256 M, Boussii\gauU s [Oct. 



which I obtained is certainly not free from objection ; and 

 I think that new experiments are necessary, to prove clearly 

 . that the air which I examined was the same as that which 

 existed in the interstices of the snow. 



In order to procure this air it is necessary to retard 

 the melting of the snow. The air of the flask is found in 

 contact with the water resulting from the snow, which con- 

 tains more or less air. Now, we know that in such circum- 

 stances the oxygen dissolves more readily in water than 

 the azote does, and that the air with which the water is 

 saturated contains always more oxygen than that of the 

 atmosphere. 



The air which remained in the phial, and which was the 

 portion I examined, might, therefore, contain less oxygen, 

 although, in reality, the air contained in the snow possessed 

 the usual composition. Such is the objection which may 

 be made to the result which I obtained. With regard to 

 that of Saussure, it would be proper, in fair criticism, to 

 know how the air examined by Sennebier, was extracted 

 from the snow. 



Philosophers who have ascended lofty mountains agree in 

 saying, that the blue colour of the sky becomes more intense 

 in proportion to the height. On Mount Blanc the sky pre- 

 sented to Saussure a deep Prussian-blue colour ; and during 

 the night, according to his own description, in one of his 

 bivouacs on the same mountain, " the moon shone with 

 great splendour in the midst of a sky black as ebony." On 

 the neck of the mountain the intensity of the colour of the 

 sky was still very great. Saussure contrived an instrument 

 for making comparative experiments upon this subject. 

 From our sf^tion at Chimborazo, the sky which on our 

 arrival presented a remarkably clear aspect, did not appear 

 to possess a deeper colour than that of Quito. However, 

 as I have had an opportunity of seeing the sky almost 

 completely black, I shall relate the facts simply as they 

 occurred: when I was in Tolima the sky appeared of its 

 ordinary colour ; I was then at an elevation of 4,686 metres 

 (15,370 feet), and, consequently, a little under the snow. 

 On the Volcano of Cumbul the sky appeared of an ex- 

 tremely deep indigo ; I was then surrounded by snow : 



* Saussure Voyage, vii. 321. 



