The red region was indistinct, and showed no prominently bright line. The bulbs were mainly of a slightly blue-grey tint, with a steady glow. Capillary stream quite pale white, with a very slight tinge of red. Violet-glow small and confined to the electrode. Upon the magnet being excited, the capillary stream became intensely brighter, and the glow in both bulbs contracted into a single bright stream, which curved towards the sides of the bulbs at right angles to the magnetic poles, and changed from side to side with the current. This effect was very marked, and was more apparent in the positive than the negative pole. A faint stratification was seen in both bulbs. Upon either bulb being placed between the armatures, the glow left the electrode point and condensed into one bright stream, running along the side of the tube and curving at each end (Plate XVII. fig. 10). No trace whatever of tendency to form a spiral was seen. The spectrum with the magnet on was very conspicuously brightened up throughout. A set of fluted bands with a bright line among them appeared in the red, and several lines or bands appeared in the violet which could not be seen before. The bright red line, upon measurement, proved to be the hydrogen-line C. It thus seemed brighter in proportion than the F line, although, with the magnet off, the latter was well seen, while the C was not. No actual change in position of the spectrum-lines could be detected. [It is to be noticed that the O tubes employed were those used by me in former experiments, and had the bright lines now attributed to hydrocarbon impurity. Their bulb-effects differed, however, entirely from those of the CO₂ tube. (Compare figs. 10 and 11, Plate XVII.)] _Hydrogen-tubes._ [Sidenote: H tube, No. 1; glow described.] A small H Geissler tube (No. 1) was selected, and lighted up by the small coil. The capillary was a bright white-pink stream, with a tendency to redden at times. The bulbs were both of a faint blue-grey tint, with coarse lenticular stratification. The violet-pole glow was pale and white as compared with that of N. [Sidenote: When the magnet was excited, whole character of tube changed. Unexcited spectrum described. Effect when magnet was excited.]