THE HIGHWAY OF THE WATERS 



mate idea of where they could find her. The use of 

 another electric appliance, of even more recent inven- 

 tion than the wireless telegraph, was necessary for 

 locating the exact position of the stricken ship. This 

 was the submarine signahng device, which utilizes 

 water instead of air as a medium for transmitting 

 sound. 



Benjamin Franklin pointed out more than a century 

 ago that water carries sound farther and faster than 

 air, and carries it with greater constancy. Density, 

 temperature, and motion of the atmosphere act upon 

 aerial sound waves to reflect and refract them in vary- 

 ing degrees; but these waves are not affected when 

 water is the medium through which they are passing. 

 The knowledge of these facts was turned to little prac- 

 tical account until the closing years of the last century 

 when Arthur J. Mundy of Boston, and a little later 

 Prof. Elisha Gray of Chicago, began experiments to- 

 gether that resulted finally in a practical submarine 

 signaling apparatus which is now installed as a system 

 on boats and buoys in dangerous places along the coasts, 

 particularly near the great highways of ocean travel. 



The principle upon which this system is based is 

 simply that of sound waves transmitted through the 

 water and detected at a distance by a submerged elec- 

 trical transmitter. The sound transmitted is usually 

 that of a submerged bell. It is possible for a person 

 whose head is submerged to hear the ringing of such 

 a bell distinctly for a long distance; but of course for 

 practical purposes such submergence is out of the 

 question. The receiving apparatus of the Mundy- 



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