LOCATING SUBMARINES.

Manawatu Standard, Volume LII, Issue 174, 24 June 1932, Page 7

LOCATING SUBMARINES.

ECHOES UNDER THE SEA. When the ill-fated submarine M2 Trent to her grave beneatli tho waters of the English Channel, the exact placo where sho was sunk was not known. Yet the wreck was located in a comparatively short time, largely through the help of the echo-sounder, one of tho most important of all marine inventions. If one goes to a place where there is an echo and calls out “Hi!” he will find there is an appreciable time between the cry and tho echoed answer. Sound travels through air at about 110 ft. a second. If the reply arrived in three seconds the distance between the caller and the cause of the echo is one and' a-half times 1100 ft., or 1650 ft., for in the three seconds the sound has made the double journey. The echo-sounder, which is attached to tho hull of the vessel, sends a sharp, clear note straight downwards. The sound travels to the sea floor, and then comes back again. The timing is done automatically and the calculations are worked out by the instrument, ( the depth being shown instantly. So accurate are echo-sounding machines that with some patterns a depth of only one foot can bo measured, though sound travels at a speed of nearly 5000 ft. a second through salt water.