(2) We compared two tubes (Si F₄ and the one marked Si Fl₆). The Si Fl₆ tube in general effect, and in its spectrum, when lighted-up, resembled Si F₄. We compared the one tube under the influence of the magnet with the other not so, by means of a comparison-prism on the slit. As the spectroscope and second tube were necessarily removed some distance from the magnet, the spectrum of the tube between the poles was not bright. We could not trace a change of position in any of the principal lines. The tube between the poles was brightened up when the magnet was in action[15]. _Sulphuric-Acid (SO₃) tubes._ [Sidenote: SO₃ tube No. 1; lighting-up described. Effect of the magnet. Changes in the spectrum.] (1) Excited by the small coil, both bulbs of this tube (No. 1) lighted-up brightly, with a misty light-blue tinted stream of opaque light, a yellow glow appearing at the negative pole. The capillary stream partook of the same blue tint, but was whiter and brighter. Under the magnet’s influence, the glow in the bulbs flew to the side of the tube in flickering streams of light, the capillary at the same time changing to a distinctly green tint. The spectrum without the magnet consisted of four fairly bright bands of light in the yellow, green, blue, and violet, connected by a faint misty continuous spectrum (O or possibly the hydrocarbon spectrum found in O tubes by way of impurity). When the magnet was excited, this spectrum entirely disappeared; and a set of bright metallic-looking lines upon a dark background (line-spectrum of S) took its place. This effect was produced whenever the magnet was excited, and we tried it several times, to make sure of the complete change. After a time, when the magnet, battery, and the coil-power were all weaker, with the magnet on, we obtained a compound of both spectra, the bright lines being seen upon the continuous spectrum in which the bands appeared. When the magnet was taken off, the bright lines disappeared, and the O spectrum alone remained. [Sidenote: SO₃ tube No. 2 examined.] (2) We also tried another SO₃ tube (No. 2) which had been worked for photographic purposes, and was suspected of a carbon impurity. Without the magnet, the spectrum was very like that of the first tube; but when the magnet was excited, the spectrum only brightened, and no bright metallic-looking lines appeared. _Sulphur-tube._ [Sidenote: Sulphur-tube. Lighting-up (without heating) described.] (1) A small bent vacuum-tube containing some solid sulphur, excited by the smaller coil, and without being heated, gave a narrow stream of bright blue-green light running straightly through it. With the magnet on, this stream was deflected in the bulbs, and the capillary changed from a blue-green to a distinct rosy tint. [Sidenote: Effect of magnet. Changes in the spectrum.]