The San Marco lock-gate, with a 1489 ledger of fines
Why a sluice gate twists under pressure, how the lock was built on piles
The upper sheet studies the gate of a canal lock (conca): a framed elevation of the sluice, a detail of the closing mechanism, and a cross-section of its foundations. Leonardo explains that the gate-leaf a n twists out of square because part m c of the gate discharges more water than part s t, so it splays at the outlet and its point n is thrown sideways, threatening to break the banks; he records how the lock of San Marco was built with walls on piles bedded in gravel and lime and cross-laid green beams. The lower sheet is a dense ledger, dated November to December 1489, of small sums received as fines for misdeeds (condanagione di malificio) from a list of named individuals, totalled at the foot. Further account entries fill the lower leaf beyond what is transcribed.
On this page
Chain and latch that close the wicket
At the gate a note marks the closing gear: here is the chain with which the little wicket (portello) is shut by means of the latch (saliscendo).
Why the lock-gate twists under water pressure
The gate-leaf a n does not stand square with its seat because part m c of the gate throws more water than part s t; it therefore splays wider at the outlet and casts the point n of the gate n m to one side, and will break the banks.
How the San Marco lock was built on piles
The San Marco lock was made of walling on piles all along a b; its whole floor was packed with gravel and lime, and while fresh, green beams were laid crosswise, their tops filled with gravel and lime, then planked over. Note that these beams are first nailed fast upon piles.
Ledger of fines, November-December 1489
A running account records small sums received day by day, from 23 November to 24 December 1489, as fines for misdeeds from named people such as Lioneto da Ferneta and Giovan Lastra, entered in lire, soldi and denari and totalled at the foot.