William Thomson to Faraday   7 November 1859

2 College, Glasgow | Nov 7, 1859

My dear Sir

The diagrams were drawn for you¹ by Clerk Maxwell but they chanced to be addressed by Mr. Macfarlane, my assistant, whose hand is often mistaken for mine. They were left for him to look at for a day at Aberdeen², as he had been engaged in drawing some similar sets of curves to illustrate atmospheric electricity.

I now send you two of them which show the lines of atmospheric force in the neighbourhood of elevations and depressions of various forms[.]

If you cover the lower part of No <³> placed with “Air” up, with the piece of white paper marked “Earth”, you will see what I said regarding the semicircular mound. If you take the same diagram with one of the sides up, and cover the lower part with the piece of paper with the curved indentation, placing it in the position indicated by the marks <plusdots> and *, you will see the aërial field of electric force over a ravine.

If you cover the central circle of the same diagram with the circle of paper, placing the two points which are marked on one side of it in the positions in which curves meet making angles outside the circle, you will see the lines of force about a conducting cylinder insulated in a uniform field of electric force. The curves cutting those lines of force at right angles, are the lines of flow of water meeting and bending round a cylinder held perpendicular to the stream: or the lines of magnetic force about a cylinder of infinitely diamagnetic substance placed in a uniform field of magnetic force.

I showed the corresponding set of diagrams for a sphere, instead of a cylinder, at the meeting of the British Assn. at Belfast in 1852.

If you cover part of No 2 with the paper marked “Tableland” &c in the manner indicated, you will see the lines of force over a piece of stratified sea coast, with land rising vertically and sloping up to a level according to a regular curve. The same diagram turned the other way shows lines of force over a straight mountain ridge, or elevated mound, of the form shown in section by the marked curve.

All these illustrations are applicable only when there are no electrified clouds or masses of air in the neighbourhood.

I must ask you to pardon me for troubling you with all this, which I do only because, from your letter, I thought you might be interested in illustrations of atmospheric electricity[.]

If you desire it I shall send you all the other diagrams immediately, or I shall bring them with me to give you the first time I have an opportunity of seeing you.

To myself it would be a great pleasure, although accompanied with not a small degree of anxiety, to have the prospect of giving a lecture on Atmospheric Electricity to the Royal Institution⁴. My time during the session of the College here is engaged with scarcely any interval long enough to allow me to undertake anything at a distance, before May. If however it should be desired that I should lecture on Atmospheric Electricity on one of the evenings after the 1st. of May, I shall be willing to do so.

I shall not omit to let you know as soon as possible how I succeed in the way of reflecting electrometers. I hope soon to have one ready to try.

I heard of you yesterday from Mr. Crawford, and was sorry to learn that you had suffered from the rough work in the Channel⁵. I hope now you are feeling quite well again.

With kind regards in which Mrs. Thomson joins, I remain,

Yours very truly | William Thomson