CHAPTER II. 



EXPENDITURE AND SUPPLY. 



NOTWITHSTANDING the sun's great mass and immense store 

 of heat, it cannot escape from the application of those 

 familiar laws of cooling that would be observed in a red- 

 hot poker when taken from the fire, or in a freshly- run 

 casting when drawn from its mould in the foundry. The 

 larger the body the longer is the time it will require 

 before it becomes cold. A knitting needle heated red-hot 

 and withdrawn from the fire will become cold in a few 

 minutes. An iron rail, after it has been drawn red-hot 

 through the rolling-mill, may remain hot for an hour. 



Our first surmise might be that the luminary is 

 simply a vast white-hot body, glowing with incandescence 

 and parting with its heat in accordance with the ordinary 

 laws of cooling. On this supposition the fact that the 

 abatement in sun heat was not perceptible in historic 

 times might be accounted for in consequence of the 

 immense size of the body. Suppose, for instance, the sun 

 were merely a globe of white-hot iron pouring forth its 

 heat, could we then explain the maintenance of its radia- 

 tion for so many thousand years at the same rate as at 

 present ? 



