Page:Popular Science Monthly Volume 58.djvu/426

418 tion, in Cepheus, we notice in the midst of the brighter region a nearly-circular patch several degrees in diameter, in which little light is seen. A little farther along we notice a similar elongated patch in Cygnus lying across the course of the belt. In this region the brighter portions are of great breadth, more than 20°.

In Cygnus begins the most remarkable feature of the Milky Way, the great bifurcation. Faintly visible near the zenith, as we trace it towards the south, we see it grow more and more distinct, until we reach the constellation Aquila, near the equator. Between Cygnus and Aquila the western branch seems to be the brighter and better marked of the two, and might, therefore, be taken for the main branch. About Aquila the two appear equal, but south of this constellation we see the western branch diverge yet farther toward the west, leaving the gap between it and the eastern yet broader and more distinct than before. This branch finally terminates in the constellation Ophiuchus, while the eastern branch, growing narrower, can still be followed toward the south.

Between the equator and the southern horizon we have the brightest and most irregular regions of all. Several round, bright patches of greater or less intensity are projected on a background sometimes moderately bright and sometimes quite dark. If the night is quite clear and moonless we shall see that, after a vacant stretch, the western branch seems to recommence just about the constellation Scorpius. In this constellation we have again a bifurcation, a dark region between two bright ones.

This is about as far as the object can be well traced in our middle latitudes. From a point of view nearer to the equator it can be traced through its whole extent. South of Scorpius and Sagittarius it becomes broad, faint and diffused through the constellations of Norma and Circinus. It reaches its farthest southern limit in the Southern Cross, where it becomes narrower and better defined. The most remarkable feature here is the 'coal sack,' a dark opening of elliptical shape in the central line of the stream. West and north of this, in the constellation Argo, is the broadest and most diffused part of the whole stream, the breadth reaching fully 30°. Here we again reach the portion which rises above our horizon.

Returning now to our starting point, we shall notice that, as we make our observations later and later in the autumn, the southern part, which we have been mostly studying, is seen night by night lower down in the west, while new regions are coming into view in the northeast and east. These regions rise earlier every evening, and, if we continue our observations to a later hour, we shall see more and more of them above the eastern or southeastern horizon. By midwinter Cassiopeia will be seen in the northwest, and we can readily trace