which, however, by at least three narrow passes he might perchance get a glimpse of the Mare Imbrium beyond.  The broadest of these aligns with the axis of the valley.  It is hardly more than a mile wide at its commencement on the S. border of the “amphitheatre,” but expands rapidly into a trumpet-shaped gorge, flanked on either side by the towering heights of the Alps as it opens out on to the Mare.  The bottom, both of the “amphitheatre” and of the long wedge-shaped valley, appears to be perfectly level, and, as regards the central portion of the latter, without visible detail.  Under morning illumination I have, however, frequently seen something resembling a ridge partially crossing “the neck,” and, near sunset, a tongue of rock jutting out from the E. flank of the constriction, and extending nearly from side to side.  At the base of the cliff bordering the valley on the S.W., five or six little circular pits have been noted, some of which appear to have rims.  They were seen very perfectly with powers of 350 and 400 on an 8 1/2 inch Calver reflector at 8 h. on January 25, 1885, and have been observed, but less perfectly, on subsequent occasions.  The most northerly is about 10 miles from the N.W. end of the formation, and the rest occur at nearly regular intervals between it and “the neck.”  In the neighbourhood of the valley, on either side, there are several bright craters.  Three stand near the N.E. edge, and one of considerable size near the N.W. end on the opposite side.  A winding cleft crosses the valley about midway, which, strange to say, is not shown in the maps, though it may be seen in a 4 inch achromatic.  It originates apparently at a bright triangular mountain on the plain S.W. of the valley, and, after crossing the latter somewhat obliquely, is lost amid the mountains on the opposite side.  That portion of it on the bottom of the valley is easily traceable under a high light as a white line.  The region N. of the Alps on the S.W. side of the valley presents many details worthy of examination.  Among them, parallel rows of little hills, all extending from N.W. to S.E.  There is also a number of still smaller objects of the same type on the E. side.  The great Alpine valley, though first described by Schroter, is said to have been discovered on September 22, 1727, by Bianchini, but it is very unlikely that an object which is so prominent when near the terminator was not often remarked before this.

ARCHYTAS.—­A bright ring-plain, 21 miles in diameter, on the edge of the Mare Frigoris, due N. of the Alpine Valley, with regular walls rising about 5000 feet above the interior on the N.W., and about 4000 feet on the opposite side.  It has a very bright central mountain.  Several spurs radiate from the wall on the S., and a wide valley, flanked by lofty heights, forming the S.W. boundary of W.C.  Bond, originates on the N side.  There is also a crater-rill running towards the N.W.  On the Mare, S.W. of Archytas, is a somewhat smaller ring-plain, Archytas A (called by Schmidt, PROTAGORAS), with lofty walls and a central hill.