ISi H. F. Blanford — On the Climate of Bengal. [Nov. 



perly so called, sets in in India. This blows from both coasts, and the two 

 branches meet along a line which about coincides with the Southern margin 

 of the Gangetic plain. Both tend towards the Panjab, the region of the 

 greatest heat at this season ; and becoming gradually drained of their vapour 

 in their passage over the land, that which remains on their reaching the 

 plains of that province, suffices only to afford a scanty rainfall, inadequate to 

 mitigate the temperature, and only rendering the heat more oppressive by 

 increasing the relative humidity and diminishing the evaporative power of 

 the air. 



As an element of climate, apart from its secondary effects on the winds 

 and consequently on the humidity, rainfall, &c, the pressure of the atmos- 

 phere is, as far as is known at present, of subordinate importance. In 

 Bengal, as in most tropical countries, its variation, except during the passage 

 of cyclones, is small ; scarcely amounting to an inch on the extremes of the 

 year. The average pressure of the air in Calcutta, 18 feet ahove sea level, is 

 equal to that of a column of mercury at the freezing point, 29'793 inches in 

 height or to 14"6 lbs. on the square inch. It is highest in December, when the 

 mean pressure. similarly estimated, amounts to 30011 ins. ; and lowest in June 

 and July when it falls to 29 551 ins. on the average of the month. The daily 

 variation is greatest in April, when the barometer falls on an average "111 inch 

 between 9 A. M. and 5 P. M. \ and least in July, when the corresponding change 

 does not exceed 090 inch, and the day and night barometric tides are nearly 

 equal. The irregular variations being small as compared with those experienced 

 in extra-tropical countries, and the regular variations so much more strongly 

 marked, it follows that, as a weather-glass, the barometer is apt to mislead per- 

 sons who are unacquainted with the laws of its local changes ; since the rough 

 generalizations, which serve to interpret its action in Europe, no longer hold 

 good even approximately in India. In certain cases indeed, its action would 

 seem to be anomalous. Thus it generally rises rapidly before one of those 

 thunder-storms that are so common in the hot weather ; and at Cherra Punji, 

 the extraordinary rainfall of which would lead most persons to anticipate a 

 generally low pressuie during the rainy season, after allowing for differences 

 of elevation, the pressure is, on an average, considerably higher than in Wes- 

 tern Bengal, the N. W. Provinces and the Panjab at this time of the year. 

 Moreover, it appears from information supplied by Major H. H. Godwin- 

 Austen that at this place the barometer rises before heavy rain, and remains 

 high as long as the rain continues. When interpreted with proper precau- 

 tions, the barometer is, nevertheless, as trustworthy and valuable a monitor 

 of impending weather in India as it is elsewhere. 



The storms prevalent in Bengal are of two classes. First those of the 

 hot weather already noticed, which are formed over the land, and are of the 

 nature of convection currents, like the summer storms of Europe ; and second, 



