CONVECTION 63 



when its temperature falls 1 C. So 1 g. of water in cooling from 100 

 C. to C. gives off 100 calories of heat. The same amount is given 

 off when 2 g. of water are cooled from 50 C. to C., and when 10 g. 

 are cooled from 10 C. to C. 



65. Ways of Distributing Heat; Conduction. If a 



flat-iron is placed on a stove, the iron becomes warm, 

 because heat (energy of molecules) from the stove is 

 given to it. If you touch the flat-iron, it gives some of 

 its heat to the hand; hence the iron feels warm. The heat 

 has been conducted, first from the stove to the flat-iron, 

 then from the flat-iron to your skin. But if you hold a 

 piece of ice in your hand, the hand becomes cold, because 

 heat is conducted from your hand to the ice. So the 

 objects you handle are either hot or cold according as 

 they give heat to the hand, or take it from the hand. 



The handle of a flat-iron can still be held comfortably after the 

 bottom is hot; but in a short time the handle, also, is heated by con- 

 duction from the part nearer the stove. To hold it then, we use a non- 

 conducting handle of cloth or of wood. It would take longer to heat 

 a brick from the bottom to the top, because it is a poorer carrier, or 

 conductor, of heat. Metals are the best heat conductors; air is 

 probably the poorest. Water, wood, and paper are poor conductors. 

 Conduction is only one of the ways in which heat is distributed; other 

 ways are by radiation and by convection. 



66. Radiation. If you stand near a stove, you become 

 warm without touching the stove. Heat is radiated to 

 you from the stove. If you are near a block of ice, you 

 become chilled, because your body is radiating heat to the 

 ice. Heat reaches the earth from the sun by radiation 

 through space. 



67. Convection. Convection is not really a new way 



