ii LIMIT OF TIME 127 



confronted this demand on time with 

 the calculations of physicists, which limit 

 the number of years since the globe 

 must have been too hot for organic life. 

 I have never myself dwelt on this objec- 

 tion to Darwinism, because I never felt 

 absolute confidence in the calculations 

 of decreasing heat which vary from tens 

 of millions to hundreds of millions of 

 years. Recently, however, Lord Kelvin 

 has placed it on strong grounds of cal- 

 culable certainty that the demands of 

 many geologists on time have been 

 extravagant and impossible. Still, when 

 we get into such high numbers as even 

 twenty millions of years, and such enor- 

 mous margins for possible error, I always 

 feel that we are handling weapons which 

 have no certain edge. But Mr. Spencer 

 now avails himself of the safer alterna- 

 tive when he escapes from the difficulty 

 by throwing overboard altogether the 



