track of 1824 is followed eighteen years later by the track of 1842 to the left, and that again by the track of 1860, and that by 1878. But now we have made three steps, each one-third of the way round; and we come back after fifty-four years nearly to the same place.
Fig. 76.
We must keep putting in the word "nearly," because none of these things happen exactly; you see that the 1878 track is just above the 1824 track, which has the 1770 track below it in turn. So that these tracks make a regular pattern on the Earth which we can almost draw for ourselves when we have got a few of them.
Since the tracks are edging a little further north each time, they will at last go over the edge of the Earth, at the North pole, and that family of eclipse tracks will be finished. It came in at the South pole 1200 years ago; travelled gradually
