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IX. myself, at its return in 1682. All the elements agree, except that there is an inequality in the times of revolution; but this is not so great that it cannot be attributed to physical causes. For example, the motion of Saturn is so disturbed by the other planets, and especially by Jupiter, that his periodic time is uncertain, to the extent of several days. How much more liable to such perturbations is a comet which recedes to a distance nearly 4 times greater than Saturn, and a slight increase in whose velocity could change its orbit from an ellipse to a parabola? The identity of these comets is confirmed by the fact that in the summer of the year 1456 a comet was seen, which passed in a retrograde direction between the Earth and the Sun, in nearly the same manner; and although it was not observed astronomically, yet, from its period and path, I infer that it was the same comet as that of the years 1531, 1607, and 1682. I may, therefore, with confidence predict its return in the year 1758. If this prediction be fulfilled, there is no reason to doubt that the other comets will return."

Halley died in 1742 and was buried in the Churchyard of St. Margaret's, Lee, not far from Greenwich, and it has lately (1909) been announced that the Admiralty have decided to repair his tomb at the public expense, no descendants of his being known. The original top slab with an inscription was illegally removed to the Greenwich Observatory in 1854. Let us hope that it will be now restored, or a new one with the original inscription put in place.

As years rolled on and 1758 began to draw near astronomers naturally recalled Halley's prediction, and thought it worth while to rely upon it in making preparations to receive the comet. The French astronomer Clairaut was the man who took the matter most seriously in hand, the important question being to ascertain the extent of the perturbations of the comet's orbit likely to be brought about by the influence of Jupiter and Saturn. The history of the steps taken cannot be better described than in the words of Hind:—"Having devised a method which appeared to possess all needful accuracy, he commenced, in conjunction with the celebrated