6 IN STARRY REALMS. 



object to pour forth its heat by radiation, and ultimately 

 to cool down to the temperature of the bodies which sur- 

 round it. It thus appears that the dispensing of heat 

 from a body at a high temperature, being essentially of 

 the nature of expenditure, cannot be maintained without 

 the source being in some manner replenished. Even the 

 greatest body, if also the hottest body, only contains a 

 limited and perfectly definite quantity of heat. In the 

 process of cooling a heated object gradually pays out from 

 its stores of heat, until, at last, its temperature approxi- 

 mates to that of the surrounding objects. From that 

 time the radiation ceases to have appreciable amount, or> 

 to speak more accurately, the heat which the body loses is 

 restored by the heat which it receives by the radiation 

 of other objects. No matter how magnificent be the 

 dimensions of the radiating mass, or how exalted be its- 

 temperature, it cannot escape from the application of these 

 principles. It must ultimately cool down and cease to 

 operate as a source of heat to the other objects around. 



It is unavoidable that the sun himself must run his course 

 in accordance with the doctrines we have been here con- 

 sidering. The great source of light and heat cannot escape 

 from the legitimate consequences of continuous expendi- 

 ture. Unless there is some process of restoration by 

 which the results of solar extravagance are neutralised, 

 impoverishment and ultimate exhaustion are inevitable. 

 If, therefore, the sun receives no supply of heat, or of 

 what is equivalent to heat, the time must ultimately arrive 

 when his stores of radiant energy shall have been all ex- 

 pended, and the great globe can then no longer remain 

 as a source of life and light to the worlds which circulate 



