From G. H. Darwin   25 April 1876

My dear Father,

I hope poor Henrietta will have got well eno’ to allow of your coming up to London & after Mother’s letter of yesterday I write to London on spec^’. Poor old mother too seems to have been baddish by what she says, but I hope she’s mended again now.¹ There’s no external news that I know of, but I’m bursting with delight at my work of the last few days. I’ve been thinking day & night over Evans’ suggested problem about the alteration in the axis of the earth.² After long thought I have got thro’ the hardest part & I think I see exactly what is the mathematical problem involved. What especially delights me is that I feel almost sure now that such an upheaval as he suggests w^d. displace the axis, but at the same time I think it w^d be a very slight displac^t. But if my argument is right there is no reason (except as to probabilities of upheavals taking place in the right places & in sufficient amount) why the pole sh^d.’nt be moved ever so much, & that without the upheavals being piled one on the top of the other, that is to say I conceive that the displaced pole would remain the pole even tho’ the upheaved part were gradually worn away by rivers & sea I have got a good deal of the mathematics down on paper, but there will be some terrible arithmetic to be done.

Altho’ the pole may be displaced in the Earth I don’t yet see what will be the effect on the climate of the earth i.e whether the arctic circle will tend to meet or recede from the tropics   I see however how to attack this question but perhaps the math^cs. will stump me   When I’ve got all of it down on paper—wh. may be some time—I think I shall go & talk to Adams about it, before I grind the arithmetic,—for wh. I hope I shall be able to employ calculators.³

I’m rather counting my chickens before they’re hatched, but I’m regular bursting with ideas on the subject & am at present much elated tho’ doubtless presently I shall get down in the mouth. I thought I never sh^d be able to master the mechanics of it, when the fertilising idea suddenly came into my head yesterday afternoon   There now I’ve let off a little steam, tho’ I confess I can hardly keep my hands & head off the subject.

I’ve not thrown up the pitch by any means but most of my work at that is purely mechanical & consists of getting my hands frightfully dirty.⁴ I don’t think I’m working too hard just now & I’ll try not to—but it wont be easy if all goes on well.

I’m sorry to say my liver is going a little wrong again, because the cold in my head has stopped but still I’m better than Ive been for many months & play tennis very vigorously

Your affec. son | G H Darwin