METHOD OF SAFE NAVIGATION IN FOG. 117 



times at short distances the jets of a steam whistle are counted, yet the sound is 

 not heard. 



These facts force us to the conclusion that present methods of navigating ves- 

 sels in a fog are totally inadequate to insure reasonable security to life and prop- 

 erty, and that danger always exists, which the skill of the personnel cannot elim- 

 inate. The recent collisions between the S. S. New York and Pretoria and 

 between the S. S. Kaiser Wilhelm II and Incemore are still fresh in the public mind. 

 There seems to be no evidence to show that these large passenger vessels were in- 

 efficiently handled. The reason that collisions are not even more frequent is due 

 solely to the fact that the oceans are vast and ships at sea so widely scattered that 

 by chance they usually have plenty of sea room. 



Fortunately, investigations have shown that water, unlike air, is an excellent 

 sovmd medium, and does not appear to suffer from the acoustic clouds and erratic 

 reflections found in air by Tyndall. 



A brief history of submarine sound signals indicates that investigations to de- 

 termine the uniform character of water as a sound medium have not been car- 

 ried out with the thoroughness of similar experiments in air, and still present a 

 fertile field for scientific cultivation. 



The results of experience demonstrate that the density, homogeneity and elas- 

 ticity of water render it many times more efficient than air in transmitting the 

 pressure waves of sound. 



Primitive man doubtless used some crude methods of submarine signaling, 

 and from time immemorial Cingalese fisherrnen have used code signals by striking 

 an earthen bowl held submerged outside their fishing boats. The sound would be 

 heard by placing the ear against the hull of another boat miles distant. 



It has long been a matter of common knowledge that sound would pass through 

 water for considerable distances, and that an observer stationed below the water- 

 line could hear the sound after it had passed through the side of the vessel. 



The classic experiments of two scientists, Colladon and Sturm, conducted in 

 Lake Geneva in 1826, furnished the most exhaustive and complete data of the early 

 investigators in sound transmission through water. They employed for this pur- 

 pose a large submerged bell, and received the sound through a very large and 

 specially constructed ear trumpet. A flame upon the end of the lever which caused 

 the bell to ring simultaneously ignited gunpowder, and the elapsed time from the 

 instantaneous flash and the reception of the sound measured its velocity. These ex- 

 perimenters found that the sound could be transmitted entirely across Lake Geneva, 

 a range of 32 kilometers being obtained. The velocity of sound was determined 

 with reasonable accuracy, and found to be 4,708 feet per second. They also discov- 

 ered that the bell tone as ordinarily understood decreases with remarkable rapidity 

 in water, so that after a few hundred yards only a percussive click could be dis- 

 tinguished. Colladon likened this sound very aptly to that made by the back of 

 two knife blades when struck together. All who are familiar with the use of the 

 submarine bell in navigation will recognize the description of the sound. Observers 



