October 17, 1919] 



SCIENCE 



359 



teetion 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 

 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. 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 

 whom was associated Professor Langevin, 

 of the College de France, realizing its im- 

 portance for submarine detection, brought 

 the apparatus to a high degree of per- 

 fection and utility shortly before the 

 armistice. Now with beams of high-fre- 

 quency sound-waves it is possible to sweep 

 the seas for the detection of any sub- 

 merged abject, such as icebergs, sub- 

 marines, 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 apparatus on land led to the sug- 

 gestion 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 be- 



ing used extensively for the determination 

 of such positions at sea as light-vessels, 

 buoys which indicate channels, and ob- 

 structions 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 tech- 

 nical systems and devices brought out 

 during the war which will find useful 

 application under peace conditions as aids 

 to navigation I may mention directional 

 wireless, 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 mine 

 fields, and afterwards used by the Allies, 

 consists of an insulated cable laid on the 

 bottom of the sea, earthed at the farther 

 end, through which an alternating current 

 is passed. By means of delicate devices 

 installed on a ship, she is able to follow the 

 cable at any speed with as much precision 

 as a railless electric ''bus can follow its 

 trolley-wire. Gables up to fifty miles long 

 have been used, and this device promises 

 to be invaluaible to ships navigating narrow 

 and tortuous channels and entering or 

 leaving harbors in a fog. 



Aircraft. — It may be justly said that the 

 development in aircraft design and manu- 

 facture is one of the astonishing engineer- 

 ing feats of the war. In August, 1914, the 

 British Air Services possessed a total of 

 272 machines, whereas in October, 1918, 

 just prior to the armistice, the Royal Air 

 Force possessed more than 22,000 effective 

 machines. During the first twelve months 

 of the war the average montlily delivery 

 of aeroplanes to our Flying Service was 

 50, while during the last twelve months of 

 the war the average deliveries were 2,700 

 per month. So far as aero-engines are 



