Radiant Heat and Light 



123 



FIG. 60. It is by radiation that we get all our heat and light from 

 the sun. 



Turning off the radiation would cause all these things 

 to happen, because it is by radiation that we get all 

 our heat from the sun and all our light from any source. 

 And it is by radiation that the earth loses heat into space 

 in the night and loses still more heat into space during 

 the winter. 



We do not get our heat from the sun by conduction ; 

 we cannot, because there is nothing between us and the 

 sun to conduct it. The earth's air, in amounts thick 

 enough to count, goes up only a hundred miles or so. 

 It is really just a thin sort of blanket surrounding the 

 earth. The sun is 93,000,000 miles away. Between 

 us and the sun there is empty space. There are no 

 molecules to speak of in that whole vast distance. So 

 if heat traveled .only by conduction, that is, if radia- 

 tion stopped, we should be so completely shut off 



