Phenomena 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
< r /> 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.







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 the quarter from which the N.W. current is advancing

laterally, also S.W., he will find that with a rising barometer _and

N.W. wind the current passes him from right to left_. Now the two

classes of phænomena are identical, and it would not be difficult to

show that, had we an instance of a rotatory storm in the northern

hemisphere moving from N.W. to S.E., it would present precisely the same

phænomena as to the direction of currents passing from left to right and

from right to left with falling and rising barometers, increase and

decrease in the force of the wind, &c., as the oppositely directed

aërial currents do which pass over western central Europe.



In the absence of direct evidence of the production of a revolving storm

from the crossing of two large waves, as suggested by Sir John Herschel,

although it is not difficult to obtain such evidence, especially from

the surface of the ocean, the identity of the two classes of phænomena

exhibited by the storms and waves as above explained amounts to a strong

presumption that there is a close connexion between them, and that a

more minute investigation of the phænomena of atmospheric waves is

greatly calculated to throw considerable light on the laws that govern

the storm paths in both hemispheres. The localities in which these

atmospheric movements, the waves, have been hitherto studied, have been

confined to the northern and central parts of Europe--the west of

Ireland, Alten in the north of Europe, Lougan near the Sea of Azov, and

Geneva, being the angular points of the included area. It will be

remarked that the greatest portion of this area is _inland_, but there

is one important feature which the study of the barometer has brought to

light, and which is by no means devoid of significance, viz. that the

oscillations are much greater in the neighbourhood of _water_, and this

appears to indicate that the junction lines of land and water form by

far the most important portions of the globe in which to study both the

phænomena of storms and waves. It is also very desirable that our

knowledge of these phænomena should, with immediate reference to the

surface of the ocean, be increased, and in this respect captains and

masters of vessels may render essential service by observing and

recording the state of the barometer, and direction and force of the

wind, several times in the course of the day and night;[3] and when it

is considered that the immediate object in view is one in which the

mariner is personally interested, and one in which, it may be, his own

safety is concerned, it is hoped that the keeping of a meteorological

register having especial reference to the indications of the barometer,

and force and direction of the wind, will not be felt as irksome, but

rather will be found an interesting occupation, the instruments standing

in the place of faithful monitors, directing when and where to avoid

danger, and the record furnishing important data whereby the knowledge

of general laws may be arrived at, having an essential bearing on the

interests of the service at large.