ON THE PHYSICAL ASPECT OF THE MOON. 18? 



which rather rapidly recedes as the sun becomes elevated above their horizon. 

 Beer and Madler have indicated, measured, and marked them respectively 

 y, J, and €. The shadows have been well seen by the writer on the floor of 

 Plato, with an additional peak. 



XXV. b. — A dark-black spot in the shadow, most probably the peak S, 

 which under the early morning illumination would present such an appear- 

 ance. My observations under the evening illumination have been too few to 

 recognize it as a b)ight spot, nor have I noticed either 7 or e as black spots 

 in the morning shadow. This black spot occupies precisely the position of 

 f, just north of the termination of the longer axis of the apparent ellipse 

 exactly opposite the rock (. It has been observed on three occasions. 



XXVI. X. — A conspicuous mountain south-west of Plato, on the ring of 

 Schrdter's Newton, and nearly abutting on the ravine Z (XXL). Beer and 

 Madler mark it X, but place it too far to the south-east. It has been observed 

 on ?iine occasions. 



Under a very early illumination it may easily be mistaken for a crater 

 (see also XXIX. r). There is a gradual rise of the land from the north- 

 west towai-ds the mountain, which itself rises from a depression, the western 

 cliff of which is very abrupt. 



XXVII. dd. — A group of mountains in the Alps, forming with \ and v an 

 isosceles triangle, X and v being the base. There is a little discrepancy here. 

 The mountain X has been brought nearer to dd on the key-plan than it would 

 be on Beer and Mtidler's map, to give it its proper position with regard to Z, 

 aa, and Y (see XXVI. X). It is the author's intention, as early as convenient, 

 carefully to triangulate the most conspicuous objects near Plato. 



XXVIII. G. — A small crater, a little to the west of d, somewhat closely 

 abutting on the summit ; it is marked G by Beer and Madler. I have 

 observed it twice. It i- very probably the same as w, in Schrdter's drawing. 



XXIX. 7: — A mountain on the exterior western slope of Plato : it is 

 situated in the line of the longer axis of the apparent ellipse. On March 22, 

 1861, it was seen with the shadow eastward ; it had a rounded summit, and 

 the western slope was shining with considerable brilliancy. It has been 

 observed eir/ht times. Its situation with regard to dd and v (see key- plan ) 

 requires to be determined ; also its real character, whether it be a mountain 

 or a crater. On some occasions, under an early illumination, it has been 

 described as a crater; on others, as a mountain. From the description of 

 March 22, 1861, it v/ould appear to be a mountain. It is very conspicuous 

 about the time of full moon as a bright lucid spot. 



XXX. ee. — A considerable depression east of r, and between it and the 

 w estern rim of Plato. Observed twice, under a very early illumination of 

 Plato. 



XXXI. cc. — A somewhat long dark line, in the nature of a shadow with 

 a short spur, apparently the shadow of a mountain across the western wall 

 of Plato ; the long dark line observed only 07ice, the spur tivice. The exact 

 direction of the line requires determination. 



XXXII. V. — A conspicuous mountain north-west of Plato, marked v by 

 Beer and Madler ; it is figured by Schrdter with some smaller mountains 

 and a crater, cp, north-west of it. It was well seen on May 18, 1861 ; also 

 on July 15, 1861 , when two well-marked, distinct rocks were seen north-west 

 of it. It has been observed on seven occasions. 



XXXIII. //. — Three mountain-masses (supposed to be v and the moun- 

 tains north-west of it; they are not given in the key-plan) in the neighbour- 

 hood of the mountain v. The westernmost of these mountains not over- 

 bright, but the others very bright. 



