THE STELLAR UNIVERSE. 



differences which are apparent in their brightness, is to be ascribed 

 to difference of distance. Assuming, then, that they are separated 

 from each other by distances analogous to their distances from the 

 sun, itself a star, the general phenomena which have been 

 described above, involving the rapid increase of stellar density in 

 approaching the galactic plane, combined with the observed form 

 of the milky way, which, following the galactic plane in its 

 general course, departs nevertheless from it at some points, 

 bifurcates resolving itself into two diverging branches at others, 

 and at others throws out irregular off"- shoots, conducted Sir W. 

 Herschel to the conclusion, that the stars of our firmament, in- 

 cluding those which the telescope renders visible, as well as those 

 i visible to the naked eye, instead of being scattered indifferently in 

 all directions around the solar system through the depths of the 

 universe, form a stratum of definite form and dimensions, of which 

 the thickness bears a very small proportion to the length and breadth, 

 and that the sun and solar system is placed within this stratum, 

 very near its point of bifurcation, relatively to its breadth near its 

 middle point, and relatively to its thickness (as would appear from 

 the more recent observations) nearer to its northern than to its 

 southern surface. 



Let A c H D, fig. 9, represent a rough outline of a section of such 

 a stratum, made by a plane passing through or near its centre. 



Fig. 



Let A B represent the intersection of this with the plane of the 

 galactic circle, so that, z being the place of the solar system, z c 

 will be the direction of the north, and z D that of the south galac- 

 tic pole. Let zn represent the two branches which bifurcate 

 from the chief stratum at B. Now, if we imagine visual lines to 

 be drawn from z in all directions, it will be apparent that those 

 z c and z D, which are directed to the galactic poles, pass through 

 a thinner bed of stars than any of the others ; and since z is sup- 

 posed to be nearer to the northern than to the southern side of 

 the stratum, z c will pass through a less thickness of stars than 

 14 



