assume the maximum capacity of the plant and the maximum load of the
system to be identical. The maximum load last winter occurred, as I
have stated, on December 20, about 4:30 o'clock in the afternoon, and
lasted less than half an hour. It should be borne in mind that the
period of maximum load only lasts for from two to three months, and
that the investment necessary to take care of that maximum load, has
to be carried the whole year. It should not be assumed from this
statement that the whole plant as an earning factor is in use 25 per
cent. of the year. The fact is that, during the period of maximum
load, the total plant is in operation only about 100 hours out of the
8,760 hours of the year; so that you are compelled, in order to get
interest on your investment, to earn the interest for the whole of the
year in about 1½ per cent. of that period, on about 50 per cent. of
your plant.

This statement must bring home to you a realization of the fact that
by far the most serious problem of central station management, and by
far the greatest item of cost of your product, is interest on the
investment. It may be that the use of storage batteries in connection
with large installations will modify this interest charge, but even
allowing the highest efficiency and the lowest cost of maintenance
ever claimed for a storage battery installation, the fact of high
interest cost must continue to be the most important factor in
calculating profit and loss. This brings home to us the fact that in
his efforts to show the greatest possible efficiency of his plant and
distribution system, it is quite possible that the station manager may
spend so much capital as to eat up many times over in interest charge
the saving that he makes in direct operating expenses. It is a common
mistake for the so-called expert to demonstrate to you that he has
designed for you a plant of the highest possible efficiency, and at