THE NATIONAL RESEARCH COUNCIL 21 



sentatives, with officers of the Navy Department, and the 

 physicists and engineers who had already studied the question 

 in this country, participated. 1 In order to make clear the 

 general nature of the methods discussed, the following brief 

 description of the apparatus employed may be of service. 



Submarine detection devices are of two principal classes : 

 listening apparatus, on the principle of the microphone or the 

 stethoscope, and instruments analogous to searchlights for use 

 under water, in which the beam of light is replaced by a beam 

 of sound. A simple physician's stethoscope, if placed under 

 water and connected to the ear by tubing, will render audible 

 the sound from a rapidly moving submarine at a distance of 

 a mile or more. Indeed, a small piece of rubber tubing, if 

 substituted for the stethoscope, will serve very well as a sound 

 detector. By connecting with the ears two stethoscopes, at 

 opposite ends of a supporting bar three or four feet long, the 

 direction of a moving submarine can be determined with con- 

 siderable accuracy by rotating the bar in a horizontal plane and 

 utilizing the same binaural discrimination with which we as- 

 certain the direction of sounds without apparatus. By re- 

 fining this apparatus, it is even possible to employ it on a sub- 

 marine destroyer moving at a speed of several knots, in spite 

 of the local sounds due to the destroyer. However, the 

 method is seriously limited in actual practice ; it cannot be used 

 on vessels moving at high speed, it cannot detect submarines 

 lying at rest or moving at low speed, and confusion may result 

 from the presence of several surface vessels, as in the case of 

 a convoy. 



We therefore look for assistance to an entirely different 

 device. A beam from a searchlight is quenched by a short 

 thickness of water, but a beam of high frequency sound waves 



1 Three able groups of investigators were already at work on this 

 question in the United States under the Bureau of Steam Engineering 

 of the Navy, and both the Naval Consulting Board and the National 

 Research Council had taken part in promoting studies of the submarine 

 problem. 



