The Hurricane Guide | Page 3

semicircle. In the
higher latitudes a ship taking the storm at E.N.E. will be in the
left-hand semicircle, and the hurricane will pass off at N.N.E. These
changes are rendered very apparent by moving the hurricane circle in
the direction in which the storm is expected to proceed.
Fig. 2 represents the whirl and hurricane winds in the south.
[Illustration: Fig. 2]
CHAPTER II.
PHÆNOMENA OF ATMOSPHERIC WAVES.

Professor Dove of Berlin has suggested that in the temperate zones the
compensating currents of the atmosphere necessary to preserve its
equilibrium may be arranged as parallel currents on the surface, and not
superposed as in or near the torrid zone. His views may be thus
enunciated:--That in the parallels of central Europe the N.E. current
flowing towards the equator to feed the ascending column of heated air
is not compensated by a current in the upper regions of the atmosphere
flowing from the S.W. as in the border of the torrid zone, but there are
also S.W. currents on each side the N.E., which to the various countries
over which they pass appear as surface-winds, the winds in fact being
disposed in alternate beds or layers, S.W., N.E., as in fig. 3.
[Illustration: Fig. 3.]
The Professor also suggests that these parallel and oppositely directed
winds are shifting, i. e. they gradually change their position with a
lateral motion in the direction of the large arrow cutting them
transversely.
In the course of the author's researches on atmospheric waves he had an
opportunity of testing the correctness of Professor Dove's suggestion,
and in addition ascertained that there existed another set of oppositely
directed winds at right angles to those supposed to exist by the
Professor. These currents were N.W. and S.E. with a lateral motion
towards the N.E. He also carefully discussed the barometric
phænomena with relation to both these sets of currents, and arrived at
the following conclusions. The details will be found in the author's
third report, presented to the British Association for the Advancement
of Science (Reports, 1846, pp. 132 to 162). During the period under
examination the author found the barometer generally to rise with N.E.
and N.W. winds, and fall with S.W. and S.E. winds, and that the
phænomena might be thus illustrated:--Let the strata a a a' a', b' b' b b,
fig. 3, represent two parallel aërial currents or winds, a a a' a' from
S.W. or S.E., and b' b' b b from N.E. or N.W. and conceive them both
to advance from the N.W. in the first instance and from the S.W. in the
second, in the direction of the large arrow. Now conceive the barometer
to commence rising just as the edge b b passes any line of country, and

to continue rising until the edge b' b' arrives at that line, when the
maximum is attained. It will be remarked that this rise is coincident
with a N.E. or N.W. wind. The wind now changes and the barometer
begins to fall, and continues falling until the edge a a coincides with
the line of country on which b b first impinged. During this process we
have all the phænomena exhibited by an atmospheric wave: when the
edge b b passes a line of country the barometer is at a minimum, and
this minimum has been termed the anterior trough. During the period
the stratum b' b' b b transits, the barometer rises, and this rise has been
called the anterior slope. When the conterminous edges of the strata a'
a' b' b' pass, a barometric maximum extends along the line of country
formerly occupied by the anterior trough, and this maximum has been
designated the crest. During the transit of the stratum a' a' a a the
barometer falls, and this fall has been characterised as the posterior
slope; and when the edge a a occupies the place of b b, the descent of
the mercurial column is completed, another minimum extends in the
direction of the former, and this minimum has been termed the
posterior trough.
It will be readily seen that the lateral passage of the N.W. and S.E.
currents towards the N.E. presents precisely the same barometric and
anemonal phænomena as the rotatory storms when moving in the same
direction. If the observer, when the barometer is at a maximum with a
N.W. wind, place himself in the same position with regard to the
laterally advancing current as he did with regard to the advancing storm,
i. e. with his face towards the quarter from which it is advancing--S.W.,
he will find that with a falling barometer and S.E. wind the current
passes him from the left to the right hand; but if at a barometric
minimum he place himself in the same position with his face directed to