Theory of Marine Currents. 165 
eally a view of all the movements of the different seas. The 
influence of the trade-winds, which, between the tropics, have 
the tendency to carry the sea towards the west, and that of 
the north and south counter currents of the trade-winds, 
which tend, on the contrary, to convey the extratropical seas 
towards the east, must be added to the predominating influ- 
ences of the forces which arise from the displacement of the 
liquid masses of the equator towards the poles, and recipro- 
cally. This direction of these regular winds must likewise 
cool the eastern sides of continents in the mean latitudes, 
and, on the contrary, warm the western sides; for the west 
winds, which prevail in these regions, carry far from land the 
heated air of the warm seas which lie along the eastern coasts ; 
while in the same latitudes, they convey this warm air along 
the western coasts. 
Without attempting here to follow all the consequences of 
these movements in the seas, we cannot avoid noticing the 
important result that may be deduced relatively to the excess 
of temperature prevailing in the northern compared with the 
southern hemisphere. We have only to cast our eyes on M. 
Duperrey’s chart to perceive that the mass of tropical waters 
conveyed towards the north by the two northern circuits of 
the Atlantic and Pacific Oceans, is much more considerable 
than that which the three other circuits convey towards the 
south, and that the advance in latitude of these three last 
circuits is at the same time much less. The eastern point 
of South America, and the eastern point of New Holland, 
which partake of the tropical waters of the Atlantic and 
Pacific Oceans, are situated geographically in such a manner 
as to determine the caloriferous circuits altogether in favour 
of the northern hemisphere. 
The following is a synoptical view of what has been 
stated :— 
1st, The waters of intertropical regions, dilated by the 
heat, rise above the level of the extratropical waters, and 
_ pour themselves on the top of the latter, conveying to them 
an excess of quickness towards the east, which produces, in 
these extratropical regions, a current from the west to the 
east; while, by a contrary effect, the waters which are con- 
