the power applied to this machine in external work.' . . .
Perhaps the writer is a humorist, and had in his mind Colonel Sellers,
etc., which he could not keep out of a serious discussion; but such
jests are not good.

"Mr. Edison has built a very interesting machine, and he has the
opportunity of making a valuable contribution to the electrical arts by
furnishing authentic accounts of its capabilities."

The foregoing extracts are unavoidably lengthy, but, viewed in the light
of facts, serve to illustrate most clearly that Edison's conceptions and
work were far and away ahead of the comprehension of his contemporaries
in the art, and that his achievements in the line of efficient dynamo
design and construction were indeed truly fundamental and revolutionary
in character. Much more of similar nature to the above could be quoted
from other articles published elsewhere, but the foregoing will serve as
instances generally representing all. In the controversy which
appeared in the columns of the Scientific American, Mr. Upton, Edison's
mathematician, took up the question on his side, and answered the
critics by further elucidations of the principles on which Edison had
founded such remarkable and radical improvements in the art. The type
of Edison's first dynamo-electric machine, the description of which gave
rise to the above controversy, is shown in Fig. 1.

Any account of Edison's work on the dynamo would be incomplete did
it omit to relate his conception and construction of the great
direct-connected steam-driven generator that was the prototype of the
colossal units which are used throughout the world to-day.

In the demonstrating plant installed and operated by him at Menlo
Park in 1880 ten dynamos of eight horse-power each were driven by a
slow-speed engine through a complicated system of counter-shafting,
and, to quote from Mr. Clarke's Historical Review, "it was found that
a considerable percentage of the power of the engine was necessarily
wasted in friction by this method of driving, and to prevent this waste
and thus increase the economy of his system, Mr. Edison conceived
the idea of substituting a single large dynamo for the several small
dynamos, and directly coupling it with the driving engine, and at the
same time preserve the requisite high armature speed by using an engine
of the high-speed type. He also expected to realize still further gains
in economy from the use of a large dynamo in place of seve