Ernst Florens Friedrich Chladni (30.11.1756—3.07.1827) was a German physicist and the founder of experimental acoustics. He was born in Wittenberg. He graduated from the University of Leipzig (1782). He worked as a physicist in Wittenberg.
His main work was in acoustics. He discovered the longitudinal vibrations of strings, rods, plates, tuning forks and bells in 1787, and the rotational vibrations of rods in 1799. He was the first to study the vibrations of a tuning fork carefully and accurately, and in 1796 he established the laws of vibration of rods. He discovered (1787) and described the “acoustic figures” produced by the vibration of an elastic plate sprinkled with sand (Chladni figures). These experimental studies posed a new problem for mathematical physics — the problem of the vibrations of a membrane. He was the first to measure the speed of sound in various gases with sufficient accuracy. Contrary to the opinion prevailing at the time, he proved that sound travels through solids not instantaneously but with a finite speed, and determined (1796) the speed of sound in solids in relation to its speed in air. He explained the echo and determined experimentally the upper threshold of audibility of sound — 22 000 Hz. He invented a number of musical instruments. In 1802 Chladni's work “Acoustics” appeared, in which he gave a systematic exposition of acoustics.
His work concerned also meteoritics, in which he developed the theory of the cosmic origin of meteorites.
A corresponding member of the St Petersburg Academy of Sciences (1794).