14 president's address. 



towed at some distance behind the chasing ship disturbing noises are 

 small, and enemy noises can be heard up to speeds of 14 knots, 

 and at considerable distances. Thermionic amplifying valves have been 

 extensively used, and have added much to the sensitiveness of the 

 hydrophone in its many forms. 



After the loss of the Titanic by collision with an iceberg, Lewis 

 Richardson was grant-ed two patents in 1912 for the detection of above- 

 water objects by their echo in the air, and underwater objects by their 

 echo transmitted through the water. The principles governing the 

 production and the concentration of beams of sound are described in 

 his specifications, and he recommends frequencies ranging from 4,786 

 to 100,000 complete vibrations per second, and also suggests that the 

 rate of approach or recession from the object may be determined from 

 the difference in the pitch of the echo from the pitch of the blast sent 

 out. Hiram Maxim also suggested similar apparatus a little later. 



The echo method of detection was not, however, practically deve- 

 loped until French and English scientists, with whom was associated 

 Professor Langevin, of the College de France, realising its importance 

 for submarine detection, brought the apparatus to a high degree of 

 perfection and utility shortly before the Armistice. Now, with beams 

 of high-frequency sound waves, it is possible to sweep the seas for the 

 detection of any submerged object, such as icebergs, submarines, surface 

 vessels, and rocks ; they may also be used to make soundings. It 

 enables a chasing ship to pick up and close in on a submarine situated 

 more than a mile away. 



The successful development of sound-ranging appai'atus on land 

 led to the suggestion by Professor Bragg that a modified form could be 

 used to locate under- water explosions. It has been found that the 

 shock of an explosion can be detected hundreds of miles from its source 

 by means of a submerged hydrophone, and that the time of the arrival 

 of the sound wave can be recorded with great precision. At the end 

 of the war the sound-ranging stations were being used for the detection 

 of positions at sea, required for strategical purposes. The same stations 

 are now being used extensively for the determination of such positions 

 at sea as light- vessels, buoys which indicate channels, and obstructions 

 such as sunken ships. By this means ships steaming in fog can be 

 given their positions with accuracy for ranges up to 500 miles. 



Among the many other important technical systems and devices 

 brought out during the war which will find useful application under 

 peace conditions as aids to navigation I may mention directional wire- 

 less, by which ships and aircraft can be given their positions and 

 directed, and on this subject we are to have a paper in Section G. 



Leader gear, first used by the Germans to direct their ships through 

 their minefields, and subsequently used by the Allies, consists of an 



