is without question unrivalled for the variety of its details, and, after Plato, has perhaps received more attention from observers than any other object.  The bright central mountain, or rather mountains, for it consists of a number of grouped masses crowned by peaks, of which the loftiest is about 4000 feet, is one of the finest on the moon.  It was carefully studied with a 6 1/4 inch Cooke-achromatic by the late Professor Phillips, the geologist, who compared it to the dolomitic or trachytic mountains of the earth.  The buttresses and spurs which it throws out give its base a digitated outline, easily seen under suitable illumination.  There are between 30 and 40 clefts in the interior, the majority being confined to the S.W. quarter of the floor.  Those most easily seen pertain to the group which radiates from the central mountain towards the S.W. wall.  They are all more or less difficult objects, requiring exceptionally favourable weather and high powers.  A fine mountain range, the Percy Mountains, is connected with the E. flank of Gassendi, extending in a S.E. direction towards Mersenius, and defining the N.E. side of the Mare Humorum.

BULLIALDUS.—­A noble object, 38 miles in diameter, forming with its surroundings by far the most notable formation on the surface of the Mare Nubium, and one of the most characteristic ring-plains on the moon.  It should be observed about the time when the morning terminator lies on the W. border of the Mare Humorum, as at this phase the best view is obtained of the two deep parallel terrace valleys which run round the bright inner slope of the E. wall, of the crater-row against which they abut on the S.E., and of the massive W. glacis, with its spurs and depressions.  The S. border of Bullialdus has been manifestly modified by the presence of the great ring-plain A, a deep irregular formation with linear walls, which is connected with it by a shallow valley.  The rampart of Bullialdus rises about 8000 feet above a concave floor, which sinks some 4000 feet below the Mare on the E. With the exception of the fine compound central mountain, 3000 feet high, there are few details in the interior.  On the S., is the fine ring-plain B, connected with the S.E. wall near the crater-row by a well-marked valley, and nearly due E. of B is another, a square-shaped enclosure, C, with a very lofty little mountain on the E. side of it, and a crater on its S. wall.  In addition to these features, there are many ridges and surface inequalities, very prominent under oblique illumination.

LUBINIEZKY.—­A regular enclosure, about 23 miles in diameter, N.E. of Bullialdus, with a low attenuated border, which is nowhere more than 1000 feet in height.  It is tolerably continuous, except on the S., where there are two or three breaks.  Its level dark interior presents no details to vary its monotony.  Close under the N.W. wall is a small crater connected with it by a ridge, and E. of this a very rugged area, traversed in every direction by narrow shallow valleys, which are well worth looking at when close to the morning terminator.  A bright spur projects from the N. wall of Lubiniezky.