Another objection to the circular theory of storms, is the uniformity of
phase. If that theory be true, we see no reason why a person should not
be sometimes on the northern side of the gale. By referring to a
diagram, we perceive that on the northern side the changes of the wind
pursue a contrary direction to what they do on the south, yet in nine
cases out of ten, each vessel meeting a hurricane will find the same
changes of wind as are due to the southern side of the storm. It is
true, that if a vessel be to the northward of a great hurricane, there
will almost certainly be a north-east gale drawn in, and this might be
set down as the outer limits of a circular storm. But when the storm
really begins, the wind comes round south-east, south, south-west,
ending at north-west, and frequently is succeeded, on the following day,
(if in middle latitude,) by a moderate breeze from the northward. Now,
if the north-east gale spoken of above, was the outer limits of an
atmospheric vortex, a vessel sailing west ought not to meet the
hurricane, as a north-east wind is indicative of being already on the
west side, or behind the storm.
Again, the characters of the winds, and appearances at the different
changes, are opposed to the circular theory. At a distance of fifty
miles from the centre of a storm, the wind which passes over a ship as a
southerly wind, will have made a rotation and a half, with the hurricane
velocity, before the same wind can again pass the ship as a northerly
wind, (supposing the progress eastward, and the ship lying to,) that is,
the same wind which in another place was a south wind two hours before,
and after only going one degree north, becomes a northerly
wind,--changed in character and temperature, as every seaman is well
aware. In a storm, if the circular theory be true, the character and
temperature should be the same, no matter from what point the wind is
blowing. This should be a conclusive argument.
Mr. Espy has also changed his ground on the storms of the United States;
he does not now contend that the winds blow inwards to a centre, but to
a line either directly or obliquely. Thus we see that while Mr. Redfield
concedes to Mr. Espy a spirally inward current, the latter also gives up
a direct current to the centre, to Mr. Redfield. This shows at least an
approximation to the truth.
It is not necessary for the support of this theory, that we should
derive any materials from the ruins of others; we shall therefore not
avail ourselves of certain discrepant results, which can be found in
many of the storms cited by Colonel Reid. With respect to Mr. Espy's
_cause_ of storms, the experiments of Regnault may be considered as
decisive of the question:--1st, because the specific heat of vapor is so
much less than Espy assumed it to be; and 2d, because the expansion of
air in a free space does not suffer any change of volume by ascending,
except what is due to diminished pressure, and the natural temperature
of that elevation.