Angles of contingency on the sphere; concentric-circle diagrams
A pouncing method for the infinite variety of tangency angles, difficult for specular perspectivists
The sheet is filled with small geometric figures: several star-like shapes formed by intersecting circles and lines, circles with appendages, and a set of seven tightly nested concentric rings. The notes set out a method for making, by pouncing (spolvero), the points needed for the almost infinite variety of the angles of contingency (tangency), a task called difficult for those working in specular perspective. The angles given on the sphere b a n and c a n are said to correspond within the circle, as the portions a n o and a m p show. Letter labels key each diagram to its caption.
On this page
Angles of contingency on the sphere
The angles of contingency given upon the sphere b a n and c a n must correspond within the circle, as the two portions a n o and a m p show. The figures explore how these tangency angles can be laid out with the aid of nested circles.
Pouncing the points for the tangency angles
The aim is to make, briefly, the pouncing (spolvero) with the points necessary for the almost infinite variety of the angles of contingency. Pouncing is the transfer technique used to prick and dust a pattern onto a surface.
A task difficult for specular perspectivists
The construction of these tangency angles is described as a thing difficult for those working in specular perspective, that is, the perspective of mirrored or reflected images. The captioned circles and star figures accompany this remark.