The powders in tubes of this description are said to contain either sulphide of strontium, or calcium, or sulphate of quinine. The first-mentioned tube shone with a white and bright light, and probably contained the latter substance. The general effect of the current on the tubes was similar in all cases. Under a sufficiently strong current, they lighted up with a brilliant, slightly green-white glow; in which, however, by looking sideways, it was possible to detect a delicate rosy tint. Any colours beyond these in the tubes seemed to depend on the powders enclosed in them. When the current was stopped, the powders alone glowed in accordance with the colours mentioned on the labels, the rarefied gas or air in the tubes not giving any after-glow, as in the case of the sulphurous-acid tube. When the ⅝-diameter tube was excited by the small coil, the effect of the magnet was to entirely suppress and extinguish the glow. When this and the other tubes were worked with the larger coil, the spectrum, without the magnet, was bright and continuous, either showing no lines or else very faint traces of them, and, extending through the whole range of colours was brightest in and about the green. [Sidenote: Magnet effect on glow. Same on spectrum.] With the magnet excited, a bright line of pink light was condensed against the upper side of the tube; while the glow in the tube generally became very decidedly fainter, except at the electrodes, which still preserved a certain amount of brilliancy. The spectrum also was much changed. The bright continuous glow became much fainter, and many sharp and fairly bright lines were seen upon it. These lines were, as to character, not easy to recognize. Hydrogen (F) was, however, plainly distinguished; and other lines, which we considered to be N, were common to all the tubes. Some lines were also remarked as being, without the magnet, not so constant. [Sidenote: Tubes examined and compared for spectra.] Calcium orange and calcium violet, compared for spectra, were identical; the two strontium tubes hardly so, but with strontium vert a bright continuous spectrum mainly hid the lines. Strontium jaune and calcium orange were not alike; strontium vert and calcium violet differed. Calcium orange and calcium vert-bleuâtre were considered alike; but the comparison was not easy, as the calcium vert was bright, and the lines were only seen faintly upon the continuous spectrum. In order not to shift the powders, the tubes were laid horizontally, and two spectra simultaneously examined across the tubes. _Lighting-up Tubes with One Wire only (Marquis of Salisbury’s Observations)._ [Sidenote: One wire only connected with an electrode.] The vacuum-tubes employed were examined in the usual way, but one wire only was connected with an electrode. The other wire was attached to the end of a glass rod, and circuit was from time to time completed while the tube was before the spectroscope.