244 
THE TELEGRAPH. 
the ink-well. This second roller draws np the ink by capillary 
attraction, and charges the inking disc without friction. The 
axle a (fig. 174) of this is moved by the armatures t and t', 
which are of soft iron kept magnetized by the permanent- 
magnet n s. Fig. 174 shows how these can be adjusted. The 
arrangement is such, that when they are once attracted by a 
current, however short, traversing the electro-magnet E, they 
remain in their places. They only revert to their normal 
position by the passage of a current oppositely directed to that 
which has attracted them. When, therefore, the armatures 
and the axle a are set in motion, the printing disc is brought 
into contact with the paper and marks it with a line until the 
opposite current arrives. A dot is produced by a momentary 
current, followed instantly by a very brief inverse current. 
A dash is produced by a short current followed by an inverse 
current arriving after an interval of time. Thus for each 
signal, two currents must be sent; these currents must be in 
opposite directions, and separated from each other by different 
intervals of time, and the perforated paper determines the 
intervals separating the opposite currents. We trust that the 
action of the apparatus will now be understood. 
Figure 175 shows the general arrangement of the apparatus 
as established at one of the terminal stations. It comprises, 
attached to the transmitter, a commutator, of the action of 
which we have not hitherto spoken. It is here shown in the 
position it assumes when the apparatus is ready for the recep¬ 
tion of the signals. The diagram shows also a key ( clej) for 
double currents which may be put into circuit by means of the 
commutator, to signal by hand when the transmitter is not in 
use. A galvanometer indicates the passage of the currents. 
The receiver (recepteur) is also provided with a commutator 
S which throws a sounder {parlour) into the local circuit when 
the receiver is stopped. This sounder serves as a call, and 
when necessary may act as a receiver for signals sent by a key. 
When the receiver is in motion, the sounder is thrown out of 
circuit. The local circuit is completed by the electro-magnet 
of the receiver, which thus acts as a relay, or as a direct printer. 
The figure shows the transmitter in a neutral position, as it 
is when no current is being sent into the line, and the lever c 
is in position to form the short circuit of the battery. E.Y. is 
