48 



THE ELECTRIC TELEGRAPH. 



the end of its axis the pointer seen on the outside face of the 

 instrument. 



One end of the coil is connected permanently with the 

 terminal screw L, to which the line wire is attached at the back 

 of the instrument, and the other end with the commutator, 



Fig. 24. 



by which a battery is put between it and the earth, and its 

 direction reversed according to the position of the handle. 



The commutator is of simple construction. The arbor 

 of the handle is divided electrically into two halves, 

 a and 6, insulated from each other by an intervening 

 thickness of dry wood, p. The half a is connected per- 

 manently, through a spring, s, with the copper plate of the 



