We subsequently tried another tin-chloride tube, purchased of Mr. Browning. This lighted up like the former tube, but brighter. There was an amber glow at the junction of the negative bulb which adjoined the capillary part. This was lost on putting on the magnet. At the same time a perceptible pattering ringing noise was heard in the tube, and metallic-looking threads of light ran through the bulbs. [Sidenote: Spectrum described.] Without the magnet, the spectrum was a continuous faint misty one, with bright lines of tin occasionally flashing up. With the magnet, the tin lines at once shone out bright, strong, and clear upon a black background, the change in effect being very marked. CHAPTER XVII. EFFECT OF MAGNET ON BULBED PHOSPHORESCENT TUBE. [Sidenote: Large phosphorescent bulbed tube. Lighting-up described. Spectrum described. Glow when discharge stopped, described.] Mr. John Browning kindly lent me a large phosphorescent tube with five bulbs, said to be filled with anhydrous sulphurous-acid gas (SO₂). (See Plate XVIII. fig. 1.) This tube lighted up beautifully with the large coil. The connecting tubular parts of it were filled with a bright, beaded, transparent, rosy light; while the bulbs glowed with a more opaque blue-tinted effect. The spectrum of the tubular part was found to agree exactly with the principal bright band seen in a SO₃ Geissler tube. The spectrum of the bulb-glow was a faint green-blue continuous one, with bright bands or lines faintly flashing up at times. When the discharge was stopped, the tube still glowed with a moderately bright, opaque, grey-green light. This glow gradually faded out, always commencing with the bulb forming the negative or violet pole, and so dying out, bulb by bulb, towards the positive pole. The negative-pole bulb at times was, on suddenly stopping the current, hardly lighted at all, the other bulbs being luminous. [Sidenote: Comparison with SO₃ Geissler tube.] (1) We compared the large tube with a SO₃ Geissler tube, by means of a comparison-prism on the slit, with the result before detailed. The Geissler tube, however, showed no after-glow. [Sidenote: Effects in bulbs on lighting-up the tube described. Effects of reversal of the current. After-glow restored by passing of current.] (2) We lighted up the Browning tube with the large coil. The negative bulb was always the least filled with the blue opaque vapour, and the other bulbs increased in vapour-density in the order they approached towards the positive bulb. When the current was reversed, so that the negative and positive glow changed places, the negative bulb still remained transparent, although the positive opaque glow had (presumably) been thrown into it. When the after-glow had quite disappeared in the bulbs, it was again strongly restored, by the passing of the current for a few seconds only through the tube. [Sidenote: Effect of reversal of current on positive-pole glow.]