_Antoine Laurent Lavoisier was born in Paris, August 26, 1743. After an early life spent in diligent study, in 1766 he was awarded a prize for his essay on the best method of lighting Paris. His attention having been called to the English experiments on gases made by Priestley and Cavendish, he attacked the current phlogiston conception of combustion and stated that Priestley’s “dephlogisticated air” was the universal acidifying gas, and gave it the name of “oxygen.” Systematizing chemistry and renaming the elements and their compounds, he came to believe that chemical reactions had the certainty of mathematical equations. From this he derived the idea of the persistence of matter, regardless of changes, now established as one of the basic concepts of modern science. During the French Revolution a charge was brought against him and he was sent to the guillotine on May 8, 1794._ THE NATURE OF COMBUSTION[19] I venture to submit to the Academy to-day a new theory of combustion, or rather, to speak with that reserve to whose law I submit myself, an hypothesis, by the aid of which all the phenomena of combustion, calcination, and even to some extent those accompanying the respiration of animals are explained in a very satisfactory manner. I had already laid the foundations of this hypothesis p. 279-280 of vol. I. of my _Opuscules physiques et chimiques_; but I admit that trusting little to my own knowledge, I did not then dare to put forward an opinion which might seem singular, and which was directly opposed to the theory of Stahl and of many celebrated men who have followed him. Though perhaps some of the reasons which then checked me still remain to-day, nevertheless, the facts which have multiplied since that time, and which seem to me favorable to my views, have confirmed me in my opinion: though not, perhaps, any stronger, I have become more confident, and I think I have sufficient proofs, or at least probabilities, so that even those who may not be of my opinion cannot blame me for having written. In general in the combustion of bodies four constant phenomena are observable, which seem to be laws from which nature never departs. Though these phenomena may be found implicitly stated in other memoirs, yet I cannot dispense with recalling them here in a few words. FIRST PHENOMENON All combustion sets free matter either of fire or light. SECOND PHENOMENON Bodies can burn only in a very small number of kinds of gases (airs), or rather there can be combustion only in one kind of air, that which Mr. Priestley has named dephlogisticated air, and which I should call pure air. Not only will the bodies which we call combustibles not burn in a vacuum or in any other kind of air, they are, on the contrary, extinguished there as promptly as if they had been plunged into water or any other liquid. THIRD PHENOMENON