406 CLIMATE OF SIKKIM. Appendix F. 



amount of elevation to be gradually less in ascending (1 ° = 320 feet 

 at 6000 to 10,000 feet, 1° = 400 feet at 14,000 to 18,000 feet). My 

 observations appear to prove this, but I do not regard them as 

 conclusive ; supposing them to be so, I attribute it to a combination 

 of various causes, especially to the increased elevation and yet 

 unsnowed condition of the mass of land elevated above 16,000 

 feet, and consequent radiation of heat ; also to the greater amount 

 of sunshine there, and to the less dense mists which obstruct the 

 sun's rays at all elevations. In corroboration of this I may 

 mention that the decrease of temperature with elevation is much 

 less in summer than in winter, 1° of Fahr. being equivalent to 

 only 250 feet in January between 7000 and 13,000 feet, and to 

 upwards of 400 feet in July. Again, at Dorjiling (7,430 feet) the 

 temperature hardly ever rises above 70° in the summer months, yet 

 it often rises even higher in Tibet at 12,000 to 14,000 feet. On 

 the other hand, the winters, and the winter nights especially, are 

 disproportionately cold at great heights, the thermometer falling 

 upwards of 40° below the Dorjiling temperature at an elevation only 

 6000 feet higher. 



The diurnal distribution of temperature is equally and similarly 

 affected by the presence of vapour at different altitudes. The lower and 

 outer ranges of 6000 to 10,000 feet, first receive the diurnal charge 

 of vapour-loaded southerly winds ; those beyond them get more of the 

 sun's rays, and the rearward ones more still. Though the summer 

 days of the northern localities are warmer than their elevation would 

 indicate, the nights are not proportionally cold ; for the light mist of 

 14,000 feet, which replaces the dense fog of 7000 feet, effectually 

 obstructs nocturnal radiation, though it is less an obstacle to solar 

 radiation. Clear nights, be it observed, are as rare at Momay 

 (15,300 feet) as at Dorjiling, the nights if windy being rainy ; or, 

 if calm, cold currents descend from the mountains, condensing 

 the moist vapours of the valleys, whose narrow floors are at sunrise 

 bathed in mist at all elevations in Sikkim. The rise and dispersion 

 of these dense mists, and their collection and recondensation on 

 the mountains in the morning, is one of the most magnificent 

 phenomena of the Himalaya, when viewed from a proper elevation ; 

 it commences as soon as the sun appears on the horizon. 



