Chladni, Ernst Florens Friedrich (1756–1827)

German physicist, a pioneer in the field of acoustics. He developed an experimental technique whereby sand is vibrated on a metal plate and settles into regular and symmetric patterns (Chladni's figures), indicating the nodes of the vibration's wave pattern.

Chladni was born in Wittenberg, Saxony, and studied law at Leipzig. His interest in sound stemmed from his love of music.

In 1786 he began studying sound waves and worked out mathematical formulas that describe their transmission. In 1809 he demonstrated Chladni's figures to a group of scientists in Paris.

He also measured the velocity of sound in various gases by measuring the change in pitch of an organ pipe filled with a gas other than air (the pitch, or sound frequency, varies depending on the molecular composition of the gas). He invented various musical instruments, including one he called the euphonium, composed of rods of glass and metal that were made to vibrate by being rubbed with a moistened finger; he demonstrated it at lectures throughout Europe.