WATER PROVED A COMPOUND. 429 



the saucer which was Uched by it, as Macquer says, that 

 the httle drops of water were deposited. The chemist, 

 however, did not dwell upon this fact ; he was not sur- 

 prised at what it contains of surprising : he simply cites 

 it without any commentary ; he does not perceive that 

 he was touching a great discovery with his finger. 



Should genius then, in the sciences of observation, 

 be reduced to the faculty of asking, at appropriate times, 

 why'? 



The physical world enrolls volcanoes that have never 

 made but one eruption. It is the same in the intellectual 

 world ; for there are men who, after a flash of genius, 

 entirely disappear from the history of science. Such 

 was Warltire, whom I am here led to cite by the chrono- 

 logical order of dates for a truly remarkable experiment. 

 At the commencement of the year 1781, this physicist 

 imagined that an electric spark could not pass through 

 certain gaseous mixtures without occasioning some de- 

 cided changes in them. So novel an idea, unsuggested 

 by any previous analogy, but of which such happy appli- 

 cations have since been made, would have merited for 

 its author, I think, some honourable mention on the part of 

 the historians of science. Warltire was wrong as to the 

 changes that electricity would create, but fortunately for 

 him he did foresee that an explosion would accompany 

 them. It was therefore that he made the experiment in 

 a metallic vase, having enclosed some air and some hy- 

 drogen in it. 



Cavendish soon repeated Warltire's experiment. The 

 positive date of his repetition (I call thus all dates re- 

 sulting from an authentic deposit, or an academical lec- 

 ture, or a printed paper) is anterior to the month of 

 April 1783, since Priestley cites Cavendisli's observations 



