Communicating vessels: a stone raises the water
A hydrostatic study of equilibrium, labelled c, a, b, n
A diagram at the upper right shows two communicating vessels: in one, a stone presses down on the water and forces it to rise in the other. The note below reasons that when the raised water c-n, multiplied by its weight, equals the water a-b pressing on the reservoir, the system halts and the two bodies of water stand 'outside their element in equilibrium as if on a balance.' It is an early study of hydrostatic balance, with further faint text continuing down the sheet.
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A stone pressing water between two vessels
Two connected vessels are drawn: a stone or weight compresses the water in one so that it climbs in the other, its parts labelled c, a, b and n. Leonardo treats the raised and the pressing columns of water as opposing quantities.
Equilibrium 'as if on a balance'
When the rising water c-n, multiplied by its weight, equals the water a-b that presses on the reservoir, the motion stops and the waters rest 'outside their element in equilibrium as if on a balance.' Leonardo frames the hydrostatic condition as a problem of weights on a scale.