643 



who have advocated Cavendish's claims. It is the more conclusive 

 as coming from Deluc, the " ami zele" as he justly terms himself, 

 of Watt, and who, in relation to this question, believed himself " a 

 portee d'en cormoitre toutes les circonstances." 



The testimony of Deluc is as follows : 



Vers la fin de 1'annee 1782 j'allai a Birmingham, ou le Dr. Priest- 

 ley s'etoit etabli depuis quelques annees. II me communiqua alors, 

 que M. Cavendish, d'apres une remarque de M. Warltire ; qui avoit 

 toujours trouve de Veau dans les vases ou il avoit brule un melange 

 d^air inflammable et d? air atmospherique ; s'etoit applique a decou- 

 vrir la source de cette eau, et qu'il avoit trouve, "qu'un melange 

 (fair inflammable et d'air dephlogistique en proportion convenable, 

 etant allume par 1'etincelle electrique, se convertissoit tout entier en 

 eau." Je fus frappe au plus haut degre de cette decouverte*. 



The italics and inverted commas are Deluc' s own. 



In this communication made by Cavendish to Priestley the theory 

 of the composition of water is clearly indicated. The two gases 

 (known to have been hydrogen and oxygen) were mixed together in 

 due proportion, and by means of the electric spark were entirely 

 converted into water. Referring to one of Cavendish's experiments, 

 as recorded in his journal, Lord Jeffrey, the most candid and 

 judicious of Watt's advocates, has said: "if he [Cavendish] had 

 even stated in the detail of it, that the airs were converted, or 

 changed, or turned into water, it would probably have been enough 

 to have secured to him the credit of this discovery, as well as to 

 have given the scientific world the benefit of it, in the event of 

 his death, before he could prevail on his modesty to claim it in 

 public, f" The evidence which this distinguished critic and judge 

 regarded as sufficient to establish Cavendish's claim is now afforded, 

 not by a note in his private journal, but by the testimony of the 

 zealous friend of Watt, who states that it was communicated to 

 Priestley towards the end of the year 1 782, that is to say, several 

 months before Watt drew his own conclusions from Priestley's 

 bungling repetition of Cavendish's experiments. It was, moreover, 

 published to the world, and suffered to remain uncontradicted, while 



* I dees sur la Meteorologie, tome ii. 1787, pp. 206-7. 

 f Edinburgh Review, vol. Ixxxvii. p. 125. 



VOL. IX. 2 X 



