32 



NATURE 



[September ii, igig 



constituting the sectional proceedings of this year's 

 meeting. Among them are "Tanlis," by Sir Eustace 

 d'Eyncourt; " Scientilic Progress of Aviation during 

 the War," by L. Bairstow; "Airships," by Lt.-Col. 

 Cave-Brown-Cave; "Directional Wireless, with 

 Special Reference to Aircraft," by Capt. Robinson; 

 " Wireless in Aircraft," by Major Erskine Murray ; 

 "Wireless Telegraphy during the First Three Years 

 of the War," by Major Vincent Smith; "Submarine 

 Mining," by Comdr. Gwynne; "Emergency Bridge 

 Construction," by Prof. Ingles; and "The Paravane," 

 by Comdr. Burney. Accordingly, it is quite unneces- 

 sary here to particularise further except in the few 

 following instances : — 



Sound-ranging and Listening Devices. — Probably 

 the most interesting development during the war has 

 been the extensive application of sound-listening 

 devices f6r detecting and localising the enemy. The 

 Indian hunter puts his ear to the ground to listen 

 for the sound of the footsteps of his eneiny. So in 

 modern warfare science has placed in the hands of 

 the sailor and soldier elaborate instruments to aid 

 the ear in the detection of noises transmitted through 

 earth, water, air, or aether, and also in some cases 

 to record these sounds graphically or photo- 

 graphically, so that their character and the time of 

 their occurrence may be tabulated. 



The sound-ranging apparatus developed by Prof. 

 Bragg and his son, by which the position of an enemv 

 gun can be determined from electricallv recorded 

 times at wnich the sound-wave from the gun passes 

 over a number of receiving stations, has enabled our 

 artillery to concentrate their fire on the enemy's guns, 

 and often to destroy them. 



The French began experimenting in September, 

 1914, with methods of locating enemy guns bv sound. 

 The English section began work in October, 1915, 

 adopting the French methods in the first instance. 

 By the end of 1916 the whole front was covered, 

 and sound-ranging began to play an important part 

 in the location of enemy batteries. During 1917 loca- 

 tions by sound-ranging reached about 30,000 for the 

 whole Army, this number being greater than that 

 given by any other means of location. A single good 

 set of observations could be relied upon to give the 

 position of an enemy gun to about 50 yards at 

 7000 yards' range. It could also be carried on during 

 considerable artillery activity. 



The apparatus for localising noises transmitted 

 through the ground has been much used for the 

 detection of enemy mining and counter-mining opera- 

 tions. Acoustic tubes, microphones, and amplifying 

 valves have been employed to increase the volume 

 of very faint noises. 



For many years befoie the war the Bell 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 pro- 

 duced by a moving submarine, those most easily 

 detected, and at the greatest distance, are the 

 pressure-waves set up in the water by vibrations pro- 

 duced by the vessel and her machinery. A great 

 variety of instruments have been devised during the 

 war for detecting these noises, depending on micro- 

 phones and magnetophones of exceedingly high sensi- 

 tivity. .^mo^g them may be particularly mentioned 

 the hydrophones devised by Capt. Ryan and Prof. 

 Bragg, being adaptations of the telephone transmitter 

 to work in water instead of air. These Instruments, 



NO. 2602, VOL. 104] 



when mounted so as to rotate, are directional, being 

 insensitive to sound-waves the front of which is per» 

 pendicular to the plane of the diaphragm, and giving 

 the loudest sound when the diaphragm is paralla|j 

 to the wave-front. « 



Another preferable method for determining direc- 

 tion 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 recognise 

 the direction from which the sound emanates. 



When the vessel is, in motion or the sea is rough, 

 the water noises from the dragging of the instrument 

 through 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 Prof. Keith explained the construc- 

 tion of the hearinf organs of the whale, the ear proper 

 being a capillary tube, too small to be capable of per- 

 forming 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 transmitted 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 porpoises were made of 

 celluloid, varnished canvas, or very thin metal, and 

 the hydrophone suitably fixed in the centre of the 

 head. The body is filled with water, and the cable 

 towing the fish contains the insulated leads to the 

 observer on board the vessel. When towed at some 

 distance behind the chasing ship disturbing noises 

 are small, and enemy noises can be heard up to 

 speeds of fourteen knots, and at considerable dis- 

 tances. Thermionic amplifying valves have been 

 extensively used, and have added much to the sensi- 

 tiveness of the hydrophone in its many forms. 



After the loss of the Titanic by collision with an 

 iceberg, Lewis Richardson was granted two patents 

 in 1912 for the detection of above-water objects by 

 their echo in the air, and under-water objects by the 

 echo transmitted through the water. The principles 

 governing the production and the concentration of 

 beams of sound are described in the specification, and 

 he recommends frequencies ranging from 4786 to 

 100,000 complete vibrations per second, and also sug- 

 gests 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. 

 Sir Hiram Maxim also suggested similar apparatus a 

 little later. 



The echo method of detection was not, however, 

 practically developed until French and English men 

 of science, with v^hom was associated Prof. 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 detec- 

 tion of any submerged object, such as icebergs, sub- 

 marines, surface vessels, and rocks ; they may also 

 be used to m.ake 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 ap- 

 paratus on land led to the suggestion by Prof. 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 



