everything in the vegetable kingdom was
parched and dry, and consequently in a fit
condition for being carried aloft and whirled
through the upper realms of air on the wings
of the wind.

If we examine the seasons of the various
parts of the great South American continent,
we shall find that the tract of country which
suffers most severely from the tropical drought
at the period of the vernal equinox is the
valley of the lower Oronoco; which is then
parched and burnt with intense heat. Its
pools are dry, its marshes and plains arid;
all vegetation has ceased; the great reptiles
have buried themselves deep in the
sands; the hum of insect hfe is hushed,
and the stillness of death reigns through the
valley.

In the autumnal equinox we find a similar
state of things in the upper Oronoco and the
great Amazonian basin. It is precisely at
these times that all vegetable matter is in
the fittest, impalpable, and feather-light
condition for being lifted up and carried
away, and it is precisely at such periods of
the year that these regions are visited by
terrific gales, whirlwinds, and tornadoes;
which, sweeping over their lifeless, death-like
plains and basins, raise up vast clouds of
microscopic organisms and bear them away
with lightning speed to be rained down in
remote countries, chroniclers of the great
wind-roads of the world.

It is quite evident from what has been here
stated, that for these "organisms" to be
carried from south-west to northeast,
immediately opposite to the course of the
prevailing surface winds of those regions, there
must be other upper currents performing
this work. This is the case, and in stating
it to be so, we arrive at a solution of the
whole secret mechanism of the atmosphere:
we learn how it is that "the wind goeth
towards the south, and turneth about unto
the north."

We on shore find the wind frequently
veering about from point to point of the
compass, often blowing in opposite directions
during a few hours. Not unfrequently we
are visited with strong gales of wind, lasting
for a day or more, and then followed by
heavy falls of rain and calms. Yet such winds,
in comparison with the general system of
atmospheric circulation, are but eddies of the
main current. They have no more effect
in deranging or disturbing that system than
the showers which they bring with them have
in altering the course of the Gulf stream or
other ocean currents.

Let us see, then, what this general
atmospheric system is. On either side of the
equator, commencing at a distance of some few
degrees from it, we find a zone of perpetual
winds extending to about thirty degrees north
and south. These blow constantly in similar
directions as steadily and perpetually as the
tides of the Thames flow and ebb, and are
called from the directions whence they come the
north-east and south-cast trades. These winds
are constantly travelling from the poles, north
and south, to the equator. Their spiral or
curved motion is accounted for by the rotation
of the earth on its axis from west to east. If,
using the language of Lieutenant Maury,
we imagine a particle of atmosphere at the
north pole, where it is at rest, to be put in
motion in a straight line towards the equator,
we can easily see how this particle of air
coming from the pole, where it did not partake
of the diurnal motion of the earth, would,
in consequence of its vis inertia, find, as it
travels south, the earth slipping under it, as
it were, from west to east, and thus it would
appear to be coming from the north-east, and
going towards the south-west: in other words,
it would be a north-east wind. A similar
course is followed by the wind coming from
the south pole towards the equator. Now
as these two winds are known to be
perpetually flowing from the poles, it is quite safe
for us to assume that the air which they
keep in motion must return by some channels
to their former places at the poles, otherwise
these winds would soon exhaust the
polar regions of their atmosphere, and
piling it up, so to speak, about the equator,
would cease to blow for the want of a fresh
supply of air.

Looking at it in this light it has been
assumed, and proved almost to a certainty,
that there exist far above these trade-winds
other and counter currents of air returning
to the poles as rapidly as they are flying from
it. In short that above the south-east trade
there is a north-west wind, and above the
north-east trade a south-west wind perpetually
blowing. We have already told how
Nature has so wonderfully and beautifully
placed tallies on the wings of the latter, by
means of the microscopic infusoria raised from
the Oronoco and Amazon valleys, and doubtless
this first outlining of the new Air Map
will, in due course, be filled up in other parts
of the world by certain indications of the
true course of the upper strata of air
returning towards the south pole.

Believing that these phenomena are those
actually in operation, we will endeavour
to show more in detail the course of the
"wind roads" of the world, and to do so by
again making use of Lieutenant Maury's
illustration of a single particle or atom of air, as
representing the entire volume.

We will start from the north pole, in
company with our fellow atom, and here
we find by some agency not yet understood
that we are travelling southwards in
the upper regions of the atmosphere, and
not along the surface of the world, until we
reach about the parallel of thirty north
latitude, in the vicinity of the Canary Islands.
Here we meet with a similar supposed
particle, travelling also in the upper
atmosphere the return journey towards the pole.