36. A battery of ten troughs, each of ten pairs of plates four inches square, charged with good mixture of sulphuric and nitric acid, and the following experiments made with it in the following order.
37. One of the coils (of a helix of copper wire 203 feet long) was connected with the flat helix, and the other (coil of same length round same block of wood) with the poles of the battery (it having been found that there was no metallic contact between the two); the magnetic needle at the indicating flat helix was affected, but so little as to be hardly sensible.
38. In place of the indicating helix, our galvanometer was used, and then a sudden jerk was perceived when the battery communication was made and broken, but it was so slight as to be scarcely visible. It was one way when made, the other when broken, and the needle took up its natural position at intermediate times.
Hence there is an inducing effect without the presence of iron, but it is either very weak or else so sudden as not to have time to move the needle. I rather suspect it is the latter.
The fifth day of experiment was October 17. Paragraph 57 describes the discovery of the production of electricity by the approximation of a magnet to a wire:—
A cylindrical bar magnet three-quarters of an inch in diameter, and eight inches and a half in length, had one end just inserted into the end of the helix cylinder (220 feet long); then it was quickly thrust in the whole length, and the galvanometer needle moved; then pulled out, and again the needle moved, but in the opposite direction. This effect was repeated every time the magnet was put in or out, and therefore a wave of electricity was so produced from mere approximation of a magnet, and not from its formation in situ.
The cause of all the earlier failures was, then, that both magnet and coil were at rest. The magnet might lie in or near the coil for a century and cause no effect. But while moving towards the coil, or from it, or by spinning near it, electric currents were at once induced.
The ninth day of his experiments was October 28, and this day he “made a copper disc turn round between the poles of the great horse-shoe magnet of the Royal Society. The axis and edge of the disc were connected with a galvanometer. The needle moved as the disc turned.” The next day that he made experiments, November 4, he found “that a copper wire one-eighth of an inch drawn between the poles and conductors produced the effect.” In his paper, when describing the experiment, he speaks of the metal “cutting” the magnetic curves, and in a note to his paper he says, “By magnetic curves I mean lines of magnetic forces which would be depicted by iron filings.”
SUCCESS AND ITS SECRET.
We here come upon those “lines of force” which played so important a part in these and many of Faraday’s later investigations. They were known before Faraday’s time—had, in fact, been known for two hundred years. Descartes had seen in them evidence for his hypothetical vortices. Musschenbroek had mapped them. But it was reserved to Faraday to point out their true significance. To the very end of his life he continued to speculate and experiment upon them.