CHAPTER XVI.
EFFECT OF MAGNET ON WIDE AIR (AURORA) TUBE.
Wide air-tube described.
A large, wide air-tube was tried; it was 14½ inches long by 1 inch in diameter, of the same bore throughout, and with straight platinum electrodes.
Magnet effect when tube placed vertically between conical armatures.
(1) To excite it the larger coil was used. The tube was filled with bright, steady, rosy light, and beautiful stratification, which, as it flickered, seemed to incline to a continuous spiral (Plate X. fig. 8). This stratification was very close and fine, and extended nearly throughout the tube. On excitation of the magnet (the tube having been placed vertically between the conical armatures), the glow was condensed into a bright solid line or stream of light at the point which lay directly between the poles. This line or stream expanded into an elongated funnel-shape as it retreated from this centre towards the extremities of the tube, the stratification showing itself more distinctly as the glow of light became less dense (Plate XVIII. fig. 3). The stream of light was driven away at right angles to the poles, and changed from side to side of the tube with the direction of the current.
[With the small coil this tube showed only a flickering stream of light, with very slight indications of stratification.]
Effect when tube placed horizontally between the armatures.
(2) The tube was placed horizontally between the conical ends of the armatures. The condensed stratified stream of light flew upwards and downwards (according to direction of current) instead of to the respective sides of the tube.
Tube placed along the poles of the magnet.