92 CAVENDISH. 



late Duke of Devonshire's great uncle, by the daugh- 

 ter of Henry Grey, Duke of Kent. His family, aware 

 of the talents which he early showed, were anxious 

 that he should take the part in public life which men 

 of his rank are wont to do, and were much displeased 

 with his steady refusal to quit the studies which he 

 loved. An uncle, disapproving of the course pursued 

 towards him made him his heir ; and so ample a for- 

 tune came into his possession that he left at his death 

 a million and a quarter of money.* The Mathematics, 

 and the various branches of Natural Philosophy, were 

 the chief subjects of his study, and of all these sciences 

 he was a consummate master. 



The discoveries of Black on carbonic acid and la- 

 tent heat, appear to have drawn his attention to the 

 cultivation of pneumatic chemistry; and in 1766 he 

 communicated to the JRoyal Society his experiments 

 for ascertaining the properties of carbonic acid and 

 hydrogen gas.j He carried his mathematical habits 

 into the laboratory ; and not satisfied with showing 

 the other qualities which make it clear that these two 

 aeriform substances are each sui generis, and the same 

 from whatever substances, by whatever processes, they 

 are obtained ; nor satisfied with the mere fact that one 

 of them is heavier, and the other much lighter, than 

 atmospheric air, he inquired into the precise nume- 

 rical relation of their specific gravities with one another 

 and with common air, and first showed an example of 

 weighing permanently elastic fluids: unless, indeed, 

 Torricelli may be said before him to have shown the 

 relative weight of a column of air and a column of 

 mercury: or the common pump to have long ago 



* M. Biot's article in the Biog. Univ. makes him the son of the Duke 

 of Devonshire, and states his yearly income at 300,000 sterling, and yet 

 gives the. property he left at only 1,200,000 so that he must have 

 spent 300,000 a-year, and also dissipated five millions. Such errors 

 seem incredible. 



f Three papers containing experiments on factitious air. Phil. Trans. 

 1766, p. 141. 



