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From the 1841 edition of the Manual of Magnetism: "In [the figure] a double helix is seen attached horizontally to the base-board by two brass bands. In the centre a bundle of soft iron wires is permanently fixed. There are two cups for the battery wires at one end of the stand; one of these is connected with the brass cup [at the right] for containing mercury. To the other cup is soldered one end of the coarse wire coil [the primary coil], the other extremity of which is connected with the brass cup [at the left], also intended to hold mercury, is fixed. A bent wire, moving on a horizontal axis supported by two pillars, dips its ends into the two mercury cups. To the opposite side of the axis is attached a curved piece of iron, the lower extremity of which approaches nearly the end of the enclosed bundle of iron wires.
When the connections are made with the battery, the current will traverse the [horizontal wire] and the inner helix, causing the iron wires to become magnetic. They will now attract the end of the iron rod; whose motion raises the bent wire out of the mercury in the [glass] cup and breaks the circuit. This destroys the magnetism of the iron wires, and [the iron rod] ceases to be attracted. The wire then falls back by its own weight, and the circuit is renewed...
In this manner a rapid vibration of the wire is produced, and brilliant sparks and deflagration of the mercury takes place in the [glass] cup."
This little instrument, which I have held in one hand, is the
first self-contained induction coil, and was first described by Charles
Grafton Page in a paper published in Silliman's American Journal of Science.
Quite independently, the device had been developed earlier by Nicholas
Callan of St. Patrick's College in Ireland.
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In the summer of 2001 I revisited Dartmouth College, and
found this apparatus that I had overlooked on my previous visit in 1979.
It is clearly a home-built version of Page's Compound Magnet and Electrotome, and one probably made no later than the middle of the nineteenth century, by which time better devices had been devised for producing high A.C. potentials. The Dartmouth library has an edition of Davis's Manual of Magnetism, making a further link. |