358 



SCIENCE 



[N. S. Vol. L. No. 1294 



yards' range. It could also be carried on 

 during considerable artillery activity. 



The apparatus for localizing noises trans- 

 mitted through the ground has been much 

 used for the detection of enemy mining 

 and counter-mining operations. Acoustic 

 tubes, microphones and amplifying valves 

 have been employed to increase the volume 

 of very faint noises. 



For many years before the war the BeU 

 Submarine Signalling Co., of which Sir 

 "William "White was one of the early 

 directors, used submerged microphones for 

 detecting sound transmitted through the 

 water, and a submerged bell for sending 

 signals to distances up to one mile. "With 

 this apparatus passing ships could be 

 heard at a distance of nearly a mile when 

 the sea was calm and the listening vessel 

 stationary. 



Of all the physical disturbances emitted 

 or produced by a moving submarine, those 

 most easily detected, and at the greatest 

 distance, are the pressure-waves set up in 

 the water by vibrations produced by the 

 vessel and her machinery. A great variety 

 of instruments have been devised during 

 the war for detecting these noises, depend- 

 ing on microphones and magnetophones of 

 exceedingly high sensitivity. Among them 

 may be particularly mentioned the hydro- 

 phones devised by Captain Ryan and Pro- 

 fessor Bragg, being adaptations of the tele- 

 phone transmitter to work in water instead 

 of air. These instruments, when mounted 

 so as to rotate, are directional, being in- 

 sensitive to sound-waves the front of which 

 is perpendicular to the plane of the 

 diaphragm, 8.nd giving the loudest sound 

 when the diaphragm is parallel to the 

 wave-front. 



Another preferable method for deter- 

 mining direction is to use two hydrophones 

 coupled to two receivers, one held to each 

 ear. This is called the biaural method, 



and enables the listener to recognize the 

 direction from which the sound emanates. 



"When the vessel is in motion or the sea 

 is rough, the water noises from the drag- 

 ging of the instrument tlirough the water 

 and from the waves striking the. ship 

 drown the noises from the enemy vessel, 

 and under such conditions the instruments 

 are useless. The assistance of eminent 

 biologists was of invaluable help at this 

 juncture. Experiments were made with 

 sea-lions by Sir Richard Paget, who found 

 that they have directional hearing under 

 water up to speeds of six knots. Also Pro- 

 fessor Keith explained the construction of 

 the hearing organs of the whale, the ear 

 proper being a capillary tube, too small 

 to be capable of performing any useful 

 function in transmitting sound to the 

 relatively large aural organs, which are 

 deep set in the head. The whale therefore 

 hears by means of the sound-waves trans- 

 mitted through the substance of the head. 

 It was further seen that the organs of 

 hearing of the whale to some degree 

 resembled the hydrophone. 



The course now became clear. Hollow 

 towing bodies in the form of fish or por- 

 poises were made of celluloid, varnished 

 canvas, or very thin metal, and the hydro- 

 phone suitably fixed in the center of the 

 head. The body is filled mth water, and 

 the cable towing the fish contains the in- 

 sulated leads to the observer on board the 

 vessel. When towed at some distance be- 

 hind the chasing ship disturbing noises are 

 small, and enemy noises can be heard up 

 to speeds of fourteen knots, and at con- 

 siderable distances. Thermionic amplify- 

 ing 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 ice'berg, Lewis Richardson was 

 granted two patents in 1912 for the de- 



