Aug. 1849. VELOCITY AND DISCHARGE OF RIVERS. 99 



Lachen valley collections previous to starting for the 

 Lachoong, whence I hoped to reach Tibet again by a 

 different route, crossing the Donkia pass, and thence 

 exploring the sources of the Teesta at the Cholamoo 

 lakes. 



Whilst here I ascertained the velocity of the currents of 

 the Lachen and Lachoong rivers. Both were torrents, 

 than which none could be more rapid, short of becoming 

 cataracts : the rains were at their height, and the melting of 

 the snows at its maximum. I first measured several hundred 

 yards along the banks of each river above the bridges, 

 repeating this several times, as the rocks and jungle 

 rendered it very difficult to do it accurately : then, sitting 

 on the bridge, I timed floating masses of different materials 

 and sizes that were thrown in at the upper point. I was 

 surprised to find the velocity of the Lachen only nine 

 miles per hour, for its waters seemed to shoot past with 

 the speed of an arrow, but the floats showed the whole 

 stream to be so troubled with local eddies and back- 

 waters, that it took from forty-three to forty-eight 

 seconds for each float to pass over 200 yards, as it was 

 perpetually submerged by under-currents. The breadth of 

 the river averaged sixty-eight feet, and the discharge was 

 4,420 cubic feet of water per second. The temperature 

 was 57°. 



At the Lachoong bridge the jungle was still denser, 

 and the banks quite inaccessible in many places. The 

 mean velocity was eight miles an hour, the breadth ninety - 

 five feet, the depth about the same as that of the Lachen, 

 giving a discharge of 5,700 cubic feet of water per 



thermometer fell to 66° at sunset, and 56° at night. In my blanket tent the 

 heat rose to upwards of 100° in calm weather. The afternoons were generally 

 squally and rainy. 



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