THE GULF STREAM. 33 



the trade-winds are not adequate to the effect ascribed. More- 

 over, the top of the Gulf Stream runs on a level with the ocean, 

 therefore we knoio it is not a descending current. 



19. When facts are wanting, it often happens that hypothesis 

 will serve, in their stead, the purposes of illustration. Let us, 

 therefore, suppose a globe of the earth's size, having a solid nu- 

 cleus, and covered all over with water two hundred fathoms deep, 

 and that every source of heat and cause of radiation be removed, 

 so that its fluid temperature becomes constant and uniform 

 throughout. On such a globe, the equilibrium remaining undis- 

 tui'bed, there would be neither wind 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 would thereby be disturbed, 

 and a general system of currents and counter currents would be 

 immediately commenced — the oil, in an unbroken sheet on the 

 surface, running toward the poles, and the water, in an under cur- 

 rent, toward the equator. The oil is supposed, as it reaches the 

 polar basin, to be reconverted into water, and the water to be- 

 come oil as it crosses Cancer and Capricorn, rising to the surface 

 in the intertropical regions 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 axis, 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. 



22. 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 in 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- 



