214 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
The amount and character of the displacement varies in 
different cases in a way that cannot be formulated. The 
only thing to be done is to take up each case as a special 
problem as we have just done. 
The effect of thisextra copper on the relative economy 
of the various methods of supply is easy to approximate. 
Recurring to the estimates at the end of the last chapter, it 
is evident that they need revision. The annual cost by 
method I will be increased by the interest and depreciation 
on the additional copper. Method II will suffer in almost 
the same ratio as method I, and hence the absolute increase 
in copper and the added annual expense will be greater, 
putting the booster method to very serious disadvantage, 
if it be used legitimately, i.e., without undue loss of 
energy. 
Method III, which really consists in transmitting 
power at high voltage from E to F (Fig. 112), is affected to 
precisely the same absolute extent as method I, and there- 
fore has practically the same relative value as before. 
Method IV must take into account the same condi- 
tions of displaced load that influence the other cases, but 
in a somewhat different way. The trolley wire alone is 
unable to carry the current for a severe load any consider- 
able distance, hence it must be reinforced unless the line 
is to be supplied with an exaggerated transformer capacity 
and the transformers are placed very near together. To 
give a good practical distribution of power there must be 
sufficient feeder capacity to easily carry the current for the 
extreme loads already mentioned without demanding trans- 
formers at too frequent intervals. The net result of the 
conditions of load will be, first, to demand the installation 
of feeder copper to distribute the energy delivered from the 
transformers, and second, extra transformer capacity 
enough to respond to the utmost calls of a displaced maxi- 
mum load. In the case before us it would not be wise to 
subdivide the transformer capacity greatly, since the in- 
dividual units would be small and expensive. ‘The maxi- 
mum load of 1200 amperes at 500 volts will be increased