PM to Faraday   July 1832¹

Sir,

From having read in the Proceedings of the [Royal]² Institution your interesting papers on magnetism,* I was tempted to try an experiment, which succeeded beyond my expectations, and which, if tried on a larger scale, I am in hopes would prove very interesting.

I thought that, in place of making use of one powerful magnet, there would be considerably more effect (like in the Voltaic pile) by having a number of smaller magnets, connected with one wire or helix; and also, instead of getting the spark at making or breaking contact, it would be still better to make the instantaneous reversal of the poles the cause. I have contrived to do this in a very simple way; and with a small battery of magnets I have actually decomposed water. You will therefore excuse me for making this communication to you in this manner.

A wheel and axle is connected to a frame, and turned by the handle; a number of magnets (there must not be an odd number) is inserted round this wheel, and firmly secured in their berths, the wheel having spaces cut out to receive them, as shown in fig. 2.; two of the magnets are shown in their place at fig. 1, b b; in the same figure are the lifters, which are secured firmly to a board fast to the frame, as will be shown immediately. In placing the magnets in the wheel, which you perceive are the horseshoe ones, every second magnet is placed differently. If the magnet at No. 1 has the north pole next the edge of the wheel, and the south next the axis, No. 2 has the south at the circumference, and the north at the axis, and so alternately; the ends of the magnets project a little beyond the surface of the wheel. There are as many lifters as magnets, placed firm in a board, exactly to correspond with the wheel, but made firm to the frame, and in such a manner as to permit the wheel to turn readily, so that the magnets will pass close to them. When any one magnet is in contact with a lifter, all the others are the same. In passing the wire round these lifters, care must be taken to make the turns of the helix be reversed in every second lifter, so that the currents of electricity will be all in one direction, although the poles of the magnets are reversed; by connecting the two ends of the wire to guarded points, and inserting them in a small tube containing water, on turning the wheel decomposition will take place rapidly.‑

I put a small projector on the wheel at every magnet, which, on touching a spring, separated the two wires every time; and at the moment the pole was reversed, the spark became visible³. Wishing you success in this very interesting field for discovery,

I am, Sir, | Your very humble Servant, | P.M.

* See Phil.Mag. and Annals, N.S. vol. xi. p. 300, 465⁴. - Edit.