diff options
| author | Roger Frank <rfrank@pglaf.org> | 2025-10-15 05:17:36 -0700 |
|---|---|---|
| committer | Roger Frank <rfrank@pglaf.org> | 2025-10-15 05:17:36 -0700 |
| commit | e6e82c5b393118340657d36e27894a08c79ff3a1 (patch) | |
| tree | aafa9b16bd2b9cc93bb8017d3dbd34ab96149d75 /1707-h | |
Diffstat (limited to '1707-h')
| -rw-r--r-- | 1707-h/1707-h.htm | 9720 |
1 files changed, 9720 insertions, 0 deletions
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. 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. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +http://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +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 + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, are critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at http://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +http://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at http://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit http://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including checks, online payments and credit card donations. +To donate, please visit: http://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart is the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + http://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. + + +</pre> + </body> +</html> |