M. Arago's Biographical Memoir of James Watt. 267 



whose life constitutes an epoch in the annals of the world. It 

 appears to me, however, that his name is also connected in a 

 distinguished manner with the greatest and most prolific dis- 

 covery of modern chemistry, namely, the discovery of the com- 

 position of water. My assertion to many may appear rash, 

 inasmuch as in the numerous works which have professedly 

 treated upon this capital point in the history of the sciences. 

 Watt has been forgotten. I trust, notwithstanding, that you 

 will be ready to follow my discussion without prejudice ; that 

 you will not be diverted from the inquiry by authorities who 

 have taken the other side of the question, and who, after all, 

 are less numerous than is generally supposed ; that you will 

 remember how few authors now-a-days go direct to the ori- 

 ginal sources, how little disposed they are to encounter the 

 musty dust of our libraries, and, on the contrary, how much 

 easier it seems to them to live upon the erudition of an- 

 other, reducing the composition of a book to the simple la- 

 bour of compilation. The warrant which I hold for your con- 

 fidence seems to me more serious ; I have examined numerous 

 published memoirs, and the whole of a very voluminous au- 

 thentic correspondence still in manuscript ; and if I now 

 come, after a lapse of fifty years, to claim for James Watt 

 an honour which was too readily conceded to one of his most 

 illustrious countrymen, it is because I consider it useful to de- 

 monstrate, that, within the walls of our scientific associations, 

 truth is sooner or later brought to light, and that, in the 

 matter of discovery at least, there is no prescription. 



The four pretended elements of fire, air, earth, and water, 

 whose various combinations were supposed to produce all 

 known bodies, constitute one of the legacies of a brilliant philo- 

 sophy, which dazzled and misled the most noble intelligences. 

 Van Helmont was the first who shook, though but slightly, one 

 of the principles of this ancient theory, by calling the attention 

 of chemists to several permanent elastic fluids or airs, which 

 he called gases, whose properties differed from those of common 

 air, or elemental air. The observations of Boyle and of 

 Hooke created still graver difficulties, for they established 

 that the common air, necessary to respiration and combus- 

 tion, undergoes very remarkable clianges in the course of these 



