138 REPORT—1846. 
distribution of pressure of a wave form gradually rising on each side the 
trough, the pressure being dependent on the velocity of the parallel currents, 
The constant ascent of air at the point of rarefaction would continually 
draw off a quantity of air from the S.E. side of the line of greatest velocity 
6 —2, fig. 3, and this would be attended with two results ; first, there would 
be a veal hollow or trough formed in the line of junction of the parallel cur- 
rents ; and secondly, this line would gradually advance towards the S.E.; for 
as more air would be drawn off from that side, the whole body of air would 
advance in that direction to supply the deficiency ; and should the rarefying 
process cease, we can readily conceive that not only will the wave-form be 
continued, but also wave-motion. The establishment of the parallel currents 
will give the air-motion ; the diminution of pressure towards the lines of 
greatest velocity will give the wave-form ; and the drawing-off of air from 
the S.E. will induce the wave-motion. The wave thus generated is negative ; 
it consists of a hollow produced by the ascending current of heated air 
carrying off a considerable portion of air set in motion by this ascending 
column, and its direction of motion is determined by more air being drawn 
off from the S.E. slope than the N.W. a 
It might be expected that as the trough passed, a motion of the air or 
wind from the N.W. (the body of air moving from that. quarter to supply 
the constant drain in feeding the ascending current) would be observed; but 
so strong must the parallel currents be which give rise to the wave, that 
such motion would doubtless be concealed by them. 
The barometric and anemonal phenomena would present very regular 
phases, provided there was only one system of waves, one set of parallel and 
opposite currents constantly passing from N.W. to S.E. I have however in 
former reports shown that different systems have contemporaneously traversed 
the area over which the observations have extended, and the discussion of 
Mr. Brown’s observations has clearly brought to light a set of parallel and 
opposite currents at right angles to those we have just been contemplating, 
namely, from N.W. and S.E. with a wave-motion towards the N.E., pro- 
ducing the cross waves which occasion the complexity before alluded to. 
The late Professor Daniell has remarked that the curves increase in range 
towards the N.W., and in general the neighbourhood of water presents 
curves remarkable for the boldness of their contour and the large extent of 
their range. In venturing a speculation on these cross waves from the S.W. 
with parallel and opposite currents from N.W.and S.E., I should be inclined 
to attribute them to the effect of the solar influence on the terrestrial sur- 
face, extending from Cape Verd in Africa to the extreme north of Lapland 
in Europe. This surface extends from S.W. to N.E., or somewhat in that 
direction. It may be remarked, that to the north-east of Cape Verd is situ- 
ated the Sahara or Great Desert of Africa, and here we have a great rarefy- 
ing surface. To the north-west or west-north-west of this extensive rarefy- 
ing surface, the broadest part of the Atlantic ocean is situated. The relative 
positions of the Great Desert and the broadest extent of the Atlantic will. 
produce a great indraught of cool air from the ocean ; the direction of this 
wind will be W.N.W. or N.W. To the north-east of this current, probably 
in the neighbourhood of Morocco, Fez, Algiers, Spain and Portugal, and 
the north-west portions of the Mediterranean sea, we ought to find the 
counter current from the S.E. or E.S.E., the two portions in juxtaposition 
moving with the greatest velocity. Somewhere in the Atlantic the turning- 
point of these oppositely directed currents should exist. The line of junc- 
tion of these parallel currents will determine the trough of the wave, and as 
before shown, in consequence of the air being drawn off from the north-east — 
to supply the ascending current, the wave will progress towards that quarter; ~ 
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