The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

70O TELEGRAPH APPARATUS.
diminish as the magnetic force becomes greater or less; when
this is combined with the so applying the finger g, by which
the local circuit is opened and closed, that the said finger is
caused to move with the armature by friction only, or its
VII.
equivalent, and, after having moved the slight distance necessary to open or close the circuit, leaves the armature free to
move as far as necessary independently of it, thereby obviating
the necessity of manual adjustment of the armature to compensate for variations of magnetic force.
VIII. IMIPROVEMENT IN FIRE-ALARM TELEGRAPH.
Patented May 19, 1857, by William F. Channing and Moses G. Farmer.
If a fire is discovered in the vicinity of a signal station z,
an authorized person opens the signal box, and turns crank a'
a number of times; the teeth b' b", on the circuit wheel, depressing the key c' c', and in this manner break and restore
the circuit at definite intervals, the key returning by its own
elasticity; this operation causes the electro-magnet and armature of the central station Y, by repeated strokes on r, to indicate the number of the district and station whence the alarm
designates. The operator at the central station Y, by turning
crank A, operates the transmitting apparatus, A B, causing the
bells at the alarm station v, to give the alarm, and, by tapping
on key m' m", the number of the signal station originating the
alarm may be transmitted to any of the signal stations, z.