64 Proceedings of the Asiatie Society. { Marcu, 
Finally I have to bring to the notice of the Society a set of curves 
shewing the mean diurnal variation of the wind for each month 
of the year at Calcutta. These have been drawn up from a dis- 
cussion of 10 years’ observations at the Surveyor General’s Office. 
The observations are recorded only to eight points, viz., N. NE. E. 
SE., &c., and I may remark how this very rough method of obser- 
vation suffices (when so long a period as 10 years is considered), to 
shew a regular variation, even when in some months it amounts to 
little more than one point of the compass. The diurnal variation 
of the wind appears at first sight somewhat anomalous, since 
Calcutta is at no very great distance from the sea, and it might 
be expected that as at coast stations, there would be a tendency to 
a southerly or sea breeze during the latter part of the day and a 
land breeze at night. The caseis, however, precisely the reverse. 
The land wind at Calcutta, ¢.e.,a WNW. wind prevails strongly 
during the day, in the cold and hot weather months, and even in 
the rains, when the variation is very small, the westerly tendency is 
still manifest ; while the southerly or sea breeze prevails or tends to 
prevail during the night. When the mean of the whole year is consi- 
dered, it appears that the WNW. wind tends to set in about 10 A. M., 
and to increase in force and steadiness up to about 4p. m., after which 
the wind veers round rapidly to south, anda little east of south, in 
which quarter it continues till midnight or 1 a.m. It then diminishes 
in force and there is a tendency to calm until about sunrise. The 
coincidence of the prevalence of the westerly wind with the period 
during which the barometric gradient is from west to east, owing 
to the advance of the afternoon minimum from the eastward, sug- 
gests the cause of this phenomenon. It is true that this gradient 
is absolutely small, and the loci of maximum and minimum are 
separated by a quadrant of the earth’s circumference; but the effect 
to be accounted for as the diurnal oscillation, when deduction is 
made of the mean monthly or annual component, is also small, being 
a predominance of 12 or 13 per cent. only, and is probably not 
greater than may be accounted for by the cause suggested, which 
must have some effect. 
Colonel the Hon’ble R. Strachey said that he thought the Society, 
and indeed all persons interested in the progress of science, were much 
