RESOUNDING THE PACIFIC

Evening Star, Issue 18399, 6 October 1923, Page 18

RESOUNDING THE PACIFIC

The business of charting the floor of the ocean is always a very troublesome and long one. But the chart which Ifts just been published by the United States Navy Department of the Pacific Coast south of San Francisco opens up a new era. Practically the whole of the work was done by the now echo-sounding gear carried in the destroyer, and the advantages of it arc shown by the fact that they were able So got an excellent running survey of the whole done in thirtyeight working days, making approximately 5,000 accurate soundings as they steamed along at a speed of twelve knots. At the depths at which they had to work it would have been quite impossible to have done the thing at anything like this speed by the old-fashioned gear. The system in use is an adaptation of tho hydrophone used during the war for hunting submarines, worked in conjunction with a sound-signalling apparatus using an explosive signal. Well-trained listeners can judge to a fractional part of a second the time taken for tho noise of the explosion to bounce off the bottom of the sea and reach the listening instrument, and, as tho rate at which sound travels through the water is known, it is quite easy to get from this the depth of the bottom. Tho trouble with the apparatus is that Poundings are, generally wanted in shallow water far more, than in deep, and in shallow water the new gear cannot he, used, ns the reverberations of the original explosion have not died down before the echoes are bark again. It is proposed to use the new system to make a survey of the South Pacific off tho Chilian roast, where last November's earthquake has made the ocean charts finite useless. In one spot where there should have been 400 fathoms a British ship was surprised to find only fifty-four.