Experiments are described to demonstrate a new method of sonic signalling at extremely long ranges in the oceans, utilizing the natural sound channel. Signals were made by causing a 4-lb. charge of TNT to explode at about 4000-foot depth.

These signals have the following qualities:

(1) Extremely long-range transmission (probably 10,000 miles).

(2) Signal is positively identifiable.

(3) Abrupt termination of the signal allows the arrival time to be read with an accuracy better than 0.05 second. This permits location of the source to within a mile, if the signal is received at three suitably located stations.

(4) The relation...