Having perceived that the elements of the comet of 1682 were nearly the same as those of two comets which had appeared respectively in 1531 and 1607, Edmund Halley concluded that all the three orbits belonged to the same comet with a period of about 76 years.
After a rough estimate of the perturbations it must sustain from the attraction of the planets, he predicted its return for 1757, a bold prediction at that time, but justified by the event, for the comet again made its appearance as was expected, though it did not pass through its perihelion till the month of March 1759, the attraction of Jupiter and Saturn having caused, as was computed by Clairault previously to its return, a retardation of 618 days.
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