DARWINISM AND OTHER BRANCHES OP SCIENCE. 34? 



(p. 32), depends upon other matters besides sunbeams, so 

 that we must be cautious in any inferences drawn in 

 this way, nor are any such inferences needed for our 

 present purpose. 



But we must not stop in our retrospect at the epoch 

 even of primeval man. We must go back earlier and 

 earlier through the long ages of the geologists, and 

 back still further to the earliest epochs, when life first 

 began to dawn on the earth. Still we find no reason to 

 suppose that the law of the sun's decreasing heat is not 

 still maintained, and thus, as far as our present knowledge 

 goes, we are bound to suppose that the sun must have been 

 larger and larger the further our retrospect extends. I 

 do not say that the rate at which the sun changes its dia- 

 meter was then the same as the four miles per century 

 which is an approximation to its present rate. It is suffi- 

 cient for our purpose that the sun is larger and larger the 

 further we peer back into the remote abyss of the past. 



There was a time when the sun must have been twice as 

 large as it is at present ; it must once have been three 

 times as large ; it must once have been ten times as large. 

 How long ago that was no one can venture to say ; it 

 would be rash to attempt any estimate. But we cannot 

 stop at the stage when the sun was even ten times as large 

 as it is at present ; the arguments we have used will still 

 apply with equal, if not greater, force. And, looking 

 back earlier yet, there was a time when the sun was once 

 swollen to such an extent that the mighty orbit of Nep- 

 tune itself would be merely a girdle around the stupendous 

 globe. At that time the sun must have been a gaseous 

 mass of almost inconceivable tenuity. We are not to 



