Julius Plücker to Faraday   30 April 1849

Sir!

I received your kind letter¹, by which you announce to me your last paper²; I am very anxious to get it and will read it, with the greatest attention.

The new facts I alluded to in my last letter³ are the following ones. Since my first experiments I was convinced, that there ought to be an influence of Magnetism on crystallisation and I expected, that any salt crystallising slowly between the poles of a strong magnet, would have its optical axes perpendicular to the line joining the two poles. Having tried in vain to prove it experimentally I did not speak about it. But when I repeated your last experiments with bismuth, I thought this metal exce[e]dingly proper, to be subjected to the former experiments, and this time I had a full success. Melted bismuth, crystallising slowly between the poles of a strong Magnet gets such a crystalline structure that the chief cleavage plan[e] becomes perpendicular to the line joining the two poles. I prove the same, even without cleaving the crystallized bismuth, by the following experiment. A piece of bismuth, crystallised between the two poles, takes, whatever may be its shape, when suspended in such a way, that it may turn freely round a vertical axis allways and exactly (according to the magnecrystallic action) the same position it had during the crystallisation.

This result proves strikingly that the force acting on the magnecrystallic axis (and also I think on the optic axes) is a molecular one. That has been allways my opinion.

All my experiments confirm that this force produces, as you call it an effect of position only and not an effect of place[.] When I say “repulsion of the optical axes” as I may say “attraction of the magnecrystallic one” I meaned only to explain the facts, without anticipating any conception about the nature of the acting forces.

About the 20th of March I gave my paper to Poggendorff⁴, as soon as I get a copy of it, I’ll send it to you by post.

Since I have been at Paris. Tired by lectures & a “changement d’air” was necessary for my health. Being restored by travelling, I’ll find time to go on in my researches, even, I may say, in spite of the government, which does not at all favour them.

Yours very sincerely | Plücker

Bonn 30th of April | 1849

Address: Professor Faraday | &c &c &c | Royal Institution | London