18 HAYES— DETECTION OF SUBMARINES. 



In operation each path through the compensator is connected in 

 series with one of the two paths leading from the receivers to the 

 ears, care being taken that the path lengths outside of the compen- 

 sator are equal. Any sound striking the two receivers can be bi- 

 naturally centered by turning the compensator to a position such that 

 the impulses from the two receivers reach the ears simultaneously. 

 The high development of the binaural sense may be appreciated from 

 the fact that an untrained listener can make a compensator setting 

 accurate to within I0"° seconds while a trained listener can do better 

 than 5 X lO"*^ seconds. 



The compensator is provided with a special switching device by 

 which different pairs of receivers can readily be connected through 

 the compensator. The movable plate of the compensator carries 

 four scales arranged in pairs, each pair referring to a definite set of 

 receivers. The scales are arranged in pairs because of the ambiguity 

 in direction at each setting of the compensator. The direction of a 

 sound source is determined by making a binaural setting on one pair 

 of receivers and noting the two angles on the double scale belonging 

 to this set of receivers. Then throw the switch so as to connect in 

 the second set of receivers and make a second binaural setting and 

 note the two angles given by the double scale which refers to this 

 second set of receivers. The common angle on the two settings gives 

 the direction. Due to errors in setting the common angle will in gen- 

 eral not give perfect agreement, and the angle is taken from the scale 

 least subject to errors for the angle in question. In Plate IV. a, 

 Figs. I and 2 show the Type T compensator assembled and dissem- 

 bled respectively. 



Submarine Detectors Developed in England. 



The principle of the English listening devices is shown in Plate 

 V. The Mark I. consists of a tuned diaphragm mounted within a 

 somewhat massive ring carrying a microphone within a small rigid 

 watertight housing at the center of the diaphragm. One side of the 

 diaphragm is screened by a heavy plate. This receiver is highly 

 resonant and is most sensitive to sounds coming from the side oppo- 

 site to the screen. The receiver is rotated in the water and the direc- 

 tion is determined by the maximum-minimum principle, and since 



