BLACK. 11 



substance is endowed with positive levity ; nor does he 

 allude to the experiments of Lavoisier on gases, on 

 combustion, and on oxidation, further than to say that 

 he had for a considerable time been engaged in these 

 inquiries. It was not indeed till 1787 that he became 

 a convert to the sound and rational doctrine, and aban- 

 doned the fanciful hypothesis, simple and ingenious 

 though it be, of Stahl. Berthollet, the earliest con- 

 vert, had come over to the truth two years before. 

 Thus, discoveries had been made which laid the foun- 

 dation of a new science, and on which the attention of 

 all philosophers was bent ; yet the greatest scientific 

 work of the age made no more mention of them than 

 if Black, Cavendish, Priestley, and Scheele had not 

 been. The conjecture may be allowed to us, that if 

 any of these great things had been done in France, M. 

 Morveau would not have been suffered to preserve the 

 same unbroken silence respecting them, even if his 

 invincible prejudices in favour of the doctrine of phlo- 

 giston had disposed him to a course so unworthy of a 

 philosopher. 



The detail into which I have entered, sufficiently 

 proves that the discovery of fixed air laid at once the 

 foundation of the great events in the chemical world 

 to which reference has just been made, because the 

 step was of incalculable importance by which we are 

 led to the fact that atmospheric air is only one of a 

 class of permanently elastic fluids. When D'Alembert 

 wrote the article ' Air,' in 1751, he gave the doctrine 

 then universally received, that all the other kinds of 

 air were only impure atmospheric air, and that this 

 fluid alone was permanently elastic, all other vapours 

 being only, like steam, temporarily aeriform. Once 

 the truth was made known that there are other gases 

 in nature, only careful observation was required to 

 find them out. Inflammable air was the next which 

 became the subject of examination, because, though it 

 had long been known, before Black's discovery it had 



