A New System for Preventing Collisions at Sea 



uniform. We next send out a powerful blast, and find that 

 this has produced a decided series of zigzag lines on the 

 strip of paper. The bells have not sounded because the 

 electric current that rings them is cut off by the act of 

 opening the steam valve of the siren. Nothing is on the 

 paper except the marks produced by the primary blast and 

 the sea waves. We repeat our experiment by pointing our 

 instruments a few degrees to both port and starboard ; still 

 no result. Therefore there is evidently no large object ahead 

 of us, and we proceed in the darkness at 'full speed, repeat- 

 ing our experiments every ten minutes if the weather is 

 foggy. At about midnight, we find a very faint indication 

 of an echo ; the wavy line due to the sea is slightly 

 modified when our instruments are pointed ten degrees to 

 the port, but not when pointed dead ahead or to the star- 

 board. We repeat at the port side with the same result as 

 before, but we find that the little bell of the indicator shows 

 an increased ringing, and a few seconds after we send out 

 our blast from the siren, or vibrator, as we should call it. 

 The echo reaches us 20 seconds after sending out the blast ; 

 consequently, it took 10 seconds for our vibrations to reach 

 the object and another 10 seconds for the reflected vibrations 

 to return ; therefore, the distance is slightly over two miles. 

 Our ship is doing 20 miles per hour, and one minute later 

 we send out another blast, but the result is no stronger than 

 before, so we change the direction of the blast and find 

 that the greatest effect is produced when the blast is sent 

 dead ahead, also that the distance between the object and 

 our ship is being reduced at the rate of 35 miles per hour ; 

 therefore the unknown object is evidently a ship making 15 



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