We know in the sky 1,034 clusters of stars and more than 11,000 nebulæ. The former are composed of associated stars; the latter may be divided into two classes: First, nebulæ which the ever-increasing progress of optics will one day resolve into stars, or which in any case are composed of stars, although their distances may be too great to enable us to prove it; second, nebulæ properly so called, of which spectrum analysis demonstrates their gaseous constitution. Here is an instructive fact. The clusters of stars present the same general distribution as the telescopic stars--they are more numerous in the plane of the Milky Way, while it is the contrary which is presented by the nebulæ properly so called; they are rare, thinly spread in the Milky Way, and thickly scattered to the north as well as to the south of this zone up to its poles. The constitution of the Milky Way--not nebulous, but stellar--is a very significant fact. The nebulæ properly so called are distributed, in a sense, contrary to the stars, being more numerous towards the poles of the Milky Way and in regions poor in stars, as if they had absorbed the matter of which the stars are formed. CHAPTER XXIX. A WHIRLING UNIVERSE. No rest, no quiet, no repose, in that great universe, which to our dim eyesight looks so fixed and still, but one perpetual rush of moving suns and worlds. For every star has its own particular motion, every sun is pressing forward in its own appointed path. And among the myriads of stars--bright, blazing furnaces of white or golden, red, blue, or green flame--sweeping with steady rush through space, our sun also hastens onwards. The rate of his speed is not very certain, but it is generally believed to be about one hundred and fifty million miles each year. Possibly he moves in reality much faster. When I speak of the sun’s movement, it must of course be understood that the earth and planets all travel with him, much as a great steamer on the sea might drag in his wake a number of little boats. From one of the little boats you could judge of the steamer’s motion quite as well as if you were on the steamer itself. Astronomers can only judge of the sun’s motion by watching the seeming backward drift of stars to the right and left of him; and the watching can be as well accomplished from earth as from the sun himself. After all, this mode of judging is, and must be, very uncertain. Among the millions of stars visible, we only know the real distances of about twenty-five; and every star has its own real motion, which has to be separated from the apparent change of position caused by the sun’s advance. It seems now pretty clear that the sun’s course is directed towards a certain point in the constellation Hercules. If the sun’s path were straight, he might be expected by and by, after long ages, to enter that constellation. But if orbits of suns, like orbits of planets, are ellipses, he will curve away sideways long before he reaches Hercules.