360 SPECIAL RESULTS IN THE URANOLOGICAL 



general and simply superficial configuration of the mountain- 

 groups of the Moon, than we do of the orography of the half 

 of the Earth's surface, which comprises the interior of Asia 

 and Africa. Generally speaking, we regard the darker parts 

 of the Moon's disk as the plains and depressions, and the 

 brighter parts, which reflect most solar light, as the more ele- 

 vated and mountainous parts. Kepler's old denomination 

 of sea and land has long been given up ; and even Heve- 

 lius, notwithstanding the similar nomenclature to which he 

 gave currency, already doubted the correctness of such an 

 interpretation, and the truth of the contrast it implied. The 

 circumstance that, on careful examination with very different 

 illumination, all parts of the so-called lunar "seas" have 

 shown themselves completely uneven, and because polyhedric, 

 or full of angles, therefore giving much polarised light, 

 has been adduced as being particularly at variance with the 

 supposition of the presence of liquid surfaces. Arago has 

 noticed, however, in regard to this reasoning, that some of 

 these surfaces might, notwithstanding their inequalities, 

 belong to a not over-deep sea-bottom covered with water ; 

 since in our own planet we find that the uneven rocky bed 

 of the ocean can be distinctly seen on looking down from a 

 great height, because the intensity of the light which ascends 

 from below surpasses that of the light which is radiated 

 from the surface of the sea (Ammaire du Bureau des Longi- 

 tudes pour 1836, p. 339343). In the forthcoming work 

 of my friend his " Astronomy and Photometry" the pro- 

 bable absence of water on the surface of our satellite will 

 be deduced from other optical reasons which we do not 

 enter upon here. Of the low " plains," the largest are in 

 the northern and eastern parts of the Moon's disk. Among 



