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.