48 PHILOSOPHICAL TRANSACTIONS. [ANNO 1781. 



the rapidity of the stream ; for, supposing the descent to have been originally 4 

 inches per mile, this will increase it to about 5-|-. Custee is about "240 miles 

 from the sea, by the course of the river ; and the surface of the river there, 

 during the dry season, is about 80 feet above the level of the sea at high water. 

 Thus far does the ocean manifest its dominion in both seasons : in the one by 

 the ebbing and flowing of its tides ; and in the other by depressing the periodical 

 flood, till its surface coincides as nearly with its own, as the descent of the 

 channel of the river will admit. 



Similar circumstances take place in the Jeilinghy, Hoogly, and Burrampooter 

 rivers ; and probably in all others that are subject either to periodical or occa- 

 sional swellings. Not only does the flood diminish near the sea, but the river 

 banks diminish in the same proportion ; so that in the dry season the height of 

 the periodical flood may be known by that of the bank. If it be objected to 

 the above solution, that the lowness of the banks in places near the sea, is the 

 true reason why the floods do not attain so considerable a height, as in places 

 farther removed from it, and where the banks are high ; for that the river, want- 

 ing a bank to confine it, diffuses itself over the surface of the country : in an- 

 swer to this, it may be observed, that it is proved by experiment, that at any 

 given time, the quantity of the increase in different places bears a just propor- 

 tion to the sum total of the increase in each place respectively : or, in other 

 words, that when the river has risen 3 feet at Dacca, where the whole rising is 

 about 14 feet ; it will have risen upwards of 64- feet at Custee, where it rises 31 

 feet in all. 



The quantity of water discharged by the Ganges, in one second of time, 

 during the drv season, is 80,000 cubic feet ; but in the place where the experi- 

 ment was made, the river, when full, has thrice the volume of water in it ; 

 and its motion is also accelerated in the proportion of 5 to 3 : so that the quan- 

 tity discharged in a second at that season is 405,000 cubic feet. If we take the 

 medium the whole year through, it will be nearly 80,000 cubic feet in a second. 



The Burrampooter, which has its source from the opposite side of the same 

 mountains that give rise to the Ganges, first takes its course eastward, or directly 

 opposite to that of the Ganges, through the country of Thibet, where it is 

 named Sanpoo or Zanciu, which bears the same interpretation as the Gonga of 

 Hindoostan, namely, the River. Its course through Thibet, as given by Father 

 Du Halde, and formed into a map by Mr. D'Anville, though sufficiently exact 

 for the purposes of general geography, is not particular enough to ascertain the 

 precise length of its course. After winding with a rapid current through Thibet, 

 it washes the border of the territory of Lassa, in which is the residence of the 

 grand Lama, and then deviating from an east to a south-east course, it ap- 

 proaches within *2'20 miles of Yunan, the westernmost province of China. Here 



