CENTRAL CONCENTRATION. 63 gradations of brightness: although, in certain cases, the eye itself might be deceived into such an idea,-the central part of the nebula of ANDROMEDA, for instance, (Plate XIV.,) when seen by an ordinary telescope, forcibly impressing one with the feeling of an actual elevation there-a positive cone of light. The phenomenon is simply as I have termed it, a concentration or condensation of stars, proceeding-in cases like the foregoingby strange gradations, as of steps or stages: and in another class of appearances, the absence or interruption of easy unbroken transition, seems more remarkable still. I refer now to the NEBULOUS STARS-objects of which Fig. 2, Plate IX., was, until lately, our best representation-each appearing as a single and perfect fixed star environed by a halo. These curious objects, which, as we shall see hereafter, have played a noticeable part in recent scientific history, are at length freed from all mystery: they are small clusters whose compression is intense, environed by a coarser spherical mass. Fain would I linger and revel again among the outward signs and wonders of these great firmaments; but a new order of meditations speedily occupies all the mind. This prevalence of the spherical shape-this growth of light towards central districts this varying intensity of central compression -are not these things pregnant with the instruction contained in the rain-drop? Why is our small earth a sphere, unless because the matter 64 CENTRAL CONCENTRATION. composing it is instinct with the energy we have named attraction the tendency of particle and particle to become an aggregate-all being disposed thereby, to arrange themselves into that most compact form? I will not, indeed, venture to transfer to these august starry Universes the formal expressions of any terrestrial scholastic science; but-shaking from my mind them all -surely, even amid those depths, and the majestic creations filling them with vitality, I behold also tendency immanent, Power ever unfolding-ay, and Progression, uniform, ceaseless, harmonious, instead of dead unchanging charts of things! III. The conception which I have felt authorized to utter thus reverentially, enables us to give considerable extension to the class of nebula we are exploring. I would term it, the class whose form and general phenomena emphatically indicate the presence and preponderating action of a clustering or concentrating energy. Now, as can easily be imagined, this special characteristic may occur although the masses are not spherical-nay, even in cases of apparent deviation from all regularity of shape. For instance, notwithstanding recent analyses by Lord Rosse, it appears not improbable that elliptic or oval nebulæ exist, and are even not not rare, in which gradual accumulations of light about the central region-that region being frequently not a |