W. Hopkins on Changes of Climate. 249 
ed on the result just enunciated. In ascending from one table- 
land to another, the decrease of temperature is much slower than 
if we should ascend in a balloon, or up the side of a steep moun- 
tain. The following table exhibits the results of Humboldt’s 
— on four of the highest table-lands on the new con- 
BGS) 
"a ne 
Pees ee Lane Height. winneneires To tor G Psa | 
; see metres, ° metres. 
eS 013s 2907 15:0 0 9 
Popayan, - - - - | 92 96N 1796 206 2881 
San. Fé di Bogota, - | 4 35 y. 2660 16°5 256-0 
Mexico, -'- - - - 19 26 w. 9277 16-9 249°3 
_ The mean of the numbers in the last column is 258-4 metres. 
This is equivalent to 478 feet of height for 1° F., instead of 350 
feet, as in the former case. The high general temperature of the 
plains of Tibet (as indicated by the nature of their produce), in 
Proportion to their enormous elevation, is doubtless due to the 
Same cause. 
From these results it appears, that we may take a decrease of 
1° F. as corresponding to an elevation varying, according to cir- 
cumstances, from 320 to 500 feet; the smaller number being ap- 
Plicable to small, or, if high, very steep mountains, and the lat- 
ter to large massive ranges presenting extensive table-lands along 
21. Before the publication of the admirable observations of 
Humboldt, it was usually assumed, in speculations respecting the 
ine of perpetual snow, that it coincided with that of + La- 
ler observations have shown the error of this hypothesis, espe- 
cially in the higher latitudes. Humboldt has given the following 
results, deduced from his own observations and those of others, 
‘Specting the mean annual temperature at the limit of perpetual 
Stow, in different latitudes : 
At Chimborazo, Apes temperature ‘ = 32°04 2°-7—34°-7 F, 
lat. = 19-997 g_ of the snow-line 
At St. rear ae “ ‘sc = 32° — §°-7=25°°3 
tat. = 46° N, 
At the Polar Circle 7 “c = 32° —10°-8=21°2 
Hence it follows that near the equator the snow-line is nearly 
000 feet lower than that of 32°, while at St. Gothard it is high- 
& than this latter line by about 2000 feet, and at some places on 
the Polar circle by about 3500 feet, according to Humboldt. But 
a that latitude in the northern hemisphere the height of the 
;LoW-line above that of 32° appears to be very variable, as might 
“pected from the very different conditions under which dif- 
are situated along the same parallel of latitude, In 
