DIRECT FEEDING SYSTEMS. 33 
$4630. This cost would have to be doubled to save 21 
per cent of the total energy. ‘The annual charge for this, 
counting interest and depreciation at ten per cent, would be 
$463, nearly $206 for each per cent saved. Now the amount 
of power, based on the average amperes, is about 2700 k.w. 
hours per day of eighteen hours; the cost of this per year 
at two cents per kilowatt hour would be $19,710, of which 
one per cent is $197.10, showing that it will not pay to in- 
crease the investment in copper. 
The art of feeder design is one that calls for great 
Jinesse and skilled judgment in assigning the proper values 
to the somewhat uncertain maximum loads. It cannot be 
reduced to formulee that will be of use in anything save 
special and unusual circumstances. The author has in this 
chapter, therefore, merely attempted to give the general 
principles to be followed and some idea of the mental pro- 
cesses by which the final approximation is reached. In 
another chapter the special case of long interurban lines 
will be considered.