Note 18 — THE NEBULAR HYPOTHESIS.

The comparative statement here given differs, slightly in most cases and in one case largely, from the statement included in this essay as originally published in 1858. As then given the table ran thus:—

Mercury. Venus. Earth. Mars. Jupiter. Saturn. Uranus.

¹⁄₃₆₂ ¹⁄₂₈₂ ¹⁄₂₈₉ ¹⁄₃₂₆ ¹⁄₁₄ ¹⁄_6·2 ¹⁄₉

1 Satellite. 4 Satellites. 8 Satellites, and three rings 4 (or 6 according to Herschel).

The calculations ending with these figures were made while the Sun's distance was still estimated at 95 millions of miles. Of course the reduction afterwards established in the estimated distance, entailing, as it did, changes in the factors which entered into the calculations, affected the results; and, though it was unlikely that the relations stated would be materially changed, it was needful to have the calculations made afresh. Mr. Lynn has been good enough to undertake this task, and the figures given in the text are his. In the case of Mars a large error in my calculation had arisen from accepting Arago's statement of his density (0·95), which proves to be something like double what it should be. Here a curious incident may be named. When, in 1877, it was discovered that Mars has two satellites, though, according to my hypothesis, it seemed that he should have none, my faith in it received a shock; and since that time I have occasionally considered whether the fact is in any way reconcilable with the hypothesis. But now the proof afforded by Mr. Lynn that my calculation contained a wrong factor, disposes of the difficulty—nay, changes the objection to a verification. It turns out that, according to the hypothesis, Mars ought to have satellites; and, further, that he ought to have a number intermediate between 1 and 4.