50 THE ELECTRIC TELEGRAPH. 



the left ; N" by two deflections to the right ; I, by three deflec- 

 tions consecutively to the right, and then one to the left ; 

 Y, by a deflection to the left, then one to the right, then 

 one to the left, and another to the right ; and so on. 



This instrument is used almost exclusively on some of the 

 railway lines in the United Kingdom and on some of those 

 in the East. Its great simplicity, inexpensiveness, and 

 little liability to derangement, have obtained it already a 

 long life. 



48. Double-needle Telegraph of WJieatstone and Cooke. 

 Another form of the needle telegraph, used also to some 

 extent on some of the English lines, is the double-needle 

 telegraph, consisting of two single-needle instruments com- 

 bined in the same case. They are, however, totally indepen- 

 dent of each other in so far as their electrical connections are 

 concerned, each being worked with a separate line wire. The 

 handles in front of the case are connected with two arbors 

 inside, similar to the one shown in Fig. 24, each of which 

 commutates the current of a battery through the galvanoscope 

 coils surrounding the needle attached to one of the pointers. 



The discs over which the pointers move are provided with 

 ivory pegs to limit the deflections on each side of the vertical 

 line. The discs are sometimes made circular, and may then 

 be turned round in the dial plate, enabling the operator to 

 shift the pegs, in order to keep the pointers midway be- 

 tween them when the magnet-needles are deflected by constant 

 atmospheric currents. 



The alphabetic code adapted for this instrument is as 

 follows : 



The left needle deflected alone, 



+ Corl A B Eor3 Dor 2 F & 



\ V \^ \\ / V / 



The left needle deflected alone, 

 Hor 4 L or 5 I K N or 7 M or 6 



\ V 



