•8 Prof. J. Joly on Scientific 



sound of the explosion would be propagated, small metal 

 cartridges containing about half an ounce of gunpowder 

 were exploded at the bottom off the coast of Dublin. The 

 explosion was heard with astonishing distinctness at least 

 a mile away in boats unprovided with any form of sound- 

 receiving apparatus. The sound was perceived in an open 

 boat as an apparent blow or percussion against the bottom 

 of the boat.* 



The apparatus both for sending out and receiving submarine 

 signals has been developed to a high pitch of reliability, 

 largely due to American initiative and to the scientific 

 methods of the Submarine Signal Company. As may be 

 imagined, a long period of suggestions, initial experiments, 

 and abortive patents preceded the existing apparatus. The 

 submarine bell has taken its place as a standard means of 

 sound-production, although invention in other directions has 

 produced wonderful results as we shall see. Repeated trials 

 of various types of bell have resulted in a pattern weighing 

 220 lb., made of bronze, and with a period of 1215 

 vibrations in water. This bell is now doing duty in every 

 part of the world : on lightships ; bell buoys ; on the bottom 

 of the sea ; at the pier-head or on ships. 



The striking mechanism is contained in a cylindrical bronze 

 -case attached above the bell (PI. I. fig. 2). The striking is 

 generally operated pneumatically. A twin rubber-hose pipe 

 connects the bell, which is suspended by a chain at a depth 

 of about 18 feet, with a reservoir of compressed air on the 

 lightship, or shore station . This reservoir is kept pumped full, 

 -of compressed air by means of a small oil or steam engine. 

 The mechanism for operating the bell-stroke is simple. 

 An air-driven codtf regulating valve forms part of the over- 

 water plant and determines the frequency and character of 

 the submarine signal. Some 30 or o5 strokes may be struck 

 per minute. In 1906 the United States Government tested 

 five of these bells for 51 days ; the ringing being continuous, 

 six seconds between the blows. Their introduction into 

 England was slower than in the States. The British 

 Admiralty tested the system later that same year and 

 reported as follows :".... The submarine bell increases 

 the range at which the fog signal can be heard by a vessel, 

 until it approximates to the range of a light-vessel's light in 

 clear weather, and moreover its bearing can be determined 



* A patent was obtained at the time (1890) for this form of sounding 

 machine. Failing any encouragement from the Admiralty, it was 

 abandoned. Some years later the" method was independently re-patented 

 by an officer in H.M. Navy. 



