86 



THE SUN'S GIFT OF HEAT 



much heat from the air and food about it and keeps them 

 cool. It also explains why so much heat is given out when 

 the steam in a steam radiator condenses into water, and 

 why steam heating is the most effective way of heating 

 houses in cold climates. 



Many of us have noticed that when we have a quiet 

 snowfall the temperature usually rises. This is because the 

 heat given out by the changing of the vapor in the air into 

 ^^___^_ snow is not carried by the air currents 



to another region but warms the local 

 atmosphere. Many similar phenomena 

 are explained by this experiment. 



FIGURE 40. COMPAR- 

 ATIVE EFFECTS OF 

 HEAT 



The amount of heat re- 

 quired to change the 

 smaller mass of water 

 into steam without 

 altering its tempera- 

 ture would raise the 

 temperature of the 

 larger volume one 

 degree. 



The Transference of Heat. Some 

 one has stated a truth playfully in 

 saying that " no substance is ever 

 selfish with the heat it possesses." 

 Any hot object left for a long enough 

 time in cooler surroundings will yield 

 up its heat until it is of the same tem- 

 perature as its surroundings. Any cold 

 object placed in warm surroundings 

 will receive heat until it is eventually 

 of the same temperature as its surroundings. 



If water is placed on a hot stove it will absorb heat until 

 it passes away in steam. If hot water is allowed to stand 

 in a room, it will give off its heat until its temperature falls 

 to that of the room. When ice is placed in a refrigerator 

 the heat of the contents of the refrigerator is yielded up to 

 the ice and melts it. If a refrigerator could be so con- 

 structed that no warmth could reach its interior, the contents 

 would eventually become as cold as the ice. 



