ON MAPPING THE SURFACE OF THE MOON. 2o7 



Area IV A^. 

 Introduction. 



The greater i)ortion of this area, which possesses much irregularity of 

 surface, is principally oecupied by four groups of objects, viz., those on the 

 rocky laud — partly surrounding a plain — in the angle formed by the N.E. 

 border of Albategnius and the N.W. border of Ptolemseus; the crater group 

 in the north angle of Albategnius ; the slightly depressed surface IV A^ 25 ; 

 and the lower land north of the crater- row from IV A^ ' to Ptolemasus. 

 These groups occupy nearly twenty superficial degrees, or about 6953 square 

 miles. The remainder of the area, about 1857 square miles, is occupied with 

 the much more level surface of the south part of Hipparchus and the region 

 east of it. 



In the four groups of lunar objects above named there are no large craters ; 

 the largest is IV A^', which measures 10"-94, mag. 0-70. The following 

 arrangement shows the distribution of 41 as to size : — 



Between 1" — 2" 2"— 3" 3"— 4" 4"— 5" 5" — 6" 6"— 7" 7" -8" 



Objects.. 3 10 11 6 6 4 4 



Points of the First Order. None. 



Points of the Second Order indicated thus x . 



X Y S.lat. W.long. 



#*1. A crater situated on the rocky land between Ptolemaeus and Hip- 

 parchus. Lohrmann, 235 on map, X in Section I., who describes it 

 as of 16-1 English mUes in diameter, 7° of brightness, the floor 

 being 5°, mag. 0^70. I suspect a central mountain in it. 

 This crater is of irregular form and not round, as given by Lohrmann. A 

 line between IV A^^ and IV A^^ measures 10"^94. The figure is that of a 

 tery ii-regular trapezium; the sides, however, are not right lines, but more or 

 less curved. The longest side, 12"-36, which is sensibly curved, is from 

 south-east to north-west, the exterior slope facing the north-east. It in- 

 cludes the promontory on the border towards IV A^ ' ^. The next longest 

 side, 9"-03, is from south-west to north-east, the exterior slope facing the 

 north-west. The two remaining sides do not much differ from this iu 

 length. At the south end of the crater, and between the south-east and 

 south-west walls, is a break or "pass," IV A^ 2^ ^o^ unlike the " gorge" at 

 the north-west point of Rhaeticus. [Qi/. Is this "pass" at the south-west 

 end of "Webb's Furrow, between the craters IV A^ * and IV A^ ^ ?] It is not 

 shown by Lohrmann, but can be traced in the position queried on Be La Rue's 

 and Rutherford's photographs. Just exterior to the south-west wall are the 

 two craters, IV A? -^ and IV A^ 5. Exterior to the south-east wall, and lying 

 close to it, are two dimples, IV A? ^ and IV A^ ^, not in any way indicated by 

 Lohrmann nor by B. & M. From these a row of five eraterlets extend to the 

 west border of Ptolemceus. B. & M. give and mention six ; probably they 

 may include the dimples, as there is some doubt about IV A^ '3, the craterlet 

 nearest the wall of Ptolemaeus, being really one, the rising ground tending to 



1866. g 



