ME. H. F. BLANFORD ON THE WINDS OF NORTHERN INDIA. 
603 
any trustworthy determinations of level *. The reduced readings of the Jhansi registers, 
here given, must be regarded as somewhat doubtful from the same cause. There remain 
those of stations on the Gangetic plain, in Central India, in Bengal, and on the coasts 
of the Bay ; and for these I have data for periods of from three to five years. These 
are given in Tables VII. and VIII., the former being the mean of the observed pressures 
reduced to 32° Fahr., the latter the sea-level values corresponding thereto. 
For the majority of the stations the mean pressure is obtained by taking the arith- 
metical mean of observations recorded daily at intervals of six hours, viz. at 4 and 10 
a.m. and p.m. The exceptions are Port Blair, Madras, Nagpore, Jubbulpore, and 
Hoshungabad, for which I have taken the means of the 10 a.m. and 4 p.m. observations, 
the corresponding night observations being wanting. Excepting Madras, all the means 
are corrected to those of the Calcutta standard barometer, which instrument reads 0*011 
inch higher than the Kew standard. 
In October, on the mean of the month, the pressure is nearly uniform in Bengal, and 
on both coasts of the Bay, in the Central Provinces, and the Gangetic valley. Such 
inequalities as are shown in the Table and Chart are small and irregularly distributed. 
Cuttack and False Point show the highest pressure, and Goalpara the lowest; but their 
difference is less than 0T inch, and generally over the whole area a mean pressure of 
29*85 or 29*86 prevails. In the North-western Provinces and Behar on one side, and 
on the Arakan coast on the other, the pressure ranges slightly above that of Bengal, 
and the difference, though small, finds f its expression in a slight converging tendency 
of the winds from both quarters. In like manner the small difference between Cuttack 
and Nagpore causes easterly winds in the direction of the latter, and that between 
Cuttack and the lower part of the coast a small excess of north-east winds in the north- 
west of the Bay. 
In the following months the pressure rises over the whole area, but chiefly in the 
North-western Provinces, Chota Nagpore, and Orissa. In December an axis of maxi- 
mum pressure lies over Cuttack, Benares, Lucknow, and Boorkee ; and Agra, Jhansi, 
and Jubbulpore on one side, and Calcutta, Hazareebagh, and Patna on the other, all 
* This cannot be ascertained with sufficient approximation from the barometric readings. Barometric dif- 
ferences in India are in general so small, that an inconsiderable error in the assigned elevation may lead to 
very deceptive results when the readings are reduced to sea-level ; and, on the other hand, owing to the per- 
sistence of these differences of pressure, small though they he, the sea-level equivalents of the mean annual 
pressure at stations one or two hundred miles apart differ sufficiently to vitiate any reasoning based on their 
assumed equality, and thus the fundamental assumption in the determination of heights by the barometer, viz. 
that when reduced to sea-level the compared pressures of the two stations are equal, is invalid. An example 
which strikingly illustrates this is given in the Bengal Meteorological Report for 1869. Cuttack and Saugor Island 
are about 160 miles apart, the former 80, the latter 6 feet, above mean sea-level ; yet, owing to a persistently 
low pressure during many months of 1868 in the neighbourhood of Cuttack, a comparison of the mean readings 
of the barometers of the two stations (recorded four times daily during the whole year), indicates a difference 
of 205 instead of 74 feet. 
t See ante, Part I. pp. 583, 584. 
4 M 
MDCCCLXXIV. 
