INTERVENTION OF PHYSICISTS 185 



himself with the reflection that after all a hundred 

 millions of years was a tolerably ample period of time, 

 and might possibly have been quite sufficient for the 

 transaction of all the prolonged sequence of events 

 recorded in the crust of the earth. He was there- 

 fore disposed to acquiesce in the limitation thus 

 imposed upon geological history. 



But physical inquiry continued to be pushed for- 

 ward with regard to the early history and the antiquity 

 of the earth. Further consideration of the influence 

 of tidal friction in retarding the earth's rotation, and 

 of the sun's rate of cooling, led to sweeping reduc- 

 tions of the time allowable for the evolution of the 

 planet. The geologist found himself in the plight of 

 Lear when his bodyguard of one hundred knights 

 was cut down. * What need you five-and- twenty, ten, 

 or five ? ' demands the inexorable physicist, as he 

 remorselessly strikes slice after slice from his allowance 

 of geological time. Lord Kelvin is willing, I believe, 

 to grant us some twenty millions of years, but Pro- 

 fessor Tait would have us content with less than ten 

 millions. 



In scientific as in other mundane questions there 

 may often be two sides, and the truth may ultimately 

 be found not to lie wholly with either. I frankly 

 confess that the demands of the early geologists for 

 an unlimited series of ages were extravagant, and 

 even, for their own purposes, unnecessary, and that 

 the physicist did good service in reducing them. It 

 may also be freely admitted that the latest conclusions, 

 from physical considerations of the extent of geological 

 time, require that the interpretation given to the record 



