| Commencement | 1h. 0m. | A.M. Nov. 14. |
| Maximum | 4 20 | " " |
| End | 5 0 | " " |
| Number of meteors per hour at maximum | 3000 | |
| Mean height on first appearance | 75 miles. | |
| " " on disappearance | 55 " | |
| Position of radiant, R. A. 151°, Decl. 22½°. | ||
The shower of 1868 was in some respects quite remarkable, though the number of meteors was less than in 1866 or 1867. At New Haven the fall commenced about midnight, and from 2 o'clock till daybreak over 5000 meteors were counted. The time of maximum could not be accurately determined, as no decrease in the numbers was observable till dawn. The display was also witnessed in England and in Cape Colony, South Africa. The times of maxima in these countries differed so materially as to indicate a decided stratification of the meteoric stream. The entire depth, moreover, where crossed by the earth in 1868, was much greater than at the part traversed either in 1866 or 1867.
In 1869 the shower was observed at Port Saïd, Lower Egypt, by G. L. Tupman, Esq.; in Florida, U. S., by Commander William Gibson, U.S.N.; and at Santa Barbara, California, by Mr. G. Davidson and Mrs. E. Davidson. The first observed 112 meteors in 1h. 54m., from 2h. 30m. to 4h. 24m., Alexandria mean time; the numbers during this interval being nearly equal, though slightly decreasing. Throughout the morning (November 14) the sky was only partly clear. The two observers at Santa Barbara saw 556 in 2h. 25m., ending at 3h. 43m. A.M. In Florida also the display was quite brilliant, though inferior to that of 1868. It should be remarked that the morning in many parts of the United States was cloudy. No considerable number of the meteors of this stream has been observed in any part of the world since 1869.
Discussion of the Phenomena.
Since the memorable display of November 13, 1833, the phenomena of shooting-stars have been observed and discussed with a very lively interest. Among the first laborers in this department of research the names of Olmsted, Herrick, and Twining must ever hold a conspicuous place. The fact that the position of the radiant point did not change with the earth's rotation at once placed the cosmical origin of the meteors wholly beyond question. The theory of a ring of nebulous matter revolving round the sun in an elliptic orbit—a theory somewhat different from that proposed by Olmsted—was found to afford a simple and satisfactory explanation of the phenomena. This hypothesis of an eccentric stream of meteors intersecting the earth's orbit was adopted by Humboldt, Arago, and others, shortly after the occurrence of the meteoric shower of 1833.
A few years previous to the display of 1866 it was shown by Professor Newton, of Yale College, that the distribution of meteoric matter around the ring or orbit is far from uniform; that the motion is retrograde; that the node of the orbit has an annual forward motion of 102´´.6 with respect to the equinox, or of 52´´.4 with respect to the fixed stars; that the periodic time must be limited to five accurately determined periods, viz.: 180.05 days, 185.54 days, 354.62 days, 376.5 days, or 33.25 years; and that the inclination of the orbit to the ecliptic is about 17°. Professor Newton, for reasons assigned, regarded the third period named as the most probable. He remarked, however, that by computing the secular motion of the node for each periodic time, and comparing the result with the known precession, it was possible to determine which of the five periods is the correct one.
For the application of this crucial test,—a problem of more than ordinary interest,—we are indebted to Professor J. C. Adams, of Cambridge, England. By an elegant analysis it was first shown that for either of the first four periods designated by Professor Newton, the annual motion of the node, resulting from planetary perturbation, would be considerably less than one half of the observed motion. It only remained, therefore, to examine whether the period of 33¼ years would give a motion of the node corresponding with observation. Professor Adams found that in this time the longitude of the node is increased 20´ by the action of Jupiter, 7´ by the action of Saturn, and 1´ by that of Uranus. The effect of the other planets is scarcely perceptible. The calculated motion in 33¼ years is therefore 28´. The observed motion in the same time, according to Professor Newton, as previously stated, is 29´. This remarkable accordance was at once accepted by astronomers as satisfactory evidence that the period is about 33.25 years.
Having determined the periodic time, the mean distance, or semi-axis major, is found by Kepler's third law to be 10.34. The aphelion is consequently situated at a comparatively short distance beyond the orbit of Uranus. The orbit is represented in Fig. 4.
Fig. 4.
