596 NOTES TO BOOK X. 



but the ratio is not the same for all. . . . For an increase of 

 pressure from two to six atmospheres, the following number 

 of degrees require to be added to the bodies named : 

 water 69, sulphureous acid 63, cyanogen 64. 5, ammonia 

 60, arseniuretted hydrogen, 54, sulphuretted hydrogen 

 56. 5, muriatic acid 43, carbonic acid 32. 5, nitrous 

 oxide 30." 



(RA.) p. 555. In the first edition I had mentioned 

 the names of De Luc and of Wilcke, in connexion with the 

 discovery of Latent Heat, along with the name of Black. 

 De Luc had observed, in 1755, that ice in melting did not 

 rise above the freezing-point of temperature till the whole 

 was melted. De Luc has been charged with plagiarizing 

 Black's discovery, but, I think, without any just ground. 

 In his Idees sur la Meteorologique, (1787,) he spoke of 

 Dr. Black as " the first who had attempted the deter- 

 minations of the quantities of latent heat." And when 

 Mr. Watt pointed out to him that from this expression it 

 might be supposed that Black had not discovered the fact 

 itself, he acquiesced, and redressed the equivocal expres- 

 sion in an Appendix to the volume. See his Letter to the 

 Editors of the Edinburgh Review, No. xu. p. 502, of the 

 Review. 



Black never published his own account of the doctrine 

 of Latent Heat; but he delivered it every year after 1760 

 in his Lectures. In J770, a surreptitious publication of 

 his Lectures was made by a London bookseller, and this 

 gave a view of the leading points of Dr. Black's doctrine. 

 In 1772, Wilcke, of Stockholm, read a paper to the Royal 

 Society of that city, in which the absorption of heat by 

 melting ice is described : and in the same year De Luc, of 

 Geneva, published his Recherche^ sur les Modifications de 



