May, 1850. ELEVATION OF THE WATERS. 259 



poraneous ones at Calcutta was + '003 in favour of 

 Calcutta, and the temperature half a degree lower ; the 

 dew-point and humidity were nearly the same at both 

 places. This being the driest season of the year, it is very 

 probable that the mean level of the water at this part of 

 the delta is not higher than that of the Bay of Bengal ; 

 but as we advanced northwards towards the Khasia, and 

 entered the Soormah itself, the atmospheric pressure 

 increased further, thus appearing to give the bed of that 

 stream a depression of thirty -five feet below the Bay of 

 Bengal, into which it flows ! This was no doubt the result 

 of unequal atmospheric pressure at the two localities, 

 caused by the disturbance of the column of atmosphere by 

 the Khasia mountains ; for in December of the same year, 

 thirty-eight observations on the surface of the Soormah 

 made its bed forty-six feet above the Bay of Bengal, whilst 

 from twenty-three observations on the Megna, the pressure 

 only differed 4- 0' 020 of an inch from that of the barometer 

 at Calcutta, which is eighteen feet above the sea-level. 



These barometric levellings, though far from satisfactory 

 as compared with trigonometric, are extremely interesting 

 in the absence of the latter. In a scientific point of view 

 nothing has been done towards determining the levels of 

 the land and waters of the great Gangetic delta, since 

 Rennell's time, yet no geodetical operation promises more 

 valuable results in geography and physical geology than 

 running three lines of level across its area ; from Chit- 

 tagong to Calcutta, from Silhet to Rampore, and from 

 Calcutta to Silhet. The foot of the Sikkim Himalaya has, 

 I believe, been connected with Calcutta by the great 

 trigonometrical survey, but I am given to understand that 

 the results are not published. 



My own barometric levellings would make the bed of the 



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