CHAPTER XVI.
ACOUSTICS (Continued).
THE TOPOPHONE—THE MEGAPHONE—THE AUTOPHONE—THE AUDIPHONE—THE TELEPHONE—THE PHONOGRAPH—THE MICROPHONE.
We propose in this chapter to give as shortly as possible a description of the various instruments lately come into use, by means of which, and electricity, sounds can be carried from place to place, and their locality identified. It is only within the last few years that these wonderful inventions have come into use, and in a measure superseded the at one time invincible electric telegraph. The Telephone is now in daily use in London and other places, and its novelty, if not all its capability, has been discounted. The Phonograph has also been frequently seen. So we will on this occasion commence with the Topophone, a rather novel instrument.
As the name indicates, the Topophone is an apparatus for discovering the position of a sound, from the Greek words signifying a “place” and “sound.” The sources of sound can be found by it, and indeed this is its actual and practical use. It is claimed for this new apparatus that it stands in the same relation to the sailor as his old and trusty friends, the compass and sextant. These in navigation inform the steersman as to his course, and tells him his position by observation. The Topophone will tell him whence a sound arises, its origin wherever it may be; and this in a fog is no mean advantage. Suppose a ship to be approaching a dangerous coast in a fog. We are all aware how deceptive sounds are when heard through such a medium. We cannot tell from what precise direction the horn, whistle, or bell is sounding. The Topophone will give us the exact spot, and we can then, from our general knowledge of the locality, work our vessel up the river, or into the harbour, in safety.
The Topophone was invented in 1880, by Professor Alfred Mayer, an American, and is based upon the well-known theory of sound waves. These, as we have already explained, exist in the air; and if the theory of sound waves has perfected the Topophone, we can fairly say that it has confirmed the supposed form of the sound waves. “Sound,” says the inventor of the apparatus, “is supposed to be a particle continually expanding in the air, composed of a wave produced by compression, and followed by rarefaction. A continuous sound is a series of these particles or globules spreading and expanding as the water-rings in a pond.” This much will be at once perceived.
Now, suppose a person up to his shoulders in a pond of water, and someone throws a stone into it. If that person extend his arms and hands at right angles facing the sound, each hand would touch the edge of a ripple as it came towards him across the pond. He would then be facing the source of the ripples or waves, and look along a radius of the circle formed by the waves. But if he please, he can move his body so that both hands shall touch the same wave at the same time, or he might turn away from the source, and only one hand would touch the wave. But when both hands are actually washed by the same circular ripple he must be facing the source of it. Any position in which his fingers did not touch the ripple almost at the same instant, would not be facing the source of the wave ripples. So by turning and extending his hands, he could with his eyes shut find out whether he was or was not facing the original source of the waves.
This applied to sound waves in the air is the whole theory of the Topophone, which, however, depends for its usefulness upon the same note being sounded by all horns and whistles. One note must be better than all the others, and that note, probably C (treble), caused by about two hundred and sixty vibrations per second, has been found most applicable. If all whistles and horns can by law be compelled to adjust themselves to this note, then the Topophone will be a real and lasting benefit.
Let us now look at the apparatus itself.