ME. H. F. BLANFOED ON THE WINDS OF NOETHEEN INDIA. 
627 
the 1st of the month to the west of the Andamans. During the last four days of 
October a considerable change had taken place in the distribution of atmospheric pres- 
sure over the Bay. On the 28th it had been lowest at Yizagapatam and Port Blair, 
and at Madras to the southward, and at all the coast stations around the north of the 
Bay, only about (M)5 in. higher than at Vizagapatam. On the three following days the 
Madras pressure remained almost unchanged ; but a general rise took place to the north- 
west, which brought the pressure at Yizagapatam up to an equality with that of Madras, 
and that of Saugor Island and False Point above all other stations. At the same time a 
fall of 0 - l inch took place at Port Blair, which reduced the pressure at that station to 
about 0T5 inch below that in the north-west of the Bay. Over the north of the Bay, 
as far down as 18° or 19° on the Indian coast, and down to Port Blair on the other side, 
the wind was from north and north-east. At Vizagapatam it was variable, and at 
Madras chiefly from the westward. On the open sea to the southward, the westerly 
monsoon, with its characteristic squally weather, prevailed ; but over a triangular area, 
extending across the Bay between Coconada, Madras, and Rangoon, calms and variable 
winds had prevailed for two weeks previously, and it was along the middle of this calm 
belt that the cyclone subsequently took its course. 
These instances show at least that the existence of opposite currents antecedently to 
the formation of a cyclone is by no means an essential condition. In the case of storms 
I., IV., and Y. no northerly or north-easterly wind was felt in the north-west of the 
Bay until the day that the storm-vortex was found, and the barometric depression which, 
in the first case certainly, and probably in the others pre-existed, must have been the 
cause both of the north-east wind and the cyclone ; and in the other cases mentioned, 
the north-east wind in no case blew further south than the place of the storm’s origin. 
It is generally difficult to ascertain the exact barometric pressure at the place at 
which a storm originates for a week or ten days before the cyclone is formed, since 
such data can be obtained only from such ships as may subsequently arrive in Calcutta, 
if even from them ; and in most cases the instruments in use on board ships are not read 
with that accuracy that is requisite to establish the existence of a depression of less than 
about 0T inch (a large amount in tropical seas), and their inherent error is generally 
unknown ; but such data as I have obtained have led me to infer that, as in the case 
of storm II., an area of barometric depression is, as a rule, formed several days before 
the cyclone is generated; and a priori considerations would lead us to expect that such 
must be the case, producing a convergence of the air around. When such a convergence 
has once been established, the formation of a cyclone is easily explained from known 
physical laws. 
I must therefore conclude that the views put forward by Mr. Meldrum with respect 
to the formation of storms in the South Indian Ocean*, viz. that they are produced 
between parallel currents flowing in opposite directions, do not hold good in the case of 
the Bay of Bengal. I infer that a calm state of the atmosphere, or one in which the 
* Proceedings of the Meteorological Society of London, 1869, vol. iv. p. 283. 
MDCCCLXXIY. 4 P 
