Book 9: water surging under a sluice-gate; how air condenses
Water forced from a narrow to a wide channel leaps the gate, with notes on air, water, smoke and dust in motion
The page opens Book 9, 'On the accidental risings of waters,' and carries at the upper right a pen sketch of channels with a sluice-gate (cateratta) and the churning waves it throws up. Leonardo argues that when water is driven from a narrow channel to a wider one under a gate, it surges up, leaps over the wider water, and its fall scours the canal bed in several places. A series of short paragraphs headed 'Air' then compare how air, water, smoke and dust condense or rarefy as they move through denser or lighter bodies.
On this page
Water driven under a sluice-gate leaps up and scours the bed
If a sluice-gate divides the wider water from the narrower, and the flow runs from the narrow side to the wide, the water surging beneath the gate leaps above the wider water. Its fall then hollows out the bed of the canal in several places with various leaps.
Air condenses when struck and when driven into a denser body
Air moving within air condenses both itself and the air it strikes; air driven into a body denser than itself condenses even more, while air driven into a lighter body rarefies. Water driven into a lighter body rarefies not in its quality but in quantity, spreading and thinning into a film.
Thick and thin smoke, and dust, rising through the air
Thick smoke born of a great flame fed by damp wood does not mingle with the air but seems denser above than in the middle, the more so when the air is cold. Thin smoke penetrates the ever-warm air and keeps thinning, while of the dust that penetrates the air the finer it is the higher it rises.