rived 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
phaenomena might be thus illustrated:--Let the strata _a a a' a', b' b' b
b_, fig. 3, represent two parallel aerial 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 phaenomena 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 phaenomena 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