Fig. 46 shows three exhausted tubes arranged in series.
A is of uranium glass, and glows dark green; B of English glass, showing a blue hue, and C of soft German glass, glowing with a bright apple-green tint.
Fig. 48.
Crystals of nitrate of calcium, nitrate of silver, benzoic acid, tungstate of calcium, lithia benzoate, sodium salicylate, zinc sulphide, and acetate of zinc fluoresce.
Fig. 47 is a highly exhausted tube, having at its lowest part a few pieces of ruby. When the secondary current is turned on at P and N the rubies shine with a brilliant rich red, as if they were glowing hot.
Fig. 48 shows the tube to exhibit the effect resulting from focussing the electric rays on a piece of iridio-platinum at B.
The cup A forms the negative pole; the metal disk C, the positive.
On increasing the intensity of the spark, the metal at B glows with extreme brilliancy, and melts if the intensity be carried too far.