14 Mr J. D. l)ana on the Volcanoes of the Moon, 



Over a large part of the north-west quarter there is only 

 hore and there an elevation, and this comparative nudity ex- 

 tends a considerable distance southward across the equator. 

 The features of the surface may be distinguished as of five 

 kinds, viz : — 



1. The ring-mountains, which are broad truncated cones 

 with immense circular craters. (See the following figures 

 from Beer and Madler.) 



2. Conical mountains, nearly like ordinary volcanoes. 



3. Linear or irregular ridges. 



4. Large depressed areas, usually termed seas, but not sup- 

 posed to contain water. 



^ 5. Broad pale streaks, of great length. 



6. Narrow lines, supposed to be fissures. 



Out of the 1095 heights measured by Beer and Madler, siv 

 are above 20,000 feet in altitude, and twenty-two exceed 

 15,750 feet. 



The broad truncated cones with large circular craters, are 

 its most common elevations, and are among the loftiest. The 

 pits, as we have remarked, are of all dimensions to 150 miles, 

 and of various depths to near 25,000 feet. The crater Baily 

 is 149^ statute miles in diameter ; Clavms is 143^ miles ; 

 Schickard is 128 miles. 20 to 60 miles is the more com- 

 mon breadth. The depth of Newton is 23,833 English feet ; 

 of Casatus 22,822 ; of Calippiis 22,209 ; of Tycho 20,181 

 feet.* The height above the surface exterior to the cone, is 



* AVe have stated that Galileo (note to page 336) made the altitude of the 

 higher of the moon's mountain 8800 metres. Ilevelius reduced their height to 

 5200 metres. Riccioli, as SI. Arago states, increased Galileo's estimate, and 

 his observations, as calculated by M. Keill, gave for the mountain St Catherine 

 more than 14,000 metres. Herschel in 1780 (Phil. Trans, for 1780, p. 507; 

 also for 1794, p. 40), reduced again the heights, concluding, from his observa- 

 tions, that the loftiest did not exceed a mile and a half. The latest investiga- 

 tions have restored them nearly to Galileo's first estimate. 



We state, for the information of some who have not paid attention to the 

 subject, that these heights are determined, either from the shadows of the peaks 

 on the central plain of a crater or the exterior surface, or by noting the posi- 

 tion of a summit when it first becomes illuminated, and calculating therefrom ; 

 the higher the peak, the longer will be the shadow, and also, the sooner its top 

 will be tipped with light. Should it hereafter be established that the moon 

 has an atmosphere, it must be too slight to affect appreciably the altitudes de- 



