From Horace Darwin to G. H. Darwin 24 April 1875

Dear George

I’ve just done the drawing, & the firm will do the job, I asked Anderson yesterday. I have made the support for the indecator longer, & the other suggestions I had made before; I had made the brass for the indecator circular so as to be able to put on 4 pointers: the whole thing will slip in & out of the wooden stand with notches to step over projections in the stand to stop it turning. I think the hot water plan very good. Now I must set to work on ϑ. I cant make up my mind on the best plan. I don’t think that it would do supporting the weight of the planet by the $\frac{1}{\mathrm{r2}}$ cell, at any rate it would want the very best workmanship to make it work; I will think of it. We will try with a long string first.

H Darwin