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, 

 concentre all 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. 



