added to them. Lavoisier turned his attention to the defects of the existing theory about 1770; and the last-named experiments probably directed him more specifically to the essential point of the inquiry. He pursued his researches with unwearied industry; and by a long series of experiments of the most laborious and precise nature, he succeeded in determining that, in all cases of combustion, that substance which is the real combustible invariably receives an addition, or enters into a new combination; and the matter with which it combines is in all cases that same substance which had now been shown by Priestley to be one of the constituents of the atmosphere, and which was then known by the name of vital air.

It was however long before Lavoisier gained a single convert. At length M. Berthollet, at a meeting of the Academy in 1785, publicly renounced the old opinions and declared himself a convert. Fourcroy followed his example. In 1787, Morveau, during a visit to Paris, became convinced, and declared the conclusions of Lavoisier irresistible. The younger chemists speedily embraced the new views; and their establishment was thus complete. There only remained some lurking prejudices in England, where the Essay of Kirwan retained its credit. Lavoisier and his coadjutors translated this essay into French, accompanying each section by a refutation. So completely was this done, that the author himself was convinced; and, with that candour which distinguishes superior minds, gave up his views as untenable, and declared himself a convert.

These discoveries introduced Lavoisier to the notice of the most eminent persons in the State; and in 1776 Turgot engaged him to superintend the manufacture of gunpowder for the Government. He introduced many valuable improvements in the process, and many judicious reforms into the establishment.

In 1778, Lavoisier having been incessantly engaged on the subject of gases and combustion, announced another great discovery, "that the respirable portion of the atmosphere is the constituent principle of acids," which he therefore denominated oxygen.

The question as to "the acidifying principle" had long formed the subject of discussion. The prevalent theory was that of Beccher with various modifications, which made the acid principle a compound of earth and water regarded as elements. Lavoisier found in the instance of a great number of the acids, that they consisted of a combustible principle united with oxygen. He showed this both analytically and synthetically, and hence proceeded to the conclusion that oxygen is the acidifying principle in all acids. Berthollet opposed this doctrine, and contended that, in general, acidity depended on the manner and proportion in which the constituents are combined. The fact is, that, in this instance, Lavoisier had advanced a little too rapidly to his conclusion. Had he contented himself with stating it as applying to a great number of acids, it would have been strictly true; but he had certainly no proof of its being universally the case. When Sir H. Davy, some years after, showed that one of the most powerful acids (the muriatic) does not contain a single particle of oxygen, and when the researches of Guy Lussac and others had exhibited other proofs of the same thing, it became evident that Lavoisier's assertion required considerable modification. And though nearly all acids have been since included under the general law of containing some supporter of combustion, yet there appear to be exceptions even to this; the cautious language of Berthollet has been completely justified; and a perfect theory of acidity is perhaps yet wanting. Nevertheless, Lavoisier's discovery is one of the first-rate magnitude and importance, and with this qualification,

certainly forms the basis of all our present knowledge of the subject.

Another important research in which Lavoisier engaged, in conjunction with Laplace, was the determination of the specific heats of bodies, by means of an ingenious apparatus, which they denominated the calorimeter: these were by far the most precise experiments on the subject which had as yet been made, though some inaccuracies in the method have since been pointed out.

Lavoisier owed much, it must be owned, to those external advantages of fortune, the absence of which, though it cannot confine the flights of real genius, yet may seriously impair the value and efficiency of its exertions; and the presence of which, though it cannot confer the powers of intellect, may yet afford most invaluable aids to the prosecution of research, and the dissemination of knowledge. In the instance before us, these advantages were enjoyed to the full extent, and turned to the best use. Lavoisier was enabled to command the most unlimited resources of instrumental aid; he pursued his researches in a laboratory furnished with the most costly apparatus, and was able to put every suggestion to the test of experiment, by the assistance of the most skilful artists, and instruments of the most perfect construction.

But as he could thus command these essential advantages for the prosecution of his own investigations, he was equally mindful of the extension of similar advantages to others: he always evinced himself ready to assist the inquiries of those who had not the same means at their disposal; and was no less liberal in aiding them by his stores of information and able advice. Indeed no one could be more sensible how much there is of mutual advantage in such intercourse between those engaged in the same scientific labours;

and this conviction, joined with a full perception of the immense benefits accruing from personal acquaintance among men of kindred pursuits, and the interchange of social good offices, led him to the regular practice of opening his house on two evenings in every week, for an assembly of all the scientific men of the French capital; which very soon became a point of general resort and reunion to the philosophers of Europe.

At these meetings general discourse and philosophic discussion were agreeably intermingled; the opinions of the most eminent philosophers were freely canvassed; the most striking and novel passages in the publications of foreign countries were made known, recited, and animadverted upon; and the progress of experiment was assisted by candid comments and comparison with theory. In these assemblies might be found, mingling in instructive and delightful conversation, all those whose names made the last century memorable in the annals of science. Priestley, Fontana, Landriani, Watt, Bolton, and Ingenhouz, were associated with Laplace, Lagrange, Borda, Cousin, Monge, Morveau, and Berthollet. There was also an incalculable advantage in bringing into communication and intimacy men engaged in distinct branches of science: the intercourse of the mathematician with the geologist, of the astronomer with the chemist, of the computer with the experimenter, and of the artist with the theorist, could not fail to be of mutual advantage. In no instance were the beneficial effects of such intercourse more strikingly displayed than in the chemical sciences; which, from this sort of comparison of ideas and methods, began now to assume a character of exactness from an infusion of the spirit of geometry; and a department hitherto abandoned to the wildest speculations, and encumbered with the most vague and undefined

phraseology (derived from the jargon of the alchymists), began to assume something like arrangement and method in its ideas, and precision and order in its nomenclature. This influence was strongly marked in the physical memoirs produced in France from this period downwards. The precision and severity of style, and the philosophical method of the mathematicians, was insensibly transfused into the papers of the physical and chemical philosophers.

Lavoisier individually profited greatly by the sources of improvement and information thus opened. Whenever any new result presented itself to him, which, perhaps, from contradicting all received theories, seemed paradoxical, or at variance with all principles hitherto recognised, it was fully laid before these select assemblies of philosophers; the experiment was exhibited in their presence, and they were invited with the utmost candour to offer their criticisms and objections. In perfect reliance on the mutual spirit of candour, they were not backward in urging whatever difficulties occurred to them, and the truth thus elicited acquired a firmness and stability in its public reception proportioned to the severity of the test it had undergone. Lavoisier seldom announced any discovery until it had passed this ordeal.

At length he combined his philosophical views into a connected system, which he published in 1789, under the title of Elements of Chemistry:' a beautiful model of scientific composition, clear and logical in its arrangement, perspicuous and even elegant in its style and manner. These perfections are rarely to be found in elementary works written by original discoverers. The genius which qualifies a man for enlarging the boundaries of science by his own inventions and researches is of a very different class from that which confers the ability to elucidate, in a simple and systematic course, the order and connexion of