1870.] Proceedings of the Asiatic Society. 225 



below ending in a downfall of rain, bnt until actual precipitation 

 took place, simply effecting an augmentation of the material of 

 the superincumbent atmosphere. It might be likened to the in- 

 crease of depth in a stream of water caused by increase of supply 

 from its source. If this were so, the like phenomenon ought to 

 be observed on similar sites, such for instance along the Western 

 Ghats. 



Mr. W. Gr. Willson said, — With reference to the observed rise 

 in the barometer at Cherrapoonjee before rainfall, I would remark 

 that, as the same phenomenon has not been noticed at other Hill 

 stations, it can hardly be explained by any increase of pressure 

 which might be caused by the vertical displacements of the aerial 

 currents as they are forced upwards, coming in contact with the 

 sloping sides of the mountains. 



Nor does it seem probable, d priori, that the forcing of masses 

 of air over an elevated region would increase the atmospheric pres- 

 sure, in that region, above its normal condition ; since the equili- 

 brium could be maintained by the lateral distribution of what 

 otherwise might cause an excess of atmosphere. 



We will probably have to look for the explanation of the pheno- 

 menon of the increase of atmospheric pressure before rain (if such 

 be the case) in the same local configuration which causes the 

 enormous rainfall for which Cherrapoonjee is celebrated. 



As I understand, Cherrapoonjee is situated at the head, or focus, 

 of a system of valleys, wide at their entrances, but narrowing up 

 and converging as they approach their common focus. 



The prevailing winds force atmospheric masses up the sides of 

 these valleys. These masses are horizontally compressed as they 

 are forced, from the much wider, to the narrower limits converging 

 to Cherrapoonjee. 



It is possible that this horizontal compression alone may be suffi- 

 cient to saturate the region about Cherrapoonjee, and thus be a 

 cause of excessive rainfall, as well as increased atmospheric pres- 

 sure before rain. 



Dr. Oldham said, he thought the peculiarity of position of Cherra- 

 poonjee, and the effect which this had on the fall of rain there and 

 on the atmospheric pressure, had scarcely been fully appreciated. 



