OP THE SURFACE OF THE MOON. 
343 
Cyrillus varies "greatly in appearance, according to the direction of the incident light. 
The interior is largely rugose, as if ridged and furrowed by lateral pressure. In parti- 
cular the great double central mountain appears in the two drawings here given (Plate 
XV. and Plate XVI.) with a difference of outline very remarkable ; as well as a dif- 
ference of shadows, for which, however, the sun’s position may perhaps account. The 
eastern border is remarkably rugged and broken, so as to become indefinite. The crater 
is unenclosed both to the south and north. Catharina seems to contain traces of more 
than one old crater enveloped and partly obliterated within it. It is incompletely 
bordered, or complicated in the boundary on all sides, and open or unenclosed on the 
south and north. If we regard Catharina and Cyrillus as twin craters of old date, broken 
into by Theophilus, we may admit the space full of old ridges and hollows to which 
Cyrillus opens, on the east of Theophilus, as a third and still older, once crateriform, 
mass which has lost almost every trace of the large ancient ring. In the same way the 
triplet of larger mountains entitled Arzachel, Alphonso, and Ptolemseus, seem to have 
been connected, Ptolemseus being the oldest, largest, and least distinct. These moun- 
tains, indeed, may be regarded as part of a vast crescent of 60° arc, extending from 
Barocius and Maurolycus, by Stoffler, Walter, and Regiomontanus, to Purbach, Arza- 
chel, Alphonso, Ptolemaeus, and Hipparchus. In each of these cases the oldest moun- 
tains, those most degraded and ruined, are near the equator. These are among the 
greatest of all the lunar mountains. 
Another arc, more directly meridional (long. W. 60°), includes the very great rings of 
Furnerius, Petavius, Yendolinus, and Langrenus, whose diameters are about 5° of lunar 
latitude. The more degraded and probably the older of these are those nearest the 
equator. 
In various parts of the moon occur twin mountains which do not communicate with 
one another ; as Aristarchus and Herodotus, one light the other dark ; Hercules and 
Atlas ; Autolycus and Aristillus ; Eudoxus and Aristoteles ; Mercator and Campanus. 
Indications of this kind of symmetry or continuity of action in the old volcanic force, 
appear worthy of special study, in relation to the physical history of the moon. 
Explanation of Plates. 
PLATE XY. 
Fig. 1. Gassendi, as seen in morning light. 
Fig. 2. Theophilus and part of Cyrillus, morning light. 
Fig. 3. The central mountain-mass of Theophilus enlarged. 
PLATE XYI. 
Group of Theophilus, Cyrillus, and Catharina. 
mdccclxviii. 3 B 
