Iyistrihuti<y3/i of Heat over the Globe. 
40® and 4S\ Observation here presents a result entirely con- 
formable to theory, for the variation of the square of the cosine, 
which expresses the law of the temperature, is a maximum to- 
wards 45° of latitude. This circumstance ought to have a favour- 
able influence on the civilization and industry of the people 
who inhabit the regions under this mean parallel. It is the 
point where the regions of the vines touch those of the olives 
and the citrons. On no other part of the globe, in advancing 
from north to. south, do we observe the temperatures increase 
more sensibly, and no where else do vegetable productions, and 
the various objects of agriculture, succeed one another with 
more rapidity. But a great difiereiice in the productions of 
contiguous countries, gives activity to commerce, and augments 
the industry of the cultivators of the soil. 
We have traced the direction of the isothermal lines from 
Europe to the Atlantic Provinces of the New World. We 
have seen them approach one another from parallelism towards 
the south, and converge towards the north, particularly be- 
tween the thermometric curves of 41° and 50" : We shall now 
endeavour to pursue them to the west, North America pre- 
sents two chains of mountains, extending from N. E. to S. W., 
and from N. W. to S. E. forming almost equal angles with the 
meridian, and nearly parallel to the coasts which are opposite 
to Europe and Asia, viz. the chain of the AUeghanys and the 
Rocky Mountains^ which divide the waters of the Missouri 
and the Columbia. Between these chains stretch the vast ba^ 
sin of the Mississippi, the plains of Lousiana, and of the Tenes- 
see, and the states of Ohio, the centre of a new civilization. It 
is generally believed in America that the climate is more mild 
to the west of the Alleghany Mountains, than under the same 
parallels in the Atlantic States *. Mr Jefierson, has estimated 
the difference at 3° of latitude ; and the Okditsia monosperma^ 
the Catalpa^ and the Aristohchia Sypho^ and other vegetable 
productions, are found so many degrees farther to the north, in 
the basin of the Ohio, than on the coast of the Atlantic -[-o 
* This is true also of the Columbian Valley. See Warden’s Account of th^ 
United iitaiesy voL iii. p- 169.— Ed. 
•j- See my Essai sw la Geographic des Plantes, p. 
