CALORIC, HEAT. FIRE. 17 



ponds and rivers, would become a solid mass. The ex- 

 pansive power of water, when converted into vapour or 

 steam, is tremendously great.* It appears that solidity 

 is the natural state of bodies ; that when solids acquire a 

 certain degree of caloric or atomicf motion, they become 

 fluids or gases ; and that fluids, by an increased degree 

 of atomic motion, become vapour. 



Caloric is popularly divided into two kinds, free caloric, 

 and latent or combined caloric. By/ree caloric is meant 

 caloric in a separate state, or, if attached to another sub- 

 stance, not chemically combined with it. Latent caloric 

 is that which is chemically combined with any substance 

 so as to make a part of it. 



The chief source or cause of caloric is the sun ; but 

 the rays of the sun seem only to produce heat when they 

 meet with an opaque substance, not when they pass 

 through a transparent one, as glass, water, <s:c. 



Colours have a striking difference in their affinity for 

 caloric ; it has been found by experiment that black has 

 the greatest degree of aifinity, then blue, next brown, 

 white having the least : the black absorbs the rays of 

 light, while the white reflects them. Although black has 

 this particular affinity for heat, it radiates it, or distri- 

 butes it to surrounding bodies sooner than any other 

 colour ; thus, a blackened vessel will become heated if 

 placed over a fire sooner than a bright one ; but when 

 removed from the fire it will not retain its heat so long. 

 If the surface of a metallic vessel be scratched or roughed, 

 the radiation will be increased, and this is attributed to 

 the exciting atoms which cause the heat having more 

 points for distributing it to surrounding bodies. 



Various experiments have been made in order to show 

 the powerful effects of the sun's rays when condensed or 

 multiplied. Archimedes appears to have been the first 



* Steam at 590 is said to have the force of one hundred atmospheres, 

 or in other words, to press at the rate of 1500 Ibs. on a square inch. 



t It is supposed that the cause which produces the sensation of 

 heat consists in the peculiar motion or vibration of the particles or 

 atoms of bodies. According as this motion is more or less rapid, & 

 higher or lower temperature is produced. 



