36 OTHER FACTS ABOUT HEAT 



necessary for the evaporation of the cologne and water was 

 taken from the air, leaving it slightly cooler. If wet hands 

 are not dried with a towel, but are left to dry by evaporation, 

 heat is taken from the hand in the process, leaving a sensa- 

 tion of coolness. Damp clothing should never be worn, be- 

 cause the moisture in it tends to evaporate at the expense of 

 the bodily heat, and this undue loss of heat from the body 

 produces chills. After a bath the body should be well rubbed, 

 otherwise evaporation occurs at the expense of heat which 

 the body cannot ordinarily afford to lose. 



Evaporation is a slow process occurring at all times ; it is 

 hastened during the summer, because of the large amount of 

 heat present in the atmosphere. Many large cities make use 

 of the cooling effect of evaporation to lower the temperature 

 of the air in summer; streets are sprinkled not only to lay 

 the dust, but in order that the surrounding, air may be cooled 

 by the evaporation of the water. 



Some thrifty housewives economize by utilizing the cooling 

 effects of evaporation. Butter, cheese, and other foods sensi- 

 tive to heat are placed in porous vessels wrapped in wet 

 cloths. Rapid evaporation of the water from the wet cloths 

 keeps the contents of the jars cool, and that without expense 

 other than the muscular energy needed for wetting the cloths 

 frequently. 



27. Rain, Snow, Frost, Dew. The heat of the sun causes 

 constant evaporation of the waters of oceans, rivers, streams, 

 and marshes, and the water vapor set free by evaporation 

 passes into the air, which becomes charged with vapor or is 

 said to be humid. Constant, unceasing evaporation of our 

 lakes, streams, and pools would mean a steady decrease in 

 the supply of water available for daily use, if the escaped water 

 were all retained by the atmosphere and lost to the earth. 

 But although the escaped vapor mingles with the atmosphere, 



