CHAPTER XIII 

 CONDUCTION AND RADIATION 



76. Transference of Heat. Whenever a body is placed in 

 surroundings cooler or warmer than itself, a transference of 

 heat at once begins, the warmer object giving up its heat to 

 the cooler ones until all are of the same temperature. Ice 

 placed in the refrigerator begins at once to melt, withdrawing 

 the heat for this change of state from the contents of the re- 

 frigerator and so cooling it. - On the other hand, a hot piece 

 of iron brought into a room will warm it by giving off its sur- 

 plus heat. After a body and its surroundings have reached 

 a uniform temperature, however, no further transference of 

 heat takes place until some new difference in temperature 

 causes it to begin again. Heat, though a form of energy and 

 not of matter, seems thus to act like water and other liquids, 

 flowing from a higher to a lower level until an exact balance 

 is reached. Such a balance, however, is seldom long undis- 

 turbed. The earth daily receives an immense amount of heat 

 upon that part of its surface which is turned toward the sun 

 and as regularly loses it from the parts upon which the sun 

 does not shine. Combustion and oxidation add a share to 

 the change of temperature which matter undergoes, hot and 

 cold winds make new distributions of heat necessary, and 

 various other causes contribute to the almost ceaseless changes 

 that take place in the temperature of matter. 



76. Conduction. One important way in which a body may 

 lose heat to, or absorb heat from, another is by actual contact, 

 as when water is boiled by being placed on a hot stove. The 

 heat, that is, the motion of the molecules, is conducted directly 



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