HEAT. 



319 



IEAT. 



WHILE almost every other branch of physical science has been made the 

 subject of systematic treatises without number, and some have been, as it were, 

 set apart from the general mass of natural philosophy, and raised to the rank 

 of distinct sciences by the badge of some characteristic title, Heat alone has 

 been left to form a chapter of chemistry, or to receive a passing notice in trea- 

 tises on general physics. Light has long enjoyed the exclusive attention of 

 philosophers, and has been elevated to the dignity of a science, under the name 

 of Optics. Electricity and Magnetism have also been thought worthy subjects 

 for separate treatises, yet, can any one who has observed the part played by 

 heat on the theatre of nature, doubt that its claims to attention are equal to those 

 of light, and superior to those of electricity and magnetism. It is possible for 

 organized matter to exist without light. Innumerable operations of nature pro- 

 ceed as regularly and as effectually in its absence as when it is present. The 

 want of that sense which it is designed to affect in the animal economy, in no 

 degree impairs the other powers of the body, nor in man does such a defect 

 interfere in any way with the faculties of the mind. Light is, so to speak, an 

 object rather of luxury than of positive necessity. Nature supplies it, there- 

 fore, not in unlimited abundance, nor at all times and places, but rather with 

 that thrift and economy which she is wont to observe in dispensing the objects 

 of our pleasures, compared with those which are necessary to our being. But 

 heat, on the contrary, she has yielded in the most unbounded plenteousness. 

 Heat is everywhere present. Every body that exists contains it in quantity 

 without known limit. The most inert and rude masses are pregnant with it. 

 Whatever we see, hear, smell, taste, or feel, is full of it. To its influence is 

 due that endless variety of forms which are spread over and beautify the sur- 

 face of the globe. Land, water, air, could not for a single instant exist as they 

 do, in its absence ; all would suddenly fall into one rude formless mass solid 

 and impenetrable. The air of heaven hardening into a crust would envelope 

 the globe, and crush within an everlasting tomb all that it contains. Heat is 





