SCIENCE OF COMMON THINGS 143 



Man only lives in all climates. Communication of heat. 



an extent as to vary the covering in the same animal 

 according to the climate and season. 



914 What one species of organized beings is fitted to live in all climates ? 



jbfan alone is capable of living in all climates, and of 

 migrating freely to all portions of the earth. 



CHAPTER IY. 



HOW HEAT IS COMMUNICATED. 



915 In what three ways may heat le communicated ? 



By direct contact, by conduction and convection, 

 by radiation. 



916 How may heat be communicated by contact f 



"When a hot body touches a cold one, the heat passes 

 directly from one into the other, as when it enters a bar 

 of iron put into the fire, or the hand immersed in hot 

 water. 



917* When is heat communicated by conduction f 



When the heat travels from particle to particle of 

 the substance, as from the end of the iron bar placed 

 in the fire to that part of the bar most remote from the 

 fire. 



91S When is heat communicated by radiation f 



"When the heat leaps, as it were, from a hot to a cold 

 body through an appreciable interval of 'space, as when 

 a body is warmed by placing it before a fire removed 

 to a little distance from it. 



919 In ivhat way does a heated body cool itself? 



first, by giving off heat from its surface, either by 

 contact or radiation, or both conjointly / and, secondly, 

 by the heat in its interior passing from particle to par- 

 ticle by conduction through its substance to the surface. 



