60 ZEMU VALLEY. Chap. XX. 



fell. A comparison of thirty observations with Dorjiling 

 gave a difference of 14° temperature, which is at the rate 

 of 1° for every 347 feet of ascent.* 



The temperature of these rivers varies extremely at dif- 

 ferent parts of their course, depending on that of their 

 affluents. The Teesta is always cool in summer (where its 

 bed is below 2000 feet), its temperature being 20° below 

 that of the air ; whereas in mid-winter, when there is less 

 cloud, and the snows are not melting, it is only a few degrees 

 colder than the air.f At this season, in descending from 

 12,000 feet to 1000 feet, its temperature does not rise 10°, 

 though that of the air rises 30° or 40°. It is a curious fact, 

 that the temperature of the northern feeders of the Teesta, 

 in some parts of their course, rises with the increasing eleva- 

 tion ! Of this the Zemu afforded a curious example : during 

 my stay at its junction with the Thlonok it was 46°, or 6° 

 warmer than that river ; at 1100 feet higher it was 48°, and 

 at 1100 feet higher still it was 49° ! These observations were 

 repeated in different weeks, and several times on the same 

 day, both in ascending and descending, and always with 

 the same result : they told, as certainly as if I had followed 

 the river to its source, that it rose in a drier and compa- 

 ratively sunny climate, and flowed amongst little snowed 

 mountains. 



* Forty-seven observations, comparative with Calcutta, gave 34 0, 8 difference, 

 and if 5°5 of temperature be deducted for northing in latitude, the result is 1° 

 for every 412 feet of ascent. My observations at the junction of the rivers 

 alt. 10,850 feet), during the early part of the month, gave 1° to 304 feet, as the 

 result of twenty-four observations with Dorjiling, and 1° to 394 feet, from seventy- 

 four observations with Calcutta. 



+ During my sojourn at Bhomsong in mid-winter of 1848 (see v. i. p. 305), the 

 mean temperature of the Teesta was 51°, and of the air 52°3; at that elevation the 

 river water rarely exceeds 60° at midsummer. Between 4000 feet and 300 (the 

 plains) its mean temperature varies about 10° between January and July; at 

 6000 feet it varies from 55° to 43° during the same period; and at 10,000 feet it 

 freezes at the edsjes in winter and rises to 50° in Jul v. 



