ON THE REDUCTION OF METEOROLOGICAL OBSERVATIONS. 69 
of 10 p.m.) is also somewhat displaced, and thrown later than usual by an irre- 
gular elevation or protuberance, which is also traceable in the Gibraltar 
curve; but the second minimum and maximum (those of the morning and 
forenoon of the 22nd) are very distinct. At Turin and Hanover the effect 
of the periodical oscillations is barely perceptible. At Geneva and Brussels 
it is perfectly distinct, as it is also, and not to be mistaken, at London, Green- 
wich, Blackheath and Oxford. At Halifax, obvious errors in the reading of 
the instrument interfere, but at Markree and Limerick these oscillations re- 
appear with perfect distinctness in the morning and forenoon of the 22nd. 
When these are smoothed off, the charts offer a fine example of a very 
regular and steady wave advancing from N.W. to S.E., perfectly identifiable 
in its greater features, though somewhat modified in its progress. Beginning 
with the Irish stations, Markree and Limerick agree in presenting us with a 
gentle fall of the mercury throughout, only that at the latter of these stations 
the descent is somewhat accelerated towards the end of the series, and 
retarded in its earlier hours (from 6 to 8 hours), so as give rise to a relative 
maximum at 1] 30™. At Halifax this descending tendency disappears. 
The curve consists of a slight fall at the commencement with a minimum 
(m') at 1 hour, followed by a steady rise continued for 13 hours, up to a 
maximum M! at 14 hours; whence it sinks with much regularity to the end 
of the series, terminating at the same level where it began. This maximum 
(M') I consider as identical with that which passed Limerick at 112 30™. 
The Oxford curve begins with a pretty steady ascent, and rising with three 
rather remarkable sub-undulations (whose summits occur at 8 hours, 10 hours, 
12 hours respectively), attains a maximum nearly coincident in respect of 
time with that of Halifax, and descends somewhat more abruptly than it rose, 
tothe end of the series. The crown of the wave was vertically over Oxford 
at 135 20". 
In London and its environs the ascent of the wave occupies the whole of 
the first 23 hours. It is very regular and gradual, but with the same traces 
of a preceding minimum. The crown of the wave was vertically over this 
locality at 22 hours, and the beginning of its descent is decidedly marked. 
At Brussels and Hanover the whole series is occupied by the ascending 
wave. Its summit, if vertically over either of these stations at all within the 
series, must have been so nearly at its termination, or at 25 hours. 
The cuive for Geneva commences with a slight fall and a decided and broad 
minimum extending over the 2nd and 3rd hours, clearly demonstrating the 
presence of the trough of a preceding wave. This having passed over to the 
south-east, the rise of our wave commences, and is maintained almost or quite 
_ to the end, where, however, some indications of a commencing descent may 
be observed. 
At Turin, the trough of the preceding wave was here, as at Geneva, in the 
act of passing during the earlier hours of the series. It is perfectly well made 
out, the epoch of the minimum being 3 hours, which is followed by a steady 
rise to a maximum, which here, as at Geneva, is just perceived to be on the 
turn where the projected series breaks off. 
At Cadiz, not only the minimum or trough of the preceding wave, but some 
considerable portion of its descent comes into view in the earlier hours, indi- 
eated by a falling barometer from 0 to 5 hours, where the minimum occurs. 
The rest of the series is occupied by the subsequent ascending wave, which 
continues to the 24th hour. Its course however is less uniform ; its upward 
slope marked by an exaggeration of the forenoon maximum; and its turn 
downwards at the end of the series unequivocally expressed. 
In the Gibraltar curve the barometer readings for the 4th and 5th hour 
