to es 
Mean heat of the year in the 
Latitude. Difference. 
Old World. | New World. 
0° 80° 80° 0° 
20 77 tes i | 0 
30 70 67 3 
40 63 54 9 
50 50 . 38 12 
60 40 iq 24 16 
Hence it appears that the old world is much a than the new, and i 
that the sr nape of score sm mee ot decrease, from Florida to the 
Gulf of St. Lawrence, in the 0 da Faeroe from Egypt to 
Scandinavia. But odttionsih in on tetipérate parts of North America, the 
mean annual heat of a given place is the same as that of Europe some 
$ 
egrees more to the ee yet the temperature of particular season 
does not won in the sa — ee ; but the colder the winters the hotter 
the sum: 
A summer e Pilih a 39° 56! N. is Wes same as 
hat of Rom - lat. 41° 53' N. 
The winter of | Philadelphia, lat. 39° 56! N. is a same as 
that of Vienna - lat, 48° 13'.N. 
The summer of Quebse, lat. 46° Ar’ N. is hotter that that ’ 
- lat. 48° 50! N. 
The winter of Anodes, lat 46° a7’ N. is colder than that 
of St. Petersburg: - lat. 59° 56' N. 
In general, the summers of the temperate parts of North America, as far 
as 40° north eae are about 4°w warmer than in Europe under the same 
isothe arallel ; whence it can be understood why magnolias and other 
uinoctial-looking trees extend so far to the north, since, in the parallel of 
, the summer heat to which these trees are exposed sea scarcely differs from 
the | mean annual heat of the equator. It is, therefore, extremely important 
in the study of vananical geography, to take na account, not only the 
the mea r heat.* 
mean temperature of the year, but also summer 
* I do not attach aoeg faith to the inferences drawn from the mean heat of a 
yon The extremes of heat and cold, and the suddenness .of the cisiaiielia. fford 
er data. The 2 plants which are dest troyed b y our sudden vici ees temperature in the 
United States, are not directly killed by cold, but are killed by the speedy subsequent heat. 
He y 
the frosts of spring and of : autumn. The sudden aprinadions a heat to frozen plants, as well 
: i 
: ce, also, in eal the tender plants in the yards on ie south S10°S 0 ouses 
ioe bop J ila while ine - 
ontthe winter. Hen Teles $0, the pase yn - se ‘ical bear: in the southern Stat s should 
ta! 
tion from reducing t e tem ae the reba iadergcowth; and, furthermore, by t 
é vegetation, keep upa notabl e degree of warmth in the surrounding ee 
