218 '/' rn-slrial Refraction in tie Western Himalayas. [Mar. 1, 



These results show that at each range of altitude the coefficient of 

 refraction was greater in the Southern than in the Northern Section ; 

 also that from the height of 13,000 ft. upwards the coefficient de- 

 creased in magnitude, as it theoretically should do, in the Northern 

 Triangulation, but, on the other hand, in the Southern it increased 

 until it became twice as great as in the Northern. These differences 

 of behaviour in the two regions are very curious and difficult to 

 account for. They point to some difference in the atmospheric condi- 

 tions to the north and south of the outer Himalayan Range, and this 

 may possibly arise from the circumstance that the atmosphere to the 

 south is more heavily laden with moisture than the atmosphere to the 

 north ; for the great southern range is the first to receive the clouds 

 which come up from the Indian Ocean, and which are the chief 

 source of Himalayan moisture ; these clouds are mostly condensed 

 into rain on the southern face of the range, and thus only a compara- 

 tively small portion of their contents is carried on beyond into the 

 more northerly regions. 



[Whatever the cause, the fact is very remarkable that the co- 

 efficient of refraction has a minimum value at an altitude of 20,000 ft. 

 on the north side of the Himalayan ranges, and a maximum value at 

 the same altitude on the south side. March 2.] 



