James David Forbes to Faraday   13 April 1832

Greenhill Edinburgh | 13th April 1832

My dear Sir

I felt so extremely interested in your fine experiment in Electro-Magnetism that on my return to Scotland¹ I could not resist immediately repeating them which I did with entire success.

I have now the satisfaction of informing you that I have obtained repeatedly & before witnesses sparks from a natural magnet. I first got a spark so far back as the 30th of March but as it was only once & from a want of coinciding circum‑stances which I did not then understand I could not repeat it, & I therefore declined giving any account of it. Believing then that it would be impracticable to obtain it with any degree of certainty at pleasure from a momentary current of magnetism I constructed an apparatus for producing a continuous current, which failed from a peculiarity in the construction which I have since met with a parallel of & which puzzles me a good deal; perhaps in another letter I may trouble you with some questions about it.

Driven back to the original simplicity of my apparatus, I availed myself of a set of experiments I had in the meantime made to determine the con‑ditions under which a spark could easiest be obtained from weak galvanic currents of low intensity. Today I am happy to say I have obtained numerous sparks. The mode in which I proceeded was the following. I had prepared a helix of copper wire about 7 inches long & containing about 150 feet of copper wire (I had one with double that length). A soft iron canister which I had properly adapted to the poles of a very large natural magnet belonging to Dr. Hope professor of chemistry here was made to traverse its axis & the magnetic current was created by making the contact with the poles of the magnet. The excellence of the contact proved to be of essential impor‑tance. One end of the helix wire was terminated in a cup of mercury whilst the other was connected with an Iron wire one end of which was brought to a fine point & was capable of being brought at pleasure in contact with the surface of the mercury in this cup. I devised the means of bringing the canister with speed & accuracy up to the magnet in the dark which an assistant did at my direction at the instant in which I broke the connection of the circuit formed at the junction of iron point with the mercury I found the instant of breaking better than that of making the circuit, & that it was more efficacious at the sides of the mercurial curved surface than in the centre². Perhaps you will favour me by informing me how the information of Nobili's Experiment published in the Literary Gazette³ came to this country & also if you know how he performed it. I have not heard of it except as a rumour, I think from yourself. I cannot help again expressing the strong sense I feel of the liberality with which you have put your fine experiments into the hands of the Scientific world at so early a period. Will you have the kindness to communicate my result to Christie & any one else who may be interested in it: & believe me my dear Sir yours very sincerely James D. Forbes

Address: Michael Faraday Esq | Royal Institution | Albemarle Street | London