Door-latch and lock mechanisms; form follows function
How a door is closed and locked, with catch a meeting b, and a rising latch on side f
The sheet treats door hardware and the principle that, once an instrument is made, the necessity of its operation dictates the form of its members, forms of infinite variety yet all subject to 'the rules of the four books'. The notes explain how a catch a meets b when a door opens from the opposite side f, and how a door is closed and locked by a nose-catch fixed to a rising latch (saliscendi). Several door leaves, frames, latches and lever mechanisms are drawn across the page.
On this page
An instrument's form follows the necessity of its function
Once the instrument is created, the necessity of its operation demands the form of its members; these are of infinite figures, yet all will be subject to the rules of the four books.
Catch a meets b as the door opens from side f
The parts are lettered a a f, and a note explains that a touches b when the door opens from the opposite side, on side f. The letters mark the moving catch and its seat on the drawn door mechanism.
A door-lock worked by a nose-catch on a rising latch
A further note gives the way a door is locked: the 'nose' (catch) is attached to the rising latch, the saliscendi, in the manner shown below on the sheet.