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equipment whose greatest ultimate usefulness was not that originally intended, but in 

 obtaining echoes from the ocean bottom. Professor R. A. Fessenden of the United 

 States was also stimulated by the Titanic disaster to experiment with echoes in water, 

 one of the principal results of which was the development of a powerful oscillator which 

 could produce sounds of great intensity in water. He also developed an instrument to 

 convert sound travel time to distance. Unfortunately this instrument was never per- 

 fected to the full stage of usefulness. A few years later Langevin and Chilowski, of 

 France, succeeded in developing supersonic-sounding apparatus beyond the experi- 

 mental stage. This was significant because most modern echo-sounding instruments 

 utilize sounds of supersonic or near supersonic frequencies. 



World War I was responsible for advanced knowledge of and developments in 

 subaqueous acoustics. Large groups of eminent scientists applied their talents to the 

 development of submarine-detecting and signaling devices, and numerous other under- 

 water sound aids to navigation. During the years immediately after World War I 

 there was increased activity in the development and use of echo-sounding equipment, 

 the major developments being made by commercial companies and the governments 

 of the United States, England, France, and Germany, 



Between the years 1918 and 1925 many important experiments led eventually to 

 the practical application of echo sounding for use in navigation and surveying. During 

 this period sounding apparatus was being rapidly developed and a knowledge of the 

 extent of the usefulness of echo soundings was being acquired as well. Among the 

 many important developments and experiments of a practical nature during this 

 period, the following are selected as being representative and especially notable, 

 although others may be considered of equal importance: 



(1) The application of submarine-listening microphones to echo sounding by the United States 

 Navy in 1918. 



(2) In 1919 the French Hydrographic Department obtained echo soundings to a depth of 60 

 meters in the Casquets Deep from a ship underway at 10 knots. 



(3) In 1919 soundings in depths of 4,000 meters were obtained in the Bay of Biscay from the 

 cable ship Charente. 



(4) The first Hne of supersonic soundings was run in 1920 by the Centre d'Etudes de Toulon. 



(5) In 1922 the French Hydrographic Department, using a Marti sonic apparatus, ran a line of 

 sonic soundings to explore the depths between Marseilles and Philippeville, preparatory to laying a 

 cable between these points. This is claimed to be the first practical application of echo sounding. 



(6) In 1922 a profile of soundings between Gibraltar and Port Said was obtained from the U. S. 

 S. Stewart, using the Hayes Sonic Depth Finder developed at the Annapolis Engineering Experiment 

 Station of the United States Navy. 



(7) In 1923 an important contribution to echo sounding was made by Dr. Herbert Grove Dorsey 

 of the United States, who devised a visual-indicating device for measuring extremely short time inter- 

 vals, by which shoal and deep depths could be automatically registered. This method of registration 

 is embodied in many of the echo-sounding instruments in use today. 



The period since 1925 has been significant for the refinement of apparatus and 

 further development of the theory of acoustics. The application of echo sounding has 

 been extended to a range from very shoal to very great depths. The accuracy and 

 reliability of echo soundings have been increased by instrumental refinements and a 

 more extensive knowledge of the effective velocity of sound in water. The use of 

 thermionic tubes in echo-sounding circuits has made many of the refinements possible. 



Sonic frequencies were used almost exclusively in the early stages of development 

 of echo sounding by all except the French. Sonic sound-producing devices, such as 

 hammer strikers, explosions, and electromagnetic oscillators, have been employed. 



