ON MAPPING THE SUKFACE OH THE MOON. 261 



is the crater IV A^**, which is opened up in the rising and elevated ground, 

 forming the east boundary. This elevated gToiind fdls the angle between 

 Albategnius and Ptolemasus, and is marked " higher level." 



The interior surface of IV A^ ^'^ is slightly depressed and irregular. It 

 is marked "lower level (2)," indicating that it is lower than the surface of 

 Hipparchus "lower level (1)." On the west portion are two conspicuous 

 mountains, one, IV A^ ^°, in the angle formed by the S.W. and N.W. boun- 

 daries, and also in a line with the mountain IV A^ ^^ and the crater IV A^ " ; 

 the other, IYA^^\ J^.E. of IVA^^°, and forming with it two elevations 

 nearly parallel with the depression or broad rill, IV A^^', 



The mountain IV A^ ^^ forms the continuation of the east boundary from 

 IV A^ *'. There are two (apparently) elevations, one nearly between IV A^ ^^ 

 and IVA^32 (IVA^^^), the other between IVA^^l ^^^^ lYA^^. 



There are three conspicuous craters on this formation; one, IV A^^'*, 

 S.W. of IV A^^ and two N.W. of IV A^^ viz. IVA^^s ^^^ IV A^ ''6, at 

 the south foot of IV A? 28_ 



26. The mountain on the S.W. boundarj- of IV A^25_ 



27. A valley forming the IST.W. boundary of IV A^-^, length from 

 IVA^29 to jY^^57 25".68. 



*28. A cliff forming part of the Jf.E. boundary of IV A^-^, length 

 W.N.W.-E.S.E. 10"-94. 

 **29. A mountain on the east border of Halley, height according to B. 

 and M. 3543 English feet or 1080 metres ; it has a spur towards 

 the N.E. ; length of spur 7"-13. 

 This mountain is very suitable for a point of the first order. The spur 

 towards the N'.E. inclines very considerably to the level of the valley IV A^ ^^. 

 As the sun rises upon it, it is seen as a fine line of light. 



*30. A mountain on the west floor of IVA^^S^ length 8"-56. 

 *31. A mountain on the north floor of IV A? -^, length 8"-56. 

 *32. A mountain nearly S.S.W. of IV A^^ 4"-28, mag. 0-29. 

 This mountain is longer than shown in the photograph. It is situated on 

 the line of cliiFs from Tj'cho, and extends nearly as far north as IVA^"- 

 It is the N.E. spur of Lohrmann's 20, Sec. I. East of and parallel with it is 

 a crater-rUl containing three adjoining craterlets, IV A^^**, IV A^^', and 

 IV A^^-. Another crater-rill branches from IV A^''^ to IV A^^^, contain- 

 ing two adjoining craterlets, IV A^^'^ and IV A^*^^. 



**33. A craterlet at the extreme north point of Albategnius 3"-80, mag. 

 0-26. It is opened on the crater rill IV A^^'^, at its western end. 

 **34. A pear-shaped depression, as seen, under some aspects, on the north 

 part of Albategnius, opening into a crater on IV A\ of which it 

 forms the north part. 

 This is imperfectly shown both by B. & M. and Lohrmann. It contains 

 three craters, the south and largest, IV A^ ^', the middle one, IV A^^", and 

 the north, IV A^". 



35. Albategnitts, the north part. 

 **36. A crater on the K.E. border of Albategnius, length 8"-56. Its real 

 form requires to be determined. Shown bv Lohrmann. 



