This triangle is shown diagrammatically at A B C, Fig. 53, mounted on an insulated rotating disk. Before commencement of rotation, and upon the current being turned on to the tubes, a simple triangle will result, but at a certain stage of rotation the Maltese cross shown is formed. A still higher rate of rotation will produce the double star, Fig. 54, and as the rotation and rate of vibration of the coil contact-breaker is varied, an apparently endless succession of stars or triangles appears to grow out into view.
Fig. 53.
Fig. 54.
Although Figs. 53 and 54 serve to illustrate a triangle of tubes and its variations, a very pretty and simple effect can be obtained with it as follows: Three strips of looking-glass are cut and scratched across their silvered surface, as described for the luminous pane, Fig. 37. The current then being allowed to pass, and the wheel being rotated, the triangle acts as in the preceding paragraphs, multiplying and forming figures, which are extremely interesting to watch.
While treating on the subject of store-window attractions, a few suggestions on a display of stationary Geissler tubes may be made. Starting with the assumption that the platform on which the goods would be displayed is of wood, a very small amount of preparation is necessary. The platform is covered with a dark material free from gloss, such as canton flannel, on which the tubes are laid in any fancy pattern, or may be scattered haphazard. Fine bare wire (No. 36 B. & S. is not any too small) is run from tube to tube, using care that it does not touch itself in such manner as to short circuit the current. There is not much necessity to cover the wires, unless the rate of vibration of the contact be so rapid as to show the brush discharge from the wire strands. In a jewelry store the cylindrical portions of the tubes may be covered with strips of dark cloth, concealing all but the bulbs. The Uranium bulbs will resemble emeralds; the yellow bulbs, topaz; and the blue, turquoise—certainly a very striking collection of gems. A few diamond-shaped pieces of the foil-coated glass scratched across, by the whiteness of the tiny sparks will aid to set off the whole. The outfit is not expensive: a coil giving a one half inch spark will light from four to six tubes to great brilliancy. Cloths with metallic threads woven in them must not be used, nor any of the metallic powders known in the trade as "glitters."