At the passing places, which are situated on inclines, the conductor
takes the inside, and the car ascending the hill also runs on the
inside, while the car descending the hill proceeds by gravity on the
outside lines.
From the brushes the current is taken to a commutator worked by a
lever, which switches resistance frames placed under the car, in or
out, as may be desired. The same lever alters the position of the
brushes on the commutator of the dynamo machine, reversing the
direction of rotation, in the manner shown by the electrical hoist.
The current is not, as it were, turned full on suddenly, but passes
through the resistances, which are afterward cut out in part or
altogether, according as the driver desires to run at part speed or
full speed.
From the dynamo the current is conveyed through the axle boxes to the
axles, thence to the tires of the wheels, and finally back by the
rails, which are uninsulated, to the generating machine. The conductor
is laid in lengths of about 21 feet, the lengths being connected by
fish plates and also by a double copper loop securely soldered to the
iron. It is also necessary that the rails of the permanent way should
be connected in a similar manner, as the ordinary fish plates give a
very uncertain electrical contact, and the earth for large currents is
altogether untrustworthy as a conductor, though no doubt materially
reducing the total resistance of the circuit.
The dynamo is placed in the center of the car, beneath the floor, and
through intermediate spur gear drives by a steel chain on to one axle
only.
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