M. Arago's Biographical Memoir of James JFatt. 269 



flash of genius, for ever disappeared from the history of 

 science. Such an one was Warltire, whose truly remark- 

 able experiments fall here in chronological order to be cited. 

 At the beginning of the year 1781, this philosopher conceived 

 that an electric spark could not traverse certain gaseous mix- 

 tures without inducing a change in them. An idea so no- 

 vel, which no previous analogy could have suggested, and of 

 which such wondrous applications have since been made, m 

 my apprehension, requires that all the historians of the science 

 should render due honour to its author. Happily for him- 

 self, he foresaw that an explosion would be a necessary conse- 

 quence ; and hence he made his first experiment in a metallic 

 vessel in which he had put a mixture of common air and 

 hydrogen. 



Cavendish speedily repeated the experiments of Warltire. 

 The certain date (and by this term I mean such an one as re- 

 sults from a paper having been given in, a communication hav- 

 ing been read in a scientific society, or a treatise having been 

 printed), the certain date, I repeat, of this investigation is pre- 

 vious to the month of April 1783 ; because Priestley quotes the 

 observations of Cavendish in a memoir dated the Slst of that 

 month. The citation, it shoiUd be noted, informs us only of a 

 single particular, viz. that Cavendish had obtained water by 

 the detonation of a mixture of oxygen and hydrogen, a result 

 which Warltire had previously obtained. 



In his memoir of the month of April, Priestley added an 

 important circumstance to those resulting from the experi- 

 ments of his predecessors : he proved that the weight of the 

 water which is deposited upon the sides of the vessel, at the 

 instant of the detonation of the oxygen and hydrogen, is pre- 

 cisely the same as the weights of the two gases. 



Watt, to whom Priestley communicated this important result, 

 immediately perceived, with the penetration of a superior man, 

 that a proof was here afforded that water was not a simple body. 

 " What," ho writes to his illustrious friend, " are the products 

 of your experiment ? They are water, light, and heat. Are wo 

 not, thence, authorized to conclude that water is a compound of 

 the two gases, oxygen and hydrogen, deprived of a portion of 

 their latent or elementary heat ; that oxygen is water deprived 



VOL. XXVII. NO. HV.— OCTOBER 1839. X 



