Such tubes are of necessity very fragile articles and should be handled with extreme care. It is a good plan to keep them wrapped in cotton and to put them away in a strong wooden box, so as to reduce the danger of breakage.
The very smallest coil, even the one-quarter inch size, will serve to light a large tube. . In fact, if too large a coil is used, there is danger of spoiling the tube.
The tubes are connected to the spark coil by running a wire from each of the small rings at the ends of the tubes to the secondary terminals. Several tubes may be connected in series when a or 1-inch coil is available.
To show the best effects, the room should be in perfect darkness and the tubes should be placed against a background of black velvet.
Experiment 4—Flickering Light.
Spread your fingers out and move your hand rapidly back and forth over a lighted Geissler tube in a darkened room. Your hand will appear to have ten or twelve fingers instead of five. This is due to the fact that the light from a Geissler tube is flickering and not at all steady. Each time the interrupter of the coil opens, the current is sent through the tube and lights it momentarily. The flickering is almost too rapid to be perceived by the naked eye until you have something like the fingers or a pencil in front of it.
Experiment 5—Rotating a Geissler Tube.
An extremely pretty effect can be secured by rotating a Geissler tube at high speed while it is lighted. This may be accomplished by means of an electric motor of small size. The tube is tied tightly to a stick of wood which has a hole drilled exactly in its center into which the motor shaft fits tightly. Two rings of metal are mounted on the motor shaft, and a wire is led from each to a terminal of the tube. A copper strip rests on each ring, and these two copper strips are connected to the secondary of the spark coil.
When the motor is started and the coil set into operation, the tube will appear like the spokes of a wheel. The intermittent light will make the tube visible for a fraction of a second in various positions around the circle as it rotates, and this gives the effect which is much like that of a pinwheel.
Experiment 6—Fluorescent Writing.