ON PRINTING TELEGRAPHS. 
295 
with insulated wire. This armature lies close to the electro- 
magnet, but does not touch it, being held back by a spring. 
When a current is caused to pass through the wire, the 
horseshoe becomes a magnet, attracts the armature over- 
coming the resistance of the spring, and presses the pencil 
upon the paper ; but as soon as the current ceases, the iron 
loses its magnetism and the pencil is withdrawn by the 
spring. We give a diagram showing the principle : — 
The duration of the current and length of the mark depend 
upon the s ending- Zsey. This key, in its simplest form, is 
merely a lever attached to the line-wire, or wire fixed from 
one station to the other, which, when at rest connects the 
wire with the earth, but when pressed places a battery 
between it and the earth, so as to send a current to the distant 
station. 
The clerk taps out his message by means of his key, pro- 
ducing a succession of currents which act on the electro-magnet 
at the distant station, attracting its armature, and embossing 
or printing corresponding dashes and dots upon the paper 
band as it passes forward between the rollers, recording every 
movement of the sending-key. 
On the conclusion of the message, if it is legible, the 
number of words is counted ; and if correct, the receiver 
acknowledges it by sending back certain signals serving to 
identify it, followed by — RT right ” (in America, 
OK, “ all correct”). This acknowledgment appears on the 
slip of the sending station; and in case the message should 
not reach the person for whom it was intended, can be pro- 
duced as a proof that it was duly transmitted. 
The paper ribbon is cut in long lengths, and each roll is 
kept entire and unbroken, so that every signal may be regis- 
tered in its proper place. If this were not done, the record 
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