My dear Father,

I must write a line to say that the great mare’s nest of which I wrote turns out wonderfully.² I have worked it with care & today I got to the arithmetic; I was so tremendously excited I really could hardly finish it, but I have done so & been thro’ it again, & I find that when the earth had half its present density (assuming the nebular hypoth)³ that it was spinning at an obliquity of 15^o instead of 23^o28′.

Now this fits in wonderfully with a lot of things I have thought of, but wh. are too long to tell. Amongst the things to wh. it will lead are the classification & explanation of the various planets according to their obliquities— this will in fact be almost the experimentum crucis⁴—a rough approximation to the date of the solidification of the earth, & some faint idea of the temperatures of the various planets   You may imagine with all this seething in me that I’m pretty excited.

Adams was very kind about reading my other paper & I took it to him yesterday, & of course I shall get him to look at this.⁵

It’s really too tremendous a discovery to be true & I can’t believe it.

I hope Frank’s Teazle discovery will go on well, & it sounds very interesting.⁶

I was very much interested to read Paget’s letter, & it shows what a very severe accident it was, but it’s a great comfort to hear that he thinks it will be all right with care. I’m afraid poor old Billy will find life rather a bore for the next few months⁷

I am going up to London tomorrow to see the machine⁸ but am coming down again at night. I’m wonderfully strong now & you see I can work now, but I’m not well by a long way yet

Y^rs affectionately | George Darwin

Of course I’d made a mistake wh. makes it rather less astound^g but the rest remains good