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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/1707-h.zip b/1707-h.zip Binary files differnew file mode 100644 index 0000000..2fa13d1 --- /dev/null +++ b/1707-h.zip diff --git a/1707-h/1707-h.htm b/1707-h/1707-h.htm new file mode 100644 index 0000000..cda1cd3 --- /dev/null +++ b/1707-h/1707-h.htm @@ -0,0 +1,9720 @@ +<?xml version="1.0" encoding="us-ascii"?> + +<!DOCTYPE html + PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" > + +<html xmlns="http://www.w3.org/1999/xhtml" lang="en"> + <head> + <title> + A History of Science, Vol. III by Henry Smith Williams + </title> + <style type="text/css" xml:space="preserve"> + + body { margin:5%; background:#faebd0; text-align:justify} + P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; } + blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;} + .mynote {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;} + .toc { margin-left: 10%; margin-bottom: .75em;} + .toc2 { margin-left: 20%;} + div.fig { display:block; margin:0 auto; text-align:center; } + div.middle { margin-left: 20%; margin-right: 20%; text-align: justify; } + .figleft {float: left; margin-left: 0%; margin-right: 1%;} + .figright {float: right; margin-right: 0%; margin-left: 1%;} + .pagenum {display:inline; font-size: 70%; font-style:normal; + margin: 0; padding: 0; position: absolute; right: 1%; + text-align: right;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} + +</style> + </head> + <body> +<pre xml:space="preserve"> + +The Project Gutenberg EBook of A History of Science, Volume 3(of 5), by +Henry Smith Williams + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: A History of Science, Volume 3(of 5) + +Author: Henry Smith Williams + +Release Date: November 18, 2009 [EBook #1707] +Last Updated: January 26, 2013 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V3 *** + + + + +Produced by Charles Keller, and David Widger + + + + + + +</pre> + <p> + <br /><br /> + </p> + <h1> + A HISTORY OF SCIENCE + </h1> + <h2> + BY HENRY SMITH WILLIAMS, M.D., LL.D. <br /> <br /> <br /> ASSISTED BY EDWARD + H. WILLIAMS, M.D. <br /> <br /> <br /> IN FIVE VOLUMES <br /> <br /> VOLUME + III. + </h2> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <blockquote> + <p class="toc"> + <big><b>CONTENTS</b></big> + </p> + <p> + <br /> <a href="#link2H_TOC"> DETAILED CONTENTS </a><br /><br /> <a + href="#link2H_4_0001"> <b>BOOK III. MODERN DEVELOPMENT OF THE PHYSICAL + SCIENCES</b> </a><br /> <br /><br /> + </p> + <p class="toc"> + <a href="#link2H_4_0002"> I. THE SUCCESSORS OF NEWTON IN ASTRONOMY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0003"> II. THE PROGRESS OF MODERN ASTRONOMY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0004"> III. THE NEW SCIENCE OF PALEONTOLOGY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0005"> IV. THE ORIGIN AND DEVELOPMENT OF MODERN + GEOLOGY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0006"> V. THE NEW SCIENCE OF METEOROLOGY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0007"> VI. MODERN THEORIES OF HEAT AND LIGHT </a> + </p> + <p class="toc"> + <a href="#link2H_4_0008"> VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND + MAGNETISM </a> + </p> + <p class="toc"> + <a href="#link2H_4_0009"> VIII. THE CONSERVATION OF ENERGY </a> + </p> + <p class="toc"> + <a href="#link2H_4_0010"> IX. THE ETHER AND PONDERABLE MATTER </a> + </p> + <p class="toc"> + <a href="#link2H_APPE"> APPENDIX </a> + </p> + </blockquote> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a name="link2H_TOC" id="link2H_TOC"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <blockquote> + <h2> + CONTENTS + </h2> + <p> + BOOK III <br /> CHAPTER I. THE SUCCESSORS OF NEWTON IN ASTRONOMY <br /> + The work of Johannes Hevelius—Halley and Hevelius—Halley's + observation <br /> of the transit of Mercury, and his method of + determining the parallax of <br /> the planets—Halley's observation + of meteors—His inability to <br /> explain these bodies—The + important work of James Bradley—Lacaille's <br /> measurement of + the arc of the meridian—The determination of the <br /> question as + to the exact shape of the earth—D'Alembert and his <br /> influence + upon science—Delambre's History of Astronomy—The <br /> + astronomical work of Euler. <br /> CHAPTER II. THE PROGRESS OF MODERN + ASTRONOMY <br /> The work of William Herschel—His discovery of + Uranus—His discovery <br /> that the stars are suns—His + conception of the universe—His deduction <br /> that gravitation + has caused the grouping of the heavenly bodies—The <br /> nebula, + hypothesis,—Immanuel Kant's conception of the formation of the + <br /> world—Defects in Kant's conception—Laplace's final + solution of the <br /> problem—His explanation in detail—Change + in the mental attitude of the <br /> world since Bruno—Asteroids + and satellites—Discoveries of Olbersl—The <br /> mathematical + calculations of Adams and Leverrier—The discovery of the <br /> + inner ring of Saturn—Clerk Maxwell's paper on the stability of + Saturn's <br /> rings—Helmholtz's conception of the action of tidal + friction—Professor <br /> G. H. Darwin's estimate of the + consequences of tidal action—Comets <br /> and meteors—Bredichin's + cometary theory—The final solution of the <br /> structure of + comets—Newcomb's estimate of the amount of cometary dust <br /> + swept up daily by the earth—The fixed stars—John Herschel's + studies <br /> of double stars—Fraunhofer's perfection of the + refracting <br /> telescope—Bessel's measurement of the parallax of + a star,—Henderson's <br /> measurements—Kirchhoff and + Bunsen's perfection of the <br /> spectroscope—Wonderful + revelations of the spectroscope—Lord Kelvin's <br /> estimate of + the time that will be required for the earth to become <br /> completely + cooled—Alvan Clark's discovery of the companion star of <br /> + Sirius—The advent of the photographic film in astronomy—Dr. + Huggins's <br /> studies of nebulae—Sir Norman Lockyer's + "cosmogonic guess,"—Croll's <br /> pre-nebular theory. <br /> + CHAPTER III. THE NEW SCIENCE OF PALEONTOLOGY <br /> William Smith and + fossil shells—His discovery that fossil rocks are <br /> arranged + in regular systems—Smith's inquiries taken up by Cuvier—His + <br /> Ossements Fossiles containing the first description of hairy <br /> + elephant—His contention that fossils represent extinct species + <br /> only—Dr. Buckland's studies of English fossil-beds—Charles + Lyell <br /> combats catastrophism,—Elaboration of his ideas with + reference to <br /> the rotation of species—The establishment of + the doctrine of <br /> uniformitarianism,—Darwin's Origin of + Species—Fossil man—Dr. <br /> Falconer's visit to the + fossil-beds in the valley of the <br /> Somme—Investigations of + Prestwich and Sir John Evans—Discovery of the <br /> Neanderthal + skull,—Cuvier's rejection of human fossils—The finding <br /> + of prehistoric carving on ivory—The fossil-beds of America—Professor + <br /> Marsh's paper on the fossil horses in America—The Warren + mastodon,—The <br /> Java fossil, Pithecanthropus Erectus. <br /> + CHAPTER IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY <br /> James + Hutton and the study of the rocks—His theory of the earth—His + <br /> belief in volcanic cataclysms in raising and forming the + continents—His <br /> famous paper before the Royal Society of + Edinburgh, 1781—-His <br /> conclusions that all strata of the + earth have their origin at the bottom <br /> of the sea—-His + deduction that heated and expanded matter caused the <br /> elevation of + land above the sea-level—Indifference at first shown this <br /> + remarkable paper—Neptunists versus Plutonists—Scrope's + classical work <br /> on volcanoes—Final acceptance of Hutton's + explanation of the origin <br /> of granites—Lyell and + uniformitarianism—Observations on the gradual <br /> elevation of + the coast-lines of Sweden and Patagonia—Observations on <br /> the + enormous amount of land erosion constantly taking place,—Agassiz + <br /> and the glacial theory—Perraudin the chamois-hunter, and his + <br /> explanation of perched bowlders—De Charpentier's acceptance + of <br /> Perraudin's explanation—Agassiz's paper on his Alpine + studies—His <br /> conclusion that the Alps were once covered with + an ice-sheet—Final <br /> acceptance of the glacial theory—The + geological ages—The work of <br /> Murchison and Sedgwick—Formation + of the American continents—Past, <br /> present, and future. <br /> + CHAPTER V. THE NEW SCIENCE OF METEOROLOGY <br /> Biot's investigations of + meteors—The observations of Brandes and <br /> Benzenberg on the + velocity of falling stars—Professor Olmstead's <br /> observations + on the meteoric shower of 1833—Confirmation of Chladni's <br /> + hypothesis of 1794—The aurora borealis—Franklin's suggestion + that <br /> it is of electrical origin—Its close association with + terrestrial <br /> magnetism—Evaporation, cloud-formation, and dew—Dalton's + demonstration <br /> that water exists in the air as an independent gas—Hutton's + theory of <br /> rain—Luke Howard's paper on clouds—Observations + on dew, by Professor <br /> Wilson and Mr. Six—Dr. Wells's essay on + dew—His observations <br /> on several appearances connected with + dew—Isotherms and ocean <br /> currents—Humboldt and + the-science of comparative climatology—His <br /> studies of ocean + currents—Maury's theory that gravity is the cause <br /> of ocean + currents—Dr. Croll on Climate and Time—Cyclones and <br /> + anti-cyclones,—Dove's studies in climatology—Professor + Ferrel's <br /> mathematical law of the deflection of winds—Tyndall's + estimate of <br /> the amount of heat given off by the liberation of a + pound of <br /> vapor—Meteorological observations and weather + predictions. <br /> CHAPTER VI. MODERN THEORIES OF HEAT AND LIGHT <br /> + Josiah Wedgwood and the clay pyrometer—Count Rumford and the + vibratory <br /> theory of heat—His experiments with boring cannon + to determine the <br /> nature of heat—Causing water to boil by the + friction of the borer—His <br /> final determination that heat is a + form of motion—Thomas Young and the <br /> wave theory of light—His + paper on the theory of light and colors—His <br /> exposition of + the colors of thin plates—Of the colors of thick <br /> plates, and + of striated surfaces,—Arago and Fresnel champion the wave <br /> + theory—opposition to the theory by Biot—The French Academy's + tacit <br /> acceptance of the correctness of the theory by its admission + of Fresnel <br /> as a member. <br /> CHAPTER VII. THE MODERN DEVELOPMENT + OF ELECTRICITY AND MAGNETISM <br /> Galvani and the beginning of modern + electricity—The construction of <br /> the voltaic pile—Nicholson's + and Carlisle's discovery that the galvanic <br /> current decomposes + water—Decomposition of various substances by Sir <br /> Humphry + Davy—His construction of an arc-light—The deflection of the + <br /> magnetic needle by electricity demonstrated by Oersted—Effect + of <br /> this important discovery—Ampere creates the science of + <br /> electro-dynamics—Joseph Henry's studies of electromagnets—Michael + <br /> Faraday begins his studies of electromagnetic induction—His + famous <br /> paper before the Royal Society, in 1831, in which he + demonstrates <br /> electro-magnetic induction—His explanation of + Arago's <br /> rotating disk—The search for a satisfactory method + of storing <br /> electricity—Roentgen rays, or X-rays. <br /> + CHAPTER VIII. THE CONSERVATION OF ENERGY <br /> Faraday narrowly misses + the discovery of the doctrine of <br /> conservation—Carnot's + belief that a definite quantity of work can be <br /> transformed into a + definite quantity of heat—The work of James Prescott <br /> Joule—Investigations + begun by Dr. Mayer—Mayer's paper of 1842—His <br /> statement + of the law of the conservation of energy—Mayer and <br /> Helmholtz—Joule's + paper of 1843—Joule or Mayer—Lord Kelvin and the <br /> + dissipation of energy-The final unification. <br /> CHAPTER IX. THE ETHER + AND PONDERABLE MATTER <br /> James Clerk-Maxwell's conception of ether—Thomas + Young and <br /> "Luminiferous ether,"—Young's and Fresnel's + conception of transverse <br /> luminiferous undulations—Faraday's + experiments pointing to the <br /> existence of ether—Professor + Lodge's suggestion of two ethers—Lord <br /> Kelvin's calculation + of the probable density of ether—The vortex theory <br /> of atoms—Helmholtz's + calculations in vortex motions—Professor <br /> Tait's apparatus + for creating vortex rings in the air—-The ultimate <br /> + constitution of matter as conceived by Boscovich—Davy's + speculations <br /> as to the changes that occur in the substance of + matter at different <br /> temperatures—Clausius's and Maxwell's + investigations of the <br /> kinetic theory of gases—Lord Kelvin's + estimate of the size of the <br /> molecule—Studies of the + potential energy of molecules—Action of gases <br /> at low + temperatures. <br /> APPENDIX <br /> + </p> + </blockquote> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <h1> + A HISTORY OF SCIENCE + </h1> + <p> + <a name="link2H_4_0001" id="link2H_4_0001"> + <!-- H2 anchor --> </a> + </p> + <h2> + BOOK III. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0002" id="link2H_4_0002"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + I. THE SUCCESSORS OF NEWTON IN ASTRONOMY + </h2> + <p> + HEVELIUS AND HALLEY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Like other astronomers of his time he 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + BRADLEY AND THE ABERRATION OF LIGHT + </p> + <p> + 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. + </p> + <p> + Bradley's studies led him to discover also the libratory motion of the + earth's axis. "As this appearance of 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) + </p> + <p> + FRENCH ASTRONOMERS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + LEONARD EULER + </p> + <p> + 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. + </p> + <p> + 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 he 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0003" id="link2H_4_0003"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + II. THE PROGRESS OF MODERN ASTRONOMY + </h2> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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; he 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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! + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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: + </p> + <p> + "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.... + </p> + <p> + "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.... + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE NEBULAR HYPOTHESIS OF KANT + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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.... + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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? + </p> + <p> + LAPLACE AND THE NEBULAR HYPOTHESIS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Let us allow Laplace to explain all this in detail: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + ASTEROIDS AND SATELLITES + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + The Discovery of Neptune + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + The Rings of Saturn + </p> + <p> + 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. + </p> + <p> + After elaborate mathematical calculations covering many pages of his paper + entitled "On the Stability of Saturn's Rings," he summarizes his + deductions as follows: + </p> + <p> + "Let us now gather together the conclusions we have been able to draw from + the mathematical theory of various kinds of conceivable rings. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + Studies of the Moon + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + COMETS AND METEORS + </p> + <p> + Until the mathematician ferreted out the secret, it surely never could + have been suspected by any one that the earth's serene attendant, + </p> +<pre xml:space="preserve"> + "That orbed maiden, with white fire laden, + Whom mortals call the moon," +</pre> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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! + </p> + <p> + THE FIXED STARS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Double Stars + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + The Distance of the Stars + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Revelations of the Spectroscope + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + The Astronomy of the Invisible + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + The Structure of Nebulae + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Lockyer's Meteoric Hypothesis + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0004" id="link2H_4_0004"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + III. THE NEW SCIENCE OF PALEONTOLOGY + </h2> + <p> + WILLIAM SMITH AND FOSSIL SHELLS + </p> + <p> + 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 + </p> +<pre xml:space="preserve"> + "teemed at a birth + Innumerous living creatures, perfect forms, + Limbed and full grown." +</pre> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + CUVIER AND FOSSIL VERTEBRATES + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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.... + </p> + <p> + "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) + </p> + <p> + 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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + CHARLES LYELL COMBATS CATASTROPHISM + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Let us see how Lyell elaborates these ideas, particularly with reference + to the rotation of species.(2) + </p> + <p> + "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.... + </p> + <p> + "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? + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "What kind of proofs, therefore, could we reasonably expect to find of the + origin at a particular period of a new species? + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE ORIGIN OF SPECIES + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + FOSSIL MAN + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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: + </p> + <p> + "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) + </p> + <p> + 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: + </p> + <p> + "First. That the flint implements are the result of design and the work of + man. + </p> + <p> + "Second. That they are found in beds of gravel, sand, and clay, which have + never been artificially disturbed. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE FOSSIL-BEDS OF AMERICA + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Marsh Describes the Fossil Horse + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + PALEONTOLOGY OF EVOLUTION + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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? + </p> + <p> + <a name="link2H_4_0005" id="link2H_4_0005"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY + </h2> + <p> + JAMES HUTTON + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + MODERN GEOLOGY + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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? + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + NEPTUNISTS VERSUS PLUTONISTS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "The consolidation of this stratum produced the gneiss formation. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + LYELL AND UNIFORMITARIANISM + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + AGASSIZ AND THE GLACIAL THEORY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + In 1840 Agassiz published a paper in which the results of his Alpine + studies were elaborated. + </p> + <p> + "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. + </p> + <p> + "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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE GEOLOGICAL AGES + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Working together, these two friends classified the + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Finally, the interior seas were filled, and the shore lines of the + continent assumed nearly their present outline. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + PAST, PRESENT, AND FUTURE + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0006" id="link2H_4_0006"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + V. THE NEW SCIENCE OF METEOROLOGY + </h2> + <p> + METEORITES + </p> + <p> + "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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + THE AURORA BOREALIS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + EVAPORATION, CLOUD FORMATION, AND DEW + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Dr. Wells's Essay on Dew + </p> + <p> + "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. + </p> + <p> + "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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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: + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + ISOTHERMS AND OCEAN CURRENTS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + CYCLONES AND ANTI-CYCLONES + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0007" id="link2H_4_0007"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + VI. MODERN THEORIES OF HEAT AND LIGHT + </h2> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + COUNT RUMFORD AND THE VIBRATORY THEORY OF HEAT + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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? + </p> + <p> + "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." + </p> + <p> + 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. + </p> + <p> + "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! + </p> + <p> + "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...." + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + THOMAS YOUNG AND THE WAVE THEORY OF LIGHT + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + Here is Young's exposition of the subject: + </p> + <p> + Of the Colors of Thin Plates + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + OF THE COLORS OF THICK PLATES + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + The Colors of Striated Surfaces + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + 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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ARAGO AND FRESNEL CHAMPION THE WAVE THEORY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0008" id="link2H_4_0008"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM + </h2> + <h3> + GALVANI AND VOLTA + </h3> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + DAVY AND ELECTRIC LIGHT + </p> + <p> + 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." + </p> + <p> + This demonstration was the beginning of the very important science of + electro-chemistry. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + In Davy's own account of his experiment he says: + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ELECTRICITY AND MAGNETISM + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + FARADAY AND ELECTRO-MAGNETIC INDUCTION + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "In these and many similar experiments no difference in action of any kind + appeared between iron and other metals. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + STORAGE BATTERIES + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + ROENTGEN RAYS, OR X-RAYS + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0009" id="link2H_4_0009"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + VIII. THE CONSERVATION OF ENERGY + </h2> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + MAYER'S PAPER OF 1842 + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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. + </p> + <p> + "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." + </p> + <p> + 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. + </p> +<pre xml:space="preserve"> +"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 + 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) +</pre> + <p> + MAYER AND HELMHOLTZ + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + JOULE'S PAPER OF 1843 + </p> + <p> + 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: + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + JOULE OR MAYER? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + LORD KELVIN AND THE DISSIPATION OF ENERGY + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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." + </p> + <p> + THE FINAL UNIFICATION + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_4_0010" id="link2H_4_0010"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + IX. THE ETHER AND PONDERABLE MATTER + </h2> + <p> + "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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + "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. + </p> + <p> + "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) + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <a name="link2H_APPE" id="link2H_APPE"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + APPENDIX + </h2> +<pre xml:space="preserve"> + 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. +</pre> + <p> + END OF VOL. III <br /> <br /> + </p> + <hr /> + <hr /> + <p> + <br /> <br /> + </p> + <h1> + TABLE OF CONTENTS <br /><br /> FOR THE FIVE VOLUMES + </h1> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0002"> <b>BOOK + I</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0003"> + I. PREHISTORIC SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0004"> + II. EGYPTIAN SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0005"> + III. SCIENCE OF BABYLONIA AND ASSYRIA </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0006"> + IV. THE DEVELOPMENT OF THE ALPHABET </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0007"> + V. THE BEGINNINGS OF GREEK SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0008"> + VI. THE EARLY GREEK PHILOSOPHERS IN ITALY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0009"> + VII. GREEK SCIENCE IN THE EARLY ATTIC PERIOD </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0010"> + VIII. POST-SOCRATIC SCIENCE AT ATHENS—PLATO, ARISTOTLE, AND + THEOPHRASTUS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0011"> + IX. GREEK SCIENCE OF THE ALEXANDRIAN OR HELLENISTIC PERIOD </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0012"> + X. SCIENCE OF THE ROMAN PERIOD </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1705/1705-h/1705-h.htm#2H_4_0013"> + XI. A RETROSPECTIVE GLANCE AT CLASSICAL SCIENCE </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0002"> <b>BOOK + II. THE BEGINNINGS OF MODERN SCIENCE</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0003"> + I. SCIENCE IN THE DARK AGE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0004"> + II. MEDIAEVAL SCIENCE AMONG THE ARABIANS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0005"> + III. MEDIAEVAL SCIENCE IN THE WEST </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0006"> + IV. THE NEW COSMOLOGY—COPERNICUS TO KEPLER AND GALILEO </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0007"> + V. GALILEO AND THE NEW PHYSICS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0008"> + VI. TWO PSEUDO-SCIENCES—ALCHEMY AND ASTROLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0009"> + VII. FROM PARACELSUS TO HARVEY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0010"> + VIII. MEDICINE IN THE SIXTEENTH AND SEVENTEENTH CENTURIES </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0011"> + IX. PHILOSOPHER-SCIENTISTS AND NEW INSTITUTIONS OF LEARNING </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0012"> + X. THE SUCCESSORS OF GALILEO IN PHYSICAL SCIENCE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0013"> + XI. NEWTON AND THE COMPOSITION OF LIGHT </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0014"> + XII. NEWTON AND THE LAW OF GRAVITATION </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0015"> + XIII. INSTRUMENTS OF PRECISION IN THE AGE OF NEWTON </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0016"> + XIV. PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO + FRANKLIN </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1706/1706-h/1706-h.htm#2H_4_0017"> + XV. NATURAL HISTORY TO THE TIME OF LINNAEUS </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0001"> <b>BOOK + III. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0002"> + I. THE SUCCESSORS OF NEWTON IN ASTRONOMY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0003"> + II. THE PROGRESS OF MODERN ASTRONOMY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0004"> + III. THE NEW SCIENCE OF PALEONTOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0005"> + IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0006"> + V. THE NEW SCIENCE OF METEOROLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0007"> + VI. MODERN THEORIES OF HEAT AND LIGHT </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0008"> + VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0009"> + VIII. THE CONSERVATION OF ENERGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1707/1707-h/1707-h.htm#2H_4_0010"> + IX. THE ETHER AND PONDERABLE MATTER </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0001"> <b>BOOK + IV. MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES</b> </a> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0002"> + I. THE PHLOGISTON THEORY IN CHEMISTRY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0003"> + II. THE BEGINNINGS OF MODERN CHEMISTRY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0004"> + III. CHEMISTRY SINCE THE TIME OF DALTON </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0005"> + IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0006"> + V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0007"> + VI. THEORIES OF ORGANIC EVOLUTION </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0008"> + VII. EIGHTEENTH-CENTURY MEDICINE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0009"> + VIII. NINETEENTH-CENTURY MEDICINE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0010"> + IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/1708/1708-h/1708-h.htm#2H_4_0011"> + X. THE NEW SCIENCE OF ORIENTAL ARCHAEOLOGY </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0001"> + <b>BOOK V. ASPECTS OF RECENT SCIENCE</b> </a><br /> + </p> + <table summary="" style="margin-right: auto; margin-left: auto"> + <tr> + <td> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0003"> + I. THE BRITISH MUSEUM </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0004"> + II. THE ROYAL SOCIETY OF LONDON FOR IMPROVING NATURAL KNOWLEDGE </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0005"> + III. THE ROYAL INSTITUTION AND THE LOW-TEMPERATURE RESEARCHES </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0006"> + IV. SOME PHYSICAL LABORATORIES AND PHYSICAL PROBLEMS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0007"> + V. THE MARINE BIOLOGICAL LABORATORY AT NAPLES </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0008"> + VI. ERNST HAECKEL AND THE NEW ZOOLOGY </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0009"> + VII. SOME MEDICAL LABORATORIES AND MEDICAL PROBLEMS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0010"> + VII. SOME UNSOLVED SCIENTIFIC PROBLEMS </a> + </p> + <p class="toc"> + <a + href="http://www.gutenberg.org/files/30495/30495-h/30495-h.htm#2H_4_0011"> + IX. RETROSPECT AND PROSPECT </a> + </p> + </td> + </tr> + </table> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> +<pre xml:space="preserve"> + + + + + +End of the Project Gutenberg EBook of A History of Science, Volume 3(of 5), by +Henry Smith Williams + +*** END OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V3 *** + +***** This file should be named 1707-h.htm or 1707-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/7/0/1707/ + +Produced by Charles Keller, and David Widger + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: A History of Science, Volume 3(of 5) + +Author: Henry Smith Williams + +Release Date: April, 1999 [Etext #1707] +Posting Date: November 18, 2009 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V3 *** + + + + +Produced by Charles Keller + + + + + +A HISTORY OF SCIENCE + + +MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES + + + +By Henry Smith Williams, M.D., Ll.D. + +Assisted By Edward H. Williams, M.D. + +In Five Volumes + +Volume III. + + + +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 Olbersl--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 he 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 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 he 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; he 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 + 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 the Project Gutenberg EBook of A History of Science, Volume 3(of 5), by +Henry Smith Williams + +*** END OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V3 *** + +***** This file should be named 1707.txt or 1707.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/7/0/1707/ + +Produced by Charles Keller + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. 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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 + diff --git a/old/3hsci10.zip b/old/3hsci10.zip Binary files differnew file mode 100644 index 0000000..eaaab10 --- /dev/null +++ b/old/3hsci10.zip |