6 o8 
Mr. mann's ‘Treatife 
the middle is produced by the aCtion of the centrifugal 
force, whereby the water endeavours to recede, in a direCt 
ratio of its velocity, from the center about which it 
moves. 
46. If rivers perfevered always nearly in the 
fame ftate (N° 5.) the belt means of diminifhing the 
velocity of the current, when it is found too great for 
the purpofes of navigation, would be by widening the ca- 
nal: but as all rivers are fubjeCt to frequent increafe 
and diminution, and confequently to very different de- 
grees of velocity and force in the current, this method 
is liable to produce very detrimental effects ; for, when 
the waters are low, if the channel is very large in pro- 
portion, the ftream will excavate a particular bed, which, 
according to the irregularities of the bottom, will form 
various turnings and windings with regard to the princi- 
pal bed ; and when the waters come to increafe, they will 
follow, to a certain degree, the directions which the bot- 
tom waters take in this particular bed, and thereby will 
ltrike againft the tides of the channel, fo as to deftroy the 
banks and caufe great damages. 
It would be poffible to prevent in part the bad effects 
proceeding from the current finking againft the banks, 
by opening, at thofe places where it ftrikes, little gulfs 
into the land, dug in fuch a form and direction as that the 
ftriking 
