SIDEEEAL SYSTEMS. 73 



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 equidis- 

 tant 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 in the same 

 manner 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 cannot, correctly speaking, be 

 any idea of depth, but merely of outer limits. In the direc- 

 tion 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 luminous vapour, 

 and are perspectively grouped, encircling as in a zone the 

 visible vault of heaven. This narrow mid branched girdle, 

 studded with radiant light, and here and there interrupted bv 

 dark spots, deviates only by a few degrees from forming a 

 perfect large circle round the concave sphere of heaven, 

 owing to our being near the centre 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 telescopic vision as a ring, and at a still greater 

 distance as a resolvable discoidal nebula. 



Amongst 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 

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

 with respect to relative motion and illumination, to the same 

 planetary dependence that characterizes our own solar system. 

 Two or more self-luminous bodies, whose planets and moon r 

 if such exist, have hitherto escaped our telescopic powers of 

 vision, certainly revolve around one common centre of gravity ; 

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

 merely by unagglomerated matter, or cosmical vapour, whilst 

 in our system the centre of gravity is often comprised within 

 the innermost limits of a visible central body. If, therefore, 



