(3) The negative pole (straight electrode) was then placed vertically on one of the poles of the electro-magnet. On excitation, the violet glow was contracted into a small upright brush or column of bright light, with a slight inclination to curvature.
Tube laid horizontally across poles of magnet.
(4) The same Plücker tube was laid horizontally across the poles of the electro-magnet (without armatures), the respective electrodes being above each pole.
Effects produced.
From the negative (straight electrode) pole sprang a dense and compact arc of violet light, in the direction of the magnetic curves, which terminated at the upper circumference of the tube, but which, if prolonged, would have followed the curves to the opposite pole. The stream from the positive pole was very considerably brightened, as in the other experiments, but did not appear in the form of rings or waves. It assumed that of a bright steady continuous glow, which formed round the tube a not perfectly continuous, but distinct and well-marked, spiral. This form of discharge seems connected with the peculiar contour of the rings mentioned in experiment 2. One might, indeed, conjecture the spiral-shaped glow to be a ring of light extended or drawn out towards the negative pole.
Effects like those obtained by Gassiot.
Experiment No. 2 seems in result very like that of Gassiot’s with his grand battery and the Royal Institution magnet, the effects (though of course upon a smaller scale) being similar to those obtained by him.
Effect of Magnet on Plücker Tube (Tin Chloride).
Plücker tube (tin chloride). Lighting-up described.
A large Plücker tube was examined, which had a bulb attached at each end, communicating with the central portion by a narrow neck or constriction. On connexion with the small coil, a narrow stream of pale diffused cobalt-blue light ran along the whole tube, from point to point of the electrodes, the positive wire at the same time glowing with an aura of amber-yellow light. (See Plate XVII. fig. 3, where the narrow stream of light is shown by dotted lines.) At the two necks or constrictions the stream of light was perceptibly brightened.