George Gabriel Stokes to Faraday   5 November 1855

69 Albert St Regents’ Park | London Nov 5th 1855

My dear Sir,

I have arranged to read your paper¹ on the day of the first meeting (Thursday the 15th). I intend only to take the first two sections that day and to take the 3rd section the next.

Would you have the goodness to favour Dr. Sharpey² with an abstract of the paper, such as you would wish to appear in the Proceedings?³

I have been thinking over the setting of phosphorus, and it certainly seems to me that a non-crystalline and unstrained elongated diamagnetic body in a perfectly uniform field ought to set along the lines of force. I recollect that Thomson, in the paper in the Cambridge mathematical journal in which he first obtained mathematically the law which you had previously enunciated about going from places of stronger to places of weaker force, stated without demonstration that a sufficiently small elongated body whether paramagnetic or diamagnetic would set along the lines of force⁴. Such I imagine ought to be the way in which an elongated piece of phosphorus would set in an absolutely uniform field. That such a set is not observed in experiment is I think no valid argument against the theoretical conclusion. For even if we could obtain a mathematically uniform field the setting force would be so excessively small that it seems doubtful whether it could be experimentally observed, and the field between flat poles is demonstrably not mathematically uniform. The setting force arising from any deviations from uniformity in the field would depend on the first power of the inductive capacity of the substance, whereas the setting force in a perfectly uniform field would depend upon its square, and would be as nothing in comparison with the former, the inductive capacity of all diamagnetics being very small. Could a diamagnetic be discovered at all approaching in inductive capacity to soft iron I suppose the setting along the lines of force could be easily observed.

Believe me | Yours very truly | G.G. Stokes

Endorsed by Faraday: Par. 2812. 2813. Exp Res⁵