1874.] Winds of Northern India. 217 



greatest humidity, these rains must be due to some other cause, which he 

 thinks to be the humidity of the anti-monsoon current. 



On the mountains the heaviest rainfall is on the lower and outer 

 slopes. The greatest recorded falls are those at Cherra-Poonji over 

 Eastern Bengal, averaging more than 500 inches in the year. On the 

 Himalaya the records show falls of from 280 inches on the east to 70 or 80 

 inches in the North-west Provinces, and 40 to 50 inches in the Punjab. 

 Local circumstances of position greatly affect the quantity. 



Generally the quantity of rainfall diminishes with increase of distance 

 from the coast ; but it increases on approaching a hill-range on the wind- 

 ward side when the rise is steep, while to leeward a decrease takes place, 

 followed eventually by another gradual increase. 



3. Atmospheric Pressure. The available data for discussing this part of 

 the subject are imperfect ; and particularly the means of reducing the 

 pressures to the sea-level are not forthcoming in many cases. The fol- 

 lowing remarks are made subject to this explanation. 



The mean pressure, reduced to sea-level, in the month of October is 

 nearly uniform over Bengal, on both sides of the bay, in the Central 

 Provinces, and the Gangetic valley, with a slight tendency to a higher 

 pressure in the North-west Provinces and Cuttack on the one side, and 

 on the Arakan coast on the other, which finds its expression in the 

 slightly converging winds of that season. 



In the following months the pressure rises over the whole area, but most 

 in the North-west Provinces and Western Bengal ; and in December an 

 axis of maximum pressure lies on a line drawn from Cuttack to the 

 North-west Provinces in a north-west and south-east direction. The 

 distribution of pressure remains much the same till the end of February. 

 In March a rapid fall takes place in Northern India ; but the line of 

 higher pressure still remains, extending now from North-western India 

 across to the coast of Arakan round the delta of the Ganges. This, 

 doubtless, is the immediate cause of the back to back winds described in 

 Part I. 



In April, with a continued rapid fall, a trough of low pressure becomes 

 apparent, which extends from the head of the delta of the Ganges into 

 Central India. In May this area of low pressure is somewhat displaced 

 towards the north, occupying a line from Western Bengal to Nagpoor, 

 along the 24th parallel of latitude. In June the conditions are generally 

 similar, but with much reduced pressure in the Punjab, in the north-west 

 of which province the absolute minimum is probably to be found. The 

 mean difference of pressure in June between Port Blair in the Bay of 

 Bengal and the upper part of the North-west Provinces is not less than 

 -5% of an inch, and between Port Blair and Calcutta -^ of an inch, Cal- 

 cutta being about as far from Port Blair as from the head of the Gangetic 

 valley, 800 miles ; the baric gradient over the Bay of Bengal, therefore, is 

 about double what it is over the axis of the Ganges valley, and amounts 



YOL. XXII. B 



