476 Mr. II. F. Blanford on the Origin of a Cyclone. [June 17, 



as appears from the accounts furnished by other vessels, eventually contri- 

 buted in a great degree to produce the cyclone, being diverted from its pre- 

 vious direction towards the place of low barometer in the south of the bay *. 



On the 24th and 25th the barometric pressure increased slightly over 

 the north and west of the bay, but chiefly at Patna. The increase was 

 from 0*04 to 0*07 inch at stations in Lower Bengal, 0*05 at Madras, and 

 0*03 at Akyab. The difference o'f pressures at Chittagong and Madras 

 amounted on the latter day to about 0'06 inch, and between Chittagong 

 and Akyab to about 0*05 inch. In the region to the west of the Nicobars 

 the pressure seems to have remained much the same as on the 23rd, and 

 was about 0'23 inch less than at Chittagong, and 0*19 less than at Madras. 

 At the same time, in lat. 5° S., the pressure was about 0*1 inch higher 

 than in the south of the bay. The figures given in the Table thus indi- 

 cate a region of slight but distinct barometric depression running from 

 Sumatra up towards Arakan, with a minimum to the west of the Nicobars, 

 or, more probably, somewhat further to the south. 



Meanwhile the northerly or north-easterly wind, which was first felt at 

 Chittagong on the afternoon of the 23rd, extended over Lower Bengal 

 and down the western half of the bay as far as the northern extremity of 

 Ceylon. It prevailed also over the northern part of the bay from N.E. 

 and E.N.E. as far down as lat. 12°, and was accompanied with fine and 

 clear weather. Below this latitude to the west and north-west of the Ni- 

 cobars the winds were light and variable, with rain and squally weather 

 ('Leonie,' 'J. C. Botelbhoe'). Still further south, on the Equator 

 ('Gauntlet'), and probably for some degrees to the north, the W.N.W. 

 winds, already noticed, prevailed with squally weather, while the S.E. trade 

 was blowing ('Gauntlet,' ' Astracan') up to 2° 30' or 3° south latitude. 



On the 26th there was a general fall of the barometer, greatest in 

 Bengal, and the pressure became nearly equal over Bengal, down the west 

 coast to Madras and over the bay (' Winchester,' ' St. Marnock') down to 

 lat. 14°. In the eastern part of the bay, between lats. 14° and 10°, there 

 was a barometric dip of 017 inch (' St. Marnock,' 'J. C. Botelbhoe'), and 

 the barometer stood at about the same height in N. lats. 10° and 4° (' J. 

 C. Botelbhoe,' 'Gauntlet'). The area of maximum depression lay evi- 

 dently between these latitudes, since in S. lat. 3° the pressure was 0*1 inch 

 and in S. lat. 7° 0*13 inch higher ('Astracan,' ' Iron King'). 



The state of the wind and weather appears to have been much the same 

 as on the previous day ; but there is some evidence in the logs of the ' J. C. 



* This W.N.W. current is very prevalent in the winter months, as is well known to 

 mariners. Its prevalence is clearly shown in the Board of Trade charts, and it is especi- 

 ally noticed by Maury (Phys. Geog. of the Sea, 12th edit. p. 375) as the winter or west- 

 erly monsoon of the line. It is usually accompanied by rain and squally weather, and 

 not improbably plays an important part in the production of all the cyclones that origi- 

 nate in the south of the bay to the west of the A.ndamans and Nicobars. On this point 

 compare the Report on the Calcutta cyclone of 1864, especially pp. 79, 85, 105. See Is 

 postea. 



