Fig. 50. Fig. 51.
Fig. 51 is a side view of the wheel, showing one manner of mounting the disk and its connections. The same figures apply to the parts as in the preceding figure. M N are the wires leading to the coil, P is a pulley on the shaft whereby the rotary power may be applied. The wires on the face of the disk are not shown, as they would impair the clearness of the diagram unnecessarily.
The greatest danger in the operation of such a piece of apparatus will be the tendency of the high tension spark to wander where it is not wanted, and to take short but forbidden paths back to the coil. However, care and perhaps experiment will prove the remedy. It will be noticed by reference to Fig. 49 that a circle has been drawn almost bisecting two of the tube-holders. This circle represents a circle of danger, and where a thin material has been used for the disk, the disk may very well be reinforced by a piece of stouter card cemented on its face.
The disk, whether of wood or of pasteboard, must have a liberal coating of insulation, either shellac varnish, paraffin, or beeswax, and be absolutely free from unnecessary holes. Moreover, the ring R must be of such a distance from the support F, if the latter be metal, as will preclude any jumping of the spark. A Ruhmkorff coil giving upward of three quarters of an inch of spark will be large enough to operate a wheel carrying four 8-inch tubes.
The wheel may be set back in a window and surrounded by dark fabrics, or built in, as it were, in a cave of such. The judicious use of pieces of looking-glass scattered on the sides of the cave, in such manner as to reflect the light of the tubes, will enhance the effect. There is no danger of fire where ordinary care is used, as the long spark necessary to the production of the luminosity will hardly ignite anything but gas, unless specially arranged to do so.
Fig. 52 is a triangle formed of three Geissler tubes, and intended for rotation as a whole. M M are two pieces of mica or glass, to prevent any possibility of the spark jumping and short circuiting, in which event the tubes would fail to light.
Fig. 52.