HAYES— DETECTION OF SUBMARINES. 25 



curacy, is simple and rapid in operation, and is capable of giving 

 long range if there are no disturbing noises present. 



The chief difficulty in submarine detection by sound lies in the 

 fact that under normal operating conditions the detecting apparatus 

 is mounted in the midst of numerous sound sources such as pro- 

 peller and machinery noises on the listening boat, breaking of waves 

 and slapping of waves on the boat, noises from promiscuous ship- 

 ping, etc. The range at which a submarine can be detected is largely 

 dependent on the ratio of the intensity of the sound from the sub- 

 marine as compared with that from other sources. Increasing the 

 sensitiveness of the receivers beyond a certain limit is of no advan- 

 tage since the disturbing noises are magnified in the same proportion 

 as are the sounds from the submarine. 



Under such circumstances it becomes necessary to devise an 

 instrument that will magnify the sound coming from a definite 

 direction without correspondingly magnifying sounds from other 

 directions. 



This result can be accomplished by using sound lenses or mirrors, 

 an example of which is the " Walser Plate," but because of the length 

 of sound waves in water their area must be so great, if they are to 

 give a marked advantage that their use is practically prohibited. As 

 soon as the principle of compensation was recognized it became evi- 

 dent that instead of a single receiver connecting with each ear it 

 would be advantageous to have several receivers spaced some dis- 

 tance apart, provided a compensator could be devised that would 

 not only make it possible to binaurally center the composite sound 

 reaching each ear from its respective group of receivers but at the 

 same time would compensate the separate air paths to the individual 

 receivers so that the sound response from all would arrive at the lis- 

 tener's ears in phase. By properly adjusting such a compensator the 

 response from the several receivers to sound from any particular 

 direction could be brought to the listener's ears in phase and since 

 under these conditions the intensity of the sound will be equal to the 

 sum of the intensities from the several receivers the sound reception 

 from this particular direction will be magnified. 



It is evident that for this same setting of the compensator the 

 response from the several receivers to sound from any other direc- 



