152 Royal Society, 



Royal Society the following brief remarks on the quotatio)i from De 

 Luc's " Idees sur la Meteorologie," wliicli has been referred to as 

 fresh evidence in the controversy as to the discovery of the Compo- 

 sition of AVater. 



It is only at first sight, and when taken in an isolated form apart 

 from the rest of De Luc's narrative, that the passage in question 

 could bear the interpretation now sought to be put upon it ; for 

 Dr. Priestley's communication of Cavendish's experiment is said 

 b)' De Luc to have been made "vers la fin de I'annee 1/82." But 

 in the same section of the same volume he distinctly and positively 

 says, that when in September [1783] he returned to Birmingham, 

 " Nous ignorions, M. Watt et moi, que M. Cavendish eut eu des 

 idees fort semblables aux siennes sur la Cause de ce Phenomene *." 



Now, we may well ask, how could this possibly have been the case 

 with De Luc in 1 783, if Priestley's communication to him in 1 782 

 had extended to the conclusions, as well as to the experiments, of 

 Cavendish ? 



De Luc adds, on" the next page of his work, that " Au mois de 

 Juiu" (an evident mistake for Janvier), " 1/84, M. Cavendish remit 

 a la Society Royale un Mcmoire, dans lequel il joignit, au recit de 

 ses experiences de 1781, sa the'orie sur la formation de VEau-\." 

 Here, for the first time in De Luc's narrative (with the exception of 

 an allusion to Blagden's statement at Paris in June 1783), occurs a 

 clear and distinct notice of Cavendish's theory or conclusions, as 

 distinguished from his experiments. What M. De Luc's opinion of 

 the memoir was, in which those conclusions were announced, when 

 be perused it in March 1784, and sent an analysis of it to Mr. Watt, 

 is well known from his letters already published:];. 



We are thus enabled to set against the interpretation attempted to 

 be put on the quotation from the " Meteorologie," the most con- 

 clusive of all testimony ; that, namely, of De Luc himself : for if 

 he had intended to say that in the end of 1782 the conclusions of 

 Cavendish had along with his expei'iment been communicated by 

 Priestley, he could not possibly have gone on to say, as he has done 

 a few pages later in the same volume, that in September 1 783 he 

 was ignorant of Cavendish having entertained any such ideas ; nor 

 would he have felt the astonishment, and entertained the suspicions 

 which he so strongly expresses, on his perusal of Cavendish's memoir 

 in March 1784. 



De Luc's account in the " Meteorologie," it must also be observed, 

 is not a contemporaneous one, published at the time of Priestley's 

 communication in 1782, and before the conclusions of Watt were 

 made known ; but is given from memory, at an interval of several 

 years, when such a mistake as that of June for January shows how 

 little it can be relied on. j ^^^ ^^^ 



Jas. p. Mvirhead. 



* " Idees sur la Meteorologie," tome ii. p. 224. 



t Ibid. p. 225. 



X M. De Luc to Mr. Watt, 1st and 4th of March, 1784. 



