My dear Sir

Tomorrow I will return registered your book, which I have kept so long.

I am most sincerely obliged for its loan, & especially for the MS. without which I sh^d have been afraid of making mistakes.²

If you require it the M.S shall be returned. Your results have been of more use to me than I think any other set of papers which I can remember.

Sir C. Lyell who is staying here is very unwilling to admit the greater warmth of the S. hemisphere during the glacial period in the N;³ 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 I go so far as to think that your conclusion is strengthened by the facts in distribution.⁴ Your discussion on the flowing of the great ice-cap southward is most interesting.⁵

I suppose that you have read Mr Moseley’s recent discussion on the force of gravity being quite insufficient to account for the downward movement of glaciers:⁶ 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, I am greatly troubled at the short duration of the world according to Sir W. Thompson, for I require for my theoretical views a very long period before the Cambrian formation.⁷ If it w^d not trouble you I sh^d like to hear what you think of Lyell’s remarks on the magnetic force which comes from the sun to the earth; might not this penetrate the crust of the earth & then be converted into heat.⁸ This w^d give a somewhat longer time during which the crust might have been solid; & this is the argument on which Sir W. Thompson seems chiefly to rest. You seem to argue chiefly on the expenditure of energy of all kinds by the sun, & in this respect Lyell’s remark wd have no bearing.

My new edition of the “origin” will be published, I suppose in about two months, & for the chance of y^r liking to have a copy, I will send one.⁹

With my very sincere thanks for all your kind assistance | I remain | yours very faithfully | Charles Darwin

I wish that you would turn your astronomical knowledge to the consideration whether the form of the globe does not become periodically slightly changed, so as to account for the many repeated ups & downs of the surface in all parts of the world.— I have always thought that some cosmical cause would some day be discovered