The Operation and Use of the Apparatus 



length of paper between the primary blast and the echo would 

 indicate the distance that the object was from the ship. It 

 might be so arranged that one inch of paper represented a mile. 



The receiving instruments can be placed anywhere on the 

 ship where they can be turned in the same direction that 

 the siren is turned, and there may be as many of them as 

 desirable. 



Of course, there are vastly more accidents caused by 

 running ashore than by collisions at sea, and it does not 

 require a very bold sea front to produce a very strong echo. 

 For example, in approaching the coast of Ireland, the echo 

 would be sufficiently strong to show itself over a distance of 

 at least ten miles. 



To many it will doubtless appear very difficult, even on the 

 verge of the impossible, to reveal the presence of objects at sea 

 by simply sending out atmospheric vibrations and receiving 

 the echo of the same. One might ask, how can it be possible 

 to judge of the size, distance, and character of the object 

 by the echo ? If, however, we make a careful study of the 

 matter, we shall find, if we send out a powerful blast of 

 sound like a deep musical note, that it will travel a long 

 distance, and if it strikes any object of considerable size, it 

 will send back a reflection or echo. Sound is nothing more 

 nor less than atmospheric vibrations. If there are less than 

 sixteen vibrations in a second of time, they are not audible 

 to our ears; we do not hear them, although we may feel 

 them. They may be of great power and able to travel a 

 long distance, and if they should happen to strike any 

 object they send back an echo which, although completely 

 inaudible to our ears, is sufficient to record itself by suitable 



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