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

25)8 DAVY'S ELECTRO-CHEMICAL TELEGRAPH.
and form a metallic connection. The key B, fig. 2, has the
same fixtures, and is similarly arranged as the key A, fig. 3.
THE RECEIVING INSTRUMENT.
Fig. 4 represents a top view of the arrangement of multipliers at the receiving station. R/ R' R/ and R R R are six
magnetic needles or bars, each of which move freely on a vertical axis passing through their centres. The lower point of
their axes is immersed in cups of mercury, in which also terminate the wires i i I and L, LI L. The wires D' A' B' and c' are
Fig. 4.
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those coming from the transmitting' station. A' B/ and c' each
enter the needle arrangement, and first passing from left to
right over the magnetic bars i' R' and R', in the direction of
their length, then down and under and round, making many
turns, leave these three needles and pass under the needles R R
and R, and in like manner from right to left round them, making a number of turns, then pass off and unite together in the
wire 9, which is a continuation of D". This wire is called the
common communicating wire, and the wires A/ B' and c/ are
called signal wires, though they too are occasionally common
communicating wires. At right angles, there projects from each
magnetic bar a metallic tapered arm, which rests aoainst the
studs v v v v v v, when the needle is undisturbed. But when
the needles are made to move in the direction to carry the arms