Popular Science Monthly/Volume 18/February 1881/The Meteors of November 13th-15th
By Professor DANIEL KIRKWOOD.
WHEN the coincidence between the orbits of the November meteors and the comet of 1866 was first clearly established a few years since, it was supposed by astronomers that the so-called Leonids formed a single cluster, diffused through an arc of such length as to require three or four years to make its perihelion passage. The meteoric period was shown by Professor Newton, of Yale College, and J. C. Adams, of Cambridge University, to be thirty-three and one fourth years. Consequently, no further displays were expected from this stream till about the close of the century. But in "Nature" for June 3, 1875, numerous facts were given, all indicating the existence of a second group, less dense in its structure, and preceding the principal swarm by twelve or thirteen years. Again, the large number of meteors seen in 1879, taken in connection with the fact that, according to Humboldt, meteors were seen in unusual abundance just thirty-three years before, viz., in 1846, suggested the probable existence of a third and perhaps still smaller cluster, passing its perihelion about 1879-'80. It was felt to be important, therefore, that in case any considerable number of meteors should be visible this year at the November epoch, the shower should be observed and the facts recorded. Accordingly, I requested Professor D. E . Hunter, Principal of the Washington (Indiana) High School, to keep watch on the mornings of November 13th, 14th, and 15th. Professor Hunter has made a comprehensive report, which I have somewhat abridged in the following statement. The morning of the 13th was cloudy, and on the 15th the moon shone brightly till daybreak. The watch was consequently restricted to the morning of the 14th. Four observers were occupied from 3h 45m to 5h 45m—precisely two hours. The position was on a hill south of Washington, where the view was unobstructed, except on the south. One hundred and sixteen meteors were counted, ninety-one of which were conformable to the radiant in Leo. During the first hour the atmosphere was hazy and the moon interfered with the observations. The second hour was clear and moonless. The following table includes only Leonids, giving the number counted in every five minutes:
Table showing the same Meteors as above by the Quarter-Hour, Half-Hour, and Hour.
Remarks.—1. The maximum was at 5h 30m, when five Leonids were seen in one minute.
2. The shortest path—two degrees—was that of a meteor nearly stationary, seen in Leo at 5h 18m. The longest forty degrees crossed Ursa Major at 5h 20m.
3. The average length of path during the first hour was six degrees; in the second, about seven; the increase being probably due to the absence of moonlight.
4. At least three distinct meteoric swarms move in the track of Tempel's comet (1866 I). One has just passed or is passing perihelion; the second will pass about 1887-'88; and the maximum group about the close of the century.
5. The meteors on the morning of the 14th inst. were more numerous than those of the August shower; a fact quite remarkable when it is remembered that it is fourteen years since the great display of the principal cluster.
6. The estimated periods of the comet and the meteor groups of the Leonid ring are as follows:
The last is derived from the showers of 1813, 1846, 1847, 1879, and 1880.
7. Oppolzer's period of Tempel's comet, as given above, is perhaps too short. If this body was a return of the comet of 1866, its mean period is 33·283 years—very nearly the same as the meteoric periods.
8. It is sufficiently obvious that we have yet much to learn in regard to the constitution of the Leonid ring, and that future observations from the 13th to the 15th of November may probably result in important discoveries.
Bloomington, Indiana, November 25, 1880.