ON ATMOSPHERIC WAVES. 135 
the crest, the posterior trough, w (the end of Mr. Scott Russell's water wave) ; 
the line w...h, as measured by the mercurial column, the altitude of the wave; 
the slope W a, the anterior slope or front of the wave; the slope W w, the 
posterior slope or back of the wave; w a constitutes the amplitude of the wave, 
and x x in the same direction, the axis of translation. 
The existence of atmospheric currents, especially the equatorial and polar, 
has been well-established ; and there is a class of philosophers who attribute 
the barometric oscillations entirely to the effects of these currents as con- 
tra-distinguished to the effects of waves such as we have just mentioned. In 
contemplating the transference of the barometric maxima and minima, we 
regard only the wave-motion—but very different must be the atr-motion. 
Prof. Dove, in his letter to Col. Sabine relative to the magnetical and mete- 
orological observations, has announced his opinion that the equipoise of the 
atmosphere is maintained in the temperate zone by currents on the same level 
flowing in opposite directions (Report, 1845, page 61) ; thus we have a bed or 
stratum of air moving from the S.W., and on each side of this are strata of 
N.E. winds. We may here inquire, how are these alternate aérial currents 
related to the waves before alluded to? Itis one of the objects of the following 
y Fig. 2. 
a i ain 
m— > > US SCO SS > = SS 
SW s—S> Sa Si SS 3—S> Sas evans sw 
PS DS Sei => >> . 
Vox =e le K << eK mE v 
NO =<—_—« <K* << <— << K <———_* NE 
pa SS ee eee << aa ee < 
discussion to exhibit this relation, which may be thus briefly expressed, at least 
in so far as the examination of the observations has yet extended*. Let the 
strataa a a! a’, b' b' bb, fig. 2, represent two parallel aérial currents, a a a! a! 
being from §.W. and 6! d' b b from N.E., and conceive them both to advance 
from the N.W. in the direction of the large arrow, that is the strata themselves 
will advance with a lateral motion. Now conceive the barometer to com- 
mence rising just as the edge 6 6 passes any line of country, and to continue 
rising until the edge 6! bd! arrives at that line, when the maximum is attained. 
The wind now changes and the barometer immediately begins to fall, and 
continues to fall until the edge a a coincides with the line of country on 
which 6 6 first impinged. During this process we have all the phenomena 
exhibited by an atmospheric wave ; when the edge 6 8, fig. 2, passes the line 
of country, the point a, fig. 1, of the wave (the anterior trough) transits that 
line of country and the barometer begins to rise with a N.E. wind. During 
the period the stratum J’ 6! dd, fig. 2, transits the line the anterior slope W a, 
fig. 1, passes; when the conterminous edges of the strata a’ a’ 5! 6’, fig. 2, 
pass, the crest W, fig. 1, extends in the direction of the preceding trough: 
the barometer now begins to fall, and when the edge a a, fig. 2, occupies the 
place of 4 6, also fig. 2, the descent of the mercurial column is completed ; the 
* For this knowledge I am indebted to Mr. Brown’s plates. 
