Popular Science Monthly/Volume 31/August 1887/The Progress of Science from 1836 to 1886

1014849Popular Science Monthly Volume 31 August 1887 — The Progress of Science from 1836 to 18861887Charles Grant Blairfindie Allen



FIFTY years ago, science was still inchoate. Much had already been done by the early pioneers. The ground had been cleared; the building-materials had been in part provided; the foundations had been duly and ably laid; but the superstructure as yet had hardly been raised a poor foot or two above the original level. The work of the last half-century has been twofold. On one side it has been accumulative merely: new stocks of organizable material—the raw bricks of science—have been laid up, as before, ready to the call of the master-mason, but in far greater profusion than by any previous age. On the other side it has been directive and architectonic; the endless stores of fact and inference, thus dug out and shaped to the hand by the brick-makers of knowledge in a thousand fields, have been assiduously built up by a compact body of higher and broader intelligences into a single grand harmonious whole. This last task forms, indeed, the great scientific triumph of our epoch. Ours has been an age of firm grasp and of wide vision. It has seen the down-fall of the anthropocentric fallacy. Cosmos has taken the place of chaos. Isolated facts have been fitted and dovetailed into their proper niche in the vast mosaic. The particular has slowly merged into the general, the general into still higher and deeper cosmical concepts. We live in an epoch of unification, simplification, correlation, and universality. When after-ages look back upon our own, they will recognize that in science its key-note has been the idea of unity.

Fifty years ago, there were many separate and distinct sciences but hardly any general conception of science at large as a single, rounded, and connected whole. Specialists rather insisted pertinaciously on the utter insularity of their own peculiar and chosen domain. Zoölogists protested, with tears in their eyes, that they had nothing to do with chemistry or with physics; geologists protested with a shrug of their shoulders, that they had nothing to do with astronomy or with cosmical genesis. It was a point of honor with each particular department, indeed, not to encroach on the territory of departments that lay nearest to it. Trespassers from the beaten path of the restricted science were prosecuted with the utmost rigor of the law. And within the realm of each separate study, in like manner, minor truths stood severely apart from one another; electricity refused to be at one with magnetism, and magnetism was hardly on speaking terms with the voltaic current. Organization and subordination of part to whole had scarcely yet begun to be even aimed at. The sciences were each a huge congeries of heterogeneous facts or unassorted laws; they waited the advent of their unknown Newtons to fall into systematic and organic order.

In the pride of our hearts, we forget for the most part how very young science still is. We—who have seen that infant Hercules strangling serpents almost from its very cradle; we, who have beheld it grow rapidly under our own eyes to virile maturity and adult robustness of thew and muscle—we forget how new a power it is in the world, and how feeble and timid was its tender babyhood in the first few decades of the present century. Among the concrete sciences, astronomy, the eldest-born, had advanced furthest when our age was still young. It had reached the stage of wide general laws and evolutionary aspirations. But geology had only just begun to emerge from the earliest plane of puerile hypothesis into the period of collection and colligation of facts. Biology, hardly yet known by any better or truer name than natural history, consisted mainly of a jumble of half-classified details. Psychology still wandered disconsolate in the misty domain of the abstract metaphysician. The sciences of man, of language, of societies, of religion, had not even begun to exist. The antiquity of our race, the natural genesis of arts and knowledge, the origin of articulate speech, or of religious ideas, were scarcely so much as debatable questions. Among sciences of the abstract-concrete class, physics, unilluminated by the clear light of the principles of correlation and conservation of energy, embraced a wide and ill-digested mass of separate and wholly unconnected departments. Light had little enough to do with heat, and nothing at all to do in any way with electricity, or sound, or motion, or magnetism. Chemistry still remained very much in the condition of Mrs. Jellaby's cupboard. Everywhere science was tentative and invertebrate, feeling its way on earth with hesitating steps, trying its wings in air with tremulous fear, in preparation for the broader excursions and wider flights of the last three adventurous decades.

The great campaign of the unity and uniformity of Nature was the first to be fought, and in that campaign the earliest decisive battle was waged over the bloody field of geology. In 1837—to accept a purely arbitrary date for the beginning of our epoch—Lyell had already published his sober and sensible "Principles," and the old doctrine of recurrent catastrophes and periodical cataclysms was tottering to its fall in both hemispheres. Wholesale destructions of faunas and floras, wholesale creations of new life-systems, were felt to be out of keeping with a humane age. Drastic cosmogonies were going out of fashion. But even the uniformitarianism for which Lyell bravely fought and conquered, was, in itself, but a scrappy and piecemeal conception side by side with the wider and far more general views which fifty years have slowly brought to us. One has only, to open the "Text-Book of Geology," by Lyell's far abler modern disciple, Archibald Geikie, in order to see the vast advance made in our ideas as to the world's history during the course of the last half-century. The science of the earth's crust no longer stands isolated as a study by itself: it falls into its proper place in the hierarchy of knowledge as the science of the secondary changes, induced under the influence of internal forces and incident energies, on the cooling and corrugated surface of a once incandescent and more extended planet. I know no better gauge of the widening which comes over the thoughts of men with the processes of the suns than to turn from the rudis indigestaque moles of the "Principles" and the "Elements" (great as they both were in their own day) to the luminous, lucid, and comprehensive arrangement of Geikie's splendid and systematic "Text-Book. The one is an agreeable and able dissertation on a number of isolated and floating geological facts; the other is a masterly and cosmically-minded account of the phenomena observable on the outer shell of a cooling world, duly considered in all their relations, and fully co-ordinated with all the chief results of all elder and younger sister sciences.

The battle of uniformitarianism itself, however, was but a passing episode in the great evolutionary movement. That movement began along several distinct lines toward the close of the previous century, and only at last consciously recognized its own informing unity of purpose some thirty-five years ago. From another point of view—in connection with its influence upon thought at large—the evolutionary crisis has been treated elsewhere in this review by a philosophic thinker: but in its purely scientific aspect it must also be briefly considered here, forming, as it does, the acknowledged mainspring of all living and active contemporary science.

Evolution is not synonymous with Darwinism. The whole immensely exceeds the part. Darwinism forms but a small chapter in the history of a far vaster and more comprehensive movement of the human mind. In its astronomical development evolution had already formulated itself with perfect distinctness before the period with which we have here especially to deal. The nebular theory of Kant and Laplace was the first attempt to withdraw the genesis of the cosmos from the vicious circle of metaphysical reasoning, and to account for it by the continuous action of physical and natural principles alone. Our own age has done much to cast doubt upon the unessential details of Kant's rough conception, but, in return, it has made clearer than ever the fundamental truth of its central idea—the idea that stars, and suns, and solar systems, consist of materials once more diffusely spread out through space and now aggregated around certain fixed and definite nuclei by the gravitative force inherent in their atoms and masses. As these masses or atoms drew closer together in union around the common center, their primitive potential energy of separation (frankly to employ the terminology of our own time) was changed, first into the kinetic energy of molar motion in the act of union, and then into the kinetic energy of molecular motion or heat, as they clashed with one another in bodily impact around the central core. Each star, thus produced, forever gathers in materials from its own outlying mass, or from meteoric bodies, upon its solidifying nucleus, and forever radiates off its store of associated energy to the hypothetical surrounding ether. The fullest expression of this profound cosmical conception has been given in our own time by Tait and Balfour Stewart, working in part upon the previous results of Kant. Laplace, the Herschels, Mayer, Joule, Clerk Maxwell, and Sir William Thomson. Deeply altered as the nebular hypothesis has been by the modern doctrine of correlation and conservation of energies, and by modern researches into the nature of comets, meteors, and the sun's envelopes, it still remains in its ultimate essence the original theory of Kant and Laplace.

Science has thus, within the period of our own half-century, exhibited to us the existing phase of the universe at large in the light of an episode in a single infinite and picturable drama, setting out long since from a definite beginning, and tending slowly to a definite end. Other phases, inconceivable to us, may or may not possibly have preceded it; yet others, equally inconceivable, may or may not possibly follow. But as realizable to ourselves, within our existing limitations, the physical universe now reveals itself as starting in a remote past from a diffuse and perhaps nebulous condition, in which all the matter, reduced to a state of extreme tenuity, occupied immeasurably wide areas of space, while all the energy existed only in the potential forms as separation of atoms or molecules; and the evidence leads us to look forward to a remote future when all the matter shall be aggregated into its narrowest possible limits, while all the energy, having assumed the kinetic mode, shall have been radiated off into the ethereal medium. Compared to the infinite cosmical vistas thus laid open before our dazzled eyes, all the other scientific expansions of our age shrink into relative narrowness and insignificance.

As in the cosmos so in the solar system itself, evolutionism has taught us to regard our sun, with its attendant planets and their ancillary satellites, all in their several orbits, as owing their shape, size, relations, and movements, not to external design and deliberate creation, but to the slow and regular working out of physical laws, in accordance with which each has assumed its existing weight, and bulk, and path, and position.

Geology here takes up the evolutionary parable, and, accepting on trust from astronomy the earth itself as a cooling spheroid of incandescent matter, it has traced out the various steps by which the crust assumed its present form, and the continents and oceans their present distribution. Lyell here set on foot the evolutionary impulse. The researches of Scrope, Judd, and others into volcanic and hypogene action, and the long observations of geologists everywhere on the effects of air, rain, ice, rivers, lakes, and oceans, have resulted in putting dynamical geology on a firm basis of ascertained fact. The heated interior has been shown almost with certainty to consist of a rigid and solid mass, incandescent, but reduced to solidity under the enormous pressure of superincumbent rocks and oceans. The age of the earth has been approximately measured, at least by plausible guess-work; and the history of its component parts has been largely reconstructed. Structural and stratigraphical geology have reached a high pitch of accuracy. It is beginning to be possible, by convergence of evidences, as the American geologists have shown, and as Geikie has exemplified, to rewrite in part the history of continents and oceans, and to realize each great land-mass as an organic whole, gradually evolved in a definite direction and growing from age to age by regular accretions. Where the old school saw cataclysms and miracles, vast submergences and sudden elevations, the new school sees slow development and substantial continuity throughout enormous periods of similar activity.

It would be impossible to pass over in silence, in however brief a résumé, the special history of the glacial epoch theory—a theory referring indeed only to a single episode in the life of our planet, but fraught with such immense consequences to plants and animals, and to man in particular, that it rises into very high importance among the scientific discoveries of our own era. Demonstration of the fact that the recent period was preceded by a long reign of ice and snow, in the northern and southern hemispheres alike, we owe mainly to the fiery and magnetic genius of Agassiz; and the proof that this glacial period had many phases of hotter and colder minor spells has been worked up in marvelous detail by James Geikie and other able coadjutors. Its theoretic explanation, its probable causes, and its alternation in the northern and southern hemispheres by turns, have been adequately set forth by Croll in a profoundly learned and plausible hypothesis. Upon the glacial epoch depend so many peculiarities in the distribution of plant and animal forms at the present day that it has come to assume a quite exceptional importance among late geological and biological theories. Standing at the very threshold of the recent period, the great ice age forms the fixed date from which everything in modern Europe and America begins—it is the real flood which stands to the true story of our continent and our race in the same relation as the Noachian deluge stood to the imagined or traditional world of our pre-scientific ancestors. Modern history begins with the glacial epoch.

The science of life has been even more profoundly affected by the evolutionary impulse than the concrete sciences of inorganic totals. In 1837 biology as such hardly existed; zoölogy and botany, its separate components, were still almost wholly concerned with minute questions of classification; "vital force" and other unimaginable metaphysical entities were the sole explanations currently offered of all the phenomena of plant and animal life. But Charles Darwin had then just returned from the cruise of the Beagle, and was revolving slowly in his own mind the observations and ideas which blossomed out at last into the "Origin of Species." The germs of evolutionism were already in the air. Lamarck's crude speculations had aroused the attention of all the best biological intellects of the era. Before long Chambers published the "Vestiges of Creation," and Herbert Spencer was hard at work upon the groundwork of the "System of Synthetic Philosophy." The paleontological work of Agassiz, Barraude, Owen, and others, and the general advance in knowledge of comparative anatomy and embryology, paved the way for the triumph of the new ideas; while simultaneously the dry bones of botany were being kindled into life by a younger school of workers in many French and German gardens and laboratories. With the appearance of the "Origin of Species" in 1859, the new departure definitely began. In twenty years the whole world was converted en bloc. Evolution on the organic side has been chiefly expounded in England by Darwin, Huxley, Spencer, and Wallace; and on the whole, though of worldwide acceptance, it has been a peculiarly English movement. Hitherto, indeed, we Britons have been remarkable as the propounders of the deepest and wisest scientific generalizations: it is only of late years that our bookish educators of the new school have conceived the noble ambition of turning us all into imitation Germans.

Life thus falls into its proper place in the scheme of things as due essentially to the secondary action of radiated solar energy, intercepted on the moist outer crust of a cooling and evolving planet. Its various forms have been gradually produced, mainly by the action of natural selection or survival of the fittest on the immense number of separate individuals ejected from time to time by pre-existing organisms. How the first organisms came to exist at all we can as yet only conjecture; to feeble and unimaginative minds the difficulty of such a conjecture seems grotesquely exaggerated; but granting the existence of a prime organism or group of organisms plus the fact of reproduction with heredity and variations, and the tendency of such reproduction to beget increase in a geometrical ratio, we can deduce from these simple elementary factors the necessary corollary of survival of the fittest, with all its far-reaching and marvelous implications. Our age has discovered for the first time the cumulative value of the infinitesimal. "Many a little makes a mickle"; that was Lyell's key in geology, that was Darwin's key in the science of life. Herbert Spencer's "Principles of Biology" most fully sum up this whole aspect of evolution as applied to the genesis of organic beings.

In 1837, the science of man, and the sciences that gather round the personality of man, had scarcely yet begun to be dreamed of. But evolutionism and geological investigation have revolutionized our conception of our own species and of the place which it holds in the hierarchy of the universe. At the very beginning of our fifty years, Boucher de Perthes was already enthusiastically engaged in grubbing among the drift of Abbeville for those rudely-chipped masses of raw flint which we now know as palæolithic hatchets. Lyell and others meanwhile were gradually extending their ideas of the age of our race on earth; and accumulations of evidence, from bone-caves and loess, were forcing upon the minds of both antiquaries and geologists the fact that man, instead of dating back a mere trifle of six thousand years or so, was really contemporary with the mammoth, the cave-bear, and other extinct quaternary animals. The mass of proofs thus slowly gathered together in all parts of the world culminated at last in Lyell's epoch-making "Antiquity of Man," published three years after Darwin's "Origin of Species." Colenso's once famous work on the Pentateuch had already dealt a serious blow from the critical side at the authenticity and literal truth of the Mosaic cosmogony. It was the task of Lyell and his coadjutors, like Evans, Keller, and Christy and Lartet, to throw back the origin of our race from the narrow limits once assigned it into a dim past of immeasurable antiquity. Boyd Dawkins, James Geikie, Huxley, Lubbock, De Mortillet, and Bourgeois have aided in elucidating, confirming, and extending this view, which now ranks as a proved truth of paleontological and historical science.

Darwin's "Descent of Man," published some years later, was an equally epoch-making book. Lubbock's "Prehistoric Times," sent forth in 1865, and "Origin of Civilization," in 1870, had familiarized men's minds with the idea that man, instead of being "an archangel ruined," had really started from the savage condition, and had gradually raised himself to the higher levels of art and learning. Tylor's "Early History of Mankind," followed a little later by his still more important work on "Primitive Culture," struck the first note of the new revolution as applied to the genesis of religious concepts. McLennan's "Primitive Marriage" directed attention to the early nature and relations of the tribe and family. Wallace's essay on the "Origin of Human Races," and Huxley's valuable work on "Man's Place in Nature," helped forward the tide of naturalistic explanation. And by the time that Darwin published his judicial summing up on the entire question of man's origin, the jury of scientific opinion throughout the world had pretty well considered its verdict on all the chief questions at issue.

The impetus thus given to the sciences which specially deal with man, has been simply incalculable. Philology has been revolutionized. Language has told us a new story. Words, like fossils, have been made to yield up their implicit secrets. Prehistoric archæology has assumed a fresh and unexpected importance. The history of our race, ever since tertiary times, and throughout the long secular winters of the glacial epoch, has been reconstructed for us from drift and bone-cave, from barrow and picture-writing, with singular ingenuity. Anthropology and sociology have acquired the rank of distinct sciences. The study of institutions has reached a sudden development under the hands of Spencer, Tylor, McLennan, Maine, Freeman, Lang, and Bagehot. Comparative mythology and folk-lore have asserted their right to a full hearing. Evolutionism has penetrated all the studies which bear upon the divisions of human life. Language, ethnography, history, law, ethics, and politics, have all felt the widening wave of its influence. The idea of development and affiliation has been applied to speech, to writing, to arts, to literature, nay, even to such a detail as numismatics. Our entire view of man and his nature has been reversed, and a totally fresh meaning has been given to the study of savage manners, arts, and ideas, as well as to the results of antiquarian and archaeological inquiry.

In psychology, the evolutionary impulse has mainly manifested itself in Herbert Spencer, and to a less degree in Bain, Sully, Romanes, Croom Robertson, and others of their school. The development of mind in man and animal has been traced pari passu with the development of the material organism. Instinct has been clearly separated from reason: the working of intelligence and of moral feeling has been recognized in horse and dog, in elephant and parrot, in bee and ant, in snail and spider. The genesis and differentiation of nervous systems have been fully worked out. Here Maudsley has carried the practical implications of the new psychology into the domain of mental pathology, and Ferrier has thrown a first ray of light upon the specific functions of portions of the brain. Galton's "Hereditary Genius" and other works have also profoundly influenced the thought of the epoch: while Bastian, Clifford, Jevons, and others have carried the same impulse with marked success into allied lines of psychological research.

But the evolutionary movement as a whole sums itself up most fully of all in the person and writings of Herbert Spencer, whose active life almost exactly covers and coincides with our half-century. It is to him that we owe the word evolution itself, and the general concept of evolution as a single, all-pervading natural process. He, too, has traced it out alone through all its modes, from sun and star, to plant and animal and human product. In his "First Principles," he has developed the system in its widest and most abstract general aspects; in the "Principles of Biology," he has applied it to organic life; in the "Principles of Psychology," to mind and habit; in the "Principles of Sociology," to societies, to politics, to religion, and to human activities and products generally. In Spencer, evolutionism finds its personal avatar: he has been at once its prophet, its priest, its architect, and its builder.

Second only in importance to the evolutionary movement among the scientific advances of our own day must be reckoned the establishment of that profound fundamental physical principle, the conservation of energy. Even before the beginning of our half-century, Davy and Rumford (especially the latter) had caught faint glimpses of the coming truth in this direction. They recognized that heat was a mode of motion, and Rumford went so far as to observe that the energy generated by a given amount of hay burned in an engine might be measured against the energy generated by the same amount of hay consumed by horses. But to Dr. Joule, of Manchester, in our own time, is due the first great onward movement, in the discovery and determination of the mechanical equivalent of heat. Joule's numerous experiments on the exact relation between heat and mechanical energy resulted in the establishment of a formula of equivalence in terms of kilogrammetres necessary to raise by one degree centigrade the temperature of one kilogramme of water. More properly put, he showed that the energy required to raise a weight of one hundred pounds through one foot was equivalent to the amount required to raise a certain fixed quantity of water through one degree in temperature.

Starting from this settled point, it soon became clear to physical thinkers that every species of energy was more or less readily convertible into every other, and that an exact numerical equivalence existed between them. This principle, which first clearly emerged into the consciousness of physicists about the middle decades of the present century, was originally known under the name of "Persistence of Force," in which form Grove's well-known little treatise helped largely to popularize its acceptance. But, as time went on, the underlying distinction between force and energy came to be more definitely realized, and the phrase conservation of energy began to supersede the older and erroneous terminology. The realization of the varying nature of energy as potential and kinetic helped in the transformation of the prime concept. At last, under the hands of Clausius, Helmholtz, Mayer, Clerk Maxwell, Tait, and Balfour Stewart, the doctrine assumed its modern form—that all energies are mutually convertible, and that the sum-total of energy, potential and kinetic, is a constant quantity throughout the cosmos.

The practical applications of the doctrine of energy are as yet only in their infancy. The whole mass of theoretical science has to be re-written in accordance with this new and fundamental law. The whole field of applied science has to be developed and enlarged by the light of this pregnant and universal principle. Its implications are all-pervading. In astronomy it has profoundly affected all our conceptions as to the sun's heat, the orbits of planets, the nature of meteors, the past, present, and future of the universe. In biology it has taught us to envisage the plant mainly as a machine in which kinetic energy is being transformed into potential; the animal mainly as a machine in which potential energy is being transformed back again into kinetic. In mechanics and the mechanical arts it has produced and is producing immense changes. And in the future it is destined still more profoundly to alter our mechanical ideas and activities: the great revolution there is only just beginning; another half-century is yet needed fully to develop it.

These two great principles—evolution and the conservation of energy—form the main bulk of our age's addition to the world's accumulated stock of knowledge. But among the separate sciences many wonderful advances have also been made which can not be overlooked in the briefest retrospect of the half-century's gains. To these a few words must next be devoted.

Among sciences of the abstract-concrete group, electricity had hardly got beyond the stage of an elegant amusement at the opening of our epoch. Statical electricity was still the department about which most was known. Galvanism as yet stood apart as a distinct study. Its connection with magnetism had not long been proved by the discoveries of Oersted. In 1837 itself, however, Wheatstone constructed the first telegraph. From that moment, under the fostering care of Faraday, Daniell, Cooke, Morse, Arago, Tyndall, Edison, and Thomson, electric science became a power in the world. The whole theory of electricity as a mode of energy has since been fully explored and expounded. A vast field has been added to science. Units and modes of absolute measurement have been invented. The telephone and microphone have been introduced; secondary batteries have been formed and improved; the dynamo has become a common object of the country; and the electric light has grown under our very eyes into a practical and extremely dazzling reality. Electricity, as we know it, with all its manifold useful applications, is almost entirely a creation of the last half-century.

In physics the present epoch, though chiefly remarkable for the series of investigations which led up to the discovery of the law of conservation, has also illustrated many minor principles of the first importance. The true theory of heat and the laws of radiant energy have been definitely formulated. The undulatory theory of light—a discovery of the previous quarter-century—has been universally adopted and justified. Thermo-dynamics have been elevated into a great and increasing branch of science. Sir William Thomson's law of dissipation of energy has completed and rounded off the theory of conservation. The causes and methods of glacier-motion have been investigated and established. Photography has almost passed through its entire life-cycle. The polarization of light has been observed and studied. Spectrum analysis has come into the front rank as an instrument of research. In short, a greater number of new physical phenomena have been discovered or old ones interpreted than in the whole space of previous time put together.

In chemistry, the advance has been more in detail than elsewhere. Chemical science alone still remains a somewhat fragmentary mass of individual facts and observations, colligated by minor laws and analogies, but unilluminated as yet by the broad light of any great and all-embracing general principles. Since Dalton's atomic theory, indeed, no philosophic generalization of the very first magnitude has been introduced into chemistry. But generalizations of the second order—vastly interesting to chemists, and to chemists alone—have been made in such numbers as to defy enumeration; wider conceptions have in many ways sprung up; the science has assumed a new form; and some of the results of spectrum analysis and of the new chemistry lead to the hope that this science too is on the eve of arriving at that stage of far-reaching fundamental truths, which it is the special function of our generation to bring about.

Mathematics has also undergone a new development, scarcely capable of being rendered comprehensible to the lay intelligence.

The applications of physical, electrical, and chemical science in the great mechanical and industrial inventions of our iron age, belong elsewhere, and are already familiar in many respects to all of us. Railways slightly antedate the epoch; the telegraph is just coeval with it. The first submarine cable was in 1851, the first transatlantic in 1866. Electro-plating, the steam-hammer, the Armstrong gun, the Bessemer process, must not be forgotten. Other triumphs of applied science fall more fitly under another heading.

Among the concrete sciences, astronomy has made vast advances during the past half-century. Lord Rosse's great telescope was set up at Parsonstown in 1844. Two years later, Leverrier and Adams made their curious simultaneous discovery of the planet Neptune. But it is not so much in new lists of suns or satellites—though the name of these alone has, indeed, been legion—as in the fresh light cast upon the nature and constitution of older ones, that our age has been most singularly successful. The invention of the spectroscope, and the rapid development of spectrum analysis, have placed in the hands of astronomers a method and an instrument inferior in value only to the telescope itself. It is not so long since Comte dogmatically declared we could never know anything of the chemical composition of the fixed stars. Scarcely were the words well out of his mouth when the invention of the spectroscope and its application to the spectra of incandescent bodies brought the investigation of the elements in the sun and stars well within the reach of human possibility. The successive researches of Wheatstone, Foucault, Secchi, Bunsen, Kirchhoff, and Norman Lockyer, exactly covering our fifty years, have at last enabled us to prove almost with certainty the presence in the solar envelopes of several metals already known in the earth's crust, such as potassium, sodium, calcium, iron, nickel, and chromium. So delicate is the spectroscopic test, that it renders possible the detection of so small a fraction as 1200,000,000 part of a grain of sodium. And by revealing bright lines in the spectrum not previously referable to any known body, it has been the means of discovering five new metals: cæsium and rubidium (detected by Bunsen), thallium (by Crookes), indium (by Richter), and gallium (by Lecoq).

Our knowledge of the sun's constitution, in particular, has advanced with extraordinary rapidity during the period here under review. Even thirty years ago we knew little of the central orb of our system save a few naked mathematical facts as to his diameter, his density, his attractive power, and the spots on his surface. Thirty years of constant investigation have now enabled us to picture to ourselves, with tolerable accuracy, the actual state of the sun's fiery exterior. The new era began with Schwabe's discovery of the periodicity of the sun's spots in 1851. The development of spectroscopic analysis between 1854 and 1870 followed hard on this first impulse. Since 1860 eclipses have yielded us valuable results. Observations on transits of Venus have largely corrected a serious error in our calculations of our primary's distance from the earth. Janssen and Lockyer have taught us how to observe at any time, by means of the spectroscope, phenomena which were previously observable only during moments of total eclipse. Huggins has shown us how to isolate those marvelous protuberances of incandescent gas which burst forth with explosive violence from time to time from the edge of the photosphere. Tacchini, Secchi, Young, and others have carried out these interesting researches to a still higher pitch of certainty and accuracy; and the sun's geography, so to speak, is to-day no longer a closed book to mundane observers. We know our central luminary now as a mass of intensely heated gas, surrounded by a shell of luminous cloud, the photosphere, formed by the cooling of condensable vapors at the surface where exposed to the cold of outer space; and floating in a chromosphere of incondensable gases (notably hydrogen) left behind by the formation of the photospheric clouds. The mysterious corona alone as yet evades our methods of research.

In the solar system at large, great advances have been made in the details of planetary astronomy. The differences in kind between the older group of interior planets, now in their cold and solid age, and the younger group of exterior planets, still in their boisterous and fiery youth, have been well ascertained. This truth—of so much interest from the evolutionary point of view—has been especially worked out by R. A. Proctor. Nasmyth's observations on our own dead satellite, the moon, have given us a graphic and appalling picture of a worn-out world in its last stage of lifeless, waterless, and airless decrepitude. New moons have been added to Mars, and several tedious additions have been made by minutely obstetrical astronomers to the already inconveniently large family of the minor planets. All our fresh knowledge of Jupiter and Saturn, those turbulent and volcanic orbs, has helped to impress the general soundness of the evolutionary hypothesis; while the increasingly important study of meteors and comets has brought us close to the very threshold of the great ultimate mystery of star-genesis and world-forming. The extreme tenuity of the mass of comets, the inconceivable rarity of the matter composing their gaseous tails, the curious phenomena of the instantaneous reversal on passing their perihelion, the proof that their light is partly reflected and partly direct, the spectroscopic determination of their composition, the discovery of the essentially planetary nature of meteor-streams, and the recognition of their vast numbers swarming through space, are among the most striking novelties of the last half-century in this direction.

In sidereal astronomy, besides the mere mechanical increase of mapping, the chief advances have been made in observations upon double stars, spectroscopic analysis of fixed stars and of nebulæ, and consequent proof of the fact that truly irresolvable nebulæ do really exist, the gaseous raw material of future stars and solar systems. It must be added that within the half-century the hypothetical ether has amply vindicated its novel claim to take its place as a mysterious entity side by side with matter and energy among the ultimate components of the objective universe.

In geology, the chief theoretical advances have been made by the recognition of the cosmical aspects of the earth's history; its relations to nebula, sun, and meteor; the importance of eccentricity and precession of the equinoxes, and the possible results of ancient changes in its rates of motion, tides, and so forth. Dynamical geology has made vast strides, especially in the investigation of volcanic phenomena, mountain-building, and the birth and growth of islands and continents. The science of earth-sculpture has been developed from the very beginning. Stratigraphical geology has been largely improved. And in paleontology an immense number of the most striking and interesting of fossil forms have been brought to light. Among them may be specially mentioned those which have proved of critical importance as evidences of the truth of organic evolution—the toothed birds of the Western American cretaceous deposits, the lizard-like bird or bird-like feathered lizard of the Solenhofen slates, Marsh's remarkable series of ancestral horses, Cope's beautiful reconstruction of the fossil progenitors of existing camels. Monkeys certainly, anthropoid apes clearly, man doubtfully, have been detected in the fossil state. India, Australia, Canada, the United States have been explored and surveyed, geologically and paleontologically; and the exploitation of the far West in particular has not only added immensely to our knowledge of life in past times, but has also revolutionized our conceptions as to the gradual growth and development of continental areas, and the occasional vast scale of volcanic phenomena. The permanence of all great continents and oceans is now a proved truth of geology. It has been re-enforced and extended from a totally different point of view by Alfred Russel Wallace, whose masterly works on the "Geographical Distribution of Animals," and on "Island Life," have immense geological as well as biological implications.

In pure biology, besides the grand advance implied in the establishment of the doctrine of descent with modification, and its subsidiary principles of survival of the fittest and sexual selection, profoundly important minor results have also been attained in many directions. Embryology in the hands of Von Baer and his successors, notably Kowalevsky and Balfour, has acquired prime importance as an instrument of geological research. Comparative osteology in the hands of Owen, Huxley, Gaudry, and Busk has given us new views of the relationships between vertebrate animals. The pedigree of fishes, amphibians, reptiles, birds, and mammals has been worked out with a considerable degree of fullness from the hints supplied us by the amphioxus, the ascidian larva, the facts of embryology, and the numerous recent discoveries of intermediate or arrested organisms, recent and extinct. Invertebrate zoölogy has been rescued from chaos and partially reduced to temporary and uncertain order. Botany, at once the dullest and the most alluring of all sciences, has been redeemed from the vicious circle of mere classificatory schemes, and vivified by the fresh and quickening breath of the evolutionary spirit. The new morphology has revolutionized our ideas of vegetal homologies; the new physiology has fastened all its attention on the adaptations of the plant to its natural environment. The fascinating study of the mutual relations between flower and insect in particular, set on foot before the dawn of our epoch by Christian Sprengel, but reintroduced to notice in recent times by Darwin's works on orchids and on cross-fertilization, has been followed out with ardor to marvelous results by Hermann Müller, Axel, Delpino, Hildebrand, Lubbock, Ogle, and others. Heer and Saporta have worked out in great detail the development of several fossil floras. Last of all, Herbert Spencer has cast the dry light of his great organizing and generalizing intelligence on the problems of heredity, genesis, variation, individuality, and the laws of multiplication. Fifty years ago biology was a mighty maze wholly without a plan. To-day the clew has been found to all its main avenues, and even the keys of its minor recesses are for the most part well within reach of the enlightened observer.

Even the actual gains in the number of new organisms added to our lists during the last half-century are in themselves astonishing; and, strange to say, the species that bear most closely upon the theory of organic evolution are almost all of them quite recent additions to our stock of knowledge. The gorilla appeared on the scene at the critical moment for the "Descent of Man." Just on the stroke when they were most needed, connecting links, both fossil and living, turned up in abundance between fish and amphibians, amphibians and reptiles, reptiles and birds, birds and mammals, and all of these together in a perfect network of curious cross-relationships. Lizards that were almost crows, marsupials that were almost ostriches, insectivores that were almost hats, rodents that were almost monkeys, have come at the very nick of time to prove the truth of descent with modification. Among the most interesting of these strange coincidences are such episodes as the discovery in the rivers of Queensland of that strange lung-bearing and gill-breathing fish, the barramunda, only known before in the fossil form as a long-extinct species, but in whose anatomical structure Günther has discerned the missing link between the antique ganoid type of fishes on the one hand, and the mud-fish and salamandroid amphibians on the other.

In the practical applications of biological and physiological science to the wants and diseases of human life two at least deserve mention here. Anæsthetics are almost entirely a growth of our half-century: chloroform was first employed in operations by Simpson in 1847, and the use of other similar agents is still more recent. Again, the discovery that zymotic diseases in men and animals are due to the multiplication within the body of very minute organisms, known as microbes, bacteria, or bacilli, now promises to revolutionize medical science. Their connection with decomposition was still earlier detected. The names of Pasteur, Tyndall, and Koch are specially identified with researches into the nature of these tiny morbid organisms and the best means of preventing or neutralizing their attacks, either on living or dead matter.

In marvelous contrast to the fragmentary and disjunctive science of fifty years ago, modern science at the present day offers us the spectacle of a simple, unified, and comprehensible cosmos, consisting everywhere of the same prime elements, drawn together everywhere by the same great forces, animated everywhere by the same constant and indestructible energies, evolving everywhere along the same lines in accordance with the self-same underlying principles. It shows us the community of ultimate material in sun and star, in nebula and meteor, in earth and air and planet and comet. It shows us identical metals and gases in fiery photosphere and in electrically-heated matter in our own laboratories. It shows us atoms of hydrogen or of sodium pulsating rhythmically with like oscillations in star-cloud or sun-cloud, and in London or Berlin. It exhibits to our eyes or to our scientific imagination a picture of the universe as a single whole, a picture of its evolution as a continuous process—one type of matter diffused throughout space; one gravitative attraction binding it together firmly in all parts; one multiform energy quivering through its molecules or traversing its ether, in many disguises of light, and heat, and sound, and electricity. It unfolds for us in vague hints the past of the universe as a diffuse mass of homogeneous matter, rolling in upon its local centers by gravitative force, and yielding up its primitive energy of separation as light and heat to the ethereal medium. It suggests to us this primitive energy of separation as the probable source of such light and heat in suns and stars as we now know them. It posits for us our own planet as an orb gathered in from the original cloud-mass, with outer surface cooled and corrugated, and with two great envelopes, atmospheric and oceanic, gaseous and liquid, still floating or precipitated around its denser core. It teaches us how the hard crust of the hot central mass has been uplifted here into elevated table-land or depressed there into hollow ocean-bed. By the aid of its newest instrument, meteorology, it lets us see how incident solar energy, raising clouds and causing rainfall, with its attendant phenomena of drainage and rivers, has carved and denuded the upheaved masses into infinite variety of hill and valley. It shows us how sediment, thus gathered by streams on the bed of the sea, is pushed up once more by volcanic power or lateral pressure into Alpine chains and massive continents, and how these in their turn have been worn down by the long-continued bombardment of aqueous or aërial action into mere stumps or relics of their primitive magnitude. It puts before us life as an ultimate result of solar energy falling on the watery and gaseous shell of such a solidified planet. It suggests to us how light, acting chemically on the leaves or fronds or cells of the green herb, stores up in them carbohydrates, rich in potential energy, which animals afterward use up as food, or man utilizes as coal in his grates and his locomotives. It exhibits to us the animal organism as essentially a food-engine in whose recesses solar energy, stored as potential by the plant, is once more let loose by slow combustion in the kinetic form as heat and motion. It enables us to regard the body as a machine in which stomach and lungs stand for furnace and boiler, the muscles for cylinder, piston, and wheels, and the nervous system for an automatic valve-gear. It traces for us from small beginnings the gradual growth of limb and organ, of flower, fruit, and seed, of sense and intellect. With the simple key of survival of the fittest it unlocks for us the secret of organic diversity and universal adaptation. It reconstructs for us from obscure half-hints the origin of man; the earliest stages of human history; the rise of speech, of arts, of societies, of religion. It unifies and organizes all our concepts of the whole consistent system of Nature, and sets before our eyes the comprehensive and glorious idea of a cosmos which is one and the same throughout, in sun and star and world and atom, in light and heat and life and mechanism, in herb and tree and man and animal, in body, soul, and spirit, mind and matter. Almost all that is most vital and essential in this conception of our illimitable dwelling-place, the last half-century has built up for us unaided.—Fortnightly Review.