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Updated: May 19, 2025
Moreover, the metallic hull of the submersible forms in itself an almost ideal shield to screen the outgoing effect of these motors. Considerable and important development has been made in the creation of sensitive sound-receiving devices, to hear the propeller vibrations and the mechanical vibrations that are present in a submersible, both of which are transmitted through the water.
If this machine were operated in such a manner as to play, in a single second of time, the entire overture of an opera which would normally occupy half an hour, we should hear only an unintelligible noise a second long. This would be due to no defect in the sound-producing mechanism, but to the limitations of the sound-receiving mechanism, our auditory apparatus.
There are three principal obstacles to the successful use of such a device: when the submersible is submerged, she employs rotary and not reciprocating prime-movers, being in consequence relatively quiet when running under water, and inaudible at any considerable distance; the noises of the vessel carrying the listening devices are difficult to exclude, as are also the noises of the sea, which are multitudinous; finally, the sound-receiving instruments are not highly directive, hence are not of great assistance in determining the position of the object from which they are receiving sounds.
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