But this partially-cooled air falls on a part of the earth's surface which is moving much more slowly towards the east, in its diurnal rotation, than the air which has descended upon it, and which is still impressed with a great proportion of its eastern velocity due to the equatorial parallels of latitude, where it was heated and raised up.

The necessary consequence of this is, to produce a rapid motion in the air from the west over the earth's surface; and this, combined with the other motion of the same portion of air, or that which has driven it from the equatorial regions, produces this remarkable prevalence of south-westerly winds in the northern hemisphere, and north-westerly winds in the southern hemisphere, in those districts lying between the latitudes of 30 deg.

and 60 deg..
In all that has been said above it has been assumed that the quickest-moving or equatorial belt of the earth is also the hottest, and consequently that over which the air has the greatest tendency to rise.

But, although this is generally true, it is not, by any means, universally so.

The variations, however, which are observed to occur in those places where the circumstances form an exception to the general rule, tend strongly to confirm the theory of Hadley.