74 



from the central meridian, and 10 north of the equator, has its 

 most conspicuous peripheral crest formed of seven principal nearly 

 straight elements, approaching to equality in length, and meeting in 

 points which are situated almost exactly in a circle of 24 geographical 

 miles radius. Here is a very important partial difference, coupled 

 with a very important general agreement. 



While Gassendi, with peaks 9000 feet high, projects like a huge 

 narrow wall into the Mare Humorum, and hangs over the interior 

 plain in precipices as steep and many times as high as those over the 

 Atrio del Cavallo, Copernicus, seated in the midst of broad land, on 

 a base of 120 geographical miles, rises in many broken stages, brist- 

 ling with a thousand silver-bright crests, a perfect network of rough 

 and complicated ground, crossed by lights and shades, which have a 

 history of their own, and toward the inside falls off by many irre- 

 gular terraces, down to an interior plain, as if the whole area had 

 yielded, and the surface had been formed by enormous land-slips. 

 Four sharp notches are traced across the narrow ridge of Gassendi 

 cutting it deeply, like the hollows left by decomposing lava dykes 

 500 feet broad ; one deeper and broader opening unites the inner 

 plain with the outer Mare Humorum, and one far wider opening 

 leads to an accessory crater, over whose awful depth the cliffs, 

 10,000 to 12,000 ft. high, spread black shadows round some central 

 rocks. In these particulars Copernicus offers a very different aspect. 

 Its high crest, of 10,000 feet, is only cut through by one straight 

 narrow meridional groove, though broken by numerous fissures in 

 other parts, and is in all parts so irregular, partially undulated, and 

 varied with small crateriform points, and enclosed areas, resembling 

 craters, as to offer little analogy to any truncated cone of eruption. 

 The highest summit, on the left hand (west) side a huge rock is 

 conspicuous by its broad, deep and extended shade. What suggests 

 a vast lava current, is equally remarkable on the northern slope. 

 Regarding now the central plains of these mountains, we remark in 

 each several low ridges of rather sinuous forms, and several small 

 mounds (half a mile or more across), of which three central digi- 

 tated masses, not pierced by craters, are the most elevated, and 

 catch the earliest lights of morning which glance over the rocky 

 borders of the basin. Had the drawings been executed at the 



