THE CONQUEST OF TIME AND SPACE 



Gray signaling device offers a substitute in the form of 

 a submerged "artificial ear" — an electrical transmit- 

 ter, connected with a telephone receiver. 



In the early experiments a small hollow brass ball 

 filled with water and containing a special form of elec- 

 trical transmitter was lowered over the side of a ship 

 and connected by insulated wires to the receiver of a 

 telephone in the pilot house. The sound of a sub- 

 merged bell could be heard in this manner at a dis- 

 tance of ten or twelve miles. The location of the bell 

 could be determined by having two such brass balls, 

 one on each side of the hull of the vessel but not sub- 

 merged to a depth below that of the hull, so that the 

 ship itself acts as a screen in obstructing the sound 

 waves coming from the bell. By listening alternately 

 to the sounds of the bell transmitted through these two 

 submerged balls it was found that the ball on the side 

 of the ship toward the bell gave a distinctly louder 

 sound. By turning the ship so that the sounds were of 

 equal intensity the direction of the bell could be deter- 

 mined as either directly ahead or astern; and by using 

 the compass the exact location could be determined. 



But such brass-ball transmitters can be used only 

 when the vessel is moving at a rate not exceeding three 

 miles an hour. They are, therefore, of little value for 

 ocean liners whose reduced speed far exceeds this. But 

 the inventors discovered presently that by using the 

 inside of the outer steel skin of the ship's hull below 

 the water line as one side of the brass ball, the trans- 

 mitter would work equally well. Indeed, with added 

 improvements, this hollow metal device fastened to the 



[86] 



