From G. H. Darwin to Horace Darwin 16 February [1875]

Dear G.

I send you a joint. I think it is good; in case you want to make one I will tell you how I did it; the card is part of a mount for a photograph; in order to make any thing of much good the card must be nearly as thick as this I think.

The bits of copper are what are used in boat building for ribeting the copper nails over. I cut out a washer of a visiting card to put between the cards, with a pen sweep. I cut the pin off very near the card with a pair of scissors. I used the tongues as an anvil put between my knees, and first I tried riveting with the back of a carvin knife, and that would not do well, as the square edges cut off bits of the pin, then I tried a carving fork which did well, any thing would do it if had two sharp edges.

I have begun the copper cell.

If you think of making your machine in card I will rivet it up if you like; but I cant get thick card here, so you must cut out & send me the card.

Yours | H Darwin

[DIAG HERE] [WITH TRIGONOMETRICAL EQUATIONS]