on Rivers and Canals. 585 : 
becaufe rivers remaining in the fame hate only widen 
their beds to a certain pitch which they do not furpafs. 
32. M. de buffon remarks, “ That people accuf- 
“ tomed to rivers can eafily foretell when there is going 
“ to be a fudden increafe of water in the bed from floods 
“ produced by fudden falls of rain in the higher countries 
“ through w’hich the rivers pafs. This they perceive by 
“ a particular motion in the w r ater, which they exprefs 
“ in their dialed!, by faying that the river's bottom moves ; 
“ that is, the water at the bottom of a channel runs off 
“ fafter than ufual; and this increafe of motion at the 
“ bottom of the river always announces a fudden in- 
“ creafe of water coming down the ftream. Nor does 
“ their opinion therein,” continues the fame author, 
“ feem to be ill-grounded on the nature of things; for 
“ the motion and weight of the waters coming down, 
“ though not yet arrived, rauft ad! upon the waters in 
<{ the lower parts of the river, and communicate by im- 
u pulfion part of their motion thereto ; fince a canal or 
“ river contained in its bed is to be confidered in fome 
t( degree as a column of water contained in a long tube, 
“ where the motion is communicated at once throughout 
“ the whole length.” In a river or canal, open above, it 
is only communicated to a certain diftance; that is, as far 
as the impullive force of the new increafe and fuperior 
rapidity 
