12th. May. 1856
My dear Tom
Ruhmkorff’s coil1 is a difficult subject for an assembly such as yours. but you might lead them up to it by experiments on induction with the spiral of your magnet. You might shock a large eel in this way. the experiment always produces a fund of amusement – a flounder is also good, but the eel is best. Could you not get a large live eel (say 18 inches long) The extra current might also be shewn, by shewing the influence of the spiral on the strength of the spark when broken in a cup of mercury. The dancing of the spirals through their own attraction is a beautiful experiment – In fact here you have a field open to you of the greatest interest at last – the mutual action of currents and magnets. With regard to the spark of Ruhmkorff a beautiful experiment may be made by connecting the ends with wires which you attach to a handle, and move quickly through the air – the sparks at first continuous are separated into wide intervals by the motion of the wire.
The diminution of the extra current by closing the secondary wire is also a very striking experiment. I don’t think you can be at a loss for material.
I send you a letter from Faraday2 and another from Tommy Grieve.3
Sadly pushed | Yours affectionately | John
I was extremely glad to her of John Martin’s release.4 I saw it as you judged in the Times
RI MS JT/1/T/898
Ruhmkorff’s coil: see letter 1226, n. 8.
A letter from Faraday: probably letter 1224.
Tommy Grieve: a former pupil of Tyndall’s at Queenwood in 1853. The letter is missing. Grieve was possibly Thomas Grieve (b.1845), son of William Grieve (b.1796), a widowed sheep farmer owning 4000 acres at Branxholm Park, Hawick, Roxburghshire, Scotland. See volume 4, letters 0817, 0832, 0887, 0913, 0968, 0977, 0989 and 1011.
John Martin’s release: see letter 1226, n. 4.
Please cite as “Tyndall1227,” in Ɛpsilon: The John Tyndall Collection accessed on