138 ASTRONOMY. 
erroneously supposed to be seas. The distinct brilliant points, so many of 
which are seen on the full moon, are only rarely elevations; oftener steeply 
precipitous depressions. The structure of the lunar mountains in general is 
very different from that which prevails on our earth, in that they present 
themselves for the most part as circular closed walls, with a hollow sloping 
cavity. They are called ring mountains, as, for instance ( pl. 11, fig.1), Pto- 
lemaeus (III. 87), Alphonso (III. '73), and Archimedes (II. 26) ; Plato (fig. 4). 
The greater of them are called walled plains when they inclose a plane 
surface: the smallest ring mountains are called craters. The most diminu- 
tive of these, on account of their small size, could not be represented in 
pl. 11 by mountain streaks, and therefore small circles have been employed 
for these. They are seen on a larger scale in fig. 3, namely, Pliny and 
Vitruvius. The walled plains occurring most frequently in the south- 
western part of the moon, appear to belong to the earlier formations of the 
moon’s surface, since they are unmistakably inferior to later forms of every 
kind. The light streaks passing frequently through walled plains, as also 
over the other regions of the moon, are not, as a whole, actual elevations, as 
they are sought in vain under an oblique illumination, when actual elevations 
are indicated as such by their shadows. 
Next to the walled plains follow, in order of size, the ring mountains proper, 
which, often truly circular, exist in great numbers. Frequently their wall 
slopes inwards and outwards in so called terraces; and in their interior, 
they generally present an elevation known as the central mountain. The 
most of these central mountains, however, do not reach as high up as the 
wall. Where the central mountain stands, the inside is sometimes dark grey ; 
commonly, however, as bright as the outer wall. In the southern hemisphere 
of the moon, the most of these mountains with their walls and environs are 
so much alike in color and light, that at full moon nothing more can be 
distinguished of them. The same thing occurs frequently in the deepest, 
most conspicuous, and most varied ring mountains and walled plains, some- 
times even in the grey spots. These latter, consequently, as for instance 
in fig. I., Mare Crisium, Mare Feecunditatis, Mare Tranquillitatis, and Mare 
Serenitatis, cannot possibly be seas. Hence it also follows that the view 
of the full moon is entirely different from that at the first or last quarter, 
since here the shadows of the mountains and craters present themselves, 
while there it is only various colors and their shading that are seen. 
Mountain chains occur here and there upon the moon, as upon the earth, 
but never of so great length. Even those mountains connected with one 
another, and termed mountain chains, have by no means the same valley 
and hill structures as the mountain chains on our earth, but they approach 
more to the crater form, and do not run out into various branches. The 
names of these mountain chains have been derived from those on the earth, 
as may be seen on the maps of the moon (pl. 11, fig.1). The greatest 
elevations of the following mountain chain are given in Paris feet. 
Gaucasus:| ) siptivedd oo. 17,188 Alina! ol. ll. Cw ee 
Appenines’). 2! #°«. . 16,934 Mountain on Sinus Iridum . 14,022 
138 
