$46 IN STARRY REALMS. 



Darwin has worked out one of the most splendid details 

 in the history of the universe. His methods and his 

 theory have intimate connections with other branches of 

 science, and some of these it is our object to consider in 

 this chapter. In particular I propose to sketch the posi- 

 tion which the Darwinian theory occupies with reference 

 to a celebrated branch of astronomical speculation. 



One hundred years ago the diameter of the sun was pos- 

 sibly four miles greater than it is at present. One thousand 

 years ago the diameter of the sun was forty miles greater 

 than it is at present. Ten thousand years ago the diameter 

 of the sun was 400 miles greater than it is now. The 

 advent of man upon the earth took place no doubt a long 

 time ago, but in the history of the earth the advent of 

 man is a comparatively recent phenomenon. Yet it seems 

 certain that when man first trod our planet, the diameter 

 of the sun must have been many hundreds, perhaps many 

 thousands, of miles greater than it is at present. We 

 must not, however, overestimate the significance of this 

 statement. The diameter of the sun is at present 860,000 

 miles, so that a diminution of 10,000 miles would be little 

 more than the hundredth part of its diameter. If the 

 diameter of the sun were to shrink to-morrow to the extent 

 of 10,000 miles, the change would not be appreciable to 

 common observation, though even a much smaller change 

 would not elude delicate astronomical measurement. The 

 world on which the primitive man trod was certainly 

 illuminated by a larger sun than that which now shines 

 upon us. It does not necessarily follow that the climates 

 must have been much hotter then than now. The ques- 

 tion of warmth, as we have seen in a previous chapter 



