August 26, 1904.] 



SCIENCE. 



275 



TABLE 11. 



Length and Average Width of Akeas Cut Expressed in 50ths of a Sq. M. 



Sheets 13 to 17 Inclusive. 



in two-hundred-and-fiftieths of a square 

 mile and classified with respect to reaches, 

 bends and meanders in the two sections of 

 the river. 



The first column of Table I. gives the 

 amount of bank cutting ; the second column 

 the amount of bar cutting. Island cutting 

 is counted right or left, as the island lies 

 on the right or left side of the line of 

 deepest channel. The fourth column gives 

 the amount of cutting involved in changing 

 a bank to a bar. This measurement is 

 necessarily somewhat indefinite. The sub- 

 totals in column five allow easy comparison 

 of cutting in meanders, bends and reaches. 

 The totals, on the other hand, furnish 

 means for rougher comparison, although it 

 is thought that, undifferentiated as totals 

 must always be, it is well to examine the 

 different sets of data separately. By a 

 careful system of checking, the percentage 

 of error in the measurements was found to 

 be but little more than one per cent. Bar- 

 cutting in every case but one is less on the 

 side on which there is the greater bank 

 cutting. In the more finely subdivided 

 records from which the sub-totals in this 

 table were made up, this fact comes out 

 even more strongly. In the bends there is 



a greater area of bar removed per length 

 of area cut or per length and area of bank 

 removed than is removed in the meanders. 



It would seem that the most significant 

 figure in the whole table is 3,054— repre- 

 senting the amount of bank cutting in 

 meanders on the right side of the river. 

 It exceeds the corresponding figure on the 

 left side by more than 16 per cent. It is 

 in this part of the channel that the divert- 

 ing tendency due to rotation gives its great- 

 est support to the maximum selective influ- 

 ence on velocities developed here under 

 centrifugal force. Moreover, it is in this 

 part of the river's course that the effect of 

 wind-waves in concealing the deflective 

 tendency is least, but a part of a right- 

 handed meander running at right angles to 

 the direction of the prevailing winds. In 

 the bends and reaches (sheets 13-17) the 

 left-handed cutting is in excess, as if the 

 winds here overcame the effect of the 

 earth's rotation. 



Although the Mississippi wears its chan- 

 nel as much on one side as on the other, 

 this fact does not contradict the theory of 

 deflection. The direction of flow in the 

 Mississippi is such that any tendency to 

 excess of right-handed over left-handed 



