1870.] On the Normal Rainfall of Bengal. 253 



Prof. Dove long ago pointed out, the southerly winds come 

 round and blow towards them from the E8E or ENE, bring- 

 ing the autumn rains. This is more especially the season of 

 Cyclones in the Bay of Bengal, their frequency being about twice 

 as great as at the beginning of the SW monsoon. The retrover- 

 sion of the monsoon is felt slightly in Orissa, as is shewn by 

 the excess of the October mean over that of the Delta already 

 noticed. 



Influence of elevation on the rainfall. — On this subject sys- 

 tematic observations are wanting in Bengal, and although the list of 

 stations here given, comprises a considerable variety of elevations, 

 the stations present such differences of exposure that their registers 

 are not comparable for the purpose of determining the effects of 

 mere elevation on the quantity of the annual precipitation. It will, 

 however, be of interest to notice such differences as they present, 

 with due regard in each case to those other circumstances which 

 affect the result ; and in so doing, I shall draw attention to the effect 

 of the proximity of hills in increasing the rainfall of stations lying 

 to the windward, and the distance to which this influence appears 

 to extend, a subject to which I have already adverted in a cursory 

 manner in the foregoing pages. In this discussion, I shall have 

 occasion to adduce some data, which I have omitted from the 

 general table on account of the short period over which the obser- 

 vations extend. To eliminate, as far as possible, the effects of 

 varying distance from the sea, and those due to the difference and 

 force of the prevailing vapour-bearing winds, I shall consider 

 separately the stations of Eastern, Northern and Western Bengal. 



The enormous rainfall of Cherra-punji at an elevation of about 

 4000 feet, has already been noticed. This is a little below the 

 elevation of maximum precipitation determined by Col. S y k e s, 

 for Southern India,* but whether the same elevation holds good for 

 the Khasi Hills cannot be determined ; the only station with which 

 a direct comparison of elevation can be made is Silhet, at 23 miles 

 from the foot of the hills and less than 100 feet above the sea. 

 Here the mean rainfall is, in round figures, 150 inches, that of Cherra 

 * Phil. Trans. 1850, p. 



