Popular Science Monflihi 



713 





by it can be made to have any 

 sustained duration desired, 

 so long as the felt-rimmed 

 wheel rubs on the steel strip 



—T 



FOUR I RON CROSS- 

 PIECES WHICH BRACE 

 HULL AROUND VI- 

 BRATING STRIP AND 

 PREVENT HULL PLATES 

 FROM SETTING UP 

 INTERFERING VI- 

 BRATIONS OF THEIR 

 rOWN 



It is a queer world, this — down "under 

 the sea." It might be supposed that no 

 sounds at all can be heard under water. 

 The opposite is true. Sounds carry 

 better in a dense medium like water than 

 in a comparativeh' "thin" gas such as 

 air. All sorts of sounds can be heard 

 under water — the throb of some distant 

 ship's propeller, the pounding of engines, 

 the explosion of distant mines, and 

 hundreds of other noises. A micro- 

 phone, placed in a chamber of water at 

 the side of the receiving vessel and con- 

 nected with a telephone receiver, aids in 

 this hearing. Singhalese fishermen, how- 

 e\er, have for centuries carried on com- 

 munication between boats by the simple 

 method of striking an earthen bowl 

 under water, the listening fisherman 



Vibrations from the interior 



ship's hull do not interfere with the signals 



placing his ear against the bare hull 

 of his boat. 



Submarine bells are already in use 

 as fog warnings. Some attempt has 

 been made to adapt them to the send- 

 ing of Morse telegraph signals between 

 one boat and another, as for instance 

 between a warship and a submarine. The 

 sound from submarine bells, however, 

 docs not endure; it is not sustained. In 

 other words, one stroke on a bell sounds 

 to the underwater listener just like any 

 other stroke. All the strokes are short — 

 have no duration. Since all the sounds are 

 "dots," it is obviously impossible to send 

 Morse signals, dependent on both dots 

 and dashes (short and long sounds). 

 Moreover, seamen who have listened to 

 these underwater bells sa>' that in a 

 few feet a bell's sound loses its char- 

 acteristic bell-like tone. The sound 

 simply comes to the ears of the listener 

 as a dull, leaden "click," something like 

 that produced when two ordinan,- table- 

 spoons or a knife and fork are struck 



