806 



Popular Science Monthly 



Although the submarine is bHnd after it dives it can be made to hear with the aid of micro- 

 phones. If two hostile submarines were equipped so that they could hear each other there 

 is no reason why they should not fight under water. Torpedoes would be the weapons 

 used — torpedoes directed solely by the sound emanating from the craft to be destroyed 



marine could locate his prey by sound; 

 suppose that he could hear a ship and 

 locate her by sound more accurately, for 

 example, than a blind man can locate the 

 position of a ticking clock in a room? 

 Might not that solve the problem? 



With this thought in mind, I have 

 worked out a method of utilizing micro- 

 phones — a method which is a modifica- 

 tion and extension of that which I 

 described in the Popular Science 

 Monthly for October, 191 5. Those 

 who read that article will remember 

 that I showed how it was possible to 

 make a torpedo guide itself toward the 

 beating propellers of a ship with the aid 

 of microphones — "electrical ears," as I 

 call them. A microphone is found in 

 every telephone transmitter. It is an 

 instrument for intensifying feeble sounds, 

 or for transmitting sounds, and it is 

 based on the principle that the transi- 

 tion between loosely joined electric con- 

 ductors decreases in proportion as they 

 are pressed together. The conductors 

 form part of a circuit through which a 



current is passing, and the variations in 

 pressure due to sound waves in the 

 vicinity of the conductors produce 

 variations of resistance, and hence 

 fluctuations of the current, so that the 

 sounds are reproduced in a telephone 

 receiver. In the modern telephone the 

 transmitter is essentially a microphone, 

 the pressure of the sound waves being 

 communicated to the conductors by 

 means of a diaphragm. 



In a torpedo of the type I described in 

 the Popular Science Monthly, the 

 microphones are mounted in pairs on 

 both sides of the nose. So long as the 

 sound of the hostile ship's beating pro- 

 pellers, traveling through water far more 

 readily than sounds travel through air, 

 affect all microphones with equal 

 intensity, the torpedo rushes on straight 

 to its mark. But if the vessel should 

 change its course, the vibrations of the 

 propellers would no longer strike the 

 two pairs of microphones with equal 

 force; one pair would be more affected 

 than the other — the pair directly ex- 



