264 Meteorological Sketches. 
of the Royal Observatory, informs us that the mean height of the 
barometer was about 29.50 inches; and a register of the observations 
for seven months from February to August, inclusive, at the observ- 
atory at Port Famine, in the Strait, shows a mean of 29.43 inches. 
This result is confirmed by the observations of other officers; and 
may serve, also, to show the error of Mr. Daniell’s position, that 
the mean pressure of the atmosphere during the year, at the level 
of the sea, is every where the same. 
Ill. The constant or periodical accumulation of atmospheric 
pressure, which arises from natural obstacles, opposed to the course 
of the general or trade winds; and the corresponding depression 
of the barometer, which results from the retardation of such winds 
by like obstacles or by an unnatural and forced route, in their pro-- 
gress towards the point of observation. 
The most remarkable variations of this character are found under 
the eastern and western monsoons, in Asia and the Indian and Pa- 
cific oceans. ‘The N. E. monsoon or regular trade wind, obstructed 
in its natural course of deflection from the tropical to the temperate 
latitudes, by the great Asiatic elevations, is forced to continue a 
sluggish course across the equator, into the N.W. monsoon. The 
effect of this resistance in raising the barometer is such, that at Can- 
ton, in China, the mean height of the barometer during four months 
of the N. E. monsoon, fora period of seven years, has been found to 
be 30.20 inches. ‘The mean height during four months of the S. W. 
monsoon, owing probably to the tardy passage of the S. EK. trade 
from which it is derived, in its unnatural course across the equator, 
being, for the same period, only 29.86 inches. 
IV. The oscillation of an extensive region of atmosphere in the 
higher or temperate latitudes, causing a rise of the barometer of some 
days or even weeks continuance ; and a corresponding depression 
for like periods at other seasons. ‘These extensive oscillations may, 
perhaps, be referred to the alternately predominating influence of 
gravitation toward the poles, and the counter force of the centrifugal 
action of the earth’s rotation towards the equator, aided probably, 
by some of the other causes to which allusion has been made. 
Although storms of wind, from the manner of their development, 
usually produce rain in some portion of the area which they occupy, 
yet the fall of the barometer, being chiefly dependent on mechanical 
causes, has no necessary connection with the fall of rain. It appears 
from the observations of the Marquis Poleni, that in one thousand one 
