relative to Black, Watt, and Cavendish. 519 



deny the author of the demonstration the credit of understand- 

 ing it, for no better reason than that in the private notes of his 

 chain of proofs we find no shout of evprj/ca ? 



1 omit here all the multiplied precautions to ensure the 

 most perfect accuracy in regard to every elementary material 

 of these experiments — I omit the singular caution and saga- 

 city which, on the unexpected intrusion of a minute quantity 

 of nitric acid in one of his varied trials, induced Cavendish to 

 wait till he had obtained evidence that this was the product of 

 the other ingredient in atmospheric air, before he would publish 

 his experiments : I put the question in a shape so simple that a 

 child may understand it; and I ask you once more, — ought you 

 not, with all this, clearly stated, before you, to feel some com- 

 punction for having admitted a suspicion of the good faith of 

 Cavendish, or made a question of his having been the sole 

 discoverer ? 



Again,— I have shown you, that though these experiments 

 were communicated to Priestley as soon as they were made, 

 and by Priestley mentioned to the public in express terms as 

 — " Mr. Cavendish's experiment on the re-conversion of air into 

 water" Priestley understood them no better than the commu- 

 nication which I have before mentioned of the discovery of 

 nitrogen, and subsequently, with the aid of Watt's opinion, 

 concluded that " water by exposing it to heat in porous earthen 

 vessels is capable of being converted into respirable air by the 

 influence of heat: " I have shown you out of that very letter of 

 Watt, communicated to the Royal Society, on which the only 

 real question rests — whether he understood the consequences 

 of Cavendish's experiments nearly two years after they were 

 finished — that Watt's doctrine about water and phlogiston 

 was built on this false supposition, and that he adhered to it 

 after Priestley had communicated to him that experiment 

 which was designed to be a repetition of Cavendish's*: I have 

 shown you that in Priestley's repetition the inflammable gas 

 which he used cannot have contained more than one-fifteenth 

 of its weight of hydrogen, and if it had proved anything, 

 would have proved that water consists chiefly of carbon^'. 

 lastly, I have shown you that both Priestley and Watt were 

 entirely ignorant of the distinction between hydrogen and the 

 inflammable gases on which they experimented and reasoned; 

 and until at a later time they were taught that distinction by 

 Cavendish, and thus learnt what the real basis of water is — 

 were obviously as incompetent to understand, as to discover its 

 composition^. 



* Report of the British Association, Postscript to Address, p. 24. 

 f Ibid. p. 27. 1 Ibid. p. 25. 



