OF NATURAL PHILOSOPHY. 323 



with which in its radiant state it holds so close an 

 analogy. 



(362.) The subject of latent heat has been far less 

 attentively studied than its great practical import- 

 ance would appear to demand, when we consider 

 that it is to this part of physical science that the 

 theory of the steam-engine is mainly referable, and 

 that material improvements may not unreasonably 

 be expected in that wonderful instrument, from a 

 more extended knowledge than we possess of the 

 latent heats of different vapours. This is not the 

 case, however, with the subject of specific heat, 

 which was followed up immediately after its first 

 promulgation with diligence by Irvine ; and, after a 

 brief interval, by Lavoisier and Laplace, as well as 

 by our countryman Crawfurd, who determined the 

 specific heats of many substances, both solid and 

 liquid. After a considerable period of inactivity, the 

 subject was again resumed by Delaroche and Berard, 

 and subsequently by Dulong and Petit : the result of 

 jvhose investigations has been the inductive esta- 

 blishment of one of those simple and elegant phy- 

 sical laws which carry with them, if not their own 

 evidence, at least their own recommendation to our 

 belief, as being in unison with every thing we know 

 of the harmony of nature. The law to which we 

 allude is this : that the atoms of all the simple 

 chemical elements have exactly the same capacity 

 for heat, or are all equally heated or cooled by equal 

 accessions or abstractions of heat. It is only among 

 laws like this that we can expect to find a clew ca- 

 pable of guiding us to a knowledge of the true na- 

 ture of heat, and its relations to ponderable matter, 

 y 2 



