HEAT OR CALORIC. G5 



It results therefore, from all our knowledge, that our atmosphere 

 is, throughout its whole extent, in every climate, and in every season, 

 a region of unmitigated cold, excepting the small spheroidal portion 

 which is nearest to the earth distant from it less than three miles in 

 the torrid climates ; rapidly approaching the earth in the other climates, 

 and almost touching it at the poles. Therefore, between the planets 

 and in space generally,* it is probable, that the temperature is very low. 



3. COMMUNICATION OF HEAT CONDUCTION, RADIATION. 



A. The name of CONDUCTION is given to the slow passage of 

 Caloric through the substance of bodies and to its cause ; that of 

 RADIATION, to the instantaneous passage, from surfaces, and through 

 a transparent medium, and also to the cause of it. 



(b.) The conducting powers of bodies arc. widely different. If a 

 cylinder of metal and one of glass, of the same size, be held by the fin- 

 gers in the fire, the metal will feel hot, and perhaps become intolera- 

 ble to the touch, while the glass will communicate little or no heat. 



Those bodies which in their ordinary state feel coldest to the touch, 

 are the best conductors, and vice versa ; hence, some bodies are sup- 

 posed to be naturally cold, as for instance, marble ; others naturally 

 warm, as woollen ; but this is an error. They may have the same tem- 

 perature by the thermometer, and still impart very different sensations, 

 as will be perceived by laying one hand on fire brick and the other 

 on trapf rock ; or more strikingly, one hand on woollen, and the other 

 on metal, both being of the same temperature by the thermometer. 



When we apply the hand to various objects in our apartment " the 

 carpet will feel nearly as warm as our body ; our book will feel 

 cold, the table cold, the marble chimney piece colder, and the can- 

 dlestick colder still, yet, a thermometer applied to them will stand in 

 all at nearly the same elevation. They are all colder than the hand ; 

 but those that carry away caloric most rapidly, excite the strongest 

 sensations of cold."J 



(c.) Bodies , taken in classes, conduct better, the more dense they 

 are, and vice versa. 



Metals conduct better than any other bodies, but there is a differ- 

 ence among them, for instance, copper and tin conduct better than 

 lead and platina. 



The following metals conduct heat, nearly in the order in which 

 they are named. 



Silver, Gold, Copper, Tin, nearly equal. 



Platina, Iron, Steel, Lead, much inferior to the others. 



(d.) Bodies conduct heat worse, the more spongy and divided their 

 parts are. 



* Except perhaps near the innumerable suns. 



t Or any stone ; trap is here mentioned, because it is a very good conductor of 

 its class. t Turner's Chemistry, pa. 11, first Edition. 



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