PORTION OF THE COSMOS. THE PLANETS. 367 



compared with Ptolemy, llipparchus, and many other lunar 

 forms. In breadth, Palma is only 3800 toises (24300 Eng. 

 feet) ; Santorin, according to Captain Graves' s recent deter- 

 mination, 5200 toises (33250 Eng. feet) ; and Teneriffe, at 

 the utmost, 7600 toises (48600 Eng. feet), or only Jth or 

 ^th of the breadths of the two above-named lunar craters. 

 The small craters of the Peak of Teneriffe and Vesuvius 

 (little more than three or four hundred feet in diameter) 

 would hardly be discernible through telescopes. In by far 

 the greater number of cases the annular mountains are 

 destitute of any central mount; and, where such exist, 

 they are described as dome-shaped or flattened (as Hevelius 

 and Macrobius), not as cones of eruption with openings 

 ( 591 ). I here mention, solely on account of the historical 

 interest which may attach to them, the accounts given of the 

 burning volcanoes supposed to have been seen on the dark 

 side of the Moon on the 4th of May, 1783, and the lumi- 

 nous appearances in Plato observed by Bianchini (16th 

 Aug. 1725) and by Short (22d April, 1751). The causes 

 of the illusion have long since been ascertained. They 

 belong to the more vivid earth-light reflected by particular 

 portions of the surface of our planet upon the dark side of 

 the Moon ( 5 92). 



It has been remarked, and doubtless with much reason, 

 that, from the absence of water on the moon (the " rills," 

 which are very narrow, and in most cases rectilinear 

 depressions ( 593 ), are not rivers) we may imagine its sur- 

 face to bear a general resemblance to that of the Earth in 

 its primitive or more ancient condition, before the deposit 

 of shelly sedimentary strata, or the formation, transporta- 

 tion, and distribution of alluvium by the continued action 



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