564 Mr. mann’s 'Treat if: 
direction of the ftream of water, and whofe limits are 
thofe of the water itfelf which runs off in that place. 
7. I call feBions of equal velocity, all thofe where the 
water runs with equal velocity ; and fedlions of greater or 
defer velocity, thofe where the water runs falter or flower 
.refpedtively, and when compared to others. 
8. I call mean velocity of a current or Jlream of wa- 
ter, that which a river or canal would have, if all the 
parts thereof, to wit, thofe of the bottom, the lides, the 
middle, and the furfaee of the fame fedtion, ran with an 
equal velocity, in fuch a manner that there would pafs juft 
as much water in the fame time by this uniform motion, 
as there does now actually pafs by the irregular flowing 
of the ftream. 
II. propositions, or laws of action in rivers and canals. 
9. The motion of water in rivers proceeds from the 
fame principle which produces the defeent of heavy bo- 
dies upon inclined planes ; 
1 1 . The defeent of heavy bodies upon inclined planes 
follows exadtly the fame laws as thofe obferved in the 
defeent of heavy bodies in a perpendicular line towards 
the center of the earth; that is, 
ift, They defeend by a motion uniformly accelerated. 
2dly, The 
