366 SPECIAL RESULTS IN THE URANOLOGICAL 



tions appeared to him to confirm his view ; and the circum- 

 vallations with their central mountains were compared by 

 him to ' the forms of Etna, the Peak of Teneriffe, Hecla, 

 and the volcanoes of Mexico described by Gage" ( 588 ). 



Galileo, as he himself relates, had been reminded, by a 

 circular wall-surrounded plain in the Moon (probably from 

 its magnitude), of the configuration of entire countries sur- 

 rounded by mountains. I have found a passage ( 589 ) in which 

 he compares these lunar forms with the great closed basin of 

 Bohemia. In fact, several of the circular wall-surrounded 

 plains of the Moon are but little less extensive, for they have 

 diameters of from 25 to 30 German geographical miles 

 (100 to 120 English) ( 5 9). On the other hand, the proper 

 annular or ring mountains scarcely exceed 2 or 3 German 

 (8 to 12 Eng.) geographical miles in diameter. Conon in 

 the Apennines is 8 English geographical miles across ; and a 

 crater belonging to the brightly shining district of Aristar- 

 chus has even a diameter of only 400 toises (or about 450 

 yards), just half the breadth of the crater of Euchu-Pichincha 

 in the mountains of Quito, measured trigonometrically by 

 myself. 



As we are here dwelling on comparisons with well-known 

 terrestrial phsenomena and dimensions, it is the proper place 

 to remark that in this view the greater part of the wall- 

 surrounded plains and annular mountains of the Moon may 

 be most directly regarded as " craters of elevation, without 

 continuous phsenomena of eruption," in the sense of Leopold 

 von Buch's geological hypothesis. What, according to the 

 European standard, is called large on the terrestrial surface 

 the craters of elevation of Eocca Monfina, Palma, Tene- 

 riffe, and Santorin are indeed altogether inconsiderable as 



