1870.] On the Normal Rainfall of Bengal. 247 



punji represents the heaviest rainfall, and that on the more eas- 

 terly parts of the hills, the rain is considerably less than on the 

 westerly portion, since the wind currents that reach it, must first 

 have traversed the hill tract of Tipperah. 



Silhet Group. — The two stations forming this group represent the 

 rainfall on the alluvial plain of the Barak and its branches, to 

 windward of the Khasi Hills. The elevation of Cachar, the higher 

 of the two stations, is 72 feet only. Silhet probably does not much 

 exceed 50. The former station is under the lea of a portion of the 

 Tipperah hills, and hence probably the difference (26 inches) in 

 their mean annual fall. 



Tipperah and Arrakan Group. — Next to the Khasi Hill Group this 

 group of stations exhibits the highest mean rainfall ; Tipperah, the 

 most northerly, receiving 95 inches, and Sandoway, the most souther- 

 ly, 236 inches. The stations are all at or near sea level ; but they lie 

 (with one exception) on the sea coast, and to windward of a continuous 

 range of forest-clad mountains that runs obliquely across the path of 

 the SW monsoon. The very great difference between the annual 

 falls of Sandoway, or Akyab and Chittagong, is probably due, partly 

 to differences in the direction of the monsoon wind in the lower 

 <and upper parts of the Arakan Coast, and partly to the greater 

 proximity of the hills to the coast line at Akyab and Sandoway, as 

 well as their greater elevation. Owing partly, it may be, to the 

 obstacle presented by the Arakan Mountains to the SW winds, but, 

 in a greater degree, to the lower barometric pressure of the plains of 

 Bengal, the wind- direction at Chittagong, during the greater part 

 of the SW monsoon, is SSE, or about parallel to the coast and 

 the hill ranges. At Akyab and Sandoway, it is from SW or SSW 

 or light and variable, in the earlier months, becoming S in the 

 later months of the monsoon. The rains begin earlier at the 

 northern than at the more southerly stations, since at the latter 

 but little rain falls in April ; and that of May is light, as compared 

 with the rainfall of the subsequent months. 



Delta Group. — In this group, I include only those stations lying 

 between the Megna, Pudda, (or lower Ganges) and the western mar- 

 gin of the Delta. In their case, as in that of the two next mentioned 

 groups, the annual fall is considerably greater on the stations 



32 



