8 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
way the distance for which a given wire will carry 100 
amperes at a given loss can be found, while the loss for a 
given wire and distance can be rapidly approximated by 
estimating the position of the intersection of the area and 
the distance co-ordinates with reference to the oblique 
lines. By noting that the area of conductor varies inverse- 
ly with E, one can extend the working range of the chart. 
Halving the area shown for E =175 gives, for instance, 
the area for E = 150, and so on. 
Taking up now the case of linear distribution, it has 
already been shown that the fall in voltage in any con- 
ductor is directly proportional to the load and the resist- 
ance. If, now, a uniform line, A B, Fig. 5, be loaded at 
B, the voltage evidently decreases uniformly throughout 
its length. ‘To make the example more concrete, the 
length A B is taken as 20,000 ft., and the voltage kept 
constant at A, e. g., 500. Now, if the drop at B under the 
given load be 100 volts, a straight line drawn from C to D 
shows the state of the voltage at every point of the line. 
An ordinate erected at any point of A B and extended to 
C D shows the voltage of the line at the point selected, and 
that part of the extended ordinate cut off between CD and 
C F shows the loss in volts. If the load be transferred 
from B to some intermediate point of the line, an ordinate 
there erected wiil show the drop and the residual voltage 
at the new point. C E similarly shows the conditions for 
a terminal drop of 200 volts. 
The average drop is evidently half the maximum in 
each case, since the minimum drop is o, and the voltage 
varies uniformly. 
Now suppose one has to deal with a load moving uni- 
formly back and forth along A B. If the maximum drop 
be 100 volts, the voltage evidently moves uniformly along 
C D, and the average voltage is 450, since half the time 
the voltage is above this, and the other half an exactly 
equal amount below. 
‘This case corresponds to a line traversed on a uniform 
schedule by a single car. Such however is not the usual