478 JAMES WATT. 



more distinct terms than Cavendish did in his Memoir read to 

 the Royal Society in January, 1784. By noticing also the 

 disengagement of latent heat in the operation, Watt added 

 very much to the clearness of his conception. 



3. There is no proof, there is not even any assertion 

 whence it would result, that the theory of Cavendish (Blag- 

 den calls it conclusion) was communicated to Priestley pre- 

 viously to Watt's delivering his ideas in the letter of the 26th 

 of April, 1783; and still more, nothing leads one to suppose, 

 especially after reading Watt's letter, that he had ever heard 

 any thing relative to the composition of water either from 

 Priestley or from any other person. 



4. Watt's theory was known by the Fellows of the Royal 

 Society several months before the conclusions of Cavendish 

 had been committed to paper ; eight months before the Me- 

 moir of that chemist was presented to that same Society. We 

 can go farther, and deduce from facts and dates now before us, 

 that Watt was the first to speak of the composition of water ; 

 that if any one was anterior to him, there is no proof of it. 



5. Finally, a repugnance to abandon the doctrine of phlo- 

 giston, a sort of timidity in separating from an opinion so long 

 established, so deeply rooted, prevented Watt and Cavendish 

 from rendering complete justice to their own theory ; whilst 

 Lavoisier, who had broken through those trammels, was the 

 first to present the new doctrine in all its perfection.* 



It might be very possible that without knowing any thing of 

 their respective labours, Watt, Cavendish, and Lavoisier had 

 nearly at the same time made the great step of concluding 

 from experiment, that water is the product of a combination 



* No one ought to have expected from Watt, writing and publish- 

 ing for the first time, exposed to the cares of an immense manufac- 

 tory and of commercial affairs equally extensive, that he could vie 

 with the eloquent and practised pen of Lavoisier; but the substance 

 of his theory (see p. 333 of his Memoir) seems, at least to me, who in 

 truth may not perhaps be an impartial judge, as luminous and as 

 remarkable in expression as the conclusions of the illustrious French 

 chemist. (Note by Mr. Walt,jun.) 



