572 Mr. Mann’s Treatlfe 
rior is increafed, and confequently the velocity of the 
whole is axigmented (N° 1 3. 1 8.). In the fame manner 
a junction of rivers in the fame bed, by excavating and 
deepening it, augment the velocity of the common cur- 
rent, as we fhall fhew more particularly hereafter. 
a 1. On the other hand, flowing waters meet with 
many powerful caufes of refiftance to their motion, 
which tend continually to diminilh their velocity. Such 
are the following: 
1 ft, The attraction and continual fridtion of the bot- 
tom and the fides of the bed, contribute greatly towards 
retarding the motion of the water. 
2dly, The fame effedt is produced likew ife by the 
many obftacles which they meet with in their way ; fuch 
as inequalities in the bottom and fides of the channel, 
banks of fand and mud, rocks, trunks of trees, and other 
‘ iuch things. 
3dly, The many windings and angles made in their 
courfe, which produce fo much the more refiftance and 
hindrance to the motion of the water, as the courfe 
varies more and oftener from a right-line. 
4thly, The diminution of their declivity the farther 
they recede from their fprings; this being generally the 
leaft towards their mouths, which are for the molt part 
in extenfive plains. 
Finally, 
