surface of these features or close to their edges.  Recent observations of these spots with a 13 inch telescope by Professor W.H.  Pickering, under the exceptionally good conditions which prevail at Arequipa, Peru, have revived interest in the subject, for they tend to show that visible changes have taken place in the aspect of the principal crater-cones and of some of the other spots since they were so carefully and zealously scrutinised nearly a quarter of a century ago.  The gradual darkening of the floor of Plato as the sun’s altitude increases from 20 deg. till after full moon may be regarded as an established fact, though no feasible hypothesis has been advanced to account for it.

On the N.E. of Plato is a large bright crater, A; and, extending in a line from this towards the E., is a number of smaller rings, the whole group being well worth examination.  On the N. there is a winding cleft, and some short crossed clefts in the rugged surface just beyond the foot of the wall, which I have seen with a 4 inch achromatic.  The region on the W., imperfectly shown in the maps, includes much unrecorded detail.  On the Mare Imbrium S. of Plato is a large area enclosed by low ridges, to which Schroter gave the name “Newton.”  It suggests the idea that it represents the ruin of a once imposing enclosure, of which the conspicuous mountain Pico formed a part.

TIMAEUS.—­A very bright ring-plain, 22 miles in diameter, with walls about 4500 feet in height, on the coast-line of the Mare Frigoris, and associated with the E. side of the great enclosed plain W.C.  Bond.  Schmidt shows a double hill, nearly central, and Neison a crater on the S.W. wall.

BIRMINGHAM.—­A large rhomboidal-shaped enclosure, defined by mountain chains and traversed by a number of very remarkable parallel ridges.  It is situated nearly due N. of Plato on the N. edge of the Mare Frigoris, and lies on the S.E. side of W.C.  Bond, to which it bears a certain resemblance.  This region is characterised by the parallelism displayed by many formations, large and small.  It is more apparent hereabouts than in any other part of the moon’s visible surface.  When favourably placed under a low morning sun, Birmingham is a striking telescopic object.

FONTINELLE.—­A fine ring-plain, 23 miles in diameter, on the N. margin of the Mare Frigoris, N.N.E. of Plato, with a wall rising on the E., 6000 feet above a bright interior.  I find its border indistinct and nebulous, excepting under very oblique light, though three of the little craters upon it are bright and prominent.  One stands on the S., another on the N.W., and a third on the E. Schmidt shows only the first of these, and Neison none of them.  Fontinelle has a low central mountain which is easily distinguished.  Fontinelle A, an isolated mountain on the S., is more than 3000 feet high.  On the N. there is a curious mountain group, also of considerable altitude, and on the W. an irregular depression surrounded by a dusky area.  North