36 PHYSICS. 
other part of the circuit—the part played by the liquid in fig. 34? In the 
case of the telegraph, the earth is substituted for the liquid, for if the wire 
which goes along the lines be attached to the copper plate of the battery, 
and a wire, attached to the zinc, be carried down into the earth, the circuit 
is complete. In fig. 38, then, L is the line-wire, and E the earth-wire, 
both of which are made continuous with the coils of wire on the electro- 
magnet, MM’; the armature, A, is attached to a lever, Jl’, which turns on 
the axis k. Whenever the current is made to pass through the wire, the 
armature is drawn down, bringing the end of the lever with it ; this raises 
the other end,’to which is fixed a sharp point, p; opposite this point is a 






ips 
a 
el 














HH 
Mt H 
iit 






























INT 
Fig. 38. 

MM i 
ti mM 

groove in the roller, r, and over this groove is made to pass a slip of paper, 
PP’, which is made to move towards P’ by the rollers, rr’. These rollers 
are worked by clock-work, independently of the rest of the machine. 
When the point p is raised into the groove on the roller 7, a raised mark 
is made on the upper surface of the paper, which will be a dot or a line 
according to the time the point is raised, that is, according to the time the . 
circuit is kept complete ; as soon as the current ceases, the armature is left 
by the magnet free to rise, and the end of the lever, with the point, is 
pulled down by the spring s. By 
means of the dots and lines thus 
made on the paper, an alphabet 
is constructed, and words can 
thus be written down at the dis- 
tance of thousands of miles. 
But now, how is this system 
of stopping and setting agoing of 
the current managed at the sta- 
tion from which the message is sent? It is done by what is called a key, 
fig. 39. This is a lever, Jl, which moves on an axis, A, and is worked by 









Fig. 39. 
