The bridge at Borgo Ognissanti and the courses of wind
River scour with a lettered diagram, bridge dimensions in braccia, and how wind bends through valleys.
The left folio combines a survey of bridge spans at Borgo Ognissanti, giving widths, curbs, piers and pillars in braccia, with a lettered diagram of how a river deposits sand and silt, raises a submerged island and breaks through at low flood. A note aligns the wall of the Casace toward the gate of San Nicolo. The facing folio explains how the wind's course is turned into another's through the mouths of valleys, behaving like water poured into a cistern, and how it gathers and condenses on mountain summits.
On this page
River flow, silt deposits and floods (labels a-r)
When the currents a b and c b prevail, the water strikes at n and raises a submerged island over all of b d, depositing sand and silt in n d f. In low floods, with only a b e running, the water cannot pass the silt already laid and meets resistance at the outlet e d f, so the stream b d breaks at d and then at r.
Dimensions of the bridge at Borgo Ognissanti
Survey notes give the widths of bridge spans in braccia together with their curbs, piers and pillars: one span 12 wide with 4 pillars, another 15 wide with 2 pillars, a bridge 152 braccia long, and a further span 12 wide with 16 piers.
How wind bends through valleys and gathers on peaks
The wind's course is turned into another by the mouths of valleys, more among low winds than high, behaving like water that enters a cistern and pours out through the readiest conduits. It grows dense over the places it strikes, most on the mountain summits, where the reflex winds gather and rise, curving and then straightening with the wind that struck them.
Alignment of the wall of the Casace
A note written upside-down records that the wall of the Casace runs straight toward the gate of San Nicolo.