Eddies at a Bend and a River Crossing a Lake
Where a current splits into a backflow (a b c), and whether a river tilts a lake's level
Two water problems share the page. First, with a forked course labelled S d a c b, Leonardo states that a backflow (retroso) always forms where the current is divided by the angle that bends it: water S a bent toward d splits at angle a, one part running on to d and the other turning back through a b c. Second, over a gridded diagram of a lake (a b c d) he poses the 'fine problem' of whether a river crossing a lake spoils the uniform distance of the lake's surface from the centre of the world, arguing from the principle that water does not move unless it descends and from equal delivery of water along a river's length, and ends 'turn the page.'
On this page
An eddy forms where a bend splits the current (S a to a d and a b c)
The backflow of the water is always where its current is divided by the angle that bends it. If water S a were bent from a to d, the angle a would divide it: one part would keep its ordinary course by a d, and the other would turn into a backflow by a b c.
Does a river passing through a lake tilt the lake's surface?
It is asked whether a river passing through a lake spoils the uniform distance the lake's surface had from the centre of the world. It is shown that the surface does spoil that uniform distance to give the river passage, provided the exit and entrance are of similar width, so that the water keeps a uniform course.
Water does not move unless it descends
The argument rests on the proposition that water does not move unless it descends, and on the proposition that every river in equal time delivers an equal weight of water along every part of its length. If the river carried water needing one braccio of fall per mile, 'turn the page.'