34 
quently, that it deviated from a circular form; but the gra- 
dually diminished force of the gale in the latter portion renders 
it impossible to fix its close with precision. The total diame- 
ter, in the direction of the progressive movement, probably 
exceeded 500 miles. The magnitude of the (nearly) quiescent 
portion of air in the centre of the vortex is better defined. At 
Armagh the lull lasted from three to four hours ; at Markree 
three hours; and at Donaghadee four hours. The diameter 
of the quiescent central portion was therefore about 50 
miles. 
‘<I shall now refer to some particulars connected with this 
gale, which appear to merit attention—although probably, in 
the present state of knowledge on this subject, we should not 
be justified in offering any suggestions in explanation. 
«« Among the first of these are the abnormal irregularities 
in the rotatory movement, especially along the track of the 
centre. Thus we have seen that, at Markree, there was a 
subsidence of the gale from 7 p.m. to 10 P.M. of the 18th. 
There was, in like manner, a temporary lull at Armagh, be- 
tween 3 and 4 a.m. of the 19th. But the most curious irre- 
gularity is that of the direction. At Armagh this began to 
change rapidly at 9 p.m. of the 18th. At 9 P.M. it was 
E.S.E.; at 10 p.m, S. E.; at midnight, S.S.E.; and at 
1 a.m. on the 19th, S. At this point it remained for several 
hours ; and the direction then retrograded through an are of 
about 45°. At 9 a.m. on the 19th, it was S.S.E.; and at 
11 a.m. it came back to S.E., after which the sudden shift to 
W.N. W. already noticed, took place. 
‘* The next point which seems to merit notice is the fact, 
that the force of the gale was considerably greater to the south 
of the line of passage of its centre, than on that line itself, or 
to the north of it. Thus, at Killiney, where I made frequent 
observations during the gale, I found the maximum velocity 
to be 55 miles an hour; at Armagh it was but 30 miles. It 
would be easy to account for this, if we could suppose that 
