430 JAMES WATT. 



in a memoir of the 21st of that month. The citation 

 besides informs us only of one circumstance ; it is, that 

 Cavendish had obtained water by the detonation of a 

 mixture of oxygen and hydrogen, a result already proved 

 by Warltire. 



In his April memoir, Priestley added a remarkable 

 circumstance to those which resulted from the experi- 

 ments of his predecessors, for he proved that the weight 

 of the water deposited on the sides of the vase at the 

 moment of the oxygen's and hydrogen's detonation, is 

 the sum of the weight of both the gases. 



Watt, to whom Priestley communicated this important 

 result, immediately saw in it, with the penetration of a 

 superior mind, that water is not a simple body. 



He therefore wrote to his illustrious friend : " What 

 are the products of your experiments, wate?; light, and 

 heat f Are we not then authorized from hence to con- 

 clude that water is a union of oxyen and hydrogen gas, 

 deprived of a portion of their latent or elementary heat ; 

 that oxygen is water deprived of its hydrogen but united 

 to latent heat and light ? " 



" If light be only a modification of heat, or only a cir- 

 cumstance attendant on its manifestation, or a component 

 part of hydrogen, oxygen gas must be water deprived of 

 its hydrogen, but united to some latent heat." 



This passage, so clear, so neat, so methodical, is ex- 

 tracted from a letter by Watt, of the 26th of April, 

 1783. The letter was communicated by Priestley to 

 several learned men in London, and referred immediately 

 after to Sir Joseph Banks, President of the Royal Society, 

 to be read at a meeting of that learned society. Some 

 circumstances, which I suppress because they are irrele- 

 vant to our present purpose, retarded the reading by a 



