0-25 foot 



per 



second 



0-50 „ 







0-70 „ 







1-00 „ 







2-25 feet 







3-33 „ 







4-00 „ 







4-50 „ 





n 



6-00 „ 





)» 



i?. Russell — On the Flow of Rwers, 8^c. 271 



Soft clay ... 



Fine sand 



Coarse sand and gravel as large as peas 

 Gravel as large as French beans 

 Gravel one inch in diameter 

 Pebbles, one inch and a half in diameter 

 Heavy shingle 



Soft rock, brick, earthenware 



Rock, various kinds 



From this table we may compute the rate at which the materials are 

 drifted along the bottom, the velocity of the current being known, 

 and also the average size of the sand and gravel of which the bed 

 and banks of the river are composed. We can always estimate the 

 pressure in lbs. on the square foot, which a given velocity will 

 produce, because if we express that velocity in feet of water, a 

 simple calculation gives us the force of the current in lbs. on the 

 square foot or square inch, as the case may be. Let v equal the 

 velocity, Ti the head of pressure due to that velocity, and p the 

 pressure in lbs. on the square foot, then li = ■—, g, being the force 

 of gravity in absolute units, per unit mass, in the latitude of the 

 place; and p ^ A 62'4:lbs. on the square foot, or j? being the 

 pressure on the square inch, p = A^*. 



Professor Eankine states " that the least velocity of the particles 

 of water in contact with the bed of the river is about as much less 

 than the mean velocity, as the greatest velocity is greater than the 

 mean, and that they might be taken as bearing to each other the 

 ratios 3, 4, and 5. In very slow currents they are nearly as 2, 3, 

 and 4."^ 



The results obtained by Messrs. Humphrey and Abbot, after a 

 long-continued series of very careful measurements on the flow of 

 the Mississippi river, and the amount of sediment annually carried 

 down by it to the ocean, give about ^^ as the solid contents, but 

 they also concluded that sand and gravel was pushed along the bed 

 to the very mouth of the river to the amount of ^ of the mud held in 

 suspension. Some observations made on the earthy matter brought 

 down by the Ganges at Ghazepoor by the Eev. Mr. Everest, show 

 how much the sediment varies at different periods. He gave the 

 average amount of sediment suspended in the water during the floods 

 as its part by weight, or —^ part in bulk. He also found that the 

 proportion of solid matter held in suspension during the dry season 

 was but small compared with that during the rainy season, being 

 only in the ratio of 1 to 159'4,^ and the ratio of the quantity during 

 the eight months of the winter and dry seasons, to that of the four 

 months of rain was 1 to 21-263. 



The ingredients held in chemical solution ought also to be taken 

 into consideration, as in some streams the amount is anything but 

 insignificant, and it also expresses a certain rate of decomposition 

 and wearing away, as proved by the suites of caverns which are 

 found to exist in all limestone formations. 



^ and s Civil Engineering, Professor Rankine. ^ and * Hydraulics, M. Du Buat. 

 ' Elements of Geology, Sir Charles Lyell. ^ Principles, Sir C. Lyell, 



