CHAPTER XIV 

 HEATING BUILDINGS 



69. Transmission of Heat. (a) Radiation is the 

 process of transferring heat in straight lines through 

 space without the aid of ordinary matter or material. 

 All of us have had the common experience of standing 

 near a hot stove or open fire in a grate, or near a steam 

 or hot water radiator, and receiving the heat directly. 

 If we stand near an open fire in a cool room, the part of 

 the body toward the fire will be warm while the opposite 

 side will feel cold. If two persons stand near an open 

 fire one behind the other, the one in front next to the fire 

 will receive the heat while the one behind will be cold. 

 If an object is placed between us and the fire or radiator, 

 the object reflects and absorbs the heat and we do not 

 get any. If we stand in the shade of a tree in summer 

 we do not feel the hot rays of the sun. All of these 

 suggested experiences show that heat radiated from a hot 

 object travels in straight lines, and many good authorities 

 think that it travels as fast as light, namely 186,000 miles 

 per second. The heat from the sun comes to the earth 

 by radiation. Radiant heat passes through air without 

 heating it, so the upper part of the atmosphere is cold. 

 The lower atmosphere is heated by the air coming in con- 

 tact with the surface of the earth and with things on it. 

 We can get warm standing before an open fire even if the 

 air is moving past us toward the fire, because the radiant 



