26 



well on the phlogistic hypothesis, but not with ideas so loose and in- 

 definite as these*. 



I am sorry to observe that my meaning has been so far mistaken, 

 as that I should be supposed to have imputed to M. Arago a wilful 

 misrepresentation of the words of Watt : I know him to be incapable 

 of any such intention. It is not bad faith that I complain of in this 

 substitution, but want of sufficient care in stating and deciding a ques- 

 tion of which the decision involved so severe a censure ; and I do not 

 despair of convincing both M. Arago and M. Dumas, who, after having 

 "attentively examined the argumentation of his colleague," and having, 

 like him, "scrupulously studied" the correspondence of Watt, preserved 

 at Aston Hall, " adopts completely, and in all its parts, the history 

 which M. Arago has written of the composition of water f;" that there 

 are still more cogent proofs of the inexpedience of this substitution, 

 and that in 1783 Watt and Priestley were almost as little acquainted 

 with the distinctive properties of the gas which we call hydrogen, as 

 they were with the word. 



Though I have not had the advantage of studying the unpublished 

 MSS. of Watt, I know that they loere submitted to the inspection of 

 the late Dr. Henry, with whose reputation as a pneumatic chemist 

 M. Dumas is well acquainted, and whose knowledge, acuteness, and 

 candour were such as eminently qualified him to judge in such a ques- 

 tion; and I learnt from Dr. Henry that these MSS. produced no change 

 in his opinion as to Cavendish's title to be considered the first disco- 

 verer of the composition of water. Had M. Dumas examined the 

 account of the experiment which M. Arago quotes from Priestley's 



* Priestley never extricated himself from the confusion arising out of these 

 indistinct conceptions ; in speaking of an experiment in 1785, he says, " the 

 water must have been so far altered as to be changed into fixed air, which 

 will be thought not to be any great paradox, if it be considered that, accord- 

 ing to the latest discoveries, fixed air and water appear to consist of the same 

 ingredients." Afterwards, we find him doubting whether inflammable gas and 

 dephlogisticated air ever form water, and conceiving that they do form phlo- 

 gisticated air and nitric acid (Phil. Trans., vol. Ixxxi, 1791) ; and in his Lectures 

 on Experimental Philosophy in 1794, he says (p. 44), " It has of late been 

 thought that water is resolvable into dephlogisticated and inflammable air ; 

 but the experiments which have been alleged to prove this do not satisfy me ; 

 so that for any thing that appeared till very lately, water might be considered a 

 simple element : by means of heat, however, it seems to be resolvable into 

 such air us that of which the atmosphere consists, viz., dephlogisticated and 

 phlogisticated, only with a greater proportion of the former." 



t Comptes rendus, p. 111. 



