174 SCIENCE OF COMMON THINGS. 



Wind generally feels cool Utility of black kettles. 



liumtmface) each volume of air carries off some portion 

 of its heat. 



1138 Does a fan cool the air f 



No ; it makes the air hotter by imparting to it the 

 heat out of our face / but it cools our face by transfer- 

 ring its heat to the air. 



1139 How does fanning the face increase the heat of the air f 



By driving the air more rapidly over the human 

 body, and causing it, consequently, to absorb more heat. 



1140 If fanning makes the air hotter, why can it make a person feel 

 cooler f 



Because it takes the heat out of the face, and gives 

 it to the air. 



Why does wind generally feel cool f 



Because it drives the air more rapidly over our body, 

 and this rapid change of air draws off a large quantity 

 of heat. 



114S Why does air absorb heat more quickly by being set in motion f 



Because every fresh gust of air absorbs a fresh por- 

 tion of heat ; and the more rapid the succession of 

 gusts, the greater will be the quantity of heat absorbed. 



1143 If the air were hotter than our body would the wind feel cool f 



No ; the air would feel insufferably hot, if it were 

 hotter than our body. 



1144 Why would the air feel intensely hot, if it were warmer than our 

 body f 



Because it would add to the heat of our body, instead 

 of diminishing it. 



1145 Is the air ever as hot as the human body f 



In the extreme of summer the temperature of the 

 air sometimes exceeds the natural temperature of the 

 body ; and when that is the case, the heat is almost 

 insupportable. 



1146 Why does a kettle boil faster when the bottom and sides are 

 fovered wiih soot f 



Because the black soot absorbs heat very quickly from 

 the fire, and the metal conducts it to the water. 



