LE MONNIER.—­A great inflection or bay on the W. border of the Mare Serenitatis S. of Posidonius.  Like many other similar formations on the edges of the Maria, it appears at one time or other to have had a continuous rampart, which on the side facing the “sea” has been destroyed.  In this, as in most of the other cases, relics of the ruin are traceable under oblique light.  A fine crescent-shaped mountain, 3000 feet high, stands near the S. side of the gap, and probably represents a portion of a once lofty wall.  It will repay the observer to watch the progress of sunrise on the whole of the W. coast-line of the Mare up to Mount Argaeus.

POSIDONIUS.—­This magnificent ring-plain is justly regarded as one of the finest telescopic objects in the first quadrant.  Its narrow bright wall with its serrated shadow, the conspicuous crater, the clefts and ridges and other details on the floor, together with the beautiful group of objects on the neighbouring plain, and the great Serpentine ridge on the E., never fail to excite the interest of the observer.  The circumvallation, which is far from being perfectly regular, is about 62 miles in diameter, and, considering its size, is not remarkable for its altitude, as it nowhere exceeds 6000 feet above the interior, which is depressed about 2000 feet below the surrounding plain.  Its continuity, especially on the E., is interrupted by gaps.  On the N., the wall is notably deformed.  It is broader and more regular on the W., where it includes a large longitudinal depression, and on the N.W. section stand two bright little ring-plains.  On the floor, which shines with a glittering lustre, are the well-marked remains of a second ring, nearly concentric with the principal rampart, and separated from it by an interval of nine or ten miles.  The most prominent object, however, is the bright crater a little E. of the centre.  This is partially surrounded on the W. by three or four small bright mountains, through which runs in a meridional direction a rill-valley, not easily traced as a whole, except under a low sun.  There is another cleft on the N.E. side of the interior, which is an apparent extension of part of the inner ring, a transverse rill-valley on the N., a fourth quasi rill on the N.W., and a fifth short cleft on the S. part of the floor.  Between the principal crater and the S.E. wall are two smaller craters, which are easy objects.  Beyond the border on the N., in addition to Daniell, are four conspicuous craters and many ridges.

CHACORNAC.—­This object, connected with Posidonius on the S.W., is remarkable for the brilliancy of its border and the peculiarity of its shape, which is very clearly that of an irregular pentagon with linear sides.  I always find the detail within very difficult to make out.  Two or more low ridges, traversing the floor from N. to S., and a small crater, are, however, clearly visible under oblique illumination.  Schmidt draws a crater-rill, and Neison two parallel rills on the floor,—­the former extends in a southerly direction to the W. side of Le Monnier.