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HEAT. 

 CHAPTER XXXIY. 



THE NATURE AND SOURCES OF HEAT. 



Nature of heat. Just as, according to the 

 theory espoused by Newton, light was supposed to be 

 due to material particles emitted by a luminous body, 

 which, travelling through space, reached the eye, and 

 by their impact gave rise to a sensation of light, so 

 heat was by many supposed also to be an actual 

 substance. By these heat was held to consist of 

 atoms which had the power of forcing their way into 

 the substance of bodies, and so attacking them as to 

 dissociate their particles from one another, and pro- 

 duce, in consequence, the liquid or gaseous state. 

 The entrance of the heat atoms into a person's body 

 produced the sensation of heat, and their exit that of 

 cold. Caloric was the name given to the material of 

 heat. Yet the material view of heat was not univer- 

 sally accepted, and many philosophers entertained the 

 notion that heat was not a thing but a motion, espe- 

 cially Bacon, Boyle, Hooke, Rumford, Davy, and 

 Thomas Young. The modern view regards heat, 

 like light and sound, as a mode of motion. The 

 dynamical theory of heat, as it is called, is the elabo- 

 ration of recent years, and of such men as Professors 

 R. Clausius of Ziirich, Rankine, and Sir William 

 Thomson of Glasgow ; but it was suggested by 



