604 
MR. H. E. BLANEORD ON THE WINDS OF NORTHERN INDIA. 
range lower. In January and February the distribution remains much the same in its 
general character, except that in the latter month it falls less over the Bundelkund 
plateau than elsewhere, and the ridge of high pressure is pushed somewhat southward 
and westward. Jhansi, Benares, Jubbulpore, and Agra now range highest in the 
Table. 
In March the pressure falls rapidly over the whole of Northern India, as represented 
in the Table, and most so in the delta, on the Hazareebagh plateau, and in Central 
India south of. the Satpooras. These two regions are still separated by a ridge of some- 
what higher pressure, 'which further extends across the Bay of Bengal between the low- 
pressure area of the delta and that of Ceylon and the south of the Bay. In the exist- 
ence of this ridge we have doubtless the immediate cause of the back-to-back winds 
described in the summary of Part I. Its existence is alluded to by Captain Mauky*^ 
though whether as an observed phenomenon or an inference from the observed course 
of the winds, does not clearly appear in the description. In either case its existence is 
now placed beyond doubt. 
In April, with a further and more rapid fall of pressure in Northern and Central India, 
the areas of minimum pressure in Central India and Western Bengal coalesce, and form 
a trough of minimum pressure, which extends from Berhampore to beyond Nagpore. 
To the north and north-west of this the pressure is but little higher, at least as far as 
Agra and Boorkee. In Southern India, and over the Bay, on the Arakan coast, and in 
Eastern Bengal the pressure exceeds that of any part of Northern India (except possibly 
the Punjab). In May the trough of low pressure formed in Western Bengal and Nagpore 
moves up somewhat to the north, and now runs east and west, from Hazareebagh along 
the Sone valley. The pressure of the North-western Provinces falls below that of the 
delta, and a still lower pressure is established in Bajpootana. 
In June the direction of the baric gradients is much the same as in May, except that, 
as appears from the Boorkee and Agra registers, the fall of pressure in the Punjab is 
much greater than elsewhere; so that the seat of minimum pressure is probably trans- 
ferred to the upper part of that province. The mean difference between Port Blair at 
the Andamans and Boorkee in June amounts to nearly 03 inch, and that between Cal- 
cutta and Port Blair to more than 02 inch. Since Calcutta is situated about midway 
between Port Blair and Boorkee in the course followed by the monsoon current, it 
follows that the baric gradient over the Bay of Bengal is about twice as great as up the 
axis of the Ganges valley. The former is about one tenth of an inch in 400 miles, the 
latter one tenth in 800 miles. Such, and no greater, are the gradients that sustain the 
steady current of the south-west monsoon. 
In July no further change of importance occurs. The pressure has reached its annual 
minimum. In August a general rise of *04 or '05 inch takes place over the whole of 
Northern India. At Madras and in Arakan the rise is about half as much, and at Port 
Blair nil. The trough of low pressure that was formed in May south of the Ganges 
* Op. at. p. 366. 
