CHANGES OCCASIONED BY HEAT. 1G1 



events in the modern history of physics. Of this step the principal 

 merit appears to belong to Black. 



[2nd Ed.] [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 Mtteoroloyique (1787), he spoke of Dr. Black as " the first who 

 had attempted the determinations 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 expression in an Appendix to 

 the volume. 5 



Black never published his own account of the doctrine of Latent 

 Heat : but he delivered it every year after 1760 in his Lectures. In 

 17^0, a surreptitious publication of his Lectures was made by a Lon- 

 don 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 

 Recherches stir Ics 'Modifications de F Atmosphere, which has been 

 alleged to contain the doctrine of latent heat, and which the author 

 asserts to have been written in ignorance of what Black had done. 

 At a later period, De Luc, adopting, in -part, Black's expression, gave 

 the name of latent fire to the heat absorbed. 6 



It appears that Cavendish determined the amount of heat produced 

 by condensing steam, and by thawing snow, as early as 1765. He had 

 perhaps already heard something of Black's investigations, but did 

 not accept his term " latent heat."] 



The consequences of Black's principle are very important, for upon 

 it is founded the whole doctrine of evaporation ; besides which, the 

 principle of latent heat has other applications. But the relations of 

 aqueous vapor to air are so important, and have been so long a sub- 



6 See his Letter to the Editors of the Edinburgh Review, No. xii. p. 502, of the 

 Review. 



6 See Ed. Rev. No. vi. p. 20. 



1 See Mr. V. Harcourt's Address to the Brit. Assoc. in 1839, and the Ap- 

 pendix. 



VOL. II 11. 



