Page:Popular Science Monthly Volume 33.djvu/101

Rh ocean-steamers. But, to make it thoroughly useful, M. Edme Genglaire, a student of the Naval School of Medicine at Toulon, has combined with the siren what purports to be the leading idea of the topophone by fixing an invariable standard for comparison. The siren being in communication with the boiler, the current of steam can be governed by an ordinary valve. The sounds produced vary in pitch and intensity in proportion to the quantity of steam emitted, so that sounds of any given pitch can be obtained. A set of resonators completes the apparatus.

It is well known that two identical resonators vibrate together for the same sound and for that only. Starting with this principle, in two similar frames containing several resonators, the corresponding resonators will vibrate or sound only when the note corresponding to them is produced. The siren will produce these sounds causing vibrations in the resonators, and two distant ships, or a shore-station and a ship, or two land-stations, supplied with sirens of a similar model and identical frames of resonators, could most conveniently communicate. For this end each resonator should have attached to it an invariable signification, the same for all the frames.

All the naval and commercial vessels possessing sirens and a frame carrying the same number of resonators, each marked with a number having its signification, might be prepared to communicate with each other or with the shore.

This is the practical way of carrying the theory out as proposed by M. Genglaire:

In front of each resonator will be placed two metallic reeds, one rigid, the other thin and producing extended oscillations with the least effort. Each of these pieces of steel communicates with one pole or battery by means of the circuit wire. When the resonator vibrates, the thin reed oscillates, touches the other bar, and the two poles of the battery being connected, an electric bell rings, thus giving a signal, so that the call, whether from ship or shore, can be recognized, while the bell of the signaling-station, by its sounds, shows that the desired vibration or note has been produced. This account of Genglaire's siren is condensed from the account published in "Électricité."

Colladon made a series of experiments at Lake Geneva in 1836 to determine the velocity of sound in water. He had a bell weighing about one hundred and fifty pounds suspended some five feet under water from the side of a boat, and struck by a hammer attached to the end of a lever. Stationed in another boat he listened for the bell-sounds, propagated beneath the