Auroræ: Their Characters and Spectra

by J. Rand Capron

The two tubes were then examined separately in detail. No. 2, excited by the magnet, showed curious effects. The glow was rendered weak and intermittent, and the rosy tint almost disappeared. The capillary changed to a decided green colour, and the positive electrode was surrounded by a yellow glow. The changes in the spectrum were no less decided. Without the magnet, the spectrum was found to be a bright continuous one of H (with a full set of principal and intermediate lines) and N—the N spectrum being rather faint and misty, with very slight, if any, traces of the iodine-spectrum. On the magnet being excited, the spectrum changed as if by magic; the H and N spectra disappeared (except hydrogen F, which still faintly remained), and the iodine lines, mostly in the yellow-green and green, shone out wonderfully sharp and bright on quite a dark ground. No. 1, upon examination, showed between the magnet-poles only the same changes as on last occasion. The spectrum seemed to be one of iodine, with the addition of slight traces of the H spectrum.

Effects discussed.

On excitation of the magnet, the misty continuous part of the spectrum nearly disappeared, and the bright lines shone up sharply upon the dark background as before. The effects in the case of both tubes were strongly marked. The impression as to tube No. 2 was that, without the magnet, the slight iodine-spectrum was overpowered and masked by the N and H spectra; while under the influence of the magnet the N and H spectra were almost altogether suppressed, the iodine-spectrum being at the same time intensified. The disappearance of the continuous spectrum under the action of the magnet in No. 1 (with the supposition it was mainly H) would be accounted for in the same way.

Bromine-tubes.

Bromine-tube No. 1. Lighting-up described. Effect of the magnet. Bromine-tube No. 2. Effect of magnet.

This tube (No. 1) had been previously worked for photographic purposes. Excited by the small coil, the whole tube was filled with a faint flickering light. The positive bulb contained a faint purple glow, with a yellow-green tinge at the electrode, a curious flickering stream of light flashing from the electrode to the side of the tube. The negative pole showed pretty much the same effect as the positive. The capillary stream expanded at the opening into the positive bulb, but ran in a condensed stream into the negative bulb. In colour it was of a rather bright lilac. Upon putting the magnet on, the light-glow in the tube was at once and permanently extinguished, the coil still working as if the current passed. The same effect happened repeatedly; but now and then the tube lighted-up for a second, showing spiral arrangement in the bulb. We tried another bromine-tube (No. 2): it lighted-up easily; both bulbs were filled with a purple stream of light; capillary stream bright grey. The glass of the tube was strongly fluorescent and of a yellow tinge. When the magnet was excited the stream of light was somewhat condensed in the bulbs, and flew to the side of the tube; while the capillary stream at the same time brightened. The spectrum without the magnet was fairly bright; it increased in brightness under the influence of the magnet, and additional lines appeared; but we considered them to be only faint existing ones brightened up. No change in the position of the principal lines was traced.

Silicic-Fluoride tubes.

Si Fl₆ tube. Lighting-up described. Effect of magnet.

(1) A tube marked Si Fl₆ had been worked for photographic purposes; it lighted-up easily. Both bulbs were filled with a brown-pink diffused light, inclined to condense into a stream in the positive bulb. The violet glow was very bright, and nearly filled the space round the electrode. The capillary stream was of a bright violet tint. The effect of the magnet was to decrease the intensity of the light throughout the whole tube.

In the positive bulb the stream broke up into a number of vibrating streamlets, with little bright threads of light intermixed, which flew towards the side of the tube at right angles to the magnetic poles. There was an inclination to spiral arrangement in the streamlets. This stream changed from side to side of the tube coincidently with change in the magnetic poles. At the negative pole the violet glow formed an arc in the direction of the magnetic curves, while a spiral of fainter (positive?) light was formed in the upper part of the bulb. A slight ringing sound was heard in the tube.