Chlandi Figures, Visualizations of vibration patterns from 1787 by Ernst Chladni: the technique consists of drawing a bow over a (circular, square, or rectangular) plate or membrane whose surface is lightly covered with sand. When stroked, a given plate will resonate at one of its natural frequencies. The sand bounces about on the plate until settling at nodal points (areas of zero movement) thereby producing intricate patterns.
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