^& Light and Colour of the Moon, 



pearance is a crater or a mountain, or if it be neither the one 

 nor the other. 



There is only one annular mountain, viz. Jristarchus, and 

 one point in Werner^ which reaches the 10th and highest degree 

 of illumination. When the sun is sufficiently elevated, all the 

 interior surface of Aristarchus, as well as the annular mountain 

 itself, shines with a light of sparkling whiteness. The central 

 mountain, and two or three points of more feeble radiance, may 

 also with difficulty be distinguished. Hard by, we find Proclus 

 whose zone, and interior very smooth slope, have a brightness 

 of 9°, whilst the interior itself is at 8°. The central mountains, 

 with a very few exceptions, are always brighter than the hollows 

 which they surround. 



But numerous as these brilliant craters are, they scarcely 

 form a half of all the forms of the total number of craters. 

 There are many, and amongst others the largest and deepest, 

 which completely disappear at full moon. It is no uncommon 

 occurrence to notice two craters very near each other, and which 

 appear to be equal in diameter, in steepness, and in depth, one 

 of which will shine at full moon with surprising splendour, 

 whilst the other cannot be distinguished but with the greatest 

 difficulty. So soon, however, 'as the shadows begin to appear, 

 the latter will begin to shine, and the other to be obscured, and 

 when the light is about to leave their neighbourhood they ap- 

 pear quite equal. Moreover, towards the epoch of the phases 

 you can scarcely any longer distinguish any difference of out- 

 line in the neighbourhood of the limits of the light ; and the 

 escarpments of mountains, which are turned towards the sun, as 

 well as the plains and more gentle slopes, shine, as if they were 

 illuminated under a greater angle. 



Among the most remarkable and most inexplicable ap- 

 pearances in the moon are the systems of rays which it pre- 

 sents. Seven of the largest annular mountains, viz. Tycho, 

 Copernicus, Kepler, Byrge, Anaxagoras, Aristarchus, and Gi- 

 bers, are surrounded with long and broad pencils or luminous 

 bands (lichtstreifen) arranged in a radiated form. Mayer, 

 Euler, Proclus, Aristillus, Timocharis, and some others exhibit 

 the same appearance on a smaller scale, and in a less striking 

 manner. These bands usually commence at a small distance 



