In accordance with our theory, the direction and force of the wind in a
storm are due to ascending columns of air, supplied from the upper
portion of the atmospheric stratum beneath the clouds. The commotion
begins at the highest limits of the cirri, and even at greater
elevations. Hence, the hazy appearance of the sky is a legitimate
precursor of the coming gale. As a general thing, the wind will blow (at
the surface) towards the centre of greatest commotion, but it is too
dependent on the ever-varying position and power of temporary nuclei of
disturbance, to be long steady, except when the disturbance is so remote
that its different centres of induction are, as it were, merged into one
common focus. When a vortex is descending, or passing from north to
south, and withal very energetic at the time, the southerly wind (which
may always be considered the principal wind of the storm in this
hemisphere) may blow steadily towards the vortex for three or even four
days. When a vortex is ascending, the induced northerly current will be
comparatively moderate, and be frequently checked by the southerly wind
overblowing the storm, and arriving the day before the vortex which
produced it.
The important point for the navigator, is to know the time of meridian
passage of the vortex, and its latitude at the time of the passage, and
then be guided by the indications of the weather and the state of
barometer. If it commences storming the day before the passage, he may
expect it much worse soon after the passage; and again, if the weather
looks bad when no vortex is near, he may have a steady gale setting
towards a storm, but no storm until the arrival of a vortex. Again, if
the barometer is low the day before the vortex passes, there may be high
barometer to the west, and the passage be attended by no great
commotion, as it requires time for the storm to mature, and consequently
its greatest violence will be to the east. If at the ship the barometer
is high, the vortex may still produce a storm on a line of low barometer
to the west, and this line may reach the ship at the time of the
passage. In tropical climates the trouble must be looked for to the
eastward; as a storm, once excited, will travel westward with that
stratum of atmosphere in which the great mass of vapor is lodged, and in
which, of course, the greatest derangement of electric tension is
produced.
It will now be seen that we do not admit, with Col. Reid, that a storm
continues in existence for a week together. Suppose a hurricane to
originate in the Antilles at the southern limits of a vortex, the
hurricane would die away, according to our theory, if the vortex did not
come round again and take up the same nucleus of disturbance. On the
third day the vortex is found still further north, and the apparent path
of the hurricane becomes more curved. In latitude 30d the vortex passes
over 3d or 5d of latitude in a day; and here being the latitude where
the lower atmospheric current changes its course, the storm passes due
north, and afterwards north-east. Now, each day of the series there is a
distinct hurricane, (caused by an increase of energy in a particular
vortex, as we have before hinted,) each one overlapping on the remains
of the preceding; but in each the same changes of the wind are gone
through, and the same general features preserved, as if it were truly a
progressive whirlwind, except that each vessel has the violent part of
it, as if she was in the southern half of the whirl. The apparent
regularity of the Atlantic storms in direction, as exhibited by Col.
Reid, are owing in a great degree to the course of the Gulf Stream, in
which a vortex, in its successive passages in different latitudes, finds
more favorable conditions for the development of its power, than in
other parts of the same ocean; thus showing the importance of regarding
the established character of storms in each locality, as determined by
observation. In this connection, also, we may remark, that the meridians
of greatest magnetic intensity are, _ceteris paribus_, also the
meridians of greatest atmospheric commotion. The discovery of this fact
is due to Capt. Sabine. The cause is explained by the theory.
As it is the author's intention to embody the practical application of
this theory to navigation, with the necessary rules and tables, in a
separate work, sufficient has been said to familiarize the reader with
the general idea of a cause external to the earth, as the active motor
in all atmospheric phenomena. We will therefore only allude in a general
way to the principal distinguishing feature of the theory. We say, then,
that the wind in a storm is not in rotation, and it is a dangerous
doctrine to teach the navigator. We also assert as distinctly, that the
wind _in_ a storm does not blow from all sides towards the centre, which
is just as dangerous to believe. If it were wise to pin our faith to any
Procrustean formula, we might endorse the following propositions: That
at the beginning of a storm the wind is from the equator towards the
poles in every part of the storm; that, at a later date, another current
(really a polar current deflected by convection) sets in at right angles
to the first one; and that at the end of the storm there is only _one_
wind blowing at right angles to the direction at the beginning. Outside
the storm, considered as a hundred, or two or three hundred miles in
diameter, there is, under certain limitations, a surface wind setting
towards the general focus of motion and condensation, and this surface
wind will be strongest from the westward, on account of the motion of
the whole atmosphere in which these other motions are performed being to
the eastward.[9] The whole phenomenon is electrical or magnetic, or
electro-magnetic or ethereal, whichever name pleases best. The vortex,
by its action, causes a current of induction below, from the equator, as
may be understood by inspecting Fig. 2, which in the northern hemisphere
brings in a southerly current by convection: the regular circular
current, however, finally penetrates below, as soon as the process of
induction has ceased; and thus the polar current of the atmosphere at
last overcomes the equatorial current in a furious squall, which ceases
by degrees, and the equilibrium is restored.
Every locality will have its peculiar features; in each, the prevailing
wind will be at right angles to the magnetic meridian, and the progress
of the storm will tend to follow the magnetic parallel, which is one
reason why the Atlantic and Indian Ocean storms have been mistaken for
progressive whirlwinds. When these views are developed in full, the
mariner can pretty certainly decide his position in the storm, the
direction of its progress, and its probable duration.