1870.] Proceedings of the Asiatic Society . 91 



VI. On certain protracted irregularities of Atmospheric 

 pressure in Bengal, in relation to the Monsoon raineall of 

 1868-69, — by Henry E. Blanford, Esq. Meteorological Ke- 

 porter to the Government of Bengal. (Abstract). 



Mr. Blanford said that the object of his paper was to bring 

 to notice certain irregularities in the distribution of barometric 

 pressure during the monsoons of 1868 and 1869, which had much 

 influenced the course of the wind currents during those two seasons, 

 and had evidently contributed largely to produce the anomalous 

 rainfall of Bengal and the N. W. Provinces, the important conse- 

 quences of which must be fresh in the recollection of all. 



Having spoken of them as irregularities, he would, before proceed- 

 ing to describe them, briefly notice what appear to be the normal 

 features of barometric pressure in the S. W. monsoon in India. On 

 this subject, unfortunately but little direct evidence is forthcoming, 

 since no records, or none admitting of comparison with those of the 

 Bengal stations, are to be had for the greater part of India. In- 

 direct evidence, however, is available ; and this indicates as pro- 

 bable that at the beginning of the S. "West monsoon a focus of 

 minimum pressure exists over the central region of the peninsula, 

 and that towards the middle or end of the monsoon, as Ool. 

 Strachey has suggested, this focus is probably transferred to 

 the Punjab. That such is the case may be inferred from the direc- 

 tion of the winds, which on the Bombay side are westerly during 

 the hot weather and early months of the S. W. monsoon, while in 

 Bengal the prevailing direction is from the South East. It is to be 

 inferred that they blow, in accordance with Buys Ballot's law, 

 towards a place of minimum pressure, with a tendency to circulate 

 round it ; the law of their movement being the same as that of the 

 winds in a cyclone. A similar inference is to be drawn from the fact 

 displayed in D o v e ' s Isothermal charts, as well as in that of Messrs. 

 Schlagintweit, viz. that in the hot weather, the focus of highest 

 mean temperature is about Nagpore, — in the rains, in the Punjab : 

 and a persistently high temperature necessarily produces a low 

 barometric pressure by the expansion and consequent overflow of the 

 air above the heated region. Again, — the course of the isobaric lines 



