SOUNDING BY SOUND

Evening Star, Issue 20138, 1 April 1929, Page 7

SOUNDING BY SOUND

THE LATEST METHOD For obvious uud imperative reasons it is often desirable to know the depth of water below a ship. In the old days tho lino and sinker provided the only means, writes Sir William JI. Bragg, F.A.S., in the ‘ Evening Nows.’ But u ship must bo moving very slowly, as we should now estimate sp. J, to make this method practicable. it lias become a serious matter if the necessary delay has to be incurred. This is true even in peace times; in times of Avar such delay is risky in the extreme. If a- sharp blow is struck upon a plate in the hull of the ship the sound trails outwards and downwards, and is reflected from the sea bottom. The sound travels at the rate of a mile a second. The instruments required for the detection of the echo have become so perfect that the time taken by the sound in going ami returning can be measured to tlie thousandth of a second. Tims the depth can be ascertained to one or lavo feet, and this can lie dmie even avlicu the ship is moving at high speed. Beautiful Avork and most ingenious design have been put into the apparatus by which this result is achieved. One of tlie greatest difficulties to be overcome has lain in the fact that the receiving instrument must bo able to stand the loud clang of the primary signal and yet to register the returning echo, thousands of times' weaker than the parent sound. There, is. I think, a special interest in the similarity between this method and one that Ave often use; for avo, when in the dark, and blind people always, are conscious of the nearness of objects by the nature of the _ echoes Avnich they return 1 o the noises Ave make.