267 
and the Distf'ihution of Heat over the Globe. 
earth’s orbit, than of the unequal division of the continents, de- 
termines * the limit between the N. E. and S* E. Trade Winds. 
But as this limit is much more to the north of the Equator in 
the Atlantic Ocean, than in the South Sea, we may conclude 
that, in a region between 130® and 150® of W. Long, the dif- 
ference of temperature between the two hemispheres, is less great 
than farther to the east in 20® or 50® of longitude. It is in- 
deed under this region in the Great Ocean, that, as far as the 
parallel of 60°, the two hemispheres are equally covered with 
water, and equally destitute of dry land, which, radiating the 
heat during summer, sends the warm air towards the poles. The 
line which limits the N. E. and S. E. Trade Winds, approaches 
the Equator, whereas the temperature of the hemispheres is dif- 
ferent ; and if, without diminishing the cold of the southern at- 
mosphere, we could increase the inflexion of the isothermal lines 
in the system of transatlantic climates, we should meet the S, E. 
winds in 20® and 50° of W. Long, to the north, and in 130® 
and 150® of W. Long, to the south of the Equator 
The low strata of the atmosphere which rest upon the aque- 
ous surface of the globe, receive the influence of the tempera- 
ture of the waters. The sea radiates less absolute heat than 
continents ; it cools the air upon the sea, by the effect of eva- 
poration ; it sends the particles of water cooled andlieavier to- 
wards the bottom ; and it is heated again, or cooled, by the cur- 
rents directed from the Equator to the Poles, or by the mixture 
of the superior and inferior strata on the sides of banks. 
It is from these causes combined, that, between the tropics, 
and perhaps as far as SO® of Lat., the mean temperatures of the 
air next the sea, are 3®. 6 or 5^.4 lower than that of the conti- 
nental air. Under high latitudes, and in climates where the 
atmosphere is coolest in winter, much below the freezing point, 
the isothermal lines rise again towards tlje Poles, or become 
convex when the continents pass below the seas 
With respect to the temperature of the ocean, we must dis- 
tinguish between four very different phenomena. The tern- 
• Prevost, Journ. de Phys. tom. xxxviii. p. 369.— Irish T’J'ans. vol. viii, p. 
Humboldt’s lidai. Histor. tom. i, p. 325, 237. Id. p. 67, 230. 2i2. 
