June 12, 1885.] 



SCIENCE. 



479 



The suggestion l that water in motion rolls 

 rather than slides,' is valuable as explaining 

 the L inner movements of the particles of water 

 among themselves,' which are aggregated in the 

 indirect currents found even in carefully pre- 

 pared beds, which are symmetrical, smooth, 

 and straight. These movements were well 

 illustrated by Mr. Francis, in a series of ex- 

 periments at Lowell in 1867, by mixing white- 

 wash with the clear water of an artificial 

 channel. But the movements of mass inaugu- 

 rated by the relative movements of the particles 

 of water among themselves appear too feeble 

 to account for the immense quantities of sedi- 

 ment observed in suspension in great alluvial 

 rivers. It also seems clear, as concluded by 

 Mr. Herschel, in his paper on the erosive and 

 abrading power of water, "that direct friction 

 tends to drag materials along the bed, or down 

 the banks, if these have a sufficiently steep 

 side-slope," and that " the effect of the simple 

 friction of a stream upon its bed and banks is 

 not a source of danger : its action is very slow, 

 and it has never been shown to be of a danger- 

 ous character in any instance." Certainly the 

 sedimentary grains have no power of motion 

 independent of the water surrounding them ; 

 and friction against a smooth bed could not 

 impart such vertical movement to the water 

 as is necessary to lift these grains, except in 

 the slight degree that may result from the 

 movement of the particles of water among 

 themselves. The conditions that prevail in 

 natural stream-beds are necessary for a great 

 suspension of sediment. The projections, in- 

 equalities, and sinuosity of such beds expose 

 the material composing them to the impact of 

 the current rather than to simple friction, and 

 also cause those extreme indirect movements 

 of large masses of water that, in great rivers, 

 develop whirls, boils, and eddies, and which 

 alone are capable of lifting numerous and 

 coarse grains of silt, sand, and even gravel. 

 When a 'boil' rises in the Mississippi River, 

 the surface may be raised many inches, and 

 the charge of sediment so dense, that it is seen 

 to roll away from the crater in cloud-shaped 

 masses. 



The suspension of sediment is, then, only an 

 indirect result of the velocity, depending more 

 directly upon the character of the bed — its 

 symmetry, smoothness, and straightness, — 

 than upon the velocity, or the relative depth 

 of its different reaches and stages. 



The amount of sediment suspended through- 

 out the Mississippi River appears, however, 

 more controlled by the tributary most largely 

 supplying its volume at the time than upon 



any or all other causes. It was noticed by 

 Capt. Brown, U. S. corps of engineers, that 

 "the Missouri was one of the greatest con- 

 tributors of sand to the Mississippi River," 

 observably even in the South Pass, 1,300 miles 

 below its mouth. 



The apparent anomalies in the following 

 table are largely explained by the relative 

 discharge of the Missouri and the clear-water 

 tributaries. It will be observed that frequent- 

 ly the aggregate bulk or weight of sediment 

 passing per second (2 x sediment in each 

 foot) is greater at or below a mean stage than 

 it is at the maximum. 



In this table the velocity is divided into 

 half-feet per second ; and in the other columns 

 are given the number of periods during the 

 series of observation in which each rate pre- 

 vailed, the number of separate measurements 

 taken in each period, and the mean quantity 

 in each period at each rate of velocity. 



Fulton, Nov. 27, 1879, to Oct. 12, 1880, 

 Mississippi River commission. 





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o 

 c3 



c3 

 > 





f cun3 





> 



o ^ 



<" a 



<o 



CB 





*- a 



o 



o . 





O to 

 O in 



■3? 



3 

 Ph 



■s a 



o § 



i 



Q <B O 



£8 



o U 



"Ss 6 



CD cS 

 .2 



H 



o ^ 



6 



las 



* So 



2.0 @ 2.5 



1st 



n 



339 



5.5 @ 6.0 



1st 



1 



235 





2d 



14 



361 





2d 



1 



530 



2.5 @ 3.0 



1st 



9 



511 





3d 



8 



536 





2d 



4 



311 





4th 



1 



355 





3d 



5 



434 





5th 



2 



915 



3.0 @ 3.5 



1st 



4 



311 





6th 



3 



813 





2d 



6 



647 



6.0 @ 6.5 



1st 



1 



335 





3d 



9 



524 





2d 



1 



200 



3.5 @ 4.0 



1st 



1 



290 





3d 



6 



317 





2d 



8 



271 





4th 



1 



380 





3d 



4 



754 





5th 



1 



275 



4.0 @ 4.5 



1st 



3 



215 





6th 



5 



1,062 





2d 



4 



386 





7th 



1 



840 





3d 



4 



281 



6.5 @ 7.0 



1st 



1 



410 





4th 



12 



538 





2d 



1 



260 





5th 



2 



825 





3d 



1 



180 



4.5 @ 5.0 



1st 



2 



240 





4th 



4 



600 





2d 



2 



460 





5th 



1 



1,085 





3d 



4 



439 



7.0 t@ 7.5 



1st 



3 



400 





4th 



5 



777 





2d 



3 



562 





5th 



3 



758 





3d 



2 



140 



5.0 @ 5.5 



1st 



1 



390 



7.5 @ 8.0 



1st 



1 



325 





2d 



2 



885 





2d 



2 



145 





3d 



3 



908 











From the theory of Mr. Login, before quot- 

 ed, the inference is drawn, that when flowing 

 water is saturated, or loaded in proportion to 

 its velocity with sediment, the erosion and 

 caving of banks will cease. In this is involved 

 the assumption that the erosive power is that 

 of friction rather than of impact. Surveys 

 have been made by the Mississippi River com- 

 mission which show the relative amount of 

 caving on the right and left banks below Cairo. 

 In this part of the river the line of demarca- 



