380 WATT. 



most important truth he arrived by a profound ex- 

 amination of all the experiments which had been made 

 by Warltire, by Macquer, and especially by Priest- 

 ley, upon the combustion of hydrogen and oxygen 

 gases, then called inflammable, and vital or dephlo- 

 gisticated airs. No former reasoner had come even 

 near the true theory of the phenomena observed in 

 those experiments. All had assumed that water was 

 a simple or elementary body ; that it was contained in 

 the airs burnt together, and was precipitated by their 

 explosion. He, on the contrary, showed that it was 

 formed by the union of the two gases, and their 

 parting with the latent heat which had held them in 

 the elastic or gaseous state, but which being with- 

 drawn by their union, left them in a state of liquid or 

 aqueous fluidity. 



As early as 1782, his attention had been closely 

 directed to the experiments in which air is produced 

 from water, and especially to those upon the com- 

 bustion of inflammable air. In December of that year 

 he had matured his theory, for we find him then an- 

 nouncing to De Luc his discovery, that " one element 

 must be dismissed from the list ;" water being, ac- 

 cording to his doctrine (stated more explicitly to Dr. 

 Black, April 1783 r ) " composed of dephlogisticated and 

 inflammable airs deprived of a portion of their latent 

 heat." To his whole correspondence with that great 

 philosopher, with Smeaton, with Priestley, De Luc, and 

 others, I have had access, and no trace is to be found 

 in it that either he or they had even entertained the 

 least suspicion of the same thing having before occurred 



