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to the secondary of a spark-coil by means of a wire fastened
to the little rings at the end, and the coil is set in operation,
they light up in the most wonderful way imaginable. The
rarefied gases and minerals in the glass throw out beautiful
iridescent colors, lighting up a dark room with a weird flick-
ering light. Every tube is usually of a difierent pattern
and has a combination of difierent colors. The most


FIG. 168. — Geissler Tubes.

beautiful tubes are those provided with a double wall con-
taining a fluorescent liquid, which heightens the color
efiects when the tube is lighted.

Eight to ten tubes may be lighted at once on an ordinary
coil by connecting them in‘ series.

Ghost Light

If you grasp the bulb of an old incandescent electric lamp
in one hand and touch the base to one side of the secondary

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