'What is water' — the nature and powers of the element
How air trapped below can lift water, and the percussion of water in an even channel
The page opens with Leonardo's celebrated aphoristic definition of water as an element: the second-lightest and second-most mobile, restless until it reaches the sea, the humour of all living bodies, taking every colour and savour yet having none of its own. A marginal well-diagram (pozzo, acqua, aria) argues that a bag of air pinned at the bottom will press upward as hard as the water presses down. A channel diagram then reasons that the straighter the return path of the water, the stronger its percussion, so the point of angle e n m is struck harder than that of x z f.
On this page
The definition and powers of water
Water is the second least heavy of the four elements and never rests until it joins the sea. It is the increase and humour of all living bodies, penetrates all porous things, rises as vapour with heat and freezes with cold, and takes on every odour, colour, and savour while having none of its own. Every small obstacle on bank or bottom causes ruin on the opposite side.
How air can hold up water: the bag in the well
A bag full of air pinned to the bottom of a well, sealing it so no water passes beneath, presses upward toward the surface with no less force than the water presses down to touch the bottom. Rising, it lifts the water above and unburdens the bottom, so that by this reasoning the well could almost stand without a floor.
Straighter return, greater percussion (angle e n m vs x z f)
The more water runs down the slope of an even channel, the more powerful its percussion on whatever opposes it, because elements return to their natural place by the shortest, straightest line. Since the lines of angle e n m are straighter than those of x z f, a thing at point m is struck harder than one at f; wind in equal-width streets does the same.