1849.] On the Snow-line in the Himalaya. 309 



It will therefore be seen that as I hold the direct action of the sun 

 to be the primary cause of the great general height to which the snow 

 line recedes, so I consider that the increase of the height in the northern 

 part of the chain chiefly depends, not on any additional destructive 

 action, but on the smaller resistance offered by a diminished quantity of 

 snow, to destructive forces, which are not indeed constant throughout 

 the whole breadth of the chain, but whose increase appears to have no 

 dependence on increase of distance from the southern limit of the belt 

 of perpetual snow. Among the more evident causes of the irregularities 

 in the melting of the snow, may be mentioned, the powerful action of 

 the heavy summer rain on the southern face, as compared with what 

 falls as little more than a drizzle on the northern ; the protection 

 afforded from the radiation of the sun by the heavy clouds so frequent 

 on the south, contrasted with the relative slight resistance of the less 

 dense, but not uncommon clouds on the north ; the differences in the 

 temperature of the air that acts on the lower edge of the snow produced 

 by the difference of height of the snow-line on the opposite faces of the 

 chain ; and lastly, the differences of the temperature of the air and of 

 the amount of radiation and reflexion dependent on the differences in 

 the state of the surface of the earth, which on the south is densely 

 clothed with vegetation, while on the north it is almost bare. 



Before concluding I will observe, that the height at which it is cer- 

 tain that snow will fall every year, in this region of the Himalaya, is 

 about 6500 feet ; and at an elevation of 5000 feet it will not fail more 

 than one year out of ten. The least height to which sporadic falls of 

 snow are known to extend, is about 2500 feet ; and of such falls there 

 are only two authentic instances on record since the British took posses- 

 ion of Kumaon, viz. in 1817 and 1847. Thus we see that the regular 

 annual fluctuation of the snow line, is from 9000 to 10,500 feet, and it 

 occasionally reaches even 13,000 feet. M. Humboldt informs us that 

 under the equator at Quito the fluctuation is 600 Ts. (3,800 feet) ; that 

 at Mexico it reaches 1350 Ts. (8,600 feet) ; and the greatest fluctuation 

 that he mentions is that in the south of Spain, which amounts to 1 700 

 Ts. (10,900 feet).* 



A brief recapitulation of the principal results of this enquiry will 

 show us, that the snow*line, or the southern edge of the belt of perpetual 

 * Asie Centrale, T. 3. p. 279. 



