36 HEAT OR CALORIC. 



laneously, one hand on ice, and the other on a living warm blooded 

 animal. 



Three persons, in the same atmosphere, may find it cold, hot or 

 temperate, according to their previous exposure their state of 

 health, or their clothing. To bring this to a trial, let one person 

 come suddenly out of a bath of 98 or 100 ; let another come from 

 an ice house, and another from the temperature of 55, into a room 

 of the same degree of heat. The first will feel cold the second 

 warm, and the third will experience no change. 



(d.) Without motion there is no sensation. 

 Tl 



motion of light - produces vision, 



That of air, - " hearing, 



That of odorant matter - - " smell, 



*That of sapid substances, - " taste, 



*And that of all bodies in contact with us, " feeling. 



Lavoisier. 



(e.) But mere sensation would not decide that there are not two 

 causes, one of cold, arid one of heat ; or that cold is not the positive 

 principle, and heat the negation. 



Only reverse the reasoning if we would contend that cold is the 

 sole principle ; or reason in both modes, if we would admit that both 

 causes operate. For instance Caloric enters us, or cold leaves us, 

 and we feel warm ; or cold enters us, or heat leaves us, and we feel 

 cold.f But, to assign two or more causes, when one is sufficient is 

 contrary to sound philosophy. 



(/".) The sun is a permanent source of heat. 

 There is no permanent source of cold, and no fact can be stated 

 on that subject which is not explained upon the supposition of the 

 privation of heat. J 



5. The common opinion, that some bodies are positively and in- 

 herently hot, and some cold, is erroneous. 



(a.) We could have no certain information on this subject, except 

 from the changes in volume, or in their qualities, which various 

 bodies undergo, when those that are supposed to contain more or 

 less of heat are applied to them. 



For instance, the thermometer is our criterion, and its fluid either 

 shrinks or swells, according as the body in contact with, or near it, 

 is colder or hotter than it. 



Fluids become solid, and again fluid, or, in other words, freeze 

 and melt, according to the variations in the quantity of heat. 



* In the two latter cases, contact produces the sensation, but without motion it is 

 soon diminished, and in the last instance, soon ceases. 



t We must in this case, substitute and for or, if we would suppose both cause* 

 .operating at the same time. 



t The apparent radiation of cold will be mentioned hereafter. 



