relative to the Earth's Surface. 45 
IV. The Motions of the Ocean. 
action of the atmosphere upon the surface of the ocean, and the 
other, the difference of density between the water near the equa- 
tor and that towards the poles, arising from a difference of tem- 
perature. ‘The general motions of the atmosphere at the surface 
of the ocean have a tendency to cause a westward motion of the 
water in the torrid zone, and an eastward motion in the middle 
and higher latitudes; and from what we know of the effects of 
strong winds upon the ocean, we have reason to think that these 
general motions of the atmosphere are adequate to produce sensv- 
ble motions, since, after thetinertia of the water is once overcome, 
which, however small the force, is only a question of time, the 
only force necessary is that which is adequate to overcome the 
resistance of friction, which is very small where the velocity is 
small. The difference of density between the equator and the 
poles causes a slight interchanging motion of the water between 
them, and consequently, where not interrupted by continents, it 
in the 
produces a system of motions in the ocean similar to those of 
the atmosphere. Hence these two causes of oceanic disturbance, 
whatever their relative weight, both act in the same directions, 
and conjointly cause the observed westward motion of the ocean 
near the equator, and eastward motion towards the poles. 
39. The westward motion of the water of the ocean in the 
torrid zone was first observed by Columbus, and is now well 
