106 



visible, and at other times invisible, to navigators 

 at equal distances. It is even probable, that the 

 chance of perceiving this volcano would not be 

 greater, if the ashy cone, at the summit of which 

 is the mouth of the crater, were equal, as in Ve- 

 suvius, to a quarter of the total height. These 

 ashes, which are pumice stone crumbled into 

 dust, do not reflect as much light as the snow of 

 the Andes ; are the cause why the mountain, 

 seen from afar, without detaching itself in a 

 bright, detaches itself more feebly in a brown co- 

 lor ; and contribute, if we may use the expres- 

 sion, to equalize the portions of aerial light, the 

 variable difference of which renders the object 

 more or less distinctly visible. Calcareous moun- 

 tains, stripped of vegetable earth, summits co- 

 vered with granitic sand, the high savannahs of 

 the Cordilleras*, which are of a golden yellow, 

 are undoubtedly distinguished at small distances 

 better than objects which are seen in a negative 

 manner ; but the theory indicates a certain limit, 

 beyond which these last detach themselves more 

 distinctly from the azure vault of the sky. 



The colossal summits of Quito and Peru, tow- 

 ering above the limit of the perpetual snows, 

 concentrexall the advantages, which render them 

 visible under very small angles. We have stat- 



* Los Pajonales, from paja, straw. It is the name of the 

 region of the gramina, which encircles the zone of the peren- 

 nial snows. Geogr. v£g. p. 70. 



