reason of this little comet having been regarded with peculiar apprehension, is, that it is the only one whose path is known to lie near the orbit of the earth. But to remove from the popular mind all apprehension of danger from this source, Prof. Arago, the distinguished French astronomer, has shown by a thorough mathematical demonstration, that the probability of a collision from this or any other comet that may visit our system, is, at the utmost, only one in two hundred and eighty millions. The remarks of Prof. Arago on this subject, may be seen in "Dick's Siderial Heavens," page 252.
But to diminish this danger still more, and in fact to reduce it to nothing, it will be remembered that two large comets, those almost immaterial forms, have come in direct collision with the satellites of Jupiter, and yet, the satellites sustained no injury. Not the slightest change was perceived in their orbits. The tables for finding longitude which are based upon the times of the eclipses of those satellites, were as accurate after the collision as before. But as the fact here stated may seem extraordinary to some persons, I will confirm it by a quotation from an author whose knowledge of such matters will not be questioned. The following passage occurs in Herschel's Astronomy, page 292:—"Comets, in passing among and near the planets, are materially drawn aside from their courses, and in some cases have their orbits entirely changed. This is remarkably the case with Jupiter, which seems by some fatality, to be constantly in their way, and to serve us a perpetual stumbling block to them. In the case of the remarkable comet of 1770, which was found by Lexell to revolve in a moderate ellipse, in a period of about five years, and whose return was predicted by him accordingly; the prediction was disappointed by the comet actually getting entangled among the satellites of Jupiter, and being completely thrown out of its orbit by the attraction of that planet, and forced into a much larger ellipse. By this extraordinary rencounter, the motion of the
