Page:Popular Science Monthly Volume 19.djvu/813

Rh It seemed very desirable that elliptic elements should be determined for this comet without making any previous assumptions in reference to any of the elements; this was undertaken independently by two astronomers of the United States Naval Observatory, each from different data. Professor Frisby made use of observations of October 25th, November 7th, and November 20th. Mr. Upton selected the following dates: October 25th, November 23d, and December 22d.

The results of these two computations agree very closely: the resulting period is only a few days less than six years. The inclination of the plane of the orbit to the plane of the ecliptic is about five and one half degrees.

To show more strikingly the remarkable situation of the comet's orbit with reference to the earth's orbit, the attention of the reader is directed to the accompanying diagram (Fig. 1), which, for the sake of



simplicity, shows the two orbits as if in one plane, when in reality the angle of inclination between them is about five and one half degrees. The line marked "line of nodes" is the line of their mutual intersection, the part of the comet's orbit in the vicinity of the perihelion being north of the plane of the ecliptic.

The relative situations of the earth and comet are shown by their positions in orbit at the date of discovery of the comet, October 10; the date of the perihelion passage, November 8, 1880, and January 1, 1881.