station, but on
the same lines, was projected for San Francisco, and in 1892 the
present Harrison Street station of the Chicago Edison company was
designed, and, benefiting by the experience of Berlin, New York and
Boston, this station produces electric current for lighting purposes
probably cheaper than any station of a similar size anywhere in this
country.

It is not necessary for me to go into detail in explanation of the
modern central station. You are all doubtless quite familiar with the
general design, but if you will examine the detail drawings of the
Harrison Street station, which I have brought with me, you will find
that every effort has been made to provide for the economical
production of steam, low cost of operating, good facilities for
repairs and consequently low cost, and for permanency of service. You
have but to go into any of the modern central stations in midwinter,
to see them turning out anywhere from 10,000 to 80,000 amperes with a
minimum of labor, to appreciate the fact that central station business
is of a permanent and lucrative character.

To go back to the question of alternating currents, the work done in
connection with the two-phase and three-phase currents and the
perfection of the rotary transformer has resulted in introducing into
central station practice a further means of economizing the cost of
production--by concentration of power. According to present
experience, it is (except in some extraordinary cases) uneconomical to
distribute direct low-tension current over more than a radius of a
mile and a half from the generating point. The possibility of
transmitting it at a very high voltage, and consequently low
investment in conductors, has resulted in the adoption of a scheme, in
many of the large cities, of alternating transmission combined with
low tension distribution. The limit to which this alternating
transmission can be economically carried has not yet been definitely
settled, but it is quite possible even now to transmit economically
from the center of any of our large cities to the distant suburbs, by
means of high potential alternating currents, distributing the current
from the subcenter distribution by means either of the alternating
current itself and large transformers for a block or district or else,
if the territory is thickly settled, by means of a system of
low-tension mains and feeders, the direct current for this purpose
being obtained through the agency of r