fore the idea of the Milky Way itself as a vast ring of closest aggregation, including a more sparsely filled region, thus giving to the whole cluster, could it be seen laterally from a sufficient distance, an appearance not unlike that of the annular nebula in Lyra, is well founded. He also finds reason for supposing a similar but independent arrangement of the brightest stars, in the peculiar localization of the nearest of them, and the sudden falling off in density at about 30° from the galactic circle, above remarked—other systems of condensation requiring gradual changes. The true figure, if his reasoning is to be trusted, would therefore be a small ring of maximum density near the center of a very large one.[1] Such speculations are, however, it is hardly necessary to say, very uncertain.
It is not easy to make out, from the general distribution of the stars, that our sun is in one direction rather than another from the center of the sidereal system, and there is even some doubt about the position which some astronomers give us, on the northern side of the plane of the Milky Way. Indeed, beyond the prevailing condensation toward this plane, it seems that no important general law governing star aggregation has yet been found. Mr. Proctor's services in calling attention to the grouping of certain portions of the heavens in subordinate systems having a common "star-drift," should not be overlooked; but his discovery that a large part of the southern hemisphere is particularly rich in stars[2] can not be admitted for several reasons: 1. Behrmann's catalogue of southern stars, in which magnitudes were observed with particular care, shows nothing of the sort; 2. Mr. Proctor's own maps show nothing of the sort, for stars brighter than the sixth magnitude; and it is far less credible that an anomalous law of distribution holds over a wide area, affecting but this one order of brightness, than that those who observed this part of the heavens included more and fainter stars in their sixth magnitude than did northern observers; 3. Mr. Proctor's own maps show that the boundary of his "rich region" is the Tropic of Capricorn; and it is far less credible that an artificial circle should limit any law of distribution than that the whole difference is due to the fact that this tropic was also the northern boundary of La Caille's observations, the source, in all probability, whence the magnitudes of Mr. Proctor's stars were originally derived. Observers, in fact, are particularly likely to differ in estimating the extent of the sixth magnitude, for it seems to have been agreed by general consent that this magnitude shall include all stars to be seen with the unaided eye on the clearest nights, and differ-
- ↑ "Photometric Researches," pages 175-178. The sun, it would seem, is to be considered as in a region of exceptional rarity as compared with other regions through which the galactic plane passes, and at the same time of exceptional density when the comparison includes stars remote from this plane.
- ↑ Most positively stated in a lecture before the Royal Institution, May, 1870; also in the introduction to his "Star Atlas."
