d feeders originally conceived by Mr. Edison is
as much a necessity in their operation as it is in the electric
lighting systems, whether those systems be operated on the old
two-wire plan, the three-wire plan or by means of alternating
currents.

Passing from a review of central station plants and distribution
system naturally bring us to the operating cost and the factors
governing profit and loss of the enterprise. In considering this
branch of the subject, I will confine my remarks to the business as
operated in Chicago by the company with which I am connected.

Our actual maximum last winter came on December 20, our load being
approximately 12,000 horse power. A comparison of the figures of
maximum capacity and maximum load of last winter shows that we had a
margin in capacity over output of about 20 per cent. The load curves
shown this evening represent the maximum output of last winter
(December 20), an average summer load last year (June 4), and an
average spring load of this year (May 2). For our purposes we will
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 11/2 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