HAYES— DETECTION OF SUBMARINES. 21 



Perrin Microphone, see Fig. i, Plate II., consists of a sensitive micro- 

 phone mounted within a massive conical-shaped shield. Like the 

 Mark I. it determines direction by the maximum-minimum principle 

 and is not capable of giving accurate bearings for the reason that 

 neither the maximum nor minimum is well defined. 



Some idea of the construction and operation of the Walser Plate 

 detector can be gained from Plate VI. The plate proper forms a 

 portion of the ship's skin. The surface is convex outward, the cur- 

 vature being such that a sound wave passing from the water through 

 the plate is brought to a focus within the boat. The plate is per- 

 forated with numerous holes, each of which is closed by a thin metal 

 diaphragm, in order that the sound may pass more freely. One such 

 plate is installed on each side of the boat. 



Each plate really serves as a sound lens and the direction of the 

 sound source is determined from the position of the sound focus 

 within the ship. The position of this focus is located by means of a 

 movable trumpet which connects with the listener's ears. The frame- 

 work upon which the trumpet arm is pivoted is suspended fore and 

 aft on gimbals and counterbalanced so that the trumpet remains in 

 the same horizontal plane that contains the focus. 



In many respects the Walser Plate is a superior device. Due to 

 its focusing effect the disturbance from local and other undesirable 

 sounds is greatly reduced while desirable sounds are concentrated 

 and intensified. The device can be operated while moving at con- 

 siderable speed and good results both as regards range and bearing 

 are claimed. It has, however, the double disadvantage that it is ex- 

 pensive and difficult to install. In fact its dimensions are such that 

 it cannot be installed on many types of boats. 



Submarine Detectors Developed in the United States, 



Plate VII. shows the principle of two types of submarine sound 

 detectors which were developed by the Submarine Signal Company 

 for locating submarine bell signals installed on light-ships. Each of 

 the small tanks attached to the ship's skin carries a microphone re- 

 ceiver tuned to the submarine bells. These microphones each con- 

 nect with a single telephone receiver on the ship's bridge. These 

 tanks are filled with oil or water. By comparing the intensity of a 



