George Biddell Airy to Faraday   19 May 1847

Royal Observatory Greenwich | 1847 May 19

My dear Sir

We trouble you as a universal referee or character-counsel on all matters of science:- and moreover Sheepshanks¹ has troubled you on this matter before²:- and it is very bad but what else can we do? So throwing myself on your justice or mercy, I will proceed to the business.

We must definitely select a metal for the bar-standard of length. And what is most durable? I incline to hard gun-metal (I cannot at this moment give you the proportions that we have tried, but a very white mixture was found very strong, broke with difficulty, did not bend first, and appeared not likely to oxidate). Sheepshanks has set his heart on a pure metal, believing theoretically (I think) that it is not likely to alter internally.

Now can you help us?

Yours very truly | G.B. Airy

Michael Faraday Esq | &c &c &c