THE PROBLEMS OF ASTRONOMY. 89 



of nature goes, there is no force in nature which would ever have set it 

 in motion and no force which can ever stop it. What, then, was the 

 history of this star, and, if there are planets circulating' around, what 

 the experience of beings who may have lived on those planets during 

 the ages which geologists and naturalists assure us our earth has 

 existed? Did they see at night only a black and starless heaven? 

 Was there a time when in that heaven a small faint patch of light 

 began gradually to appear? Did that patch of light grow larger and 

 larger as million after million of years elapsed? Did it at last fill the 

 heavens and break up into constellations as we now see them? As 

 millions more of years elapse will the constellations gather together in 

 the opposite quarter and gradually diminish to a patch of ligbt as the 

 star pursues its irresistible course of 200 miles per second through the 

 wilderness of space, leaving our universe farther and farther behind it, 

 until it is lost in the distance? If the conceptions of modern science 

 are to be considered as good for all time — a point on which I confess to 

 a large measure of scepticism — then these questions must be answered 

 in the affirmative. 



Intimately associated with these problems is that of the duration of 

 the universe in time. The modern discovery of the conservation of 

 energy has raised the question of the period during which our sun has 

 existed and may continue in the future to give us light and heat. Mod- 

 ern science tells us that the quantity of light and heat which can be 

 stored in it is necessarily limited, and that, when radiated as the sun 

 radiates, the supply must in time be exhausted. A very simple calcu- 

 lation shows that were there no source of supply the sun would be 

 cooled off in three or four thousand years. Whence, then, comes the sup- 

 ply? During the past thirty years the source has been sought for in a 

 hypothetical contraction of the sun itself. True, this contraction is 

 too small to be observed. Several thousand years must elapse before 

 it can be measurable with our instruments. Granting that this is and 

 always has been the sole source of supply, a simple calculation shows 

 that the sun could scarcely have been giving its present amount of 

 heat for more than twenty or thirty millions of years. Before that time 

 the earth and the sun must have formed one body, a great nebula, 

 by the condensation of which both are supposed to have been formed. 

 But the geologists tell us that the age of the earth is to be reckoned 

 by hundreds of millions of years. Thus arises a question to which 

 physical science has not been able to give an answer. 



The problems of which I have so far spoken are those of what may 

 be called the older astronomy. If I apply this title it is because that 

 branch of the science to which the spectroscope has given birth is 

 often called the new astronomy. It is commonly to be expected that a 

 new and vigorous form of scientific research will supersede that which 

 is hoary with antiquity. But I am not willing to admit that such is 

 the case with the old astronomy, if old we may call it. It is more 



