ON THE PHYSICAL ASPECT OP THE MOON. 185 



XII. t. — A small crater south of eastward of the rock f : it is described, 

 March 22, 9 30 (1861), to be almost due east of the longest diameter of 

 Plato. It is situated on one of the spurs of i,. 



The rock i^, the spot s, and the crater t, form a conspicuous triangle, seen 

 to great advantage on March 21, 1861. They have been observed in con- 

 nexion on three occasions. 



XIII. A. — The largest crater in the neighbourhood of Plato, figured by 

 Schroter, t. xxiii., and marked c by him, but A by Beer and Miidler. 



XIV. y^. — Schroter also gives another crater of about the same size, which 

 he marks x, north of Plato. In his delineation it is placed about midway 

 between Plato and the Mare Frigoris. In the whole course of my observa- 

 tions I have not met with this crater, nor have I seen anytliing similar to 

 that delineated by Schroter. On the night of August 27, 1861, moon's age 

 21'53 days, I found a very interesting object on the northern boundary of 

 the bright ground north of Plato. It consisted of a semi-elliptical range of 

 mountains very similar to a half-crater, the existing portion of the ring not 

 greatly elevated above the surface ; the south-east side was more elevated 

 than the south-west, so that its external slope caught the rays of the after- 

 noon sun, which rendei'ed it the most brilliant object in the immediate 

 locality. The south-west portion of this half-ring was seen to terminate a 

 little short of the line of junction of the bright ground north of Plato and 

 the dark ground of the Mare Frigoris, the south-east portion being cut 

 off sharply by the south edge of the Mare Frigoris. I did not observe any 

 difference of level between the lighter rugged ground on which the half-ring 

 was seen and the darker and smoother surface of the Mare Frigoris. The 

 situation of this half-ring is very near the locality given by Schroter for the 

 perfect crater. I have indicated it on the key-plan by Schroter's mark y^. 



I also observed this object on September 13, 1861, under the morning 

 illumination, moon's age 8'87 days ; a,nd again on September 25, moon's age 

 2P08 days. It requires the precise angle of illumination and visual ray to 

 catch it. 



XV. W. — An interesting marking just south of the rock ^, somewhat of 

 the character of a crater, apparently triangular in its form, but on closely 

 scrutinizing it seen to be a somewhat shallow depression having a gently 

 curved rampart. Under a suitable illumination, the shadow of this rampart 

 has been seen well defined within the enclosure. The south-east rim of this 

 apparent crater, with the contiguous portion of the rim of Plato, forms the 

 continuation of a ci'.ain of mountains which takes its rise at an isolated 

 mountain south-east of Plato (c) (see key-plan, fig. 1). This chain of moun- 

 tains is well seen under the evening illumination about 21 '5 days of the, 

 moon's age. 



The position of this depression is on the upper part of the eastern slope of 

 Plato. It is separated from the large crater by a portion of the eastern rim 

 of Plato, which also forms its western rim. On May 2, 1860, the colour of 

 the interior was very slightly, if any, darker than the surface exterior to 

 Plato, and much lighter than the floor of Plato. It has been observed on 

 fifteen occasions. 



XVI. o. — A small crater at the external common base of the rock 'C, and 

 the depression W. It has been observed tiuice. 



XVil. — The south-east rim of the crater Plato. 



XVIII. c. — A mountain south-east of Plato. The chain of mountains, of 

 low altitude, running from it in a curved direction to Plato formed part of 

 the ring of the ancient crater called Newton by Schroter, It has been 

 observed at least on three occasions. 



