River currents, rolling stones, and a spinning wheel
How opposed currents break each other; why the water rolls great stones; weights fly from the centre
Three studies share the sheet. If water strikes an obstacle at a it rebounds onto bank b and ruins it; to protect the bank, set a matching obstacle at c d so the rebounding currents meet and break each other in mid-river at f. A second passage, with a sketch of a boulder in the current, explains how great stones are turned by water — the current either encircles the stone and scours the bed in front of it, or overtops it and scours beneath, undercutting its supports until it topples, working through a whole river bed. A cross-shaped figure of the orthogonal diameters of a wheel (a b c d) notes that in motion the weights seek to leave the centre, so their cords stay straight.
On this page
Breaking opposed currents to save the far bank
Water striking obstacle a rebounds onto bank b and damages it; setting a similar obstacle at c d makes the rebounding currents meet and break one another in mid-river at f, so the weakened water can no longer damage the opposite bank.
How the current rolls great stones along the bed
Stones are turned because the water either encircles them — scouring the earth or gravel in front until the stone topples — or overtops them, falling and penetrating to the bottom to undercut their supports; and so it works from stone to stone through a whole river.
Weights on a turning wheel fly from the centre
In the motion of this wheel the weights a b c d desire to depart from the centre, and therefore their cords stand straight.