HAYES— DETECTION OF SUBMARINES. 



17 



carries two projecting blocks carefully formed to give a sliding fit in 

 the grooves of the upper plate. The lower plate is perforated by 

 four holes, numbered i, 2, 3, and 4 in the figure, which open respec- 

 tively through the ends of the two blocks B and C. Thus two con- 



Plate IV. a. Double-groove binaural compensator. 



tinuous air-paths traverse the compensator, one connecting from i to 

 3 through that part of the groove marked R and the other connecting 

 from 2 to 4 through the other part of the groove marked L. By 

 rotating the top plate the difference in the length of the two air-paths 

 can be varied at will up to the capacity of the compensator. 



PROC. AMER. PHIL. SOC, VOL. LIX, H, MAR. I9, I92O. 



