Had the vast mass of matter postulated by Lord Kelvin acquired no motion of revolution, but have fallen continuously towards the centre of mass, the motions developed when the more distant bodies approached that centre would have been extremely rapid; while, as they must have fallen in from every direction, they would have become more and more densely aggregated, and collisions of the most catastrophic nature would frequently have occurred, and this would have rendered the central portion of the universe the _least_ stable and the _least_ fitted to develop life. But, under the conditions that actually prevail, the very reverse is the case. The quantity of matter remaining between our cluster and the Milky Way being comparatively small, the aggregation into suns has gone on more regularly and more slowly. The motions acquired by our sun and its neighbours have been rendered moderate by two causes: (1) their nearness to the centre of the very slowly aggregating cluster where the motion due to gravitation is least in amount; and (2) the slight differential attraction away from the centre by the Milky Way on the side nearest to us. Again, this protective action of the Milky Way has been repeated, on a smaller scale, by the formation of the outer ring of the solar cluster, which has thus preserved the inner central cluster itself from a too abundant direct inflow of large masses of matter. But although the matter composing the outer portion of the original universe has been to a large extent aggregated into the vast system of the Milky Way, it seems probable, perhaps even certain, that some portion would escape its attractive forces and would pass through its numerous open spaces--indicated by the dark rifts, channels, and patches, as already described--and thus flow on unchecked towards the centre of mass of the whole system. The quantity of matter thus reaching the central cluster from the enormously remote spaces beyond the Milky Way might be very small in comparison with what was retained to build up that wonderful star-system; but it might yet be so large in total amount as to play an important part in the formation of the central group of suns. It would probably flow inwards almost continuously, and when it ultimately reached the solar cluster, it would have attained a very high velocity. If, therefore, it were widely diffused, and consisted of masses of small or moderate size as compared with planets or stars, it would furnish the energy requisite for bringing these slowly aggregating stars to the required intensity of heat for forming luminous suns.