CHAP. IV.] 



ELECTRIC TELEGRAPHY. 



movement is made by which no current is passed into the line wire. 

 At each motion of the rocking cradle, a momentary contact is made 

 between the line wire and the earth, so 

 that after each successive elevation of 

 either current-passing pin, the line is dis- 

 charged to earth ; thus the line is connected 

 for discharge at regular intervals, irre- 

 spective of its charge by the elevation of 

 a pin, a current only passing into the line 

 by the contact made with the battery on 

 the elevation of either pin. 



This discharge to earth to clear the 

 line, especially on submarine wires, is 

 necessary from the sensible retention in 

 the insulated wire of a portion of the 

 transmitted current, which unless drawn 

 out would interfere with the integrity of 

 the succeeding current, and reduce the 

 transmitting speed of the wire. In this 

 mechanical arrangement therefore, the 

 necessary contacts with the battery and 

 the regular discharge of the line are pro- 

 duced automatically and mistakes are 

 avoided. The " receiver," or apparatus 

 for recording at the distant station the 

 rapid sequence of currents passed into 

 the line wire upon a paper ribbon in the 

 Morse code, will now be described. Fig. 

 387 represents the Wheatstone " dot " 

 receiver, in which the lower line of dots 

 is read off as "dashes/' and the upper 

 line of dots as " dots." The paper ribbon 

 mechanically advances forward and passes 

 under a shallow dish containing the ink ; 

 two fine holes are made in the bottom of 

 this reservoir in a position to correspond 



with the two lines of dots to be printed upon the paper ribbon as it 

 passes underneath the reservoir. 



Q Q 2 



