ON ATMOSPHERIC WAVES. 53 
tions, using these elements, may be expressed as *251 inch. Other features 
#f the mean curve may be employed for this purpose ; but whatever value 
may be adopted as a measure of the departure from symmetry, the points of 
the curves from which such value has been deduced should be particu'arly 
specified. 
PART III. 
The possibility of measuring at any one station the departure from sym- 
etry which that particular curve known as the “symmetrical curve ” 
manifests, brings us to the third part of this report,—‘‘ The notice of any 
results that may have been obtained during the past year of a character 
not contemplated, or but slightly indicated in our former reports, and which 
have particularly originated in the observations of the last return of the 
November curve.” ‘The “ symmetrical curve” on its last return was very 
distinct ; it however presented some minor features which occasioned it to 
differ slightly from the type, as expressed in the Report of 1846, p. 125. 
‘The central apex was depressed at London below two of the subordinate 
-maxima on either side. Had these subordinate maxima exhibited the same 
“altitudes, and the interior minima preceding and succeeding the central apex 
also exhibited similar altitudes, the symmetry on the last return would have ~ 
been complete at London, although the central apex was lower than those 
preceding and succeeding it; as it was, the first maximum, that of the 10th, 
as depressed ‘051 inch below that of the 18th, the second. We have ac- 
London during the last autumn, a mode of expressing numerically the 
deviation from symmetry at any station; and it is clear that this deviation 
‘may be expressed for single years, as deduced from the individual curves, 
or the mean deviation may be taken from several years’ observations, as we 
have done for Greenwich. The last method would be the most desirable in 
etermining the value of the deviation at other stations. We are not, how- 
er, in possession of series of observations executed at such short intervals, 
ending over so long a period, and noting such minute changes of pressure 
the Greenwich observations, in other parts of Great Britain, and also in 
Ireland ; nor can we find observations even at longer intervals at stations 
sufficiently near each other to enable us to determine either the law of 
he departure from symmetry as we recede from the point of greatest sym- 
try, or the directions in which such deviations increase more rapidly than 
| others, by this methad ; but we may attempt some approximation to the 
etermination of such a law, or the indication of such directions, by taking 
ertain points of the symmetrical curves for individual years, as indicated 
1e Observations of last autumn regarding the differences between such 
s as measures of the deviations from symmetry, and constructing charts 
qual deviation. The observations forming the subject of my last report, 
embracing as they do the whole of Great Britain and Ireland, are admirably 
nited for such an attempt. I have accordingly selected the maxima of the 
th and 12th (see plate 25, Report, 1847) as the points from which the 
on from symmetry may he deduced, and laid down on a map of the 
tish Islands the differences between these maxima, and from them have 
structed the lines of equal deviation from *050 inch to *550 inch, being 
ly the range of these differences. 
