Knowledge & Memory

The Scientific Volvelle as a Layered Circular Lookup and Transformation Engine

Period and origin

Medieval and early modern manuscripts and printed books

What it was built to do

To perform calendrical, astronomical, navigational and logical operations on a page, by turning paper discs.

How the mechanism works

Each layer carries a scale or a partition of a cyclic variable, and a pivot enforces a common centre. Rotation creates a physical relation among the variables; windows and pointers select the output.

Input

One or more angles, set by rotating the discs.

Transformation

Constrained superposition of the layers’ cyclic scales about a shared centre.

Output

A value read through a window, at a pointer, or off an engraved curve.

What is evidenced

Established: the artefact or the documentary record carries this directly.

What it demonstrates

That data, transformation, control and display can occupy one surface - an executable graphical interface. Llull’s combinatorial figures and the later astronomical volvelles should not be collapsed into one machine type beyond that common rotary interface.

All mechanisms