Art. VIII.—Partial Impact: a possible Explanation of the Origin of the Solar System, Comets, and other Phenomena of the Universe. By Professor A. W. Bickerton,F.C.S., Associate Royal School of Mines, London. [Read before the Philosophical Institute of Canterbury, 1st August, 1878.] In the last paper which I submitted to the Institute, I gave a short sketch of some hypothetical cases of partial collisions, and suggested that such cases might possibly be of frequent occurrence throughout space, and might offer an explanation of many phenomena of the universe. I especially showed the application of the hypothesis to temporary and variable stars. To-night I intend to show that it appears competent to explain the formation of the solar system, of comets, of meteors, and of some variety of nebulæ. I shall, however, in the first place point out the very great difference which exists in the capabilities of cases of partial and complete collision, the first offering a field of possibilities of cosmical phenomena which is really surprising, the latter being probably confined to but a few rare cases. In the last paper I assumed that the partial collision of two attracting bodies having an original proper motion in space, would be much more likely than entire coalescence. It appeared, however, to be a very general idea, that if the bodies struck at all, it must be that their mutual attraction would certainly produce complete coalescence. On the other hand, it was generally admitted that two bodies when attracted by each other would seldom come into contact, but would in most cases be carried by their original velocity away once more from each other's influence. It is only necessary to assume that the size of the bodies has increased enormously without increase of mass for a case of mere disturbance to become one of partial collision; the generality of the case is thus practically demonstrated. As cases of partial collisions may be of infinite variety, for the sake of simplicity I have in this paper (except where stated to the contrary) assumed that all the colliding bodies are of the same size; composed of the same chemical elements; with the same initial proper motions, the velocity of which is small compared with that developed by attraction; also that the mass of each of the two bodies of any one pair is the same. If two bodies come into direct collision from rest, a definite energy of velocity will be acquired at the moment of contact, depending solely on the mass. After coalescence, if a single particle were attracted from infinite space, the particle being attracted by the whole coalesced mass, and this mass not appreciably moving towards the particle, twice the force would act through twice the space, and would develope twice the velocity, or four times the energy. Hence, also, a particle to leave the body must have this double velocity. Therefore, as it does not appear reasonable to expect that