HAYES— DETECTION OF SUBMARINES. 13 



either arrow 3 or arrow 4 it reaches the left ear first and will there- 

 fore appear to the listener to come from his left. It is readily seen 

 from the diagram that a rotation of the receivers in an anti-clock- 

 wise direction will make the sound appear binaiirally centered when 

 the small arrow at the center of the line of receivers points in the 

 direction of these sounds respectively. 



In order to make this rule effective, the importance of attaching 

 the proper receiver to the proper ear is obvious. 



A device that depends upon rotation for determining direction 

 has two distinct disadvantages : first, it cannot be operated when the 

 boat is running and second, it must be lowered before taking a 

 bearing and hoisted before the boat can again get under way, thus 

 causing considerable labor and loss of time. This defect was early, 

 recognized and overcome by the workers at the Naval Experimental 

 Station who developed a method whereby the binaural principle for 

 determining direction could be employed without the inconvenience 

 of rotating the two receivers. This development opened up a wide 

 field for research which has resulted in the most serviceable types 

 of submarine detectors. 



The Principle of Binaural Compensation is readily understood 

 by referring to Fig. i, Plate III. Suppose the two receivers R and 

 L are connected to the right and left ear respectively and sound 

 comes from the direction indicated by arrow i. This sound reaches 

 R first and as a result appears to the listener to be located on his 

 right. If the tube leading to the right ear is lengthened by an 

 amount equal to -/4oo the distance from R to C, the impulses from 

 receiver R will be delayed so that the impulses from both receivers 

 reach their respective ears simultaneously and the sound will appear 

 to the listener to be binaurally centered. The same result could 

 obviously be accomplished by shortening the sound path to the left 

 ear or by lengthening the path from R half the amount and at the 

 same time shortening the path L by the same amount, the only re- 

 quirement for binaural centering being that the path difference be 

 made equal to -/4oo of the distance R io C (-%oo being the ratio of 

 the velocity of sound in air to the velocity in water). 



The path difference between the two receivers is directly de- 

 pendent on the angular separation between the line of the receivers 



