/ 
S76 M. Humboldt on Isothermal Lmes\ 
Places situated between 
46°— 4.7* of North 
Lat. 
Elevations. 
Mean Temperatures. 
Metres. 
Feet. 
Of the 
Year. 
Of the 
Coldest 
Months. 
Of the 
Warmest 
Months. 
Level of the sea, 
0 
53!60 
36?32 
69!80 
Geneva, 
359 
1177 
49.64 
34.16 
66.56 
Tegernsee, 
744 
2440 
42.44 
22.10 
59.36 
Peissenberg, 
995 
3264 
41.00 
20.84 
57.02 
Chamouni, 
1028 
3372 
39.20 
55.40 
Hospice de St Gothard, 
2076 
6809 
30.38 
15.08 
46.22 
Col de Geant, 
3436 
11270 
21.20 
36.50 
In comparing the mean temperature of superincumbent beds 
of air, I find that the isothermal line of 41°, which, in the pa- 
rallel of 45°, is found at the height of 1000 metres, (3280 feet), 
makes the equatorial mountains of an absolute elevation of 4250 
metres, (13,940 feet). It had, however, been long believed, 
after Bouguer, that the inferior limits of perpetual snows cha- 
racterised every where a bed of air, whose mean temperature 
was 32° but I have shewn in a Memoir read to the Institute 
in 1808 that this supposition is contrary to experience. By 
uniting good observations, I have found, that at the limit of per- 
petual snows, the mean temperature of the air is,— 
At the Equator, 
In Temperate Zone, 
In Frigid Zone, in ) 
Lat. 68°— 69”, J 
Metres. 
Feet. 
4800 
15,744 
2700 
8,856 
1050 
3,444 
Mean Temp, of Limit 
of Perpetual Snows. 
34°.70 
25.34. 
21.20 
As the heat of the higher regions of the atmosphere depends 
on the radiation of the plains, we may conceive, that, under the 
same geographical parallels, w'e cannot find, in the transatlan- 
tic climates, (on the declivities of rocky mountains), the isother- 
mal lines at the same height above the level of the sea as in Eu- 
ropean climates. The inflexions which these lines experience, 
when traced on the surface of the globe, necessarily influence 
their position in a vertical plane, whether we unite in the atmo- 
sphere points placed under the same meridians, or consider only 
those that have the same latitude. 
Hitherto we have attempted to determine the mean tempera- 
tures which correspond under the Equator and in Lat. 45° and 
Observations Astronomiqves-, tom. i. p. 136. 
