BOOK V. 
GEOGRAPHY. 
487 
T .afif iinP 
J-i d i>i L U U C « 
Mean Heat of the Year in the 
Tl 1 ftp T P n p p 
Old World. 
New World. 
0° 
80° 
80° 
0° 
20 
77 
77 
0 
30 
70 
67 
3 
40 
63 
54 
9 
50 
50 
38 
12 
60 
40 
24 
16 
Hence it appears that the old world is much warmer than 
the new, and that the temperature of America does not de- 
crease, from Florida to the Gulf of St. Lawrence, in the 
same ratio as in Europe, from Egypt to Scandinavia. But 
although, in the tempei'ate parts of North America, the mean 
annual heat of a given place is the same as that of Europe 
some degrees more to the northward, yet the temperature of 
particular seasons does not accord in the same degree ; but the 
colder the winters the hotter the summers are found : thus, — 
The summer of Philadelphia, lat. 39° 56' N. is the 
same as that of Rome . _ - lat. 41° 53' N. 
The winter of Philadelphia, lat. 39° 56' N. is the 
same as that of Vienna . _ _ lat. 48° 13' N. 
The summer of Quebec, lat. 46° 47' N. is hotter 
than that of Paris - - - - lat. 48° 50' N. 
The winter of Quebec, lat. 46° 47' N. is colder 
than thatof St. Petersburgh - - - lat. 59° 56' N. 
In general, the summers of the temperate parts of North 
America, as far as 40° N. lat., are about 4° warmer than in 
Europe under the saiJie isothermal parallel ; whence it can be 
understood why magnolias and other equinoctial-looking trees 
extend so far to the north, since, in the parallel of 36°, th^ 
summer heat to which these trees are exposed scarcely differs 
from the mean annual heat of the equator. It is, therefore, 
extremely important in the study of botanical geography, to 
take into account, not only the mean temperature of the year, 
but also the mean summer heat. 
According to Barton, the climate to the west of the Alle- 
ghany mountains is much warmer than that on the east, or 
iVtlantic side, where the same plants exist 3° or 4° higher up 
I T 4 
