ON THE REDUCTION OF METEOROLOGICAL OBSERVATIONS. 81 
is as remarkable for inequalities and abrupt fluctuations in its barometric 
changes as Brussels is for the reverse. ‘Turin seems to be much affected by 
its proximity to the Alps, which gives its barometric curves frequently a very 
disjointed character. Between the Italian stations (Turin and Parma) and 
the Spanish (Cadiz, Gibraltar, Tangier) no community of character and no 
mutual dependence prevails. Cadiz, Gibraltar and Tangier are subject to an 
anomalous rise and fall of the mercury between midnight and sunrise, which 
interferes with and often counteracts and overcomes the regular tendency to 
depression in that interval, a peculiarity which is probably owing to the proxi- 
mity of the great radiating surface of the African deserts. At Tangier the 
barometric fluctuations seem to be remarkably small. Markree is remark- 
able for the boldness and freedom of contour in its barometric curves, and 
the great range of their fluctuations compared with stations to the south-east 
of it. 
Asiatic group. 
The only stations admitting of mutual comparison are those of the Indian 
Peninsula, Mauritius and Van Diemen’s Land being too remote. Out of the 
nine terms observed in any part of India also, four were only ebserved at one 
station, and neither of the remaining five at more than two, and those in only 
two instances the same. Under these circumstances we could not expect to 
trace out the propagation of waves even were any great fluctuations included 
in the series. It so happens, however, that in none of the terms, and in no 
station (except Van Diemen’s Land) was this the case. ‘The chief interest, 
therefore, in the discussion of this group consists in the information to be 
- derived from the separate consideration of each station in respect of its baro- 
metric character, as to the comparative smoothness or abruptness of its varia- 
tion, and the extent and law of its diurnal oscillations. And these will be 
found by no means devoid of interest, but on the contrary to furnish occa- 
sion for some remarks of moment. 
Mauritius —Owing to the indefatigable diligence of Captain Lloyd, late 
Surveyor-General of this colony, we possess nearly a complete series for this 
station (Sept. 1838 alone being wanting), and the observations having been 
made half-hourly in every term, we are enabled to trace more minutely on 
each occasion the progress of the barometric march. It appears to be ex- 
tremely regular, a certain ¢repidation however frequently prevailing in the 
rise and fall through the diurnal phases, which contrasts very remarkably with 
the exceedingly smooth character of several of the curves at the Indian sta- 
tions. 
In all the Mauritius terms there is not one in which the diurnal maxima 
and minima are not fairly and strikingly developed ; neither is there any one. 
in which (laying out of consideration these phases) any material departure 
from a mean of the whole day is observed. Such a state of things is highly 
favourable for the exact determination of the elements of diurnal oscillation. 
I have therefore assembled in the Table (Appendix B.) the observations on 
all the terms reduced to 32° Fahr., and having taken the means for each hour, 
projected them in a curve on a scale of one inch to the hour of time, and to 
the hundredth of an inch barometric altitude. A straight line being then 
drawn from the point commencing this curve to the point terminating it will 
represent the mean march of the barometer during the 24 hours included. And 
our object being only to represent fluctuations above and below such a mean, 
this line has been taken as an abscissa (representing the level of 30°0000 
inches), and from it, in the direction of the original ordinates, the altitudes 
were read off (by which process all that remains of casual or non-periodical 
movement is obviously eliminated), and thus have been obtained the follow- 
1843. G 
