A History of Science - Volume 3 E-Book

Edward Huntington Williams

• Herausgeber: libreka classics
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2019

Seitenzahl: 418

Beschreibung

Volume 3: Modern development of the physical sciences libreka classics – These are classics of literary history, reissued and made available to a wide audience. Immerse yourself in well-known and popular titles!

Leseprobe

Titel: A History of Science — Volume 3

von William Shakespeare, H. G. Wells, Henry Van Dyke, Thomas Carlyle, Oscar Wilde, Joseph Conrad, Henry James, Anthony Hope, Henry Fielding, Giraldus Cambrensis, Daniel Defoe, Grammaticus Saxo, Edgar Rice Burroughs, Hugh Lofting, Agatha Christie, Sinclair Lewis, Eugène Brieux, Upton Sinclair, Booth Tarkington, Sax Rohmer, Jack London, Anna Katharine Green, Sara Jeannette Duncan, Xenophon, Alexandre Dumas père, John William Draper, Alice Christiana Thompson Meynell, Bram Stoker, Honoré de Balzac, William Congreve, Louis de Rougemont, Nikolai Vasilievich Gogol, Rolf Boldrewood, François Rabelais, Lysander Spooner, B. M. Bower, Henry Rider Haggard, William Hickling Prescott, Lafcadio Hearn, Robert Herrick, Jane Austen, Mark Twain, Mary Roberts Rinehart, Charles Babbage, Kate Douglas Smith Wiggin, Frank L. Packard, George Meredith, John Merle Coulter, Irvin S. Cobb, Edwin Mims, John Tyndall, Various, Charles Darwin, Sidney Lanier, Henry Lawson, Niccolò Machiavelli, George W. Crile, Théophile Gautier, Noah Brooks, James Thomson, Zane Grey, J. M. Synge, Virginia Woolf, Conrad Aiken, Edna St. Vincent Millay, Helen Cody Wetmore, Ayn Rand, Sir Thomas Malory, Gustave Flaubert, Edmond Rostand, Charlotte Brontë, Edith Wharton, Giles Lytton Strachey, Myrtle Reed, Ernest Bramah, Jules Verne, H. L. Mencken, H. Stanley Redgrove, Victor Lefebure, Edna Lyall, John Masefield, Charles Kingsley, Robert Burns, Edgar Lee Masters, Victor [pseud.] Appleton, Ellis Parker Butler, Mary Lamb, Charles Lamb, Johann Wolfgang von Goethe, Kenneth Grahame, Charles Dickens, John Ruskin, John Galt, James J. Davis, Owen Wister, William Blades, Sir Hall Caine, Sir Max Beerbohm, Baron Edward John Moreton Drax Plunkett Dunsany, Bret Harte, E. Phillips Oppenheim, Thomas Henry Huxley, A. B. Paterson, John N. Reynolds, Walter Dill Scott, Hans Gustav Adolf Gross, T. S. Eliot, Walt Whitman, Arthur Ransome, Jane Addams, Elizabeth, David Lindsay, Helen Bannerman, Charles A. Oliver, J. M. Barrie, Robert F. Murray, Andrew Lang, Jerome K. Jerome, Francis Thompson, Sydney Waterlow, Andrew Dickson White, Benjamin N. Cardozo, Karl Marx, Edouard Louis Emmanuel Julien Le Roy, Margaret Hill McCarter, Sir Donald Mackenzie Wallace, Howard Trueman, L. M. Montgomery, Frank T. Bullen, Baron Alfred Tennyson Tennyson, Jonathan Nield, Henry Wadsworth Longfellow, Charles Reade, Ouida, Washington Irving, Benjamin Louis Eulalie de Bonneville, Sir Walter Scott, Stewart Edward White, Arthur Hugh Clough, Baron Edward Bulwer Lytton Lytton, C.-F. Volney, T. Troward, graf Leo Tolstoy, Christopher Morley, James Madison, Alexander Hamilton, John Jay, Gilbert White, Percival Lowell, Frederick Marryat, Robert Graves, Thomas Holmes, Wilkie Collins, Maria Edgeworth, Katherine Mansfield, E. Nesbit, Olive Schreiner, Jeronimo Lobo, O. Henry, James Slough Zerbe, Donald Ogden Stewart, Johanna Spyri, Eleanor H. Porter, William Tatem Tilden, Sol Plaatje, Rafael Sabatini, William Makepeace Thackeray, George Gissing, Maksim Gorky, Baron Thomas Babington Macaulay Macaulay, H. G. Keene, Saki, R. B. Cunninghame Graham, Thomas Hughes, David Nunes Carvalho, Vicente Blasco Ibáñez, Carry Amelia Nation, John Fiske, Bernard Shaw, Elbridge Streeter Brooks, William Holmes McGuffey, Edward Everett Hale, Louis Ginzberg, Chester K. Steele, Christopher Marlowe, Plato, John Lord, Shakespeare, Martin Luther, Frances Hodgson Burnett, Howard Pyle, Charles Morris, Edward Carpenter, Maurice Leblanc, James Boswell, William Osler, William Ernest Henley, Theron Q. Dumont, Horatio Alger, Abraham Myerson, Joel Benton, Eden Phillpotts, Anonymous, Robert Louis Stevenson, Lloyd Osbourne, Cleland Boyd McAfee, Robert Williams Wood, H. C. Andersen, Edna Ferber, James Stephens, John Jacob Astor, Alexandre Dumas fils, Hilda Conkling, J. Storer Clouston, Julian Hawthorne, Ernest Albert Savage, Mary Eleanor Wilkins Freeman, Fernando de Rojas, Richard Harding Davis, Charles Whibley, Thomas Dixon, Sir Arthur Conan Doyle, George MacDonald, Thomas H. Burgoyne, Belle M. Wagner, Émile Gaboriau, à Kempis Thomas, United States. Central Intelligence Agency, Herbert Darling Foster, John Chipman Farrar, Lucius Apuleius, Olive Gilbert, Sojourner Truth, Arthur Judson Brown, Burbank L. Todd, Gaston Leroux, Margaret Sanger, Jr. Martin Luther King, Mary Johnston, S. A. Reilly, G. K. Chesterton, Elizabeth Cleghorn Gaskell, George Iles, E. W. Hornung, Edward Huntington Williams, Henry Smith Williams

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A HISTORY OF SCIENCE

BY HENRY SMITH WILLIAMS, M.D., LL.D.

ASSISTED BY EDWARD H. WILLIAMS, M.D.

IN FIVE VOLUMES

VOLUME III.

Contents

DETAILED CONTENTSBOOK III. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES

I. THE SUCCESSORS OF NEWTON IN ASTRONOMY

II. THE PROGRESS OF MODERN ASTRONOMY

III. THE NEW SCIENCE OF PALEONTOLOGY

IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY

V. THE NEW SCIENCE OF METEOROLOGY

VI. MODERN THEORIES OF HEAT AND LIGHT

VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM

VIII. THE CONSERVATION OF ENERGY

IX. THE ETHER AND PONDERABLE MATTER

APPENDIX

CONTENTS

BOOK III CHAPTER I. THE SUCCESSORS OF NEWTON IN ASTRONOMY The work of Johannes Hevelius—Halley and Hevelius—Halley's observation of the transit of Mercury, and his method of determining the parallax of the planets—Halley's observation of meteors—His inability to explain these bodies—The important work of James Bradley—Lacaille's measurement of the arc of the meridian—The determination of the question as to the exact shape of the earth—D'Alembert and his influence upon science—Delambre's History of Astronomy—The astronomical work of Euler. CHAPTER II. THE PROGRESS OF MODERN ASTRONOMY The work of William Herschel—His discovery of Uranus—His discovery that the stars are suns—His conception of the universe—His deduction that gravitation has caused the grouping of the heavenly bodies—The nebula, hypothesis,—Immanuel Kant's conception of the formation of the world—Defects in Kant's conception—Laplace's final solution of the problem—His explanation in detail—Change in the mental attitude of the world since Bruno—Asteroids and satellites—Discoveries of Olbersl—The mathematical calculations of Adams and Leverrier—The discovery of the inner ring of Saturn—Clerk Maxwell's paper on the stability of Saturn's rings—Helmholtz's conception of the action of tidal friction—Professor G. H. Darwin's estimate of the consequences of tidal action—Comets and meteors—Bredichin's cometary theory—The final solution of the structure of comets—Newcomb's estimate of the amount of cometary dust swept up daily by the earth—The fixed stars—John Herschel's studies of double stars—Fraunhofer's perfection of the refracting telescope—Bessel's measurement of the parallax of a star,—Henderson's measurements—Kirchhoff and Bunsen's perfection of the spectroscope—Wonderful revelations of the spectroscope—Lord Kelvin's estimate of the time that will be required for the earth to become completely cooled—Alvan Clark's discovery of the companion star of Sirius—The advent of the photographic film in astronomy—Dr. Huggins's studies of nebulae—Sir Norman Lockyer's "cosmogonic guess,"—Croll's pre-nebular theory. CHAPTER III. THE NEW SCIENCE OF PALEONTOLOGY William Smith and fossil shells—His discovery that fossil rocks are arranged in regular systems—Smith's inquiries taken up by Cuvier—His Ossements Fossiles containing the first description of hairy elephant—His contention that fossils represent extinct species only—Dr. Buckland's studies of English fossil-beds—Charles Lyell combats catastrophism,—Elaboration of his ideas with reference to the rotation of species—The establishment of the doctrine of uniformitarianism,—Darwin's Origin of Species—Fossil man—Dr. Falconer's visit to the fossil-beds in the valley of the Somme—Investigations of Prestwich and Sir John Evans—Discovery of the Neanderthal skull,—Cuvier's rejection of human fossils—The finding of prehistoric carving on ivory—The fossil-beds of America—Professor Marsh's paper on the fossil horses in America—The Warren mastodon,—The Java fossil, Pithecanthropus Erectus. CHAPTER IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY James Hutton and the study of the rocks—His theory of the earth—His belief in volcanic cataclysms in raising and forming the continents—His famous paper before the Royal Society of Edinburgh, 1781—-His conclusions that all strata of the earth have their origin at the bottom of the sea—-His deduction that heated and expanded matter caused the elevation of land above the sea-level—Indifference at first shown this remarkable paper—Neptunists versus Plutonists—Scrope's classical work on volcanoes—Final acceptance of Hutton's explanation of the origin of granites—Lyell and uniformitarianism—Observations on the gradual elevation of the coast-lines of Sweden and Patagonia—Observations on the enormous amount of land erosion constantly taking place,—Agassiz and the glacial theory—Perraudin the chamois-hunter, and his explanation of perched bowlders—De Charpentier's acceptance of Perraudin's explanation—Agassiz's paper on his Alpine studies—His conclusion that the Alps were once covered with an ice-sheet—Final acceptance of the glacial theory—The geological ages—The work of Murchison and Sedgwick—Formation of the American continents—Past, present, and future. CHAPTER V. THE NEW SCIENCE OF METEOROLOGY Biot's investigations of meteors—The observations of Brandes and Benzenberg on the velocity of falling stars—Professor Olmstead's observations on the meteoric shower of 1833—Confirmation of Chladni's hypothesis of 1794—The aurora borealis—Franklin's suggestion that it is of electrical origin—Its close association with terrestrial magnetism—Evaporation, cloud-formation, and dew—Dalton's demonstration that water exists in the air as an independent gas—Hutton's theory of rain—Luke Howard's paper on clouds—Observations on dew, by Professor Wilson and Mr. Six—Dr. Wells's essay on dew—His observations on several appearances connected with dew—Isotherms and ocean currents—Humboldt and the-science of comparative climatology—His studies of ocean currents—Maury's theory that gravity is the cause of ocean currents—Dr. Croll on Climate and Time—Cyclones and anti-cyclones,—Dove's studies in climatology—Professor Ferrel's mathematical law of the deflection of winds—Tyndall's estimate of the amount of heat given off by the liberation of a pound of vapor—Meteorological observations and weather predictions. CHAPTER VI. MODERN THEORIES OF HEAT AND LIGHT Josiah Wedgwood and the clay pyrometer—Count Rumford and the vibratory theory of heat—His experiments with boring cannon to determine the nature of heat—Causing water to boil by the friction of the borer—His final determination that heat is a form of motion—Thomas Young and the wave theory of light—His paper on the theory of light and colors—His exposition of the colors of thin plates—Of the colors of thick plates, and of striated surfaces,—Arago and Fresnel champion the wave theory—opposition to the theory by Biot—The French Academy's tacit acceptance of the correctness of the theory by its admission of Fresnel as a member. CHAPTER VII. THE MODERN DEVELOPMENT OF ELECTRICITY AND MAGNETISM Galvani and the beginning of modern electricity—The construction of the voltaic pile—Nicholson's and Carlisle's discovery that the galvanic current decomposes water—Decomposition of various substances by Sir Humphry Davy—His construction of an arc-light—The deflection of the magnetic needle by electricity demonstrated by Oersted—Effect of this important discovery—Ampere creates the science of electro-dynamics—Joseph Henry's studies of electromagnets—Michael Faraday begins his studies of electromagnetic induction—His famous paper before the Royal Society, in 1831, in which he demonstrates electro-magnetic induction—His explanation of Arago's rotating disk—The search for a satisfactory method of storing electricity—Roentgen rays, or X-rays. CHAPTER VIII. THE CONSERVATION OF ENERGY Faraday narrowly misses the discovery of the doctrine of conservation—Carnot's belief that a definite quantity of work can be transformed into a definite quantity of heat—The work of James Prescott Joule—Investigations begun by Dr. Mayer—Mayer's paper of 1842—His statement of the law of the conservation of energy—Mayer and Helmholtz—Joule's paper of 1843—Joule or Mayer—Lord Kelvin and the dissipation of energy-The final unification. CHAPTER IX. THE ETHER AND PONDERABLE MATTER James Clerk-Maxwell's conception of ether—Thomas Young and "Luminiferous ether,"—Young's and Fresnel's conception of transverse luminiferous undulations—Faraday's experiments pointing to the existence of ether—Professor Lodge's suggestion of two ethers—Lord Kelvin's calculation of the probable density of ether—The vortex theory of atoms—Helmholtz's calculations in vortex motions—Professor Tait's apparatus for creating vortex rings in the air—-The ultimate constitution of matter as conceived by Boscovich—Davy's speculations as to the changes that occur in the substance of matter at different temperatures—Clausius's and Maxwell's investigations of the kinetic theory of gases—Lord Kelvin's estimate of the size of the molecule—Studies of the potential energy of molecules—Action of gases at low temperatures. APPENDIX

A HISTORY OF SCIENCE

BOOK III. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES

With the present book we enter the field of the distinctively modern. There is no precise date at which we take up each of the successive stories, but the main sweep of development has to do in each case with the nineteenth century. We shall see at once that this is a time both of rapid progress and of great differentiation. We have heard almost nothing hitherto of such sciences as paleontology, geology, and meteorology, each of which now demands full attention. Meantime, astronomy and what the workers of the elder day called natural philosophy become wonderfully diversified and present numerous phases that would have been startling enough to the star-gazers and philosophers of the earlier epoch.

Thus, for example, in the field of astronomy, Herschel is able, thanks to his perfected telescope, to discover a new planet and then to reach out into the depths of space and gain such knowledge of stars and nebulae as hitherto no one had more than dreamed of. Then, in rapid sequence, a whole coterie of hitherto unsuspected minor planets is discovered, stellar distances are measured, some members of the starry galaxy are timed in their flight, the direction of movement of the solar system itself is investigated, the spectroscope reveals the chemical composition even of suns that are unthinkably distant, and a tangible theory is grasped of the universal cycle which includes the birth and death of worlds.

Similarly the new studies of the earth's surface reveal secrets of planetary formation hitherto quite inscrutable. It becomes known that the strata of the earth's surface have been forming throughout untold ages, and that successive populations differing utterly from one another have peopled the earth in different geological epochs. The entire point of view of thoughtful men becomes changed in contemplating the history of the world in which we live—albeit the newest thought harks back to some extent to those days when the inspired thinkers of early Greece dreamed out the wonderful theories with which our earlier chapters have made our readers familiar.

In the region of natural philosophy progress is no less pronounced and no less striking. It suffices here, however, by way of anticipation, simply to name the greatest generalization of the century in physical science—the doctrine of the conservation of energy.

I. THE SUCCESSORS OF NEWTON IN ASTRONOMY

HEVELIUS AND HALLEY

STRANGELY enough, the decade immediately following Newton was one of comparative barrenness in scientific progress, the early years of the eighteenth century not being as productive of great astronomers as the later years of the seventeenth, or, for that matter, as the later years of the eighteenth century itself. Several of the prominent astronomers of the later seventeenth century lived on into the opening years of the following century, however, and the younger generation soon developed a coterie of astronomers, among whom Euler, Lagrange, Laplace, and Herschel, as we shall see, were to accomplish great things in this field before the century closed.

One of the great seventeenth-century astronomers, who died just before the close of the century, was Johannes Hevelius (1611-1687), of Dantzig, who advanced astronomy by his accurate description of the face and the spots of the moon. But he is remembered also for having retarded progress by his influence in refusing to use telescopic sights in his observations, preferring until his death the plain sights long before discarded by most other astronomers. The advantages of these telescope sights have been discussed under the article treating of Robert Hooke, but no such advantages were ever recognized by Hevelius. So great was Hevelius's reputation as an astronomer that his refusal to recognize the advantage of the telescope sights caused many astronomers to hesitate before accepting them as superior to the plain; and even the famous Halley, of whom we shall speak further in a moment, was sufficiently in doubt over the matter to pay the aged astronomer a visit to test his skill in using the old-style sights. Side by side, Hevelius and Halley made their observations, Hevelius with his old instrument and Halley with the new. The results showed slightly in the younger man's favor, but not enough to make it an entirely convincing demonstration. The explanation of this, however, did not lie in the lack of superiority of the telescopic instrument, but rather in the marvellous skill of the aged Hevelius, whose dexterity almost compensated for the defect of his instrument. What he might have accomplished could he have been induced to adopt the telescope can only be surmised.

Halley himself was by no means a tyro in matters astronomical at that time. As the only son of a wealthy soap-boiler living near London, he had been given a liberal education, and even before leaving college made such novel scientific observations as that of the change in the variation of the compass. At nineteen years of age he discovered a new method of determining the elements of the planetary orbits which was a distinct improvement over the old. The year following he sailed for the Island of St, Helena to make observations of the heavens in the southern hemisphere.

It was while in St. Helena that Halley made his famous observation of the transit of Mercury over the sun's disk, this observation being connected, indirectly at least, with his discovery of a method of determining the parallax of the planets. By parallax is meant the apparent change in the position of an object, due really to a change in the position of the observer. Thus, if we imagine two astronomers making observations of the sun from opposite sides of the earth at the same time, it is obvious that to these observers the sun will appear to be at two different points in the sky. Half the angle measuring this difference would be known as the sun's parallax. This would depend, then, upon the distance of the earth from the sun and the length of the earth's radius. Since the actual length of this radius has been determined, the parallax of any heavenly body enables the astronomer to determine its exact distance.

The parallaxes can be determined equally well, however, if two observers are separated by exactly known distances, several hundreds or thousands of miles apart. In the case of a transit of Venus across the sun's disk, for example, an observer at New York notes the image of the planet moving across the sun's disk, and notes also the exact time of this observation. In the same manner an observer at London makes similar observations. Knowing the distance between New York and London, and the different time of the passage, it is thus possible to calculate the difference of the parallaxes of the sun and a planet crossing its disk. The idea of thus determining the parallax of the planets originated, or at least was developed, by Halley, and from this phenomenon he thought it possible to conclude the dimensions of all the planetary orbits. As we shall see further on, his views were found to be correct by later astronomers.

In 1721 Halley succeeded Flamsteed as astronomer royal at the Greenwich Observatory. Although sixty-four years of age at that time his activity in astronomy continued unabated for another score of years. At Greenwich he undertook some tedious observations of the moon, and during those observations was first to detect the acceleration of mean motion. He was unable to explain this, however, and it remained for Laplace in the closing years of the century to do so, as we shall see later.

Halley's book, the Synopsis Astronomiae Cometicae, is one of the most valuable additions to astronomical literature since the time of Kepler. He was first to attempt the calculation of the orbit of a comet, having revived the ancient opinion that comets belong to the solar system, moving in eccentric orbits round the sun, and his calculation of the orbit of the comet of 1682 led him to predict correctly the return of that comet in 1758. Halley's Study of Meteors.

Like other astronomers of his time he was greatly puzzled over the well-known phenomena of shooting-stars, or meteors, making many observations himself, and examining carefully the observations of other astronomers. In 1714 he gave his views as to the origin and composition of these mysterious visitors in the earth's atmosphere. As this subject will be again referred to in a later chapter, Halley's views, representing the most advanced views of his age, are of interest.

"The theory of the air seemeth at present," he says, "to be perfectly well understood, and the differing densities thereof at all altitudes; for supposing the same air to occupy spaces reciprocally proportional to the quantity of the superior or incumbent air, I have elsewhere proved that at forty miles high the air is rarer than at the surface of the earth at three thousand times; and that the utmost height of the atmosphere, which reflects light in the Crepusculum, is not fully forty-five miles, notwithstanding which 'tis still manifest that some sort of vapors, and those in no small quantity, arise nearly to that height. An instance of this may be given in the great light the society had an account of (vide Transact. Sep., 1676) from Dr. Wallis, which was seen in very distant counties almost over all the south part of England. Of which though the doctor could not get so particular a relation as was requisite to determine the height thereof, yet from the distant places it was seen in, it could not but be very many miles high.

"So likewise that meteor which was seen in 1708, on the 31st of July, between nine and ten o'clock at night, was evidently between forty and fifty miles perpendicularly high, and as near as I can gather, over Shereness and the buoy on the Nore. For it was seen at London moving horizontally from east by north to east by south at least fifty degrees high, and at Redgrove, in Suffolk, on the Yarmouth road, about twenty miles from the east coast of England, and at least forty miles to the eastward of London, it appeared a little to the westward of the south, suppose south by west, and was seen about thirty degrees high, sliding obliquely downward. I was shown in both places the situation thereof, which was as described, but could wish some person skilled in astronomical matters bad seen it, that we might pronounce concerning its height with more certainty. Yet, as it is, we may securely conclude that it was not many more miles westerly than Redgrove, which, as I said before, is about forty miles more easterly than London. Suppose it, therefore, where perpendicular, to have been thirty-five miles east from London, and by the altitude it appeared at in London—viz., fifty degrees, its tangent will be forty-two miles, for the height of the meteor above the surface of the earth; which also is rather of the least, because the altitude of the place shown me is rather more than less than fifty degrees; and the like may be concluded from the altitude it appeared in at Redgrove, near seventy miles distant. Though at this very great distance, it appeared to move with an incredible velocity, darting, in a very few seconds of time, for about twelve degrees of a great circle from north to south, being very bright at its first appearance; and it died away at the east of its course, leaving for some time a pale whiteness in the place, with some remains of it in the track where it had gone; but no hissing sound as it passed, or bounce of an explosion were heard.

"It may deserve the honorable society's thoughts, how so great a quantity of vapor should be raised to the top of the atmosphere, and there collected, so as upon its ascension or otherwise illumination, to give a light to a circle of above one hundred miles diameter, not much inferior to the light of the moon; so as one might see to take a pin from the ground in the otherwise dark night. 'Tis hard to conceive what sort of exhalations should rise from the earth, either by the action of the sun or subterranean heat, so as to surmount the extreme cold and rareness of the air in those upper regions: but the fact is indisputable, and therefore requires a solution."

From this much of the paper it appears that there was a general belief that this burning mass was heated vapor thrown off from the earth in some mysterious manner, yet this is unsatisfactory to Halley, for after citing various other meteors that have appeared within his knowledge, he goes on to say:

"What sort of substance it must be, that could be so impelled and ignited at the same time; there being no Vulcano or other Spiraculum of subterraneous fire in the northeast parts of the world, that we ever yet heard of, from whence it might be projected.

"I have much considered this appearance, and think it one of the hardest things to account for that I have yet met with in the phenomena of meteors, and I am induced to think that it must be some collection of matter formed in the aether, as it were, by some fortuitous concourse of atoms, and that the earth met with it as it passed along in its orb, then but newly formed, and before it had conceived any great impetus of descent towards the sun. For the direction of it was exactly opposite to that of the earth, which made an angle with the meridian at that time of sixty-seven gr., that is, its course was from west southwest to east northeast, wherefore the meteor seemed to move the contrary way. And besides falling into the power of the earth's gravity, and losing its motion from the opposition of the medium, it seems that it descended towards the earth, and was extinguished in the Tyrrhene Sea, to the west southwest of Leghorn. The great blow being heard upon its first immersion into the water, and the rattling like the driving of a cart over stones being what succeeded upon its quenching; something like this is always heard upon quenching a very hot iron in water. These facts being past dispute, I would be glad to have the opinion of the learned thereon, and what objection can be reasonably made against the above hypothesis, which I humbly submit to their censure."(1)

These few paragraphs, coming as they do from a leading eighteenth-century astronomer, convey more clearly than any comment the actual state of the meteorological learning at that time. That this ball of fire, rushing "at a greater velocity than the swiftest cannon-ball," was simply a mass of heated rock passing through our atmosphere, did not occur to him, or at least was not credited. Nor is this surprising when we reflect that at that time universal gravitation had been but recently discovered; heat had not as yet been recognized as simply a form of motion; and thunder and lightning were unexplained mysteries, not to be explained for another three-quarters of a century. In the chapter on meteorology we shall see how the solution of this mystery that puzzled Halley and his associates all their lives was finally attained.

BRADLEY AND THE ABERRATION OF LIGHT

Halley was succeeded as astronomer royal by a man whose useful additions to the science were not to be recognized or appreciated fully until brought to light by the Prussian astronomer Bessel early in the nineteenth century. This was Dr. James Bradley, an ecclesiastic, who ranks as one of the most eminent astronomers of the eighteenth century. His most remarkable discovery was the explanation of a peculiar motion of the pole-star, first observed, but not explained, by Picard a century before. For many years a satisfactory explanation was sought unsuccessfully by Bradley and his fellow-astronomers, but at last he was able to demonstrate that the stary Draconis, on which he was making his observations, described, or appeared to describe, a small ellipse. If this observation was correct, it afforded a means of computing the aberration of any star at all times. The explanation of the physical cause of this aberration, as Bradley thought, and afterwards demonstrated, was the result of the combination of the motion of light with the annual motion of the earth. Bradley first formulated this theory in 1728, but it was not until 1748—twenty years of continuous struggle and observation by him—that he was prepared to communicate the results of his efforts to the Royal Society. This remarkable paper is thought by the Frenchman, Delambre, to entitle its author to a place in science beside such astronomers as Hipparcbus and Kepler.

Bradley's studies led him to discover also the libratory motion of the earth's axis. "As this appearance of Draconis indicated a diminution of the inclination of the earth's axis to the plane of the ecliptic," he says; "and as several astronomers have supposed THAT inclination to diminish regularly; if this phenomenon depended upon such a cause, and amounted to 18" in nine years, the obliquity of the ecliptic would, at that rate, alter a whole minute in thirty years; which is much faster than any observations, before made, would allow. I had reason, therefore, to think that some part of this motion at the least, if not the whole, was owing to the moon's action upon the equatorial parts of the earth; which, I conceived, might cause a libratory motion of the earth's axis. But as I was unable to judge, from only nine years observations, whether the axis would entirely recover the same position that it had in the year 1727, I found it necessary to continue my observations through a whole period of the moon's nodes; at the end of which I had the satisfaction to see, that the stars, returned into the same position again; as if there had been no alteration at all in the inclination of the earth's axis; which fully convinced me that I had guessed rightly as to the cause of the phenomena. This circumstance proves likewise, that if there be a gradual diminution of the obliquity of the ecliptic, it does not arise only from an alteration in the position of the earth's axis, but rather from some change in the plane of the ecliptic itself; because the stars, at the end of the period of the moon's nodes, appeared in the same places, with respect to the equator, as they ought to have done, if the earth's axis had retained the same inclination to an invariable plane."(2)

FRENCH ASTRONOMERS

Meanwhile, astronomers across the channel were by no means idle. In France several successful observers were making many additions to the already long list of observations of the first astronomer of the Royal Observatory of Paris, Dominic Cassini (1625-1712), whose reputation among his contemporaries was much greater than among succeeding generations of astronomers. Perhaps the most deserving of these successors was Nicolas Louis de Lacaille (1713-1762), a theologian who had been educated at the expense of the Duke of Bourbon, and who, soon after completing his clerical studies, came under the patronage of Cassini, whose attention had been called to the young man's interest in the sciences. One of Lacaille's first under-takings was the remeasuring of the French are of the meridian, which had been incorrectly measured by his patron in 1684. This was begun in 1739, and occupied him for two years before successfully completed. As a reward, however, he was admitted to the academy and appointed mathematical professor in Mazarin College.

In 1751 he went to the Cape of Good Hope for the purpose of determining the sun's parallax by observations of the parallaxes of Mars and Venus, and incidentally to make observations on the other southern hemisphere stars. The results of this undertaking were most successful, and were given in his Coelum australe stelligerum, etc., published in 1763. In this he shows that in the course of a single year he had observed some ten thousand stars, and computed the places of one thousand nine hundred and forty-two of them, measured a degree of the meridian, and made many observations of the moon—productive industry seldom equalled in a single year in any field. These observations were of great service to the astronomers, as they afforded the opportunity of comparing the stars of the southern hemisphere with those of the northern, which were being observed simultaneously by Lelande at Berlin.

Lacaille's observations followed closely upon the determination of an absorbing question which occupied the attention of the astronomers in the early part of the century. This question was as to the shape of the earth—whether it was actually flattened at the poles. To settle this question once for all the Academy of Sciences decided to make the actual measurement of the length of two degrees, one as near the pole as possible, the other at the equator. Accordingly, three astronomers, Godin, Bouguer, and La Condamine, made the journey to a spot on the equator in Peru, while four astronomers, Camus, Clairaut, Maupertuis, and Lemonnier, made a voyage to a place selected in Lapland. The result of these expeditions was the determination that the globe is oblately spheroidal.

A great contemporary and fellow-countryman of Lacaille was Jean Le Rond d'Alembert (1717-1783), who, although not primarily an astronomer, did so much with his mathematical calculations to aid that science that his name is closely connected with its progress during the eighteenth century. D'Alembert, who became one of the best-known men of science of his day, and whose services were eagerly sought by the rulers of Europe, began life as a foundling, having been exposed in one of the markets of Paris. The sickly infant was adopted and cared for in the family of a poor glazier, and treated as a member of the family. In later years, however, after the foundling had become famous throughout Europe, his mother, Madame Tencin, sent for him, and acknowledged her relationship. It is more than likely that the great philosopher believed her story, but if so he did not allow her the satisfaction of knowing his belief, declaring always that Madame Tencin could "not be nearer than a step-mother to him, since his mother was the wife of the glazier."

D'Alembert did much for the cause of science by his example as well as by his discoveries. By living a plain but honest life, declining magnificent offers of positions from royal patrons, at the same time refusing to grovel before nobility, he set a worthy example to other philosophers whose cringing and pusillanimous attitude towards persons of wealth or position had hitherto earned them the contempt of the upper classes.

His direct additions to astronomy are several, among others the determination of the mutation of the axis of the earth. He also determined the ratio of the attractive forces of the sun and moon, which he found to be about as seven to three. From this he reached the conclusion that the earth must be seventy times greater than the moon. The first two volumes of his Researches on the Systems of the World, published in 1754, are largely devoted to mathematical and astronomical problems, many of them of little importance now, but of great interest to astronomers at that time.

Another great contemporary of D'Alembert, whose name is closely associated and frequently confounded with his, was Jean Baptiste Joseph Delambre (1749-1822). More fortunate in birth as also in his educational advantages, Delambre as a youth began his studies under the celebrated poet Delille. Later he was obliged to struggle against poverty, supporting himself for a time by making translations from Latin, Greek, Italian, and English, and acting as tutor in private families. The turning-point of his fortune came when the attention of Lalande was called to the young man by his remarkable memory, and Lalande soon showed his admiration by giving Delambre certain difficult astronomical problems to solve. By performing these tasks successfully his future as an astronomer became assured. At that time the planet Uranus had just been discovered by Herschel, and the Academy of Sciences offered as the subject for one of its prizes the determination of the planet's orbit. Delambre made this determination and won the prize—a feat that brought him at once into prominence.

By his writings he probably did as much towards perfecting modern astronomy as any one man. His History of Astronomy is not merely a narrative of progress of astronomy but a complete abstract of all the celebrated works written on the subject. Thus he became famous as an historian as well as an astronomer.

LEONARD EULER

Still another contemporary of D'Alembert and Delambre, and somewhat older than either of them, was Leonard Euler (1707-1783), of Basel, whose fame as a philosopher equals that of either of the great Frenchmen. He is of particular interest here in his capacity of astronomer, but astronomy was only one of the many fields of science in which he shone. Surely something out of the ordinary was to be expected of the man who could "repeat the AEneid of Virgil from the beginning to the end without hesitation, and indicate the first and last line of every page of the edition which he used." Something was expected, and he fulfilled these expectations.

In early life he devoted himself to the study of theology and the Oriental languages, at the request of his father, but his love of mathematics proved too strong, and, with his father's consent, he finally gave up his classical studies and turned to his favorite study, geometry. In 1727 he was invited by Catharine I. to reside in St. Petersburg, and on accepting this invitation he was made an associate of the Academy of Sciences. A little later he was made professor of physics, and in 1733 professor of mathematics. In 1735 he solved a problem in three days which some of the eminent mathematicians would not undertake under several months. In 1741 Frederick the Great invited him to Berlin, where he soon became a member of the Academy of Sciences and professor of mathematics; but in 1766 he returned to St. Petersburg. Towards the close of his life he became virtually blind, being obliged to dictate his thoughts, sometimes to persons entirely ignorant of the subject in hand. Nevertheless, his remarkable memory, still further heightened by his blindness, enabled him to carry out the elaborate computations frequently involved.

Euler's first memoir, transmitted to the Academy of Sciences of Paris in 1747, was on the planetary perturbations. This memoir carried off the prize that had been offered for the analytical theory of the motions of Jupiter and Saturn. Other memoirs followed, one in 1749 and another in 1750, with further expansions of the same subject. As some slight errors were found in these, such as a mistake in some of the formulae expressing the secular and periodic inequalities, the academy proposed the same subject for the prize of 1752. Euler again competed, and won this prize also. The contents of this memoir laid the foundation for the subsequent demonstration of the permanent stability of the planetary system by Laplace and Lagrange.

It was Euler also who demonstrated that within certain fixed limits the eccentricities and places of the aphelia of Saturn and Jupiter are subject to constant variation, and he calculated that after a lapse of about thirty thousand years the elements of the orbits of these two planets recover their original values.

II. THE PROGRESS OF MODERN ASTRONOMY

A NEW epoch in astronomy begins with the work of William Herschel, the Hanoverian, whom England made hers by adoption. He was a man with a positive genius for sidereal discovery. At first a mere amateur in astronomy, he snatched time from his duties as music-teacher to grind him a telescopic mirror, and began gazing at the stars. Not content with his first telescope, he made another and another, and he had such genius for the work that he soon possessed a better instrument than was ever made before. His patience in grinding the curved reflective surface was monumental. Sometimes for sixteen hours together he must walk steadily about the mirror, polishing it, without once removing his hands. Meantime his sister, always his chief lieutenant, cheered him with her presence, and from time to time put food into his mouth. The telescope completed, the astronomer turned night into day, and from sunset to sunrise, year in and year out, swept the heavens unceasingly, unless prevented by clouds or the brightness of the moon. His sister sat always at his side, recording his observations. They were in the open air, perched high at the mouth of the reflector, and sometimes it was so cold that the ink froze in the bottle in Caroline Herschel's hand; but the two enthusiasts hardly noticed a thing so common-place as terrestrial weather. They were living in distant worlds.

The results? What could they be? Such enthusiasm would move mountains. But, after all, the moving of mountains seems a liliputian task compared with what Herschel really did with those wonderful telescopes. He moved worlds, stars, a universe—even, if you please, a galaxy of universes; at least he proved that they move, which seems scarcely less wonderful; and he expanded the cosmos, as man conceives it, to thousands of times the dimensions it had before. As a mere beginning, he doubled the diameter of the solar system by observing the great outlying planet which we now call Uranus, but which he christened Georgium Sidus, in honor of his sovereign, and which his French contemporaries, not relishing that name, preferred to call Herschel.

This discovery was but a trifle compared with what Herschel did later on, but it gave him world-wide reputation none the less. Comets and moons aside, this was the first addition to the solar system that had been made within historic times, and it created a veritable furor of popular interest and enthusiasm. Incidentally King George was flattered at having a world named after him, and he smiled on the astronomer, and came with his court to have a look at his namesake. The inspection was highly satisfactory; and presently the royal favor enabled the astronomer to escape the thraldom of teaching music and to devote his entire time to the more congenial task of star-gazing.

Thus relieved from the burden of mundane embarrassments, he turned with fresh enthusiasm to the skies, and his discoveries followed one another in bewildering profusion. He found various hitherto unseen moons of our sister planets; he made special studies of Saturn, and proved that this planet, with its rings, revolves on its axis; he scanned the spots on the sun, and suggested that they influence the weather of our earth; in short, he extended the entire field of solar astronomy. But very soon this field became too small for him, and his most important researches carried him out into the regions of space compared with which the span of our solar system is a mere point. With his perfected telescopes he entered abysmal vistas which no human eve ever penetrated before, which no human mind had hitherto more than vaguely imagined. He tells us that his forty-foot reflector will bring him light from a distance of "at least eleven and three-fourths millions of millions of millions of miles"—light which left its source two million years ago. The smallest stars visible to the unaided eye are those of the sixth magnitude; this telescope, he thinks, has power to reveal stars of the 1342d magnitude.

But what did Herschel learn regarding these awful depths of space and the stars that people them? That was what the world wished to know. Copernicus, Galileo, Kepler, had given us a solar system, but the stars had been a mystery. What says the great reflector—are the stars points of light, as the ancients taught, and as more than one philosopher of the eighteenth century has still contended, or are they suns, as others hold? Herschel answers, they are suns, each and every one of all the millions—suns, many of them, larger than the one that is the centre of our tiny system. Not only so, but they are moving suns. Instead of being fixed in space, as has been thought, they are whirling in gigantic orbits about some common centre. Is our sun that centre? Far from it. Our sun is only a star like all the rest, circling on with its attendant satellites—our giant sun a star, no different from myriad other stars, not even so large as some; a mere insignificant spark of matter in an infinite shower of sparks.

Nor is this all. Looking beyond the few thousand stars that are visible to the naked eye, Herschel sees series after series of more distant stars, marshalled in galaxies of millions; but at last he reaches a distance beyond which the galaxies no longer increase. And yet—so he thinks—he has not reached the limits of his vision. What then? He has come to the bounds of the sidereal system—seen to the confines of the universe. He believes that he can outline this system, this universe, and prove that it has the shape of an irregular globe, oblately flattened to almost disklike proportions, and divided at one edge—a bifurcation that is revealed even to the naked eye in the forking of the Milky Way.

This, then, is our universe as Herschel conceives it—a vast galaxy of suns, held to one centre, revolving, poised in space. But even here those marvellous telescopes do not pause. Far, far out beyond the confines of our universe, so far that the awful span of our own system might serve as a unit of measure, are revealed other systems, other universes, like our own, each composed, as he thinks, of myriads of suns, clustered like our galaxy into an isolated system—mere islands of matter in an infinite ocean of space. So distant from our universe are these now universes of Herschel's discovery that their light reaches us only as a dim, nebulous glow, in most cases invisible to the unaided eye. About a hundred of these nebulae were known when Herschel began his studies. Before the close of the century he had discovered about two thousand more of them, and many of these had been resolved by his largest telescopes into clusters of stars. He believed that the farthest of these nebulae that he could see was at least three hundred thousand times as distant from us as the nearest fixed star. Yet that nearest star—so more recent studies prove—is so remote that its light, travelling one hundred and eighty thousand miles a second, requires three and one-half years to reach our planet.

As if to give the finishing touches to this novel scheme of cosmology, Herschel, though in the main very little given to unsustained theorizing, allows himself the privilege of one belief that he cannot call upon his telescope to substantiate. He thinks that all the myriad suns of his numberless systems are instinct with life in the human sense. Giordano Bruno and a long line of his followers had held that some of our sister planets may be inhabited, but Herschel extends the thought to include the moon, the sun, the stars—all the heavenly bodies. He believes that he can demonstrate the habitability of our own sun, and, reasoning from analogy, he is firmly convinced that all the suns of all the systems are "well supplied with inhabitants." In this, as in some other inferences, Herschel is misled by the faulty physics of his time. Future generations, working with perfected instruments, may not sustain him all along the line of his observations, even, let alone his inferences. But how one's egotism shrivels and shrinks as one grasps the import of his sweeping thoughts!

Continuing his observations of the innumerable nebulae, Herschel is led presently to another curious speculative inference. He notes that some star groups are much more thickly clustered than others, and he is led to infer that such varied clustering tells of varying ages of the different nebulae. He thinks that at first all space may have been evenly sprinkled with the stars and that the grouping has resulted from the action of gravitation.

"That the Milky Way is a most extensive stratum of stars of various sizes admits no longer of lasting doubt," he declares, "and that our sun is actually one of the heavenly bodies belonging to it is as evident. I have now viewed and gauged this shining zone in almost every direction and find it composed of stars whose number... constantly increases and decreases in proportion to its apparent brightness to the naked eye.

"Let us suppose numberless stars of various sizes, scattered over an indefinite portion of space in such a manner as to be almost equally distributed throughout the whole. The laws of attraction which no doubt extend to the remotest regions of the fixed stars will operate in such a manner as most probably to produce the following effects:

"In the first case, since we have supposed the stars to be of various sizes, it will happen that a star, being considerably larger than its neighboring ones, will attract them more than they will be attracted by others that are immediately around them; by which means they will be, in time, as it were, condensed about a centre, or, in other words, form themselves into a cluster of stars of almost a globular figure, more or less regular according to the size and distance of the surrounding stars....

"The next case, which will also happen almost as frequently as the former, is where a few stars, though not superior in size to the rest, may chance to be rather nearer one another than the surrounding ones,... and this construction admits of the utmost variety of shapes....

"From the composition and repeated conjunction of both the foregoing formations, a third may be derived when many large stars, or combined small ones, are spread in long, extended, regular, or crooked rows, streaks, or branches; for they will also draw the surrounding stars, so as to produce figures of condensed stars curiously similar to the former which gave rise to these condensations.

"We may likewise admit still more extensive combinations; when, at the same time that a cluster of stars is forming at the one part of space, there may be another collection in a different but perhaps not far-distant quarter, which may occasion a mutual approach towards their own centre of gravity.

"In the last place, as a natural conclusion of the former cases, there will be formed great cavities or vacancies by the retreating of the stars towards the various centres which attract them."(1)

Looking forward, it appears that the time must come when all the suns of a system will be drawn together and destroyed by impact at a common centre. Already, it seems to Herschel, the thickest clusters have "outlived their usefulness" and are verging towards their doom.

But again, other nebulae present an appearance suggestive of an opposite condition. They are not resolvable into stars, but present an almost uniform appearance throughout, and are hence believed to be composed of a shining fluid, which in some instances is seen to be condensed at the centre into a glowing mass. In such a nebula Herschel thinks he sees a sun in process of formation.

THE NEBULAR HYPOTHESIS OF KANT