Light and Colour of the Moon. 59 -• 



are linear, equal in size, breadth, and clearness ; for a certain 

 distance they augment in capacity, then diminish in intensity, 

 and insensibly fade away. There are also in the Mare Nu- 

 hiunii and in the northern part of the Oceanus Procellarum, 

 many craters of a mile, and a mile and a half in diameter, sur- 

 rounded by a brilliant space, which is not subdivided into rays, 

 but which is partly concentric and partly eccentric ; this space 

 extends only from four to six miles, and insensibly loses itself 

 in the darker surface which surrounds it. Finally, we may 

 also perceive in these same' seas, pale rays running in different 

 directions, which do not exhibit any distinct mutual depen- 

 dence, or any common point of origin, but some of which pre^ 

 sent, towards the time of the change, the appearance of small 

 mountainous ramifications, though the majority are still inde- 

 pendent ; for, by a somewhat more direct illumination, they pre- 

 sent precisely, or very nearly so, the same tint of colour as the 

 surrounding surface, and disappear from our view. 



In the preceding remarks we have considered only the diffe- 

 rent degrees of illumination which the surface of the moon pre- 

 sents ; but it should likewise be observed that we may also 

 perceive under favourable circumstances, differences in colour 

 which are really specific. All the Mare Serenitatis^ with the 

 exception of the marginal portion, which is darkish, has a shade 

 of beautiful green. In the Mare Crisium, the green is mixed 

 with a dark grey. These two colours are separated in the Mare 

 Humorum, the green occupying the greater part of its surface. 

 The sea called the Cold Sea presents a palfr^reenish-yellow, which 

 is uniform throughout. The enigmatical colour of what is termed 

 the Marsh of Sleep, which is a region of well-defined hills, appears 

 to be yellow, and exhibits a reddish lustre in a few places. The 

 dark grey appears to exhibit in many places differences which 

 are somewhat analogous to those just stated. Whilst in certain 

 regions it appears to be a mixture of white and black, many 

 others have all the appearance of an entirely uniform steel -grey 

 tint. As the different shades of light only manifest themselves 

 distinctly at the time of full moon, so it is the same in a still 

 greater degree with respect to the colours which are specifically 

 different, which the most careful investigation will fail in dis- 

 covering two or three days either before or after the luminary's 



