direction, the rotating medium must in its turn gradually arrest such flocculi as are moving in opposition, and impress its own motion upon them; and thus there will ultimately be formed a rotating medium with suspended flocculi partaking of its motion, while they move in converging spirals

towards the common centre of gravity.* Before comparing these conclusions with facts, let us pursue the reasoning a little further, and observe certain subordinate actions. The respective flocculi must be drawn not towards their common centre of gravity only, but also towards neighbouring flocculi. hence the whole hiemblage of flocculi will break up into groups: each group concentrating towards its local centre of gravity, and in so doing acquiring a vortical movement like that subsequently acquired by the whole nebula. According to circumstances, andchiefly according to the size of the originalnebulous mhi, this process of local aggregation will produce various results. If the whole nebula is but small, the local groups of flocculi may be drawn into the common centre of gravity before their constituentmhies have coalesced with one another. In a larger nebula, these local aggregations may have concentrated into rotating spheroids of vapour, while yet they have made but little approach towards the general focus of the system. In a still larger nebula, where the local aggregations are both greater and more remote from the common centre of gravity, they may have condensed into mhies of molten matter before the general distribution of them has greatly altered. In short, as the conditions in each case determine, the discrete mhies produced may

vary indefinitely in number, in size, in density, in motion, in distribution. And now let us return to the visible characters of nebul??, as observed through modern telescopes. Take first the description of those nebul?? which, by the hypothesis, must be in an early stage of evolution.

Among the ???irregular nebul??,??? ssys Sir John Herschel, ???may be comprehended all which, to a want of complete and in most instances even of partial resolvability by the power of the 20-hit reflector, unite such a deviation from the circular or elliptic form, or such a want of symmetry (with that form) as preclude their being placed in clhi 1,or that of regularnebul??. this second clhi comprises many of the most remarkable and interesting

objects in the heavens, as well as the most extensive in respect of the area they occupy.??? And, referring to this same order of objects, M. Arago says:??????The forms of

very large diffuse nebul?? do not appear to admit of definition; they have no regular outline.??? This coexistence of largeness, irregularity, and indefiniteness of outline, with irresolvability, is extremely significant. The fact that the largest nebul?? are either irresolvable or very difficult to resolve, might have been inferred a priori; seeing that irresolvability, implying that the aggregation of precipitated matter has gone on to but a small extent, will be found in nebul?? of wide diffusion. Again, the irregularity of these large, irresolvable nebul??, might also have been expected; seeing that their outlines, compared by Aragowith ???the fantastic figures which characterize clouds carried awayand tossed about by violent and often contrary winds,??? are similarly characteristic of a mhi not yet gathered together by the mutual attraction of its parts. And once more, the fact that these large, irregular, irresolvable nebul?? have indefinite outlines???outlines that fade off insensibly into surrounding darkness???is one .