ARGUMENTS FROM PHYSICS 207 



present time is in direct opposition to the principles 

 of natural philosophy/ 1 In pressing once more the 

 original argument derived from the downward increase 

 of terrestrial temperature, he now reinforced it by two 

 further arguments, the one based on the retardation 

 of the earth's angular velocity by tidal friction, the 

 other on the limitation of the age of the sun. 



These three lines of attack remain still those along 

 which the assault from physics is delivered against the 

 strongholds of geology. Lord Kelvin has repeatedly 

 returned to the charge since 1868, his latest contri- 

 bution to the controversy having been pronounced two 

 years ago. 2 While his physical arguments remain the 

 same, the limits of time which he deduces from them 

 have been successively diminished. The original maxi- 

 mum of 400 millions of years has now been restricted 

 by him to not much more than 20 millions, while 

 Professor Tait grudgingly allows something less than 

 10 millions. 3 



Soon after the appearance of Lord Kelvin's indict- 

 ment of modern geology in 1868, the defence of the 

 science was taken up by Huxley, who happened at 

 the time to be President of the Geological Society 

 of London. In his own inimitably brilliant way, half 

 seriously, half playfully, this doughty combatant, with 

 evident relish, tossed the physical arguments to and 

 fro in the eyes of his geological brethren, as a barrister 

 may flourish his brief before a sympathetic jury. He 



1 Trans. Geol. Soc. Glasgow, vol. iii. (February, 1868), pp. I, 16. 

 2 ' The Age of the Earth/ being the Annual Address to the 

 Victoria Institute, June 2, 1897. Phil. Mag., January, 1899, p. 66. 

 3 Recent Advances in Physical Science, p. 1 74. 



