184 REPORT— 1861. 



the nature of fissures. Thej', with the circular range, have only been 

 observed 07ice. (See key-plan, fig. 1.) 



VI. i. — The westernmost of the two oval markings. 



YII. k. — The easternmost of the two oval markings. 



Schrdter appears to have observed them on December 11, 1788: he has 

 figured them on t. xxi. fig. 6. They have been observed by the writer ou 

 fifteen or sixteen occasions at least. 



VIII. 7;. — A bay-like indentation in the north-east rim seen under the 

 mid-day illumination. It has been observed on Jive occasions. It is not 

 shown in the key-plan, but its locality is indicated by the letter p. 



This indentation, which is best seen about full moon, or about fifteen or 

 sixteen days of the moon's age, marks, I appreliend, the form of the rim of 

 Plato hereabout. It is well shown in a sketch by Webb, under date of 1855, 

 October 24, ten to eleven hours ; the sketch is preserved in the volume of 

 Observations on Plato deposited in the library of the Royal Astronomical 

 Society. It is approximately figured aX jJ, detached from the key-plan of the 

 crater, as it is only visible for about two days near the full. 



IX. q. — A short, light spur in the neighbourhood of 7^, which, with the 

 shadow w ithin the cavity i, appears to indicate the existence of a ledge or 

 terrace in this part of Plato. It has only been observed once. 



X. ^. — A bold rock jutting intq the interior, casting a well-defined shadow 

 eastward in the morning and forenoon, and westward on the floor of the 

 crater towards sunset : it is more frequently observed as the eastern extre- 

 mity of the longest diameter of the apparent ellipse. 



This rock is one of the finest and most conspicuous objects in the neigh- 

 bourhood of Plato during the morning illumination, glowing in the rays of 

 the sun like molten silver. From about 7*5 to 8*5 days of the moon's age, 

 it is seen as a very brilliant point at the eastern extremity of the crater; 

 during the next two days (from 8"5 to 10\5 days of the moon's age) it is 

 very distinguishable, standing out as a bold rock, and casting a well-defined 

 shadow eastward ; during the next three days (from 10"5 to 13*5) it loses its 

 shadow, but continues a perceptibly bright object, imparting to the eastern 

 extremity its peculiar brilliancy at this age of the moon. It is now lost for 

 some time. About nineteen days of the moon's age it has been seen very 

 distinctly ; two days later, viz. at twenty-one days, its shadow has been seen 

 on the floor of Plato ; and about this time, or rather later, it has been seen 

 standing out in fine and bold relief, a magnificent object, its height above 

 the general altitude of the ring being apparent not only by the acuminated 

 character of its shadow on the floor of the crater, but by its towering consi- 

 derably above the general summit. It appears to be a formation in a mea- 

 sure distinct from the ring itself, and greatly allied in its character to that of 

 Pico on the south of Plato; indeed, it deserves as conspicuous a position on 

 a map as Pico. It possesses two bold spurs on the north-east and south- 

 east. Its very appearance is exceedingly suggestive, especially when taken 

 in connexion with a formation immediately south of it. Both should be most 

 carefully and scrupulously watched, in order to determine if any degrading 

 forces are at work hereabout. 



This rock has been observed under the morning and forenoon illumina- 

 tions on eighteen occasions, and under the evening on four occasions. 

 Schrdter gives a rude figure of it in t. xxiii. 



XI. s. — A spot situated on the eastern exterior slope of Plato : it is slightly 

 to the north of eastward of the rock i^, and was seen, on October 14, 1861, 

 moon's age 10"55 days, to be a gently rising protuberance on the eastern 

 slope of the rock 'C, in the neighbourhood of the north-eastern spur. 



