method of determining by geometrical construction the visible portion of the path of the comet, and invited astronomers to apply these principles to the comets on record, or some of them. He considered that it was very probable that some comets might move in elongated ellipses which near perihelion would scarcely be distinguishable from parabolas; and he even thought that the recent Comet of 1680[1] might be moving in an ellipse the circuit of which would occupy about 575 years.
Fig. 40.
MEDAL STRUCK IN GERMANY TO ALLAY THE TERROR CAUSED BY THE COMET OF 1680.
"The star threatens evil things: Only Trust!
God will make things turn to good."
Halley (to whose exertions the publication of the Principia was in great measure due, for he bore the labour and expense of its publication) also took this view. Although we now know that the period of that comet is measured by thousands of years Halley's investigations were not without good fruit, for they may be said to have drawn him into a systematic
- ↑ It should perhaps be mentioned, if only in the humble form of a footnote, that this Comet of 1680 gave rise to a special sensation some years after its appearance. A clergyman named Whiston, best known to fame as the editor of a standard edition of the works of the Jewish historian Josephus, published in 1696 A New Theory of the Earth, in which he sought to explain by the supposed agency of a comet the geological records of the Book of Genesis. At first he based his theory upon nothing except his own imagination, but when he found that Halley had (erroneously) ascribed to the Comet of 1680 a periodic time of 575 years, Whiston, working backwards the materials of history and fable within his reach, ascribed the Noachian Deluge to one of the regular visits of this comet, and added that it would be by a future visit of the same comet that the prophecies of Holy Scripture as to the destruction of the World would be made good. I think this is sufficient to indicate the value of the Rev. William Whiston's labours in the field of comets.
