90 HUXLEY 



regard to the known rate of retardation of the earth's 

 rotation, this event occurred not more than one hun- 

 dred million years ago." 



As to the third, physicists are agreed that the main- 

 tenance of the sun's energy is to be explained as due 

 to the heat generated by the falling-in and resulting 

 collision of the particles of matter of which he is 

 composed, involving the shrinkage of his diameter at 

 the rate of two hundred and twenty feet yearly, or 

 four miles per century. Lord Kelvin, admitting that 

 " the estimates are necessarily very vague," is of 

 opinion that " the sun may have already illuminated 

 the earth for as many as one hundred million years ; 

 but it is almost certain that he has not illuminated the 

 earth for five hundred million years." 



Commenting on the indeflniteness of these and the 

 foregoing estimates, Huxley aptly remarks that — 



Mathematics may be compared to a mill of exquisite 

 workmanship, which grinds you stuff" in any degree of 

 fineness, but, nevertheless, what you get out depends 

 on what you put in ; and as the grandest mill in the 

 world will not extract wheat-flour from peascods, so 

 pages of formulae will not get a definite result out of 

 loose data. 1 



But although some mathematicians of lesser calibre 

 thought that Lord Kelvin had conceded too long a 



1 Lay Sermons, p. 216. 



