TRANSFER OF HEAT 83 



In order to explain how heat can be thus transferred, 

 scientists assume that all space is filled with some 

 medium which is very elastic, and they call it the ether. 

 Through this very elastic medium energy may travel at 

 an exceedingly great speed. The energy is supposed 

 to be transferred by the vibrating of the ether. From 

 its source, then, energy may travel through the ether in 

 straight lines ; and this traveling energy is called radiant 

 energy or radiation. It does not heat the ether through 

 which it travels, but upon reaching certain bodies of mat- 

 ter the radiant energy may stop and become changed 

 into heat in those bodies, the degree of heat being greater 

 or less according to the nature of the substance. 



We must understand, of course, that this is only sup- 

 posed to be the method by which heat is radiated. The 

 ether is not a substance that can be seen, felt, or 

 weighed, and it does not conform to our usual ideas of 

 matter. Still, scientists are so very sure that the ether 

 really exists that we have come to accept it as a fact 

 and to discuss its behavior without any doubts or hesi- 

 tation. The source of heat radiation must of course be 

 a heated mass, and in giving off the radiant energy it 

 loses some of its own energy or heat. 



QUESTIONS 



1. In what ways may heat be transferred? 



2. Define conduction. Explain how heat is conducted through 

 a body. What is a conductor? Are solids, liquids, and gases 

 equally good conductors ? Why are wooden handles better than 

 iron for stove lifters ? 



3. Explain the cause of convection. How is it different from 

 conduction ? 



