George Biddell Airy to Faraday   7 June 1854

Royal Observatory Greenwich | 1854 June 7

My dear Sir

Mr. Latimer Clark at my request has been so good as to make experiments on his long lines for the velocities of galvanic currents from batteries of different numbers of cells. This is of some importance to us longitudinarians, because we cannot always be sure that the number of cells at the opposite stations is the same, and our ultimate result would be erroneous to the amount of half the difference of the times of traverse corresponding to the two sets of battery cells.

The result, in a range from 62 to 500 cells, is very satisfactory, that there is no sensible difference of time.

I should not have thought this worth the trouble of your reading, only that pro tanto it seems to shew that there is no real difference depending on intensity in the application to signal communications. I do not mean that there is no difference in other effects.

The velocity in the subterraneous wires is low, somewhere about 1000 miles per second.

I am, my dear Sir, | Yours very truly | G.B. Airy

Professor Faraday | &c &c &c