20 



HAYES— DETECTION OF SUBMARINES. 



motors are required to rotate the receivers. They are also subject 

 to the defects which are inherent in resonance receivers, viz., their 

 sound response is devoid of quality and their operation is strongly 

 interfered with by local noises and noises from neighboring shipping. 



Submarine Detectors Developed by the French. 

 Two types of submarine detectors have been developed by the 

 French— the " Perrin Microphone " and " The Walser Plate." The 



Plate VI. Installation of Walzer Plate (sound lens) apparatus. 



