330 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



ing the character of a current pulse is called distortion. Land 

 lines distort current pulses to some extent, and the distortion 

 seriously impairs the distinctness of telephonic transmission if the 

 land line is fairly long (see Art. 147). 



The curve a, Fig. 33, represents four short current pulses 



a 



Fig. 33. 



sent into a cable at one end, and the curve b represents the re- 

 sultant pulse of current which flows out of the cable at the other 

 end. The receiving instrument in submarine telegraphy is a gal- 

 vanometer which is arranged to trace the resultant current curve at 

 the receiving end of the cable, and the separate current pulses that 

 are sent into the cable at the sending end are inferred from the 

 slight kinks in the curve which is traced by the receiving instrument. 

 The distortion of electric current pulses by a submarine cable 

 is analogous to the distortion of pulses of water current by a long 

 thin-walled rubber tube. 



35. The syphon recorder is the receiving instrument used in 

 submarine telegraphy. It consists of a D' Arson val-type gal- 

 vanometer, the moving coil of which is attached by means of a 

 fine thread to a syphon of very fine glass tube. This syphon 

 takes ink from a small reservoir and traces an ink line upon a 

 moving paper ribbon. When the galvanometer coil is quiet a 

 straight line is traced upon the moving paper. When signals are 

 being received the varying current which flows through the gal- 

 vanometer coil causes the coil to move and the glass tube traces 

 a wavy line upon the moving paper. It is necessary for the 



