The conductor is
connected by an underground cable to a single shunt-wound dynamo
machine, placed in the engine shed, and worked by a small agricultural
steam engine of about 25 indicated horse power. The current is
conveyed from the conductor by means of two springs, made of steel,
rigidly held by two steel bars placed one at each end of the car, and
projecting about six inches from the side. Since the conducting rail
is iron, while the brushes are steel, the wear of the latter is
exceedingly small. In dry weather they require the rail to be slightly
lubricated; in wet weather the water on the surface of the iron
provides all the lubrication required. The double brushes, placed at
the extremities of the car, enable it to bridge over the numerous
gaps, which necessarily interrupt the conductor to allow cart ways
into the fields and commons adjoining the shore. On the diagram the
car is shown passing one of these gaps: the front brush has broken
contact, but since the back brush is still touching the rail, the
current has not been broken. Before the back brush leaves the
conductor, the front brush will have again risen upon it, so that the
current is never interrupted. There are two or three gaps too broad to
be bridged in this way. In these cases the driver will break the
current before reaching the gap, the momentum of the car carrying it
the 10 or 12 yards it must travel without power.
The current is conveyed under the gaps by means of an insulated copper
cable carried in wrought-iron pipes, placed at a depth of 18 inches.
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