PHYSICAL ASTRONOMY. 139 
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Again, perfectly insulated mountains, cailed cone mountains, exist in great 
numbers on the moon. With respect to the grey level regions of the moon, 
at one time called seas, they are universally intersected by ranges of heights, 
either Jong and straight, or running in great free curves. The latter are 
with some inaccuracy termed mountain spurs, since they are not ramifica- 
tions and extensions of greater mountains, and vanish entirely at full moon, 
casting a shadow only at sunrise and sunset, by which they are then recog- 
nised. The streaks of light must be considered as very remarkable and 
difficult of explanation, many of which run along singly, but most form radi- 
ating systems. These streaks of light stretch indifferently over mountains, 
valleys, and plains, without altering their shape, direction, or color. They 
are almost always four to twelve miles broad, and vanish under an oblique 
illumination. Equally singular are the channels, those extremely narrow but 
deep furrows, which run generally in rectilineal directions through plains, 
and more rarely through mountainous regions. These channels cannot be 
streams or their beds, nor can they remind us of canals and highways. 
These channels are indicated by narrow parallel lines on the map of the 
moon. 
As regards the colors of the moon, we can only indicate them on our 
chart in the most general outlines. At least ten different shades, from dark 
grey to the most brilliant white, can be distinguished. In general, the eleva- 
tion is the brighter, and the depression the darker; this relation is, 
however, sometimes inverted. The brightest spots very rarely belong to 
the higher mountains; it is rather great depths that shine with uncommon 
brilliancy. 
55. For the sake of giving a clear idea of the appearance of particular 
regions of the moon through a good refractor of 200-300 magnifying power, 
we have furnished the figures 2, 3, 4, and 5, which surround fig. 1, pl. 11. 
The region fig. 2 contains the mountains Caucasus, Calippus, Eudoxus, and 
Aristotle, found in quadrant I. ( fig.1); fig. 3, the mountains Jansen, Plinius, 
Vitruvius, and Littrow, with a part of Mare Serenitatis, also occurring in 
quadrant I. fig.4 represents the mountains found in quadrant Il. (fig. 1), 
namely, Kirch, Pico, Alps, Plato; as also a part of Mare Imbrium and of 
Palus Nebulum. Finally, fig. 5 represents the mountains Saussure, 
Pictet, Tycho, Sasserides, and Gauricus, of quadrant II. (fig. 1.) 
A degree of the equator, or 335 part, is equal to 60 geographical miles ; a 
degree of the moon’s equator is equal to 16 3%, geographical miles; the 
whole surface of the moon is therefore about equal to the area of America. 
The visible hemisphere of the moon is represented in fig. 1, pl. 11, as it 
appears at the time of mean libration. Consequently only the central parts 
appear in their true proportions; for nearer the borders all circular crater 
groups must appear oblong. 
It is erroneous to suppose that with better instruments and higher magni- 
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