Four or five connected in series will work quite a long line if the
contacts are in good condition.
A reversing switch is needed to alter the direction of the current flow.
The construction of one is an exceedingly simple matter. Fig. 48 gives a
plan of switch and connection, from which the principle of the apparatus
will be gathered. The two links, LL, are thin springy brass strips slightly
curved, and at the rear end pivoted on the binding posts T1 T2. Underneath
the other ends solder the heads of a couple of brass nails. The links are
held parallel to one another by a wooden yoke, from the centre of which
projects a handle. The three contacts C1 C2 C3 must be the same distance
apart as the centres of the link heads, and so situated as to lie on the
arcs of circles described by the links. The binding post T3 is connected
with the two outside contacts--which may be flat-headed brass nails driven
in almost flush with the top of the wooden base--by wires lying in grooves
under the base, and T4 with the central contact. As shown, the switch is in
the neutral position and the circuit broken.
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