frequencies and potentials are very high gaseous matter should be
carefully kept away from the charged surfaces. If Leyden jars are
used, they should be immersed in oil, as otherwise considerable
dissipation may occur if the jars are greatly strained. When high
frequencies are used, it is of equal importance to combine a condenser
with the primary. One may use a condenser connected to the ends of the
primary or to the terminals of the alternator, but the latter is not
to be recommended, as the machine might be injured. The best way is
undoubtedly to use the condenser in series with the primary and with
the alternator, and to adjust its capacity so as to annul the
self-induction of both the latter. The condenser should be adjustable
by very small steps, and for a finer adjustment a small oil condenser
with movable plates may be used conveniently.

I think it best at this juncture to bring before you a phenomenon,
observed by me some time ago, which to the purely scientific
investigator may perhaps appear more interesting than any of the
results which I have the privilege to present to you this evening.

It may be quite properly ranked among the brush phenomena--in fact, it
is a brush, formed at, or near, a single terminal in high vacuum.

In bulbs provided with a conducting terminal, though it be of
aluminium, the brush has but an ephemeral existence, and cannot,
unfortunately, be indefinitely preserved in its most sensitive state,
even in a bulb devoid of any conducting electrode. In studying the
phenomenon, by all means a bulb having no leading-in wire should be
used. I have found it best to use bulbs constructed as indicated in
Figs. 12 and 13.