ON THE REDUCTION OF METEOROLOGICAL OBSERVATIONS. 61 
thereby causing partial ascensional and descensional movements and local 
generations and precipitations of vapour, we shall clearly perceive that, so far 
as our present purpose is concerned, the particular dimensions and form of 
our planet have little to do with our inquiry, and that for the immediate pur- 
poses of that inquiry we may regard our globe as a plane surface of infinite 
extent, over particular districts of which systems of oscillation of local origin, 
and independent of each other, are in progress, and in which we may regard 
ourselves fortunate if we can now and then succeed in obtaining distinct 
evidence of the direction, extent, height and velocity of a single wave. The 
distribution of our stations into groups, grounded on this view of the subject, 
and the mode of referring the observations of each group to a central station 
within it, have been described in my report for 1840, and need not therefore 
here be recapitulated. These groups, it is true, abstractedly considered, are 
far from those which would be chosen @ priori. For example, Mauritius 
and Van Diemen’s Land are but ill adapted to form a group with Indian sta- 
tions. But for this there is no remedy, and the Mauritius observations (of 
which, owing to the diligence and zeal of Captain Lloyd, Surveyor-General 
of that island, we possess a nearly complete series) merit and will receive a 
separate discussion. 
Two objects have been chiefly kept in view in the present inquiry. First, 
the tracing, where it can be accomplished, the course of one particular wave 
over the whole area embraced within one of our groups; and secondly, 
where this cannot be done, the observation of connexions between particular 
localities with a view to the subdivision of the total area into barometric dis- 
tricts, in which the atmospheric fluctuations shall be, generally speaking, 
similar in their phases. With these objects the projection of the barometric 
curves, for all the stations of a group, one sheet for each separate term, has 
been executed with great care and delicacy by Mr. Birt, and on a scale so 
large as to allow of the minutest corresponding changes, if any, to be 
distinctly followed out. The number of sheets so projected is fifty-three, on 
a scale of an inch to the hour in time, and one inch to 0-066 of barometric 
altitude ; and I must not lose this opportunity of acknowledging many valua- 
ble remarks received from that gentleman on the subject of particular cases 
of much interest, which will be given in his own words, under their several 
heads as they occur. 
I proceed now, therefore, to the discussion of the observations of each 
term, so reduced and projected, seriatim. 
As the whole of the curves of the American group, and seventeen others 
of the European series, together with their tabulated reductions, have been 
on a former occasion submitted to the inspection of the meeting, to the num- 
ber of 105, it has not been thought necessary to risk the loss or damage of 
the remainder by transmitting them herewith, they being in all respects 
similar. 
European Group. 
June 1835.—This term affords only two series, those of London and Brus- 
sels. The projected curves exhibit a pretty regular descent, and tolerably 
well-maintained parallelism during the first sixteen projected hours, or until 
3 a.m. of the 22nd, when the Brussels curve attains a minimum, and pretty 
abruptly ascends again to the end of the series. The London curve, on the 
other hand, continues to descend till 11 a.m. of the 22nd, where it also attains 
a minimum, and begins to reascend. If this minimum represent, as it pro- 
bably does, the trough of a barometric wave which’ at 3 a.m. was verti- 
cally over Brussels, and at 11 a.m. over London, the wave must have been 
