SOUND-SIGNALS AT SEA. 91 



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 com- 

 parison. 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 to- 

 gether 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 pro- 

 duce 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 significa- 

 tion, 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 pro- 

 posed 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-sta- 

 tion, 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 " Electricity." 



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 sur- 



* " Memoirs of the Institute of France," vol. v, 1838, pp. 329-399 ; Sir John Herschel, 

 "Sound," sections 94, 95 ; "Journal of Science," vol. i, 1828, pp. 480, 481; "Edinburgh 

 New Philosophical Journal," vol. v, 1828, pp. 91-94. 



