1856.] Silt held in suspension by the Hooghly. 157 



foot of water will give 433.63 grs. or nearly T %ths (nine-tenths) of 

 an ounce for the whole solid contents of the cubic foot of water. 



The proportion of carbonate of lime to the total of solid matter 

 is also less, for in 1842 of the 13.99 grains of solid matter, 7.95 

 were carbonate of lime, which proportion should give 6.06 for the 

 10.66 grains of solid matter of 1854-55, whereas we find it to be 

 4.63 only, or one-third less. 



Again : in 1842, the four months of March, April, May and June 

 were those in which the largest amount of sediment was brought 

 down whereas in 1854-55 the four months of July, August, Sep- 

 tember and October give the largest amount of solid matter ; which 

 is, for the whole year, as 7.34 only to 13.99 in 1842 and for the 

 four heaviest months as follows. 



In 1842. In 1854 55. 



Average quantity of j by former paper at 3 fs. depth. 



water in the four > 25.50 oz. or 44.19 24.12 oz. or 41.80 



heaviest months,. . ) cubic inches. cubic inches. 



of silt, 24.77 grs. 7.S3 



of carb. lime, 13.56 grs. 0.72 



of silt in each cubic 



foot of water, 1678.92 grs. 353.46 grs. 



which last (i. e. the 353.46 grs.) are equal to 0.8366 cubic inches 

 or 2-^-2" one * wo thousand and seventy-second part of its bulk ; of 

 which however only about -^th is carbonate of lime. 



The cubic inch of the dry solid silt, as deposited, I shewed in my 

 former paper to weigh about 424 grains. To this our present result 

 433.63 grains to a cubic foot of water (see page 156) is so near an 

 approach that we may take it as the average, and in round numbers 

 say, for facility of recollection, that every cubic foot of water contains 

 a cubic inch of silt ; or more exactly in fractions, not 13 1 33 , one thirteen 

 hundred and thirty-third, part of its bulk of silt, as before found for 

 1842, but yyVs-th (one seventeen hundred and twenty-eighth part.) 

 This is still, however, an enormous proportion when we recollect the 

 mass of water discharged by the Hooghly alone, which Mr. Bedford, 

 the late Eiver Surveyor, by careful sectional measurement calculates 

 as follows at Moyapore, which is thirteen miles below Calcutta. 



