The aggregation of stars to which our system is believed to belong, is that of the Milky Way—that faint zone of light seen on a clear night circling the heavens. The Milky Way or galaxy is believed to be a stratum of stars in which our system is embedded I as a constituent element—the thickness of the stratum being small compared to its other dimensions. If the eye of the observer be situated near the centre of the stratum, the greatest number will be seen in the direction of the circumference; and these are so numerous, that their intermingling rays produce the impression of a zone of light. On looking towards either side of the stratum comparatively few stars will be seen. A section of the Milky Way may be compared to a long narrow belt of trees. The eye, situated in the middle of such belt, would, on looking: along the length, see all the trunks of the trees blending in one mass without seeing through. On looking, however, to either side, there would be few seen, and these quite separated from one another. All the stars visible to the naked eye, as well as those constituting the galaxy, are believed to belong to the same system. There is good reason for supposing that the stars do not vary much from a certain average size, consequently those which appear largest are nearest us. The stratum of which our firmament consists, is cleft into two branches. This is shewn by the zone of light dividing itself, for a considerable part of its course, into two pathways across the heavens. The
