206 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1915. 



follow each other, the different intervals being peculiar to the dif- 

 ferent signal stations, so that the captain of a ship by counting the 

 strokes of the bell can determine what lightship is producing the 

 sound. 



In order to receive the sound it has been found absolutely necessary 

 to suspend the microphone in a tank of water, for this is the only 

 method of cutting out the water noises and the noises due to ma- 

 chinery, etc., on board the ship which otherwise drown out the sound 

 of the bell. 



One of these small water tanks, containing a microphone of a spe- 

 cial type, is attached to each side of the bow inside of the ship. 

 From each tank wires are run to a device which is called the indi- 

 cator box, so arranged that by throwing the handle to one side the 

 starboard microphone is connected to the telephone, and by throw- 

 ing the handle to the other side the port microphone is connected. 



It will be obvious that once the bell is picked up the captain has 

 only to turn his vessel until the sound is heard with equal intensity 

 on each side, to know that his ship is then pointing in the direction 

 from which the sound is coming, and in this way he can take com- 

 pass bearings of the lightship on Avhich the bell is situated. 



The importance of this method will be at once perceived. No 

 matter how stormy or how foggy the weather may be, it enables the 

 captain of a ship, on making land, to obtain at once the compass 

 bearings of the nearest lightship or lighthouse fitted with a bell. 



How many vessels and how many lives this device has saved even 

 in the few years during which it has been in use it Avould be im- 

 possible to tell. Less sensational than the wireless telegraph, it may 

 be questioned whether its actual practical utility to the merchant 

 marine has not been greater. 



Compressed air, or an electromagnetic mechanism, may swing the 

 hammer, or the bell may be operated by the Avaves themselves. A 

 type much used is a bell buoy which may be anchored off a shoal, 

 and will give submarine Avarning day and night without further 

 attention. A large vane extends from one side of the mechanism. As 

 the buoy swings up and doAvn in the water, the vane by means of a 

 ratchet compresses a spring Avhich automatically releases and operates 

 the bell hammer. 



It will be evident that even if no further development had been 

 made the system would be and is a complete and practical one. Its 

 universal adoption would greatly minimize, if not entirely prevent, 

 disasters due to errors of ship position. 



But, with the very success of this system it became evident to those 

 in charge of its development that still further advances might be 

 conceived as possible, especially in three directions. 



