SIDEREAL SYSTEMS. 89 



third of its .ength into two branches ; it is supposed that we 

 are near this division, and nearer to the region of Sirius than 

 to the constellation Aquila, almost in the middle of the stra- 

 tum in the line of its thickness or minor axis. 



This position of our solar system, and the form of the whole 

 discoidal stratum, have been inferred from sidereal scales, that 

 is to say, from that method of counting the stars to which I 

 have already alluded, and which is based upon the equidistant 

 subdivision of the telescopic field of view. The relative depth 

 of the stratum in all directions is measured by the greater or 

 smaller number of stars appearing in each division. These 

 divisions give the length of the ray of vision iiTthe same man- 

 ner as we measure the depth to which the plummet has been 

 thrown, before it reaches the bottom, although in the case of 

 a starry stratum there can not, correctly speaking, be any idea 

 of depth, but merely of outer limits. In the direction of the 

 longer axis, where the stars lie behind one another, the more 

 remote ones appear closely crowded together, united, as it were, 

 by a milky- white radiance or lummous vapor, and are perspec- 

 tively grouped, encircling, as in a zone, the visible vault of 

 heaven. This narrow and branched girdle, studded with ra- 

 diant light, and here and there interrupted by dark spots, de- 

 viates only by a few degrees from forming a perfect large cir- 

 cle round the concave sphere of heaven, owing to our being 

 near the center of the large starry cluster, and almost on the 

 plane of the Milky Way. If our planetary system were far 

 outside this cluster, the Milky Way would appear to tele- 

 scopic vision as a ring, and at a still greater distance as a re- 

 solvable discoidal nebula. 



Among the many self-luminous moving suns, erroneously 

 called fixed stars, which constitute our cosmical island, our 

 own sun is the only one known by direct observation to be a 

 central body in its relations to spherical agglomerations of 

 matter directly depending upon and revolving round it, either 

 in the form of planets, comets, or aerolite asteroids. As far 

 as we have hitherto been able to investigate multiple stara 

 (double stars or suns), these bodies are not subject, with re- 

 spect to relative motion and illumination, to the same planet- 

 ary dependence that characterizes our own solar system. Two 

 or more self-luminous bodies, whose planets and moon, if such 

 exist, have hitherto escaped our telescopic powers of vision, 

 certainly revolve around one common center of gravity ; but 

 this is in a portion of space which is probably occupied merely 

 by unagglomerated matter or cosmical vapor, while in our sys- 



