Opposite sections of the commutator are
connected together internally as in most four-pole machines, so that
only two brushes are necessary, at 90 deg. apart.

The section of iron in the field is 60 square inches and rectangular
in form, and the whole machine measures 4 ft. 3 in. in length, and 2
ft. in height, without including the height of the bed plate. The
armature is 17 in. in length and the same in diameter, measured over
the winding, and develops at the machine terminals 70 volts and 200
amperes at 480 revolutions. The moving parts of the engine are well
balanced, and run remarkably well and without noise at this high rate
of speed.

This dynamo serves to develop power to run a motor in an adjoining
inclosure, containing some fine specimens of lathes and machine tools
constructed by the Oerlikon Works. These are driven by the motor
through the medium of a countershaft, and the power and speed are
controlled from the switch board seen at the left of the exhibit, and
in Fig. 11. The resistance, R1, serves to vary the intensity of the
shunt field of the dynamo, the volts being indicated by the voltmeter
V1, and a resistance separate from the switch board is inserted in
the main circuit of the two machines. The ammeter, A2, is directly
connected to the dynamo, and therefore indicates the current, whatever
circuit this machine is running.

[Illustration: Figs. 5-9, 11 plus THE PARIS EXHIBITION--STAND OF THE
OERLIKON WORKS.]

A larger combined engine and dynamo, seen in the center of the stand,
serves to run the lighting of the galleries. The engine is a 60 horse
power compound, running at 350 revolutions, and fitted with a governor
on the fly wheel, like that described above.

The dynamo is a two-pole machine, the upper pole and yoke being cast
in one, and the lower pole, yoke, and combined bed plate forming a
separate casting. The two vertical cores, over which the field bobbins
are slipped, are of wrought iron, and are turned with a shoulder at
either end, the yokes being recessed to fit them exactly. The cores
are then bolted to the yokes vertically from the top and horizontally
below. The field of this machine is shunt-wound, and in order to
maintain the potential constant a hand-regulated resistance--R2 on
the switch board--is added in circuit with the shunt field. The
voltmeter, V2, immediately above this resistance, serves to
indicate the difference of potential at the machine terminals. Both
voltmeters