THE MOON. 491 



the lower and more level; the brighter parts, reflecting much 

 Sun-light, are the more elevated and mountainous Kepler's 

 old description of the two as sea and land, has long been 

 given up; and the accuracy of the explanation, and the oppo- 

 sition, was already doubted by Hevel, notwithstanding the 

 similar nomenclature introduced by him. The circumstance 

 principally brought forward as disproving the presence of 

 surfaces of water on the Moon, was that in the so-called 

 seas of the Moon, the smallest parts showed themselves, upon 

 closer examination aud very different illumination, to be 

 completely uneven, polyhedric, and consequently giving much 

 polarized light. Arago has pointed out, in opposition to the 

 arguments which have been derived from the irregularities, 

 that some of these surfaces may, notwithstanding the irregu- 

 larities, be covered with water, and belong to the bottoms of 

 seas of no great depth, since the uneven craggy bottom of the 

 ocean of our planet is distinctly seen when viewed from a 

 great height, on account of the preponderance of the light 

 issuing from below its surface, over the intensity of that 

 which is reflected from it. (Annuaire du Bureau des Lon- 

 gitudes pour 1836, pp. 339-343.) In the work of my 

 friend, which will shortly appear, on astronomy and photo- 

 metry, the probable aosence of Mater upon our satellite will 

 be deduced from other optical grounds, which cannot be 

 developed in this place. Among the low plains, the largest 

 surfaces are situated in the northern and eastern parts. The 

 indistinctly bounded Oceanus Procellarum, has the greatest 

 extension of all these, being 360,000 geographical miles. 

 Connected with the Mare Imbrium (64,000 square miles), 

 the Mare Nubium, and to some extent with the Mare Humo- 

 rum, and surrounding insular mountain districts (the Riphcei, 

 Kepler, Copernicus, and the Carpathians}, this eastern part of 

 the Moon's disc presents the most decided contrast to the 

 luminous south-western district, in which mountain is crowded 



