1871.] Proceedings of the Asiatic Society. 63 
stations in the positions of Simla and the St. Bernard, and so dimi- 
nish relatively the loss of pressure due to overflow in the highest 
regions of the atmosphere. Plantamour’s law of the difference 
between stations on ridges and those on table-lands is borne out 
by our local experience, in so far that while Darjeeling, a ridge- 
station, in several months of the year has, like Simla, an absolute 
minimum at or about 4 a. m., both Shillong (4,800) feet and Huzari- 
baugh (2000 feet) which are on table-lands, have, like Calcutta, an 
absolute minimum in the afternoon. 
The next sheet to which I have to direct attention is one shew- 
ing the mean curves of pressure and temperature for the year, 
as given by the mean daily values of these elements at Calcutta 
for 15 years. The temperature curve exhibits great irregu- 
larities, as if there were a tendency to rapid changes at certain 
periods. Father Secchi has noticed a similar result on discussing the 
Roman registers for a much longer period, and Mr. Buchan has 
pointed out that the registers of Scotland show a tendency to the 
recurrence of warm and cold days at certain periods of the year. 
It would, however, be premature to draw any such conclusion from 
the registers of only 15 years. 
I have here two sheets that shew the variation of the mean 
daily pressure at a considerable number of stations, for the years 
1869 and 1870. The northernmost station is Roorkee, the sou- 
thernmost Port Blair. The chief noticeable feature that these 
curves present is the almost exact coincidence of all their irregula- 
rities, these being greatest at Roorkee and least at Port Blair. This 
correspondence of the barometric wavesand the decrease in the amount 
of their variations in proceeding from north to south, was first pointed 
out in the case of European stations, many years ago, I believe, by 
Professor Daniell ; and the explanation of the phenomenon given by 
Professor Dove is, that the alternations of the crests and troughs 
forming these irregular waves, depends on the prevalence of Polar 
and equatorial currents, the trade and antitrade currents which cross 
and alternate with each other in the Temperate Zone. These 
curves shew that the same phenomenon is presented here in the 
Monsoon region at all periods of the year, the variations being 
absolutely less, however, than in Europe, and decreasing in like 
manner as the stations are in lower latitudes 
