Signalling and Safety at Sea, 1 



about the advent of submarine signalling. The idea is really 

 an old one. It has long been known that sound travels 

 under water with remarkably little loss of clearness and 

 intensity. In 1826 (•ollodon and Sturm carried out their 

 well-known experiment on the Lake of Geneva. The object 

 of this experiment was to ascertain the velocity of sound in 

 water. A submerged bell was used. The hammer which 

 struck the bell was so connected with a trigger above the 

 water that a charge of gunpowder was ignited at the instant 

 of the striking of the bell. An observer in a boat at a 

 certain measured distance listened at a hearing trumpet 

 immersed in the lake. He heard the sound of the bell as 

 propagated through the water and saw the flash of the 

 explosion as propagated through the aether. Assuming the 

 velocity of the latter to be comparatively infinite, the interval 

 between the seeing of the flash and the hearing of the bell 

 affords the velocity of sound in water. Obviously we can 

 reverse the objective of this experiment. Knowing the 

 velocity of sound in water and measuring the interval of 

 time elapsing between the flash and the sound, we can 

 determine the distance over which the latter has travelled. 



The fact of the easy propagation of sound through w r ater 

 is an old discovery of the diver. The perfect audibility is 

 even startling. It is said that a lost watch, which being 

 watertight continued to go, was recovered by a diver tracing 

 the tick of the watch to its source *. 



Many years ago I experimented on the audibility of ex- 

 plosive sound signals beneath water. The object in view 

 was to test a method of determining the depth beneath a ship 

 travelling at full speed, by the dropping of a sinker which 

 would detonate a small charge of explosive on contact with 

 the bottom. The time interval between the moment of 

 releasing the sinker and hearing the explosion, knowing the 

 rate of descent of the sinker, gives the depth w r ith sufficient 

 accuracy. In order to test the distance to which the 



* We may note parenthetically the curious fact that marine animals 

 do uot seem to avail themselves of this property of the medium in which 

 they live to the extent we might have expected. The organism appears 

 to be ever ready to avail itself of every advantage which the nature of 

 the medium offers it. In this case evidence that it does so seems 

 wanting. True it may develop listening orgaus but, whether it seeks 

 to preserve the secrecy which is the chief protection of the submarine, 

 or whether its silence benefits it in some other way, the fact remains 

 that the sounds emitted by rattlesnake or cricket do not appear to be 

 emulated by fish or crustacean. Our sensitive microphones must have 

 discovered the existence of any such devices. The matter deserves 

 further investigation. 



