408 OBSERVATIONS ON TIIE ATMOSPHERE. 
and Guaduas in JNew Granada. A serenity, uninterrupted 
during a great part of the year, prevails only in the low- 
regions at the level of the sea, and at considerable heights 
on those vast table-lands, where the uniform radiation of 
the soil seems to contribute to the perfect dissolution of 
vesicidar vapours. The intermediate zone is at the same 
height as the first strata of clouds which surround the 
surface of the earth; and the climate of this zone, the 
temperature of which is so mild, is essentially misty and 
variable. 
Notwithstanding the elevation of the spot, the sky is 
generally less blue at Caracas than at Cumana. The 
aqueous vapour is less perfectly dissolved ; and here, as in 
our climates, a greater ditfusion of light diminishes the 
intensity of the aerial colour, by introducing white into the 
blue of the air. This intensity, measured with the cyano- 
meter of Saussure, was found from November to January 
generally 18°, never above 20°. On the coasts it was from 
22° to 25°. I remarked, in the village of Caracas, that the 
wind of Petare sometimes contributes singularly to give a 
pale tint to the celestial vault. On the 22nd of January, 
the blue of the sky was at noon in the zenith feebler than 
I ever saw it in the torrid zone. # It corresponded only to 
12° of the cyanometer. The atmosphere was then remark- 
ably transparent, without clouds, and of extraordinary dry- 
ness. The moment the wind of Petare ceased, the blue 
colour rose at the zenith as high as 16°. I have often 
observed at sea, but in a smaller degree, a similar effect of 
the wind on the colour of the serenest sky. 
We know less exactly the mean temperature of Caracas, 
than that of Santa Pd de Bogota and of Mexico. I believe, 
however, I can demonstrate, that it cannot be very distant 
from twenty to twenty-two degrees. I found by my own 
observations, during the three very cool months of Novem- 
ber, December, and January, taking each day the maximum 
and minimum of the temperature, the heights were 202° • 
20 - 1 °; 20 - 2 °. 
* At noon, thermometer in the shade 23.7” (in Che sun, out of the 
wind, 30-4°); De Luc’s hygrometer, 36-2°; cyanometer, at the zenith, 12°, 
at the horizon 9°. The wind ceased at three in the afternoon. Therm, 
21 c ; hygr. 39'3°; cyan. 16°. At six o’clock, therm. 20.2°; hygr. 39°. 
