Notes on a Proportional Compass, with a Tool List
Fixed compass arms, a workshop list of materials, and an instruction to make fine subdivisions
A mixed leaf on drawing instruments: sketches of hinged compasses and dividers accompany a note that the arms are to be kept unchanging (immutable) from the centre of the semicircles, and a margin memorandum naming a proportional compass among a short list of tools and materials. Leonardo weighs whether the sides should be straight or curved ('better curved') and closes with the instruction to make fine subdivisions. A faint winding watercourse is drawn at the lower left, and the sheet carries further untranscribed jottings not included in the transcription.
On this page
Fixed arms of a proportional compass
The central figure is annotated so that the arms stay unchanging from the centre of the semicircles to the centre of convergence, with a correction: better, unchanging as far as the centres of the semicircles. The note governs how the hinged instrument keeps its proportion as it opens.
Workshop list of tools and materials
A left-margin memorandum lists items apparently needed at the bench: cap, small scissors, board and emery, bowl, bench prop, fine thread, dressing the set-square, a proportional compass, and silk laces. It reads as a supply note beside the instrument studies.
Straight or curved sides, and fine subdivision
Beside the list Leonardo notes that abc is straight and fdo is straight, 'and so all of them,' then judges 'better curved.' A closing line instructs him to make fine subdivisions, tying the instrument to the geometric task of dividing arcs.
Sketches of dividers and hinged compasses
The upper and middle of the sheet carry several drawings of two-armed instruments resembling dividers or proportional compasses seen open at an angle. They visualise the device the accompanying notes describe.
Faint winding watercourse
At the lower left a faint double line meanders down the sheet like a river course. It is drawn only, without accompanying transcribed text, and its purpose is not stated in the bundle.