HOW THE HEAT IS KEPT UP. 35 



we may rather anticipate that the character of the sun as 

 a dispenser of heat cannot be eternal. Doubtless the orb 

 of day contains a magnificent supply of either actual heat 

 or potential heat adequate for all the requirements of life 

 for a cycle of ages that must be reckoned by millions of 

 years. It is, however, impossible to overlook the fact that 

 this excessive expenditure must at length produce its 

 natural consequences, and that a bankruptcy of sunbeams 

 is the inevitable destiny of our system. I say inevitable 

 of course with this proviso, that the ordinary conditions 

 of nature as we now find them shall continue to exist. 



Seeing that the sun must ultimately become a dark 

 globe, with no higher temperature than that of the sur- 

 rounding space, it is needless to add that life must ulti- 

 mately vanish from this earth. We, therefore, learn as a 

 simple consequence from the laws of science as we now 

 find them, that the duration of our earth as the abode of 

 organized beings has a term beyond which it cannot 

 extend. 



It would be interesting to inquire whether some con- 

 firmation of these views may not be obtained from other 

 parts of space. We remember that cardinal doctrine of 

 astronomy which asserts that our sun is only a star ; and 

 as there are millions of stars, it is natural to compare the 

 present phase of our sun with the phases through which 

 other suns are passing. We may for the moment liken 

 the development of a sun to the growth of a tree, which, 

 after passing through every grade of youth, of maturity, 

 and of decrepitude, is finally overthrown to return to the 

 dust from whence it came. In a similar way our sun, 

 which is at present at the height of maturity, is destined 



