ON MAPPING THE SURFACE OF THE MOON. 21 
to advantage shortly after the time of sunrise and a little before sunset, and 
is lost to view as a separate formation under a high illumination, to mark 
more clearly the territory of which it forms the western part, and which is of 
a much more individual character than Hipparchus, it is proposed to group 
the various objects which this territory contains under the general designation 
of “ Terra Astronomica,” as suitable for the district, a portion of which is com- 
memorated by the name of the greatest astronomer of his time, and which is 
surrounded by walled plains and craters, named in commemoration of cele- 
brated ancient and modern astronomers. The term is also suitable as a com- 
panion to the region in the south, which has been named “ Terra Photogra- 
phica,” to commemorate the labours of De La Rue in Celestial Photography. 
See Report, 1865, p. 305. 
Terra AsTRONOMICA. 
An extensive formation situated on the following areas :— 
mera” 6 LY Af IIT As 
ipvoar. “TV-A*. Tit A* 
It is N. of Albategnius, N.W. 
of Ptolemceus, and extends from 
these walled plains as far N. as 
the equator. 
This interesting region may 
be described under the heads of 
* Boundaries ” and “ Interior 
Formations.” 
Bovunparres. — Commencing 
at the angle formed by the 
junction of the walls of Alba- 
tegnius and Ptolemcus, at which 
point we find the crater [TV As}2, 
and proceeding W.N.W. as far 
as the small crater IV A$ 33, 
along the crest of a range of 
hills on which IV A$ 36 is 
situated upon the highest point, we traverse the common boundary of Terra 
Astronomica and Albategnius. At the point IV A$3 we leave Albategnius, and 
proceeding along IV A¢26, we arrive at the mountain IV A¢ 29, on the EK. of 
Halley, which is a fine crater just exterior to the S.W. border of Hippar- 
chus. From the N. angle of Halley, the cliff IV A” 14, terminating the high 
land from IV A“? to IV A"® facing Hipparchus and forming the continua- 
tion of its §8.W. border, proceeds in nearly the same direction as IV A$ 6 
towards the depression IV A”®, This cliff terminates with the peak IV A”), 
a of B. & M. and 29 of Sec. I. of Lohrmann ; but the range of mountains 
of which it forms a part preserves its nearly rectilineal direction from the 
junction of the 8.W. border of Ptolemeus with the N.W. border of Al- 
phonsus to Ritter and Sabine (see ante, p. 13). It is between this cliff and 
IV A®™ that we meet with certain valleys which break through the wall 
of Hipparchus, viz. IV A"18 and IV A"®, N.W. of IV A"6 is the peak 
IVA", 30 Sec. I. of Lohrmann, immediately adjoining which on the N.W. is 
the long narrow valley IV A" 41, described by Julius Schmidt as a crater-rill 
(cleft) in his Catalogue of Rills, No. 362. The openings of these valleys to- 
