on Rivers and Canals. 
573 
Finally, the natural cohefion of the particles of water 
in an horizontal bed contributes to retard its motion pre- 
cifely by the fame force which contributes to accelerate 
it in an inclined bed. By diminifhing or taking away the 
above obftacles to the free motion of water in rivers and 
canals, the velocity of their currents will be increafed in 
the fame proportion, and thereby alfo all the dangers and 
ravages of inundations may be prevented, as we fhall 
fhew hereafter. 
But if fome or all of thefe caufes, in a greater or lefTer 
degree, did not exift in rivers of confiderable depth and 
declivity, it is demonftrated ( "\ that the velocity of their 
currents would be accelerated to twelve, fifteen, and, in 
fome cafes, even to twenty times more than it is at pre- 
fent in the fame rivers, whereby they would become ab- 
abfolutely un navigable. 
22. The waters in a river or open canal have their 
motion accelerated, fo long as the effects proceeding from 
gravitation, declivity, depth, in a word, fo long as thefum 
of accelerations furpaffes the fnm of rejiflances. 
When thefe different funds, become equal to each 
other, the motion of the water is neither accelerated nor 
retarded, but remains equal, till fomething anew deftroys 
the equilibrium. . 
( a) Vide lecchi, Hvdroftat. et stattleri, Phyfic, tom. III. p. 252. 
Vol. LXIX. 4 F When 
