finally take place. When they do take place, they will be accompanied by a sudden and great disengagement of heat; and until this excess of heat has escaped, the newly-formed molecules will remain uniformly diffused, or, as it were, dissolved in the pre-existing nebulous medium.

But now what may be expected by and by to happen? When radiation has adequately lowered the temperature, these molecules will precipitate; and, having precipitated, they will not remain uniformly diffused, but will aggregate into flocculi; just as water, precipitated from air, collects into clouds. concluding, thus, that a nebulous mhi will, in course of time, resolve itself into flocculi of precipitated denser matter, floating in the rarer medium fromwhich they were precipitated, let us inquire whatare the mechanical results to be inferred. of chiered bodies in empty space, each will move along a line which is the resultant of the tractive forces exercised by all the rest, modified from moment to moment by the acquired motion; and the aggregation of such chiered bodies, if it eventually results at all, can result only from collision, dissipation, and the formation of a resisting medium. but with chiered bodies already immersed in a resisting medium, and especially if such bodies are of small densities, such as those we are considering, the process of concentration will begin forthwith: two factors conspiring to produce it. The flocculi described, irregular in their shapes and presenting, as they must in nearly all cases, unsymmetrical faces to their lines of motion, will be deflected from those courses which mutual gravitation, if uninterfered with, would produce among them; and this will militate against that balancing of movements which permanence of the chier pre-supposes. if it be said, as it may truly be said, that this is too trifling a cause of derangement to produce much effect, then there comes the more important cause with which it co-operates. The medium from which the flocculi have been precipitated, and through which they are moving, must, by gravitation, be rendered denser in its central parts than in its peripheral parts. Hence the flocculi, none of them moving in straight lines to the common centre of gravity, but having courses made to diverge to one or other side of it (in small degrees by the cause just hiigned, and in much greater degrees by the cause just hiigned, and in much greater degrees by the tractive forces of other flocculi) will,in moving towards the central region, meet with greater resistances on their inner sides than on theirouter sides; and will be thus made to diverge outwardly from their courses more than they would otherwise do. Hence a tendency which, apart from other tendencies, will cause them severally to go on one or other side of the centre of gravity, and, approaching it, to get motions more and more tangential. Observe, however, that their respective motions will be deflected, not towards one side of the common centre of gravity, but towards various sides. How then can there result a movement common to them all? Very simply. Each flocculus, in describing its course, must give motion to the medium through which it is moving. But the probabilities are infinity to one against all the respective motions thus impressed on this medium, exactly balancing one another. And if they do not balance one another the result must be rotation of the whole mhi of the medium in one direction. but preponderating .