HAYES— DETECTION OF SUBMARINES. 



19 



neither the maximum nor minimum is well defined it is impossible to 

 determine direction with any degree of accuracy. 



The Mark II. receiver is very similar to the Mark I. except that 

 it carries no sound screen. It is equally sensitive to sounds striking 



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Plate V. Principle of English listening devices. 



either side of the diaphragm. Thus there are two positions for the 

 receiver where the sound intensity will be at a maximum and neither 

 of these positions is" sharply defined. A sound proceeding in a 

 direction parallel to the diaphragm afitects the two sides equally and 

 in opposite sense so there is no motion of the diaphragm and the in- 

 tensity of the received sound is practically zero. This minimum 

 position is very sharply defined and will determine the direction of a 

 sound with high accuracy except for an ambiguity of i8o degrees. 



In the Nash Fish and certain submarine installations both the 

 Mark I. and the Mark II. are used, the line of direction being de- 

 termined by the minimum setting on the Mark II. and the ambiguity 

 being removed by the Mark I. These installations, especially the 

 Nash Fish, are complicated due to the fact that remote control 



