HEAT AND COLD. 



A linen shirt when first put on will feel colder than a cotton 

 one, and a flannel shirt will actually feel warm ; yet all these 

 have the same temperature. 



The sheets of the bed feel cold, and blankets warm ; the 

 blankets and sheets, however, are equally warm. A still, calm 

 atmosphere, in summer, feels warm ; but if a wind arises, the 

 same atmosphere feels cold. Xow a thermometer, suspended under 

 shelter, and in a calm place, will indicate exactly the same 

 temperature as a thermometer on which the wind blows. 



11. These circumstance may be satisfactorily explained, when it 

 is considered that the human body maintains itself almost invari- 

 ably, in all situations, and at all parts of the globe, at the tem- 

 perature of 96 ; that a sensation of cold is produced when heat 

 is withdrawn from any part of the body faster than it is generated 

 in the animal system ; and, on the other hand, warmth is felt 

 when either the natural escape of the heat generated is 

 intercepted, or when some object is placed in contact with 

 the body which has a higher temperature than that of the 

 body, and consequently imparts heat to it. The transition of 

 heat from the body to any object when that object has a 

 lower temperature, or from the object to the body when it has 

 a higher temperature, depends, in a certain degree, on the 

 conducting power of the objects severally, and the transition 

 will be slow or rapid, according to that conducting power. An 

 object, therefore, which is a good conductor of heat, if it has a 

 lower temperature than the body, carries off heat quickly, and 

 feels cold ; if it has a higher temperature than the body, it com- 

 municates heat quickly, and feels hot. 



A bad conductor, on the other hand, carries off and communi- 

 cates heat very slowly, and therefore, though at a lower tem- 

 perature than the body, is not felt to be colder, and, though at 

 a higher temperature, not felt to be warm. 



Most of the apparent contradictions which have been already 

 adduced in the results of sensation, compared with thermometric 

 indications, may be easily understood by these principles. 



When we pass from a hot bath into a room of the same 

 temperature, the air, though at a higher temperature than our 

 body, communicates heat to it more slowly than the water 

 because, being a more rare and attenuated substance, a less 

 number of its particles are in actual contact with the body ; and 

 also such particles as are in contact with the body take almost 

 the same temperature as the body, and adhere to it, forming a 

 sort of coating or shield, by which the body is defended from the 

 effects of the hotter part of the surrounding atmosphere. A 

 carpet, being a bad conductor of heat, fails to transmit heat to 



