128 | REPORT—1845. 
Tas_e XV. Exhibiting the Order of Succession of the Crests. 
1842. ; 
Noy. 6:21 | Crest of A} about entering on the area at Glasgow. 
a eek A© entered on the area at Bardsey, South Bishop, Scilly. 
yoo " B} entering on the area at Scilly. 
» 9:15 77 Bo extending from Dublin to Geneva. 
» 10:2 5 A’ entered on the area between Dublin and Bardsey. 
Should A? be found to be the succeeding wave to A!, the above Table indi- 
cates an interval of 3 days 5 hours (about) between these two successive crests. 
Thealtitudes are very different in consequence of the large posterior slope of A°. 
At the commencement of this investigation, it was stated that the only ef- 
ficient test that can be brought to bear on the theory that the non-periodic 
oscillations of the barometer are due to waves, appears to be the comparison 
of barometric observations reduced to the level of the sea. This view appears 
to be supported as far as the investigation has yet proceeded. It is cha- 
racteristic of waves that different systems pass onward without destroying 
each other ; each wave of each system pursues its own path, although crossed 
by others; and it can be followed in all its individuality. In the course of 
this inquiry three systems of waves have been detected, or at least three 
barometric maxima; these maxima have been found to move across the area 
in three different directions, having on each side a diminution of pressure. The 
progress of each of these maxima appears to have been quite independent of 
the others: thus at the opening of the observations, the line of greatest 
diminution of pressure on the English area was from Glasgow to St. Cathe- 
rine’s Point ; at alater period the observations indicated the direction of max- 
ima at right angles to this line, and that a line cutting this transversely passed 
through Geneva and Brussels; it is in this latter direction that the wave 
was considered to have been moving. The barometric phenomena in this 
direction progressed very slowly. While these movements were proceeding 
over the area, the barometric differences between Scilly and Longstone in- 
creased ; and the latter station exhibited a much less pressure than the former ; 
at length a decided line of maximum pressure is traced from Dublin to Ge- 
neva, after which the barometric affections at the stations are reversed, Scilly 
being the lowest and Longstone the highest. We have therefore a cause simul- 
taneously operating on the barometer with that which produced the move- 
ments from Glasgow to St. Catherine’s Point, and from Brussels to Geneva, - 
but evidently distinct, as the phenomena progressed in a different direction, 
namely from Scilly to Longstone. During the period that these two distinct 
but contemporaneous causes are in operation, producing certain barometric - 
phzenomena in certain directions, and from the last of which we should expect 
at certain stations, Scilly and Longstone, for instance, a rising barometer, we 
actually find it falling rapidly, but not without exhibiting the same phzno- 
mena that we apprehend characterizes this fall as resulting from a wave.. A 
decided line of maxima is observed; and in the same line, at a subsequent 
period, we find a line of minima; we can therefore, as previously remarked, 
trace each of these distinct sets of barometric phenomena in their own pe- 
culiar directions. It is however the reduction of the observations to the level 
of the sea that alone enables us to do this. The rise and fall at any one 
station, as exhibited by the curves (times being used as abscisse), give us 
the combined effects of the three systems, and unless they are carefully sepa- 
rated, as we have endeavoured to do in the preceding investigation, and which 
can only be done by taking the distance of the stations into account, we are 
perplexed with the apparent irregularity and capriciousness of the atmo- 
spheric changes. a 
