^74' M. Humboldt 07t Isothermal Lines ^ 
nocturnal radiation, does not exceed from S°.7 to 4°.14'. This, 
augmentation is a little greater in the lower regions of the 
Andes, in those large valleys whose smooth bottoms reach the 
height of from 1,31^ to 1640 feet, principally in the valley of 
La Madaleine, between Neiva and Houda. It is singular to 
find in the middle of mountains heats which equal those of the 
plains, and which are more insupportable, as the air of the val- 
leys is almost never agitated by the winds. If we compare, 
however, the mean temperatures of these same places with those 
of the strata of the true atmosphere, or on the declivity of moun- 
tains, we shall find them only from 3°. 6 to 5°. 4. 
On these grounds, we may place some confidence on the four 
insults which we have deduced from such a great number of ob- 
servations, for the perpendicular heights of 1000, 2000, 3000, 
and 4000 metres. I have confined myself to a simple arithme- 
tical mean, and to the fortuitous compensation of irregularities ; 
for I could not have avoided employing an hypothesis on the 
decrease of heat, if I had wished to reduce to a standard 
height those heights which approach it the most. I have added 
the observations with which an intimate knowledge of localities 
has furnished me. 
1. Fqt 10€0 Metres {S2Q0 feet) of Efevation. Alt. in 
Feet. 
Convent of Caripe, (thick and damp forests), - 2959 
Caraccas, (a foggy sky, valley of small extent,) - 2906 
La Plata^ (very warm, valley communicating with that of L^Alto 
Magdalena,) _ . . . 3437 
Carthago^ (very warm valley of Cauca), - - 3149 
2. For 200© Metres {6660 feet) of Elevation. 
Loxa, (a plateau of small extent), - - 6&55 
Almaguer<f declivity covered with very thick vegetation), - 7413 
Popayauy (small phiteau, a little elevated above the valley of Cau- 
ca,) .... - 5815. 
3. For 3000 Metres {9%A>0 feet) of Elevation. 
Caxamarca, (very extensive plateau, sky serene,) - 9381 
Quito, (at the foot of Pinchincha, a narrow valley,) - 9539 
Tunja, (mountains of New Grenada), - - 9522 
Malvasa. (elevated^ plains, cooled by the snows of the volcano of 
Purace,) - - - » 9971 
Los Pastos, (very cold plateau, from which rise snow- covered sum- 
mits,) - - ... 10099 
Mlactacunga, (temperate valley), - - 9473 
Miobamba Nuevo, (arid plains of Tupia, covered with pumice-stone,) 9482 
Temp. 
Fahr. 
65!3 
69.44, 
74.66 
74.84 
64.4 
62.6 
65.66 
60.80. 
57.92 
56.66 
54.50 
54.50 
59.0 
61.16 
