HAYES— DETECTION OF SUBMARINES. 9 



passes in through the rubber housing and attaches to the aluminum 

 strip and a second lead in a similar way is attached to the tin-foil. 

 These rubber-covered electric leads are both vulcanized to the 

 rubber condenser-housing so as to give water-tight joints. The elec- 

 tric charge held by the condenser, when a" battery is connected to the 

 ' two leads, depends, among other things on the separation between 

 the tin-foil and the aluminum strip. The variation in hydrostatic 

 pressure in a submarine sound-wave causes this distance to vary 

 slightly when the condenser is placed in the water, thereby pro- 

 ducing slight current fluctuations through the battery and leads. 

 These current fluctuations can be carried through a telephone re- 

 . ceiver and converted into sound at the listener's ear. 



The magnetophone and the electrostatic condenser give a more 

 faithful reproduction of the sound than does the microphone, but 

 they have the disadvantage of requiring an amplifier to increase 

 their sensitivity. As a result only two types of receivers have been 

 generally used — the microphone and the acoustic receivers. 



Requirements of a Submarine Detector. 



The requirements of a listening apparatus which embodies all 

 that is desired may be stated as follows : It must be able to detect a 

 submarine at considerable distance without interference, from noise 

 produced by other shipping, or by wave noise, or by noise produced 

 by the boat upon which it is installed. It should be able to give the 

 distance and direction of the submarine accurately. It should be sea- 

 worthy, of robust mechanical construction, convenient and rapid of 

 operation. 



No instrument has been devised that satisfies all of these re- 

 quirements. In fact no single instrument can give the distance of 

 the submarine. The other requirements have been fairly satis- 

 factorily met. These instruments are being continually improved, 

 but even in their present state they give results far beyond what was 

 considered probable or even possible at the time the developmental 

 work was first started. 



Determination of Direction. 



Maximum and Minimum. — A submarine receiver can be made 

 more sensitive to sound coming from certain directions with respect 



