William Whewell to Faraday   30 January 1853

Trin. Lodge, Cambridge | Jan. 30, 1853

My dear Dr Faraday,

As I expected, a single line¹ from you has turned my darkness into day. I ought never to have been so dark; and I believe I had formerly understood you better; but I have not attended to such subjects for a long time; and turning to them again for a few hours, I found myself in a puzzle of which you had the result, and which is now quite dissipated. I think, at the same time, that it may be useful to others of your readers that you should draw some figures in which you delineate the currents inside the magnets; for readers are much led by the eye. To explain my getting into such perplexity, I may say that I have been generally in the habit of thinking of your curves as identical with the old magnetic curves, which only give the active part of the curves. Also, when I gave you the word sphondyl ² I thought rather of a solid generated by the revolution of this figure

than this.

though the word may describe either. The sphondyl is in fact an annulus described by the revolution of a closed curve round an axis.

You will find a calculation of the properties of the magnetic curve, besides the places you have mentioned, in Leslie’s³ Geometrical Analysis (1821)⁴ but undoubtedly I have seen it in much older books.

With regard to Newton’s views of lines of force, I have given some account of them, as well as of other ways of expressing gravity, in the Philosophy of the Inductive Sciences. B. III. Ch. IX, Sect. 7⁵[.]

I know that you try carefully to keep yourself free from all assumptions as to the mode and machinery of the actions which you investigate: but I think the incautious followers of the same line of speculation may run into something very like Descartes’⁶ system of vortices ⁷. I do not at all mean that because it is a system of vortices it must be wrong; but if it be that it must be an assumption which requires a good deal of proof.

Believe me dear Dr Faraday | Yours very truly | W. Whewell