ON ATMOSPHERIC WAVES. 131 
wich, Haisboro and Heligoland, but it increases in value as we approach 
the N.E. Now this state of things would result from a large wave passing 
from W.S.W., the posterior slope from Heligoland to Scilly. The readings 
for contemporaneous epochs at each E.N.E. station would be higher, and the 
fall greater. Taking the Helstone curve as the type of greatest symmetry— 
consisting in the equality of the three depressions above named, and the whole 
of the readings being above these depressions,—we have St. Catherine’s 
Point and Portsmouth slightly departing from this symmetry, in the move- 
ments from the 7th to the 11th being thrown higher than those at Scilly and 
Helstone. 
The curves in which we have traced the increase of the fall from the 7th 
to the 11th, exhibit a much greater departure from symmetry, in the depres- 
sion of the 19th being lower than that of the 11th; and this difference in- 
creases in the order in which the curves are arranged, viz. London, Yarmouth, 
Haisboro, and Heligoland ; and so great is this difference in the last three 
curves, that when combined with the fall from the 7th to the 11th, the baro- 
metric movements (abstracting the secondary waves) are of a downward 
character, that is, from the 7th to the 19th at these stations the tendency in 
the mercurial column is to fall very slowly and gently. At Scilly, Helstone, 
Portsmouth and the Isle of Wight, this tendency to fall did not exist. 
Birmingham offers a striking difference from the last-named curves; the 
departure from symmetry is more apparent, but the downward movement is 
confined to the period between the depressions of the 11th and 19th. On 
this hand the Birmingham curve is connected with the south-eastern group, 
and clearly shows that the symmetry is greatly departed from to the N.E. of 
Scilly and Helstone. On the other hand, it is connected with the Scilly and 
Helstone curves by the movements of the 7th to the 11th, with aslighter de- 
velopment of the two anterior waves; if there is any difference, there is a 
slight rise from the 7th to the 11th. 
Stokesley in Yorkshire presents features nearly approaching Birmingham, 
with a greater departure from symmetry, more especially in the depression of 
the 19th, which is deeper. 
Belfast in Ireland exhibits the same departure from symmetry, in the de- 
pression of the 19th being thrown considerably below that of the 11th; but 
there is in this curve a certain return to a symmetrical arrangement of a 
somewhat different character to that exhibited by the curves of Scilly and 
Helstone; this consists in a most decided rise from the depression of the 7th 
_ to that of the 11th: the depressions of the 7th and 19th are thus brought 
_ Hhearer to an equality. In these respects (especially the latter) the curves of 
| Belfast and Galway strikingly agree, and offer a decided contrast to the south- 
_ eastern group, which exhibits a fall to the depression of the 11th. 
We thus have the area included by the angular points, Scilly, St. Catherine’s 
Point, Heligoland, Belfast and Galway, parcelled out into three barometric 
_ areas. Near the extreme southern station the greatest symmetrical move- 
ments occurred ; the south-western portion of our island may therefore be re- 
garded as the area of greatest symmetry. A line passing from Scilly to 
Stokesley will divide the area into two portions, each characterized by dif- 
_ ferent and opposite barometric movements, as far as the observations from 
_ the 7th to the 11th are concerned. On the N.W. of this line the barometer 
~ was rising, while on the S.E. of it, it was falling. 
___ We noticed that the fall might be occasioned by a wave passing off toward 
i the E.N.E.; now as a rise is occasioned by an anterior slope, a wave coming 
_ up from the N.W. would occasion the phenomena observed. In that por- 
_ tion of the area covered by the advancing wave the barometer would rise ; 
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