Instrument to demonstrate the vibration of a glas bell, early 19th century.
© Science Museum / Science & Society Picture Library
This instrument was designed to illustrate Ernst Chladni's work on the vibration of bells. Chladni (1756-1821) is widely regarded as the father of acoustics. A wine glas-shaped glas bell is set up on a mahogany base, above which is an eight-pointed star mounted on a vertical bras rod. Eight pith balls are suspended from the points of the star, so as to touch the inside rim of the glas. If the bell is held at one point of the rim and bowed at another, the motion of the pith balls indicates the vibration pattern of the bell.