notice. It was not published in book form till the last decade of the century, when Hutton had lived with and worked over his theory for almost fifty years. Then it caught the eye of the world. A school of followers expounded the Huttonian doctrines; a rival school, under Werner, in Germany, opposed some details of the hypothesis; and the educated world as a whole viewed the disputants askance. The very novelty of the new views for bade their immediate acceptance. Bitter attacks were made upon the "heresies," and that was meant to be a soberly tempered judgment which in 1800 pronounced Hutton's theories "not only hostile to sacred history, but equally hostile to the principles of probability, to the results of the ablest observations on the mineral kingdom, and to the dictates of rational philosophy." And all this because Hutton's theory presupposed the earth to have been in existence more than six thousand years.

Thus it appears that though the thoughts of men had widened, in these closing days of the eighteenth century, to include the stars, they had not as yet expanded to receive the most patent records that are written everywhere on the surface of the earth. Before Hutton's views could be accepted, his pivotal conception that time. is long must be established by convincing proofs. The evidence was being gathered by William Smith, Cuvier, and other devotees of the budding science of paleontology in the last days of the century, but the record of their completed labors belongs to another epoch.

IV.

The eighteenth-century philosopher made great strides in his studies of the physical properties of matter, and the application of these properties in mechanics, as the steam-engine, the balloon, the optic telegraph, the spinning-jenny, the cottongin, the chronometer, the perfected compass, the Leyden jar, the lightning-rod, and a host of minor inventions testify. In a speculative way he had thought out more or less tenable conceptions as to the ultimate nature of matter, as witness the theories of Leibnitz and Boscovich and Davy, to which we may recur. But he had not as yet conceived the notion of a distinction between matter and energy, which is so fundamental to the physics of a later epoch. He did not speak of

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heat, light, electricity, as forms of energy or force"; he conceived them as subtile forms of matter-as highly attenuated yet tangible fluids, subject to gravitation and chemical attraction; though he had. learned to measure none of them but heat with accuracy, and this one he could test only within narrow limits until late in the century, when Josiah Wedgwood, the famous potter, taught him to gauge the highest temperatures with the clay pyrometer.

He spoke of the matter of heat as being the most universally distributed fluid in nature; as entering in some degree into the composition of nearly all other substances; as being sometimes liquid, sometimes condensed or solid, and as having weight that could be detected with the balance. Following Newton, he spoke of light as a "corpuscular emanation" or fluid.composed of shining particles which possibly are transmutable into particles of heat, and which enter into chemical combination with the particles of other forms of matter. Electricity he considered a still more subtile kind of matter-perhaps an attenuated form of light. netism, vital fluid," and by some even a “gravic fluid" and a fluid of sound, were placed in the same scale; and taken together, all these supposed subtile forms of matter were classed as "imponderables."

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This view of the nature of the "imponderables" was in some measure a retrogression, for many seventeenth-century philosophers, notably Hooke and Huygens and Boyle, had held more correct views; but the materialistic conception accorded so well with the eighteenth-century tendencies of thought that only here and there a philosopher, like Euler, called it in question, until well on toward the close of the century. Current speech referred to the materiality of the "imponderables" unquestioningly. Students of meteorology — a science that was just dawning-explained atmospheric phenomena on the supposition that heat, the heaviest imponderable, predominated in the lower atmosphere, and that light, electricity, and magnetism prevailed in successively higher strata. And Lavoisier, the most philosophical chemist of the century, retained heat and light on a par with oxygen, hydrogen, iron, and the rest, in his list of elementary substances.

But just at the close of the century the confidence in the status of the imponder

ables was rudely shaken in the minds of philosophers by the revival of the old idea of Fra Paolo and Bacon and Boyle, that heat, at any rate, is not a material fluid, but merely a mode of motion or vibration among the particles of "ponderable" matter. The new champion of the old doctrine as to the nature of heat was a very distinguished philosopher and diplomatist of the time, who, it may be worth recalling, was an American. He was a sadly expatriated American, it is true, as his name, given all the official appendages, will amply testify; but he had been born and reared in a Massachusetts village none the less, and he seems always to have retained a kindly interest in the land of his nativity, even though he lived abroad in the service of other powers during all the later years of his life, and was knighted by England, ennobled by Bavaria, and honored by the most distinguished scientific bodies of Europe. The American, then, who championed the vibratory theory of heat, in opposition to all current opinion, in this closing era of the eighteenth century, was LieutenantGeneral Sir Benjamin Thompson, Count Rumford, F.R.S.

Rum ford showed that heat may be produced in indefinite quantities by friction of bodies that do not themselves lose any appreciable matter in the process, and claimed that this proves the immateriality of heat. Later on he added force to the argument by proving, in refutation of the experiments of Bowditch, that no body either gains or loses weight in virtue of being heated or cooled. He thought it proved that heat is only a mode of motion.

But contemporary judgment, while it listened respectfully to Rumford, was little minded to accept his verdict. The cherished beliefs of a generation are not to be put down with a single blow. Where many minds have a similar drift, however, the first blow may precipitate a general conflict; and so it was here. Young Humphry Davy had duplicated Rumford's experiments, and reached similar conclusions; and soon others fell into line. Then, in 1800, Dr. Thomas Young-"Phenomenon Young" they called him at Cambridge, because he was reputed to know everything-took up the cudgels for the vibratory theory of light, and it began to be clear that the two "imponderables," heat and light, must stand or

fall together; but no one as yet made a claim against the fluidity of electricity.

But before this speculative controversy over the nature of the "imponderables had made more than a fair beginning, in the last year of the century, a discovery was announced which gave a new impetus to physical science, and for the moment turned the current of speculation into another channel. The inventor was the Italian scientist Volta; his invention, the apparatus to be known in future as the voltaic pile-the basis of the galvanic battery. Ten years earlier Galvani had discovered that metals placed in contact have the power to excite contraction in the muscles of animals apparently dead. Working along lines suggested by this discovery, Volta developed an apparatus composed of two metals joined together and acted on by chemicals, which appeared to accumulate or store up the galvanic influence, whatever it might be. The effect could be accentuated by linking together several such "piles" into a "battery."

This invention took the world by storm. Nothing like the enthusiasm it created in the philosophic world had been known since the invention of the Leyden jar, more than half a century before. Within a few weeks after Volta's announcement, batteries made according to his plan were being experimented with in every important laboratory in Europe. The discovery was made in March. Early in May two Englishmen, Messrs. Nicholson and Carlyle, practising with the first battery made in their country, accidentally discovered the decomposition of water by the action of the pile. And thus in its earliest infancy the new science of "galvanism" had opened the way to another new science-electro-chemistry.

As the century closed, half the philosophic world was speculating as to whether “galvanic influence" were a new imponderable or only a form of electricity; and the other half was eagerly seeking to discover what new marvels the battery might reveal. The least imaginative man could see that here was an invention that would be epoch-making, but the most visionary dreamer could not even vaguely adumbrate the real measure of its importance. Hitherto electricity had been only a laboratory aid or a toy of science, with no suggestion of practical utility beyond its doubtful application in medi

cine; in future, largely as the outgrowth of Volta's discovery, it was destined to become a great economic agency, whose limitations not even the enlarged vision of our later century can pretend to outline.

V.

Of all the contests that were waging in the various fields of science in this iconoclastic epoch, perhaps the fiercest and most turbulent was that which fell within the field of chemistry. Indeed, this was one of the most memorable warfares in the history of polemics. It was a battle veritably Napoleonic in its inception, scope, and incisiveness. As was fitting, it was a contest of France against the world; but the Napoleonic parallel fails before the end, for in this case France won not only speedily and uncompromisingly, but for all time.

The main point at issue concerned the central doctrine of the old chemistrythe doctrine of Becher and Stahl, that the only combustible substance in nature is a kind of matter called phlogiston, which enters into the composition of other bodies in varying degree, thus determining their inflammability. This theory seems crude enough now, since we know that phlogiston was a purely fictitious element, yet it served an excellent purpose when it was propounded and it held its place as the central doctrine of chemical philosophy for almost a century.

At the time when this theory was put forward, it must be recalled, the old Aristotelian idea that the four primal elements are earth, air, fire, and water still held sway as the working foundation of all chemical philosophies. Air and water were accepted as simple bodies. Only a few acids and alkalies were known, and these but imperfectly; and the existence of gases as we now know them, other than air, was hardly so much as suspected.

All the known facts of chemistry seemed then to harmonize with the phlo giston hypothesis; and so, later on, did the new phenomena which were discovered in such profusion during the third quarter of the eighteenth century-the epoch of pneumatic chemistry. Hydrogen gas, discovered by Cavendish in 1776, and called inflammable air, was thought by some chemists to be the very principle of phlogiston itself. Other "airs" were adjudged "dephlogisticated" or "phlogisticated," in proportion as they sup

ported or failed to support combustion. The familiar fact of a candle flame going out when kept in a confined space of ordinary air was said to be due to the saturation of this air with phlogiston. And all this seemed to tally beautifully with the prevailing theory.

But presently the new facts began, as new facts always will, to develop an iconoclastic tendency. The phlogiston theory had dethroned fire from its primacy as an element by alleging that flame is due to a union of the element heat with the

element phlogiston. Now earths were decomposed, air and water were shown to be compound bodies, and at last the existence of phlogiston itself was to be called in question. The structure of the old chemical philosophy had been completely riddled; it was now to be overthrown. The culminating observation which brought matters to a crisis was the discovery of oxygen, which was made by Priestley in England and Scheele in Sweden, working independently, in the year 1774. Priestley called the new element dephlogisticated air"; Scheele called it “empyreal air.”

But neither Priestley nor Scheele realized the full import of this discovery; nor, for that matter, did any one else at the moment. Very soon, however, one man at least had an inkling of it. This was the great French chemist Antoine Laurent Lavoisier. It has sometimes been claimed that he himself discovered oxygen independently of Priestley and Scheele. At all events, he at once began experimenting with it, and very soon it dawned upon him that this remarkable substance might furnish a key to the explanation of many of the puzzles of chemistry. He found that oxygen is consumed or transformed during the combustion of any substance in air. He reviewed the phenomena of combustion in the light of this new knowledge. It seemed to him that the new element explained them all without aid of the supposititious element phlogiston. What proof, then, have we that phlogiston exists? Very soon he is able to answer that there is no proof, no reason to believe that it exists. Then why not denounce phlogiston as a myth, and discard it from the realm of chemistry?

Precisely this is what Lavoisier purposes to do. He associates with him three other famous French chemists, Berthol

let, Guyton de Morveau, and Fourcroy, and sets to work to develop a complete system of chemistry based on the new conception. In 1788 the work is completed and given to the world. It is not merely an epoch-making book; it is revolutionary. It discards phlogiston altogether, alleging that the elements really concerned in combustion are oxygen and heat. It claims that acids are compounds of oxygen with a base, instead of mixtures of "earth" and water; that metals are simple elements, not compounds of "earth" and "phlogiston"; and that water itself, like air, is a compound of oxygen with another element.

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In applying these ideas the new system proposes an altogether new nomenclature for chemical substances. Hitherto the terminology of the science has been a matter of whim and caprice. Such names as "liver of sulphur," " mercury of life," "horned moon," "the double secret, the salt of many virtues," and the like, have been accepted without protest by the chemical world. With such a terminology continued progress was as impossible as human progress without speech. The new chemistry of Lavoisier and his confrères, following the model set by zoology half a century earlier, designates each substance by a name instead

JOSEPH PRIESTLEY.

of a phrase, applies these names according to fixed rules, and, in short, classifies the chemical knowledge of the time and brings it into a system, lacking which no body of knowledge has full title to the name of science.

Though Lavoisier was not alone in developing this revolutionary scheme, posterity remembers him as its originator. His dazzling and comprehensive genius obscured the feebler lights of his confrères. Perhaps, too, his tragic fate was not without influence in augmenting his posthumous fame. In 1794 he fell by the guillotine, guiltless of any crime but patriotism-a victim of the "Reign of Terror." "The Republic has no need of savants," remarked the functionary who signed the death-warrant of the most famous chemist of the century.

The leader of the reform movement in chemistry thus died at the hands of bigotry and fanaticism-rather, let us say, as the victim of a national frenzy-while the cause he championed was young, yet not too soon to see the victory as good as won. The main body of French chemists had accepted the new doctrines almost from the first, and elsewhere the opposition had been of that fierce, eager type which soon exhausts itself in the effort. At Berlin they began by burning Lavoisier in effigy, but they ended speedily by accepting the new theories. In England the fight was more stubborn, but equally decisive. At first the new chemistry was opposed by such great men as Black, of "latent heat" fame; Rutherford, the discoverer of nitrogen; and Cavendish, the inventor of the pneumatic trough and the discoverer of the composition of water, not to mention a coterie of lesser lights; but one by one they wavered and went over to the enemy. Oddly enough, the doughtiest and most uncompromising of all the champions of the old "phlogistic" ideas was Dr. Priestley, the very man whose discovery of oxygen had paved the way for the "antiphlogistic " movement-a fact which gave rise to Cuvier's remark that Priestley was undoubtedly one of the fathers of modern chemistry, but a father who never wished to recognize his daughter.

A most extraordinary man was this Dr. Priestley. Davy said of him, a generation later, that no other person ever discovered so many new and curious substances as he; yet to the last he was only an amateur in science, his profession being the ministry. There is hardly an