208 Hydraulics of the Mississippi River. 
results. The data were not in all the cases known with equal 
degrees of exactness; but the small ratio of the errors to the 
distances on which the computations severally depend is not 
only satisfactory, but even os eet In the last example but 
one, the error is regarded by the authors, as having been proba- 
bly i in great measure sitetiinad by the occurrence of crevasses 
‘between the points observed. The error which is largest in 
absolute amount is that between the Arkansas and Ohio rivers 
at low water, whieb! is regarded as possibly due to sand bars. 
The final test, and, as it seems to us, the most satisfactory ¢ 
all, consists in the application of the new formula to the so 
tion of the important question, how much will the level of a 
river be raised at a ee locality, at which the cross-section and 
discharge are kno any given definite i rescines? of the dis- 
charge? In Seenstttteels F this question, it is commonly assumed 
that the slope of the river is unaltered by the fucteased voll 
discharge. But, as this assumption is not true, the results 
which are deducéd from it are equally erroneous. In order to 
which fopalaten't the change 
The level of the water at de mouth of a river is not wai 
ffected “ite a flood. For a certain distance up the course of the 
yet begun to rise. It is thereon evident that the same stand of 
the river is not always accompanied by the same eee at any 
e same for the same stand of the river in rising and P fallin ng 
It is evident that observations on the passage of the great fl 
waves may be best conducted in the upper parts of the valley; 
inasmuch as the wave in its progress down the river tends, from 
the greater slope on the lower side, to spread itself over a 
and wider base, and loses therefore in the degree of its convexity 
Columbus, Kentuky, Me on this Pimathte first selec 
stu The cross-sectio , perimeter, width, gauge-level ‘ia 
dischs e of the river oie  aeternituied: for different dates during — 
the Baer 4 o— of six marked rises of the river, and the 
computed from the f formula for those dates. « 
ured, of course, the change pro- 
jot npg the i ev fp sa of discharge. : . 
