RE-SOUNDING THE PACIFIC

Thames Star, Volume LVII, Issue 15959, 25 October 1923, Page 6

RE-SOUNDING THE PACIFIC

The business of charting the floor of the ocean is always a very troublesome and 'long one. But the chart which has 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 new echo-sounding gear carried in the destroyer, and the advantages ,of it are shown by the fact that they were able to get an excellent running survey of the whole done in 38 working days, making approximately 5000 accurate soundings as they steamed along at a speed of 12 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 oldfashioned gear. The system in use is an adaptation of the 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 the noise of y the explosion to bounce off the bottom of the sea and reach the listdtaing instrument, and, as the rate at which sound travels through the water is known, it is quite easy to get from this the depth of the bottom. The trouble with the apparatus is that soundings are generally wanted in shallow water far more than in deep, and in shallow water the new gear cannot be used, as the reverberations of the original explosion have not died down before the echoes are back again. It is proposed to use the new system to make a survey of the South Pacific off the Chilian Coast, where last November’s earthquake has made the ocean charts . quite useless. In one spot where there should have been 400 fathoms a British ship was surprised to find only 54 fathoms.