The nebular hypothesis, it is thus seen, accounts satisfactorily for the origin of comets, aerolites, fire-balls, shooting-stars, and meteoric rings; regarding them all as bodies of the same nature, moving in cometary orbits about the sun. In this theory, the zodiacal light is an immense swarm of meteor-asteroids; so that the meteoric theory of solar heat, explained in a previous chapter, finds its place as a part of the same hypothesis. CONCLUSION. Some of the prominent results of observation and research in meteoric astronomy may be summed up as follows: 1. The shooting-stars of November, August, and other less noted epochs, are derived from elliptic rings of meteoric matter which intersect the earth's orbit. 2. Meteoric stones and the matter of shooting-stars coexist in the same rings; the former being merely collections or aggregations of the latter. 3. The most probable period of the November meteors is thirty-three years and three months. Leverrier's elements of this ring agree so closely with Oppolzer's elements of the comet of 1866 as to render it probable that the latter is merely _a large meteor_ belonging to the same annulus. 4. The spectroscopic examination of this comet (of 1866) by William Huggins, F.R.S., indicated that the nucleus was self-luminous, that the coma was rendered visible by reflecting solar light, and that "the material of the comet was similar to the matter of which the gaseous nebulæ consist." 5. The time of revolution of the August meteors is believed to be about 105 years. M. Schiaparelli has found a striking similarity between the elements of this ring and those of the third comet of 1862. The same distinguished astronomer has shown, moreover, that a nebulous mass of considerable extent, drawn into the solar system _ab extra_, would form a _ring_ or _stream_. 6. The aerolitic epochs, established with more or less certainty, are the following: 1. February 15th-19th. 2. March 12th-15th. 3. April 10th-12th. 4. April 18th-26th. 5. May 8th-14th; or especially, 12th-13th. 6. May 19th. 7. July 13th-14th. 8. July 26th. 9. August 7th-11th. 10. October 13th-14th. 11. November 11th-14th. 12. November 27th-30th. 13. December 7th-13th. About one-half of this number are also known as shooting-star epochs. 7. The epoch of November 27th-30th corresponds with that of the earth's crossing the orbit of Biela's two comets. The aerolites of this epoch may therefore have been moving in nearly the same path. 8. A greater number of aerolitic falls are observed-- 1. By day than by night. 2. In the afternoon than in the forenoon. 3. When the earth is in aphelion than when in perihelion.