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a race; but if it is a long race, such as a mile, we have seen some of the runners get far behind the leaders, sometimes a whole lap behind. If you stood inside the track close enough for the runners to graze you as they went by, you would be touched a good many times as the leaders went by, but only occasionally by the stragglers: and I suppose that the Sun is close up to the meteor track in this way, Fig. 59.—Waxing and waning of Sunspots. so that he shows numerous spots when the leaders are going by and only a few as the stragglers tail off. But how does this notion help us to explain why the leaders should come round the track sometimes in eight years and sometimes in thirteen years, sticking a sort of average of eleven years? That is the really important point, and supplies the reason for putting forward this notion at all. Let me go back for a moment to Halley's comet. His attention was first drawn to the