George Biddell Airy to Faraday   17 February 1854

Royal Observatory Greenwich | 1854 Feb 17

My dear Sir

From time to time I look at your lecture of January 20¹ and reflect thereon.

Page 3 at the bottom², you refer very pointedly to the great extent of surface of the copper wire as producing the striking results, and you do not refer to any other character of the metal. But do you not suppose that the longitudinal extension had much to do with it:- or in plain words that it depended on the wire’s being long and thin? Do you suppose that a set of copper sheets amounting in the aggregate to 8300 square feet would produce the same effect?

As the world is full of sheets of copper, I should think that this experiment might be tried without great expense, if desirable.

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In your lecture you have not adverted to the peculiar character which the galvanic pulse seemed to have acquired at the third galvanometer, namely a double or treble throb lasting in the whole a full second of time. When I was making longitude-signals with Edinburgh we remarked something of the same kind, so that we were induced by what we then saw to extend our interval of certain signals from 2s to 3s in order to avoid confusion. There is always a difficulty in ascertaining the state of force at intervals shorter than or comparable with the time of natural vibration of the needle. Can you devise any thing which will exhibit it for shorter intervals? I conjecture it as quite possible that there is a nascent affection of the same kind at Galvanometer No. 2.

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

Professor Faraday