404 CLIMATE OF SIKKIM. Appendix F. 



it is chiefly to be accounted for by tbe more frequent sunshine at the 

 lower stations, the power of the sun often raising the thermometer 

 in shade to 80°, at Mr. Muller's ; whereas during the summer I spent 

 at Mr. Hodgson's it never rose much above 70°, attaining that 

 height very ^seldom and for a very short period only. The nights, 

 again, are uniformly and equally cloudy at both stations, so that 

 there is no corresponding cold of nocturnal radiation to reduce 

 the temperature. 



The mean decrease of temperature due to elevation, I have 

 stated (Appendix I.) to be about 1° for every 300 feet of ascent ; 

 according to which law Mr. Hodgson's should not be more than 

 1\° colder than Mr. Muller's. These facts prove how difficult it is 

 to choose unexceptionable sites for meteorological observatories in 

 mountainous countries ; discrepancies of so great an amount being 

 due to local causes, which, as in this case, are perhaps transient ; 

 for should the top of the spur be wholly cleared of timber, its 

 temperature would be materially raised ; at the expense, probably, 

 of a deficiency of water at certain seasons. Great inequalities of 

 temperature are also produced by ascending currents of heated air 

 from the Great Bungeet valley, which affect certain parts of the 

 station only ; and these raise the thermometer 10° (even when the 

 sun is clouded) above what it indicates at other places of equal 

 elevation. 



The mean temperature of Dorjiling (elev. 7,430 feet) is very 

 nearly 50°, or 2° higher than that of London, and 26° below that 

 of Calcutta (78°,* or 78° 5 in the latest published tables f) ; which, 

 allowing 1° of diminution of temperature for every degree of latitude 

 leaves 1 ° due to every 300 feet of ascent above Calcutta to the 

 height of Dorjiling, agreeably to my own observations. This diminu- 

 tion is not the same for greater heights, as I shall have occasion 

 to show in a separate chapter of this Appendix, on the decrement 

 of heat with elevation. 



A remarkable uniformity of temperature prevails throughout the 

 year at Dorjiling, there being only 22° difference between the mean 

 temperatures of the hottest and coldest months ; whilst in London, 



* Prinsep, in As. Soc. Journ., Jan. 1832, p. 30. 

 f Darnell's Met. Essays, vol. ii. p. 341. 



