to produce a sudden rush of current through the primary. The scheme of
connections in the present experiment is indicated in Fig. 2.

[Illustration: FIG. 2.--IMITATING THE SPARK OF A HOLTZ MACHINE.]

G is an ordinarily constructed alternator, supplying the primary P of
an induction coil, the secondary S of which charges the condensers or
jars CC. The terminals of the secondary are connected to the inside
coatings of the jars, the outer coatings being connected to the ends
of the primary pp of a second induction coil. This primary pp has a
small air gap ab.

The secondary s of this coil is provided with knobs or spheres KK of
the proper size and set at a distance suitable for the experiment.

A long arc is established between the terminals AB of the first
induction coil. MM are the mica plates.

Each time the arc is broken between A and B the jars are quickly
charged and discharged through the primary pp, producing a snapping
spark between the knobs KK. Upon the arc forming between A and B the
potential falls, and the jars cannot be charged to such high potential
as to break through the air gap ab until the arc is again broken by
the draught.

In this manner sudden impulses, at long intervals, are produced in the
primary pp, which in the secondary s give a corresponding number of
impulses of great intensity. If the secondary knobs or spheres, KK,
are of the proper size, the sparks show much resemblance to those of a
Holtz machine.