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October, 1921 tiple-pole, double-throw switch. The sound will be off the side of the ves- sel carrying the line of receivers giv- ing the loudest response. A sound pro- ceeding from the direction indicated in Fig. 1 would give a loud response on the starboard receivers, but, due is the shielding effect of the sound screen, it would appear very weak on the port line of receivers. Gives More Information In thus determining whether a sound source is located off the port or star- board side of a vessel, the MV _ hy- drophone furnishes the navigator with all the information which. the pres- ent types of sound apparatus installed on vessels for navigational purposes can furnish. Moreover, because of its ability to bring into focus the sound which it is desired to hear and at the same time weaken the local dis- turbing sounds, it is able to detect sounds too’ faint to be heard on other types of receivers and in general, to hear all sounds at a greater range. But the information furnished by the MV hydrophone :s not limited to telling on which side of a vessel a is located. It readily sound source determines, with considerable accur- acy, the actual bearing of the sound source. The method of doing this may be understood vy considering Fig: 2. This figure represents a line of receivers and their respective circuits through the compensator. All 12 re- ceivers, numbered 1 to 12 inclusive, are connected in parallel with battery B. The battery circuit can be opened or closed by means of switch, S. Each receiver circuit contains the primary coil of a small transformer. The 12 transformers are identical and are used to prevent the direct current furnished by the battery from »assing through the telephone receivers. One terminal of the secondary coil of each trans- former is connected to a common lead from the two telephone receivers. An electrical retardation line, represented schematically by an extended coil, at- taches to the other terminal of the secondary coil of each of the 12 trans- formers. The point of current take- off from each of the retardation lines can be varied by means of a movable contact point represented on each of the lines by an arrow-head. The cur- rent induced in the secondary coils of the transformers connected with the first six receivers meet at a common junction, J, and from there pass through the receiver, L. In a like manner, the currents induced in the secondary coils of the other six trans- formers unite at the common junction, MARINE REVIEW, FIG. 2—SCHEMATIC WIRING DIAGRAM OF AN ELECTRICAL M-V COMPENSATOR CONNECTED TO A LINE OF RECEIVERS r, and from there pass through the re- ceiver, FR. | Consider a sound from a_ distant source to be approaching from a di- rection perpendicular to tne line of receivers. Its wave front will then be parallel with the line or receivers, as represented by the full line, U-U, and its direction will be represented by the five arrows abutting on this line. It is evident that the electrical im- ‘pulses which the sound waves set up in each of the 12 receivers will be alike, providing the receivers are all alike, and that corresponding varia- tions in the current from each of the receivers will take place simultane- ously. Will Not Be Simultaneous It also is evident that if the sound approaches from any other direction, such that its wave front, as repre- sented by the broken line, V-V, is not parallel to the line of receivers, then the current impulses which the sound waves set up in the several receivers will be identical, but corresponding variations of the current in the sev- ‘and those “enit’ of amount and so on progressively for eral circuits will not take place simui- . taneously, or, in other words, the cur- rent in the several circuits will not be in phase. For the wave having front V-V, the phase of the current impulses in the circuit of receiver (1) are in advance of those in the circuit of receiver (2), in the circuit of. receiver (2) are in advance of those in the cir- receiver (3) by the same receivers, until for re- ceiver (12) the current impulses of its circuit lag behind those of the circuit of receiver (1) by an amount that is eleven times that between the impulses in circuits (1) and (2). Final- ly, it is to be noticed that the actual value of the phase difference between any or all of the currents of the sev- eral circuits depends upon the direc- tion of the sound, or its wave front, with respect to the line of receivers. The phase relations between the cur- rent in the several secondary circuits can be varied at will by introducing more or less of the retardation lines into the several circuits by means of the various