1S41-1882] [i E-A< TION 163 



and especially for the MS., without which I should have been Letter 510 

 afraid of making mistakes. If you require it, the MS. shall 

 be returned. Your results have b< en of more use to me than, 

 I think, any other set of papers which I can remember. Sir 

 C. Lyell, who is staying lure, is very unwilling to admit 

 the greater warmth of the S. hemisphere during the Glacial 

 period in the X. ; but, as I have told him, this conclusion 

 which you have arrived at from physical considerations, 

 explains so well whole classes of facts in distribution, that I 

 must joyfully accept it ; indeed, 1 go so far as to think that 

 your conclusion is strengthened by the facts in distribution. 

 Your discussion on the flowing of the great ice-cap south- 

 ward is most interesting. I suppose that you have read Mr. 

 Moseley's 1 recent discussion on the force of gravity being 

 quite insufficient to account for the downward movement of 

 glaciers : if he is right, do you not think that the unknown 

 force may make more intelligible the extension of the great 

 northern ice-cap? Notwithstanding your excellent remarks 

 on the work which can be effected within a million years, 3 I 

 am greatly troubled at the short duration of the world accord- 

 ing to Sir \V. Thomson, 3 for I require for my theoretical 



1 Canon Henry Moseley. "On the Mechanical Impossibility of the 

 Descent of Glaciers by their Weight only." Proc. R. Soc, Vol. XVII., 

 p. 202, 1S69; Phil. Mag., Vol. XXXVII., p. 229, 1869. 



* In his paper "On deological Time, and the probable Date of 

 the Glacial and the Upper Miocene Period'' {Phil. Mag., Vol. XXXV., 

 p 363, 1868), Croll endeavours to convey to the mind some idea of what 

 a million years really is : " Take a narrow strip of paper, an inch broad 

 or more, and 83 ft. 4 in. in length, and stretch it along the wall of 

 a large hall, or round the walls of an apartment somewhat over 20 ft. 

 square. Recall to memory the days oi your boyhood, so as to get some 

 adequate conception of what a period of a hundred years is. Then mark 

 off from one of the ends of the strip one-tenth of an inch. The one-tenth 

 of an inch will then represent a hundred years, and the entire length of 

 the strip a million of years " {foe. cil., p. 375). 



3 In a paper communicated to the Royal Society of Edinburgh, Lord 

 Kelvin (then Sir William Thomson) stated his belief that the age of our 

 planet must be more than twenty million oi years, but not more than 

 four hundred millions of years (Trans. R. i , Vol. XXIII., p. 157, 



1861, "On the Secular Cooling of the Earth"). This subject has been 

 recently dealt with by Sir Archibald Ceikie in his address as President 

 of the Geological Section of the British Association, 1S99 {Brit. A 

 Report, Dover Meeting, 1S99, p. 718). 



