98 REPORT—1843. 
nothing to be desired on this important head. I need not insist on each ob- 
server reducing his own observations. The time is arrived in meteorology 
wher unreduced observations (at least barometrical ones) can no longer be 
tolerated, and must henceforward (except at very peculiar stations) be con- 
sidered as not having been made, The tables for the purpose are in every 
one’s possession who can be considered competent to use the barometer sci- 
entifically ; and if the correction be applied at once at the time of reading off, 
the trouble is so subdivided as to be reduced almost to nothing, It should, 
however, be remembered by all who may undertake such obseryations, that 
unless made at each hour of the twenty-five and at the exact hours, a sevies 
loses much of its yalue; and if two or more hours he deficient, it is hardly 
worth using, as its comparability with others ceases. We haye seen, from 
the instance of Mauritius (and the remark applies to most inter-tropical sta- 
tions), that from twelye to sixteen unexceptionable series of the kind in 
question suffice to afford a perfect solution of the problem of the diurnal 
moyements wlien mean quantities only are concerned ; and in all probability 
three or four years’ continuance of monthly terms would lead to a knowledge 
of the annually periodic variations in their coetticients. For such an object, 
dew-points, clouds, temperatures (other than needed to reduce the barometer 
to the freezing standard), and even winds, might be pretermitted, though I am 
far from advising their neglect, 
As regards, however, the exceedingly interesting subject of the atmospherie¢ 
waves, it is right I should observe that, without setting on foot (except with 
special views and in highly civilized localities) any express series of observa- 
tions, but simply by comparing and reducing what already stand on record, 
—or even by projecting them unreduced, where great undulations only are 
to be traced,—the way lies open to most yaluable conclusions. The fluetua- 
tions we have been able to trace by projecting the term observations, are 
those only whose total duration of rise and fall is comprised within or does 
not much exceed the twenty-four or thirty-six hours over which the term 
extends. But these are by no means those which either theoretically or in- 
deed practically speaking are to be regarded as most important. I have the 
pleasure to lay before the Section specimens of barometric projections by 
Mr. Birt, laid down from his own observation, in which the interval between 
two successive maxima of pressure occupied in the one case seventeen days 
without any intervening maximum; in another, a similar period with two 
subordinate maxima interposed ; and another where a beautifully symmetrical 
wave of an extremely remarkable character occupied thirteen days for its 
complete rise and fall. [See curves designated as ‘‘ Barometric Waves,” 
respectively annexed. Plates I. and II. ] 
For such objects (as before observed) we need not travel beyond existing 
records. In the records of our own magnetic and meteorological observa- 
tories, and those which stand in correspondence with them throughout the 
world, we have ample materials ; and when dealing with undulations of such 
extent, it is by no means a visionary speculation to consider the possibility of 
tracing them over the whole of our globe; nay, perhaps of obtaining evidence 
of their performing, tide-like, two or more revolutions round its surface. And 
although the pressure of other avocations will (unfortunately perhaps for 
myself ) entirely preclude my taking any further personal share in this most 
interesting inquiry, Iam authorized by Mr. Birt to state, that should it be the 
pleasure of the British Association to intrust the subject to his inquiries by 
appointing him a committee for that purpose, he is prepared to pursue it if 
provided with a moderate grant to clear unavoidable expense, 


