480 Mr. H. F. Blanford on the Origin of a Cyclone, [June 17, 



with occasional squalls, especially on the latter days ; and the same stormy 

 damp wind prevailed over the south of the bay up to the Great Andaman 

 on the 1st and 2nd. The greater northern extension of this current is, 

 doubtless, connected with the above-mentioned difference in the position 

 of the storm's birthplace. At Port Blair, on the 29th and 30th, and over 

 the greater part of the bay as far south as Madras, southerly and 

 east-south-easterly winds prevailed up to the 3rd of October. In Eastern 

 Bengal alone the wind was northerly, becoming N.E. on the 1st and 2nd ; 

 but it was not until the 3rd of October that a N.E. wind established itself 

 over the north and west of the bay. It may, however, be noticed that 

 during the five days preceding the cyclone, an unusually high barometer 

 prevailed in Bengal, and this may have been due to the existence of an 

 upper northerly current. A north-east wind was also felt in lat. 15° on 

 the north-west limb of the vortex, on the 2nd, but was evidently merely 

 the indraught of the south-east current. 



The barometer data for the storm of 1864 were few in number, and not 

 comparable inter se ; but we adduced some reason for the inference that a 

 low barometric pressure prevailed near the Andamans for some days pre- 

 viously to the 2nd of October. 



It appears, then, that the same three wind-currents eventually took part 

 in the formation of both storms, viz. a south-east wind in the south-east of 

 the bay, a north-east wind along the west coast, and a westerly wind to the 

 south ; but that while in the storm of 1864 the north-east wind did not pre- 

 vail until after the formation of the vortex, up to which time the south-east 

 current held possession of the bay, in that of 1867 the former current 

 had established itself three days prior to the commencement of the cyclone. 

 These facts, coupled with the further fact that neither the north-east nor 

 (at this time of year) the south-east currents are stormy winds capable 

 of feeding the vortex and increasing the barometric depression, tend to 

 confirm the view enunciated in the Report on the Calcutta Cyclone of 1864, 

 viz. that the formation of the vortex was mainly determined by the inrush 

 of a saturated westerly current towards the place of low barometer. 



The fact above mentioned, that the majority of the Bay of Bengal 

 cyclones arise along a line parallel to, and immediately to the west of, the 

 chain of islands that form the eastern boundary of the bay, indicates the 

 operation of some general cause tending to produce a low atmospheric 

 pressure in that region at those seasons at which cyclones are most pre- 

 valent. Such a cause may be suggested, but the data available to me are 

 not sufficiently precise to establish its existence. If it can be shown that, 

 either owing to a predominance of marine currents from the south, or to 

 any other cause, the water along the eastern side of the bay has a higher 

 temperature than that of the western side during those months at which 

 cyclones prevail, the increased evaporation thus arising, together with the 



but despite the difference in mean direction, the wet squally character of this wind permits 

 of its identification with Maury's westerly monsoon of the line. 



