MR. H. F. BLANFORD ON THE WINDS OF NORTHERN INDIA. 
625 
over the east and south of the Bay. The mean (sea-level) pressure at Port Blair is then 
29-861, at Akyab 29*867, at Madras 29-855, and at Calcutta 28-859. Hence the 
pressure is nearly uniform around the coasts of the Bay, and, as might be expected, 
calms are very frequent. Here, again, although less decidedly than in May, there can 
hardly be any question of conflicting currents other than such as are temporary and due 
to local irregularities. The north-east monsoon has not yet set in; and it is to be 
remarked that at False Point, where north-east winds are most frequent, calms are also 
more frequent than in any other month in the year. 
The atmosphere over the Bay is, then, calmer in October than in May ; but storms are 
most frequent in the former month, and indeed, if we regard only those which disturb 
the northern part of the Bay, one and a half times as frequent in October as in May *. 
Consequently a calm atmosphere or variable winds would appear to be a condition 
favouring the formation of cyclones ; and this is verified by the facts of the few storms 
of which I have been able to trace the antecedent conditions. 
I. The Calcutta storm of the 5th October, 1864, appears to have originated on or 
about the 2nd of the month, to the west of the Northern Andaman. For several days 
previously the winds in the north of the Bay were variable, but on the whole southerly ; 
at Madras they were from east-south-east ; at Port Blair from south-west, then south- 
east, and finally west-south-west ; and the pressure was lower at Port Blair than at any 
other station. It was not until the 2nd (that is, the day on which the storm formed) 
that a north-east wind set in down the Madras coast. From the readings of an uncom- 
pared barometer at Port Blair, it would appear that the pressure at the Andamans had 
been lower than in Ceylon or at Madras or Calcutta, at all events since the 26th of 
September, perhaps earlier, and that it fell not less than 0-12 from noon of the 30th 
September to noon of the 1st October. 
II. The Calcutta cyclone of the 2nd November, 1867, was formed on the 27th October, 
in latitude 10° to the west of the Nicobar Islands f. For at least four days previously 
the barometric pressure in this region was lower than elsewhere in or around the Bay. 
Si It was also lower (on the 24th October certainly, and probably on the previous day 
also) than on the open sea to the southward. The depression was gradually intensified 
up to the 27th, when it began to blow a hurricane on the northern limit of the area.' 5 
It appeared that over the greater part of the Bay the pressure was nearly equable, and 
that the depression was local and bounded by a high barometric gradient. For many 
days prior to the 24th, light south-easterly winds had prevailed on the Indian coast, 
while in Bengal the wind was variable with a predominance of easting. To the south, 
between the equator and north latitude 5°, a squally, damp, west-north-west wind blew 
continuously, having prevailed at least from the 11th of the month. On the 27th it 
became west-south-west, drawing round towards the area of depression. On the 24th 
* See Report on the Calcutta Cyclone of October 1865, p. 101. 
f The origin of this storm was described at length in the Proc. Roy. Soc. vol. xyii. p. 472. I quote above 
ome passages from this paper. 
