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

290 THE MAGNETO-ELECTRIC TELEGRAPH.
pillars in an inclined position, this being thelo lct for reading
the indications, besides reducing the fricticn c(f i lh needle
pivots to one twentieth part. Undcler the dial two eleetromagnets, D u are fixed, one for each needle. It may be mentioned, that electro-magnets have been attempted to be used
before for deflecting the needle, by placing one end of the needle
between the poles of the magnet, but never succeeded, owing
to the residual magnetism left after the battery current had
ceased. This was always sufficient to keep the needle deflected, except they made it very heavy at the bottom, or used
a strong spring to keep it in the upright position; it then reFig 3. quired a strong current to overcome that resistance,
and the spring or weight required adjusting according to the strength of the battery, or the state of the
weather. In the magneto-electric telegraph two
pieces of soft iron are placed on the poles of the electro-magnet of a semicircular shape, which thus forms
four poles. (See fig. 3.) Within these is suspended a magnetic needle, the axis of which is prolonged through the dial,
carrying an index or pointer. This, as well as the magnetic
needle, is limited in its motion by stops on the dial.
Fig. 4 Figs. 4 and 5 represent the magnetic
needle, and the horns of the magnet. On
/pressing down the lever, the ends of the armature change place with respect to the poles
O /0 ~of the magnet. This produces a current of
0 1, electrieityin the armature, and through the circuit, which, passing round the wire on the elecN'\s' / tro-magnet, causes it to become magnetic. As
shown in the diagram, fig. 4, there are then
Fig, 5. four distinct forces acting on
the needle to deflect it in the
1'-s uln\^ position shown; the two south
poles of the electro magnet
l ^ \% attracting one end of the needle, and repelling the other,
U1" li k!?~,,iil' and the two north poles the!~ / same with the other end.,
While the handle is kept down,
although no electricity is passing, the needle is kept deflected by the residual magnetism
in the horns. On allowing the
lever to return by the force
of the spring on the base, the
ends of the armatures and
l'- ma.inet again change places,