54 THE EEASOX WHY 



"Hesendeth out his word, and melteth them: he causeth his wind to blow, 

 and the waters to flow." PSALM CXLVII. 



Because their coverings, being non-conductors of heat, preserve 

 the warmth of the bodies of the animals. 



168. How is the greater warmth of animals provided for 

 in the winter ? 



It is observed that, as winter approaches, there comes a short 

 woolly or downy growth, which, adding to the non-conducting pro- 

 perty of their coats, confines their animal warmth. 



Tin small birds during winter, let the external colour of the feathers be 

 what it may, there will be found a kind of Hack down next their bodies. 

 Black is the warmest colour, and thn purpose here is to keep in the heat, arising 

 from the respiration of the animal.] 



169. ILow is warmth provided for in animals that have no 

 such coats ? 



They are furnished with a layer of fat, which lies underneath the 

 skin. Fat consists chiefly of carbon, and is a non-conductor. 



170. Why are summer breezes said to be cool ? 



Because, as they pass over the heated surface of the body, they 

 bear away a part of its heat. 



171. Why is a still summer air said to be sultry ? 

 Because, being heated by the sun's rays, and being a lad 



conductor, it does not relieve the body by carrying off its heat. 



172. Why does fanning the face make it feel cooler? 

 Because, by inducing currents of air to pass over the face, a part 



of the excessive heat is taken up and carried away. 



173. Why docs perspiration cool the body ? 



Because it takes up a part of the heat, and, evaporating, carries 

 it into the air. 



174. Why does blowing upon hot tea cool it ? 



Because it directs currents of air over the surface of the tea, and 

 these currents take up a part of the heat and bear it away. 



175. Why does air in motion feel cooler than air that is 



still ? 



Because each wave of air carries away a certain portion of heat 



