HAYES— DETECTION OF SUBMARINES. 31 



within a large tank inside the ship or more usually underneath a pro- 

 tecting bhster on the outside of the ship's skin. The line of receivers 

 is in all cases mounted as near parallel to the ship's keel as conditions 

 will permit, one such line being mounted on each side of the ship and 

 directly opposite one another. The receivers in each half of the line 

 are grouped together, each group connecting with one ear respec- 

 tively, in order that the binaural principle may be employed in deter- 

 mining direction. 



Theoretically the focusing effect is intensified by increasing the 

 length of line and the number of receivers, but practically the me- 

 chanical difficulties encountered in compensation tends to limit both 

 the length of line and the number of receivers. The principle of 

 operation of a Hne of twelve receivers is shown in Plate XII. 



In Fig. 2 let numerals i, 2, and 3 represent three receivers equally 

 spaced and connecting to the common junction through the three 

 separate paths a, b, and c respectively. Paths a and c are provided 

 with a trombone arrangement such that their length can be varied at 

 will while path b has a fixed length equal to that of both a and c 

 when the trombone slides are adjusted to have equal paths. The 

 response from the three receivers will reach the junction A in phase 

 for sound travelling in a direction perpendicular to the line of the re- 

 ceivers, that represented by the arrow. 



Sound proceeding in a direction as represented by the arrow in 

 Fig. I does not actuate the three receivers simultaneously but in the 

 order i, 2, 3. It is evident that a proper lengthening of the path a 

 and the same shortening of the path c will bring the responses from 

 the three receivers in phase at the junction A. If the sound comes 

 from a direction as indicated in Fig. 3 the variation of the paths a 

 and c must be in the opposite order to bring the responses from the 

 receivers in phase at junction A. 



Consider a line of twelve equally spaced receivers divided into 

 four groups of three receivers each, as shown in Fig. 4. Receivers 

 I and 3 connect to the junction A through a simple "2-Spot" com- 

 pensator of the type already described, while receiver 2 is connected 

 to A through a fixed path equal to that from both receivers i and 3 

 when the compensator is so adjusted that their path lengths are 

 equal. The responses from the three receivers can be brought to A 



