NOTES TO BOOK X. 597 



r Atmosphere, which has been alleged to contain the doc- 

 trine of latent heat, and which De Luc 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. See Ed. 

 Rev. No. vi. p. 20. 



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 some- 

 thing of Black's investigations, but did not accept his term 

 "latent heat." See Mr. V. Harcourt^s Address to the 

 Brit. Assoc. in 1839, and the Appendix. 



(SA.) p. 557- It was found by M. Cagniard de la Tour 

 (in 1823), that at a certain temperature, a liquid, under 

 sufficient pressure, becomes clear transparent vapour or 

 gas, having the same bulk as the liquid. This condition 

 Dr. Faraday calls the Cagniard le la Tour state, (the 

 Tourian state?) It was also discovered by Dr. Faraday 

 that carbonic-acid gas, and many other gases, which were 

 long conceived to be permanently elastic, are really redu- 

 cible to a liquid state by pressure. (Phil. Trans. 1823.) 

 And in 1835, M. Thilorier found the means of reducing 

 liquid carbonic acid to a solid form, by means of the cold 

 produced in evaporation. More recently Dr. Faraday has 

 added several substances usually gaseous to the list of 

 those which could previously be shown in the liquid state, 

 and has reduced others, including ammonia, nitrous oxide, 

 and sulphuretted hydrogen, to a solid consistency. (Phil. 

 Trans. Pt. i, 1845.) After these discoveries, we may, 

 I think, reasonably doubt whether all bodies are not 

 cap;iblu of existing in the three consistencies of solid, liquid 

 and air. 



