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Parlor Harmonograph

Two swinging pendulums and a slowly decaying pen. Nudge the frequencies a hair off a whole ratio and watch the figure drift.

ratio 3 : 2

Lateral pendulum moves the pen side to side

Frequency 3.00

Phase 0°

Damping 0.010

Lateral pendulum moves the pen up and down

Frequency 2.00

Phase 90°

Damping 0.010

Rotary pendulum swings the paper in a circle

Frequency 1.00

Amount 0.20

Damping 0.008

Pen how fast you watch it draw

Speed 2

1 is slow enough to follow the pen with your eye. Changing speed doesn't restart the drawing.

Whole-number ratios give closed figures. Damping is what makes the line spiral inward, the way a real pendulum runs down.