THE SUBMARINE CABLE 



INSTRUMENTAL AIDS 



The instruments used for sending and receiving 

 messages over two thousand miles of cable are not the 

 comparatively simple transmitters and receivers of land 

 telegraphy, where relays can be installed and the current 

 increased at various points along the line. The instru- 

 ment first used for receiving cable messages was Lord 

 Kelvin's "marine galvanometer" referred to a moment 

 ago. When this little instrument is suspended near a 

 fine-wire coil, it takes a position at right angles to the 

 plane of the coil when the current is on, being deflected 

 to right or left according to the direction of the current. 

 These movements to right or left are interpreted as 

 dots and dashes respectively, and thus the Morse code 

 can be used as in land telegraphy. 



Another instrument that came into use shortly was 

 the "spark recorder" an instrument so arranged that 

 sparks were projected against a surface of paper, or some 

 other sensitized surface, passing at uniform speed. The 

 message was thus recorded as an undulating line of 

 dots or perforations which could be read and transcribed 

 into writing by the operator. 



But this instrument was soon replaced by another in- 

 strument, the "siphon recorder," first patented by Lord 

 Kelvin in 1867. In this, a tube of ink is so arranged 

 that as the message comes over the wire fine drops of 

 ink are projected upon a piece of paper in a wavy line, 

 the dots and dashes of the Morse code being represented 

 by deflections of the line of ink-dots to one side or the other 

 of a central line on the paper. 



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