42 HEAT. 



power of the glass, mentioned in the last paragraph. 

 But this absorbing power is very slight for heat which 

 comes from an intense source like the sun, so that such 

 mirrors reflect the solar heat quite perfectly. 



82. ABSORPTION OF HEAT. Surfaces are 



What bodies 



absorb heat good absorbers, in proportion as they are 

 poor reflectors. All the heat that falls on 

 any surface, must be either reflected or absorbed. In 

 proportion, therefore, as little is reflected much is ab- 

 sorbed. 



83. ABSORPTION CONTINUED. Dark cloth- 



What effect /-,, > r 



has color on ing is warmer than that of light color, for 



the warmth of ^ reason t fr a t heat associated with light 



clothing ? 



seems to follow the laws of the latter and 

 undergo absorption or reflection with it. Now we know 

 that dark objects owe their dark color to the fact that they 

 absorb much light, and reflect but little to the eye. Ex- 

 periment shows that they absorb much heat also, if the 

 heat be associated with light. The absorbed light must 

 show the way, as it were, for the entrance of the heat. 

 Dr. Franklin proved what has been stated, by the ob- 

 servation that when different colored cloths are spread 

 upon snow, it melts most rapidly under those which are 

 darkest. 



84. EQUILIBRIUM OF TEMPERATURE. 



How is equili- 



brium of tem- It has before been stated that heat is con- 

 ^11^ Stantl 7 radiated from all bodies. Absorp- 

 tion of heat, is also universal. If any num- 

 ber of bodies are equally hot, they remain so, each ac- 

 cording to its surface, imparting to the rest and receiv- 

 ing from all the rest, taken together, the same quantity 



