46 CONTEMPORARY SCIENCE 



enables the listener to recognize the direction from which 

 the sound emanates. 



When the vessel is in motion or the sea is rough the 

 water noises from the dragging of the instrument through 

 the water and from the waves striking the ship drown 

 the noises from the enemy vessel, and under such condi- 

 tions the instruments are useless. The assistance of emi- 

 nent biologists was of invaluable help at this juncture. 

 Experiments were made with sea-lions by Sir Richard 

 Paget, who found that they have directional hearing 

 under water up to speeds of six knots. Also Professor 

 Keith explained the construction of the hearing organs 

 of the whale, the ear proper being a capillary tube, too 

 .small to be capable of performing any useful function in 

 transmitting sound to the relatively large aural organs, 

 which are deep set in the head. The whale therefore 

 hears by means of the sound waves transmitted through 

 the substance of the head. It was further seen that the 

 organs of hearing of the whale to some degree resembled 

 the hydrophone. 



The course now became clear. Hollow towing bodies 

 in the form of fish or porpoises were made of celluloid, 

 varnished canvas, or very thin metal, and the hydrophone 

 .suitably fixed in the center of the head. The body is 

 filled with water, and the cable towing the fish contains 

 the insulated leads to the observer on board the vessel. 

 When towed at some distance behind the chasing ship 

 disturbing noises are small, and enemy noises can be 

 heard up to speeds of 14 knots, and at considerable dis- 

 tances. Thermionic amplifying valves have been exten- 

 sively used, and have added much to the sensitiveness of 

 the hydrophone in its many forms. 



After the loss of the Titanic by collision with an iceberg, 

 Lewis Richardson was granted two patents in 1912 for 

 the detection of above- water objects by their echo in the 

 .air, and underwater objects by their echo transmitted 

 through the water. The principles governing the produc- 



