rn velocity than those parts of the earth which form the southern
shores of Mexico, a westerly wind must be produced by the relative
difference in these two motions. At that particular season of the year
when the sun is in high southern declination, Mexico is not exposed to
his perpendicular rays. The equatorial regions are then more heated
than Mexico, and accordingly we actually find north-easterly breezes
nearly as they would be if Mexico were out of the way, and quite in
accordance with our theory.

In like manner, in the Atlantic, when the sun is far to the north,
the great deserts of the western angle, or shoulder of Africa, become
as vehemently heated, or more so, perhaps, than Mexico, and this draws
the air from the equator, so as to produce the south-westerly winds I
have already spoken of in the troublesome range called the Variables.

Finally, the great monsoons of the Indian ocean and China sea
contribute to establish this theory of Hadley, though I am not aware
that he ever brought it to bear on these very interesting phenomena.
They are eminently deserving of such notice, however, from being
periodical Trade-winds of the highest order of utility in one of the
busiest commercial regions of the world. Their periodical or shifting
character is the circumstance upon which their extensive utility in a
great measure depends, amongst nations where the complicated science
of navigation is but in a rude state. Myriads of vessels sail from
their homes during one monsoon before the wind, or so nearly before
it, that there is no great skill required in reaching all the ports at
which they wish to touch; and when the wind shifts to the opposite
quarter, they steer back again, in like manner, with a flowing sheet.
Thus, with an exceedingly small portion of nautical skill, they
contrive to make their passages by means of what we blue-jackets call
"a soldier's wind, there and back again." It will sometimes happen
that these rude navigators miscalculate their time, or meet with
accidents to retard them till the period of change has gone past, and
then they have no resource but to wait for half-a-year till the
monsoon shifts.

Experienced sailors, in like circumstances, acquainted with the
varieties of winds prevailing in those seas, would speedily get their
vessels out of this scrape, into which the lubberly Chinese junks
sometimes fall. They might, and certainly would, lose time in making a
roundabout of some two or th