s against a straight two-wire system throughout of the "tree" kind.
He soon foresaw that still greater economy would be necessary for
commercial success not alone for the larger territory opening, but for
the compact districts of large cities. Being firmly convinced that there
was a way out, he pushed aside a mass of other work, and settled down to
this problem, with the result that on November 20, 1882, only two
months after current had been sent out from Pearl Street, he executed an
application for a patent covering what is now known as the "three-wire
system." It has been universally recognized as one of the most valuable
inventions in the history of the lighting art. [13] Its use resulted in a
saving of over 60 per cent. of copper in conductors, figured on the most
favorable basis previously known, inclusive of those calculated under
his own feeder and main system. Such economy of outlay being effected in
one of the heaviest items of expense in central-station construction,
it was now made possible to establish plants in towns where the large
investment would otherwise have been quite prohibitive. The invention
is in universal use today, alike for direct and for alternating current,
and as well in the equipment of large buildings as in the distribution
system of the most extensive central-station networks. One cannot
imagine the art without it.

[Footnote 13: For technical description and illustration of
this invention, see Appendix.]

The strong position held by the Edison system, under the strenuous
competition that was already springing up, was enormously improved by
the introduction of the three-wire system; and it gave an immediate
impetus to incandescent lighting. Desiring to put this new system into
practical use promptly, and receiving applications for licenses from all
over the country, Edison selected Brockton, Massachusetts, and Sunbury,
Pennsylvania, as the two towns for the trial. Of these two Brockton
required the larger plant, but with the conductors placed underground.
It was the first to complete its arrangements and close its contract.
Mr. Henry Villard, it will be remembered, had married the daughter of
Garrison, the famous abolitionist, and it was through his relationship
with the Garrison family that Brockton came to have the honor of
exemplifying so soon the principles of an entirely new art. Sunbury,
however, was a much smaller installation, employed overhead conductors,
and hence w