102 M. Boussingault's Account of 



having the deepest king's blue tint ;* and at night, during a 

 bivouac on the same mountain, the moon, as he himself expressed 

 it, shone with great brilliancy in a heaven as black as ebony. 



On the Col du Geant the intensity of the colour was even 

 more striking. Saussure invented an instrument in order to 

 make comparisons of such observations. At our station at Chim- 

 borazo, the heaven, which, on our arrival was of remarkable 

 purity, seemed to us to present no darker tint than that of the 

 sky at Quito. But as I had an opportunity of seeing the sky 

 of almost a black colour at a much lower elevation, I now re- 

 port the facts as I have observed them. 



When I was on Tolima, the sky had its usual colour, al- 

 though I was at a height of 4686 metres, therefore little under 

 the snow line. 



On the Volcano of Cumbal the sky seemed to me of a re- 

 markably deep indigo-blue colour. I was then surrounded by 

 snow, for the dome of the volcano is crowned with a glacier. 

 During the whole of my ascent to the Cumbal, so long as I had 

 not reached the snow boundary, the colour seemed much less 

 dark. This blackness alarmed the Negro who carried my baro- 

 meter. In the evening we both were attacked by inflammation 

 of the eyes, which rendered us blind for several days. 



When I ascended Cotopaxi, I provided myself and my com- 

 panion with coloured glasses. After we had wandered for five 

 hours on snow, we halted at an elevation of 5716 metres. The 

 heaven, as seen by the naked eye, did not seem to us darker 

 than it did from the plain, just as we found on Chimborazo, the 

 sky of Rio-Bamba and Quito. I will not, however, deny, that, 

 in reality, the sky, as seen from high mountains, is darker than 

 when seen from the surface of the sea ; I did not possess a cy- 

 anometer, and am, besides, quite inclined to admit the correct- 

 ness of the general results attained by Saussure with this instru- 

 ment. I merely assert that this difference of colours is only to 

 be remarked by comparison, and that the blackness of the sky 

 which has been sometimes observed on glaciers, has been occa- 

 sioned by a dulness in the organs of vision, and also, perhaps, 

 by the operation of an easily understood contrast. 



* Saussure's Voyage, vol. vii. p. 32 1 r 



