342 
PROFESSOR PHILLIPS ON SOME PARTS 
10° to 20°, and in west longitude 21° to 28°, form a remarkable triplet of ring-mountains 
nearly equal in magnitude, and in contact, yet offering singular differences of structure. 
They are not of the same date: Theophilus intrudes its continuous outline within the 
northern part of the older crater of Cyrillus ; Cyrillus is linked to Catharina by a con- 
cave isthmus ; Catharina includes the half-preserved ring of an older and smaller crater. 
In the centre of Theophilus is an aggregation of peaks ; in the same part of Cyrillus 
is a huge double-horned mountain, and near it a considerable crater ; neither of these 
features occurs in Catharina. 
Theophilus, situated in lat. S. 10° to 13° and long. W. 25° to 28°, though nearly cir- 
cular in figure, shows some diversity in this respect according to the incidence of light, 
being sometimes almost hexagonal. Copernicus also exhibits this diversity. 
The longest diameter of Theophilus is above fifty-five miles in length. Sunrise hap- 
pens when the moon is 5 ‘2 days old, midday when about 12 - 7, and sunset at twenty 
days. 
At sunrise the central mountain and all the surrounding ring are brightly illumi- 
nated, only narrow channels of darkness running into Cyrillus. But the interior of the 
crater is then wholly dark, except for a small breadth within and under the eastern crest 
(1863, April 24). When the sun’s rays fall at a low angle on the surface of Theo- 
philus, the shadow thrown from the lofty western crest (15,000 feet high) spreads widely 
over the interior of the deep crater, and is undulated on the edge so as to mark the 
effect of higher and lower parts of the crest. Between this shadow and the base of the 
central mountain the area appears clear like a floor ; but beyond this, toward the north, 
east, and south, all is curiously uneven in heapy little ridges, and long partly fissured 
surfaces parallel to the ring. I can discern only one distinct crater in this surface, and 
that is under the north-eastern part of the ring, but there are several smaller pits. 
Perhaps larger instruments may show that some of the small heaps and ridges have cups 
on their surface. 
To the central mountain (Plate XV.) I have given much and frequent attention, 
for the purpose of ascertaining the form of its much divided mass, and of discovering 
whether it contained any cup-formed summits. None were observed among the ten or 
more bosses Avhich go to make up the rugged mass, elevated about 5000 feet above the 
central area. 
When the sun’s rays fall with less obliquity on Theophilus, the part which was 
wholly in shade under the western crest assumes a quite different aspect — many bold 
ridges and furrows showing themselves distinctly with light falling at 15° elevation. 
Some of these appear in the lower part of the figure in Plate XVI., but they really exist 
all round the inner and western part of the crater. 
The phenomena which appear where Theophilus joins Cyrillus, are extremely curious 
and complicated, not in the least like as if one cone of volcanic eruption had intruded 
its convex sloping surface within another, but rather as if one great blister had pushed 
aside another and then burst, leaving a sort of double folding along the line of junction. 
