SUBMARINE SIGNALING BLAKE. 207 



1. Suppose the sound-producing apparatus could be so constructed 

 as to be operated from moving ships by a telegraph key. If this 

 were achieved, it would be possible for one ship to signal to another 

 in fog, to communicate its position, its direction and its speed, and 

 eliminate all dangers of collision. It would also be possible to signal 

 between submarines or betw^een battleships and submarines, and to 

 communicate betAveen battleships in action without interference from 

 the enemy, and though all masts were shot away. 



2. Suppose the range of the sound-producing apparatus could be 

 extended so as to cover a radius of 25 or 50 miles. Then it would be 

 within our power so to encircle the coast of every nation with wiiat 

 has been felicitously termed " a wall of sound," that no vessel, under 

 whatsoever circumstances of loss of reckoning, of variable currents, 

 of fogs, and storms, could approach the coast without being w^arned 

 of that fact and notified of its exact position on that coast and of 

 the direction of the nearest lightship. 



3. If the sound-producing apparatus could be constructed so as 

 to be actuated by telephonic currents, it would be possible to trans- 

 mit speech through the water. 



It will be of interest to consider some of the difficulties which 

 had to be overcome before the desired results could be obtained. 



The most serious of these obstacles was the fact that water is 

 almost incompressible. 



Now, since sound is a compressional wave in the medium through 

 which it is transmitted, it is evident that any apparatus which is 

 to transmit sound through water must be capable of exerting very 

 great force. In the bell this is accomplished by the hammer blow 

 of the clapper, and any electric or other apparatus which is to be 

 used for submarine signaling must have a force comparable with 

 that produced by the impact of a hammer on an anvil. 



A second and very grave difficulty arises from the fact that if 

 the water is to be compressed, some material object must be set in 

 motion to compress it, and that object, which must have sufficient 

 mechanical strength to stand the stress, and must therefore be of 

 considerable size, must start from rest, reach its highest velocity, 

 and come to rest in one one-thousandth part of a second, if a musical 

 note having a pitch of 500 per second is to be produced. The forces 

 of acceleration thus necessitated are very large. 



A third difficulty arises from the fact that in order to telegraph 

 at a speed of 20 words per minute the time allowable for a single 

 dot is very small. As the average word consists of 5 letters, and 

 the average letter has a length equivalent to 7 dots, an apparatus 

 capable of telegraphing at the rate of 20 words per minute must 

 be capable of making 700 dots per minute, or a single dot in some- 

 thing less than one-tenth of a second. 



