Astronomy for the use of schools and academies (1882) (14761173261)

Identifier: astronomyforuseo00gill (find matches)
Title: Astronomy for the use of schools and academies
Year: 1882 (1880s)
Authors: Gillet, J. A. (Joseph Anthony), 1837-1908 Rolfe, W. J. (William James), 1827-1910
Subjects: Astronomy
Publisher: New York : Potter, Ainsworth, & Co.
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress



Text Appearing Before Image:
Fig. 320. Comets move in every direction in their orbits, and theserbits have every conceivable inclination to the ecliptic. 286 ASTRONOMY.
Text Appearing After Image:
11 Fig. 321. 292. Periodic Cornets. — There are quite a number of ASTRONOMY. 287 comets which are known to be periodic, returning to thesun at regular intervals in elliptic orbits. Some of thesehave been observed at sev- eral returns, so that theirperiod has been determinedwith great certainty. In thecase of others the perio-dicity is inferred from thefact that the velocity fellso far short of the paraboliclimit that the comet mustmove in an ellipse. Thenumber of known periodiccomets is increasing every Fig. 322. year, three having been added to the list in 1881. The velocity of most comets is so near the parabolic limitthat it is not possible to decide, from observations, whether it