Villalpando's proportionatrix secunda
Construction of the proportionatrix secunda in a semicircle of diameter AG. Steps to find a point K of the curve from a point F of the semicircle:
- Semicircle of diameter AG and center D(diagram).
- Semicircle of diameter DG.
- A point F is selected on the large semicircle, FG is drawn cutting the small semicircle in H.
- Perpendicular HI from H to AG.
- Semicircle of center I and radius IG.
- K is the intersection of this semicircle with FG.
- L is the intersection of this semicircle with AG. FL is drawn.