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CALORIC. 



one, the feeling experienced on touching a hot body, 

 the other the cause of that sensation. 



The degree of heat which a body gives out is 

 called its temperature. All substances in nature con- 

 tain heat, whether solid, liquid, or aeriform, even 

 when they appear cold to the touch : for, by expo- 

 sing them to a greater degree of cold, we can prove 

 that it is extracted from them. If we suppose heat 

 to be material, its particles repel each other, and are 

 attracted by all other substances. Thus, caloric dif- 

 fuses itself among all bodies with which it comes in 

 contact, until they are all of the same temperature, 

 although they may contain different quantities of 

 heat. Thus, if we seize a heated body, Its heat pass- 

 es to the hand ; if a cold one, the heat of the hand 

 passes to the cold body. There is a great differ- 

 ence in the conducting properties of bodies, which 

 causes a piece of marble, for example, to feel colder 

 than a piece of wood, though both are of the same 

 temperature. Thus heat may be communicated by 

 contact ; by radiation, where it passes through the 

 air; and by conduction, where it is transmitted from 

 particle to particle of the same substance. 



The sun is the great source of heat as well as 

 light. It is generally believed that the sun is a great 

 body of fire ; but, since Herschel's discoveries, it is 

 considered by philosophers an inhabitable world, and 

 that the light and heat which it gives out are occa- 

 sioned by the decomposition of certain elastic fluids. 

 Latent caloric is distinguished from free caloric in not 

 being perceptible to our senses. That a cold bar of 

 iron contains caloric is proved by hammering it on 

 an anvil for a few minutes, when it will be brought 

 to a red heat. So also fire can be produced by 

 rubbing two sticks of wood together. If we turn 

 aquafortis on to sulphuric acid, and then pour the 

 mixture into a vessel of oil of turpentine, the whole 

 mass will burst out into a flame. So also flame can be 

 produced by mixing together two aeriform substan- 



