Note 12 — TELEPHONIC EXPERIMENTS.

Mr. Warwick describes his experiments as follows: ‘The magnets employed were nearly of the usual size, 1½ inch in diameter, and nearly eight times as long. At first I employed iron disks, but I found them to be unnecessary. When I had discarded them, I tried several substances: first a thin disk of iron, which answered perfectly both for sender and receiver. A disk of sheet iron, about ⅒ of an inch in thickness, did not act so well, but all that was said was quite understood. In making experiments with the disks, I simply placed them above the instrument, without fixing them in any way: the wooden cover and the conical cavity were also laid aside, because the transmission and reception could be effected as well without them. This part of the instrument seems to be superfluous, since, when the disk is simply placed level to the ear, the sound seems to be increased by being brought nearer. Although iron acts better than anything, it appears that iron disks are not absolutely necessary, and that diamagnetic substances also act perfectly. I wished that my assistant, who was at some distance, and could not hear any direct sound, should continue his calculations. I took away the iron disk and placed across the instrument a wide iron bar, an inch thick. On applying my ear to it, I could hear every sound distinctly, but somewhat more faintly. A piece of copper, three inches square, was substituted for it: although the sound was still distinct, it was fainter than before. Thick pieces of lead, zinc, and steel were alternately tried. The steel acted in almost the same way as the iron, and, as in the other cases, each word was heard faintly but distinctly. Some of these metals are diamagnetic, and yet the action took place. Some non-metallic substances were next tried; first a piece of window-glass, which acted very well. The action was faint with a piece of a wooden match-box; but on using pieces of gradually increasing thickness the sound was sensibly increased, and with a piece of solid wood, 1½ inch in thickness, the sound was perfectly distinct. I next replaced it by an empty wooden box, which acted very well. A piece of cork, ½ inch thick, acted, but somewhat faintly. A block of razor-stone, 2 inches thick, was placed upon the instrument; and, on applying the ear to it, it was quite easy to follow the speaker. I then tried to hear without the insertion of any substance, and, on applying my ear quite close to the coil and magnet, I heard a faint sound, and on listening attentively I understood all that was said. In all these experiments the sounds were perceived, but the sounds transmitted or attempted did not act precisely alike. The sound of a tuning-fork, placed on the iron disk itself or on the case of the instrument, was clearly heard: thin iron disks were more effective for articulate speech. With other substances, stone, solid wood, glass, zinc, &c., the sound of the tuning-fork was heard, whether it rested upon them, or the vibrating fork was held above them. These substances were not adapted for transmitting the sound of the voice. These were all laid aside, and the sounding instrument was held directly above the pole of the magnet: the sound was clearly heard, although there was nothing but air between the end of the magnet and the tuning-fork. The sound was perhaps less intense when the tuning-fork was held directly above the pole, than when it was at the end of the magnet. I next tried if my voice could be heard with this arrangement. The result was rather doubtful, but I think that some action must have taken place, for the tuning-fork was heard when it was simply vibrated near the pole. The effect of the voice can only have differed in the degree of intensity: it was too faint to be heard at the other extremity. I repeated these effects; I assured myself of them, and I succeeded in transmitting sounds distinctly on the pole without a disk, and, on the other hand, by applying my ear to the instrument, I was able to hear distinctly all that was said, although there was no disk.’