FRICTION. 101 



Q. Why is a mountain-top COLDER than a 

 valley, " because the AIR there is LESS HEATED by 



REFLECTION ?" 



A. Air is not heated by the sun, but 

 by reflection from the surface of the earth; 

 and as there is no earth round a mountain- 

 top to reflect heat, therefore the air there 

 is intensely cold. 



Q. Why does RUBBING our HANDS and FACES 

 make them feel WARM? 



A. Chiefly because the friction ex- 

 cites the latent heat of our hands and 

 faces, and makes it sensible to our feel- 

 ing. 



Q. When a man has been almost DROWNED, 

 why is suspended animation RESTORED by RUBBING? 



A. The vital heat of the body (which 

 had become latent by the action of the 

 water) is again developed by friction : 

 and, as soon as this animal heat can be 

 excited, the vital powers of the body are 

 restored. 



Q. Why do two pieces of ICE ( 'rubbed together) 



MELT 



A. Ice contains 140 degrees of latent 

 heat, and (when two pieces are nibbed 



K3 



