13. The meteoric masses encountered by Encke's comet may account for the shortening of the period of the latter without the hypothesis of an ethereal medium.
[APPENDIX.]
A.
The Meteors of November 14th.
The American Journal of Science and Arts for May, 1867 (received by the author after the first chapters of this work had gone to press), contains an interesting article by Professor Newton "On certain recent contributions to Astro-Meteorology." Of the five possible periods of the November ring, first designated by Professor N, it is now granted that the longest, viz., 33¼ years, is most probably the true one. The results of Leverrier's researches in regard to the epoch at which this meteoric mass was introduced into the solar system, are given in the same article. This distinguished astronomer supposes the group of meteors to have been thrown into an elliptic orbit by the disturbing influence of Uranus. The meteoric stream, according to the most trustworthy elements of its orbit, passed extremely near that planet about the year 126 of our era; which date is therefore assigned by Leverrier as the probable time of its entrance into the planetary system. This result, however, requires confirmation.
Although the earliest display of the November meteors, so far as certainly known, was that of the year 902, several more ancient exhibitions may, with some probability, be referred to the same epoch. These are the phenomena of 532, 599, and 600, A.D., and 1768, B.C. (See Quetelet's Catalogue.) The time of the year at which these showers occurred is not given. The years, however, correspond very well with the epochs of the maximum display of the November meteors. The intervals arranged in consecutive order, are as follows:
| From | B.C. | 1768 | to | A.D. | 532, | 69 | periods of | 33·319 | years each. |
| " | A.D. | 532 | to | " | 599·5, | 2 | " | 33·750 | " |
| " | " | 599·5 | to | " | 902, | 9 | " | 33·614 | " |
| " | " | 902 | to | " | 934, | 1 | " | 32·000 | " |
| " | " | 934 | to | " | 1002, | 2 | " | 34·000 | " |
| " | " | 1002 | to | " | 1101, | 3 | " | 33·000 | " |
| " | " | 1101 | to | " | 1202, | 3 | " | 33·667 | " |
| " | " | 1202 | to | " | 1366, | 5 | " | 32·800 | " |
| " | " | 1366 | to | " | 1533, | 5 | " | 33·400 | " |
| " | " | 1533 | to | " | 1698, | 5 | " | 33·000 | " |
| " | " | 1698 | to | " | 1799, | 3 | " | 33·667 | " |
| " | " | 1799 | to | " | 1833, | 1 | " | 34·000 | " |
| " | " | 1833 | to | " | 1866, | 1 | " | 33·000 | " |
The first three dates are alone doubtful. The whole number of intervals from B.C. 1768 to A.D. 1866 is 109, and the mean length is 33·33 years.
The perturbations of the ring by Jupiter, Saturn, and Uranus, are doubtless considerable. It is worthy of note that—