines at Bex, a skilled geologist who had been a
+fellow-pupil of Von Buch and Von Humboldt under
+Werner at the Freiberg School of Mines. Charpentier
+laughed at the mountaineer's grotesque idea, and
+thought no more about it. And ten years elapsed
+before Perraudin could find any one who treated his
+notion with greater respect. Then he found a listener
+in M. Venetz, a civil engineer, who read a paper on the
+novel glacial theory before a local society in 1823.
+This brought the matter once more to the attention of
+De Charpentier, who now felt that there might be
+something in it worth investigation.
+
+A survey of the field in the light of the new theory
+soon convinced Charpentier that the chamois-hunter
+had all along been right. He became an enthusiastic
+supporter of the idea that the Alps had once been imbedded
+in a mass of ice, and in 1836 he brought the
+notion to the attention of Louis Agassiz, who was
+spending the summer in the Alps. Agassiz was sceptical
+at first, but soon became a convert.
+
+In 1840 Agassiz published a paper in which the results
+of his Alpine studies were elaborated.
+
+"Let us consider," he says, "those more considerable
+changes to which glaciers are subject, or rather, the
+immense extent which they had in the prehistoric
+period. This former immense extension, greater than
+any that tradition has preserved, is proved, in the case
+of nearly every valley in the Alps, by facts which are
+both many and well established. The study of these
+facts is even easy if the student is looking out for
+them, and if he will seize the least indication of their
+presence; and, if it were a long time before they were
+observed and connected with glacial action, it is because
+the evidences are often isolated and occur at
+places more or less removed from the glacier which
+originated them. If it be true that it is the prerogative
+of the scientific observer to group in the field of his
+mental vision those facts which appear to be without
+connection to the vulgar herd, it is, above all, in such a
+case as this that he is called upon to do so. I have
+often compared these feeble effects, produced by the
+glacial action of former ages, with the appearance of
+the markings upon a lithographic stone, prepared for
+the purpose of preservation, and upon which one
+cannot see the lines of the draughtsman's work unless
+it is known beforehand where and how to search for
+them.
+
+"The fact of the former existence of glaciers which
+have now disappeared is proved by the survival of the
+various phenomena which always accompany them,
+and which continue to exist even after the ice has
+melted. These phenomena are as follows:
+
+"1. Moraines.--The disposition and composition
+of moraines enable them to be always recognized, even
+when they are no longer adjacent to a glacier nor
+immediately surround its lower extremities. I may remark
+that lateral and terminal moraines alone enable
+us to recognize with certainty the limits of glacial
+extension, because they can be easily distinguished from
+the dikes and irregularly distributed stones carried
+down by the Alpine torrents, The lateral moraines
+deposited upon the sides of valleys are rarely affected
+by the larger torrents, but they are, however, often
+cut by the small streams which fall down the side of
+a mountain, and which, by interfering with their
+continuity, make them so much more difficult to recognize.
+
+"2. The Perched Bowlders.--It often happens that
+glaciers encounter projecting points of rock, the sides
+of which become rounded, and around which funnel-
+like cavities are formed with more or less profundity.
+When glaciers diminish and retire, the blocks which
+have fallen into these funnels often remain perched
+upon the top of the projecting rocky point within it, in
+such a state of equilibrium that any idea of a current of
+water as the cause of their transportation is completely
+inadmissible on account of their position. When
+such points of rock project above the surface of the
+glacier or appear as a more considerable islet in the
+midst of its mass (such as is the case in the Jardin of
+the Mer de Glace, above Montavert), such projections
+become surrounded on all sides by stones which ultimately
+form a sort of crown around the summit whenever
+the glaciers decrease or retire completely. Water
+currents never produce anything like this; but, on the
+contrary, whenever a stream breaks itself against a
+projecting rock, the stones which it carries down are
+turned aside and form a more or less regular trail.
+Never, under such circumstances, can the stones remain
+either at the top or at the sides of the rock, for, if
+such a thing were possible, the rapidity of the current
+would be accelerated by the increased resistance, and
+the moving bowlders would be carried beyond the obstruction
+before they were finally deposited.
+
+"3. The polished and striated rocks, such as have
+been described in Chapter XIV., afford yet further evidence
+of the presence of a glacier; for, as has been said
+already, neither a current nor the action of waves upon
+an extensive beach produces such effects. The general
+direction of the channels and furrows indicates the
+direction of the general movement of the glacier, and
+the streaks which vary more or less from this direction
+are produced by the local effects of oscillation and retreat,
+as we shall presently see.
+
+"4. The Lapiaz, or Lapiz, which the inhabitants of
+German Switzerland call Karrenfelder, cannot always
+be distinguished from erosions, because, both produced
+as they are by water, they do not differ in their exterior
+characteristics, but only in their positions.
+Erosions due to torrents are always found in places
+more or less depressed, and never occur upon large inclined
+surfaces. The Lapiaz, on the contrary, are
+frequently found upon the projecting parts of the sides
+of valleys in places where it is not possible to suppose
+that water has ever formed a current. Some geologists,
+in their embarrassment to explain these phenomena,
+have supposed that they were due to the infiltration
+of acidulated water, but this hypothesis is purely
+gratuitous.
+
+"We will now describe the remains of these various
+phenomena as they are found in the Alps outside the
+actual glacial limits, in order to prove that at a certain
+epoch glaciers were much larger than they are to-day.
+
+"The ancient moraines, situated as they are at a
+great distance from those of the present day, are nowhere
+so distinct or so frequent as in Valais, where
+MM. Venetz and J. de Charpentier noticed them for
+the first time; but as their observations are as yet
+unpublished, and they themselves gave me the information,
+it would be an appropriation of their discovery
+if I were to describe them here in detail. I will limit
+myself to say that there can be found traces, more or
+less distinct, of ancient terminal moraines in the form
+of vaulted dikes at the foot of every glacier, at a distance
+of a few minutes' walk, a quarter of an hour, a
+half-hour, an hour, and even of several leagues from
+their present extremities. These traces become less
+distinct in proportion to their distance from the glacier,
+and, since they are also often traversed by torrents,
+they are not as continuous as the moraines which are
+nearer to the glaciers. The farther these ancient
+moraines are removed from the termination of a glacier,
+the higher up they reach upon the sides of the valley,
+which proves to us that the thickness of the glacier
+must have been greater when its size was larger. At
+the same time, their number indicates so many stopping-places
+in the retreat of the glacier, or so many extreme
+limits of its extension--limits which were never
+reached again after it had retired. I insist upon this
+point, because if it is true that all these moraines
+demonstrate a larger extent of the glacier, they also prove
+that their retreat into their present boundaries, far
+from having been catastrophic, was marked on the
+contrary by periods of repose more or less frequent,
+which caused the formation of a series of concentric
+moraines which even now indicate their retrogression.
+
+"The remains of longitudinal moraines are less frequent,
+less distinct, and more difficult to investigate,
+because, indicating as they do the levels to which the
+edges of the glacier reached at different epochs, it is
+generally necessary to look for them above the line of
+the paths along the escarpments of the valleys, and
+hence it is not always possible to follow them along a
+valley. Often, also, the sides of a valley which enclosed
+a glacier are so steep that it is only here and
+there that the stones have remained in place. They
+are, nevertheless, very distinct in the lower part of the
+valley of the Rhone, between Martigny and the Lake
+of Geneva, where several parallel ridges can be observed,
+one above the other, at a height of one thousand,
+one thousand two hundred, and even one thousand
+five hundred feet above the Rhone. It is between
+St. Maurice and the cascade of Pissevache, close to
+the hamlet of Chaux-Fleurie, that they are most accessible,
+for at this place the sides of the valley at different
+levels ascend in little terraces, upon which the
+moraines have been preserved. They are also very
+distinct above the Bains de Lavey, and above the
+village of Monthey at the entrance of the Val d'Illiers,
+where the sides of the valley are less inclined than in
+many other places.
+
+"The perched bowlders which are found in the Alpine
+valleys, at considerable distances from the glaciers,
+occupy at times positions so extraordinary that they
+excite in a high degree the curiosity of those who see
+them. For instance, when one sees an angular stone
+perched upon the top of an isolated pyramid, or resting
+in some way in a very steep locality, the first inquiry
+of the mind is, When and how have these stones been
+placed in such positions, where the least shock would
+seem to turn them over? But this phenomenon is not
+in the least astonishing when it is seen to occur also
+within the limits of actual glaciers, and it is recalled
+by what circumstances it is occasioned.
+
+"The most curious examples of perched stones
+which can be cited are those which command the
+northern part of the cascade of Pissevache, close to
+Chaux-Fleurie, and those above the Bains de Lavey,
+close to the village of Morcles; and those, even more
+curious, which I have seen in the valley of St. Nicolas
+and Oberhasli. At Kirchet, near Meiringen, can be seen
+some very remarkable crowns of bowlders around several
+domes of rock which appear to have been projected
+above the surface of the glacier which surrounded
+them. Something very similar can be seen around the
+top of the rock of St. Triphon.
+
+"The extraordinary phenomenon of perched stones
+could not escape the observing eye of De Saussure,
+who noticed several at Saleve, of which he described
+the positions in the following manner: 'One sees,'
+said he, 'upon the slope of an inclined meadow, two
+of these great bowlders of granite, elevated one upon
+the other, above the grass at a height of two or three
+feet, upon a base of limestone rock on which both rest.
+This base is a continuation of the horizontal strata of
+the mountain, and is even united with it visibly on its
+lower face, being cut perpendicularly upon the other
+sides, and is not larger than the stone which it
+supports.' But seeing that the entire mountain is
+composed of the same limestone, De Saussure naturally
+concluded that it would be absurd to think that it was
+elevated precisely and only beneath the blocks of
+granite. But, on the other hand, since he did not
+know the manner in which these perched stones are
+deposited in our days by glacial action, he had recourse
+to another explanation: He supposes that the
+rock was worn away around its base by the continual
+erosion of water and air, while the portion of the rock
+which served as the base for the granite had been protected
+by it. This explanation, although very ingenious,
+could no longer be admitted after the researches
+of M. Elie de Beaumont had proved that the
+action of atmospheric agencies was not by a good deal
+so destructive as was theretofore supposed. De Saussure
+speaks also of a detached bowlder, situated upon
+the opposite side of the Tete-Noire, 'which is,' he says,
+'of so great a size that one is tempted to believe that it
+was formed in the place it occupies; and it is called
+Barme russe, because it is worn away beneath in the
+form of a cave which can afford accommodation for
+more than thirty persons at a time."[4]
+
+But the implications of the theory of glaciers extend,
+so Agassiz has come to believe, far beyond the
+Alps. If the Alps had been covered with an ice sheet,
+so had many other regions of the northern hemisphere.
+Casting abroad for evidences of glacial action, Agassiz
+found them everywhere in the form of transported
+erratics, scratched and polished outcropping rocks,
+and moraine-like deposits. Finally, he became convinced
+that the ice sheet that covered the Alps had
+spread over the whole of the higher latitudes of the
+northern hemisphere, forming an ice cap over the globe.
+Thus the common-sense induction of the chamois-
+hunter blossomed in the mind of Agassiz into the
+conception of a universal ice age.
+
+In 1837 Agassiz had introduced his theory to the
+world, in a paper read at Neuchatel, and three years
+later he published his famous Etudes sur les Glaciers,
+from which we have just quoted. Never did idea make
+a more profound disturbance in the scientific world.
+Von Buch treated it with alternate ridicule, contempt,
+and rage; Murchison opposed it with customary vigor;
+even Lyell, whose most remarkable mental endowment
+was an unfailing receptiveness to new truths,
+could not at once discard his iceberg theory in favor
+of the new claimant. Dr. Buckland, however, after
+Agassiz had shown him evidence of former glacial action
+in his own Scotland, became a convert--the more
+readily, perhaps, as it seemed to him to oppose the
+uniformitarian idea. Gradually others fell in line, and
+after the usual imbittered controversy and the inevitable
+full generation of probation, the idea of an ice
+age took its place among the accepted tenets of geology. All
+manner of moot points still demanded attention--the
+cause of the ice age, the exact extent of the
+ice sheet, the precise manner in which it produced its
+effects, and the exact nature of these effects; and not
+all of these have even yet been determined. But, details
+aside, the ice age now has full recognition from
+geologists as an historical period. There may have
+been many ice ages, as Dr. Croll contends; there was
+surely one; and the conception of such a period is one
+of the very few ideas of our century that no previous
+century had even so much as faintly adumbrated.
+
+
+THE GEOLOGICAL AGES
+
+But, for that matter, the entire subject of historical
+geology is one that had but the barest beginning before
+our century. Until the paleontologist found out the
+key to the earth's chronology, no one--not even Hutton--
+could have any definite idea as to the true story
+of the earth's past. The only conspicuous attempt to
+classify the strata was that made by Werner, who divided
+the rocks into three systems, based on their supposed
+order of deposition, and called primary, transition,
+and secondary.
+
+Though Werner's observations were confined to the
+small province of Saxony, he did not hesitate to affirm
+that all over the world the succession of strata would be
+found the same as there, the concentric layers, according
+to this conception, being arranged about the earth
+with the regularity of layers on an onion. But in this
+Werner was as mistaken as in his theoretical explanation
+of the origin of the "primary" rocks. It required
+but little observation to show that the exact succession
+of strata is never precisely the same in any widely separated
+regions. Nevertheless, there was a germ of
+truth in Werner's system. It contained the idea, however
+faultily interpreted, of a chronological succession
+of strata; and it furnished a working outline for the
+observers who were to make out the true story of
+geological development. But the correct interpretation
+of the observed facts could only be made after the
+Huttonian view as to the origin of strata had gained
+complete acceptance.
+
+When William Smith, having found the true key to
+this story, attempted to apply it, the territory with
+which he had to deal chanced to be one where the surface
+rocks are of that later series which Werner termed
+secondary. He made numerous subdivisions within
+this system, based mainly on the fossils. Meantime it
+was found that, judged by the fossils, the strata that
+Brongniart and Cuvier studied near Paris were of a still
+more recent period (presumed at first to be due to the
+latest deluge), which came to be spoken of as tertiary.
+It was in these beds, some of which seemed to have
+been formed in fresh-water lakes, that many of the
+strange mammals which Cuvier first described were
+found.
+
+But the "transition" rocks, underlying the "secondary"
+system that Smith studied, were still practically
+unexplored when, along in the thirties, they were taken
+in hand by Roderick Impey Murchison, the reformed
+fox-hunter and ex-captain, who had turned geologist to
+such notable advantage, and Adam Sedgwick, the brilliant
+Woodwardian professor at Cambridge.
+
+Working together, these two friends classified the
+
+transition rocks into chronological groups, since familiar
+to every one in the larger outlines as the Silurian
+system (age of invertebrates) and the Devonian system
+(age of fishes)--names derived respectively from the
+country of the ancient Silures, in Wales and Devonshire,
+England. It was subsequently discovered that
+these systems of strata, which crop out from beneath
+newer rocks in restricted areas in Britain, are spread
+out into broad, undisturbed sheets over thousands of
+miles in continental Europe and in America. Later on
+Murchison studied them in Russia, and described them,
+conjointly with Verneuil and Von Kerserling, in a
+ponderous and classical work. In America they were
+studied by Hall, Newberry, Whitney, Dana, Whitfield,
+and other pioneer geologists, who all but anticipated
+their English contemporaries.
+
+The rocks that are of still older formation than those
+studied by Murchison and Sedgwick (corresponding in
+location to the "primary" rocks of Werner's conception)
+are the surface feature of vast areas in Canada,
+and were first prominently studied there by William I.
+Logan, of the Canadian Government Survey, as early as
+1846, and later on by Sir William Dawson. These rocks
+--comprising the Laurentian system--were formerly
+supposed to represent parts of the original crust of the
+earth, formed on first cooling from a molten state; but
+they are now more generally regarded as once-stratified
+deposits metamorphosed by the action of heat.
+
+Whether "primitive" or metamorphic, however,
+these Canadian rocks, and analogous ones beneath the
+fossiliferous strata of other countries, are the oldest
+portions of the earth's crust of which geology has any
+present knowledge. Mountains of this formation, as
+the Adirondacks and the Storm King range, overlooking
+the Hudson near West Point, are the patriarchs of their
+kind, beside which Alleghanies and Sierra Nevadas are
+recent upstarts, and Rockies, Alps, and Andes are mere
+parvenus of yesterday.
+
+The Laurentian rocks were at first spoken of as representing
+"Azoic" time; but in 1846 Dawson found a
+formation deep in their midst which was believed to b e
+the fossil relic of a very low form of life, and after that it
+became customary to speak of the system as "Eozoic."
+Still more recently the title of Dawson's supposed fossil
+to rank as such has been questioned, and Dana's suggestion
+that the early rocks be termed merely Archman
+has met with general favor. Murchison and Sedgwick's
+Silurian, Devonian, and Carboniferous groups
+(the ages of invertebrates, of fishes, and of coal plants,
+respectively) are together spoken of as representing
+Paleozoic time. William Smith's system of strata,
+next above these, once called "secondary," represents
+Mesozoic time, or the age of reptiles. Still higher, or
+more recent, are Cuvier and Brongniart's tertiary rocks,
+representing the age of mammals. Lastly, the most
+recent formations, dating back, however, to a period
+far enough from recent in any but a geological sense,
+are classed as quaternary, representing the age of
+man.
+
+It must not be supposed, however, that the successive
+"ages" of the geologist are shut off from one another in
+any such arbitrary way as this verbal classification
+might seem to suggest. In point of fact, these "ages"
+have no better warrant for existence than have the
+"centuries" and the "weeks" of every-day computation.
+They are convenient, and they may even stand
+for local divisions in the strata, but they are bounded
+by no actual gaps in the sweep of terrestrial events.
+
+Moreover, it must be understood that the "ages" of
+different continents, though described under the same
+name, are not necessarily of exact contemporaneity.
+There is no sure test available by which it could be
+shown that the Devonian age, for instance, as outlined
+in the strata of Europe, did not begin millions of years
+earlier or later than the period whose records are said
+to represent the Devonian age in America. In attempting
+to decide such details as this, mineralogical
+data fail us utterly. Even in rocks of adjoining regions
+identity of structure is no proof of contemporaneous
+origin; for the veritable substance of the rock of one
+age is ground up to build the rocks of subsequent ages.
+Furthermore, in seas where conditions change but little
+the same form of rock may be made age after age. It
+is believed that chalk-beds still forming in some of our
+present seas may form one continuous mass dating back
+to earliest geologic ages. On the other hand, rocks
+different in character maybe formed at the same time in
+regions not far apart--say a sandstone along shore, a
+coral limestone farther seaward, and a chalk-bed beyond.
+This continuous stratum, broken in the process
+of upheaval, might seem the record of three different
+epochs.
+
+Paleontology, of course, supplies far better chronological
+tests, but even these have their limitations.
+There has been no time since rocks now in existence
+were formed, if ever, when the earth had a uniform
+climate and a single undiversified fauna over its entire
+land surface, as the early paleontologists supposed.
+Speaking broadly, the same general stages have attended
+the evolution of organic forms everywhere, but there
+is nothing to show that equal periods of time witnessed
+corresponding changes in diverse regions, but quite the
+contrary. To cite but a single illustration, the marsupial
+order, which is the dominant mammalian type
+of the living fauna of Australia to-day, existed in Europe
+and died out there in the tertiary age. Hence a
+future geologist might think the Australia of to-day
+contemporaneous with a period in Europe which in
+reality antedated it by perhaps millions of years.
+
+All these puzzling features unite to render the subject
+of historical geology anything but the simple matter
+the fathers of the science esteemed it. No one
+would now attempt to trace the exact sequence of
+formation of all the mountains of the globe, as Elie de
+Beaumont did a half-century ago. Even within the
+limits of a single continent, the geologist must proceed
+with much caution in attempting to chronicle the order
+in which its various parts rose from the matrix of the
+sea. The key to this story is found in the identification
+of the strata that are the surface feature in each
+territory. If Devonian rocks are at the surface in any
+given region, for example, it would appear that this
+region became a land surface in the Devonian age, or
+just afterwards. But a moment's consideration shows
+that there is an element of uncertainty about this, due
+to the steady denudation that all land surfaces undergo.
+The Devonian rocks may lie at the surface simply because
+the thousands of feet of carboniferous strata that
+once lay above them have been worn away. All that
+the cautious geologist dare assert, therefore, is that the
+region in question did not become permanent land surface
+earlier than the Devonian age.
+
+But to know even this is much--sufficient, indeed, to
+establish the chronological order of elevation, if not its
+exact period, for all parts of any continent that have
+been geologically explored--understanding always that
+there must be no scrupling about a latitude of a few
+millions or perhaps tens of millions of years here and
+there.
+
+Regarding our own continent, for example, we learn
+through the researches of a multitude of workers that
+in the early day it was a mere archipelago. Its chief
+island--the backbone of the future continent--was a
+great V-shaped area surrounding what is now Hudson
+Bay, an area built tip, perhaps, through denudation of a
+yet more ancient polar continent, whose existence is
+only conjectured. To the southeast an island that is
+now the Adirondack Mountains, and another that is now
+the Jersey Highlands rose above the waste of waters,
+and far to the south stretched probably a line of islands
+now represented by the Blue Ridge Mountains.
+Far off to the westward another line of islands
+foreshadowed our present Pacific border. A few minor
+islands in the interior completed the archipelago.
+
+From this bare skeleton the continent grew, partly
+by the deposit of sediment from the denudation of the
+original islands (which once towered miles, perhaps,
+where now they rise thousands of feet), but largely also
+by the deposit of organic remains, especially in the interior
+sea, which teemed with life. In the Silurian
+ages, invertebrates--brachiopods and crinoids and
+cephalopods--were the dominant types. But very
+early--no one knows just when--there came fishes of
+many strange forms, some of the early ones enclosed
+in turtle-like shells. Later yet, large spaces within the
+interior sea having risen to the surface, great marshes
+or forests of strange types of vegetation grew and
+deposited their remains to form coal-beds. Many times
+over such forests were formed, only to be destroyed by
+the oscillations of the land surface. All told, the strata
+of this Paleozoic period aggregate several miles in thickness,
+and the time consumed in their formation stands
+to all later time up to the present, according to Professor
+Dana's estimate, as three to one.
+
+Towards the close of this Paleozoic era the Appalachian
+Mountains were slowly upheaved in great convoluted
+folds, some of them probably reaching three or
+four miles above the sea-level, though the tooth of time
+has since gnawed them down to comparatively puny
+limits. The continental areas thus enlarged were
+peopled during the ensuing Mesozoic time with multitudes
+of strange reptiles, many of them gigantic in size.
+The waters, too, still teeming with invertebrates and
+fishes, had their quota of reptilian monsters; and in the
+air were flying reptiles, some of which measured twenty-
+five feet from tip to tip of their batlike wings. During
+this era the Sierra Nevada Mountains rose. Near the
+eastern border of the forming continent the strata were
+perhaps now too thick and stiff to bend into mountain
+folds, for they were rent into great fissures, letting out
+floods of molten lava, remnants of which are still in
+evidence after ages of denudation, as the Palisades
+along the Hudson, and such elevations as Mount Holyoke
+in western Massachusetts.
+
+Still there remained a vast interior sea, which later
+on, in the tertiary age, was to be divided by the slow
+uprising of the land, which only yesterday--that is to
+say, a million, or three or five or ten million, years ago--
+became the Rocky Mountains. High and erect these
+young mountains stand to this day, their sharp angles
+and rocky contours vouching for their youth, in strange
+contrast with the shrunken forms of the old Adirondacks,
+Green Mountains, and Appalachians, whose lowered
+heads and rounded shoulders attest the weight of
+ages. In the vast lakes which still remained on either
+side of the Rocky range, tertiary strata were slowly
+formed to the ultimate depth of two or three miles, enclosing
+here and there those vertebrate remains which
+were to be exposed again to view by denudation when
+the land rose still higher, and then, in our own time, to
+tell so wonderful a story to the paleontologist.
+
+Finally, the interior seas were filled, and the shore
+lines of the continent assumed nearly their present outline.
+
+Then came the long winter of the glacial epoch--perhaps
+of a succession of glacial epochs. The ice sheet
+extended southward to about the fortieth parallel, driving
+some animals before it, and destroying those that
+were unable to migrate. At its fulness, the great ice
+mass lay almost a mile in depth over New England, as
+attested by the scratched and polished rock surfaces
+and deposited erratics in the White Mountains. Such
+a mass presses down with a weight of about one hundred
+and twenty-five tons to the square foot, according
+to Dr. Croll's estimate. It crushed and ground everything
+beneath it more or less, and in some regions
+planed off hilly surfaces into prairies. Creeping slowly
+forward, it carried all manner of debris with it. When
+it melted away its terminal moraine built up the nucleus
+of the land masses now known as Long Island
+and Staten Island; other of its deposits formed the
+"drumlins" about Boston famous as Bunker and
+Breed's hills; and it left a long, irregular line of ridges
+of "till" or bowlder clay and scattered erratics clear
+across the country at about the latitude of New York
+city.
+
+As the ice sheet slowly receded it left minor moraines
+all along its course. Sometimes its deposits dammed
+up river courses or inequalities in the surface, to form
+the lakes which everywhere abound over Northern territories.
+Some glacialists even hold the view first suggested
+by Ramsey, of the British Geological Survey,
+that the great glacial sheets scooped out the basins of
+many lakes, including the system that feeds the St.
+Lawrence. At all events, it left traces of its presence
+all along the line of its retreat, and its remnants exist
+to this day as mountain glaciers and the polar ice cap.
+Indeed, we live on the border of the last glacial epoch,
+for with the closing of this period the long geologic past
+merges into the present.
+
+
+PAST, PRESENT, AND FUTURE
+
+And the present, no less than the past, is a time of
+change. This is the thought which James Hutton conceived
+more than a century ago, but which his contemporaries
+and successors were so very slow to appreciate.
+Now, however, it has become axiomatic--one can hardly
+realize that it was ever doubted. Every new scientific
+truth, says Agassiz, must pass through three stages
+--first, men say it is not true; then they declare it hostile
+to religion; finally, they assert that every one has
+known it always. Hutton's truth that natural law is
+changeless and eternal has reached this final stage.
+Nowhere now could you find a scientist who would dispute
+the truth of that text which Lyell, quoting from
+Playfair's Illustrations of the Huttonian Theory, printed
+on the title-page of his Principles: "Amid all the
+revolutions of the globe the economy of Nature has been
+uniform, and her laws are the only things that have
+resisted the general movement. The rivers and the
+rocks, the seas and the continents, have been changed
+in all their parts; but the laws which direct those
+changes, and the rules to which they are subject, have
+remained invariably the same."
+
+But, on the other hand, Hutton and Playfair, and in
+particular Lyell, drew inferences from this principle
+which the modern physicist can by no means admit.
+To them it implied that the changes on the surface of
+the earth have always been the same in degree as well
+as in kind, and must so continue while present forces
+hold their sway. In other words, they thought of the
+world as a great perpetual-motion machine. But the
+modern physicist, given truer mechanical insight by the
+doctrines of the conservation and the dissipation of energy,
+will have none of that. Lord Kelvin, in particular,
+has urged that in the periods of our earth's in
+fancy and adolescence its developmental changes must
+have been, like those of any other infant organism,
+vastly more rapid and pronounced than those of a later
+day; and to every clear thinker this truth also must
+now seem axiomatic.
+
+Whoever thinks of the earth as a cooling globe can
+hardly doubt that its crust, when thinner, may have
+heaved under strain of the moon's tidal pull--whether
+or not that body was nearer--into great billows, daily
+rising and falling, like waves of the present seas vastly
+magnified.
+
+Under stress of that same lateral pressure from contraction
+which now produces the slow depression of the
+Jersey coast, the slow rise of Sweden, the occasional
+belching of an insignificant volcano, the jetting of a
+geyser, or the trembling of an earthquake, once large
+areas were rent in twain, and vast floods of lava flowed
+over thousands of square miles of the earth's surface,
+perhaps, at a single jet; and, for aught we know to the
+contrary, gigantic mountains may have heaped up their
+contorted heads in cataclysms as spasmodic as even the
+most ardent catastrophist of the elder day of geology
+could have imagined.
+
+The atmosphere of that early day, filled with vast
+volumes of carbon, oxygen, and other chemicals that
+have since been stored in beds of coal, limestone, and
+granites, may have worn down the rocks on the one
+hand and built up organic forms on the other, with a
+rapidity that would now seem hardly conceivable.
+
+And yet while all these anomalous things went on,
+the same laws held sway that now are operative; and a
+true doctrine of uniformitarianism would make no
+unwonted concession in conceding them all--though
+most of the imbittered geological controversies of the
+middle of the nineteenth century were due to the failure
+of both parties to realize that simple fact.
+
+And as of the past and present, so of the future. The
+same forces will continue to operate; and under operation
+of these unchanging forces each day will differ
+from every one that has preceded it. If it be true, as
+every physicist believes, that the earth is a cooling
+globe, then, whatever its present stage of refrigeration,
+the time must come when its surface contour will assume
+a rigidity of level not yet attained. Then, just
+as surely, the slow action of the elements will continue
+to wear away the land surfaces, particle by particle,
+and transport them to the ocean, as it does to-day,
+until, compensation no longer being afforded by the
+upheaval of the continents, the last foot of dry land will
+sink for the last time beneath the water, the last mountain-
+peak melting away, and our globe, lapsing like
+any other organism into its second childhood, will be
+on the surface--as presumably it was before the first
+continent rose--one vast "waste of waters." As puny
+man conceives time and things, an awful cycle will
+have lapsed; in the sweep of the cosmic life, a pulse-
+beat will have throbbed.
+
+
+
+V. THE NEW SCIENCE OF METEOROLOGY
+
+METEORITES
+
+"An astonishing miracle has just occurred in our district,"
+wrote M. Marais, a worthy if undistinguished
+citizen of France, from his home at L'Aigle, under date
+of "the 13th Floreal, year 11"--a date which outside
+of France would be interpreted as meaning May 3,
+1803. This "miracle" was the appearance of a "fireball"
+in broad daylight--"perhaps it was wildfire,"
+says the naive chronicle--which "hung over the meadow,"
+being seen by many people, and then exploded
+with a loud sound, scattering thousands of stony fragments
+over the surface of a territory some miles in extent.
+
+Such a "miracle" could not have been announced at
+a more opportune time. For some years the scientific
+world had been agog over the question whether such a
+form of lightning as that reported--appearing in a clear
+sky, and hurling literal thunderbolts--had real existence.
+Such cases had been reported often enough, it
+is true. The "thunderbolts" themselves were exhibited
+as sacred relics before many an altar, and those
+who doubted their authenticity had been chided as
+having "an evil heart of unbelief." But scientific
+scepticism had questioned the evidence, and late in the
+eighteenth century a consensus of opinion in the French
+Academy had declined to admit that such stones had
+been "conveyed to the earth by lightning," let alone
+any more miraculous agency.
+
+In 1802, however, Edward Howard had read a paper
+before the Royal Society in which, after reviewing the
+evidence recently put forward, he had reached the conclusion
+that the fall of stones from the sky, sometimes
+or always accompanied by lightning, must be admitted
+as an actual phenomenon, however inexplicable. So
+now, when the great stone-fall at L'Aigle was announced,
+the French Academy made haste to send the
+brilliant young physicist Jean Baptiste Biot to investigate
+it, that the matter might, if possible, be set finally
+at rest. The investigation was in all respects successful,
+and Biot's report transferred the stony or metallic
+lightning-bolt--the aerolite or meteorite--from the realm
+of tradition and conjecture to that of accepted science.
+
+But how explain this strange phenomenon? At
+once speculation was rife. One theory contended
+that the stony masses had not actually fallen, but had
+been formed from the earth by the action of the lightning;
+but this contention was early abandoned. The
+chemists were disposed to believe that the aerolites had
+been formed by the combination of elements floating in
+the upper atmosphere. Geologists, on the other hand,
+thought them of terrestrial origin, urging that they
+might have been thrown up by volcanoes. The astronomers,
+as represented by Olbers and Laplace, modified
+this theory by suggesting that the stones might,
+indeed, have been cast out by volcanoes, but by volcanoes
+situated not on the earth, but on the moon.
+
+And one speculator of the time took a step even
+more daring, urging that the aerolites were neither of
+telluric nor selenitic origin, nor yet children of the sun,
+as the old Greeks had, many of them, contended, but
+that they are visitants from the depths of cosmic space.
+This bold speculator was the distinguished German
+physicist Ernst F. F. Chladni, a man of no small repute
+in his day. As early as 1794 he urged his cosmical
+theory of meteorites, when the very existence of meteorites
+was denied by most scientists. And he did
+more: he declared his belief that these falling stones
+were really one in origin and kind with those flashing
+meteors of the upper atmosphere which are familiar
+everywhere as "shooting-stars."
+
+Each of these coruscating meteors, he affirmed, must
+tell of the ignition of a bit of cosmic matter entering
+the earth's atmosphere. Such wandering bits of matter
+might be the fragments of shattered worlds, or, as
+Chladni thought more probable, merely aggregations
+of "world stuff" never hitherto connected with any
+large planetary mass.
+
+Naturally enough, so unique a view met with very
+scant favor. Astronomers at that time saw little to
+justify it; and the non-scientific world rejected it with
+fervor as being "atheistic and heretical," because its
+acceptance would seem to imply that the universe is
+not a perfect mechanism.
+
+Some light was thrown on the moot point presently
+by the observations of Brandes and Benzenberg, which
+tended to show that falling-stars travel at an actual
+speed of from fifteen to ninety miles a second. This observation
+tended to discredit the selenitic theory, since
+an object, in order to acquire such speed in falling
+merely from the moon, must have been projected with
+an initial velocity not conceivably to be given by any
+lunar volcanic impulse. Moreover, there was a growing
+conviction that there are no active volcanoes on the
+moon, and other considerations of the same tenor led
+to the complete abandonment of the selenitic theory.
+
+But the theory of telluric origin of aerolites was by
+no means so easily disposed of. This was an epoch
+when electrical phenomena were exciting unbounded
+and universal interest, and there was a not unnatural
+tendency to appeal to electricity in explanation of
+every obscure phenomenon; and in this case the seeming
+similarity between a lightning flash and the flash
+of an aerolite lent color to the explanation. So we
+find Thomas Forster, a meteorologist of repute, still
+adhering to the atmospheric theory of formation of
+aerolites in his book published in 1823; and, indeed, the
+prevailing opinion of the time seemed divided between
+various telluric theories, to the neglect of any cosmical
+theory whatever.
+
+But in 1833 occurred a phenomenon which set the
+matter finally at rest. A great meteoric shower occurred
+in November of that year, and in observing it
+Professor Denison Olmstead, of Yale, noted that all the
+stars of the shower appeared to come from a single
+centre or vanishing-point in the heavens, and that
+this centre shifted its position with the stars, and hence
+was not telluric. The full significance of this observation
+was at once recognized by astronomers; it demonstrated
+beyond all cavil the cosmical origin of the
+shooting-stars. Some conservative meteorologists kept
+up the argument for the telluric origin for some decades
+to come, as a matter of course--such a band trails
+always in the rear of progress. But even these doubters
+were silenced when the great shower of shooting-
+stars appeared again in 1866, as predicted by Olbers
+and Newton, radiating from the same point of the
+heavens as before.
+
+Since then the spectroscope has added its confirmatory
+evidence as to the identity of meteorite and shooting-star,
+and, moreover, has linked these atmospheric
+meteors with such distant cosmic residents as comets
+and nebulae. Thus it appears that Chladni's daring
+hypothesis of 1794 has been more than verified, and
+that the fragments of matter dissociated from planetary
+connection--which be postulated and was declared
+atheistic for postulating--have been shown to
+be billions of times more numerous than any larger
+cosmic bodies of which we have cognizance--so widely
+does the existing universe differ from man's preconceived
+notions as to what it should be.
+
+Thus also the "miracle" of the falling stone, against
+which the scientific scepticism of yesterday presented
+"an evil heart of unbelief," turns out to be the most
+natural phenomena, inasmuch as it is repeated in our
+atmosphere some millions of times each day.
+
+
+THE AURORA BOREALIS
+
+If fire-balls were thought miraculous and portentous
+in days of yore, what interpretation must needs have
+been put upon that vastly more picturesque phenomenon,
+the aurora? "Through all the city," says the
+Book of Maccabees, "for the space of almost forty days,
+there were seen horsemen running in the air, in cloth
+of gold, armed with lances, like a band of soldiers: and
+troops of horsemen in array encountering and running
+one against another, with shaking of shields and multitude
+of pikes, and drawing of swords, and casting of
+darts, and glittering of golden ornaments and harness."
+Dire omens these; and hardly less ominous the aurora
+seemed to all succeeding generations that observed it
+down well into the eighteenth century--as witness
+the popular excitement in England in 1716 over the
+brilliant aurora of that year, which became famous
+through Halley's description.
+
+But after 1752, when Franklin dethroned the lightning,
+all spectacular meteors came to be regarded as
+natural phenomena, the aurora among the rest. Franklin
+explained the aurora--which was seen commonly
+enough in the eighteenth century, though only recorded
+once in the seventeenth--as due to the accumulation of
+electricity on the surface of polar snows, and its discharge
+to the equator through the upper atmosphere.
+Erasmus Darwin suggested that the luminosity might
+be due to the ignition of hydrogen, which was supposed
+by many philosophers to form the upper atmosphere.
+Dalton, who first measured the height of the aurora,
+estimating it at about one hundred miles, thought the
+phenomenon due to magnetism acting on ferruginous
+particles in the air, and his explanation was perhaps the
+most popular one at the beginning of the last century.
+
+Since then a multitude of observers have studied the
+aurora, but the scientific grasp has found it as elusive in
+fact as it seems to casual observation, and its exact
+nature is as undetermined to-day as it was a hundred
+years ago. There has been no dearth of theories concerning
+it, however. Blot, who studied it in the Shetland
+Islands in 1817, thought it due to electrified
+ferruginous dust, the origin of which he ascribed to
+Icelandic volcanoes. Much more recently the idea of
+ferruginous particles has been revived, their presence
+being ascribed not to volcanoes, but to the meteorites
+constantly being dissipated in the upper atmosphere.
+Ferruginous dust, presumably of such origin, has been
+found on the polar snows, as well as on the snows of
+mountain-tops, but whether it could produce the phenomena
+of auroras is at least an open question.
+
+Other theorists have explained the aurora as due to
+the accumulation of electricity on clouds or on spicules
+of ice in the upper air. Yet others think it due merely
+to the passage of electricity through rarefied air itself.
+Humboldt considered the matter settled in yet another
+way when Faraday showed, in 1831, that magnetism
+may produce luminous effects. But perhaps the prevailing
+theory of to-day assumes that the aurora is due
+to a current of electricity generated at the equator and
+passing through upper regions of space, to enter the
+earth at the magnetic poles--simply reversing the
+course which Franklin assumed.
+
+The similarity of the auroral light to that generated
+in a vacuum bulb by the passage of electricity lends
+support to the long-standing supposition that the aurora
+is of electrical origin, but the subject still awaits
+complete elucidation. For once even that mystery-
+solver the spectroscope has been baffled, for the line it
+sifts from the aurora is not matched by that of any
+recognized substance. A like line is found in the
+zodiacal light, it is true, but this is of little aid, for the
+zodiacal light, though thought by some astronomers to
+be due to meteor swarms about the sun, is held to be,
+on the whole, as mysterious as the aurora itself.
+
+Whatever the exact nature of the aurora, it has long
+been known to be intimately associated with the phenomena
+of terrestrial magnetism. Whenever a brilliant
+aurora is visible, the world is sure to be visited
+with what Humboldt called a magnetic storm--a
+"storm" which manifests itself to human senses in no
+way whatsoever except by deflecting the magnetic
+needle and conjuring with the electric wire. Such
+magnetic storms are curiously associated also with
+spots on the sun--just how no one has explained,
+though the fact itself is unquestioned. Sun-spots, too,
+seem directly linked with auroras, each of these phenomena
+passing through periods of greatest and least
+frequency in corresponding cycles of about eleven
+years' duration.
+
+It was suspected a full century ago by Herschel that
+the variations in the number of sun-spots had a direct
+effect upon terrestrial weather, and he attempted to
+demonstrate it by using the price of wheat as a criterion
+of climatic conditions, meantime making careful observation
+of the sun-spots. Nothing very definite came
+of his efforts in this direction, the subject being far too
+complex to be determined without long periods of observation.
+Latterly, however, meteorologists, particularly
+in the tropics, are disposed to think they find
+evidence of some such connection between sun-spots
+and the weather as Herschel suspected. Indeed, Mr.
+Meldrum declares that there is a positive coincidence
+between periods of numerous sun-spots and seasons
+of excessive rain in India.
+
+That some such connection does exist seems intrinsically
+probable. But the modern meteorologist,
+learning wisdom of the past, is extremely cautious
+about ascribing casual effects to astronomical phenomena.
+He finds it hard to forget that until recently all
+manner of climatic conditions were associated with
+phases of the moon; that not so very long ago showers
+of falling-stars were considered "prognostic" of certain
+kinds of weather; and that the "equinoctial storm"
+had been accepted as a verity by every one, until
+the unfeeling hand of statistics banished it from the
+earth.
+
+Yet, on the other hand, it is easily within the possibilities
+that the science of the future may reveal associations
+between the weather and sun-spots, auroras,
+and terrestrial magnetism that as yet are hardly
+dreamed of. Until such time, however, these phenomena
+must feel themselves very grudgingly admitted
+to the inner circle of meteorology. More and
+more this science concerns itself, in our age of concentration
+and specialization, with weather and climate.
+Its votaries no longer concern themselves with stars or
+planets or comets or shooting-stars--once thought the
+very essence of guides to weather wisdom; and they are
+even looking askance at the moon, and asking her to
+show cause why she also should not be excluded from
+their domain. Equally little do they care for the interior
+of the earth, since they have learned that the
+central emanations of heat which Mairan imagined as a
+main source of aerial warmth can claim no such
+distinction. Even such problems as why the magnetic
+pole does not coincide with the geographical, and why
+the force of terrestrial magnetism decreases from the
+magnetic poles to the magnetic equator, as Humboldt
+first discovered that it does, excite them only to
+lukewarm interest; for magnetism, they say, is not
+known to have any connection whatever with climate
+or weather.
+
+
+EVAPORATION, CLOUD FORMATION, AND DEW
+
+There is at least one form of meteor, however, of
+those that interested our forebears whose meteorological
+importance they did not overestimate. This is the
+vapor of water. How great was the interest in this
+familiar meteor at the beginning of the century is attested
+by the number of theories then extant regarding
+it; and these conflicting theories bear witness also to
+the difficulty with which the familiar phenomenon of
+the evaporation of water was explained.
+
+Franklin had suggested that air dissolves water much
+as water dissolves salt, and this theory was still popular,
+though Deluc had disproved it by showing that
+water evaporates even more rapidly in a vacuum than
+in air. Deluc's own theory, borrowed from earlier
+chemists, was that evaporation is the chemical union
+of particles of water with particles of the supposititious
+element heat. Erasmus Darwin combined the
+two theories, suggesting that the air might hold a
+variable quantity of vapor in mere solution, and in
+addition a permanent moiety in chemical combination
+with caloric.
+
+Undisturbed by these conflicting views, that strangely
+original genius, John Dalton, afterwards to be known
+as perhaps the greatest of theoretical chemists, took the
+question in hand, and solved it by showing that water
+exists in the air as an utterly independent gas. He
+reached a partial insight into the matter in 1793, when
+his first volume of meteorological essays was published;
+but the full elucidation of the problem came to him in
+1801. The merit of his studies was at once recognized,
+but the tenability of his hypothesis was long and ardently
+disputed.
+
+While the nature of evaporation was in dispute, as a
+matter of course the question of precipitation must be
+equally undetermined. The most famous theory of the
+period was that formulated by Dr. Hutton in a paper
+read before the Royal Society of Edinburgh, and published
+in the volume of transactions which contained
+also the same author's epoch-making paper on geology.
+This "theory of rain" explained precipitation as due to
+the cooling of a current of saturated air by contact with
+a colder current, the assumption being that the surplusage
+of moisture was precipitated in a chemical
+sense, just as the excess of salt dissolved in hot water is
+precipitated when the water cools. The idea that the
+cooling of the saturated air causes the precipitation of
+its moisture is the germ of truth that renders this paper
+of Hutton's important. All correct later theories build
+on this foundation.
+
+"Let us suppose the surface of this earth wholly
+covered with water," said Hutton, "and that the sun
+were stationary, being always vertical in one place;
+then, from the laws of heat and rarefaction, there would
+be formed a circulation in the atmosphere, flowing
+from the dark and cold hemisphere to the heated and
+illuminated place, in all directions, towards the place
+of the greatest cold.
+
+"As there is for the atmosphere of this earth a constant
+cooling cause, this fluid body could only arrive
+at a certain degree of heat; and this would be regularly
+decreasing from the centre of illumination to the opposite
+point of the globe, most distant from the light and
+heat. Between these two regions of extreme heat and
+cold there would, in every place, be found two streams
+of air following in opposite directions. If those streams
+of air, therefore, shall be supposed as both sufficiently
+saturated with humidity, then, as they are of different
+temperatures, there would be formed a continual condensation
+of aqueous vapor, in some middle region of
+the atmosphere, by the commixtion of part of those
+two opposite streams.
+
+"Hence there is reason to believe that in this supposed
+case there would be formed upon the surface of
+the globe three different regions--the torrid region, the
+temperate, and the frigid. These three regions would
+continue stationary; and the operations of each would
+be continual. In the torrid region, nothing but evaporation
+and heat would take place; no cloud could be
+formed, because in changing the transparency of the
+atmosphere to opacity it would be heated immediately
+by the operation of light, and thus the condensed water
+would be again evaporated. But this power of the
+sun would have a termination; and it is these that
+would begin the region of temperate heat and of continual
+rain. It is not probable that the region of temperance
+would reach far beyond the region of light; and
+in the hemisphere of darkness there would be found a
+region of extreme cold and perfect dryness.
+
+"Let us now suppose the earth as turning on its axis
+in the equinoctial situation. The torrid region would
+thus be changed into a zone, in which there would be
+night and day; consequently, here would be much
+temperance, compared with the torrid region now
+considered; and here perhaps there would be formed
+periodical condensation and evaporation of humidity,
+corresponding to the seasons of night and day. As temperance
+would thus be introduced into the region of
+torrid extremity, so would the effect of this change be
+felt over all the globe, every part of which would now
+be illuminated, consequently heated in some degree.
+Thus we would have a line of great heat and evaporation,
+graduating each way into a point of great cold
+and congelation. Between these two extremes of heat
+and cold there would be found in each hemisphere a
+region of much temperance, in relation to heat, but of
+much humidity in the atmosphere, perhaps of continual
+rain and condensation.
+
+"The supposition now formed must appear extremely
+unfit for making this globe a habitable world in
+every part; but having thus seen the effect of night
+and day in temperating the effects of heat and cold in
+every place, we are now prepared to contemplate the
+effects of supposing this globe to revolve around the
+sun with a certain inclination of its axis. By this
+beautiful contrivance, that comparatively uninhabited
+globe is now divided into two hemispheres, each of
+which is thus provided with a summer and a winter
+season. But our present view is limited to the
+evaporation and condensation of humidity; and, in this
+contrivance of the seasons, there must appear an ample
+provision for those alternate operations in every part;
+for as the place of the vertical sun is moved alternately
+from one tropic to the other, heat and cold, the original
+causes of evaporation and condensation, must be carried
+over all the globe, producing either annual seasons
+of rain or diurnal seasons of condensation and
+evaporation, or both these seasons, more or less--that
+is, in some degree.
+
+"The original cause of motion in the atmosphere is
+the influence of the sun heating the surface of the earth
+exposed to that luminary. We have not supposed
+that surface to have been of one uniform shape and
+similar substance; from whence it has followed that
+the annual propers of the sun, perhaps also the diurnal
+propers, would produce a regular condensation of rain
+in certain regions, and the evaporation of humidity in
+others; and this would have a regular progress in certain
+determined seasons, and would not vary. But
+nothing can be more distant from this supposition, that
+is the natural constitution of the earth; for the globe
+is composed of sea and land, in no regular shape or
+mixture, while the surface of the land is also irregular
+with respect to its elevations and depressions, and
+various with regard to the humidity and dryness of
+that part which is exposed to heat as the cause of
+evaporation. Hence a source of the most valuable
+motions in the fluid atmosphere with aqueous vapor,
+more or less, so far as other natural operations
+will admit; and hence a source of the most irregular
+commixture of the several parts of this elastic
+fluid, whether saturated or not with aqueous vapor.
+
+"According to the theory, nothing is required for the
+production of rain besides the mixture of portions of
+the atmosphere with humidity, and of mixing the
+parts that are in different degrees of heat. But we
+have seen the causes of saturating every portion of
+the atmosphere with humidity and of mixing the
+parts which are in different degrees of heat. Consequently,
+over all the surface of the globe there should
+happen occasionally rain and evaporation, more or
+less; and also, in every place, those vicissitudes should
+be observed to take place with some tendency to regularity,
+which, however, may be so disturbed as to be
+hardly distinguishable upon many occasions. Variable
+winds and variable rains should be found in proportion
+as each place is situated in an irregular mixture
+of land and water; whereas regular winds should be
+found in proportion to the uniformity of the surface;
+and regular rains in proportion to the regular changes
+of those winds by which the mixture of the atmosphere
+necessary to the rain may be produced. But as it will
+be acknowledged that this is the case in almost all this
+earth where rain appears according to the conditions
+here specified, the theory is found to be thus in conformity
+with nature, and natural appearances are thus
+explained by the theory."[1]
+
+
+The next ambitious attempt to explain the phenomena
+of aqueous meteors was made by Luke Howard, in
+his remarkable paper on clouds, published in the
+Philosophical Magazine in 1803--the paper in which
+the names cirrus, cumulus, stratus, etc., afterwards so
+universally adopted, were first proposed. In this paper
+Howard acknowledges his indebtedness to Dalton for
+the theory of evaporation; yet he still clings to the idea
+that the vapor, though independent of the air, is combined
+with particles of caloric. He holds that clouds
+are composed of vapor that has previously risen from
+the earth, combating the opinions of those who believe
+that they are formed by the union of hydrogen and
+oxygen existing independently in the air; though he
+agrees with these theorists that electricity has entered
+largely into the modus operandi of cloud formation. He
+opposes the opinion of Deluc and De Saussure that
+clouds are composed of particles of water in the form
+of hollow vesicles (miniature balloons, in short, perhaps
+filled with hydrogen), which untenable opinion
+was a revival of the theory as to the formation of all
+vapor which Dr. Halley had advocated early in the
+eighteenth century.
+
+Of particular interest are Howard's views as to the
+formation of dew, which he explains as caused by the
+particles of caloric forsaking the vapor to enter the cool
+body, leaving the water on the surface. This comes as
+near the truth, perhaps, as could be expected while the
+old idea as to the materiality of heat held sway. Howard
+believed, however, that dew is usually formed in
+the air at some height, and that it settles to the surface,
+opposing the opinion, which had gained vogue in France
+and in America (where Noah Webster prominently advocated
+it), that dew ascends from the earth.
+
+The complete solution of the problem of dew formation--
+which really involved also the entire question of
+precipitation of watery vapor in any form--was made
+by Dr. W. C. Wells, a man of American birth, whose
+life, however, after boyhood, was spent in Scotland
+(where as a young man he enjoyed the friendship of
+David Hume) and in London. Inspired, no doubt,
+by the researches of Mack, Hutton, and their confreres
+of that Edinburgh school, Wells made observations on
+evaporation and precipitation as early as 1784, but
+other things claimed his attention; and though he asserts
+that the subject was often in his mind, he did not
+take it up again in earnest until about 1812.
+
+Meantime the observations on heat of Rumford and
+Davy and Leslie had cleared the way for a proper
+interpretation of the facts--about the facts themselves
+there had long been practical unanimity of opinion.
+Dr. Black, with his latent-heat observations, had really
+given the clew to all subsequent discussions of the
+subject of precipitation of vapor; and from this time on
+it had been known that heat is taken up when water
+evaporates, and given out again when it condenses.
+Dr. Darwin had shown in 1788, in a paper before the
+Royal Society, that air gives off heat on contracting
+and takes it up on expanding; and Dalton, in his
+essay of 1793, had explained this phenomenon as due
+to the condensation and vaporization of the water contained
+in the air.
+
+But some curious and puzzling observations which
+Professor Patrick Wilson, professor of astronomy in
+the University of Glasgow, had communicated to the
+Royal Society of Edinburgh in 1784, and some similar
+ones made by Mr. Six, of Canterbury, a few years later,
+had remained unexplained. Both these gentlemen
+observed that the air is cooler where dew is forming than
+the air a few feet higher, and they inferred that the dew
+in forming had taken up heat, in apparent violation of
+established physical principles.
+
+It remained for Wells, in his memorable paper of
+1816, to show that these observers had simply placed
+the cart before the horse. He made it clear that the
+air is not cooler because the dew is formed, but that the
+dew is formed because the air is cooler--having become
+so through radiation of heat from the solids on which
+the dew forms. The dew itself, in forming, gives out
+its latent heat, and so tends to equalize the temperature.
+
+Wells's paper is so admirable an illustration of the
+lucid presentation of clearly conceived experiments
+and logical conclusions that we should do it injustice
+not to present it entire. The author's mention of the
+observations of Six and Wilson gives added value to his
+own presentation.
+
+
+Dr. Wells's Essay on Dew
+
+"I was led in the autumn of 1784, by the event of a
+rude experiment, to think it probable that the formation
+of dew is attended with the production of cold.
+In 1788, a paper on hoar-frost, by Mr. Patrick Wilson,
+of Glasgow, was published in the first volume of the
+Transactions of the Royal Society of Edinburgh, by
+which it appeared that this opinion bad been entertained
+by that gentleman before it had occurred to
+myself. In the course of the same year, Mr. Six, of
+Canterbury, mentioned in a paper communicated to
+the Royal Society that on clear and dewy nights he
+always found the mercury lower in a thermometer laid
+upon the ground in a meadow in his neighborhood than
+it was in a similar thermometer suspended in the air six
+feet above the former; and that upon one night the
+difference amounted to five degrees of Fahrenheit's
+scale. Mr. Six, however, did not suppose, agreeably to
+the opinion of Mr. Wilson and myself, that the cold was
+occasioned by the formation of dew, but imagined that
+it proceeded partly from the low temperature of the
+air, through which the dew, already formed in the
+atmosphere, had descended, and partly from the
+evaporation of moisture from the ground, on which his
+thermometer had been placed. The conjecture of Mr.
+Wilson and the observations of Mr. Six, together with
+many facts which I afterwards learned in the course
+of reading, strengthened my opinion; but I made no
+attempt, before the autumn of 1811, to ascertain by
+experiment if it were just, though it had in the mean
+time almost daily occurred to my thoughts. Happening,
+in that season, to be in that country in a clear and
+calm night, I laid a thermometer upon grass wet with
+dew, and suspended a second in the air, two feet above
+the other. An hour afterwards the thermometer on
+the grass was found to be eight degrees lower, by
+Fahrenheit's division, than the one in the air. Similar
+results having been obtained from several similar
+experiments, made during the same autumn, I determined
+in the next spring to prosecute the subject with
+some degree of steadiness, and with that view went
+frequently to the house of one of my friends who lives
+in Surrey.
+
+At the end of two months I fancied that I had
+collected information worthy of being published; but,
+fortunately, while preparing an account of it I met by
+accident with a small posthumous work by Mr. Six,
+printed at Canterbury in 1794, in which are related
+differences observed on dewy nights between thermometers
+placed upon grass and others in the air that
+are much greater than those mentioned in the paper
+presented by him to the Royal Society in 1788. In this
+work, too, the cold of the grass is attributed, in agreement
+with the opinion of Mr. Wilson, altogether to the
+dew deposited upon it. The value of my own observations
+appearing to me now much diminished, though
+they embraced many points left untouched by Mr. Six,
+I gave up my intentions of making them known. Shortly
+after, however, upon considering the subject more
+closely, I began to suspect that Mr. Wilson, Mr. Six,
+and myself had all committed an error regarding the
+cold which accompanies dew as an effect of the formation
+of that fluid. I therefore resumed my experiments,
+and having by means of them, I think, not only
+established the justness of my suspicions, but ascertained
+the real cause both of dew and of several other
+natural appearances which have hitherto received no
+sufficient explanation, I venture now to submit to the
+consideration of the learned an account of some of
+my labors, without regard to the order of time in
+which they were performed, and of various conclusions
+which may be drawn from them, mixed with facts and
+opinions already published by others:
+
+"There are various occurrences in nature which
+seem to me strictly allied to dew, though their relation
+to it be not always at first sight perceivable. The
+statement and explanation of several of these will form
+the concluding part of the present essay.
+
+"1. I observed one morning, in winter, that the insides
+of the panes of glass in the windows of my bedchamber
+were all of them moist, but that those which
+had been covered by an inside shutter during the night
+were much more so than the others which had been
+uncovered. Supposing that this diversity of appearance
+depended upon a difference of temperature, I
+applied the naked bulbs of two delicate thermometers
+to a covered and uncovered pane; on which I found
+that the former was three degrees colder than the
+latter. The air of the chamber, though no fire was
+kept in it, was at this time eleven and one-half degrees
+warmer than that without. Similar experiments
+were made on many other mornings, the results of
+which were that the warmth of the internal air exceeded
+that of the external from eight to eighteen degrees,
+the temperature of the covered panes would be
+from one to five degrees less than the uncovered; that
+the covered were sometimes dewed, while the uncovered
+were dry; that at other times both were free from
+moisture; that the outsides of the covered and uncovered
+panes had similar differences with respect to heat,
+though not so great as those of the inner surfaces; and
+that no variation in the quantity of these differences
+was occasioned by the weather's being cloudy or fair,
+provided the heat of the internal air exceeded that of
+the external equally in both of those states of the
+atmosphere.
+
+"The remote reason of these differences did not immediately
+present itself. I soon, however, saw that
+the closed shutter shielded the glass which it covered
+from the heat that was radiated to the windows by
+the walls and furniture of the room, and thus kept it
+nearer to the temperature of the external air than
+those parts could be which, from being uncovered, received
+the heat emitted to them by the bodies just
+mentioned.
+
+"In making these experiments, I seldom observed
+the inside of any pane to be more than a little damped,
+though it might be from eight to twelve degrees colder
+than the general mass of the air in the room; while, in
+the open air, I had often found a great dew to form on
+substances only three or four degrees colder than the
+atmosphere. This at first surprised me; but the cause
+now seems plain. The air of the chamber had once
+been a portion of the external atmosphere, and had
+afterwards been heated, when it could receive little accessories
+to its original moisture. It constantly required
+being cooled considerably before it was even
+brought back to its former nearness to repletion with
+water; whereas the whole external air is commonly, at
+night, nearly replete with moisture, and therefore
+readily precipitates dew on bodies only a little colder
+than itself.
+
+"When the air of a room is warmer than the external
+atmosphere, the effect of an outside shutter on the
+temperature of the glass of the window will be directly
+opposite to what has just been stated; since it must
+prevent the radiation, into the atmosphere, of the heat
+of the chamber transmitted through the glass.
+
+"2. Count Rumford appears to have rightly conjectured
+that the inhabitants of certain hot countries,
+who sleep at nights on the tops of their houses, are
+cooled during this exposure by the radiation of their
+heat to the sky; or, according to his manner of expression,
+by receiving frigorific rays from the heavens.
+Another fact of this kind seems to be the greater chill
+which we often experience upon passing at night from
+the cover of a house into the air than might have been
+expected from the cold of the external atmosphere.
+The cause, indeed, is said to be the quickness of transition
+from one situation to another. But if this were
+the whole reason, an equal chill would be felt in the day,
+when the difference, in point of heat, between the internal
+and external air was the same as at night, which
+is not the case. Besides, if I can trust my own observation,
+the feeling of cold from this cause is more remarkable
+in a clear than in a cloudy night, and in the
+country than in towns. The following appears to be
+the manner in which these things are chiefly to be explained:
+
+"During the day our bodies while in the open air,
+although not immediately exposed to the sun's rays, are
+yet constantly deriving heat from them by means of
+the reflection of the atmosphere. This heat, though it
+produces little change on the temperature of the air
+which it traverses, affords us some compensation for
+the heat which we radiate to the heavens. At night,
+also, if the sky be overcast, some compensation will be
+made to us, both in the town and in the country,
+though in a less degree than during the day, as the
+clouds will remit towards the earth no inconsiderable
+quantity of heat. But on a clear night, in an open part
+of the country, nothing almost can be returned to us
+from above in place of the heat which we radiate upward.
+In towns, however, some compensation will be
+afforded even on the clearest nights for the heat
+which we lose in the open air by that which is radiated
+to us from the sun round buildings.
+
+To our loss of heat by radiation at times that we
+derive little compensation from the radiation of other
+bodies is probably to be attributed a great part of the
+hurtful effects of the night air. Descartes says that
+these are not owing to dew, as was the common opinion
+of his contemporaries, but to the descent of certain
+noxious vapors which have been exhaled from the earth
+during the heat of the day, and are afterwards condensed
+by the cold of a serene night. The effects in
+question certainly cannot be occasioned by dew, since
+that fluid does not form upon a healthy human body
+in temperate climates; but they may, notwithstanding,
+arise from the same cause that produces dew on those
+substances which do not, like the human body, possess
+the power of generating heat for the supply of what
+they lose by radiation or any other means."[2]
+
+
+This explanation made it plain why dew forms on a
+clear night, when there are no clouds to reflect the radiant
+heat. Combined with Dalton's theory that vapor
+is an independent gas, limited in quantity in any given
+space by the temperature of that space, it solved the
+problem of the formation of clouds, rain, snow, and
+hoar-frost. Thus this paper of Wells's closed the epoch
+of speculation regarding this field of meteorology, as
+Hutton's paper of 1784 had opened it. The fact that
+the volume containing Hutton's paper contained also
+his epoch-making paper on geology finds curiously a
+duplication in the fact that Wells's volume contained
+also his essay on Albinism, in which the doctrine of
+natural selection was for the first time formulated, as
+Charles Darwin freely admitted after his own efforts
+had made the doctrine famous.
+
+
+ISOTHERMS AND OCEAN CURRENTS
+
+The very next year after Dr. Wells's paper was published
+there appeared in France the third volume of
+the Memoires de Physique et de Chimie de la Societe
+d'Arcueil, and a new epoch in meteorology was inaugurated.
+The society in question was numerically an inconsequential
+band, listing only a dozen members; but every name was a famous
+one: Arago, Berard, Berthollet, Biot, Chaptal, De Candolle,
+Dulong, Gay-Lussac, Humboldt, Laplace, Poisson, and Thenard--rare
+spirits every one. Little danger that the memoirs of such a band
+would be relegated to the dusty shelves where most proceedings of
+societies belong--no milk-for-babes fare would be served to such
+a company.
+
+The particular paper which here interests us closes
+this third and last volume of memoirs. It is entitled
+"Des Lignes Isothermes et de la Distribution de la
+Chaleursurle Globe." The author is Alexander Humboldt.
+Needless to say, the topic is handled in a masterly
+manner. The distribution of heat on the surface of the
+globe, on the mountain-sides, in the interior of the
+earth; the causes that regulate such distribution; the
+climatic results--these are the topics discussed. But
+what gives epochal character to the paper is the introduction
+of those isothermal lines circling the earth in
+irregular course, joining together places having the
+same mean annual temperature, and thus laying the
+foundation for a science of comparative climatology.
+
+It is true the attempt to study climates comparatively
+was not new. Mairan had attempted it in those
+papers in which he developed his bizarre ideas as to
+central emanations of heat. Euler had brought his
+profound mathematical genius to bear on the topic,
+evolving the "extraordinary conclusion that under the
+equator at midnight the cold ought to be more rigorous
+than at the poles in winter." And in particular Richard
+Kirwan, the English chemist, had combined the
+mathematical and the empirical methods and calculated
+temperatures for all latitudes. But Humboldt
+differs from all these predecessors in that he grasps the
+idea that the basis of all such computations should be
+not theory, but fact. He drew his isothermal lines not
+where some occult calculation would locate them on an
+ideal globe, but where practical tests with the thermometer
+locate them on our globe as it is. London,
+for example, lies in the same latitude as the southern
+extremity of Hudson Bay; but the isotherm of London,
+as Humboldt outlines it, passes through Cincinnati.
+
+Of course such deviations of climatic conditions between
+places in the same latitude had long been known.
+As Humboldt himself observes, the earliest settlers of
+America were astonished to find themselves subjected
+to rigors of climate for which their European experience
+had not at all prepared them. Moreover, sagacious
+travellers, in particular Cook's companion on his second
+voyage, young George Forster, had noted as a general
+principle that the western borders of continents in
+temperate regions are always warmer than corresponding
+latitudes of their eastern borders; and of course the
+general truth of temperatures being milder in the vicinity
+of the sea than in the interior of continents had
+long been familiar. But Humboldt's isothermal lines
+for the first time gave tangibility to these ideas, and
+made practicable a truly scientific study of comparative
+climatology.
+
+In studying these lines, particularly as elaborated by
+further observations, it became clear that they are by
+no means haphazard in arrangement, but are dependent
+upon geographical conditions which in most cases
+are not difficult to determine. Humboldt himself
+pointed out very clearly the main causes that tend to
+produce deviations from the average--or, as Dove
+later on called it, the normal--temperature of any given
+latitude. For example, the mean annual temperature
+of a region (referring mainly to the northern hemisphere)
+is raised by the proximity of a western coast;
+by a divided configuration of the continent into peninsulas;
+by the existence of open seas to the north or of
+radiating continental surfaces to the south; by mountain
+ranges to shield from cold winds; by the infrequency
+of swamps to become congealed; by the absence
+of woods in a dry, sandy soil; and by the serenity
+of sky in the summer months and the vicinity of an
+ocean current bringing water which is of a higher
+temperature than that of the surrounding sea.
+
+Conditions opposite to these tend, of course,
+correspondingly to lower the temperature. In a word,
+Humboldt says the climatic distribution of heat depends
+on the relative distribution of land and sea, and
+on the "hypsometrical configuration of the continents";
+and he urges that "great meteorological phenomena
+cannot be comprehended when considered independently
+of geognostic relations"--a truth which,
+like most other general principles, seems simple enough
+once it is pointed out.
+
+With that broad sweep of imagination which characterized
+him, Humboldt speaks of the atmosphere as the
+"aerial ocean, in the lower strata and on the shoals of
+which we live," and he studies the atmospheric phenomena
+always in relation to those of that other ocean
+of water. In each of these oceans there are vast permanent
+currents, flowing always in determinate directions,
+which enormously modify the climatic conditions
+of every zone. The ocean of air is a vast maelstrom,
+boiling up always under the influence of the sun's heat
+at the equator, and flowing as an upper current towards
+either pole, while an undercurrent from the poles,
+which becomes the trade-winds, flows towards the
+equator to supply its place.
+
+But the superheated equatorial air, becoming chilled,
+descends to the surface in temperate latitudes, and continues
+its poleward journey as the anti-trade-winds.
+The trade-winds are deflected towards the west, because
+in approaching the equator they constantly pass
+over surfaces of the earth having a greater and greater
+velocity of rotation, and so, as it were, tend to lag behind--
+an explanation which Hadley pointed out in
+1735, but which was not accepted until Dalton independently
+worked it out and promulgated it in 1793.
+For the opposite reason, the anti-trades are deflected
+towards the east; hence it is that the western, borders
+of continents in temperate zones are bathed in moist
+sea-breezes, while their eastern borders lack this cold-
+dispelling influence.
+
+In the ocean of water the main currents run as more
+sharply circumscribed streams--veritable rivers in the
+sea. Of these the best known and most sharply circumscribed
+is the familiar Gulf Stream, which has its
+origin in an equatorial current, impelled westward by
+trade-winds, which is deflected northward in the main
+at Cape St. Roque, entering the Caribbean Sea and Gulf
+of Mexico, to emerge finally through the Strait of
+Florida, and journey off across the Atlantic to warm
+the shores of Europe.
+
+Such, at least, is the Gulf Stream as Humboldt understood
+it. Since his time, however, ocean currents in
+general, and this one in particular, have been the subject
+of no end of controversy, it being hotly disputed
+whether either causes or effects of the Gulf Stream are
+just what Humboldt, in common with others of his
+time, conceived them to be. About the middle of the
+century Lieutenant M. F. Maury, the distinguished
+American hydrographer and meteorologist, advocated
+a theory of gravitation as the chief cause of the currents,
+claiming that difference in density, due to difference
+in temperature and saltness, would sufficiently
+account for the oceanic circulation. This theory
+gained great popularity through the wide circulation
+of Maury's Physical Geography of the Sea, which is said
+to have passed through more editions than any other
+scientific book of the period; but it was ably and
+vigorously combated by Dr. James Croll, the Scottish
+geologist, in his Climate and Time, and latterly the old
+theory that ocean currents are due to the trade-winds
+has again come into favor. Indeed, very recently a
+model has been constructed, with the aid of which it is
+said to have been demonstrated that prevailing winds
+in the direction of the actual trade-winds would produce
+such a current as the Gulf Stream.
+
+Meantime, however, it is by no means sure that
+gravitation does not enter into the case to the extent
+of producing an insensible general oceanic circulation,
+independent of the Gulf Stream and similar marked
+currents, and similar in its larger outlines to the polar-
+equatorial circulation of the air. The idea of such
+oceanic circulation was first suggested in detail by
+Professor Lenz, of St. Petersburg, in 1845, but it
+was not generally recognized until Dr. Carpenter
+independently hit upon the idea more than twenty
+years later. The plausibility of the conception is obvious;
+yet the alleged fact of such circulation has
+been hotly disputed, and the question is still sub
+judice.
+
+But whether or not such general circulation of ocean
+water takes place, it is beyond dispute that the recognized
+currents carry an enormous quantity of heat
+from the tropics towards the poles. Dr. Croll, who has
+perhaps given more attention to the physics of the
+subject than almost any other person, computes that
+the Gulf Stream conveys to the North Atlantic one-
+fourth as much heat as that body receives directly from
+the sun, and he argues that were it not for the transportation
+of heat by this and similar Pacific currents,
+only a narrow tropical region of the globe would be
+warm enough for habitation by the existing faunas.
+Dr. Croll argues that a slight change in the relative
+values of northern and southern trade-winds (such as
+he believes has taken place at various periods in the
+past) would suffice to so alter the equatorial current
+which now feeds the Gulf Stream that its main bulk
+would be deflected southward instead of northward,
+by the angle of Cape St. Roque. Thus the Gulf Stream
+would be nipped in the bud, and, according to Dr.
+Croll's estimates, the results would be disastrous for the
+northern hemisphere. The anti-trades, which now are
+warmed by the Gulf Stream, would then blow as cold
+winds across the shores of western Europe, and in all
+probability a glacial epoch would supervene throughout
+the northern hemisphere.
+
+The same consequences, so far as Europe is concerned
+at least, would apparently ensue were the Isthmus
+of Panama to settle into the sea, allowing the
+Caribbean current to pass into the Pacific. But the
+geologist tells us that this isthmus rose at a comparatively
+recent geological period, though it is hinted that
+there had been some time previously a temporary land
+connection between the two continents. Are we to
+infer, then, that the two Americas in their unions and
+disunions have juggled with the climate of the other
+hemisphere? Apparently so, if the estimates made of
+the influence of the Gulf Stream be tenable. It is a
+far cry from Panama to Russia. Yet it seems within
+the possibilities that the meteorologist may learn from
+the geologist of Central America something that will
+enable him to explain to the paleontologist of Europe
+how it chanced that at one time the mammoth and
+rhinoceros roamed across northern Siberia, while at
+another time the reindeer and musk-ox browsed along
+the shores of the Mediterranean.
+
+Possibilities, I said, not probabilities. Yet even the
+faint glimmer of so alluring a possibility brings home to
+one with vividness the truth of Humboldt's perspicuous
+observation that meteorology can be properly comprehended
+only when studied in connection with the
+companion sciences. There are no isolated phenomena
+in nature.
+
+
+CYCLONES AND ANTI-CYCLONES
+
+Yet, after all, it is not to be denied that the chief
+concern of the meteorologist must be with that other
+medium, the "ocean of air, on the shoals of which we
+live." For whatever may be accomplished by water
+currents in the way of conveying heat, it is the wind
+currents that effect the final distribution of that heat.
+As Dr. Croll has urged, the waters of the Gulf Stream
+do not warm the shores of Europe by direct contact,
+but by warming the anti-trade-winds, which subsequently
+blow across the continent. And everywhere
+the heat accumulated by water becomes effectual in
+modifying climate, not so much by direct radiation as
+by diffusion through the medium of the air.
+
+This very obvious importance of aerial currents led
+to their practical study long before meteorology had
+any title to the rank of science, and Dalton's explanation
+of the trade-winds had laid the foundation for a
+science of wind dynamics before the beginning of the
+nineteenth century. But no substantial further advance
+in this direction was effected until about 1827,
+when Heinrich W. Dove, of Konigsberg, afterwards to
+be known as perhaps the foremost meteorologist of his
+generation, included the winds among the subjects of
+his elaborate statistical studies in climatology.
+
+Dove classified the winds as permanent, periodical,
+and variable. His great discovery was that all winds,
+of whatever character, and not merely the permanent
+winds, come under the influence of the earth's rotation
+in such a way as to be deflected from their course, and
+hence to take on a gyratory motion--that, in short, all
+local winds are minor eddies in the great polar-equatorial
+whirl, and tend to reproduce in miniature the character
+of that vast maelstrom. For the first time, then,
+temporary or variable winds were seen to lie within the
+province of law.
+
+A generation later, Professor William Ferrel, the
+American meteorologist, who had been led to take up
+the subject by a perusal of Maury's discourse on ocean
+winds, formulated a general mathematical law, to the
+effect that any body moving in a right line along the
+surface of the earth in any direction tends to have its
+course deflected, owing to the earth's rotation, to the
+right hand in the northern and to the left hand in
+the southern hemisphere. This law had indeed been
+stated as early as 1835 by the French physicist Poisson,
+but no one then thought of it as other than a mathematical
+curiosity; its true significance was only understood
+after Professor Ferrel had independently rediscovered
+it (just as Dalton rediscovered Hadley's forgotten
+law of the trade-winds) and applied it to the
+motion of wind currents.
+
+Then it became clear that here is a key to the phenomena
+of atmospheric circulation, from the great
+polar-equatorial maelstrom which manifests itself in
+the trade-winds to the most circumscribed riffle which
+is announced as a local storm. And the more the phenomena
+were studied, the more striking seemed the
+parallel between the greater maelstrom and these lesser
+eddies. Just as the entire atmospheric mass of each
+hemisphere is seen, when viewed as a whole, to be carried
+in a great whirl about the pole of that hemisphere,
+so the local disturbances within this great tide are
+found always to take the form of whirls about a local
+storm-centre--which storm-centre, meantime, is carried
+along in the major current, as one often sees a
+little whirlpool in the water swept along with the main
+current of the stream. Sometimes, indeed, the local
+eddy, caught as it were in an ancillary current of the
+great polar stream, is deflected from its normal course
+and may seem to travel against the stream; but such
+deviations are departures from the rule. In the great
+majority of cases, for example, in the north temperate
+zone, a storm-centre (with its attendant local whirl)
+travels to the northeast, along the main current of the
+anti-trade-wind, of which it is a part; and though
+exceptionally its course may be to the southeast instead,
+it almost never departs so widely from the main channel
+as to progress to the westward. Thus it is that
+storms sweeping over the United States can be announced,
+as a rule, at the seaboard in advance of their
+coming by telegraphic communication from the interior,
+while similar storms come to Europe off the
+ocean unannounced. Hence the more practical availability
+of the forecasts of weather bureaus in the former
+country.
+
+But these local whirls, it must be understood, are
+local only in a very general sense of the word, inasmuch
+as a single one may be more than a thousand miles in
+diameter, and a small one is two or three hundred miles
+across. But quite without regard to the size of the
+whirl, the air composing it conducts itself always in one
+of two ways. It never whirls in concentric circles; it
+always either rushes in towards the centre in a descending
+spiral, in which case it is called a cyclone, or it
+spreads out from the centre in a widening spiral, in
+which case it is called an anti-cyclone. The word
+cyclone is associated in popular phraseology with a
+terrific storm, but it has no such restriction in technical
+usage. A gentle zephyr flowing towards a "storm-
+centre" is just as much a cyclone to the meteorologist
+as is the whirl constituting a West-Indian hurricane.
+Indeed, it is not properly the wind itself that is called
+the cyclone in either case, but the entire system of
+whirls--including the storm-centre itself, where there
+may be no wind at all.
+
+What, then, is this storm-centre? Merely an area
+of low barometric pressure--an area where the air has
+become lighter than the air of surrounding regions.
+Under influence of gravitation the air seeks its level
+just as water does; so the heavy air comes flowing in
+from all sides towards the low-pressure area, which thus
+becomes a "storm-centre." But the inrushing currents
+never come straight to their mark. In accordance with
+Ferrel's law, they are deflected to the right, and the
+result, as will readily be seen, must be a vortex current,
+which whirls always in one direction--namely, from
+left to right, or in the direction opposite to that of the
+hands of a watch held with its face upward. The
+velocity of the cyclonic currents will depend largely
+upon the difference in barometric pressure between the
+storm-centre and the confines of the cyclone system.
+And the velocity of the currents will determine to some
+extent the degree of deflection, and hence the exact
+path of the descending spiral in which the wind approaches
+the centre. But in every case and in every
+part of the cyclone system it is true, as Buys Ballot's
+famous rule first pointed out, that a person standing
+with his back to the wind has the storm-centre at his
+left.
+
+The primary cause of the low barometric pressure
+which marks the storm-centre and establishes the cyclone
+is expansion of the air through excess of temperature.
+The heated air, rising into cold upper regions,
+has a portion of its vapor condensed into clouds,
+and now a new dynamic factor is added, for each particle
+of vapor, in condensing, gives up its modicum of
+latent heat. Each pound of vapor thus liberates, according
+to Professor Tyndall's estimate, enough heat
+to melt five pounds of cast iron; so the amount given
+out where large masses of cloud are forming must enormously
+add to the convection currents of the air, and
+hence to the storm-developing power of the forming
+cyclone. Indeed, one school of meteorologists, of
+whom Professor Espy was the leader, has held that,
+without such added increment of energy constantly
+augmenting the dynamic effects, no storm could long
+continue in violent action. And it is doubted whether
+any storm could ever attain, much less continue, the
+terrific force of that most dreaded of winds of temperate
+zones, the tornado--a storm which obeys all the laws
+of cyclones, but differs from ordinary cyclones in having
+a vortex core only a few feet or yards in diameter--
+without the aid of those great masses of condensing
+vapor which always accompany it in the form of storm-
+clouds.
+
+The anti-cyclone simply reverses the conditions of
+the cyclone. Its centre is an area of high pressure,
+and the air rushes out from it in all directions towards
+surrounding regions of low pressure. As before, all
+parts of the current will be deflected towards the right,
+and the result, clearly, is a whirl opposite in direction
+to that of the cyclone. But here there is a tendency
+to dissipation rather than to concentration of energy,
+hence, considered as a storm-generator, the anti-
+cyclone is of relative insignificance.
+
+In particular the professional meteorologist who
+conducts a "weather bureau"--as, for example, the
+chief of the United States signal-service station in
+New York--is so preoccupied with the observation of
+this phenomenon that cyclone-hunting might be said
+to be his chief pursuit. It is for this purpose, in the
+main, that government weather bureaus or signal-
+service departments have been established all over the
+world. Their chief work is to follow up cyclones, with
+the aid of telegraphic reports, mapping their course
+and recording the attendant meteorological conditions.
+Their so-called predictions or forecasts are essentially
+predications, gaining locally the effect of predictions
+because the telegraph outstrips the wind.
+
+At only one place on the globe has it been possible
+as yet for the meteorologist to make long-time
+forecasts meriting the title of predictions. This is in the
+middle Ganges Valley of northern India. In this country
+the climatic conditions are largely dependent upon
+the periodical winds called monsoons, which blow
+steadily landward from April to October, and seaward
+from October to April. The summer monsoons bring
+the all-essential rains; if they are delayed or restricted
+in extent, there will be drought and consequent famine.
+And such restriction of the monsoon is likely to result
+when there has been an unusually deep or very late
+snowfall on the Himalayas, because of the lowering of
+spring temperature by the melting snow. Thus here
+it is possible, by observing the snowfall in the mountains,
+to predict with some measure of success the average
+rainfall of the following summer. The drought of
+1896, with the consequent famine and plague that devastated
+India the following winter, was thus predicted
+some months in advance.
+
+This is the greatest present triumph of practical meteorology.
+Nothing like it is yet possible anywhere in
+temperate zones. But no one can say what may not
+be possible in times to come, when the data now being
+gathered all over the world shall at last be co-ordinated,
+classified, and made the basis of broad inductions.
+Meteorology is pre-eminently a science of the future.
+
+
+
+VI
+
+MODERN THEORIES OF HEAT AND LIGHT
+
+THE eighteenth-century philosopher made great
+strides in his studies of the physical properties of
+matter and the application of these properties in
+mechanics, as the steam-engine, the balloon, the optic
+telegraph, the spinning-jenny, the cotton-gin, the
+chronometer, the perfected compass, the Leyden jar,
+the lightning-rod, and a host of minor inventions testify.
+In a speculative way he had thought out more or
+less tenable conceptions as to the ultimate nature of
+matter, as witness the theories of Leibnitz and Boscovich
+and Davy, to which we may recur. But he had
+not as yet conceived the notion of a distinction between
+matter and energy, which is so fundamental to the
+physics of a later epoch. He did not speak of heat,
+light, electricity, as forms of energy or "force"; he conceived
+them as subtile forms of matter--as highly attenuated
+yet tangible fluids, subject to gravitation and
+chemical attraction; though he had learned to measure
+none of them but heat with accuracy, and this one he
+could test only within narrow limits until late in the
+century, when Josiah Wedgwood, the famous potter,
+taught him to gauge the highest temperatures with the
+clay pyrometer.
+
+He spoke of the matter of heat as being the most universally
+distributed fluid in nature; as entering in some
+degree into the composition of nearly all other substances;
+as being sometimes liquid, sometimes condensed
+or solid, and as having weight that could be detected
+with the balance. Following Newton, he spoke
+of light as a "corpuscular emanation" or fluid, composed
+of shining particles which possibly are transmutable
+into particles of heat, and which enter into chemical
+combination with the particles of other forms of
+matter. Electricity he considered a still more subtile
+kind of matter-perhaps an attenuated form of
+light. Magnetism, "vital fluid," and by some even
+a "gravic fluid," and a fluid of sound were placed
+in the same scale; and, taken together, all these supposed
+subtile forms of matter were classed as "imponderables."
+
+This view of the nature of the "imponderables" was
+in some measure a retrogression, for many seventeenth-
+century philosophers, notably Hooke and Huygens and
+Boyle, had held more correct views; but the materialistic
+conception accorded so well with the eighteenth-
+century tendencies of thought that only here and there
+a philosopher like Euler called it in question, until well
+on towards the close of the century. Current speech
+referred to the materiality of the "imponderables "
+unquestioningly. Students of meteorology--a science
+that was just dawning--explained atmospheric phenomena
+on the supposition that heat, the heaviest
+imponderable, predominated in the lower atmosphere,
+and that light, electricity, and magnetism prevailed in
+successively higher strata. And Lavoisier, the most
+philosophical chemist of the century, retained heat and
+light on a par with oxygen, hydrogen, iron, and the
+rest, in his list of elementary substances.
+
+
+COUNT RUMFORD AND THE VIBRATORY THEORY OF HEAT
+
+But just at the close of the century the confidence in
+the status of the imponderables was rudely shaken in
+the minds of philosophers by the revival of the old idea
+of Fra Paolo and Bacon and Boyle, that heat, at any
+rate, is not a material fluid, but merely a mode of motion
+or vibration among the particles of "ponderable"
+matter. The new champion of the old doctrine as to
+the nature of heat was a very distinguished philosopher
+and diplomatist of the time, who, it may be worth recalling,
+was an American. He was a sadly expatriated
+American, it is true, as his name, given all the official
+appendages, will amply testify; but he had been born
+and reared in a Massachusetts village none the less, and
+he seems always to have retained a kindly interest in
+the land of his nativity, even though he lived abroad in
+the service of other powers during all the later years of
+his life, and was knighted by England, ennobled by
+Bavaria, and honored by the most distinguished scientific
+bodies of Europe. The American, then, who
+championed the vibratory theory of heat, in opposition
+to all current opinion, in this closing era of the eighteenth
+century, was Lieutenant-General Sir Benjamin
+Thompson, Count Rumford, F.R.S.
+
+Rumford showed that heat may be produced in indefinite
+quantities by friction of bodies that do not
+themselves lose any appreciable matter in the process,
+and claimed that this proves the immateriality of heat.
+Later on he added force to the argument by proving,
+in refutation of the experiments of Bowditch, that no
+body either gains or loses weight in virtue of being
+heated or cooled. He thought he had proved that heat
+is only a form of motion.
+
+His experiment for producing indefinite quantities
+of heat by friction is recorded by him in his paper entitled,
+"Inquiry Concerning the Source of Heat Excited
+by Friction."
+
+"Being engaged, lately, in superintending the boring
+of cannon in the workshops of the military arsenal
+at Munich," he says, "I was struck with the very
+considerable degree of heat which a brass gun acquires
+in a short time in being bored; and with the still more
+intense heat (much greater than that of boiling water,
+as I found by experiment) of the metallic chips separated
+from it by the borer.
+
+"Taking a cannon (a brass six-pounder), cast solid,
+and rough, as it came from the foundry, and fixing it
+horizontally in a machine used for boring, and at the
+same time finishing the outside of the cannon by turning,
+I caused its extremity to be cut off; and by turning
+down the metal in that part, a solid cylinder was
+formed, 7 3/4 inches in diameter and 9 8/10 inches long;
+which, when finished, remained joined to the rest of the
+metal (that which, properly speaking, constituted the
+cannon) by a small cylindrical neck, only 2 1/5 inches
+in diameter and 3 8/10 inches long.
+
+"This short cylinder, which was supported in its
+horizontal position, and turned round its axis by
+means of the neck by which it remained united to the
+cannon, was now bored with the horizontal borer used
+in boring cannon.
+
+"This cylinder being designed for the express purpose
+of generating heat by friction, by having a blunt
+borer forced against its solid bottom at the same time
+that it should be turned round its axis by the force of
+horses, in order that the heat accumulated in the cylinder
+might from time to time be measured, a small,
+round hole 0.37 of an inch only in diameter and 4.2
+inches in depth, for the purpose of introducing a small
+cylindrical mercurial thermometer, was made in it, on
+one side, in a direction perpendicular to the axis of the
+cylinder, and ending in the middle of the solid part of
+the metal which formed the bottom of the bore.
+
+"At the beginning of the experiment, the temperature
+of the air in the shade, as also in the cylinder, was
+just sixty degrees Fahrenheit. At the end of thirty
+minutes, when the cylinder had made 960 revolutions
+about its axis, the horses being stopped, a cylindrical
+mercury thermometer, whose bulb was 32/100 of an inch
+in diameter and 3 1/4 inches in length, was introduced
+into the hole made to receive it in the side of the cylinder,
+when the mercury rose almost instantly to one
+hundred and thirty degrees.
+
+"In order, by one decisive experiment, to determine
+whether the air of the atmosphere had any part or not
+in the generation of the heat, I contrived to repeat the
+experiment under circumstances in which it was evidently
+impossible for it to produce any effect whatever.
+By means of a piston exactly fitted to the mouth of the
+bore of the cylinder, through the middle of which piston
+the square iron bar, to the end of which the blunt
+steel borer was fixed, passed in a square hole made perfectly
+air-tight, the excess of the external air, to the
+inside of the bore of the cylinder, was effectually prevented.
+I did not find, however, by this experiment
+that the exclusion of the air diminished in the smallest
+degree the quantity of heat excited by the friction.
+
+"There still remained one doubt, which, though it
+appeared to me to be so slight as hardly to deserve any
+attention, I was, however, desirous to remove. The
+piston which choked the mouth of the bore of the cylinder,
+in order that it might be air-tight, was fitted into
+it with so much nicety, by means of its collars of leather,
+and pressed against it with so much force, that,
+notwithstanding its being oiled, it occasioned a considerable
+degree of friction when the hollow cylinder was
+turned round its axis. Was not the heat produced, or
+at least some part of it, occasioned by this friction of
+the piston? and, as the external air had free access to
+the extremity of the bore, where it came into contact
+with the piston, is it not possible that this air may have
+had some share in the generation of the heat produced?
+
+"A quadrangular oblong deal box, water-tight, being
+provided with holes or slits in the middle of each of its
+ends, just large enough to receive, the one the square
+iron rod to the end of which the blunt steel borer was
+fastened, the other the small cylindrical neck which
+joined the hollow cylinder to the cannon; when this
+box (which was occasionally closed above by a wooden
+cover or lid moving on hinges) was put into its place--
+that is to say, when, by means of the two vertical opening
+or slits in its two ends, the box was fixed to the
+machinery in such a manner that its bottom being in
+the plane of the horizon, its axis coincided with the
+axis of the hollow metallic cylinder, it is evident,
+from the description, that the hollow, metallic cylinder
+would occupy the middle of the box, without touching
+it on either side; and that, on pouring water into the
+box and filling it to the brim, the cylinder would be
+completely covered and surrounded on every side by
+that fluid. And, further, as the box was held fast by
+the strong, square iron rod which passed in a square
+hole in the centre of one of its ends, while the round or
+cylindrical neck which joined the hollow cylinder to
+the end of the cannon could turn round freely on its
+axis in the round hole in the centre of the other end of
+it, it is evident that the machinery could be put in
+motion without the least danger of forcing the box out
+of its place, throwing the water out of it, or deranging
+any part of the apparatus."
+
+Everything being thus ready, the box was filled with
+cold water, having been made water-tight by means of
+leather collars, and the machinery put in motion.
+"The result of this beautiful experiment," says Rumford,
+"was very striking, and the pleasure it afforded
+me amply repaid me for all the trouble I had had in
+contriving and arranging the complicated machinery
+used in making it. The cylinder, revolving at the rate
+of thirty-two times in a minute, had been in motion
+but a short time when I perceived, by putting my
+hand into the water and touching the outside of the
+cylinder, that heat was generated, and it was not long
+before the water which surrounded the cylinder began
+to be sensibly warm.
+
+"At the end of one hour I found, by plunging a thermometer
+into the box, . . . that its temperature had
+been raised no less than forty-seven degrees Fahrenheit,
+being now one hundred and seven degrees Fahrenheit.
+... One hour and thirty minutes after the machinery
+had been put in motion the heat of the water in the
+box was one hundred and forty-two degrees. At the
+end of two hours ... it was raised to one hundred
+and seventy-eight degrees; and at two hours and
+thirty minutes it ACTUALLY BOILED!
+
+"It would be difficult to describe the surprise and
+astonishment expressed in the countenances of the bystanders
+on seeing so large a quantity of cold water
+heated, and actually made to boil, without any fire.
+Though there was, in fact, nothing that could justly be
+considered as a surprise in this event, yet I acknowledge
+fairly that it afforded me a degree of childish
+pleasure which, were I ambitious of the reputation of
+a GRAVE PHILOSOPHER, I ought most certainly rather to
+hide than to discover...."
+
+Having thus dwelt in detail on these experiments,
+Rumford comes now to the all-important discussion as
+to the significance of them--the subject that had been
+the source of so much speculation among the philosophers--
+the question as to what heat really is, and if
+there really is any such thing (as many believed) as an
+igneous fluid, or a something called caloric.
+
+"From whence came this heat which was continually
+given off in this manner, in the foregoing experiments?"
+asks Rumford. "Was it furnished by the small particles
+of metal detached from the larger solid masses
+on their being rubbed together? This, as we have already
+seen, could not possibly have been the case.
+
+"Was it furnished by the air? This could not have
+been the case; for, in three of the experiments, the machinery
+being kept immersed in water, the access
+of the air of the atmosphere was completely prevented.
+
+"Was it furnished by the water which surrounded
+the machinery? That this could not have been the
+case is evident: first, because this water was continually
+RECEIVING heat from the machinery, and could not, at
+the same time, be GIVING TO and RECEIVING HEAT FROM the
+same body; and, secondly, because there was no chemical
+decomposition of any part of this water. Had any
+such decomposition taken place (which, indeed, could
+not reasonably have been expected), one of its component
+elastic fluids (most probably hydrogen) must, at
+the same time, have been set at liberty, and, in making
+its escape into the atmosphere, would have been detected;
+but, though I frequently examined the water
+to see if any air-bubbles rose up through it, and had
+even made preparations for catching them if they
+should appear, I could perceive none; nor was there
+any sign of decomposition of any kind whatever, or
+other chemical process, going on in the water.
+
+"Is it possible that the heat could have been supplied
+by means of the iron bar to the end of which the
+blunt steel borer was fixed? Or by the small neck of
+gun-metal by which the hollow cylinder was united to
+the cannon? These suppositions seem more improbable
+even than either of the before-mentioned; for heat
+was continually going off, or OUT OF THE MACHINERY, by
+both these passages during the whole time the experiment
+lasted.
+
+"And in reasoning on this subject we must not forget
+to consider that most remarkable circumstance,
+that the source of the heat generated by friction in
+these experiments appeared evidently to be INEXHAUSTIBLE.
+
+"It is hardly necessary to add that anything which
+any INSULATED body, or system of bodies, can continue
+to furnish WITHOUT LIMITATION cannot possibly be a MATERIAL
+substance; and it appears to me to be extremely
+difficult, if not quite impossible, to form any distinct
+idea of anything capable of being excited and communicated,
+in the manner the heat was excited and communicated
+in these experiments, except in MOTION."[1]
+
+
+THOMAS YOUNG AND THE WAVE THEORY OF LIGHT
+
+But contemporary judgment, while it listened respectfully
+to Rumford, was little minded to accept his
+verdict. The cherished beliefs of a generation are not
+to be put down with a single blow. Where many minds
+have a similar drift, however, the first blow may precipitate
+a general conflict; and so it was here. Young
+Humphry Davy had duplicated Rumford's experiments,
+and reached similar conclusions; and soon others
+fell into line. Then, in 1800, Dr. Thomas Young--
+"Phenomenon Young" they called him at Cambridge,
+because he was reputed to know everything--took up
+the cudgels for the vibratory theory of light, and it
+began to be clear that the two "imponderables," heat
+and light, must stand or fall together; but no one as
+yet made a claim against the fluidity of electricity.
+
+Before we take up the details of the assault made by
+Young upon the old doctrine of the materiality of light,
+we must pause to consider the personality of Young
+himself. For it chanced that this Quaker physician
+was one of those prodigies who come but few times in
+a century, and the full list of whom in the records of
+history could be told on one's thumbs and fingers. His
+biographers tell us things about him that read like the
+most patent fairy-tales. As a mere infant in arms he
+had been able to read fluently. Before his fourth
+birthday came he had read the Bible twice through, as
+well as Watts's Hymns--poor child!--and when seven
+or eight he had shown a propensity to absorb languages
+much as other children absorb nursery tattle and Mother
+Goose rhymes. When he was fourteen, a young lady
+visiting the household of his tutor patronized the pretty
+boy by asking to see a specimen of his penmanship.
+The pretty boy complied readily enough, and mildly rebuked
+his interrogator by rapidly writing some sentences
+for her in fourteen languages, including such as,
+Arabian, Persian, and Ethiopic.
+
+Meantime languages had been but an incident in the
+education of the lad. He seems to have entered every
+available field of thought--mathematics, physics, botany,
+literature, music, painting, languages, philosophy,
+archaeology, and so on to tiresome lengths--and once
+he had entered any field he seldom turned aside until he
+had reached the confines of the subject as then known
+and added something new from the recesses of his own
+genius. He was as versatile as Priestley, as profound
+as Newton himself. He had the range of a mere dilettante,
+but everywhere the full grasp of the master. He
+took early for his motto the saying that what one man
+has done, another man may do. Granting that the
+other man has the brain of a Thomas Young, it is a
+true motto.
+
+Such, then, was the young Quaker who came to
+London to follow out the humdrum life of a practitioner of
+medicine in the year 1801. But incidentally the young
+physician was prevailed upon to occupy the interims
+of early practice by fulfilling the duties of the chair of
+Natural Philosophy at the Royal Institution, which
+Count Rumford had founded, and of which Davy was
+then Professor of Chemistry--the institution whose
+glories have been perpetuated by such names as Faraday
+and Tyndall, and which the Briton of to-day
+speaks of as the "Pantheon of Science." Here it was
+that Thomas Young made those studies which have
+insured him a niche in the temple of fame not far removed
+from that of Isaac Newton.
+
+As early as 1793, when he was only twenty, Young
+had begun to Communicate papers to the Royal Society
+of London, which were adjudged worthy to be printed
+in full in the Philosophical Transactions; so it is not
+strange that he should have been asked to deliver the
+Bakerian lecture before that learned body the very first
+year after he came to London. The lecture was delivered
+November 12, 1801. Its subject was "The
+Theory of Light and Colors," and its reading marks
+an epoch in physical science; for here was brought forward
+for the first time convincing proof of that undulatory
+theory of light with which every student of
+modern physics is familiar--the theory which holds
+that light is not a corporeal entity, but a mere pulsation
+in the substance of an all-pervading ether, just as
+sound is a pulsation in the air, or in liquids or solids.
+
+Young had, indeed, advocated this theory at an
+earlier date, but it was not until 1801 that he hit upon
+the idea which enabled him to bring it to anything
+approaching a demonstration. It was while pondering
+over the familiar but puzzling phenomena of colored
+rings into which white light is broken when reflected
+from thin films--Newton's rings, so called--that an
+explanation occurred to him which at once put the entire
+undulatory theory on a new footing. With that sagacity
+of insight which we call genius, he saw of a sudden
+that the phenomena could be explained by supposing
+that when rays of light fall on a thin glass, part of the
+rays being reflected from the upper surface, other rays,
+reflected from the lower surface, might be so retarded
+in their course through the glass that the two sets
+would interfere with one another, the forward pulsation
+of one ray corresponding to the backward pulsation
+of another, thus quite neutralizing the effect.
+Some of the component pulsations of the light being
+thus effaced by mutual interference, the remaining
+rays would no longer give the optical effect of white
+light; hence the puzzling colors.
+
+Here is Young's exposition of the subject:
+
+Of the Colors of Thin Plates
+
+"When a beam of light falls upon two refracting
+surfaces, the partial reflections coincide perfectly in
+direction; and in this case the interval of retardation
+taken between the surfaces is to their radius as twice
+the cosine of the angle of refraction to the radius.
+
+"Let the medium between the surfaces be rarer than
+the surrounding mediums; then the impulse reflected
+at the second surface, meeting a subsequent undulation
+at the first, will render the particles of the rarer
+medium capable of wholly stopping the motion of the
+denser and destroying the reflection, while they themselves
+will be more strongly propelled than if they had
+been at rest, and the transmitted light will be increased.
+So that the colors by reflection will be destroyed, and
+those by transmission rendered more vivid, when the
+double thickness or intervals of retardation are any
+multiples of the whole breadth of the undulations; and
+at intermediate thicknesses the effects will be reversed
+according to the Newtonian observation.
+
+"If the same proportions be found to hold good with
+respect to thin plates of a denser medium, which is,
+indeed, not improbable, it will be necessary to adopt
+the connected demonstrations of Prop. IV., but, at any
+rate, if a thin plate be interposed between a rarer and
+a denser medium, the colors by reflection and transmission
+may be expected to change places.
+
+
+Of the Colors of Thick Plates
+
+"When a beam of light passes through a refracting
+surface, especially if imperfectly polished, a portion of
+it is irregularly scattered, and makes the surface visible
+in all directions, but most conspicuously in directions
+not far distant from that of the light itself; and if
+a reflecting surface be placed parallel to the refracting
+surface, this scattered light, as well as the principal
+beam, will be reflected, and there will be also a new
+dissipation of light, at the return of the beam through
+the refracting surface. These two portions of scattered
+light will coincide in direction; and if the surfaces
+be of such a form as to collect the similar effects, will
+exhibit rings of colors. The interval of retardation is
+here the difference between the paths of the principal
+beam and of the scattered light between the two surfaces;
+of course, wherever the inclination of the scattered
+light is equal to that of the beam, although in
+different planes, the interval will vanish and all the
+undulations will conspire. At other inclinations, the
+interval will be the difference of the secants from the
+secant of the inclination, or angle of refraction of the
+principal beam. From these causes, all the colors of
+concave mirrors observed by Newton and others are
+necessary consequences; and it appears that their production,
+though somewhat similar, is by no means as
+Newton imagined, identical with the production of
+thin plates."[2]
+
+
+By following up this clew with mathematical precision,
+measuring the exact thickness of the plate and
+the space between the different rings of color, Young
+was able to show mathematically what must be the
+length of pulsation for each of the different colors of the
+spectrum. He estimated that the undulations of red
+light, at the extreme lower end of the visible spectrum,
+must number about thirty-seven thousand six hundred
+and forty to the inch, and pass any given spot at a rate
+of four hundred and sixty-three millions of millions of
+undulations in a second, while the extreme violet numbers
+fifty-nine thousand seven hundred and fifty undulations
+to the inch, or seven hundred and thirty-five
+millions of millions to the second.
+
+
+The Colors of Striated Surfaces
+
+Young similarly examined the colors that are produced
+by scratches on a smooth surface, in particular
+testing the light from "Mr. Coventry's exquisite micrometers,"
+which consist of lines scratched on glass at
+measured intervals. These microscopic tests brought
+the same results as the other experiments. The colors
+were produced at certain definite and measurable
+angles, and the theory of interference of undulations
+explained them perfectly, while, as Young affirmed
+with confidence, no other hypothesis hitherto advanced
+would explain them at all. Here are his
+words:
+
+"Let there be in a given plane two reflecting points
+very near each other, and let the plane be so situated
+that the reflected image of a luminous object seen in it
+may appear to coincide with the points; then it is obvious
+that the length of the incident and reflected ray,
+taken together, is equal with respect to both points,
+considering them as capable of reflecting in all directions.
+Let one of the points be now depressed below
+the given plane; then the whole path of the light reflected
+from it will be lengthened by a line which is to
+the depression of the point as twice the cosine of incidence
+to the radius.
+
+"If, therefore, equal undulations of given dimensions
+be reflected from two points, situated near enough to
+appear to the eye but as one, whenever this line is equal
+to half the breadth of a whole undulation the reflection
+from the depressed point will so interfere with the reflection
+from the fixed point that the progressive motion
+of the one will coincide with the retrograde motion
+of the other, and they will both be destroyed; but
+when this line is equal to the whole breadth of an
+undulation, the effect will be doubled, and when to a
+breadth and a half, again destroyed; and thus for a
+considerable number of alternations, and if the reflected
+undulations be of a different kind, they will be
+variously affected, according to their proportions to
+the various length of the line which is the difference
+between the lengths of their two paths, and which may
+be denominated the interval of a retardation.
+
+"In order that the effect may be the more perceptible,
+a number of pairs of points must be united into
+two parallel lines; and if several such pairs of lines be
+placed near each other, they will facilitate the
+observation. If one of the lines be made to revolve
+round the other as an axis, the depression below the
+given plane will be as the sine of the inclination; and
+while the eye and the luminous object remain fixed
+the difference of the length of the paths will vary as
+this sine.
+
+"The best subjects for the experiment are Mr. Coventry's
+exquisite micrometers; such of them as consist
+of parallel lines drawn on glass, at a distance of one-
+five-hundredth of an inch, are the most convenient.
+Each of these lines appears under a microscope to consist
+of two or more finer lines, exactly parallel, and at a
+distance of somewhat more than a twentieth more than
+the adjacent lines. I placed one of these so as to reflect
+the sun's light at an angle of forty-five degrees,
+and fixed it in such a manner that while it revolved
+round one of the lines as an axis, I could measure its
+angular motion; I found that the longest red color
+occurred at the inclination 10 1/4 degrees, 20 3/4 degrees, 32
+degrees, and 45 degrees; of
+which the sines are as the numbers 1, 2, 3, and 4. At
+all other angles also, when the sun's light was reflected
+from the surface, the color vanished with the inclination,
+and was equal at equal inclinations on either side.
+
+This experiment affords a very strong confirmation
+of the theory. It is impossible to deduce any explanation
+of it from any hypothesis hitherto advanced;
+and I believe it would be difficult to invent any other
+that would account for it. There is a striking analogy
+between this separation of colors and the production
+of a musical note by successive echoes from equidistant
+iron palisades, which I have found to correspond pretty
+accurately with the known velocity of sound and the
+distances of the surfaces.
+
+"It is not improbable that the colors of the integuments
+of some insects, and of some other natural bodies,
+exhibiting in different lights the most beautiful
+versatility, may be found to be of this description, and
+not to be derived from thin plates. In some cases a
+single scratch or furrow may produce similar effects,
+by the reflection of its opposite edges."[3]
+
+
+This doctrine of interference of undulations was the
+absolutely novel part of Young's theory. The all-
+compassing genius of Robert Hooke had, indeed, very
+nearly apprehended it more than a century before, as
+Young himself points out, but no one else bad so much
+as vaguely conceived it; and even with the sagacious
+Hooke it was only a happy guess, never distinctly outlined
+in his own mind, and utterly ignored by all others.
+Young did not know of Hooke's guess until he himself
+had fully formulated the theory, but he hastened then
+to give his predecessor all the credit that could possibly
+be adjudged his due by the most disinterested observer.
+To Hooke's contemporary, Huygens, who was the
+originator of the general doctrine of undulation as the
+explanation of light, Young renders full justice also.
+For himself he claims only the merit of having demonstrated
+the theory which these and a few others of his
+predecessors had advocated without full proof.
+
+The following year Dr. Young detailed before the
+Royal Society other experiments, which threw additional
+light on the doctrine of interference; and in 1803
+he cited still others, which, he affirmed, brought the
+doctrine to complete demonstration. In applying this
+demonstration to the general theory of light, he made
+the striking suggestion that "the luminiferous ether
+pervades the substance of all material bodies with little
+or no resistance, as freely, perhaps, as the wind passes
+through a grove of trees." He asserted his belief also
+that the chemical rays which Ritter had discovered
+beyond the violet end of the visible spectrum are but
+still more rapid undulations of the same character as
+those which produce light. In his earlier lecture he
+had affirmed a like affinity between the light rays and
+the rays of radiant heat which Herschel detected below
+the red end of the spectrum, suggesting that "light
+differs from heat only in the frequency of its undulations
+or vibrations--those undulations which are
+within certain limits with respect to frequency affecting
+the optic nerve and constituting light, and those
+which are slower and probably stronger constituting
+heat only." From the very outset he had recognized
+the affinity between sound and light; indeed, it had
+been this affinity that led him on to an appreciation
+of the undulatory theory of light.
+
+But while all these affinities seemed so clear to the
+great co-ordinating brain of Young, they made no such
+impression on the minds of his contemporaries. The
+immateriality of light had been substantially demonstrated,
+but practically no one save its author accepted
+the demonstration. Newton's doctrine of the emission
+of corpuscles was too firmly rooted to be readily dislodged,
+and Dr. Young had too many other interests to
+continue the assault unceasingly. He occasionally
+wrote something touching on his theory, mostly papers
+contributed to the Quarterly Review and similar periodicals,
+anonymously or under pseudonym, for he had
+conceived the notion that too great conspicuousness in
+fields outside of medicine would injure his practice as a
+physician. His views regarding light (including the
+original papers from the Philosophical Transactions of
+the Royal Society) were again given publicity in full in
+his celebrated volume on natural philosophy, consisting
+in part of his lectures before the Royal Institution, published
+in 1807; but even then they failed to bring conviction
+to the philosophic world. Indeed, they did not
+even arouse a controversial spirit, as his first papers
+had done.
+
+
+ARAGO AND FRESNEL CHAMPION THE WAVE THEORY
+
+So it chanced that when, in 1815, a young French
+military engineer, named Augustin Jean Fresnel, returning
+from the Napoleonic wars, became interested
+in the phenomena of light, and made some experiments
+concerning diffraction which seemed to him to controvert
+the accepted notions of the materiality of light,
+he was quite unaware that his experiments had been
+anticipated by a philosopher across the Channel. He
+communicated his experiments and results to the
+French Institute, supposing them to be absolutely
+novel. That body referred them to a committee, of
+which, as good fortune would have it, the dominating
+member was Dominique Francois Arago, a man as versatile
+as Young himself, and hardly less profound, if
+perhaps not quite so original. Arago at once recognized
+the merit of Fresnel's work, and soon became a
+convert to the theory. He told Fresnel that Young
+had anticipated him as regards the general theory, but
+that much remained to be done, and he offered to associate
+himself with Fresnel in prosecuting the investigation.
+Fresnel was not a little dashed to learn that
+his original ideas had been worked out by another
+while he was a lad, but he bowed gracefully to the
+situation and went ahead with unabated zeal.
+
+The championship of Arago insured the undulatory
+theory a hearing before the French Institute, but by no
+means sufficed to bring about its general acceptance.
+On the contrary, a bitter feud ensued, in which Arago
+was opposed by the "Jupiter Olympus of the Academy,"
+Laplace, by the only less famous Poisson, and by
+the younger but hardly less able Biot. So bitterly
+raged the feud that a life-long friendship between
+Arago and Biot was ruptured forever. The opposition
+managed to delay the publication of Fresnel's papers,
+but Arago continued to fight with his customary enthusiasm
+and pertinacity, and at last, in 1823, the
+Academy yielded, and voted Fresnel into its ranks,
+thus implicitly admitting the value of his work.
+
+It is a humiliating thought that such controversies as
+this must mar the progress of scientific truth; but fortunately
+the story of the introduction of the undulatory
+theory has a more pleasant side. Three men, great both
+in character and in intellect, were concerned in pressing
+its claims--Young, Fresnel, and Arago--and the relations
+of these men form a picture unmarred by any
+of those petty jealousies that so often dim the lustre
+of great names. Fresnel freely acknowledged Young's
+priority so soon as his attention was called to it; and
+Young applauded the work of the Frenchman, and
+aided with his counsel in the application of the undulatory
+theory to the problems of polarization of light,
+which still demanded explanation, and which Fresnel's
+fertility of experimental resource and profundity
+of mathematical insight sufficed in the end to
+conquer.
+
+After Fresnel's admission to the Institute in 1823
+the opposition weakened, and gradually the philosophers
+came to realize the merits of a theory which
+Young had vainly called to their attention a full quarter-
+century before. Now, thanks largely to Arago, both
+Young and Fresnel received their full meed of appreciation.
+Fresnel was given the Rumford medal of the
+Royal Society of England in 1825, and chosen one of
+the foreign members of the society two years later,
+while Young in turn was elected one of the eight foreign
+members of the French Academy. As a fitting culmination
+of the chapter of felicities between the three
+friends, it fell to the lot of Young, as Foreign Secretary
+of the Royal Society, to notify Fresnel of the honors
+shown him by England's representative body of scientists;
+while Arago, as Perpetual Secretary of the French
+Institute, conveyed to Young in the same year the notification
+that he had been similarly honored by the
+savants of France.
+
+A few months later Fresnel was dead, and Young
+survived him only two years. Both died prematurely,
+but their great work was done, and the world will remember
+always and link together these two names in
+connection with a theory which in its implications and
+importance ranks little below the theory of universal
+gravitation.
+
+
+
+VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM
+
+GALVANI AND VOLTA
+
+The full importance of Young's studies of light
+might perhaps have gained earlier recognition
+had it not chanced that, at the time when they were
+made, the attention of the philosophic world was turned
+with the fixity and fascination of a hypnotic stare
+upon another field, which for a time brooked no rival.
+How could the old, familiar phenomenon, light, interest
+any one when the new agent, galvanism, was in view?
+As well ask one to fix attention on a star while a meteorite
+blazes across the sky.
+
+Galvanism was so called precisely as the Roentgen
+ray was christened at a later day--as a safe means of
+begging the question as to the nature of the phenomena
+involved. The initial fact in galvanism was the discovery
+of Luigi Galvani (1737-1798), a physician of
+Bologna, in 1791, that by bringing metals in contact
+with the nerves of a frog's leg violent muscular contractions
+are produced. As this simple little experiment
+led eventually to the discovery of galvanic electricity
+and the invention of the galvanic battery, it
+may be regarded as the beginning of modern electricity.
+
+The story is told that Galvani was led to his discovery
+while preparing frogs' legs to make a broth for his
+invalid wife. As the story runs, he had removed the
+skins from several frogs' legs, when, happening to touch
+the exposed muscles with a scalpel which had lain in
+close proximity to an electrical machine, violent muscular
+action was produced. Impressed with this phenomenon,
+he began a series of experiments which finally
+resulted in his great discovery. But be this story authentic
+or not, it is certain that Galvani experimented
+for several years upon frogs' legs suspended upon wires
+and hooks, until he finally constructed his arc of two
+different metals, which, when arranged so that one was
+placed in contact with a nerve and the other with a
+muscle, produced violent contractions.
+
+These two pieces of metal form the basic principle of
+the modern galvanic battery, and led directly to Alessandro
+Volta's invention of his "voltaic pile," the immediate
+ancestor of the modern galvanic battery.
+Volta's experiments were carried on at the same time
+as those of Galvani, and his invention of his pile followed
+close upon Galvani's discovery of the new form
+of electricity. From these facts the new form of electricity
+was sometimes called "galvanic" and sometimes
+"voltaic" electricity, but in recent years the
+term "galvanism" and "galvanic current" have almost
+entirely supplanted the use of the term voltaic.
+
+It was Volta who made the report of Galvani's wonderful
+discovery to the Royal Society of London, read
+on January 31, 1793. In this letter he describes Galvani's
+experiments in detail and refers to them in
+glowing terms of praise. He calls it one of the "most
+beautiful and important discoveries," and regarded it
+as the germ or foundation upon which other discoveries
+were to be made. The prediction proved entirely correct,
+Volta himself being the chief discoverer.
+
+Working along lines suggested by Galvani's discovery,
+Volta constructed an apparatus made up of a
+number of disks of two different kinds of metal, such
+as tin and silver, arranged alternately, a piece of some
+moist, porous substance, like paper or felt, being interposed
+between each pair of disks. With this "pile,"
+as it was called, electricity was generated, and by linking
+together several such piles an electric battery could
+be formed.
+
+This invention took the world by storm. Nothing
+like the enthusiasm it created in the philosophic world
+had been known since the invention of the Leyden jar,
+more than half a century before. Within a few weeks
+after Volta's announcement, batteries made according
+to his plan were being experimented with in every
+important laboratory in Europe.
+
+As the century closed, half the philosophic world
+was speculating as to whether "galvanic influence"
+were a new imponderable, or only a form of electricity;
+and the other half was eagerly seeking to discover
+what new marvels the battery might reveal. The
+least imaginative man could see that here was an
+invention that would be epoch-making, but the most
+visionary dreamer could not even vaguely adumbrate
+the real measure of its importance.
+
+It was evident at once that almost any form of galvanic
+battery, despite imperfections, was a more satisfactory
+instrument for generating electricity than the
+frictional machine hitherto in use, the advantage lying
+in the fact that the current from the galvanic battery
+could be controlled practically at will, and that the
+apparatus itself was inexpensive and required
+comparatively little attention. These advantages were
+soon made apparent by the practical application of the
+electric current in several fields.
+
+It will be recalled that despite the energetic endeavors
+of such philosophers as Watson, Franklin, Galvani,
+and many others, the field of practical application of
+electricity was very limited at the close of the
+eighteenth century. The lightning-rod had come into
+general use, to be sure, and its value as an invention
+can hardly be overestimated. But while it was the
+result of extensive electrical discoveries, and is a most
+practical instrument, it can hardly be called one that
+puts electricity to practical use, but simply acts as a
+means of warding off the evil effects of a natural
+manifestation of electricity. The invention, however, had
+all the effects of a mechanism which turned electricity
+to practical account. But with the advent of the new
+kind of electricity the age of practical application began.
+
+
+DAVY AND ELECTRIC LIGHT
+
+Volta's announcement of his pile was scarcely two
+months old when two Englishmen, Messrs. Nicholson
+and Carlisle, made the discovery that the current from
+the galvanic battery had a decided effect upon certain
+chemicals, among other things decomposing water
+into its elements, hydrogen and oxygen. On May 7,
+1800, these investigators arranged the ends of two
+brass wires connected with the poles of a voltaic pile,
+composed of alternate silver and zinc plates, so that
+the current coming from the pile was discharged
+through a small quantity of "New River water." "A
+fine stream of minute bubbles immediately began
+to flow from the point of the lower wire in the tube
+which communicated with the silver," wrote Nicholson,
+"and the opposite point of the upper wire became
+tarnished, first deep orange and then black. . . ." The
+product of gas during two hours and a half was two-
+thirtieths of a cubic inch. "It was then mixed with
+an equal quantity of common air," continues Nicholson,
+"and exploded by the application of a lighted
+waxen thread."
+
+This demonstration was the beginning of the very
+important science of electro-chemistry.
+
+The importance of this discovery was at once recognized
+by Sir Humphry Davy, who began experimenting
+immediately in this new field. He constructed a
+series of batteries in various combinations, with which
+he attacked the "fixed alkalies," the composition of
+which was then unknown. Very shortly he was able
+to decompose potash into bright metallic globules,
+resembling quicksilver. This new substance he named
+"potassium." Then in rapid succession the elementary
+substances sodium, calcium, strontium, and magnesium
+were isolated.
+
+It was soon discovered, also, that the new electricity,
+like the old, possessed heating power under certain
+conditions, even to the fusing of pieces of wire. This
+observation was probably first made by Frommsdorff,
+but it was elaborated by Davy, who constructed a
+battery of two thousand cells with which he produced
+a bright light from points of carbon--the prototype of
+the modern arc lamp. He made this demonstration
+before the members of the Royal Institution in 1810.
+But the practical utility of such a light for illuminating
+purposes was still a thing of the future. The expense
+of constructing and maintaining such an elaborate
+battery, and the rapid internal destruction of its plates,
+together with the constant polarization, rendered its
+use in practical illumination out of the question. It
+was not until another method of generating electricity
+was discovered that Davy's demonstration could be
+turned to practical account.
+
+In Davy's own account of his experiment he says:
+
+"When pieces of charcoal about an inch long and
+one-sixth of an inch in diameter were brought near each
+other (within the thirtieth or fortieth of an inch), a
+bright spark was produced, and more than half the
+volume of the charcoal became ignited to whiteness;
+and, by withdrawing the points from each other, a constant
+discharge took place through the heated air, in a
+space equal to at least four inches, producing a most
+brilliant ascending arch of light, broad and conical in
+form in the middle. When any substance was introduced
+into this arch, it instantly became ignited;
+platina melted as readily in it as wax in a common candle;
+quartz, the sapphire, magnesia, lime, all entered
+into fusion; fragments of diamond and points of charcoal
+and plumbago seemed to evaporate in it, even
+when the connection was made in the receiver of an
+air-pump; but there was no evidence of their having
+previously undergone fusion. When the communication
+between the points positively and negatively electrified
+was made in the air rarefied in the receiver of the
+air-pump, the distance at which the discharge took
+place increased as the exhaustion was made; and when
+the atmosphere in the vessel supported only one-
+fourth of an inch of mercury in the barometrical gauge,
+the sparks passed through a space of nearly half an
+inch; and, by withdrawing the points from each other,
+the discharge was made through six or seven inches,
+producing a most brilliant coruscation of purple light;
+the charcoal became intensely ignited, and some platina
+wire attached to it fused with brilliant scintillations
+and fell in large globules upon the plate of the pump.
+All the phenomena of chemical decomposition were
+produced with intense rapidity by this combination."[1]
+
+But this experiment demonstrated another thing
+besides the possibility of producing electric light and
+chemical decomposition, this being the heating power
+capable of being produced by the electric current.
+Thus Davy's experiment of fusing substances laid the
+foundation of the modern electric furnaces, which are
+of paramount importance in several great commercial
+industries.
+
+While some of the results obtained with Davy's
+batteries were practically as satisfactory as could be
+obtained with modern cell batteries, the batteries
+themselves were anything but satisfactory. They were
+expensive, required constant care and attention, and,
+what was more important from an experimental standpoint
+at least, were not constant in their action except
+for a very limited period of time, the current soon
+"running down." Numerous experimenters, therefore,
+set about devising a satisfactory battery, and
+when, in 1836, John Frederick Daniell produced the
+cell that bears his name, his invention was epoch-
+making in the history of electrical progress. The
+Royal Society considered it of sufficient importance
+to bestow the Copley medal upon the inventor, whose
+device is the direct parent of all modern galvanic cells.
+From the time of the advent of the Daniell cell experiments
+in electricity were rendered comparatively
+easy. In the mean while, however, another great discovery
+was made.
+
+
+ELECTRICITY AND MAGNETISM
+
+For many years there had been a growing suspicion,
+amounting in many instances to belief in the close
+relationship existing between electricity and magnetism.
+Before the winter of 1815, however, it was a belief
+that was surmised but not demonstrated. But in that
+year it occurred to Jean Christian Oersted, of Denmark,
+to pass a current of electricity through a wire
+held parallel with, but not quite touching, a suspended
+magnetic needle. The needle was instantly deflected
+and swung out of its position.
+
+"The first experiments in connection with the subject
+which I am undertaking to explain," wrote Oersted,
+"were made during the course of lectures which
+I held last winter on electricity and magnetism. From
+those experiments it appeared that the magnetic needle
+could be moved from its position by means of a galvanic
+battery--one with a closed galvanic circuit.
+Since, however, those experiments were made with an
+apparatus of small power, I undertook to repeat and
+increase them with a large galvanic battery.
+
+"Let us suppose that the two opposite ends of the
+galvanic apparatus are joined by a metal wire. This
+I shall always call the conductor for the sake of brevity.
+Place a rectilinear piece of this conductor in a horizontal
+position over an ordinary magnetic needle so that
+it is parallel to it. The magnetic needle will be set in
+motion and will deviate towards the west under that
+part of the conductor which comes from the negative
+pole of the galvanic battery. If the wire is not more
+than four-fifths of an inch distant from the middle of
+this needle, this deviation will be about forty-five degrees.
+At a greater distance the angle of deviation
+becomes less. Moreover, the deviation varies according
+to the strength of the battery. The conductor can
+be moved towards the east or west, so long as it remains
+parallel to the needle, without producing any
+other result than to make the deviation smaller.
+
+"The conductor can consist of several combined
+wires or metal coils. The nature of the metal does not
+alter the result except, perhaps, to make it greater or
+less. We have used wires of platinum, gold, silver,
+brass, and iron, and coils of lead, tin, and quicksilver
+with the same result. If the conductor is interrupted
+by water, all effect is not cut off, unless the stretch
+of water is several inches long.
+
+"The conductor works on the magnetic needle
+through glass, metals, wood, water, and resin, through
+clay vessels and through stone, for when we placed a
+glass plate, a metal plate, or a board between the conductor
+and the needle the effect was not cut off; even
+the three together seemed hardly to weaken the effect,
+and the same was the case with an earthen vessel, even
+when it was full of water. Our experiments also demonstrated
+that the said effects were not altered when
+we used a magnetic needle which was in a brass case
+full of water.
+
+"When the conductor is placed in a horizontal plane
+under the magnetic needle all the effects we have described
+take place in precisely the same way, but in
+the opposite direction to what took place when the
+conductor was in a horizontal plane above the needle.
+
+"If the conductor is moved in a horizontal plane so
+that it gradually makes ever-increasing angles with the
+magnetic meridian, the deviation of the magnetic
+needle from the magnetic meridian is increased when
+the wire is turned towards the place of the needle; it
+decreases, on the other hand, when it is turned away
+from that place.
+
+"A needle of brass which is hung in the same way as
+the magnetic needle is not set in motion by the influence
+of the conductor. A needle of glass or rubber likewise
+remains static under similar experiments. Hence
+the electrical conductor affects only the magnetic
+parts of a substance. That the electrical current is
+not confined to the conducting wire, but is comparatively
+widely diffused in the surrounding space, is
+sufficiently demonstrated from the foregoing observations."[2]
+
+
+The effect of Oersted's demonstration is almost
+incomprehensible. By it was shown the close relationship
+between magnetism and electricity. It showed
+the way to the establishment of the science of electrodynamics;
+although it was by the French savant
+Andre Marie Ampere (1775-1836) that the science was
+actually created, and this within the space of one week
+after hearing of Oersted's experiment in deflecting the
+needle. Ampere first received the news of Oersted's
+experiment on September 11, 1820, and on the 18th
+of the same month he announced to the Academy the
+fundamental principles of the science of electro-dynamics--
+seven days of rapid progress perhaps unequalled
+in the history of science.
+
+Ampere's distinguished countryman, Arago, a few
+months later, gave the finishing touches to Oersted's
+and Ampere's discoveries, by demonstrating conclusively
+that electricity not only influenced a magnet,
+but actually produced magnetism under proper circumstances
+--a complemental fact most essential in
+practical mechanics
+
+Some four years after Arago's discovery, Sturgeon
+made the first "electro-magnet" by winding a soft
+iron core with wire through which a current of electricity
+was passed. This study of electro-magnets
+was taken up by Professor Joseph Henry, of Albany,
+New York, who succeeded in making magnets of enormous
+lifting power by winding the iron core with several
+coils of wire. One of these magnets, excited by
+a single galvanic cell of less than half a square foot
+of surface, and containing only half a pint of dilute
+acids, sustained a weight of six hundred and fifty
+pounds.
+
+Thus by Oersted's great discovery of the intimate
+relationship of magnetism and electricity, with further
+elaborations and discoveries by Ampere, Volta, and
+Henry, and with the invention of Daniell's cell, the
+way was laid for putting electricity to practical use.
+Soon followed the invention and perfection of the
+electro-magnetic telegraph and a host of other but
+little less important devices.
+
+
+FARADAY AND ELECTRO-MAGNETIC INDUCTION
+
+With these great discoveries and inventions at hand,
+electricity became no longer a toy or a "plaything for
+philosophers," but of enormous and growing importance
+commercially. Still, electricity generated by
+chemical action, even in a very perfect cell, was both
+feeble and expensive, and, withal, only applicable in a
+comparatively limited field. Another important scientific
+discovery was necessary before such things as
+electric traction and electric lighting on a large scale
+were to become possible; but that discovery was soon
+made by Sir Michael Faraday.
+
+Faraday, the son of a blacksmith and a bookbinder
+by trade, had interested Sir Humphry Davy by his
+admirable notes on four of Davy's lectures, which he
+had been able to attend. Although advised by the
+great scientist to "stick to his bookbinding" rather
+than enter the field of science, Faraday became, at
+twenty-two years of age, Davy's assistant in the Royal
+Institution. There, for several years, he devoted all
+his spare hours to scientific investigations and experiments,
+perfecting himself in scientific technique.
+
+A few years later he became interested, like all the
+scientists of the time, in Arago's experiment of rotating
+a copper disk underneath a suspended compass-
+needle. When this disk was rotated rapidly, the needle
+was deflected, or even rotated about its axis, in a manner
+quite inexplicable. Faraday at once conceived the
+idea that the cause of this rotation was due to electricity,
+induced in the revolving disk--not only conceived
+it, but put his belief in writing. For several years,
+however, he was unable to demonstrate the truth of
+his assumption, although he made repeated experiments
+to prove it. But in 1831 he began a series of
+experiments that established forever the fact of
+electro-magnetic induction.
+
+In his famous paper, read before the Royal Society
+in 1831, Faraday describes the method by which he first
+demonstrated electro-magnetic induction, and then explained
+the phenomenon of Arago's revolving disk.
+
+"About twenty-six feet of copper wire, one-twentieth
+of an inch in diameter, were wound round a cylinder
+of wood as a helix," he said, "the different spires of
+which were prevented from touching by a thin interposed
+twine. This helix was covered with calico, and
+then a second wire applied in the same manner. In this
+way twelve helices were "superposed, each containing
+an average length of wire of twenty-seven feet, and all
+in the same direction. The first, third, fifth, seventh,
+ninth, and eleventh of these helices were connected at
+their extremities end to end so as to form one helix;
+the others were connected in a similar manner; and
+thus two principal helices were produced, closely interposed,
+having the same direction, not touching anywhere,
+and each containing one hundred and fifty-five
+feet in length of wire.
+
+One of these helices was connected with a galvanometer,
+the other with a voltaic battery of ten pairs
+of plates four inches square, with double coppers
+and well charged; yet not the slightest sensible
+deflection of the galvanometer needle could be observed.
+
+"A similar compound helix, consisting of six lengths
+of copper and six of soft iron wire, was constructed.
+The resulting iron helix contained two hundred and
+eight feet; but whether the current from the trough
+was passed through the copper or the iron helix, no
+effect upon the other could be perceived at the galvanometer.
+
+"In these and many similar experiments no difference
+in action of any kind appeared between iron and
+other metals.
+
+"Two hundred and three feet of copper wire in one
+length were passed round a large block of wood; other
+two hundred and three feet of similar wire were interposed
+as a spiral between the turns of the first, and
+metallic contact everywhere prevented by twine. One
+of these helices was connected with a galvanometer and
+the other with a battery of a hundred pairs of plates
+four inches square, with double coppers and well
+charged. When the contact was made, there was a
+sudden and very slight effect at the galvanometer, and
+there was also a similar slight effect when the contact
+with the battery was broken. But whilst the voltaic
+current was continuing to pass through the one helix,
+no galvanometrical appearances of any effect like induction
+upon the other helix could be perceived, although
+the active power of the battery was proved to
+be great by its heating the whole of its own helix, and
+by the brilliancy of the discharge when made through
+charcoal.
+
+"Repetition of the experiments with a battery of
+one hundred and twenty pairs of plates produced no
+other effects; but it was ascertained, both at this and
+at the former time, that the slight deflection of the
+needle occurring at the moment of completing the connection
+was always in one direction, and that the
+equally slight deflection produced when the contact
+was broken was in the other direction; and, also, that
+these effects occurred when the first helices were used.
+
+"The results which I had by this time obtained with
+magnets led me to believe that the battery current
+through one wire did, in reality, induce a similar current
+through the other wire, but that it continued for
+an instant only, and partook more of the nature of the
+electrical wave passed through from the shock of a
+common Leyden jar than of that from a voltaic battery,
+and, therefore, might magnetize a steel needle although
+it scarcely affected the galvanometer.
+
+"This expectation was confirmed; for on substituting
+a small hollow helix, formed round a glass tube, for the
+galvanometer, introducing a steel needle, making contact
+as before between the battery and the inducing
+wire, and then removing the needle before the battery
+contact was broken, it was found magnetized.
+
+"When the battery contact was first made, then an
+unmagnetized needle introduced, and lastly the battery
+contact broken, the needle was found magnetized to
+an equal degree apparently with the first; but the poles
+were of the contrary kinds."[3]
+
+To Faraday these experiments explained the phenomenon
+of Arago's rotating disk, the disk inducing the
+current from the magnet, and, in reacting, deflecting
+the needle. To prove this, he constructed a disk that
+revolved between the poles of an electro-magnet, connecting
+the axis and the edge of the disk with a galvanometer.
+". . . A disk of copper, twelve inches in
+diameter, fixed upon a brass axis," he says, "was
+mounted in frames so as to be revolved either vertically
+or horizontally, its edge being at the same time introduced
+more or less between the magnetic poles. The
+edge of the plate was well amalgamated for the purpose
+of obtaining good but movable contact; a part round
+the axis was also prepared in a similar manner.
+
+"Conductors or collectors of copper and lead were
+constructed so as to come in contact with the edge of the
+copper disk, or with other forms of plates hereafter to
+be described. These conductors we're about four inches
+long, one-third of an inch wide, and one-fifth of an inch
+thick; one end of each was slightly grooved, to allow
+of more exact adaptation to the somewhat convex edge
+of the plates, and then amalgamated. Copper wires,
+one-sixteenth of an inch in thickness, attached in the
+ordinary manner by convolutions to the other ends of
+these conductors, passed away to the galvanometer.
+
+"All these arrangements being made, the copper
+disk was adjusted, the small magnetic poles being
+about one-half an inch apart, and the edge of the plate
+inserted about half their width between them. One
+of the galvanometer wires was passed twice or thrice
+loosely round the brass axis of the plate, and the other
+attached to a conductor, which itself was retained by
+the hand in contact with the amalgamated edge of the
+disk at the part immediately between the magnetic
+poles. Under these circumstances all was quiescent,
+and the galvanometer exhibited no effect. But the
+instant the plate moved the galvanometer was influenced,
+and by revolving the plate quickly the needle
+could be deflected ninety degrees or more."[4]
+
+
+This rotating disk was really a dynamo electric
+machine in miniature, the first ever constructed, but
+whose direct descendants are the ordinary dynamos.
+Modern dynamos range in power from little machines
+operating machinery requiring only fractions of a horsepower
+to great dynamos operating street-car lines and
+lighting cities; but all are built on the same principle
+as Faraday's rotating disk. By this discovery the use
+of electricity as a practical and economical motive
+power became possible.
+
+
+STORAGE BATTERIES
+
+When the discoveries of Faraday of electro-magnetic
+induction had made possible the means of easily generating
+electricity, the next natural step was to find a
+means of storing it or accumulating it. This, however,
+proved no easy matter, and as yet a practical storage
+or secondary battery that is neither too cumbersome,
+too fragile, nor too weak in its action has not been
+invented. If a satisfactory storage battery could be
+made, it is obvious that its revolutionary effects could
+scarcely be overestimated. In the single field of aeronautics,
+it would probably solve the question of aerial
+navigation. Little wonder, then, that inventors have
+sought so eagerly for the invention of satisfactory storage
+batteries. As early as 1803 Ritter had attempted
+to make such a secondary battery. In 1843 Grove
+also attempted it. But it was not until 1859, when
+Gaston Planche produced his invention, that anything
+like a reasonably satisfactory storage battery
+was made. Planche discovered that sheets of lead
+immersed in dilute sulphuric acid were very satisfactory
+for the production of polarization effects. He
+constructed a battery of sheets of lead immersed in
+sulphuric acid, and, after charging these for several
+hours from the cells of an ordinary Bunsen battery,
+was able to get currents of great strength and considerable
+duration. This battery, however, from its construction
+of lead, was necessarily heavy and cumbersome.
+Faure improved it somewhat by coating the
+lead plates with red-lead, thus increasing the capacity
+of the cell. Faure's invention gave a fresh impetus
+to inventors, and shortly after the market was filled
+with storage batteries of various kinds, most of them
+modifications of Planche's or Faure's. The ardor of
+enthusiastic inventors soon flagged, however, for all
+these storage batteries proved of little practical account
+in the end, as compared with other known
+methods of generating power.
+
+Three methods of generating electricity are in general
+use: static or frictional electricity is generated by
+"plate" or "static" machines; galvanic, generated by
+batteries based on Volta's discovery; and induced, or
+faradic, generated either by chemical or mechanical
+action. There is still another kind, thermo-electricity,
+that may be generated in a most simple manner. In
+1821 Seebecle, of Berlin, discovered that when a
+circuit was formed of two wires of different metals, if
+there be a difference in temperature at the juncture of
+these two metals an electrical current will be established.
+In this way heat may be transmitted directly
+into the energy of the current without the interposition
+of the steam-engine. Batteries constructed in
+this way are of low resistance, however, although by
+arranging several of them in "series," currents of
+considerable strength can be generated. As yet, however,
+they are of little practical importance.
+
+About the middle of the century Clerk-Maxwell
+advanced the idea that light waves were really electro-
+magnetic waves. If this were true and light proved
+to be simply one form of electrical energy, then the
+same would be true of radiant heat. Maxwell advanced
+this theory, but failed to substantiate it by
+experimental confirmation. But Dr. Heinrich Hertz,
+a few years later, by a series of experiments, demonstrated
+the correctness of Maxwell's surmises. What
+are now called "Hertzian waves" are waves apparently
+identical with light waves, but of much lower pitch or
+period. In his experiments Hertz showed that, under
+proper conditions, electric sparks between polished balls
+were attended by ether waves of the same nature as those
+of light, but of a pitch of several millions of vibrations
+per second. These waves could be dealt with as if they
+were light waves--reflected, refracted, and polarized.
+These are the waves that are utilized in wireless telegraphy.
+
+
+ROENTGEN RAYS, OR X-RAYS
+
+In December of 1895 word came out of Germany of
+a scientific discovery that startled the world. It came
+first as a rumor, little credited; then as a pronounced
+report; at last as a demonstration. It told of a new
+manifestation of energy, in virtue of which the interior
+of opaque objects is made visible to human eyes. One
+had only to look into a tube containing a screen of a
+certain composition, and directed towards a peculiar
+electrical apparatus, to acquire clairvoyant vision more
+wonderful than the discredited second-sight of the
+medium. Coins within a purse, nails driven into wood,
+spectacles within a leather case, became clearly visible
+when subjected to the influence of this magic tube; and
+when a human hand was held before the tube, its bones
+stood revealed in weird simplicity, as if the living, palpitating
+flesh about them were but the shadowy substance
+of a ghost.
+
+Not only could the human eye see these astounding
+revelations, but the impartial evidence of inanimate
+chemicals could be brought forward to prove that the
+mind harbored no illusion. The photographic film recorded
+the things that the eye might see, and ghostly
+pictures galore soon gave a quietus to the doubts of the
+most sceptical. Within a month of the announcement
+of Professor Roentgen's experiments comment
+upon the "X-ray" and the "new photography" had
+become a part of the current gossip of all Christendom.
+
+It is hardly necessary to say that such a revolutionary
+thing as the discovery of a process whereby opaque
+objects became transparent, or translucent, was not
+achieved at a single bound with no intermediate discoveries.
+In 1859 the German physicist Julius Plucker
+(1801-1868) noticed that when there was an electrical
+discharge through an exhausted tube at a low pressure,
+on the surrounding walls of the tube near the negative
+pole, or cathode, appeared a greenish phosphorescence.
+This discovery was soon being investigated by a number
+of other scientists, among others Hittorf, Goldstein,
+and Professor (now Sir William) Crookes. The
+explanations given of this phenomenon by Professor
+Crookes concern us here more particularly, inasmuch
+as his views did not accord exactly with those held by
+the other two scientists, and as his researches were more
+directly concerned in the discovery of the Roentgen 
+rays. He held that the heat and phosphorescence
+produced in a low-pressure tube were caused by streams
+of particles, projected from the cathode with great
+velocity, striking the sides of the glass tube. The
+composition of the glass seemed to enter into this
+phosphorescence also, for while lead glass produced
+blue phosphorescence, soda glass produced a yellowish
+green. The composition of the glass seemed to be
+changed by a long-continued pelting of these particles,
+the phosphorescence after a time losing its initial
+brilliancy, caused by the glass becoming "tired," as
+Professor Crookes said. Thus when some opaque substance,
+such as iron, is placed between the cathode and
+the sides of the glass tube so that it casts a shadow in
+a certain spot on the glass for some little time, it is
+found on removing the opaque substance or changing
+its position that the area of glass at first covered by
+the shadow now responded to the rays in a different
+manner from the surrounding glass.
+
+The peculiar ray's, now known as the cathode rays,
+not only cast a shadow, but are deflected by a magnet,
+so that the position of the phosphorescence on the sides
+of the tube may be altered by the proximity of a powerful
+magnet. From this it would seem that the rays
+are composed of particles charged with negative electricity,
+and Professor J. J. Thomson has modified the
+experiment of Perrin to show that negative electricity
+is actually associated with the rays. There is reason
+for believing, therefore, that the cathode rays are rapidly
+moving charges of negative electricity. It is possible,
+also, to determine the velocity at which these particles
+are moving by measuring the deflection produced
+by the magnetic field.
+
+From the fact that opaque substances cast a shadow
+in these rays it was thought at first that all solids were
+absolutely opaque to them. Hertz, however, discovered
+that a small amount of phosphorescence occurred
+on the glass even when such opaque substances as
+gold-leaf or aluminium foil were interposed between
+the cathode and the sides of the tube. Shortly afterwards
+Lenard discovered that the cathode rays can be
+made to pass from the inside of a discharge tube to the
+outside air. For convenience these rays outside the
+tube have since been known as "Lenard rays."
+
+In the closing days of December, 1895, Professor
+Wilhelm Konrad Roentgen, of Wurzburg, announced
+that he had made the discovery of the remarkable effect
+arising from the cathode rays to which reference
+was made above. He found that if a plate covered
+with a phosphorescent substance is placed near a discharge
+tube exhausted so highly that the cathode rays
+produced a green phosphorescence, this plate is made
+to glow in a peculiar manner. The rays producing
+this glow were not the cathode rays, although
+apparently arising from them, and are what have since
+been called the Roentgen rays, or X-rays.
+
+Roentgen found that a shadow is thrown upon the
+screen by substances held between it and the exhausted
+tube, the character of the shadow depending upon the
+density of the substance. Thus metals are almost
+completely opaque to the rays; such substances as
+bone much less so, and ordinary flesh hardly so at all.
+If a coin were held in the hand that had been interposed
+between the tube and the screen the picture
+formed showed the coin as a black shadow; and the
+bones of the hand, while casting a distinct shadow,
+showed distinctly lighter; while the soft tissues produced
+scarcely any shadow at all. The value of such
+a discovery was obvious from the first; and was still
+further enhanced by the discovery made shortly that,
+photographic plates are affected by the rays, thus
+making it possible to make permanent photographic
+records of pictures through what we know as opaque
+substances.
+
+What adds materially to the practical value of
+Roentgen's discovery is the fact that the apparatus for
+producing the X-rays is now so simple and relatively
+inexpensive that it is within the reach even of amateur
+scientists. It consists essentially of an induction coil
+attached either to cells or a street-current plug for generating
+the electricity, a focus tube, and a phosphorescence
+screen. These focus tubes are made in various
+shapes, but perhaps the most popular are in the form
+of a glass globe, not unlike an ordinary small-sized
+water-bottle, this tube being closed and exhausted,
+and having the two poles (anode and cathode) sealed
+into the glass walls, but protruding at either end for
+attachment to the conducting wires from the induction
+coil. This tube may be mounted on a stand at a
+height convenient for manipulation. The phosphorescence
+screen is usually a plate covered with some
+platino-cyanide and mounted in the end of a box of
+convenient size, the opposite end of which is so shaped
+that it fits the contour of the face, shutting out the
+light and allowing the eyes of the observer to focalize
+on the screen at the end. For making observations
+the operator has simply to turn on the current of electricity
+and apply the screen to his eyes, pointing it
+towards the glowing tube, when the shadow of any
+substance interposed between the tube and the screen
+will appear upon the phosphorescence plate.
+
+The wonderful shadow pictures produced on the
+phosphorescence screen, or the photographic plate,
+would seem to come from some peculiar form of light,
+but the exact nature of these rays is still an open question.
+Whether the Roentgen rays are really a form of
+light--that is, a form of "electro-magnetic disturbance
+propagated through ether," is not fully determined.
+Numerous experiments have been undertaken to determine
+this, but as yet no proof has been found that
+the rays are a form of light, although there appears to
+be nothing in their properties inconsistent with their
+being so. For the moment most investigators are content
+to admit that the term X-ray virtually begs the
+question as to the intimate nature of the form of energy
+involved.
+
+
+
+VIII. THE CONSERVATION OF ENERGY
+
+As we have seen, it was in 1831 that Faraday opened
+up the field of magneto-electricity. Reversing
+the experiments of his predecessors, who had found
+that electric currents may generate magnetism, he
+showed that magnets have power under certain circumstances
+to generate electricity; he proved, indeed,
+the interconvertibility of electricity and magnetism.
+Then he showed that all bodies are more or less subject
+to the influence of magnetism, and that even light
+may be affected by magnetism as to its phenomena of
+polarization. He satisfied himself completely of the
+true identity of all the various forms of electricity, and
+of the convertibility of electricity and chemical action.
+Thus he linked together light, chemical affinity, magnetism,
+and electricity. And, moreover, he knew full
+well that no one of these can be produced in indefinite
+supply from another. "Nowhere," he says, "is there
+a pure creation or production of power without a corresponding
+exhaustion of something to supply it."
+
+When Faraday wrote those words in 1840 he was
+treading on the very heels of a greater generalization
+than any which he actually formulated; nay, he had it
+fairly within his reach. He saw a great truth without
+fully realizing its import; it was left for others,
+approaching the same truth along another path, to point
+out its full significance.
+
+The great generalization which Faraday so narrowly
+missed is the truth which since then has become familiar
+as the doctrine of the conservation of energy--the
+law that in transforming energy from one condition to
+another we can never secure more than an equivalent
+quantity; that, in short, "to create or annihilate energy
+is as impossible as to create or annihilate matter;
+and that all the phenomena of the material universe
+consist in transformations of energy alone." Some philosophers
+think this the greatest generalization ever
+conceived by the mind of man. Be that as it may, it is
+surely one of the great intellectual landmarks of the
+nineteenth century. It stands apart, so stupendous
+and so far-reaching in its implications that the generation
+which first saw the law developed could little appreciate
+it; only now, through the vista of half a century,
+do we begin to see it in its true proportions.
+
+A vast generalization such as this is never a mushroom
+growth, nor does it usually spring full grown from
+the mind of any single man. Always a number of
+minds are very near a truth before any one mind fully
+grasps it. Pre-eminently true is this of the doctrine of
+the conservation of energy. Not Faraday alone, but
+half a dozen different men had an inkling of it before
+it gained full expression; indeed, every man who advocated
+the undulatory theory of light and heat was
+verging towards the goal. The doctrine of Young and
+Fresnel was as a highway leading surely on to the
+wide plain of conservation. The phenomena of electro-
+magnetism furnished another such highway. But there
+was yet another road which led just as surely and
+even more readily to the same goal. This was the
+road furnished by the phenomena of heat, and the
+men who travelled it were destined to outstrip their
+fellow-workers; though, as we have seen, wayfarers on
+other roads were within hailing distance when the
+leaders passed the mark.
+
+In order to do even approximate justice to the men
+who entered into the great achievement, we must recall
+that just at the close of the eighteenth century Count
+Rumford and Humphry Davy independently showed
+that labor may be transformed into heat; and correctly
+interpreted this fact as meaning the transformation of
+molar into molecular motion. We can hardly doubt
+that each of these men of genius realized--vaguely, at
+any rate--that there must be a close correspondence
+between the amount of the molar and the molecular
+motions; hence that each of them was in sight of the
+law of the mechanical equivalent of heat. But neither
+of them quite grasped or explicitly stated what each
+must vaguely have seen; and for just a quarter of a
+century no one else even came abreast their line of
+thought, let alone passing it.
+
+But then, in 1824, a French philosopher, Sadi Carnot,
+caught step with the great Englishmen, and took a
+long leap ahead by explicitly stating his belief that a
+definite quantity of work could be transformed into a
+definite quantity of heat, no more, no less. Carnot did
+not, indeed, reach the clear view of his predecessors as
+to the nature of heat, for he still thought it a form of
+"imponderable" fluid; but he reasoned none the less
+clearly as to its mutual convertibility with mechanical
+work. But important as his conclusions seem now
+that we look back upon them with clearer vision, they
+made no impression whatever upon his contemporaries.
+Carnot's work in this line was an isolated phenomenon
+of historical interest, but it did not enter into the
+scheme of the completed narrative in any such way as
+did the work of Rumford and Davy.
+
+The man who really took up the broken thread where
+Rumford and Davy had dropped it, and wove it into
+a completed texture, came upon the scene in 1840.
+His home was in Manchester, England; his occupation
+that of a manufacturer. He was a friend and
+pupil of the great Dr. Dalton. His name was James
+Prescott Joule. When posterity has done its final
+juggling with the names of the nineteenth century,
+it is not unlikely that the name of this Manchester
+philosopher will be a household word, like the names
+of Aristotle, Copernicus, and Newton.
+
+For Joule's work it was, done in the fifth decade of
+the century, which demonstrated beyond all cavil that
+there is a precise and absolute equivalence between
+mechanical work and heat; that whatever the form of
+manifestation of molar motion, it can generate a definite
+and measurable amount of heat, and no more.
+Joule found, for example, that at the sea-level in
+Manchester a pound weight falling through seven
+hundred and seventy-two feet could generate enough
+heat to raise the temperature of a pound of water one
+degree Fahrenheit. There was nothing haphazard,
+nothing accidental, about this; it bore the stamp of
+unalterable law. And Joule himself saw, what others in
+time were made to see, that this truth is merely a
+particular case within a more general law. If heat cannot
+be in any sense created, but only made manifest as a
+transformation of another kind of motion, then must
+not the same thing be true of all those other forms of
+"force"--light, electricity, magnetism--which had
+been shown to be so closely associated, so mutually
+convertible, with heat? All analogy seemed to urge the
+truth of this inference; all experiment tended to confirm
+it. The law of the mechanical equivalent of heat
+then became the main corner-stone of the greater law
+of the conservation of energy.
+
+But while this citation is fresh in mind, we must turn
+our attention with all haste to a country across the
+Channel--to Denmark, in short--and learn that even
+as Joule experimented with the transformation of heat,
+a philosopher of Copenhagen, Colding by name, had
+hit upon the same idea, and carried it far towards a
+demonstration. And then, without pausing, we must
+shift yet again, this time to Germany, and consider the
+work of three other men, who independently were on
+the track of the same truth, and two of whom, it must
+be admitted, reached it earlier than either Joule or
+Colding, if neither brought it to quite so clear a
+demonstration. The names of these three Germans are
+Mohr, Mayer, and Helmholtz. Their share in establishing
+the great doctrine of conservation must now
+claim our attention.
+
+As to Karl Friedrich Mohr, it may be said that his
+statement of the doctrine preceded that of any of his
+fellows, yet that otherwise it was perhaps least important.
+In 1837 this thoughtful German had grasped
+the main truth, and given it expression in an article
+published in the Zeitschrift fur Physik, etc. But the
+article attracted no attention whatever, even from
+Mohr's own countrymen. Still, Mohr's title to rank
+as one who independently conceived the great truth,
+and perhaps conceived it before any other man
+in the world saw it as clearly, even though he
+did not demonstrate its validity, is not to be disputed.
+
+It was just five years later, in 1842, that Dr. Julius
+Robert Mayer, practising physician in the little German
+town of Heilbronn, published a paper in Liebig's
+Annalen on "The Forces of Inorganic Nature," in
+which not merely the mechanical theory of heat, but
+the entire doctrine of the conservation of energy, is explicitly
+if briefly stated. Two years earlier Dr. Mayer,
+while surgeon to a Dutch India vessel cruising in the
+tropics, had observed that the venous blood of a
+patient seemed redder than venous blood usually is
+observed to be in temperate climates. He pondered
+over this seemingly insignificant fact, and at last reached
+the conclusion that the cause must be the lesser
+amount of oxidation required to keep up the body
+temperature in the tropics. Led by this reflection to
+consider the body as a machine dependent on outside
+forces for its capacity to act, he passed on into a novel
+realm of thought, which brought him at last to independent
+discovery of the mechanical theory of heat,
+and to the first full and comprehensive appreciation
+of the great law of conservation. Blood-letting, the
+modern physician holds, was a practice of very doubtful
+benefit, as a rule, to the subject; but once, at least,
+it led to marvellous results. No straw is go small that
+
+it may not point the receptive mind of genius to new
+and wonderful truths.
+
+
+MAYER'S PAPER OF 1842
+
+The paper in which Mayer first gave expression to
+his revolutionary ideas bore the title of "The Forces
+of Inorganic Nature," and was published in 1842. It
+is one of the gems of scientific literature, and fortunately
+it is not too long to be quoted in its entirety.
+Seldom if ever was a great revolutionary doctrine expounded
+in briefer compass:
+
+"What are we to understand by 'forces'? and how
+are different forces related to each other? The term
+force conveys for the most part the idea of something
+unknown, unsearchable, and hypothetical; while the
+term matter, on the other hand, implies the possession,
+by the object in question, of such definite properties as
+weight and extension. An attempt, therefore, to render
+the idea of force equally exact with that of matter
+is one which should be welcomed by all those who desire
+to have their views of nature clear and unencumbered
+by hypothesis.
+
+"Forces are causes; and accordingly we may make
+full application in relation to them of the principle
+causa aequat effectum. If the cause c has the effect e,
+then c = e; if, in its turn, e is the cause of a second
+effect of f, we have e = f, and so on: c = e = f ... = c.
+In a series of causes and effects, a term or a part of a
+term can never, as is apparent from the nature of an
+equation, become equal to nothing. This first property
+of all causes we call their indestructibility.
+
+"If the given cause c has produced an effect e equal
+to itself, it has in that very act ceased to be--c has become
+e. If, after the production of e, c still remained
+in the whole or in part, there must be still further
+effects corresponding to this remaining cause: the total
+effect of c would thus be > e, which would be contrary
+to the supposition c = e. Accordingly, since c becomes
+e, and e becomes f, etc., we must regard these
+various magnitudes as different forms under which
+one and the same object makes its appearance. This
+capability of assuming various forms is the second
+essential property of all causes. Taking both properties
+together, we may say, causes an INDESTRUCTIBLE
+quantitatively, and quantitatively CONVERTIBLE objects.
+
+"There occur in nature two causes which apparently
+never pass one into the other," said Mayer. "The
+first class consists of such causes as possess the properties
+of weight and impenetrability. These are kinds
+of matter. The other class is composed of causes
+which are wanting in the properties just mentioned--
+namely, forces, called also imponderables, from the
+negative property that has been indicated. Forces are
+therefore INDESTRUCTIBLE, CONVERTIBLE, IMPONDERABLE OBJECTS.
+
+"As an example of causes and effects, take matter:
+explosive gas, H + O, and water, HO, are related
+to each other as cause and effect; therefore H + O =
+HO. But if H + O becomes HO, heat, cal., makes its
+appearance as well as water; this heat must likewise
+have a cause, x, and we have therefore H + O + X =
+HO + cal. It might be asked, however, whether H + O
+is really = HO, and x = cal., and not perhaps H + O =
+cal., and x = HO, whence the above equation could
+equally be deduced; and so in many other cases. The
+phlogistic chemists recognized the equation between
+cal. and x, or phlogiston as they called it, and in so doing
+made a great step in advance; but they involved
+themselves again in a system of mistakes by putting
+x in place of O. In this way they obtained H =
+HO + x.
+
+"Chemistry teaches us that matter, as a cause, has
+matter for its effect; but we may say with equal justification
+that to force as a cause corresponds force as
+effect. Since c = e, and e = c, it is natural to call one
+term of an equation a force, and the other an effect of
+force, or phenomenon, and to attach different notions
+to the expression force and phenomenon. In brief,
+then, if the cause is matter, the effect is matter; if the
+cause is a force, the effect is also a force.
+
+"The cause that brings about the raising of a
+weight is a force. The effect of the raised weight is,
+therefore, also a force; or, expressed in a more general
+form, SEPARATION IN SPACE OF PONDERABLE OBJECTS IS A
+FORCE; and since this force causes the fall of bodies, we
+call it FALLING FORCE. Falling force and fall, or, still more
+generally, falling force and motion, are forces related
+to each other as cause and effect--forces convertible
+into each other--two different forms of one and the
+same object. For example, a weight resting on the
+ground is not a force: it is neither the cause of motion
+nor of the lifting of another weight. It becomes so,
+however, in proportion as it is raised above the ground.
+The cause--that is, the distance between a weight and
+the earth, and the effect, or the quantity of motion
+produced, bear to each other, as shown by mechanics,
+a constant relation.
+
+'Gravity being regarded as the cause of the falling
+of bodies, a gravitating force is spoken of; and thus the
+ideas of PROPERTY and of FORCE are confounded with each
+other. Precisely that which is the essential attribute
+of every force--that is, the UNION of indestructibility
+with convertibility--is wanting in every property:
+between a property and a force, between gravity and
+motion, it is therefore impossible to establish the equation
+required for a rightly conceived causal relation.
+If gravity be called a force, a cause is supposed which
+produces effects without itself diminishing, and incorrect
+conceptions of the causal connections of things
+are thereby fostered. In order that a body may fall, it
+is just as necessary that it be lifted up as that it should
+be heavy or possess gravity. The fall of bodies,
+therefore, ought not to be ascribed to their gravity
+alone. The problem of mechanics is to develop the
+equations which subsist between falling force and
+motion, motion and falling force, and between different
+motions. Here is a case in point: The magnitude
+of the falling force v is directly proportional
+(the earth's radius being assumed--oo) to the magnitude
+of the mass m, and the height d, to which it is
+raised--that is, v = md. If the height d = l, to
+which the mass m is raised, is transformed into the
+final velocity c = l of this mass, we have also v = mc;
+but from the known relations existing between d and c,
+it results that, for other values of d or of c, the measure
+of the force v is mc squared; accordingly v = md = mcsquared. The
+law of the conservation of vis viva is thus found to
+be based on the general law of the indestructibility of
+causes.
+
+"In many cases we see motion cease without having
+caused another motion or the lifting of a weight. But
+a force once in existence cannot be annihilated--it can
+only change its form. And the question therefore
+arises, what other forms is force, which we have become
+acquainted with as falling force and motion,
+capable of assuming? Experience alone can lead us to
+a conclusion on this point. That we may experiment
+to advantage, we must select implements which, besides
+causing a real cessation of motion, are as little as
+possible altered by the objects to be examined. For
+example, if we rub together two metal plates, we see
+motion disappear, and heat, on the other hand, make
+its appearance, and there remains to be determined only
+whether MOTION is the cause of heat. In order to reach
+a decision on this point, we must discuss the question
+whether, in the numberless cases in which the expenditure
+of motion is accompanied by the appearance of
+heat, the motion has not some other effect than the
+production of heat, and the heat some other cause
+than the motion.
+
+"A serious attempt to ascertain the effects of ceasing
+motion has never been made. Without wishing to
+exclude a priori the hypothesis which it may be possible
+to establish, therefore, we observe only that, as a
+rule, this effect cannot be supposed to be an alteration
+in the state of aggregation of the moved (that is,
+rubbing, etc.) bodies. If we assume that a certain
+quantity of motion v is expended in the conversion of
+a rubbing substance m into n, we must then have
+m + v - n, and n = m + v; and when n is reconverted
+into m, v must appear again in some form or other.
+
+By the friction of two metallic plates continued for a
+very long time, we can gradually cause the cessation
+of an immense quantity of movement; but would it
+ever occur to us to look for even the smallest trace of
+the force which has disappeared in the metallic dust
+that we could collect, and to try to regain it thence?
+We repeat, the motion cannot have been annihilated;
+and contrary, or positive and negative, motions cannot
+be regarded as = o any more than contrary motions
+can come out of nothing, or a weight can raise
+itself.
+
+"Without the recognition of a causal relation between
+motion and heat, it is just as difficult to explain
+the production of heat as it is to give any account of
+the motion that disappears. The heat cannot be derived
+from the diminution of the volume of the rubbing
+substances. It is well known that two pieces of ice
+may be melted by rubbing them together in vacuo; but
+let any one try to convert ice into water by pressure,
+however enormous. The author has found that water
+undergoes a rise of temperature when shaken violently.
+The water so heated (from twelve to thirteen degrees
+centigrade) has a greater bulk after being shaken than
+it had before. Whence now comes this quantity of
+heat, which by repeated shaking may be called into
+existence in the same apparatus as often as we please?
+The vibratory hypothesis of heat is an approach towards
+the doctrine of heat being the effect of motion,
+but it does not favor the admission of this causal relation
+in its full generality. It rather lays the chief
+stress on restless oscillations.
+
+"If it be considered as now established that in many
+cases no other effect of motion can be traced except
+heat, and that no other cause than motion can be found
+for the heat that is produced, we prefer the assumption
+that heat proceeds from motion to the assumption
+of a cause without effect and of an effect without
+a cause. Just as the chemist, instead of allowing
+oxygen and hydrogen to disappear without further
+investigation, and water to be produced in some
+inexplicable manner, establishes a connection between
+oxygen and hydrogen on the one hand, and water on
+the other.
+
+"We may conceive the natural connection existing
+between falling force, motion, and heat as follows:
+We know that heat makes its appearance when the
+separate particles of a body approach nearer to each
+other; condensation produces heat. And what applies
+to the smallest particles of matter, and the smallest
+intervals between them, must also apply to large
+masses and to measurable distances. The falling of a
+weight is a diminution of the bulk of the earth, and
+must therefore without doubt be related to the quantity
+of heat thereby developed; this quantity of heat
+must be proportional to the greatness of the weight
+and its distance from the ground. From this point of
+view we are easily led to the equations between falling
+force, motion, and heat that have already been discussed.
+
+"But just as little as the connection between falling
+force and motion authorizes the conclusion that the
+essence of falling force is motion, can such a conclusion
+be adopted in the case of heat. We are, on the contrary,
+rather inclined to infer that, before it can
+become heat, motion must cease to exist as motion,
+whether simple, or vibratory, as in the case of light
+and radiant heat, etc.
+
+"If falling force and motion are equivalent to heat,
+heat must also naturally be equivalent to motion and
+falling force. Just as heat appears as an EFFECT of the
+diminution of bulk and of the cessation of motion, so
+also does heat disappear as a CAUSE when its effects are
+produced in the shape of motion, expansion, or raising
+of weight.
+
+"In water-mills the continual diminution in bulk
+which the earth undergoes, owing to the fall of the
+water, gives rise to motion, which afterwards disappears
+again, calling forth unceasingly a great quantity
+of heat; and, inversely, the steam-engine serves to
+decompose heat again into motion or the raising of
+weights. A locomotive with its train may be compared
+to a distilling apparatus; the heat applied under
+the boiler passes off as motion, and this is deposited
+again as heat at the axles of the wheels."
+
+Mayer then closes his paper with the following deduction:
+"The solution of the equations subsisting between
+falling force and motion requires that the space
+fallen through in a given time--e. g., the first second--
+should be experimentally determined. In like manner,
+the solution of the equations subsisting between falling
+force and motion on the one hand and heat on the
+other requires an answer to the question, How great
+is the quantity of heat which corresponds to a given
+quantity of motion or falling force? For instance,
+we must ascertain how high a given weight requires to
+be raised above the ground in order that its falling
+force maybe equivalent to the raising of the temperature
+of an equal weight of water from 0 degrees to 1 degrees
+centigrade. The attempt to show that such an
+equation is the expression of a physical truth may
+be regarded as the substance of the foregoing remarks.
+
+"By applying the principles that have been set forth
+to the relations subsisting between the temperature
+and the volume of gases, we find that the sinking of a
+mercury column by which a gas is compressed is equivalent
+to the quantity of heat set free by the compression;
+and hence it follows, the ratio between the capacity
+for heat of air under constant pressure and its capacity
+under constant volume being taken as = 1.421,
+that the warming of a given weight of water from
+ 0 degrees to 1 degrees centigrade corresponds to the fall of an
+equal
+weight from the height of about three hundred and
+sixty-five metres. If we compare with this result the
+working of our best steam-engines, we see how small a
+part only of the heat applied under the boiler is really
+transformed into motion or the raising of weights; and
+this may serve as justification for the attempts at the
+profitable production of motion by some other method
+than the expenditure of the chemical difference between
+carbon and oxygen--more particularly by the
+transformation into motion of electricity obtained by
+chemical means."[1]
+
+
+MAYER AND HELMHOLTZ
+
+Here, then, was this obscure German physician, leading
+the humdrum life of a village practitioner, yet
+seeing such visions as no human being in the world had
+ever seen before.
+
+The great principle he had discovered became the
+dominating thought of his life, and filled all his leisure
+hours. He applied it far and wide, amid all the phenomena
+of the inorganic and organic worlds. It taught
+him that both vegetables and animals are machines,
+bound by the same laws that hold sway over inorganic
+matter, transforming energy, but creating nothing.
+Then his mind reached out into space and met a universe
+made up of questions. Each star that blinked
+down at him as he rode in answer to a night-call seemed
+an interrogation-point asking, How do I exist? Why
+have I not long since burned out if your theory of
+conservation be true? No one had hitherto even tried
+to answer that question; few had so much as realized
+that it demanded an answer. But the Heilbronn physician
+understood the question and found an answer.
+His meteoric hypothesis, published in 1848, gave for the
+first time a tenable explanation of the persistent light
+and heat of our sun and the myriad other suns--an
+explanation to which we shall recur in another connection.
+
+All this time our isolated philosopher, his brain aflame
+with the glow of creative thought, was quite unaware
+that any one else in the world was working along the
+same lines. And the outside world was equally heedless
+of the work of the Heilbronn physician. There
+was no friend to inspire enthusiasm and give courage,
+no kindred spirit to react on this masterful but lonely
+mind. And this is the more remarkable because there
+are few other cases where a master-originator in science
+has come upon the scene except as the pupil or friend
+of some other master-originator. Of the men we have
+noticed in the present connection, Young was the friend
+and confrere of Davy; Davy, the protege of Rumford;
+Faraday, the pupil of Davy; Fresnel, the co-worker
+with Arago; Colding, the confrere of Oersted; Joule,
+the pupil of Dalton. But Mayer is an isolated
+phenomenon--one of the lone mountain-peak intellects of
+the century. That estimate may be exaggerated
+which has called him the Galileo of the nineteenth
+century, but surely no lukewarm praise can do him
+justice.
+
+Yet for a long time his work attracted no attention
+whatever. In 1847, when another German physician,
+Hermann von Helmholtz, one of the most massive and
+towering intellects of any age, had been independently
+led to comprehension of the doctrine of the conservation
+of energy and published his treatise on the subject, he
+had hardly heard of his countryman Mayer. When he
+did hear of him, however, he hastened to renounce all
+claim to the doctrine of conservation, though the
+world at large gives him credit of independent even
+though subsequent discovery.
+
+
+JOULE'S PAPER OF 1843
+
+Meantime, in England, Joule was going on from one
+experimental demonstration to another, oblivious of his
+German competitors and almost as little noticed by his
+own countrymen. He read his first paper before the
+chemical section of the British Association for the
+Advancement of Science in 1843, and no one heeded it in
+the least. It is well worth our while, however, to
+consider it at length. It bears the title, "On the Calorific
+Effects of Magneto-Electricity, and the Mechanical
+Value of Heat." The full text, as published in the
+Report of the British Association, is as follows:
+
+"Although it has been long known that fine platinum
+wire can be ignited by magneto-electricity, it
+still remained a matter of doubt whether heat was
+evolved by the COILS in which the magneto-electricity
+was generated; and it seemed indeed not unreasonable
+to suppose that COLD was produced there in order to
+make up for the heat evolved by the other part of the
+circuit. The author therefore has endeavored to clear
+up this uncertainty by experiment. His apparatus
+consisted of a small compound electro-magnet, immersed
+in water, revolving between the poles of a powerful
+stationary magnet. The magneto-electricity developed
+in the coils of the revolving electro-magnet
+was measured by an accurate galvanometer; and the
+temperature of the water was taken before and after
+each experiment by a very delicate thermometer.
+The influence of the temperature of the surrounding
+atmospheric air was guarded against by covering the
+revolving tube with flannel, etc., and by the adoption
+of a system of interpolation. By an extensive series
+of experiments with the above apparatus the author
+succeeded in proving that heat is evolved by the coils
+of the magneto-electrical machine, as well as by any
+other part of the circuit, in proportion to the resistance
+to conduction of the wire and the square of the
+current; the magneto having, under comparable
+circumstances, the same calorific power as the voltaic
+electricity.
+
+"Professor Jacobi, of St. Petersburg, bad shown that
+the motion of an electro-magnetic machine generates
+magneto-electricity in opposition to the voltaic current
+of the battery. The author had observed the
+same phenomenon on arranging his apparatus as an
+electro-magnetic machine; but had found that no additional
+heat was evolved on account of the conflict of
+forces in the coil of the electro-magnet, and that the
+heat evolved by the coil remained, as before, proportional
+to the square of the current. Again, by turning
+the machine contrary to the direction of the attractive
+forces, so as to increase the intensity of the voltaic current
+by the assistance of the magneto-electricity, he
+found that the evolution of heat was still proportional
+to the square of the current. The author discovered,
+therefore, that the heat evolved by the voltaic current
+is invariably proportional to the square of the current,
+however the intensity of the current may be varied
+by magnetic induction. But Dr. Faraday has shown
+that the chemical effects of the current are simply as
+its quantity. Therefore he concluded that in the electro-
+magnetic engine a part of the heat due to the
+chemical actions of the battery is lost by the circuit,
+and converted into mechanical power; and that when
+the electro-magnetic engine is turned CONTRARY to the
+direction of the attractive forces, a greater quantity
+of heat is evolved by the circuit than is due to the
+chemical reactions of the battery, the over-plus quantity
+being produced by the conversion of the mechanical
+force exerted in turning the machine. By a dynamometrical
+apparatus attached to his machine, the
+author has ascertained that, in all the above cases, a
+quantity of heat, capable of increasing the temperature
+of a pound of water by one degree of Fahrenheit's
+scale, is equal to the mechanical force capable of raising
+a weight of about eight hundred and thirty pounds
+to the height of one foot."[2]
+
+
+JOULE OR MAYER?
+
+Two years later Joule wished to read another paper,
+but the chairman hinted that time was limited, and
+asked him to confine himself to a brief verbal synopsis
+of the results of his experiments. Had the chairman
+but known it, he was curtailing a paper vastly more
+important than all the other papers of the meeting put
+together. However, the synopsis was given, and one
+man was there to hear it who had the genius to appreciate
+its importance. This was William Thomson, the
+present Lord Kelvin, now known to all the world as
+among the greatest of natural philosophers, but then
+only a novitiate in science. He came to Joule's aid,
+started rolling the ball of controversy, and subsequently
+associated himself with the Manchester experimenter
+in pursuing his investigations.
+
+But meantime the acknowledged leaders of British
+science viewed the new doctrine askance. Faraday,
+Brewster, Herschel--those were the great names in
+physics at that day, and no one of them could quite
+accept the new views regarding energy. For several
+years no older physicist, speaking with recognized
+authority, came forward in support of the doctrine of
+conservation. This culminating thought of the first
+half of the nineteenth century came silently into the
+world, unheralded and unopposed. The fifth decade
+of the century had seen it elaborated and substantially
+demonstrated in at least three different countries, yet
+even the leaders of thought did not so much as know
+of its existence. In 1853 Whewell, the historian of the
+inductive sciences, published a second edition of his
+history, and, as Huxley has pointed out, he did not so
+much as refer to the revolutionizing thought which even
+then was a full decade old.
+
+By this time, however, the battle was brewing. The
+rising generation saw the importance of a law which
+their elders could not appreciate, and soon it was noised
+abroad that there were more than one claimant to the
+honor of discovery. Chiefly through the efforts of
+Professor Tyndall, the work of Mayer became known
+to the British public, and a most regrettable controversy
+ensued between the partisans of Mayer and those
+of Joule--a bitter controversy, in which Davy's contention
+that science knows no country was not always
+regarded, and which left its scars upon the hearts and
+minds of the great men whose personal interests were
+involved.
+
+And so to this day the question who is the chief discoverer
+of the law of the conservation of energy is not
+susceptible of a categorical answer that would satisfy all
+philosophers. It is generally held that the first choice
+lies between Joule and Mayer. Professor Tyndall has
+expressed the belief that in future each of these men
+will be equally remembered in connection with this
+work. But history gives us no warrant for such a hope.
+Posterity in the long run demands always that its heroes
+shall stand alone. Who remembers now that
+Robert Hooke contested with Newton the discovery
+of the doctrine of universal gravitation? The judgment
+of posterity is unjust, but it is inexorable. And
+so we can little doubt that a century from now one
+name will be mentioned as that of the originator of the
+great doctrine of the conservation of energy. The man
+whose name is thus remembered will perhaps be spoken
+of as the Galileo, the Newton, of the nineteenth century;
+but whether the name thus dignified by the final
+verdict of history will be that of Colding, Mohr, Mayer,
+Helmholtz, or Joule, is not as, yet decided.
+
+
+LORD KELVIN AND THE DISSIPATION OF ENERGY
+
+The gradual permeation of the field by the great
+doctrine of conservation simply repeated the history
+of the introduction of every novel and revolutionary
+thought. Necessarily the elder generation, to whom
+all forms of energy were imponderable fluids, must pass
+away before the new conception could claim the field.
+Even the word energy, though Young had introduced
+it in 1807, did not come into general use till some time
+after the middle of the century. To the generality of
+philosophers (the word physicist was even less in favor
+at this time) the various forms of energy were still
+subtile fluids, and never was idea relinquished with
+greater unwillingness than this. The experiments of
+Young and Fresnel had convinced a large number of
+philosophers that light is a vibration and not a substance;
+but so great an authority as Biot clung to the
+old emission idea to the end of his life, in 1862, and held
+a following.
+
+Meantime, however, the company of brilliant young
+men who had just served their apprenticeship when the
+doctrine of conservation came upon the scene had
+grown into authoritative positions, and were battling
+actively for the new ideas. Confirmatory evidence
+that energy is a molecular motion and not an
+"imponderable" form of matter accumulated day by day.
+The experiments of two Frenchmen, Hippolyte L.
+Fizeau and Leon Foucault, served finally to convince
+the last lingering sceptics that light is an undulation;
+and by implication brought heat into the same category,
+since James David Forbes, the Scotch physicist,
+had shown in 1837 that radiant heat conforms to the
+same laws of polarization and double refraction that
+govern light. But, for that matter, the experiments
+that had established the mechanical equivalent of heat
+hardly left room for doubt as to the immateriality
+of this "imponderable." Doubters had indeed, expressed
+scepticism as to the validity of Joule's experiments,
+but the further researches, experimental and
+mathematical, of such workers as Thomson (Lord Kelvin),
+Rankine, and Tyndall in Great Britain, of Helmholtz
+and Clausius in Germany, and of Regnault in
+France, dealing with various manifestations of heat,
+placed the evidence beyond the reach of criticism.
+
+Out of these studies, just at the middle of the century,
+to which the experiments of Mayer and Joule had
+led, grew the new science of thermo-dynamics. Out of
+them also grew in the mind of one of the investigators
+a new generalization, only second in importance to the
+doctrine of conservation itself. Professor William
+Thomson (Lord Kelvin) in his studies in thermodynamics
+was early impressed with the fact that
+whereas all the molar motion developed through labor
+or gravity could be converted into heat, the process is
+not fully reversible. Heat can, indeed, be converted
+into molar motion or work, but in the process a certain
+amount of the heat is radiated into space and lost. The
+same thing happens whenever any other form of energy
+is converted into molar motion. Indeed, every transmutation
+of energy, of whatever character, seems complicated
+by a tendency to develop heat, part of which
+is lost. This observation led Professor Thomson to his
+doctrine of the dissipation of energy, which he formulated
+before the Royal Society of Edinburgh in 1852,
+and published also in the Philosophical Magazine the
+same year, the title borne being, "On a Universal
+Tendency in Nature to the Dissipation of Mechanical
+Energy."
+
+From the principle here expressed Professor Thomson
+drew the startling conclusion that, "since any restoration
+of this mechanical energy without more than
+an equivalent dissipation is impossible," the universe,
+as known to us, must be in the condition of a machine
+gradually running down; and in particular that the
+world we live on has been within a finite time unfit for
+human habitation, and must again become so within a
+finite future. This thought seems such a commonplace
+to-day that it is difficult to realize how startling
+it appeared half a century ago. A generation trained, as
+ours has been, in the doctrines of the conservation and
+dissipation of energy as the very alphabet of physical
+science can but ill appreciate the mental attitude of a
+generation which for the most part had not even
+thought it problematical whether the sun could continue
+to give out heat and light forever. But those
+advance thinkers who had grasped the import of the
+doctrine of conservation could at once appreciate the
+force of Thomson's doctrine of dissipation, and realize
+the complementary character of the two conceptions.
+
+Here and there a thinker like Rankine did, indeed,
+attempt to fancy conditions under which the energy lost
+through dissipation might be restored to availability,
+but no such effort has met with success, and in time
+Professor Thomson's generalization and his conclusions
+as to the consequences of the law involved came to be
+universally accepted.
+
+The introduction of the new views regarding the nature
+of energy followed, as I have said, the course of
+every other growth of new ideas. Young and imaginative
+men could accept the new point of view; older philosophers,
+their minds channelled by preconceptions,
+could not get into the new groove. So strikingly true
+is this in the particular case now before us that it is
+worth while to note the ages at the time of the revolutionary
+experiments of the men whose work has been
+mentioned as entering into the scheme of evolution of
+the idea that energy is merely a manifestation of matter
+in motion. Such a list will tell the story better
+than a volume of commentary.
+
+Observe, then, that Davy made his epochal experiment
+of melting ice by friction when he was a youth of
+twenty. Young was no older when he made his first
+communication to the Royal Society, and was in his
+twenty-seventh year when he first actively espoused
+the undulatory theory. Fresnel was twenty-six when
+he made his first important discoveries in the same
+field; and Arago, who at once became his champion,
+was then but two years his senior, though for a decade
+he had been so famous that one involuntarily thinks of
+him as belonging to an elder generation.
+
+Forbes was under thirty when he discovered the polarization
+of heat, which pointed the way to Mohr, then
+thirty-one, to the mechanical equivalent. Joule was
+twenty-two in 1840, when his great work was begun;
+and Mayer, whose discoveries date from the same year,
+was then twenty-six, which was also the age of Helmholtz
+when he published his independent discovery of
+the same law. William Thomson was a youth just past
+his majority when he came to the aid of Joule before
+the British Society, and but seven years older when he
+formulated his own doctrine of the dissipation of energy.
+And Clausius and Rankine, who are usually mentioned
+with Thomson as the great developers of thermo-dynamics,
+were both far advanced with their novel studies
+before they were thirty. With such a list in mind, we
+may well agree with the father of inductive science
+that "the man who is young in years may be old in
+hours."
+
+Yet we must not forget that the shield has a reverse
+side. For was not the greatest of observing astronomers,
+Herschel, past thirty-five before he ever saw a
+telescope, and past fifty before he discovered the heat
+rays of the spectrum? And had not Faraday reached
+middle life before he turned his attention especially to
+electricity? Clearly, then, to make this phrase complete,
+Bacon should have added that "the man who is
+old in years may be young in imagination." Here,
+however, even more appropriate than in the other case
+--more's the pity--would have been the application
+of his qualifying clause: "but that happeneth rarely."
+
+
+THE FINAL UNIFICATION
+
+There are only a few great generalizations as yet
+thought out in any single field of science. Naturally,
+then, after a great generalization has found definitive
+expression, there is a period of lull before another forward
+move. In the case of the doctrines of energy, the
+lull has lasted half a century. Throughout this period,
+it is true, a multitude of workers have been delving in
+the field, and to the casual observer it might seem as if
+their activity had been boundless, while the practical
+applications of their ideas--as exemplified, for example,
+in the telephone, phonograph, electric light, and so on
+--have been little less than revolutionary. Yet the
+most competent of living authorities, Lord Kelvin,
+could assert in 1895 that in fifty years he had learned
+nothing new regarding the nature of energy.
+
+This, however, must not be interpreted as meaning
+that the world has stood still during these two generations.
+It means rather that the rank and file have been
+moving forward along the road the leaders had already
+travelled. Only a few men in the world had the range
+of thought regarding the new doctrine of energy that
+Lord Kelvin had at the middle of the century. The
+few leaders then saw clearly enough that if one form of
+energy is in reality merely an undulation or vibration
+among the particles of "ponderable" matter or of ether,
+all other manifestations of energy must be of the same
+nature. But the rank and file were not even within
+sight of this truth for a long time after they had partly
+grasped the meaning of the doctrine of conservation.
+When, late in the fifties, that marvellous young Scotchman,
+James Clerk-Maxwell, formulating in other words
+an idea of Faraday's, expressed his belief that electricity
+and magnetism are but manifestations of various
+conditions of stress and motion in the ethereal medium
+(electricity a displacement of strain, magnetism a whirl
+in the ether), the idea met with no immediate popularity.
+And even less cordial was the reception given the
+same thinker's theory, put forward in 1863, that the
+ethereal undulations producing the phenomenon we call
+light differ in no respect except in their wave-length
+from the pulsations of electro-magnetism.
+
+At about the same time Helmholtz formulated a
+somewhat similar electro-magnetic theory of light; but
+even the weight of this combined authority could not
+give the doctrine vogue until very recently, when the
+experiments of Heinrich Hertz, the pupil of Helmholtz,
+have shown that a condition of electrical strain may be
+developed into a wave system by recurrent interruptions
+of the electric state in the generator, and that
+such waves travel through the ether with the rapidity
+of light. Since then the electro-magnetic theory of
+light has been enthusiastically referred to as the greatest
+generalization of the century; but the sober thinker
+must see that it is really only what Hertz himself
+called it--one pier beneath the great arch of conservation.
+It is an interesting detail of the architecture,
+but the part cannot equal the size of the whole.
+
+More than that, this particular pier is as yet by no
+means a very firm one. It has, indeed, been demonstrated
+that waves of electro-magnetism pass through
+space with the speed of light, but as yet no one has
+developed electric waves even remotely approximating
+the shortness of the visual rays. The most that can
+positively be asserted, therefore, is that all the known
+forms of radiant energy-heat, light, electro-magnetism--
+travel through space at the same rate of speed,
+and consist of traverse vibrations--"lateral quivers,"
+as Fresnel said of light--known to differ in length,
+and not positively known to differ otherwise. It has,
+indeed, been suggested that the newest form of radiant
+energy, the famous X-ray of Professor Roentgen's discovery,
+is a longitudinal vibration, but this is a mere
+surmise. Be that as it may, there is no one now to
+question that all forms of radiant energy, whatever
+their exact affinities, consist essentially of undulatory
+motions of one uniform medium.
+
+A full century of experiment, calculation, and controversy
+has thus sufficed to correlate the "imponderable
+fluids" of our forebears, and reduce them all to
+manifestations of motion among particles of matter.
+At first glimpse that seems an enormous change of
+view. And yet, when closely considered, that change
+in thought is not so radical as the change in phrase
+might seem to imply. For the nineteenth-century
+physicist, in displacing the "imponderable fluids" of
+many kinds--one each for light, heat, electricity,
+magnetism--has been obliged to substitute for them one
+all-pervading fluid, whose various quivers, waves, ripples,
+whirls or strains produce the manifestations
+which in popular parlance are termed forms of force.
+This all-pervading fluid the physicist terms the ether,
+and he thinks of it as having no weight. In effect,
+then, the physicist has dispossessed the many imponderables
+in favor of a single imponderable--though the
+word imponderable has been banished from his vocabulary.
+In this view the ether--which, considered as
+a recognized scientific verity, is essentially a nineteenth-
+century discovery--is about the most interesting thing
+in the universe. Something more as to its properties,
+real or assumed, we shall have occasion to examine as
+we turn to the obverse side of physics, which demands
+our attention in the next chapter.
+
+
+
+IX. THE ETHER AND PONDERABLE MATTER
+
+"Whatever difficulties we may have in forming
+a consistent idea of the constitution of the
+ether, there can be no doubt that the interplanetary
+and interstellar spaces are not empty, but are occupied
+by a material substance or body which is certainly the
+largest and probably the most uniform body of which
+we have any knowledge."
+
+Such was the verdict pronounced some thirty years
+ago by James Clerk-Maxwell, one of the very greatest
+of nineteenth-century physicists, regarding the
+existence of an all-pervading plenum in the universe,
+in which every particle of tangible matter is
+immersed. And this verdict may be said to express
+the attitude of the entire philosophical world of our
+day. Without exception, the authoritative physicists
+of our time accept this plenum as a verity, and reason
+about it with something of the same confidence they
+manifest in speaking of "ponderable" matter or of,
+energy. It is true there are those among them who are
+disposed to deny that this all-pervading plenum merits
+the name of matter. But that it is a something, and
+a vastly important something at that, all are agreed.
+Without it, they allege, we should know nothing of
+light, of radiant heat, of electricity or magnetism;
+without it there would probably be no such thing as
+gravitation; nay, they even hint that without this
+strange something, ether, there would be no such
+thing as matter in the universe. If these contentions
+of the modern physicist are justified, then this
+intangible ether is incomparably the most important
+as well as the "largest and most uniform substance or
+body" in the universe. Its discovery may well be
+looked upon as one of the most important feats of the
+nineteenth century.
+
+For a discovery of that century it surely is, in the
+sense that all the known evidences of its existence were
+gathered in that epoch. True dreamers of all ages
+have, for metaphysical reasons, imagined the existence
+of intangible fluids in space--they had, indeed, peopled
+space several times over with different kinds of
+ethers, as Maxwell remarks--but such vague dreamings
+no more constituted the discovery of the modern
+ether than the dream of some pre-Columbian visionary
+that land might lie beyond the unknown waters constituted
+the discovery of America. In justice it must
+be admitted that Huyghens, the seventeenth-century
+originator of the undulatory theory of light, caught a
+glimpse of the true ether; but his contemporaries and
+some eight generations of his successors were utterly
+deaf to his claims; so he bears practically the same
+relation to the nineteenth-century discoverers of ether
+that the Norseman bears to Columbus.
+
+The true Columbus of the ether was Thomas Young.
+His discovery was consummated in the early days of
+the nineteenth century, when he brought forward the
+first, conclusive proofs of the undulatory theory of light.
+To say that light consists of undulations is to postulate
+something that undulates; and this something could
+not be air, for air exists only in infinitesimal quantity, if
+at all, in the interstellar spaces, through which light
+freely penetrates. But if not air, what then? Why,
+clearly, something more intangible than air; something
+supersensible, evading all direct efforts to detect it, yet
+existing everywhere in seemingly vacant space, and also
+interpenetrating the substance of all transparent liquids
+and solids, if not, indeed, of all tangible substances.
+This intangible something Young rechristened
+the Luminiferous Ether.
+
+In the early days of his discovery Young thought of
+the undulations which produce light and radiant heat as
+being longitudinal--a forward and backward pulsation,
+corresponding to the pulsations of sound--and as such
+pulsations can be transmitted by a fluid medium with
+the properties of ordinary fluids, he was justified in
+thinking of the ether as being like a fluid in its properties,
+except for its extreme intangibility. But about
+1818 the experiments of Fresnel and Arago with polarization
+of light made it seem very doubtful whether the
+theory of longitudinal vibrations is sufficient, and it
+was suggested by Young, and independently conceived
+and demonstrated by Fresnel, that the luminiferous
+undulations are not longitudinal, but transverse; and
+all the more recent experiments have tended to confirm
+this view. But it happens that ordinary fluids--
+gases and liquids--cannot transmit lateral vibrations;
+only rigid bodies are capable of such a vibration. So it
+became necessary to assume that the luminiferous ether
+is a body possessing elastic rigidity--a familiar property
+of tangible solids, but one quite unknown among fluids.
+
+The idea of transverse vibrations carried with it another
+puzzle. Why does not the ether, when set
+aquiver with the vibration which gives us the sensation
+we call light, have produced in its substance subordinate
+quivers, setting out at right angles from the
+path of the original quiver? Such perpendicular vibrations
+seem not to exist, else we might see around a
+corner; how explain their absence? The physicist could
+think of but one way: they must assume that the ether is
+incompressible. It must fill all space--at any rate, all
+space with which human knowledge deals--perfectly full.
+
+These properties of the ether, incompressibility and
+elastic rigidity, are quite conceivable by themselves;
+but difficulties of thought appear when we reflect upon
+another quality which the ether clearly must possess--
+namely, frictionlessness. By hypothesis this rigid,
+incompressible body pervades all space, imbedding every
+particle of tangible matter; yet it seems not to retard
+the movements of this matter in the slightest degree.
+This is undoubtedly the most difficult to comprehend
+of the alleged properties of the ether. The physicist
+explains it as due to the perfect elasticity of the ether,
+in virtue of which it closes in behind a moving particle
+with a push exactly counterbalancing the stress required
+to penetrate it in front.
+
+To a person unaccustomed to think of seemingly
+solid matter as really composed of particles relatively
+wide apart, it is hard to understand the claim that
+ether penetrates the substance of solids--of glass, for
+example--and, to use Young's expression, which we
+have previously quoted, moves among them as freely
+as the wind moves through a grove of trees. This
+thought, however, presents few difficulties to the mind
+accustomed to philosophical speculation. But the
+question early arose in the mind of Fresnel whether
+the ether is not considerably affected by contact with
+the particles of solids. Some of his experiments led
+him to believe that a portion of the ether which penetrates
+among the molecules of tangible matter is held
+captive, so to speak, and made to move along with
+these particles. He spoke of such portions of the ether
+as "bound" ether, in contradistinction to the great
+mass of "free" ether. Half a century after Fresnel's
+death, when the ether hypothesis had become an accepted
+tenet of science, experiments were undertaken
+by Fizeau in France, and by Clerk-Maxwell in England,
+to ascertain whether any portion of ether is
+really thus bound to particles of matter; but the results
+of the experiments were negative, and the question
+is still undetermined.
+
+While the undulatory theory of light was still fighting
+its way, another kind of evidence favoring the existence
+of an ether was put forward by Michael Faraday, who,
+in the course of his experiments in electrical and magnetic
+induction, was led more and more to perceive definite
+lines or channels of force in the medium subject to
+electro-magnetic influence. Faraday's mind, like that
+of Newton and many other philosophers, rejected the
+idea of action at a distance, and he felt convinced that
+the phenomena of magnetism and of electric induction
+told strongly for the existence of an invisible plenum
+everywhere in space, which might very probably be
+the same plenum that carries the undulations of light
+and radiant heat.
+
+Then, about the middle of the century, came that final
+revolution of thought regarding the nature of energy
+which we have already outlined in the preceding chapter,
+and with that the case for ether was considered to
+be fully established. The idea that energy is merely a
+"mode of motion" (to adopt Tyndall's familiar phrase),
+combined with the universal rejection of the notion of
+action at a distance, made the acceptance of a plenum
+throughout space a necessity of thought--so, at any
+rate, it has seemed to most physicists of recent decades.
+The proof that all known forms of radiant energy
+move through space at the same rate of speed is
+regarded as practically a demonstration that but one
+plenum--one ether--is concerned in their transmission.
+It has, indeed, been tentatively suggested, by Professor
+J. Oliver Lodge, that there may be two ethers,
+representing the two opposite kinds of electricity, but
+even the author of this hypothesis would hardly claim
+for it a high degree of probability.
+
+The most recent speculations regarding the properties
+of the ether have departed but little from the early
+ideas of Young and Fresnel. It is assumed on all sides
+that the ether is a continuous, incompressible body,
+possessing rigidity and elasticity. Lord Kelvin has
+even calculated the probable density of this ether, and
+its coefficient of rigidity. As might be supposed, it is
+all but infinitely tenuous as compared with any tangible
+solid, and its rigidity is but infinitesimal as compared
+with that of steel. In a word, it combines properties
+of tangible matter in a way not known in any tangible
+substance. Therefore we cannot possibly conceive its
+true condition correctly. The nearest approximation,
+according to Lord Kelvin, is furnished by a mould of
+transparent jelly. It is a crude, inaccurate analogy, of
+course, the density and resistance of jelly in particular
+being utterly different from those of the ether; but the
+quivers that run through the jelly when it is shaken,
+and the elastic tension under which it is placed when
+its mass is twisted about, furnish some analogy to the
+quivers and strains in the ether, which are held to constitute
+radiant energy, magnetism, and electricity.
+
+The great physicists of the day being at one regarding
+the existence of this all-pervading ether, it would
+be a manifest presumption for any one standing without
+the pale to challenge so firmly rooted a belief.
+And, indeed, in any event, there seems little ground on
+which to base such a challenge. Yet it may not be altogether
+amiss to reflect that the physicist of to-day is
+no more certain of his ether than was his predecessor
+of the eighteenth century of the existence of certain
+alleged substances which he called phlogiston, caloric,
+corpuscles of light, and magnetic and electric fluids.
+It would be but the repetition of history should it
+chance that before the close of another century the
+ether should have taken its place along with these discarded
+creations of the scientific imagination of earlier
+generations. The philosopher of to-day feels very sure
+that an ether exists; but when he says there is "no
+doubt" of its existence he speaks incautiously, and
+steps beyond the bounds of demonstration. He does
+not KNOW that action cannot take place at a distance;
+he does not KNOW that empty space itself may not perform
+the functions which he ascribes to his space-filling
+ether.
+
+Meantime, however, the ether, be it substance or be
+it only dream-stuff, is serving an admirable purpose in
+furnishing a fulcrum for modern physics. Not alone
+to the student of energy has it proved invaluable, but to
+the student of matter itself as well. Out of its hypothetical
+mistiness has been reared the most tenable
+theory of the constitution of ponderable matter which
+has yet been suggested--or, at any rate, the one that
+will stand as the definitive nineteenth-century guess at
+this "riddle of the ages." I mean, of course, the vortex
+theory of atoms--that profound and fascinating doctrine
+which suggests that matter, in all its multiform
+phases, is neither more nor less than ether in motion.
+
+The author of this wonderful conception is Lord Kelvin.
+The idea was born in his mind of a happy union
+of mathematical calculations with concrete experiments.
+The mathematical calculations were largely
+the work of Hermann von Helmholtz, who, about the
+year 1858, had undertaken to solve some unique problems
+in vortex motions. Helmholtz found that a vortex
+whirl, once established in a frictionless medium,
+must go on, theoretically, unchanged forever. In a
+limited medium such a whirl may be V-shaped, with
+its ends at the surface of the medium. We may imitate
+such a vortex by drawing the bowl of a spoon
+quickly through a cup of water. But in a limitless
+medium the vortex whirl must always be a closed ring,
+which may take the simple form of a hoop or circle, or
+which may be indefinitely contorted, looped, or, so to
+speak, knotted. Whether simple or contorted, this
+endless chain of whirling matter (the particles revolving
+about the axis of the loop as the particles of a string
+revolve when the string is rolled between the fingers)
+must, in a frictionless medium, retain its form and
+whirl on with undiminished speed forever.
+
+While these theoretical calculations of Helmholtz
+were fresh in his mind, Lord Kelvin (then Sir William
+Thomson) was shown by Professor P. G. Tait, of Edinburgh,
+an apparatus constructed for the purpose of
+creating vortex rings in air. The apparatus, which
+any one may duplicate, consisted simply of a box with
+a hole bored in one side, and a piece of canvas stretched
+across the opposite side in lieu of boards. Fumes of
+chloride of ammonia are generated within the box,
+merely to render the air visible. By tapping with the
+band on the canvas side of the box, vortex rings of the
+clouded air are driven out, precisely similar in appearance
+to those smoke-rings which some expert tobacco-
+smokers can produce by tapping on their cheeks, or to
+those larger ones which we sometimes see blown out
+from the funnel of a locomotive.
+
+The advantage of Professor Tait's apparatus is its
+manageableness and the certainty with which the desired
+result can be produced. Before Lord Kelvin's interested
+observation it threw out rings of various sizes,
+which moved straight across the room at varying rates
+of speed, according to the initial impulse, and which behaved
+very strangely when coming in contact with one
+another. If, for example, a rapidly moving ring overtook
+another moving in the same path, the one in advance
+seemed to pause, and to spread out its periphery
+like an elastic band, while the pursuer seemed to contract,
+till it actually slid through the orifice of the other,
+after which each ring resumed its original size, and
+continued its course as if nothing had happened. When,
+on the other hand, two rings moving in slightly different
+directions came near each other, they seemed to
+have an attraction for each other; yet if they impinged,
+they bounded away, quivering like elastic solids. If
+an effort were made to grasp or to cut one of these rings,
+the subtle thing shrank from the contact, and slipped
+away as if it were alive.
+
+And all the while the body which thus conducted
+itself consisted simply of a whirl in the air, made visible,
+but not otherwise influenced, by smoky fumes.
+Presently the friction of the surrounding air wore the
+ring away, and it faded into the general atmosphere--
+often, however, not until it had persisted for many seconds,
+and passed clear across a large room. Clearly, if
+there were no friction, the ring's inertia must make it a
+permanent structure. Only the frictionless medium
+was lacking to fulfil all the conditions of Helmholtz's
+indestructible vortices. And at once Lord Kelvin bethought
+him of the frictionless medium which physicists
+had now begun to accept--the all-pervading ether.
+What if vortex rings were started in this ether, must
+they not have the properties which the vortex rings
+in air had exhibited--inertia, attraction, elasticity?
+And are not these the properties of ordinary tangible
+matter? Is it not probable, then, that what we call
+matter consists merely of aggregations of infinitesimal
+vortex rings in the ether?
+
+Thus the vortex theory of atoms took form in Lord
+Kelvin's mind, and its expression gave the world what
+many philosophers of our time regard as the most
+plausible conception of the constitution of matter
+hitherto formulated. It is only a theory, to be sure;
+its author would be the last person to claim finality for
+it. "It is only a dream," Lord Kelvin said to me, in
+referring to it not long ago. But it has a basis in
+mathematical calculation and in analogical experiment
+such as no other theory of matter can lay claim to, and
+it has a unifying or monistic tendency that makes it,
+for the philosophical mind, little less than fascinating.
+True or false, it is the definitive theory of matter of the
+twentieth century.
+
+Quite aside from the question of the exact constitution
+of the ultimate particles of matter, questions as to
+the distribution of such particles, their mutual relations,
+properties, and actions, came in for a full share
+of attention during the nineteenth century, though the
+foundations for the modern speculations were furnished
+in a previous epoch. The most popular eighteenth-
+century speculation as to the ultimate constitution of
+matter was that of the learned Italian priest, Roger
+Joseph Boscovich, published in 1758, in his Theoria
+Philosophiae Naturalis. "In this theory," according
+to an early commentator, "the whole mass of which
+the bodies of the universe are composed is supposed to
+consist of an exceedingly great yet finite number of
+simple, indivisible, inextended atoms. These atoms
+are endued by the Creator with REPULSIVE and ATTRACTIVE
+forces, which vary according to the distance. At very
+small distances the particles of matter repel each other;
+and this repulsive force increases beyond all limits as
+the distances are diminished, and will consequently
+forever prevent actual contact. When the particles
+of matter are removed to sensible distances, the repulsive is
+exchanged for an attractive force, which decreases
+in inverse ratio with the squares of the distances,
+and extends beyond the spheres of the most remote
+comets."
+
+This conception of the atom as a mere centre of force
+was hardly such as could satisfy any mind other than
+the metaphysical. No one made a conspicuous attempt
+to improve upon the idea, however, till just at
+the close of the century, when Humphry Davy was led,
+in the course of his studies of heat, to speculate as to
+the changes that occur in the intimate substance of
+matter under altered conditions of temperature. Davy,
+as we have seen, regarded heat as a manifestation of
+motion among the particles of matter. As all bodies
+with which we come in contact have some temperature,
+Davy inferred that the intimate particles of every substance
+must be perpetually in a state of vibration.
+Such vibrations, he believed, produced the "repulsive
+force" which (in common with Boscovich) he admitted
+as holding the particles of matter at a distance from
+one another. To heat a substance means merely to
+increase the rate of vibration of its particles; thus also,
+plainly, increasing the repulsive forces and expanding
+the bulk of the mass as a whole. If the degree of heat
+applied be sufficient, the repulsive force may become
+strong enough quite to overcome the attractive force,
+and the particles will separate and tend to fly away
+from one another, the solid then becoming a gas.
+
+Not much attention was paid to these very suggestive
+ideas of Davy, because they were founded on the
+idea that heat is merely a motion, which the scientific
+world then repudiated; but half a century later, when
+the new theories of energy had made their way, there
+came a revival of practically the same ideas of the particles
+of matter (molecules they were now called)
+which Davy had advocated. Then it was that Clausius
+in Germany and Clerk-Maxwell in England took up
+the investigation of what came to be known as the
+kinetic theory of gases--the now familiar conception
+that all the phenomena of gases are due to the helter-
+skelter flight of the showers of widely separated molecules
+of which they are composed. The specific idea
+that the pressure or "spring" of gases is due to such
+molecular impacts was due to Daniel Bournelli, who
+advanced it early in the eighteenth century. The idea,
+then little noticed, had been revived about a century
+later by William Herapath, and again with some success
+by J. J. Waterston, of Bombay, about 1846; but it
+gained no distinct footing until taken in hand by
+Clausius in 1857 and by Clerk-Maxwell in 1859.
+
+The considerations that led Clerk-Maxwell to take
+up the computations may be stated in his own words,
+as formulated in a paper "On the Motions and Collisions
+of Perfectly Elastic Spheres."
+
+"So many of the properties of matter, especially
+when in the gaseous form," he says, "can be deduced
+from the hypothesis that their minute parts are in
+rapid motion, the velocity increasing with the temperature,
+that the precise nature of this motion becomes
+a subject of rational curiosity. Daniel Bournelli,
+Herapath, Joule, Kronig, Clausius, etc., have
+shown that the relations between pressure, temperature,
+and density in a perfect gas can be explained by
+supposing the particles to move with uniform velocities
+in straight lines, striking against the sides of the containing
+vessel and thus producing pressure. It is not
+necessary to suppose each particle to travel to any
+great distance in the same straight line; for the effect
+in producing pressure will be the same if the particles
+strike against each other; so that the straight line
+described may be very short. M. Clausius has determined
+the mean length of path in terms of the average
+of the particles, and the distance between the centres
+of two particles when the collision takes place. We
+have at present no means of ascertaining either of these
+distances; but certain phenomena, such as the internal
+friction of gases, the conduction of heat through a gas,
+and the diffusion of one gas through another, seem to
+indicate the possibility of determining accurately the
+mean length of path which a particle describes between
+two successive collisions. In order to lay the
+foundation of such investigations on strict mechanical
+principles, I shall demonstrate the laws of motion of
+an indefinite number of small, hard, and perfectly
+elastic spheres acting on one another only during impact.
+If the properties of such a system of bodies are
+found to correspond to those of gases, an important
+physical analogy will be established, which may lead
+to more accurate knowledge of the properties of matter.
+If experiments on gases are inconsistent with the hypothesis
+of these propositions, then our theory, though
+consistent with itself, is proved to be incapable of
+explaining the phenomena of gases. In either case it is
+necessary to follow out these consequences of the hypothesis.
+
+"Instead of saying that the particles are hard,
+spherical, and elastic, we may, if we please, say the
+particles are centres of force, of which the action is
+insensible except at a certain very small distance,
+when it suddenly appears as a repulsive force of very
+great intensity. It is evident that either assumption
+will lead to the same results. For the sake of avoiding
+the repetition of a long phrase about these repulsive
+bodies, I shall proceed upon the assumption of perfectly
+elastic spherical bodies. If we suppose those
+aggregate molecules which move together to have a
+bounding surface which is not spherical, then the
+rotatory motion of the system will close up a certain
+proportion of the whole vis viva, as has been shown by
+Clausius, and in this way we may account for the value
+of the specific heat being greater than on the more
+simple hypothesis."[1]
+
+
+The elaborate investigations of Clerk-Maxwell served
+not merely to substantiate the doctrine, but threw a
+flood of light upon the entire subject of molecular dynamics.
+Soon the physicists came to feel as certain of
+the existence of these showers of flying molecules making
+up a gas as if they could actually see and watch their
+individual actions. Through study of the viscosity of
+gases--that is to say, of the degree of frictional opposition
+they show to an object moving through them or
+to another current of gas--an idea was gained, with the
+aid of mathematics, of the rate of speed at which the
+particles of the gas are moving, and the number of collisions
+which each particle must experience in a given
+time, and of the length of the average free path traversed
+by the molecule between collisions, These measurements were
+confirmed by study of the rate of diffusion
+at which different gases mix together, and also by
+the rate of diffusion of heat through a gas, both these
+phenomena being chiefly due to the helter-skelter flight
+of the molecules.
+
+It is sufficiently astonishing to be told that such
+measurements as these have been made at all, but the
+astonishment grows when one hears the results. It appears
+from Clerk-Maxwell's calculations that the mean
+free path, or distance traversed by the molecules between
+collisions in ordinary air, is about one-half-millionth of
+an inch; while the speed of the molecules is such that
+each one experiences about eight billions of collisions
+per second! It would be hard, perhaps, to cite an
+illustration showing the refinements of modern physics
+better than this; unless, indeed, one other result that
+followed directly from these calculations be considered
+such--the feat, namely, of measuring the size of the
+molecules themselves. Clausius was the first to point
+out how this might be done from a knowledge of the
+length of free path; and the calculations were made by
+Loschmidt in Germany and by Lord Kelvin in England,
+independently.
+
+The work is purely mathematical, of course, but the
+results are regarded as unassailable; indeed, Lord Kelvin
+speaks of them as being absolutely demonstrative
+within certain limits of accuracy. This does not mean,
+however, that they show the exact dimensions of the
+molecule; it means an estimate of the limits of size
+within which the actual size of the molecule may lie.
+These limits, Lord Kelvin estimates, are about the one-
+ten-millionth of a centimetre for the maximum, and the
+one-one-hundred-millionth of a centimetre for the
+minimum. Such figures convey no particular meaning
+to our blunt senses, but Lord Kelvin has given a
+tangible illustration that aids the imagination to at
+least a vague comprehension of the unthinkable smallness
+of the molecule. He estimates that if a ball, say
+of water or glass, about "as large as a football, were to
+be magnified up to the size of the earth, each constituent
+molecule being magnified in the same proportion,
+the magnified structure would be more coarse-grained
+than a heap of shot, but probably less coarse-grained
+than a heap of footballs."
+
+Several other methods have been employed to estimate
+the size of molecules. One of these is based upon
+the phenomena of contact electricity; another upon the
+wave-theory of light; and another upon capillary attraction,
+as shown in the tense film of a soap-bubble!
+No one of these methods gives results more definite
+than that due to the kinetic theory of gases, just outlined;
+but the important thing is that the results obtained
+by these different methods (all of them due to
+Lord Kelvin) agree with one another in fixing the
+dimensions of the molecule at somewhere about the
+limits already mentioned. We may feel very sure indeed,
+therefore, that the molecules of matter are not the
+unextended, formless points which Boscovich and his
+followers of the eighteenth century thought them. But
+all this, it must be borne in mind, refers to the molecule,
+not to the ultimate particle of matter, about which we
+shall have more to say in another connection. Curiously
+enough, we shall find that the latest theories as
+to the final term of the series are not so very far afield
+from the dreamings of the eighteenth-century philosophers;
+the electron of J. J. Thompson shows many
+points of resemblance to the formless centre of Boscovich.
+
+Whatever the exact form of the molecule, its outline
+is subject to incessant variation; for nothing in molecular
+science is regarded as more firmly established than
+that the molecule, under all ordinary circumstances,
+is in a state of intense but variable vibration. The
+entire energy of a molecule of gas, for example, is not
+measured by its momentum, but by this plus its energy
+of vibration and rotation, due to the collisions already
+referred to. Clausius has even estimated the
+relative importance of these two quantities, showing
+that the translational motion of a molecule of gas accounts
+for only three-fifths of its kinetic energy. The
+total energy of the molecule (which we call "heat")
+includes also another factor--namely, potential energy,
+or energy of position, due to the work that has been
+done on expanding, in overcoming external pressure,
+and internal attraction between the molecules themselves.
+This potential energy (which will be recovered
+when the gas contracts) is the "latent heat" of Black,
+which so long puzzled the philosophers. It is latent in
+the same sense that the energy of a ball thrown into
+the air is latent at the moment when the ball poises at
+its greatest height before beginning to fall.
+
+It thus appears that a variety of motions, real and
+potential, enter into the production of the condition
+we term heat. It is, however, chiefly the translational
+motion which is measurable as temperature; and this,
+too, which most obviously determines the physical
+state of the substance that the molecules collectively
+compose--whether, that is to say, it shall appear to
+our blunt perceptions as a gas, a liquid, or a solid. In
+the gaseous state, as we have seen, the translational
+motion of the molecules is relatively enormous, the
+molecules being widely separated. It does not follow,
+as we formerly supposed, that this is evidence of a repulsive
+power acting between the molecules. The physicists
+of to-day, headed by Lord Kelvin, decline to
+recognize any such power. They hold that the molecules
+of a gas fly in straight lines by virtue of their inertia,
+quite independently of one another, except at
+times of collision, from which they rebound by virtue of
+their elasticity; or on an approach to collision, in which
+latter case, coming within the range of mutual attraction,
+two molecules may circle about each other, as a
+comet circles about the sun, then rush apart again, as
+the comet rushes from the sun.
+
+It is obvious that the length of the mean free path of
+the molecules of a gas may be increased indefinitely by
+decreasing the number of the molecules themselves in a
+circumscribed space. It has been shown by Professors
+Tait and Dewar that a vacuum may be produced artificially
+of such a degree of rarefaction that the mean
+free path of the remaining molecules is measurable in
+inches. The calculation is based on experiments made
+with the radiometer of Professor Crookes, an instrument
+which in itself is held to demonstrate the truth of
+the kinetic theory of gases. Such an attenuated gas
+as this is considered by Professor Crookes as constituting
+a fourth state of matter, which he terms ultra-
+gaseous.
+
+If, on the other hand, a gas is subjected to pressure,
+its molecules are crowded closer together, and the
+length of their mean free path is thus lessened. Ultimately,
+the pressure being sufficient, the molecules are
+practically in continuous contact. Meantime the enormously
+increased number of collisions has set the molecules
+more and more actively vibrating, and the temperature
+of the gas has increased, as, indeed, necessarily
+results in accordance with the law of the conservation
+of energy. No amount of pressure, therefore, can
+suffice by itself to reduce the gas to a liquid state. It
+is believed that even at the centre of the sun, where the
+pressure is almost inconceivably great, all matter is to
+be regarded as really gaseous, though the molecules
+must be so packed together that the consistency is
+probably more like that of a solid.
+
+If, however, coincidently with the application of
+pressure, opportunity be given for the excess of heat
+to be dissipated to a colder surrounding medium, the
+molecules, giving off their excess of energy, become
+relatively quiescent, and at a certain stage the gas becomes
+a liquid. The exact point at which this transformation
+occurs, however, differs enormously for
+different substances. In the case of water, for example,
+it is a temperature more than four hundred degrees
+above zero, centigrade; while for atmospheric air
+it is one hundred and ninety-four degrees centigrade
+below zero, or more than a hundred and fifty degrees
+below the point at which mercury freezes.
+
+Be it high or low, the temperature above which any
+substance is always a gas, regardless of pressure, is
+called the critical temperature, or absolute boiling-
+point, of that substance. It does not follow, however,
+that below this point the substance is necessarily a
+liquid. This is a matter that will be determined by
+external conditions of pressure. Even far below the
+critical temperature the molecules have an enormous
+degree of activity, and tend to fly asunder, maintaining
+what appears to be a gaseous, but what technically is
+called a vaporous, condition--the distinction being that
+pressure alone suffices to reduce the vapor to the liquid
+state. Thus water may change from the gaseous to
+the liquid state at four hundred degrees above zero,
+but under conditions of ordinary atmospheric pressure
+it does not do so until the temperature is lowered three
+hundred degrees further. Below four hundred degrees,
+however, it is technically a vapor, not a gas; but
+the sole difference, it will be understood, is in the degree
+of molecular activity.
+
+It thus appeared that the prevalence of water in a
+vaporous and liquid rather than in a "permanently"
+gaseous condition here on the globe is a mere incident
+of telluric evolution. Equally incidental is the fact
+that the air we breathe is "permanently" gaseous and
+not liquid or solid, as it might be were the earth's surface
+temperature to be lowered to a degree which, in
+the larger view, may be regarded as trifling. Between
+the atmospheric temperature in tropical and in arctic
+regions there is often a variation of more than one hundred
+degrees; were the temperature reduced another
+hundred, the point would be reached at which oxygen
+gas becomes a vapor, and under increased pressure
+would be a liquid. Thirty-seven degrees more would
+bring us to the critical temperature of nitrogen.
+
+Nor is this a mere theoretical assumption; it is a
+determination of experimental science, quite independent
+of theory. The physicist in the laboratory has
+produced artificial conditions of temperature enabling
+him to change the state of the most persistent gases.
+Some fifty years since, when the kinetic theory was in
+its infancy, Faraday liquefied carbonic-acid gas, among
+others, and the experiments thus inaugurated have
+been extended by numerous more recent investigators,
+notably by Cailletet in Switzerland, by Pictet in France,
+and by Dr. Thomas. Andrews and Professor James Dewar
+in England. In the course of these experiments
+not only has air been liquefied, but hydrogen also, the
+most subtle of gases; and it has been made more and
+more apparent that gas and liquid are, as Andrews long
+ago asserted, "only distant stages of a long series of
+continuous physical changes." Of course, if the temperature
+be lowered still further, the liquid becomes a
+solid; and this change also has been effected in the case
+of some of the most "permanent" gases, including air.
+
+The degree of cold--that is, of absence of heat--
+thus produced is enormous, relatively to anything of
+which we have experience in nature here at the earth
+now, yet the molecules of solidified air, for example, are
+not absolutely quiescent. In other words, they still
+have a temperature, though so very low. But it is
+clearly conceivable that a stage might be reached at
+which the molecules became absolutely quiescent, as
+regards either translational or vibratory motion. Such
+a heatless condition has been approached, but as yet
+not quite attained, in laboratory experiments. It is
+called the absolute zero of temperature, and is
+estimated to be equivalent to two hundred and seventy-
+three degrees Centigrade below the freezing-point of
+water, or ordinary zero.
+
+A temperature (or absence of temperature) closely
+approximating this is believed to obtain in the ethereal
+ocean of interplanetary and interstellar space, which
+transmits, but is thought not to absorb, radiant energy.
+We here on the earth's surface are protected
+from exposure to this cold, which would deprive every
+organic thing of life almost instantaneously, solely by
+the thin blanket of atmosphere with which the globe is
+coated. It would seem as if this atmosphere, exposed
+to such a temperature at its surface, must there be
+incessantly liquefied, and thus fall back like rain to be
+dissolved into gas again while it still is many miles
+above the earth's surface. This may be the reason why
+its scurrying molecules have not long ago wandered
+off into space and left the world without protection.
+
+But whether or not such liquefaction of the air now
+occurs in our outer atmosphere, there can be no question
+as to what must occur in its entire depth were we
+permanently shut off from the heating influence of the
+sun, as the astronomers threaten that we may be in a
+future age. Each molecule, not alone of the atmosphere,
+but of the entire earth's substance, is kept
+aquiver by the energy which it receives, or has received,
+directly or indirectly, from the sun. Left to itself, each
+molecule would wear out its energy and fritter it off
+into the space about it, ultimately running completely
+down, as surely as any human-made machine whose
+power is not from time to time restored. If, then, it
+shall come to pass in some future age that the sun's
+rays fail us, the temperature of the globe must gradually
+sink towards the absolute zero. That is to say,
+the molecules of gas which now fly about at such
+inconceivable speed must drop helpless to the earth;
+liquids must in turn become solids; and solids themselves,
+their molecular quivers utterly stilled, may perhaps
+take on properties the nature of which we cannot
+surmise.
+
+Yet even then, according to the current hypothesis,
+the heatless molecule will still be a thing instinct with
+life. Its vortex whirl will still go on, uninfluenced by
+the dying-out of those subordinate quivers that produced
+the transitory effect which we call temperature.
+For those transitory thrills, though determining the
+physical state of matter as measured by our crude
+organs of sense, were no more than non-essential incidents;
+but the vortex whirl is the essence of matter
+itself. Some estimates as to the exact character of
+this intramolecular motion, together with recent theories
+as to the actual structure of the molecule, will
+claim our attention in a later volume. We shall also
+have occasion in another connection to make fuller
+inquiry as to the phenomena of low temperature.
+
+
+
+APPENDIX
+
+REFERENCE-LIST
+
+CHAPTER I
+
+THE SUCCESSORS OF NEWTON IN ASTRONOMY
+[1] (p. 10). An Account of Several Extraordinary Meteors or
+Lights in the Sky, by Dr. Edmund Halley. Phil. Trans. of
+Royal Society of London, vol. XXIX, pp. 159-162. Read
+before the Royal Society in the autumn of 1714.
+[2] (p. 13). Phil. Trans. of Royal Society of London for 1748,
+vol. XLV., pp. 8, 9. From A Letter to the Right Honorable
+George, Earl of Macclesfield, concerning an Apparent Motion
+observed in some of the Fixed Stars, by James Bradley, D.D.,
+Astronomer Royal and F.R.S.
+
+CHAPTER II
+
+THE PROGRESS OF MODERN ASTRONOMY
+
+[1] (p. 25). William Herschel, Phil. Trans. for 1783, vol.
+LXXIII.
+[2] (p. 30). Kant's Cosmogony, ed. and trans. by W. Hartie,
+D.D., Glasgow, 900, pp. 74-81.
+[3] (p. 39). Exposition du systeme du monde (included in
+oeuvres Completes), by M. le Marquis de Laplace, vol. VI., p.
+498.
+[4] (p. 48). From The Scientific Papers of J. Clerk-Maxwell,
+edited by W. D. Nevin, M.A. (2 vols.), vol. I., pp. 372-374.
+This is a reprint of Clerk-Maxwell's prize paper of 1859.
+
+CHAPTER III
+
+THE NEW SCIENCE OF PALEONTOLOGY
+
+[1] (p. 81). Baron de Cuvier, Theory of the Earth, New York,
+1818, p. 98.
+[2] (p. 88). Charles Lyell, Principles of Geology (4 vols.),
+London,
+1834.
+(p. 92). Ibid., vol. III., pp. 596-598.
+[4] (p. 100). Hugh Falconer, in Paleontological Memoirs, vol.
+II., p. 596.
+[5] (p. 101). Ibid., p. 598.
+[6] (p. 102). Ibid., p. 599.
+[7] (p. 111). Fossil Horses in America (reprinted from American
+Naturalist, vol. VIII., May, 1874), by O. C. Marsh, pp.
+288, 289.
+
+CHAPTER IV
+
+THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY
+
+[1] (p. 123). James Hutton, from Transactions of the Royal
+Society of Edinburgh, 1788, vol. I., p. 214. A paper on
+the "Theory of the Earth," read before the Society in
+1781.
+[2] (p. 128). Ibid., p. 216.
+[3] (p. 139). Consideration on Volcanoes, by G. Poulett Scrope,
+Esq., pp. 228-234.
+[4] (p. 153). L. Agassiz, Etudes sur les glaciers, Neufchatel,
+1840, p. 240.
+
+CHAPTER V
+
+THE NEW SCIENCE OF METEOROLOGY
+
+[1] (p. 182). Theory of Rain, by James Hutton, in Transactions
+of the Royal Society of Edinburgh, 1788, vol. 1 , pp.
+53-56.
+[2] (p. 191). Essay on Dew, by W. C. Wells, M.D., F.R.S.,
+London, 1818, pp. 124 f.
+
+CHAPTER VI
+
+MODERN THEORIES OF HEAT AND LIGHT
+
+[1] (p. 215). Essays Political, Economical, and Philosophical,
+by Benjamin Thompson, Count of Rumford (2 vols.), Vol. II.,
+pp. 470-493, London; T. Cadell, Jr., and W. Davies, 1797.
+[2] (p. 220). Thomas Young, Phil. Trans., 1802, p. 35.
+[3] (p. 223). Ibid., p. 36.
+
+CHAPTER VII
+
+THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM
+
+[1] (p. 235). Davy's paper before Royal Institution, 1810.
+[2] (p. 238). Hans Christian Oersted, Experiments with the
+Effects of the Electric Current on the Magnetic Needle, 1815.
+[3] (p. 243). On the Induction of Electric Currents, by Michael
+Faraday, F.R.S., Phil. Trans. of Royal Society of London for
+1832, pp. 126-128.
+[4] (p. 245). Explication of Arago's Magnetic Phenomena, by
+Michael Faraday, F.R.S., Phil. Trans. Royal Society of London
+for 1832, pp. 146-149.
+
+CHAPTER VIII
+
+THE CONSERVATION OF ENERGY
+
+[1] (p. 267). The Forces of Inorganic Nature, a paper by Dr.
+Julius Robert Mayer, Liebig's Annalen, 1842.
+[2] (p. 272). On the Calorific Effects of Magneto-Electricity and
+the Mechanical Value of Heat, by J. P. Joule, in Report of the
+British Association for the Advancement of Science, vol. XII.,
+p. 33.
+
+CHAPTER IX
+
+THE ETHER AND PONDERABLE MATTER
+
+[1] (p. 297). James Clerk-Maxwell, Philosophical Magazine
+for January and July, 1860.
+
+END OF VOL. III
+
+
+
+
+
+End of Project Gutenberg Etext of A History of Science, V 3, by Williams
+
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