not partaking of the
diurnal motion of the earth would appear as if it came from the
north-east. Another mass starting from the equator towards the pole in
consequence of the impetus given it, would be going faster towards the
east than the earth, and would, consequently, appear as if it came from
the south-west. This actually takes place, but in the upper regions of
the air. The same exchange takes place between the south pole and the
equator. Now, let us see what becomes of these masses. That which
started from the north pole meets in the air at about the parallel of 30
degrees; the mass which started from the equator meeting with equal
force, they balance each other, and produce a calm and an accumulation
of atmosphere pressing downward, and ejecting from below two
surface-currents--one towards the equator, which are the north-east
trade-winds; the other towards the pole, called the south-west
passage-winds. This moving mass of air, which constitutes the
north-east trade-wind, meets near the equator with another mass which
has been moving on as the south-east trade--meeting with equal force,
they form a calm; and then, warmed by the heat of the sun, they ascend,
one-half streaming off high up towards the south-east--that is, counter
to the surface-current--till it reaches the southern calm belt; another
mass coming from the south-west, where it descends, and rushes as a
north-west surface-wind towards the south pole. We have traced the mass
which started from the north pole. Reaching the southern regions, it is
whirled round till, at the pole itself, a perfect calm is produced, when
it ascends and starts off as an upper current towards the equator; but
meeting another current near the tropic of Capricorn, then descends,
one-half flowing out at the surface, as I have before described, as the
south-east trade, the other towards the south pole. This is the most
beautiful and regular system of atmospheric circulation kept up around
our globe. It has not been ascertained exactly why the masses I have
spoken of take certain directions, but we know the directions they do
take. The red dust we found off the Cape de Verds assists us in certain
degrees. We know some of the agents--the diurnal motion of the earth,
and the sun's heating rays. There are certain counteracting or
disturbing causes from which the surface-winds deviate from the courses
I have described. Some lands are covered with forests, others with
ma