A New System for Preventing Collisions at Sea 



or at a very great distance from the ship, a very small bell 

 rings, while a large object at a distance of two miles would 

 ring a larger bell, and a very large object a still larger bell. 

 This apparatus gives an audible notice if anything is ahead 

 of the ship. 



The other apparatus is similar, but instead of ringing a bell 

 it produces a diagram of the disturbances in the air that is, 

 when there is no noise except that due to the action of the ship 

 or the seawaves, a wavy line is produced, but whenever the 

 vibrations sent out by the vibrator strike an object and return, 

 the wavy line on the paper becomes very much increased in 

 amplitude so as to be easily observed (see frontispiece), and 

 the distance that the object is from the ship can be measured 

 by the length of the paper strip between the giving off of the 

 vibrations and the receiving of the echo ; therefore, the distance 

 can be determined with a considerable degree of nicety, and 

 the size of the object may be determined by the amplitude of 

 the waves that return. 



Very extensive experiments were conducted about forty years 

 ago by Professor Tyndall at the South Foreland. He found 

 that a deep note emitted by a powerful siren travelled a very 

 long distance, and he was rather surprised at the volume of 

 sound that was reflected back from a ship. At that time it 

 was generally supposed that snow, rain, and fog were very un- 

 favourable to the travel of sound, but in his experiments he 

 found that such was not the case. I quote the following from 

 his work on " Sound " : 



u Rain has no sensible power to obstruct Sound. 

 " Hail has no sensible power to obstruct Sound. 

 <4 Snow has no sensible power to obstruct Sound. 

 " Fog has no sensible power to obstruct Sound." 



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