sistance would be equal to the internal resistance.
He said he was just about going to do the opposite; he wanted a large
external resistance and a low internal one. He said he wanted to sell
the energy outside of the station and not waste it in the dynamo and
conductors, where it brought no profits.... In these later days, when
these ideas of Edison are used as common property, and are applied in
every modern system of distribution, it is astonishing to remember that
when they were propounded they met with most vehement antagonism from
the world at large." Edison, familiar with batteries in telegraphy,
could not bring himself to believe that any substitute generator of
electrical energy could be efficient that used up half its own possible
output before doing an equal amount of outside work.

Undaunted by the dicta of contemporaneous science, Mr. Edison attacked
the dynamo problem with his accustomed vigor and thoroughness. He chose
the drum form for his armature, and experimented with different kinds
of iron. Cores were made of cast iron, others of forged iron; and still
others of sheets of iron of various thicknesses separated from each
other by paper or paint. These cores were then allowed to run in an
excited field, and after a given time their temperature was measured and
noted. By such practical methods Edison found that the thin, laminated
cores of sheet iron gave the least heat, and had the least amount of
wasteful eddy currents. His experiments and ideas on magnetism at that
period were far in advance of the time. His work and tests regarding
magnetism were repeated later on by Hopkinson and Kapp, who then
elucidated the whole theory mathematically by means of formulae and
constants. Before this, however, Edison had attained these results by
pioneer work, founded on his original reasoning, and utilized them in
the construction of his dynamo, thus revolutionizing the art of building
such machines.

After thorough investigation of the magnetic qualities of different
kinds of iron, Edison began to make a study of winding the cores,
first determining the electromotive force generated per turn of wire at
various speeds in fields of different intensities. He also considered
various forms and shapes for the armature, and by methodical and
systematic research obtained the data and best conditions upon which
he could build his generator. In the field magnets of his dynamo he
constructed the cores and yoke of forged ir