Julius Plücker to Faraday   28 September 1848

Dear Sir!

Being returned home, I feel it my first duty to thank you for the great kindness, with which you received my [sic], when I came to London¹. I never will forget it, my thank[s] is, believe me Sir, very sincere; so are my sentiments of veneration, but I cant express them in a proper way, and I would not speak in the terms of an English toast at a public dinner. Instigated by the novelty of your discoveries I began, sixteen months ago, my experimental researches. Encouraged by you I'II go on with more pleasure and confidence.

Since a few days I began again to work and I got already some new facts. But, struck by one of your observations, the first thing I did, was to direct my attention to the experiments respecting the different laws of intensity for Magnetism and Diamagnetism. The result has been, that these laws are exactly such as I have stated them. The paradox I pointed out to you plainly disappears. Allow me to give you a short account of it.

To repeat my former experiments, I choosed [sic] a piece of charcoal, a little longer than I did before. It pointed 1) axially with one of Grove's elements, 2) equatorially with seven and 3) was kept an [sic] intermediate fixed position with three elements. The third case is a new conformation of the given law, that by increasing power (and particularly by diminuishing [sic] the distance from the poles) Diamagnetism increases more rapidly than Magnetism.

I thence concluded that a mixture of magnetic and diamagnetic substances might at a greater distance from the poles be attracted and at a smal[l]er distance repulsed by the Electromagnet; and I proved it by a watchglass filled with Mercury and kept by a Magnet at a short distance (one millimetre) from the poles. The conclusion as well as the experiment and its explication are correct. The same experiment may be repeated with a substance showing a very strong Magnetism by suspending it at the balance and increasing the distance from the poles. The experiment, w[h]ich in this case at first struck me very much, proves nothing at all. The tendency of the balance to return to its position of equilibrium acts here like de [sic] diamagnetic force in the original experiment. This tendency increasing more rapidly than the magnetic power, we will have quite the same appearances, even when Diamagnetism had fully disappeared. & Here I have been wrong. The above mentioned experiment with Mercury where the questioned tendency of the balance may be neglected, remaining fully conclusive, nevertheless I thought it proper, to afford new proves. I succeded in different way, using allways my large balance. The following experiment is striking.

I brought a watchglass (being magnetic) over the two poles by suspending it at the balance, and put into it a sphere of Bismuth (12mm diameter). The balance was in a state of horisontal equilibrium and the glass at a distance of 5mm from the poles. The current being produced by one element of Grove, the Glass moved towards a fixed equilibrium at a distance of only 2,mm 5 from the poles; but by using seven elements the movement of the glass towards the poles was nearly insensible. Therefore the magnetic action of the Electromagnet, instead of increasing, by strengthening the power of the current considerably diminishes. The balance being then brought into horisontal equilibrium, the glass with the sphere of Bismuth being at a distance of only 2mm from the poles: with one element there was attraction by Magnetism, with seven elements strong repulsion by Diamagnetism.

In trying this experiment I observed that, even in the case of strong diamagnetic repulsion, at the first moment there was magnetic attraction. This is in full accordance to my views, the fact being produced either by the increasing power of the Electromagnet, after the current has been established, or there being more resistance (wanting more time) in inducing Diamagnetism than in inducing Magnetism.

In a few days I'll send to Mr Taylor the changement [sic] to be made to some numbers of my last paper, happily not yet printed².

I hope my letter will find you in perfect good health | Very truly yours | Plücker

Bonn 28 Sept. 1848

Address: Mr. M. Faraday | &c &c &c | London | Royal Institution