Shift. 1849. HALO. OBSERVATIONS ON DONKIA PASS. 129 



which I attained on Donkia, I saw a tine illustration of 

 that atmospheric phenomenon called the " spectre of the 

 Brocken," my own shadow being projected on a mass of 

 thin mist that rose above the tremendous precipices over 

 which I hung. My head was surrounded with a brilliant 

 circular glory or rainbow.* 



The temperature of the Donkia pass is much higher 

 than might be anticipated from its great elevation, and 

 from the fact of its being always bitterly cold to the 

 feelings. This is no doubt due to the warmth of the 

 ascending currents, and to the heat evolved during the 

 condensation of their vapours. I took the following 

 observations : — 



^mp. D.P. «**■ Ten- ^^ 



Sept. 9 1-30— 3-30 p.m. 41° 8 30° 3 ll°-5— C1876 0'665 



„ 27 1-15— 315 p.m. 49° 2 32° 6 1 6°-6— 0-2037 0-560 



Oct. 19 3-0 —3-30 p.m. 40° 1 25° 15°1 -01551 0'585 



The first and last of these temperatures were respectively 

 42° 3 and 46° 4 lower than Calcutta, which, with the 

 proper deduction for latitude, allows 508 and 460 feet as 

 equivalent to 1° Eahr. I left a minimum thermometer on 

 the summit on the 9th of September, and removed it on 

 the 27th, but it had been lifted and turned over by the 

 action of the frost and snow on the loose rocks amongst 

 which I had placed it ; the latter appearing to have 

 been completely shifted. Fortunately, the instrument 

 escaped unhurt, with the index at 28°. 



naked rock and soil absorb much more heat than surfaces covered with vegetation- 

 and this heat again radiated is infinitely more rapidly absorbed by snow (or other 

 white surfaces) than the direct heat of the sun's rays is. Hence, at equal eleva- 

 tions the ground heats sooner, and the snow is more exposed to the heat thus 

 radiated in arid Tibet, than in the wooded and grassed mountains of Sikkim. 



* Probably caused byspiculae of ice floating in the atmosphere, the lateral surfaces 

 of which would then have an uniform inclination of 60^ : this, according to the 

 observations of Mariotte, Venturi, and Fraunhcefer being the angle necessary for 

 the formation of halos. 



VOL. II. k 



