d
uncoupling would be involved by the comparative frequent changes of
train lengths. In an eight-car multiple-unit express train, the first,
third, fifth, sixth, and eighth cars will be motor cars, while the
second, fourth, and seventh will be trail cars. An eight-car train can
be reduced, therefore, to a six-car train by uncoupling two cars from
either end, to a five-car train by uncoupling three cars from the rear
end, or to a three-car train by uncoupling five cars from either end.
In each case a motor car will remain at each end of the reduced train.
In like manner, a five-car local train may be reduced to three cars,
still leaving a motor car at each end by uncoupling two cars from
either end, since in the normal five-car local train the first, third,
and fifth cars will be motor cars.

[Illustration: 200 H. P. RAILWAY MOTOR]

[Sidenote: _Motors_]

The motors are of the direct current series type and are rated 200
horse power each. They have been especially designed for the subway
service in line with specifications prepared by engineers of the
Interborough Company, and will operate at an average effective
potential of 570 volts. They are supplied by two manufacturers and
differ in respect to important features of design and construction,
but both are believed to be thoroughly adequate for the intended
service.

[Illustration: 200 H. P. RAILWAY MOTOR]

The photographs on this page illustrate motors of each make. The
weight of one make complete, with gear and gear case, is 5,900 pounds.
The corresponding weight of the other is 5,750 pounds. The ratio of
gear reduction used with one motor is 19 to 63, and with the other
motor 20 to 63.

[Illustration: 200 H. P. RAILWAY MOTOR]

[Sidenote: _Motor
Control_]

By the system of motor control adopted for the trains, the power
delivered to the various motors throughout the train is simultaneously
controlled and regulated by the motorman at the head of the train.
This is accomplished by means of a system of electric circuits
comprising essentially a small drum controller and an organization of
actuating circuits conveying small currents which energize electric
magnets placed beneath the cars, and so open and close the main power
circuits which supply energy to the motors. A controller is mounted
upon the platform at each end of each motor car, and the entire train
may be operated from any one of the points, the motorman normally
taking his post on the front platf