2x6 
THE TELEGRAPH. 
The key c gives signals to the right and left, and these 
stand for the points and dashes of "the Morse code. The 
apparatus is sometimes supplemented by a commutator or 
distributor, not represented in the figure. 
By means of this distributor (fig. 154) the line can be 
alternately put in communication with the receiving instru- 
F:g, 150. 
ment (3) or the transmitting key (1). A passing contact (2) 
at the same time allows the line to be discharged into the 
earth. The piece d made of copper, turns on an axle by which 
it may be placed in contact with 1, 2, or 3, as required. It 
communicates with the binding screw (4), by which it is con¬ 
nected with the line. In the figure, the line and the receiving 
instrument are connected together. It is sometimes neces¬ 
sary to diminish the range of the movement of the mirror so 
that the spot of light may not pass off the screen. In such 
