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

488 TELEGRAPH ELECTRIC CIRCUITS.
magnet at A can not be wholly demagnetized, but the strength
of the magnet force will be minus and plus, according to the
manipulation of B. The armature of A wili have to be removed farther from the cores of the spools, so that the breaking of the circuit at B, will be effective in the attraction of
the armature of the magnet at A. When the circuit at B is
broken, the seventy-five per cent. current that passes off at a,
creates in the soft iron cores at A, seventy-five per cent. of attractive force. The adjustable spring of the armature may
draw it beyond that power, but the moment B closes the circuit, the magnetic force of the cores at A, becomes increased
twenty-five per cent., and the spring no longer holds the
armature, and it is attracted so that the armature-lever closes
the local circuit, and thus the apparatus at A becomes subservient to the will of the operator at B.
The difficulties hereinbefore described are not always chargeable to the causes given. Sometimes the fault will be found
in the connections of the wire, and many times I have found it
to be with the earth wire. The earth must be moist where
the connection with the telegraphic conductor is made. The
metal surface in the earth should be large. In my experience,
for an iron wire line, I have found it best to have an earth
wire of copper, number 12, Birmingham gauge, well soldered
to a copper plate, at least two feet square, or its equivalent
surface, and buried in the wet earth. If the earth be not wet,
the working of the whole line will be less effective. Dry earth
is considered a non-conductor; therefore, in order to consummate a perfect circuit, it is necessary for the metallic surface,
in contact with the water of the earth, to be commensurate
with the conductibility of the line wire. If the earth connection be inferior, the electrical action of the battery will be
minus in the same proportion. It is better to have the conductor uniform, equalling the generative powers of the battery, so that the voltaic streams can be sufficient for the
consummation of the most certain and effective telegraphic
manipulation.
EARLY EXPERIMENTAL CIRCUITS.
In July, 1747, Dr. Watson, Bishop of Llandaff, together
with several other electricians, ascertained the passage of electricity through the water, by sending shocks across the Thames,
and in August, 1747, they transmitted shocks through two
miles of wire and two miles of earth at Shooter's Hill.
On the experimental line, erected by Professor Steinheil from
Munich to Bogenhausen, in 1836, two lines of wire were