310 DISCOURSE ON THE STUDY 



CHAP. V. 



OF THE IMPONDERABLE FORMS OF MATTER. 



Heat. 



(344.) ONE of the chief agents in chemistry, on 

 whose proper application and management the 

 success of a great number of its enquiries depends, 

 and many of whose most important laws are dis- 

 closed to us by phenomena of a chemical nature, 

 is HEAT. Although some of its effects are con- 

 tinually before our eyes as matters of the mosc 

 common occurrence, insomuch that there is scarcely 

 any process in the useful arts and manufactures 

 which does not call for its intervention, and al- 

 though, independent of this high utility, and the 

 proportionate importance of a knowledge of its 

 nature and laws, it presents in itself a subject of 

 the most curious speculation ; yet there is scarcely 

 any physical agent of which we have so imperfect 

 a knowledge, whose intimate nature is more hidden, 

 or whose kws are of such delicate and difficult in- 

 vestigation. 



(345.) The word heat generally implies the sens- 

 ation which we experience on approaching a fire; 

 but, in the sense it carries in physics, it denotes the 

 cause, whatever it be, of that sensation, and of all 



