162 Theory of Marine Currents. 
north, while the three others convey the tropical waters to 
the south. 
It is a common notion, that the quickness of rotation to- 
wards the east of a mass situate at the surface of the earth, 
is so much greater in proportion as this mass is situate nearer 
the equator; so that a mass of whatsoever kind transported 
towards the poles, maintains in its passage an excess of 
quickness towards the east, while a mass conveyed towards 
the equator, on leaving the medium latitudes, and having 
only a smaller rapidity towards the east, is precisely in the 
same condition as if it had a movement towards the west, in 
virtue of the quantity with which it has been advanced to- 
wards the east by the more southern masses in the midst of 
which it is transported. 
According to this view, if we consider what happens with 
the warm superficial waters diffused over those of mean 
latitudes, in the northern basin of the Atlantic, for example, 
it is evident that these tropical waters, preserving a greater 
quickness towards the east than the quickness towards the 
east of the waters which occupy mean latitudes, must not 
only advance towards the north, but also towards the east. 
Of this nature is the phenomenon presented by the upper 
part of the great circuit of which the Gulf Stream forms 
apart. A contrary movement, that is to say, towards the 
south and west, would be taken by the waters which flow to- 
wards the equator on leaving the mean Jatitudes to replace 
the preceding ; for their movement, being less considerable 
towards the east, will produce a real transport towards the 
west. Such, indeed, isthe direction of the ocean’s movement 
in the equatorial part of the great circuit, which, after its 
waters have travelled from the west to the east by the mean 
latitudes, turns towards the south in the latitudes of Europe 
and Africa, again to repair to the coast of tropical America, 
by crossing the Atlantic at its greatest breadth. If we keep 
in mind that a very small difference in latitude produces very 
ereat differences of quickness towards the east or west, we 
will perceive that it is more especially towards the limits of 
the circuit that the movements must be most perceptible. 
If we observe the motion of water in a vessel heated on the 
