Page 3 Advertisements Column 2

Dominion, Volume 13, Issue 274, 13 August 1920, Page 3

Conspicuous among the devices developed, orginally for anti-submarine purposes, but certain to bei'invaluable fo shipping under peifce conditions, is tho hydrophone—an instrument which detects under-water vibrations set up by a moving vessel. Microphones and magnetophones of exceedingly high sensitiveness were employed, sometimes with attachments which enabled the listener to ascertain the direction from which the disturbance was coming. The "silent submarine" was, nowever, introduced to circumvent the hydrophone, and this development was countered by the echo mothod," under which a beam of sound was sent out by chasing the vessel, eireeping the seas like a searchlight, and causing an echo when it strikes a solid object, such as a sub marine. The echo method can al?o bo used for sounding, for locating icebergs, surface vessels, and rock-bound coasts in « fog.

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