68 HEAT 



If a substance is a good conductor of heat and it is 

 colder than our bodies, it will take heat away from us if 

 we touch it, and we will say that the body is cold. Yet 

 there may be another substance which is just as cold as 

 the first one, but is a poor conductor of heat, and this one 

 will not conduct the heat away from us, and we may say 

 that it is warm. Thus we find that standing with bare 

 feet upon a rug is pleasanter than standing upon the bare 

 floor, or upon an oilcloth. The rug is not a conductor of 

 heat. It is called a non-conductor. Therefore our feet 

 remain warm. The oilcloth, or the bare floor, is a much 

 better conductor of heat and takes it away from our feet 

 and they feel cold. Linen, cotton, and silk feel cold 

 because they are good conductors, while woolen goods 

 and furs feel warm because they are poor conductors of 

 heat. Poor conductors make the warmest clothing. 



If the substance is warmer than we are, and is a 

 jrood conductor, it feels warm because it readily gives 

 its heat to us. A non-conductor does not seern as warm, 

 although it may be. warmer, because it does not conduct 

 the heat to us. Here again we must not trust our sensa- 

 tions but must depend upon a thermometer, if we wish 

 to learn the real temperature of the substance. 



It is not a good plan to stand upon, or sit upon, 

 materials which are good conductors, when they are 

 colder than we are, for they take our heat away and 

 make us cold. Stones are good conductors and many a 

 chill has been caused by sitting upon stone walls. 



If heat is not desired it may be kept out by the use 

 of non - conductors. For this reason milk cans are 

 wrapped in jackets to keep out the heat of the sun on hot 

 days. 



