How struck water divides: eddies, angles, and the scoured bank
The four principal motions of reflected water and the angle of incidence against an embankment
A figure of four eddies accompanies the rule that any water struck against an object divides into four principal, varied motions, right and left, high and low, of which the low is harmful to the bottom. A second sketch distinguishes an acute angle a from an obtuse angle b, stating that of the four motions of dividing water the fastest is the one that reflects at the more acute angle. A third figure shows an embankment struck by water with a diagram of the angle of incidence a, b, d e c: when that angle is formed between very dissimilar angles the percussion at b is weak, so the water does not reflect upward and does not scour the bottom at e.
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Struck water divides into four principal motions
Every water struck against an object divides into four varied and principal motions, that is right and left, high and low. The low motion is harmful to the bottom. A drawing of four eddies illustrates the rule.
The most acute reflecting angle gives the fastest motion
Of the four principal motions that water makes as it divides in reflecting, the swiftest is the one that reflects through the more acute angle. The sketch marks a as the acute angle and b as the obtuse angle.
A weak angle of incidence spares the embankment's bed
If the course of the water strikes the embankment a c along the line d e, the angles a b d and d b c are very dissimilar, so the percussion at b is weak; it does not reflect upward and does not strike or scour the bottom e.