98 



mountains." It seemed to me, that in the chain 

 of the Andes these appearances make less im- 

 pression on the mind of the natives, because 

 those among them, who scale the summits of the 

 Cordilleras to gather snow, do not come from the 

 region of the low lands, but from elevated plains, 

 which are themselves twelve or fifteen hundred 

 toises above the level of the sea. 



I found on examining the cyanometrical ob- 

 servations recorded in my journal, that, from the 

 coasts of Spain and Africa to those of South- 

 America, the azure color of the heavenly vault 

 progressively augmented from thirteen to twenty- 

 three degrees. From the 8th to the 12th of 

 July, in twelve and a half and fourteen degrees 

 of latitude, the sky was of an extraordinary 

 paleness, without any concrete or vesicular vapor 

 being visible. The cyanometer indicated at the 

 zenith, between noon and two in the afternoon*, 

 only sixteen or seventeen degrees ; though the 



* The observations were always made at the zenith itself, 

 or near the zenith, but at times when the Sun was distant 

 from that part of the sky, of which the intensity of the blue 

 color was measured. At ten or twelve degrees distance 

 around the sun, the tint has a local paleness ; as on the con. 

 trary it has a local intensity, when the blue of the sky is seen, 

 either between two clouds, or above a mountain covered with 

 snow, or between the sails of a ship, or the tops of trees. It 

 is scarcely necessary to remark, that this intensity is only ap- 

 parent, and that it is the effect of a contrast of two colors of 

 different shades. 



