ral small
machines by a more than correspondingly lower armature resistance, less
energy for magnetizing the field, and for other minor reasons. To the
same end, he intended to supply steam to the engine under a much higher
boiler pressure than was customary in stationary-engine driving at that
time."

The construction of the first one of these large machines was commenced
late in the year 1880. Early in 1881 it was completed and tested, but
some radical defects in armature construction were developed, and it was
also demonstrated that a rate of engine speed too high for continuously
safe and economical operation had been chosen. The machine was laid
aside. An accurate illustration of this machine, as it stood in the
engine-room at Menlo Park, is given in Van Nostrand's Engineering
Magazine, Vol. XXV, opposite page 439, and a brief description is given
on page 450.

With the experience thus gained, Edison began, in the spring of 1881, at
the Edison Machine Works, Goerck Street, New York City, the construction
of the first successful machine of this type. This was the great machine
known as "Jumbo No. 1," which is referred to in the narrative as having
been exhibited at the Paris International Electrical Exposition, where
it was regarded as the wonder of the electrical world. An intimation of
some of the tremendous difficulties encountered in the construction of
this machine has already been given in preceding pages, hence we shall
not now enlarge on the subject, except to note in passing that the
terribly destructive effects of the spark of self-induction and the
arcing following it were first manifested in this powerful machine, but
were finally overcome by Edison after a strenuous application of his
powers to the solution of the problem.

It may be of interest, however, to mention some of its dimensions
and electrical characteristics, quoting again from Mr. Clarke: "The
field-magnet had eight solid cylindrical cores, 8 inches in diameter
and 57 inches long, upon each of which was wound an exciting-coil of 3.2
ohms resistance, consisting of 2184 turns of No. 10 B. W. G. insulated
copper wire, disposed in six layers. The laminated iron core of the
armature, formed of thin iron disks, was 33 3/4 inches long, and had an
internal diameter of 12 1/2 inches, and an external diameter of 26 7/16
inches. It was mounted on a 6-inch shaft. The field-poles were 33 3/4
inches long, and 27 1/2 inches inside diameter The armature