1847. J Notes of an Excursion to the Pindree Glacier. 261 



and so furious in Hoondes and upper Kunawar as to preclude the use 

 of pitched roofs, and to render it necessary to secure the flat ones 

 by heavy stones. On the other hand, along the hase of the mountains 

 at Hurdwar, Dikkolee (on the Kossillah), Bhumouree, and Burmdeo, 

 we find, so far as my own experience goes, that from November till 

 April, from perhaps 2 till 7 or 8 a. m. a perfect hurricane rashes down 

 the great vallies from the mountains, and being greatly cooler than the 

 surrounding air, and soon followed by an oppressive calm, is perhaps 

 the cause of much of the insalubrity of the tarai ; as the reverse gale 

 probably originates much goitre in the mountains. The explanation 

 which suggests itself is as follows : Sir J. Herschel states that at 10,600 

 feet about the sea, one-third of the atmosphere is below us, and at 

 18,000 feet, one half. For the sake of round numbers, let us assume the 

 attenuated stratum of air resting 1 ! on the Himalaya and Tibet, to be 

 deficient by about half the weight of the whole atmosphere ; during 

 the day time, owing to the heat reflected and radiated from this elevated 

 plateau, and the rocks and snows of the Main Chain, (a source of 

 heat wanting of course to the corresponding stratum over the plains,) 

 this is further expanded or rarified, so that it becomes specifically 

 lighter, and ascends. Hence, owing to the great pressure of the whole 

 mass of the atmosphere incumbent on the plains, the air thence is forced 

 to flow upwards, to fill the comparative vacuum, and the current is 

 generated, which commencing at the outer range, reaches the higher 

 one in the afternoon, laden with vapor, which is there condensed by 

 the cold, and astonishes the traveller by those storms of rain and snow 

 which succeed, and are indeed a necessary result of the serene morn- 

 ing. It is for this reason that the guides are always so anxious to set 

 out betimes, so as to cross the passes by noon. It may be objected 

 that as the process of rarefaction commences at the summit of the 

 mountains, and must be gradually communicated to each stratum beneath, 

 where it comes in contact with the heated ground, the current should 

 begin instead of ending at the higest elevations ; but it would appear 

 probable that the movements of the air from this cause is trifling ; the 

 main agency being the pressure of the atmosphere on the plains, which 

 necessarily commences its operation with the outer ranges. During 

 the night, the atmosphere, like Penelope, undoes what it did by dav. 

 From the absence of the sun, the mountain air is cooled and condensed. 



