Drops of Water and Grasses on the River Bed
How a drop clings until its weight beats its bond, and how a 'wedge' of current sways bottom-rooted grass
Opening a section labelled 'the beginning of the book', Leonardo defines a drop as water that will not detach unless the power of its weight exceeds the power of its cohesion with the surrounding water. He states that motions made at the water's surface are repeated at every depth and across its whole breadth, a truth learned from grasses rooted on riverbeds. A small marginal sketch of water-borne grass, labelled n m b a o, shows how the 'wedge' (conio) of the current drives the blade first one way then the other as its impetus is spent.
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A drop holds until its weight overcomes its bond to the water
A drop is that which does not detach from the rest of the water unless the power of its weight is greater than the power of the bond it has with the water to which it is joined. The drop that has slower motion of water at its creation is generated more slowly.
Surface motions repeat at every depth and breadth
All the motions made by the water at its surface are likewise made at every degree of depth below it, and similarly in every part of its breadth. This, he notes, is learned from the grasses attached to the bottom of rivers.
The wedge of water (conio n m a o) drives grass n a toward b
Because every impetus is consumed by the motion of the moving body over time and length of travel, the grass n a, having spent its impetus and left oblique, is pushed from its place by the wedge of water n m a o and driven with impetus toward b. Once that impetus is spent, the wedge acts on this side as it did on the other, and so it continues while the accompanying bodies last, from surface to bottom and in every direction.