248 REPORT — 1866. 



figure, and this is increased by the more gentle slope of the north interior as 

 compared with the interior slopes of the east and west walls which arc steeper. 

 The exterior slopes, although rugged, are much more gentle than the interior. 

 The north wall is disturbed by the same fault that has dislocated the west, 

 the effects of which may be seen in the crater Triesnecker. 



The level of the floor of this interesting formation is the lowest between 

 jY^alO and the Sinus Medii. B, & M. mention and delineate a central 

 mountain in Ehaeticus. Lohrmann also gives it. I observed and sketched 

 it 1864, April 14, and again 1867, April 1]. On the west and south, and 

 including the valley IV A" ^^ on the east, Eha^ticiis may be said to be partly 

 surrounded by a second wall nearly equidistant from its centre, and about the 

 same distance from the east and west walls as the length of the east and 

 west diameter of Ehaeticus. The portion of the second wall on the west is 

 parallel with the west wall of Eha?ticus, and is also the highest. 



Longest diameter from summit of north wall to the summit of south wall 

 eastof "Pass" 29"-48. 



Shortest diameter at right angles to the longest, from summit of east to 

 summit of west wall 27"*10. Eiccioli's Eha)ticus is situated between Stadius 

 and Copernicus. 



**2. Reattmur. — A somewhat depressed plain surrounded by a " wreath" 

 of mountains, V of Lohnnann, Sect. I. 236, of his map. 



Schmidt mentions a rill, No. 364, south to north across Eeaumur. I do 

 not find it on the photograph. It was discoveied in 1853, May 14, with the 

 Berlin refractor. 



3. HipPARcnrs.- — Lohrmann's map, 233. The north-east part. 



This formation, which is very strongly individualized by Lohrmann in his 

 Section I. {Topoc/rapMc der Sichtharen Mondoherjlache'), and nearly as much 

 so by B. & M., can hardly be said to possess so distinct a character, for it is 

 onlj' when the terminator is in its neighbourhood that its real features are 

 well seen. Indeed, B. ife M. describe it as an assemblage of diverse lunar 

 forms, rather than a general T^hole, which arc onl}' seen to advantage near 

 the time of sunrise and sunset ; for at these times, especially at sunrise, the 

 interior surface, of a dark-grey and furrowed through by long shadows, sepa- 

 rates itself distinctly from the brighter environs. According to later obser- 

 vations, it appears to consist of a tract of land between two depressions, 

 Albategnius, and the low land IV A" ' ' , which surrounds the crater IV A" ^. 

 Of these depressions Albategnius is the lowest. The surface of Hi2)parchus 



is slightly convex, the highest point being near the formation IVA^^^. Its 

 boimdaries differ vcrj- considerably from the ordinaiy boundaries of walled 

 plains, so much so that it can scarcely be regai'ded as a formation of this class. 

 As figured by Lohrmann and B. & M., its S.W. boundary commences near the 

 bright crater IV A^ •'■^, and is continued in a nearly straight line to the valley 

 IV A'' *'. This boundary is really that of the mass of high laud in which 

 Halley, Hind, IV A** ^ and IV A'' ^, are opened, and which appears to be the 

 highest in this part of the moon; and the boundary is continued as a high 

 steep range of mountains E.S.E. along the steep crater rill IV A^^'^ on the 

 north of Albategnius to the junction of the S.W. and west borders of Ptolc- 

 ma^us and Alphonsus. The west border of Hipparchus coincides with the 

 "fault" IV A'' ", IVA/5-", IVA« '2 (this fault extends as far as or beyond 

 Triesnecker). The north boundary differs in a ver^' marked degree from the 

 S.W., inasmuch as the land on the S.W. rises to a considerable elevation. 



