Winding among the constellations, and forming a gigantic belt round the whole star-sphere, lies that most wonderful feature of the heavens familiar to all under the name of the Milky Way. This great luminous girdle of the sky may be seen in some portion of its extent, and at some hour of the night, at all seasons of the year, though in May it is somewhat inconveniently placed for observation. Roughly speaking, it presents the appearance of a broad arch or pathway of misty light, 'whose groundwork is of stars'; but the slightest attention will reveal the fact that in reality its structure is of great complexity. It throws out streamers on either side and at all angles, condenses at various points into cloudy masses of much greater brilliancy than the average, strangely pierced sometimes by dark gaps through which we seem to look into infinite and almost tenantless space (Plate XXVII.), while in other quarters it spreads away in considerable width, and to such a degree of faintness that the eye can scarcely tell where it ends. At a point in the constellation Cygnus, well seen during autumn and the early months of winter, it splits up into two great branches which run separate to the Southern horizon with a well-marked dark gap dividing them. When examined with any telescopic power, the Milky Way reveals itself as a wonderful collection of stars and star-clusters; and it will also be found that there is a very remarkable tendency among the stars to gather in the neighbourhood of this great starry belt. So much is this case that, in the words of Professor Newcomb, 'Were the cloud-forms which make up the Milky Way invisible to us, we should still be able to mark out its course by the crowding of the lucid stars towards it.' Not less remarkable is the fact that the distribution of the nebulæ with regard to the Galaxy is precisely the opposite of that of the stars. There are, of course, many nebulæ in the Galaxy; but, at the same time, they are comparatively less numerous along its course, and grow more and more numerous in proportion as we depart from it. It seems impossible to avoid the conclusion that these twin facts are intimately related to one another, though the explanation of them is not yet forthcoming.