04 Proceedings of the Asiatic Society. [Mar. 



i directly towards that station across the delta, and speedily 

 broke up on the north of the Ganges. 



The third, in the beginning of October, when the lowest pressure 

 was distributed over Monghyr, Patna and Hazareebagh, took an 

 unusual course to the north west and between these stations. 



The President said that in inviting discussion upon the paper 

 which had just been read, lie need not dwell upon the great value of 

 Mr. Blanford's investigations. It had long been understood 

 that the dominant cause of monsoon winds was the periodic occur- 

 rence of a terrestrial locus of minimum barometric pressure. And 

 a persistent condition of low barometric pressure simply meant, that 

 for some reason or another the spot in the earth's surface where 

 it occurred, was a focus of maximum heat. He believed that 

 Schlagintweit's map of isothermal lines exhibited a centre of 

 maximum heat in the Punjab, during the rainy season, and no doubt 

 the S. W. monsoon of our Presidency was greatly influenced by 

 such a centre. Mr. Blanford's observations led to the remark- 

 able conclusion, that in some seasons, if not always, there were 

 other minor centres, or at least one centre in Bengal itself, which 

 materially interfered with and disturbed the action of the principal 

 centre. It was curious that an area of maximum rainfall should 

 be found at a certain distance on the north side of this minor centre, 

 and Mr. Blanford had offered a very ingenious theory to ac- 

 count for the fact. He (the President) however, felt some difficulty 

 in accepting this theory. It appeared to him inconsistent with the 

 maintenance of the barometric depression, which could only be 

 attributable to the continuance of local surface heat in excess of that 

 in the neighbourhood. The effect of the greater local heat was, by' 

 a process of internal expansion to lift the superincumbent column of 

 air relatively to the surrounding air, by reason of which the upper 

 portions of it became, as it were, poured awa} r s sideways, and so the 

 amount of atmospheric material in the vertical column was lessened ; 

 and as long as the relatively low barometer obtained, this operation 

 must be going on. Therefore, the passing monsoon current must be 

 affected by it, and if so, the motion of the particles of vapour in it 

 could not safely be calculated as if they were sliding under the action 

 of gravity upon the gradient lines of equal pressure. He would 



