CAVENDISH 37 



consists of this acid united to phlogiston, yet it might 

 fairly be doubted whether the whole is of this kind, or 

 whether there are not in reality many different substances 

 compounded together by us under the name of phlogisti- 

 cated air. I therefore made an experiment to determine 

 whether the whole of a given portion of the phlogisticated 

 air of the atmosphere could be reduced to nitrous acid, or 

 whether there was not a part of a different nature from 

 the rest which would refuse to undergo that change. . . . 

 If there is any part of the phlogisticated air of our atmo- 

 sphere which differs from the rest, and cannot be reduced 

 to nitrous acid, we may safely conclude that it is not more 

 than y^ part of the whole." This is of vast importance, 

 if we bear in mind the discovery of argon as a constituent 

 of the atmosphere by Rayleigh and Ramsay in 1894, and 

 the later work of Ramsay and Travers on krypton, neon, 

 and metargon. 



Although Cavendish's work on atmospheric gases was 

 of great importance, it led him to a still more famous dis- 

 covery, namely, the composition of water in 1781 ; and in 

 his paper of 1784 he says : " By the experiments with the 

 globe it appeared that when inflammable air (hydrogen) 

 and common air are exploded in a proper proportion, almost 

 all the inflammable air, and nearly one-fifth of the common 

 air, lose their elasticity and are condensed into dew. And 

 by this experiment it appears that this dew is plain water, 

 and, consequently, that almost all the inflammable air, and 



