resistance of the exterior
circuit, although the application of this principle entailed the useless
expenditure of at least 50 per cent. of the applied energy.

It seems almost incredible that only a little over thirty years ago the
sum of scientific knowledge in regard to dynamo-electric machines was so
meagre that the experts of the period should settle upon such a dictum
as this, but such was the fact, as will presently appear. Mechanical
generators of electricity were comparatively new at that time; their
theory and practice were very imperfectly understood; indeed, it is
quite within the bounds of truth to say that the correct principles were
befogged by reason of the lack of practical knowledge of their actual
use. Electricians and scientists of the period had been accustomed for
many years past to look to the chemical battery as the source from which
to obtain electrical energy; and in the practical application of such
energy to telegraphy and kindred uses, much thought and ingenuity had
been expended in studying combinations of connecting such cells so as to
get the best results. In the text-books of the period it was stated as a
settled principle that, in order to obtain the maximum work out of a
set of batteries, the internal resistance must approximately equal the
resistance of the exterior circuit. This principle and its application
in practice were quite correct as regards chemical batteries, but not as
regards dynamo machines. Both were generators of electrical current, but
so different in construction and operation, that rules applicable to the
practical use of the one did not apply with proper commercial efficiency
to the other. At the period under consideration, which may be said to
have been just before dawn of the day of electric light, the philosophy
of the dynamo was seen only in mysterious, hazy outlines--just emerging
from the darkness of departing night. Perhaps it is not surprising,
then, that the dynamo was loosely regarded by electricians as
the practical equivalent of a chemical battery; that many of the
characteristics of performance of the chemical cell were also attributed
to it, and that if the maximum work could be gotten out of a set of
batteries when the internal and external resistances were equal (and
this was commercially the best thing to do), so must it be also with a
dynamo.

It was by no miracle that Edison was far and away ahead of his time
when he undertook to improve the dy