The reversing levers, and also the levers working the mechanical
brakes, are connected to both ends of the car, so that the driver can
always stand at the front and have uninterrupted view of the rails,
which is of course essential in the case of a line laid by the side of
the public road.
The cars are first and third class, some open and some covered, and
are constructed to hold twenty people, exclusive of the driver. At
present, only one is fitted with a dynamo, but four more machines are
now being constructed by Messrs. Siemens Bros., so that before the
beginning of the heavy summer traffic five cars will be ready; and
since two of these will be fitted with machines capable of drawing a
second car, there will be an available rolling stock of seven cars. It
is not intended at present to work electrically the portion of the
line in the town at Portrush, though this will probably be done
hereafter; and a portion, at least, of the mineral traffic will be
left for the two steam-tramway engines which were obtained for the
temporary working of the line pending the completion of the electrical
arrangements.
Let us now put in a form suitable for calculation the principles with
which Mr. Siemens has illustrated in a graphic form more convenient
for the purposes of explanation, and then show how these principles
have been applied in the present case.
Let L be the couple, measured in foot-pounds, which the dynamo must
exert in order to drive the car, and _w_ the necessary angular
velocity.
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