NATURE OF HEAT. 25 



CHAPTER III. 



HEAT. 



Section 1. Nature and Sources of Heat. 

 Has heat 4Q. NATURE OF HEAT. It was remarked 



weiqht? Give . , 



an Illustration in the commencement 01 the chapter on 

 light, that philosophers, although acquainted with its 

 facts and laws, differed in opinion as to its nature. The 

 same is true of heat. It is agreed, however, that heat, 

 like light, is imponderable, or without appreciable 

 weight ; this being known from the fact that a heated 

 body weighs no more than a cold one. 



41. If the end of a bar of iron is heated, the 

 other end soon becomes hot. There is no doubt 

 as to the effect, and it would seem that something 

 must have passed from the fire, along through the 

 rod to produce it. But we do not certainly know 

 that any substance has been thus transmitted. It may 

 be that heat is analogous to sound, and produced by 

 vibrations. Being thus in doubt, we say that the na- 

 ture of heat is not understood. 



42. MECHANICAL THEORY. One view is 



State the me- . r- ^ 



chemical theo- that a very subtle fluid coming from the 

 ry ' fire has actually passed along through the 



mass of metal, and from that into the hand, and so 

 caused the sensation of warmth or heat. And this 

 supposed substance is called heat, or caloric. 



2 



