192 IN STARRY REALMS. 



them, can possibly be adequate to evaporate enough fluid 

 on Jupiter to give rise to that vast mass of clouds which 

 surrounds him. More clouds require for their explana- 

 tion a larger supply of heat than that on the earth. Yet 

 the sun only conveys to the great planet less than four 

 per cent, of the heat on the same area that he sends to us. 

 There is only one interpretation to be put on these facts. 

 We must admit that the sun's heat is utterly inadequate 

 to the accomplishment of the work in progress on Jupiter, 

 and hence we must look to the presence of some other 

 source of heat. 



Whence can Jupiter derive heat if not from the sun ? 

 Assuredly there is no other body in the universe which 

 can radiate even the millionth part of what he gets from 

 the sun. The stars are no doubt hot enough, but they 

 are so enormously distant that the influence of their heat 

 is evanescent, and need not for a moment be considered. 

 The other planets and their satellites can of course render 

 no assistance. Like Jupiter himself, they are recipients 

 of heat from the sun in varying degrees, according to 

 their distance. The only heat they can dispense will be 

 of the very feeblest, and be quite imperceptible. It i& 

 certainly true that Jupiter cannot receive heat from any 

 external body to any appreciable extent, except from the 

 sun, and yet the utmost that the sun can do is quite inade- 

 quate to account for the warmth of the great planet. 



At first it might be thought that we had arrived at a 

 paradox, but this is not really so. There is a most 

 rational explanation of the phenomenon entirely consi^ 

 tent with all the facts. 



There are many reasons for knowing that the diffeient 



