HAYES— DETECTION OF SUBMARINES. 



23 



before the boat can get under way. Plate VIII. a shows one form 

 of the C-Tube developed at Nahant. (See page 30.) 



The " S'Spot" detector operates on the principle of binaural 

 compensation and was developed soon after this principle was estab- 

 lished at the Naval Experimental Station. An improved type of 

 microphonic submarine receiver called a " rat " was developed which 

 proved highly sensitive, non-resonant, and durable. The construc- 

 tion is shown in Plate VIII. h. The microphone is carried by a rubber 

 diaphragm which encloses a water-tight space housing the micro- 



Plate VIII. b. The microphone housing or " rat," developed by the General 

 Electric Company for "3-Spot" detectors. 



phone. The leads to the microphone pass through a water-tight 

 stitffing-box at the end of the cylindrical shaped chamber opposite to 

 the diaphragm. Three of these receivers are fixed in position at the 

 vertices of an equilateral triangle four feet on a side. One lead 

 from each microphone attaches to a common lead into which a bat- 

 tery is connected in series. The other three leads, one from each re- 

 ceiver, pass through small inductance coils and thence to the com- 

 mon. A special type of telephone receiver connected in series with 

 a condenser is shunted across the inductance. This wiring scheme 

 is shown in Fig. i, Plate IX. Figs. 2 and 3 show other schemes used 

 for connecting in the telephone which are employed in devices de- 

 veloped at the Naval Experimental Station. 



The two telephone receivers are attached respectively to the two 

 inlets to the compensator so that the sound is required to pass 

 through the compensator and the stethoscope leads before reaching 

 the ears. 



A neatly designed switch arrangement makes it possible to con- 



