IDENTICAL CHANGES 



body is only incidental, and not a necessary result 

 of the incandescence. 



Yet heat is not incandescence, and a degree of 

 incandescence is not an absolute indication of a 

 corresponding degree of heat, for all substances 

 differ in capacity for incandescence. And while 

 light and incandescence are in a manner words of 

 like meaning, yet light is not always the result of 

 heat. The light of the glow worm can hardly be 

 considered as incandescence, the direct product of 

 heat. 



A red hot sheet of iron gives off as much heat 

 and light as a cube of equally hot iron which has 

 equal surface area. It is then apparent that in an 

 incandescent body the surface only undergoes that 

 peculiar change which produces light. That this 

 peculiar change may be produced by means other 

 than heat becomes evident when it is considered 

 that heat is not an occult power, but a mechanical 

 displacement. As a general rule, a solid substance 

 is capable of incandescence in direct proportion to 

 its ability to preserve the solid state under the 

 influence of heat. 



Because atoms as atoms can undergo no change 

 except a change of position, which is common to 

 any body, or aggregation of bodies in one organiza- 

 tion j and the further change of life, existence and 

 death ; therefore, no amount of heat can make any 

 single atom incandescent. And when any aggrega- 

 tion of atoms in the gaseous state are incapable of 

 chemical combinations, then no amount of heat will 

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