Note:  Do not rely on this information. It is very old.

Chladni Figures

Chladni Figures, in Acoustics, a convenient method of illustrating the vibration of plates or membranes. If a square brass plate be clamped in a horizontal position at its mid-point, and be covered with a thin layer of fine sand, its vibrations under varying conditions may be exhibited by the disposition of the sand, the particles being shaken from the vibrating parts of the surface on to the non-vibrating parts or nodes. Vibration of the plate is usually induced by drawing a well-resined bow across any definite point on the edge of the plate. The positions of the nodes are varied by placing one's finger at various points round the edge. If lycopodium powder be used instead of sand, it will accumulate at the middle of each vibrating segment instead of at the nodes. This is due to the disturbance of the air in the immediate neighbourhood of the plate, and to the lightness of the powder.