THEOPHILUS.--The most northerly of three of the noblest ring-mountains on the visible surface of the moon, situated on the N.W. side of the Mare Nectaris. It is nearly 64 miles in diameter, and is enclosed by a mighty rampart towering above the floor at one peak on the E. to the height of 18,000 feet, and at two other peaks on the opposite side to nearly 16,000 and 14,000. The border, though appearing nearly circular with low powers, is seen, under greater magnification, to be made up of several more or less linear sections, which give it a polygonal outline. It is prominently terraced within, the loftier terraces on the E. rising nearly to the height of the crest of the wall, and including several craters and elongated depressions. On the E. glacis is a row of large inosculating craters; and near its foot, S.W. of Madler, a short unrecorded rill- valley. The magnificent bright central mountain is composed of many distinct masses surmounted by lofty peaks, one of which is about 6,000 feet above the floor, and covers an area of at least 300 square miles. Except a distinct crater on the S.E. quarter, this appears to be the only object within the ring.