156 Miscellaneous Intelligence. 
1.) Maximum velocity. The Mississippi hydraulicians place 
this, on a calm day, at 8, the depth, and in general at depths 
varying with the force and direction of the wind, as represented 
by the following empirical formula, 
d=(0°317-+-0°06/)r, 
the maximum force, and 7 the hydraulic mean depth. 
e author reaches, from his discussion, the conclusion, that “in 
large rivers, we may consider the surface velocity in a calm 
time to be nearly the same as the maximum; while in narrow 
canals, especially when their sides are vertical, it may be consider- 
ably less.” 
onacalm day. He finds the parabola to be especially inaccurate 
A applied to the results of his own observations in the St. Clair 
iver, 
(3.) Mean velocity. One of the most important results obtained 
by the hydraulicians of the Mississippi was the establishment of 
a simple empirical formula connecting the mean with the mid- 
depth velocity, by means of which the mean velocity in the cross 
section of a stream could henceforth be deduced from mid-depth 
velocities observed at several points of the cross section. Henry 
maintains that the mean velocity obtains at 35, the depth, and 
recommends as a still easier method of measuring the dischar; 
of a stream, “to obtain the velocities at several points at 4% the 
depth, and multiply the mean by the area of the cross section.” 
We must reserve, for the present, any decided expression of 
opinion relative to the several points at issue between our author 
accurate determination, seems to have been effectually answered 
by Henry, by showing that his coefficient has withstood the most 
