WATT. 63 



in April at the latest.) For the conclusions are identical, 

 with the single difference, that Mr. Cavendish calls dephlo- 

 gisticated air, water deprived of its phlogiston, and Mr. 

 Watt says that water is composed of dephlogisticated air 

 and phlogiston. 



We may remark, there is the same uncertainty or vague- 

 ness introduced into Mr. Watt's theory, which we before 

 observed in Mr. Cavendish's, by the use of the term Phlo- 

 giston, without exactly defining it. Mr. Cavendish leaves 

 it uncertain, whether or not he meant by phlogiston simply 

 inflammable air, and he inclines rather to call inflammable 

 air, water united to phlogiston. Mr. Watt says expressly, 

 even in his later paper (of November, 1783), and in a pas- 

 sage not to be found in the letter of April, 1783, that he 

 thinks that inflammable air contains a small quantity of 

 water, arid much elementary heat. It must be admitted 

 that such expressions as these on the part of both of those 

 great men, betoken a certain hesitation respecting the theory 

 of the composition of water. If they had ever formed to 

 themselves the idea that water is a compound of the two 

 gases deprived of their latent heat, that is, of the two 

 gases, with the same distinctiveness which marks M. La- 

 voisier's statement of the theory, such obscurity and uncer- 

 tainty would have been avoided. 



Several further propositions may now be stated, as the 

 result of the facts regarding Mr. Watt. 



First, That there is no evidence of any person having 

 reduced the theory of composition to writing, in a shape 

 which now remains, so early as Mr. Watt. 



Secondly, That he states the theory, both in April and 

 November, 1783, in language somewhat more distinctly 

 referring to composition than Mr. Cavendish does in 1784, 

 and that his reference to the evolution of latent heat renders 

 it more distinct than Mr. Cavendish's. 



Thirdly, That there is no proof, nor even any assertion, 

 of Mr. Cavendish's theory (what Sir C. Blagden calls his 

 conclusion) having been communicated to Dr. Priestley 

 before Mr. Watt "stated his theory in 1783, still less of 

 Mr. Watt having heard of it, while his whole letter shows 

 that he never had been aware of it, either from Dr. Priest- 

 ley, or from any other quarter. 



