bearing his name, but
not now marketed except second hand.

For adequate information he might search in vain the books usually
regarded as authorities on the subject of dynamo-electric machinery,
for with slight exceptions there has been a singular unanimity in
the omission of writers to give Edison credit for his great and basic
contributions to heavy-current technics, although they have been
universally acknowledged by scientific and practical men to have laid
the foundation for the efficiency of, and to be embodied in all modern
generators of current.

It might naturally be expected that the essential facts of Edison's
work would appear on the face of his numerous patents on dynamo-electric
machinery, but such is not necessarily the case, unless they are
carefully studied in the light of the state of the art as it existed
at the time. While some of these patents (especially the earlier ones)
cover specific devices embodying fundamental principles that not only
survive to the present day, but actually lie at the foundation of
the art as it now exists, there is no revelation therein of Edison's
preceding studies of magnets, which extended over many years, nor of his
later systematic investigations and deductions.

Dynamo-electric machines of a primitive kind had been invented and were
in use to a very limited extent for arc lighting and electroplating for
some years prior to the summer of 1819, when Edison, with an embryonic
lighting SYSTEM in mind, cast about for a type of machine technically
and commercially suitable for the successful carrying out of his plans.
He found absolutely none. On the contrary, all of the few types then
obtainable were uneconomical, indeed wasteful, in regard to efficiency.
The art, if indeed there can be said to have been an art at that time,
was in chaotic confusion, and only because of Edison's many years' study
of the magnet was he enabled to conclude that insufficiency in quantity
of iron in the magnets of such machines, together with poor surface
contacts, rendered the cost of magnetization abnormally high. The
heating of solid armatures, the only kind then known, and poor
insulation in the commutators, also gave rise to serious losses. But
perhaps the most serious drawback lay in the high-resistance armature,
based upon the highest scientific dictum of the time that in order
to obtain the maximum amount of work from a machine, the internal
resistance of the armature must equal the