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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- 
