WATT. 397 



mable air contains a small quantity of water, and 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 distinctive- 

 ness which marks M. Lavoisier's statement of the theory, 

 such obscurity and uncertainty would have been avoided. 



Several further propositions may now be stated, as the re- 

 sult of the facts regarding Mr. Watt. 



First, That there is no evidence of any person having re- 

 duced 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 No- 

 vember 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 dis- 

 tinct 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 con- 

 clusion) 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. Priestley, or from any 

 other quarter. 



Fourthly, That Mr. Watt's theory was well known among 

 the members of the Society, some months before Mr. Caven- 

 dish's statement appears to have been reduced into writing, 

 and eight months before it was presented to the Society. We 

 may, indeed, go further, and affirm, as another deduction from 

 the facts and dates, that as far as the evidence goes, there is 

 proof of Mr. Watt having first drawn the conclusion, at least 

 that no proof exists of any one having drawn it so early as 

 he is proved to have done. 



Lastly, That a reluctance to give up the doctrine of phlo- 

 giston, a kind of timidity on the score of that long-established 

 and deeply rooted opinion, prevented both Mr. Watt and Mr. 

 Cavendish from doing full justice to their own theory ; while 



