ABSENCE OE VEGETATION. 
85 
by Saussure’s experiment, that this intensity increases with 
the rarity of the air, and that the same instrument marked 
at the same period 39° at the priory of Chnmouni, and 40° 
at the top of Mont Blanc. This last mountain is 510 toises 
higher than the volcano of Tencriffe; and if, notwithstand- 
ing this difference, the sky is observed there to be of a less 
deep blue, we must attribute this phenomenon to the dryness 
oi the African air, and the proximity of the torrid zone. 
We collected on the brink of the crater, some air which we 
meant to analyse on our voyage to America. The phial re- 
mained so well corked, that on opening it ten days after, the 
water rushed in with impetuosity. Several experiments, 
made by means of nitrous gas in the narrow tube of Fontana's 
eudiometer, seemed to prove that the air of the crater con- 
tained 0 09° less oxygen than the air of the sea; but 1 have 
little confidence in this result obtained by means which we 
now consider as very inexact. The crater of the l’cak lias so 
little depth, and the air is renewed with so much facility, 
that it is scarcely probable the quantity of azote is greater 
there than on the coasts. AVe know also, from the experi- 
ments of MM. Gay-Lussac and Theodore de Saussure, that 
in the highest as well as in the lowest regions of the atmo- 
sphere, the air equally contains 0 21 of oxygen.* 
AVe saw on the summit of the 1’eak no trace of psora, 
iccidea, or other cryptogainous plants ; no insect fluttered 
m the air. AVe found however a few hymenoptera adhering 
to masses of sulphur moistened with sulphurous acid, and 
lining the mouths of the funnels. These are bees, which 
appear to have been attracted by the flowers of the Spartium 
nubigenum, and which oblique currents of air had carried 
up to these high regious, like the butterflies found by M. 
Ramond at the top of Mont Perdu. The butterflies perished 
from cold, while the bees on the Peak were scorched on im- 
prudently approaching the crevices where they came in 
search of warmth. 
* During the stay of M. Gay-Lussac and myself at the hospice 
of Mont Cenis, in Marcli 1805, we collected air in the midst of a 
cloud loaded with electricity. This air, analysed in Volta’s eudiometer, 
contained no hydrogen, and its purity did not differ 0‘002 of oxygen from 
the air of I’aris, which we lnd carried with us in phials hermeticallj 
tealed. 
