120 Report on the Progress of the Magnetic Survey. [No. 2. 



isolated low snow beds in protected places and the subterranean 

 Bas-Neves above mentioned had, comparatively speaking, very much 

 diminished by the melting which still continued in the lower parts 

 of the slopes and valleys. 



The dryness of the atmosphere appears to be greatest in the 

 environs of Karakorum, but it rapidly decreases in the direction of 

 Khotan. From various and apparently very consistent data, which 

 we obtained from the inhabitants we estimate inches. 



The direction of the wind is chiefly northerly. The south winds 

 which predominate in Central Ladak and in Kunawer are perfectly 

 unknown on the northern side of the Kuenluen. 



The phenomenon of the second illumination of snow- clad moun- 

 tains after sunset (analogous to the glowing of the Alpine snows) 

 was seen several times on those nights when there was no moon. 

 We saw it particularly well near Chibra to the north of Karako- 

 rum. Judging of it as we saw it there, we think it to be quite 

 independent of a spontaneous development of light from snow. It 

 was evidently caused by an illumination of the snow-fields from 

 the west north-western parts of the sky. This illumination is only 

 visible sometime after the sun has set, namely, when the projec- 

 tion of the earth's shade has reached an angular height exceeding 

 that of the mountains, and when the atmospheric light has de- 

 creased so much that the atmosphere behind the mountains reflects 

 less light than the snow-clad slopes of the mountains exposed to 

 the west north-west. 



At heights above 17,000 feet we found in the Kuenluen, the 

 transparency of the atmosphere so great, that the small and the 

 large circles in Saussure's diaphanometer (as we had used it also 

 formerly in the Alps of Europe, and described in our " Ee- 

 searches") disappeared under the same angles, and therefore the 

 transparency above 17,000 feet was so great that a stratum of air, 

 3,000 to 3,500 feet thick, absorbed the light in so small a degree, 

 that the absorption to our eyes became unappreciable. It was 

 then determined by another method, by which a stratum of much 

 greater thickness could be examined. 



The transparency of the atmosphere is often very much affected 

 by a peculiar haze not affecting the psychrometer ; we found this 



