32 THE PHYSICAL GEOGRAPHY OF THE SEA. 
and that every source of heat and cause of radiation be removed, 
so that its fluid temperature becomes constant and uniform through- 
out. On such a globe, the equihbrium remaining undisturbed, 
there w^ould be neither v^^md nor current. 
20. Let us now suppose that all the water within the tropics, 
to the depth of one hundred fathoms, suddenly becomes oil. The 
aqueous equilibrium of the planet is thereby disturbed, and a gen- 
eral system of currents and counter currents is immediately com- 
menced — the oil, in an unbroken sheet on the surface, running to- 
ward the poles, and the water, in an under current, toward the 
equator. The oil is supposed, as it reaches the polar basin, to be 
reconverted into water, and the water to become oil as it crosses 
Cancer and Capricorn, rising to the surface and returning as before. 
21. Thus, without wind, we should have a perpetual and uni- 
form system of tropical and polar currents. In consequence of 
diurnal rotation of the planet on its axisj each particle of oil, were 
resistance small, would approach the poles on a spiral turning to 
the east, with a relative velocity greater and greater, until, finally, 
it would reach the pole and whirl about it at the rate of nearly a 
thousand miles the hour. Becoming water and losing its velocity, 
it would approach the tropics by a similar, but inverted spiral, 
turning toward the west. Owing to the principle here alluded to, 
all currents from the equator to the poles should have an eastward 
tendency, and all from the poles toward the equator a westward, 
212. Let us now suppose the solid nucleus of this hypothetical 
globe to assume the exact form' and shape of the bottom of our 
seas, and iix all respects, as to figure and size, to represent the 
shoals and islands of the sea, as well as the coast lines and con- 
tinents of the earth. The uniform system of currents just de- 
scribed would now be interrupted by obstructions and local causes 
of various kinds, such as unequal depth of water, contour of shore- 
lines, &c. ; and we should have at certain places currents greater 
in volume and velocity than at others. But still there would be 
a system of currents and counter currents to and from either pole 
and the equator., Now do not the cold waters of the north, and 
the warm waters of the Gulf, made specifically lighter by tropical 
heat, which we see actually preserving such a system of counter 
currents, hold, at least in some degree, the relation of the sup- 
posed water and oil 1 
