ON ATMOSPIIERIC WAVES. 49 
bounding troughs, as exhibited on the chart alluded to. How far the con- 
ditions above named exist, we are unable to determine in the present state 
of our knowledge. The elements of the waves already ascertained, indicate, 
owever, the localities from which we may seek to obtain observations that 
will immediately illustrate these desiderata ; and should we not be able to 
obtain them for the year in question, viz. 1842, observations in future years 
on the lines of country indicated by the discussion of the observations in 
1842, already obtained, may be very available for distinctly marking out 
the great tracts of country over which the waves extend, and furnishing 
data from which charts, such as have been alluded to, may be constructed. 
The three waves above specified, in consequence of the minute inves- 
tigation which the observations have undergone, may be considered as 
exhibiting the nearest approach to accuracy in the determination of their 
elements ; there are, however, other waves succeeding them, which, although 
not so precisely determined as to their extent, velocity, &c., yet are so 
elearly placed before us as to warrant the conclusion that the same close 
discussion of the observations for succeeding days would furnish similar 
results with regard to them. These waves are particularized in the table 
as No. 3 or B°, No. 5 and No. 4. 
PART II. 
Taking a single station in the extended area, to which allusion has been 
made in the first part of this report, and examining the barometric phzeno- 
mena exhibited at that station, the result of such an examination has in- 
dicated,—first, that the barometric curve is compounded of the effects pro- 
duced by each individual wave as it passes the station in its onward progress ; 
nd secondly, that so far as the symmetrical curve is concerned, the essential 
racters of this symmetrical curve are repeated year after year. The objects 
the second branch of our inquiry are, therefore, essentially different from 
rst—they consist of the seasonal barometric types or curves, such 
ves being obtained from observations of the barometer at the station 
Selected, without reference to observations at other stations. In my report 
845, pp. 121 to 123, illustrated by plate 3, we have the characteristics 
of the symmetrical curve for 1842, 1843, and 1844. Further notices of the 
ymmetrical curves for 1845 and 1846 occur in the reports for 1846 (pp. 130 
) 132) and 1847. The last-report has more especial reference to the curve 
or 1846, and plate 25. (vol. 1847) illustrates the departure from symmetry 
is we proceed from Brussels to the north-west. The most prominent re- 
of this branch of our subject, up to the last meeting of the Association, 
been the determination that each station possesses its own barometric 
e; that at other stations, more or less, according to their distance or 
mity, certain differences from this type obtain: these differences are 
ngly exhibited in plate 25, Report, 1847. Such a result was certainly 
: expected, as the points of intersection of each wave of each system must 
ssarily be different at different stations, so that the barometric curves 
e various stations must necessarily differ from each other. The con- 
y of the symmetrical characters of the curves appertaining to the 
iddle of November renders it important to deduce the mean symmetrical 
turve for the fifteen days constituting the period of the “ great wave,” for 
any stations as observations can be obtained from. Without doubt, the 
A curve at Brussels would be highly valuable ; it has, however, been out 
ur power to determine it during the last year; but the Greenwich 
ep have afforded the opportunity of determining the mean curve 
1848, E 
ch 
