Purbach is sixty miles broad, and south of that comes a wonderful region where the ring mountains Hell, Ball, Lexell, and others, more or less connected with walls, inclose an area even larger than Ptolemæus, but which, not being so distinctly bordered as some of the other inclosed plains, bears no distinctive name.
If a strange comet undertakes to run across Jupiter's bows the latter brings it to, and makes prize of it by throwing it into a relatively small ellipse with the sun for its focus. Thenceforth, unless, as happened to the unhappy comet of Lexell, it encounters Jupiter again in such a way as to be diverted by him into a more distant orbit, it can never get away.
Euler, Lexell, and Kraft undertook the task of examining them, and selecting those that were best fitted for publication, but we believe that no steps have yet been taken for executing this task, nor are we aware that science would derive any advantage from its completion.
Though no large formation is found thereon; many ridges, short crater-rows, and ordinary craters figure on its rugged superficies; and on its borders stand some very noteworthy objects, among them, on the S., the walled-plain Lexell, about 32 miles in diameter, which presents many points of interest.
The interior, the tone of which is conspicuously darker than that of the region outside, contains a small central hill, with two craters connected with it. The low N.W. margin is traversed by a delicate valley, which, originating on the N. side of the great plain, crosses the W. quarter of Lexell and terminates apparently on the S.W. side of the floor.
The labors of Kepler were mathematical, optical, cosmographical, and astronomical, but chiefly astronomical. His whole published works comprise some thirty or forty volumes, while twenty folio volumes of manuscript lie in the Library at St. Petersburg. These Euler, Lexell, and Kraft undertook some years ago to examine and publish, but the result of this examination has never appeared.
Lexell was the first to suspect that this was a new planet eighteen times as far from the sun as the earth is. In January, 1783, Laplace published the elliptic elements. The discoverer of a planet has a right to name it, so Herschel called it Georgium Sidus, after the king. But Lalande urged the adoption of the name Herschel. Bode suggested Uranus, and this was adopted.
About midway between its extremities, this great gorge is crossed by a wall of rock, like a narrow bridge. JANSSEN. An immense irregular enclosure, reminding one of the very similar area, bordered by Walter, Lexell, Hell, &c., in the third quadrant. It extends about 150 miles from E. to W., and more than 100 from N. to S., its limits on the N. being rather indefinite.
Near the E. corner of the floor there is another large deep crater, and, ranging in a line from the centre to the S.E. wall, three smaller craters. LEXELL. On the E. of Walter extends an immense plain of irregular outline, which is at least equal to it in area.
In 1770 Lexell discovered a comet which, as was afterwards proved by investigations of Lexell, Burchardt, and Laplace, had in 1767 been deflected by Jupiter out of an orbit in which it was invisible from the earth into an orbit with a period of 5-1/2 years, enabling it to be seen.