20 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
the cost of installing and keeping up conduits adds very 
materially to the disadvantage of elaborate feeding systems 
from a distant point. 
Another class of cases in which special attention to the 
location of power station is needed may be found in the 
interurban and cross country roads now becoming common. 
Generally the distribution is linear or branched, rather 
than a network. We should not, however, assume that 
the power station should lie at the middle, end or any 
other point on the line of the road. It very often happens 
that the center of gravity of the load, which is the most 
economical point for distribution, as we have just seen, is 
1ot on the line at all. For example, take the line shown 
in Fig. 13. It conmsists of three sections connecting, we 
  
F1G: <13, 
may suppose, four towns, A, B, C, D. The configuration of 
the system is here determined by the topography of the 
region, the amount of business at each point, and similar 
considerations familiar in the art of railway location. We 
may suppose the load of each section concentrated at its 
middle point as before, forming the load points, a, 4, c. 
Suppose the loads to be as follows : @ = 15, b= 10, c=35. 
These loads may be taken in any convenient units pro- 
vided the same units are used throughout. 
Now, proceeding as before, draw & ¢ and locate the 
center of gravity of theloads, #and ¢. This proves to be 
d, where the concentrated load is 15. Then drawing a4, 
the center of gravity of the system is found to be at O, quite 
off the line of the road, although not inconveniently distant 
from B. In other instances the center of gravity might 
very readily be as far from any of the towns, A, B, C, D,