

I JOSEPH PRIESTLEY 15 



ising the strongest alkalies; and it took the world 

 some time to become accustomed to the notion. 



A dozen years later, one of the most sagacious 

 and accurate investigators who has adorned this, 

 or any other, country, Henry Cavendish, published 

 a memoir in the " Philosophical Transactions, 

 in which he deals not only with the " fixed air 

 (now called carbonic acid or carbonic anhydride) 

 of Black, but with " inflammable air,^' or what we 

 now term hydrogen. 



By the rigorous application of weight and 

 measure to all his processes, Cavendish implied the 

 belief subsequently formulated by Lavoisier, that, 

 in chemical processes, matter is neither created 

 nor destroyed, and indicated the path along which 

 all future explorers must travel. Nor did he him- 

 self halt until this path led him, in 1784, to the 

 brilliant and fundamental discovery that water is 

 composed of two gases united in fixed and con- 

 stant proportions. 



It is a trying ordeal for any man to be com- 

 pared with Black and Cavendish, and Priestley 

 cannot be said to stand on their level. Neverthe- 

 less his achievements are not only great in them- 

 selves, but truly wonderful, if we consider the dis- 

 advantages under which he^ laboured. Without 

 the careful scientific training of Black, without the 

 leisure and appliances secured by the wealth of 

 Cavendish, he scaled the walls of science as so 

 many Englishmen have done before and since his 



