Geometry: radius of an arc, a perpendicular, and a self-stopping door
Two compass constructions and a hinged door designed to halt as it swings
The upper part of the sheet carries two compass-and-straightedge exercises: one finds the center and size of the circle that would complete an arc a b by raising perpendiculars from it, the other raises a perpendicular over a base line c d. In the lower third Leonardo sketches a door whose hinge-beam is deliberately set out of true, so that the door stops before it can fall fully open. Additional geometric figures are drawn on the sheet beyond the three transcribed notes.
On this page
Finding the circle of an arc a b
At two points along an arc whose ends are labeled a and b, perpendiculars are raised and extended until they meet. Their intersection fixes the center of the circle that would contain the arc, and so tells how large that circle is.
Raising a perpendicular over base c d
Over a line segment with endpoints c and d, a perpendicular is erected, the figure taking the form of a pointed oval (vesica) crossed by the horizontal base and the vertical.
A self-stopping door
In the lower third of the folio a door on hinges is drawn whose supporting beam is not perpendicular. Because the beam is set out of true, the door will stop below the place where it tends to fall, arresting its own swing.