“I made a calculation about the November meteors to see how close they must go to the path of Uranus in order to be captured, and found that they must approach nearly as close as the nearest satellite. Only those which came almost in contact with the planet could be captured. Now, if they were shot out when Uranus was in a sun-like condition, then it would be explained, whereas we find great difficulty in imagining that a comet coming out of space would be captured bodily by a planet like Uranus. Let us consider the matter thus: if comets are expelled from a planet, they will be carried along with the forward motion. If it could appear that some of them went backward, then we would have no evidence of the theory I have been advancing. If most of them travel forward, then we would have some evidence for the theory. Now there is the curious fact that among the comets of short period the whole of Jupiter’s family travel forward. They do not travel in all directions of slope; all have a very moderate slope to the paths of the planets. They do not have the slope even of the asteroids. That is precisely what we notice—that they travel very much with Jupiter. Taking the balance between the two theories—that of expulsion and that of capture—it seems to be in favor of the more startling one—that Jupiter has had the power to expel these objects.” It is interesting, in connection with this extract from the report of a lecture given by my father some fifty years ago at present time of writing (1925), to turn to a passage in the chapter on comets, by Dr. A. C. D. Crommelin, in the _Splendour of the Heavens_, page 414, where he refers as follows to the capture theory: “The fact that the members of the Jupiter family (of comets) have direct motion in all cases appears to give a fatal blow to the capture theory. Practically as many comets would approach the planet with retrograde motion as with direct; there is, indeed, the point that those travelling in the same direction as the planet would remain longer in its neighbourhood, and so have more time to be perturbed, which would have some weight; but that out of some fifty comets there is not a single retrograde one is too remarkable a fact to pass over, and it clearly suggests that Jupiter played a different part from that of a mere enslaver, and was concerned with the origin of these bodies in a more intimate manner.