5 i2 THE POPULAR SCIENCE MONTHLY. 



fore the idea of the Milky Way itself as a vast ring of closest aggrega- 

 tion, including a more sparsely filled region, thus giving to the whole 

 cluster, could it be seen laterally from a sufficient distance, an appear- 

 ance not unlike that of the annular nebula in Lyra, is well founded. 

 He also finds reason for supposing a similar but independent arrange- 

 ment 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 re- 

 quiring 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.* 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 subor- 

 dinate systems having a common " star-drift," should not be over- 

 looked ; but his discovery that a large part of the southern hemisphere 

 is particularly rich in stars f 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 in- 

 cluded more and fainter stars in their sixth magnitude than did north- 

 ern 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 proba- 

 bility, whence the magnitudes of Mr. Proctor's stars were originally 

 derived. Observers, in fact, are particularly likely to differ in esti- 

 mating 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 consid- 

 ered 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 compari- 

 son includes stars remote from this plane. 



f Most positively stated in a lecture before the Royal Institution, May, 1870; also in 

 the introduction to his " Star Atlas." 



