Bi-angular surfaces and the curvi-hollow square
Faint verso continuing the quadrature studies with lettered lune and ring-area equalities
The verso, faint and largely legible only in its lower half, continues the recto's quadrature studies with small geometric figures. A square inscribed between two circles is used to show that the white area equals the ring-shaped 'circular parallel' once the four greatest portions are removed. A row of five lettered bi-angles introduces a short section 'on bi-angular surfaces', followed by a 'curvi-hollow square' equated with the circular parallel and a compound figure keyed to a circle K, closed by a short column of numbers.
On this page
The white area equals the circular parallel
The white (empty) area is worth the circular parallel, because by removing from it the four greatest portions ... The passage breaks off but ties the empty square to the ring-shaped area of the recto's method.
On bi-angular surfaces
A heading, 'On bi-angular surfaces', labels a set of five bi-angles marked a b c d e f, cataloguing the lune-like two-cornered figures used throughout the quadrature demonstrations.
The curvi-hollow square equals the circular parallel
Labelled 'curvi-hollow square', this surface is declared worth the circular parallel by the first proposition above. It applies the recto's equal-area rule to a square hollowed by curved cuts.