Page:A Voyage in Space (1913).djvu/223

Rh find plain indications of disturbance near the years 1766, 1799, 1833, 1866, 1899, which are a set of occasions already well known to astronomers from the great showers of meteors which were seen then. It has been shown that these showers are all due to a great meteor swarm called the Leonids, travelling round the Sun in about thirty-three years. My notion is that the sunspot swarm is disturbed by these Leonids every time they come round: I think that, as already stated, one end of the track grazes the Sun, but the other end is close to the track of the Leonids, so that it is particularly easy for the Leonids to attract the sunspot swarm, and to upset its regularity. Every time the Leonids come round we open a new chapter of sunspot history. Why should the end of the one track lie so close to the other? Of course we can say that there is no reason why it shouldn't, but it would be much more satisfactory if we could mention a reason why it should; and a very good reason seems to me to be that the sunspot swarm was broken off from the other near the point where they now approach so closely. Here again it is desirable to give a reason for the breakage, and here again we find one in the planet Saturn, which passes close to this same spot in its journey round the Sun (Fig. 60). It does not always meet the Leonids there, because when Saturn comes to the critical spot the Leonids may be in quite a different part of their track: indeed, they generally are. But about every 265½ years Saturn and the Leonids hit off the same moment for being at the meeting-place: and when this happens we find (by looking at the