Page:The story of the comets.djvu/77

IV. surmise that such comets had been "captured" by the particular planets, and this theory has now met with general acceptance. Flammarion, making use of the labours of some who went before him, including especially an American named Kirkwood, who was great at coincidences, has worked out the idea in a way which has yielded some results too curious and interesting to be passed over. In addition to the Jupiter group to which reference has been made above, he finds that every major planet beyond Jupiter seems to have a group of comets revolving in elliptic orbits attached to it; and, moreover, as there is a group of comets without a known planetary leader, he makes bold to speculate that this fact is a proof that a trans-Neptunian planet exists and will one day be found. Since Flammarion published this scheme of his about a quarter of a century ago, the last-named notion has been vigorously taken up and pushed by Professor G. Forbes, but he assigns to his planet a period of 1076 years ,—more than three times the period assigned by Flammarion to his hypothetical planet.

The following are Flammarion's groups, the figures appended representing in radii of the Earth's orbit the mean distances of the respective planets and the aphelion distances of the respective comets:—