1'ALIi 01’ THE TEM l’E it AT U HE . 
84 
The cold we felt on the top of the Peak, was vert consi- 
derable for the season. The centigrade thermometer, at a 
distance from the ground, and from the apertures that emitted 
the hot vapours, fell in the shade to 2‘7°. 4 he wind was 
west, and consequently opposite to that which brings to 
Teneriffo, during a great part of the year, the warm air that 
floats above the burning desert ot Africa. As the temperature 
of the atmosphere, observed at the port of Orotava by M. 
Savam, was 22'8°, the decrement of caloric was one degree 
every’ 94 toises. This result perfectly corresponds with those 
obtained by Lamanon and Saussure on the summits of the 
Peak and Etna, though in very different seasons. The tall 
slender form of these mountains facilitates the means ot com- 
paring the temperature ot two strata ol the atmosphere, which 
are nearly in the same perpendicular plane; and in tins 
point of view the observations made in an excursion to the 
volcano of Tcnerifl'e resemble those of an ascent in a balloon. 
We must nevertheless remark, that the ocean, on account of 
its transparency and evaporation, reflects less caloric than 
the plains, into the upper regions of the air ; and also that 
summits which arc surrounded by the sea are colder in sum- 
mer, than mountains which rise from a continent ; but this 
circumstance has very little influence on the decrement of 
atmospherical heat ; the temperature of the low regions being 
equally diminished by the proximity of the ocean. 
It is not the same with respect to the influence exercised 
by the direction of the wind, and the rapidity of the ascending 
current ; the latter sometimes increases in an astonishing 
manner the temperature of the loftiest mountains. I have 
seen the thermometer rise, oil the slope ot the volcano ot 
Antisana, in. the kingdom of Quito, to 19’, when we were 
2837 toises high. M. Labillardiere has seen it, on the edge 
of the crater of the peak of Teneriffe, at 1S 7°, though he 
had used every possible precaution to avoid the effect of 
accidental causes. 
On the summit of the Peak, we beheld with admiration 
the azure colour of the sky. Its intensity at the zenith ap- 
peared to correspond to 41° of the cyanometer. We know, 
was ceded in the 16th century, by tlie King of Portugal, to Lewis Per. 
digon, at the time the latter was preparing to take possession of it by 
conquest. 
