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

.DESCRIPTION OF HENLEY'S APPARATUS. 291
and a current of electricity is produced in the opposite direction, which entirely neutralizes the residual magnetism, and
Athen reverses the poles of the electro-magnet, bringing the needie to the opposite side; but in the single-needle telegraph, the
armature takes a midway position between the poles, which
has the effect of neutralizing the residual magnetism only. Fig.
5 represents the electro-magnets, with the horns attached.
In the ordinary needle telegraph, a diamond-shaped Fig 6.
needle is suspended within coils of wire. (See fig. 6.)'M
On the passing of an electric current the needle has a l|i
tendency to move at right angles to the wire. When a flash i(j i
of lightning strikes the wires, the needle cannot move
quickly enough, but the poles move, that is to say, the polarity
of the needle is placed at right angles to its former position;
consequently, on the passing of ths battery current, it has a
tendency to remain stationary; in this way 200 or 300 miles
of telegraph are rendered inoperative in a single night. On inspecting the magneto-electric telegraph, it will be obvious this
cannot occur-the lightning in passing through the instrument
will not act primarily on the needle, but secondarily by the
electro-magnet; this becoming magnetic will deflect the needle if the current is passed in one direction, and if in the other
will have a tendency to retain it in its ordinary position; and
if any change occurs, it would be by the needle becoming
stronger. Should the telegraph remain a long time out of action, the horns of the electro-magnet form keepers to the needle, and maintain its power; and, likewise, by the arrangement of armatures and permanent bar magnets, the latter will
always retain their power; the poles are brought so near
together, that the armature before leaving one magnet is on the
other. This arrangement gives three advantages: the magnets
always have the protection of a soft iron keeper, and the two
currents produced by leaving one magnet and approaching the
other, are combined in. one, doubling the strength and duration
of the current; and it is evident, if the magnets were farther
apart, when the armature was quite free of both poles, it would
alter the magnetic character of the other armature, and thus
produce a current in it, and move the wrong needle.
The signals are indicated on the dial by the separate or combined motions of the two needles, for instance, A, B, and c,
are separately indicated by one, two, and three motions of the
left needle; D, E, and F, by similar motions of the right needle; G, one left and one right; H, one left and two right; I,
K, by the reversed motions of the needles; for the remainder of
the letters, the simultaneous motions of both needles are used