70 POWER DISTRIBUTION FOR EIL ECTRIC RATILROADS.
prove convenient. If any extensions are contemplated, as
at K, H, dot them in as they will enter into subsequent cal-
culations. As shown, E H is supposed to be 5000 ft.
Now divide the road into sections so that in each one of
them the service shall be under ordinary conditions fairly
constant. For example, the main double track would
present tolerably uniform conditions throughout and could
be considered as a single section. Owing to the change in
direction at B, however, which might conceivably affect
the location of the power station, it is better to take A B as
one section and BD as a separate one. CE, the long
single track branch, will naturally form a third section;
while H E may be taken tentatively as a fourth.
Step 2. Now as to the loads upon each section. The
number of cars on a road, of course, depends entirely on the
trafic. 'With the advantage of a good population to draw
upon, such a line as we are considering might operate as
many as twenty motor cars. These would naturally be six-
teen or cighteen foot, single truck cars, probably the latter.
We may then assume, say, ten such cars on section A B,
six on B D and four on C E. Those on C E in the natural
course of events would run quite independently, simply
serving their own line. We can then assume as the total
load twenty eighteen foot cars, each equipped with a pair
of standard motors, such as are usually rated at twenty-
five horse power each. The power required to operate
these cars is, of course, exceedingly dependent on the
density of the traffic. So long however as the cars are
equally loaded the center of gravity of the system is quite
independent of the absolute amount of horse power re-
quired for each car. Recurring now to the theorems re-
garding center of gravity in Chap. I, we are in a position
to determine the best position for the power station. The
only question to be first decided is what is to be done
with respect to the proposed extension. If it is installed
as an extension of C K, probably two additional cars would
be needed.
Step 3. As the service on each section is uniform the
