The temperature of these rivers varies extremely at different 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 degrees 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.* [During my sojourn at Bhomsong in mid-winter of 1848 (see v. i. chapter xiii), the mean temperature of the Teesta was 51 degrees, and of the air 52.3 degrees; at that elevation the river water rarely exceeds 60 degrees at midsummer. Between 4000 feet and 300 (the plains) its mean temperature varies about 10 degrees between January and July; at 6000 feet it varies from 55 degrees to 43 degrees during the same period; and at 10,000 feet it freezes at the edges in winter and rises to 50 degrees in July.] At this season, in descending from 12,000 feet to 1000 feet, its temperature does not rise 10 degrees, though that of the air rises 30 degrees or 40 degrees. 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 elevation! Of this the Zemu afforded a curious example: during my stay at its junction with the Thlonok it was 46 degrees, or 6 degrees warmer than that river; at 1100 feet higher it was 48 degrees, and at 1100 feet higher still it was 49 degrees! 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 comparatively sunny climate, and flowed amongst little snowed mountains.