on Rivers and Canals. 6 0 1 
42. I call center of the current , or, more properly, line 
of great c.Jl current y that line which pagfes through all the fee- 
tions of a river , in the point where the velocity of the current 
is the great ejl-o f all. W e have feen above (N° 25.) that if the 
current of a river is regular, and in a right line, its center 
or line of greateft velocity will be precifely in the center 
of the fedtions (N° 6.) : but, on the contrary, if the bed 
is irregular and full of turns and windings, the center or 
line of greateft current will likewile be irregular, and 
often change its diftance and direction with regard to the 
centers of the fedtions through which the waters flow, 
approaching fucceflively, and more or lefs, to all parts of 
the bed, but always in proportion and conformably to the 
irregularities in the bed itfelf. 
This deviation of the line of greateft current from the 
centers of the fedtions through which it pafles, is a caufe 
of many and great changes in the beds of rivers, fuch as 
the following : 
lit, In a ftraight and regular bed, the greateft corro- 
fion of the current will be in the middle of the bottom 
of the bed; becaufe it is that part which is' neareft to the 
line of greateft current, and at the fame time which is 
mo ft adted upon by the perpendicular compreflion of 
the water. In this cafe, whatever matters are carried off 
from the bottom will be thrown, by the force of the 
% 
current, 
