Quite distinct from these nebulae are others of perfectly regular form, very small, purely gaseous, without intermingling of any stars, but usually with one bright star-like nucleus at the centre. One form is the ring nebula, of which much the best known is that in the northern constellation of the Lyre. There are, however, some in the south. In a large telescope they appear like little golden wedding-rings against the dark sky background. Another regular form is the “planetary nebula,” so called because they look much like planets in large telescopes, being perfectly round or oval with a sharply-defined edge, and in several cases there are handle-like appendages, which may possibly be encircling rings, like the rings of Saturn. These nebulae shine with a peculiar bluish-green light, the colour of the unknown gas nebulium, of which they are chiefly composed. In Hydra, south of the star Mu, is one of the brightest and largest, known as H 27—that is, No. 27 on William Herschel’s list. It is elliptical and of a lovely bluish colour, with a bright nucleus exactly in the centre. By means of these sharply-defined central nuclei it has been found possible to measure the approaching or receding movements of these nebulae, and although the one just mentioned is receding from us with a speed of only 3½ miles a second, their average speed is high, amounting to 40 or 50 miles a second. One in Sagittarius is receding at more than 80 miles a second, and another in Lupus attains a speed of over a hundred. These are movements comparable with those of stars, but the average is higher than even for the most rapidly moving class of stars, the red-solar and Antarians. May we, then, place the planetary nebulae at the end of our star-series, since we saw that from the blue down to the red the average movements became faster and faster, and may we believe that all stars eventually become gaseous nebulae, as “new stars” seem to do? But we saw that in spectrum these nebulae rather resemble the stars at the other end of the series, the Wolf-Rayet, which lead directly to the hottest and brightest of all, the Orion stars. Planetary nebulae also resemble Wolf-Rayet, Orion, and Sirian stars, and differ from solar and red stars in that they cluster near the Milky Way, and are scarcely ever found far from it. Their place in the universe cannot be established yet.