Chladni, Ernst Florenz Friedrich
Chladni, Ernst Florenz Friedrich
(b. Wittenberg, Germany, 30 November 1756; d. Breslau, Germany, 3 April 1827),
physics.
Except for a few publications on meteorites, in which he proposed their extraterrestrial origin, Chladni devoted his research to the study of acoustics and vibration. His most important work was in providing demonstrations of the vibrations of surfaces, using the sand pattern technique which he devised.
The son of Ernst Martin Chladni, a jurist whose family had come from Hungary in the seventeenth century, and Johanna Sophia Chladni, he himself was obliged, against his will, to study jurisprudence. He received his degree at Leipzig in 1782; but after the death of his father he turned to science, choosing acoustics as his particular area of experimental investigation. His choice was almost certainly influenced by his interest in music. An amateur musician, Chladni designed and constructed two keyboard instruments, the euphonium and the clavicylinder, both being variations of the glass harmonica. The results of his first project, a study of the vibrations of plates, were published in 1787. For the remainder of his life he alternated between periods at his home in Wittenberg, where he continued his experimental studies and wrote several treatises on acoustics, and travel in Europe, demonstrating the vibrations of plates by his sand figure method (see below) and performing on his musical instruments. His travels also brought him into personal contact with Goethe, Lichtenberg, Olbers, Laplace, and others.
During the eighteenth century, scientists had undertaken experimental and theoretical work on the vibration of strings and had made attempts to study the vibration of rods and membranes. The vibrations of solid plates had not been treated, and Chladni, in his first report, emphasized that although the vibration of strings was understood, the production of sound by solid plates was not.
By spreading sand over plates and running a violin bow over their edges, Chladni was able to observe the structure of the resulting vibrations, because the sand collected along the nodal curves where there was no motion. Patterns formed in this way were symmetrical and often spectacular, the lines of sand forming circles, stars, and other geometric patterns. Chladni first used circular and rectangular plates of glass and copper, three to six inches in diameter. Later he extended his observations to ellipses, semicircles, triangles, and six-sided polygons. He generally fixed the plates at one internal point, which became a node, and left the sides free. In a few cases a stationary point or line occurred on the edge of the plate.
Chladni analyzed the sand patterns by classifying them according to geometrical shape and noting for each the corresponding pitch. Thus he was able to emphasize that the patterns and sounds of a vibrating plate are analogous to the shapes and tones of the modes in the harmonic series of a string.
In addition to his analysis of surface vibrations, Chladni studied the vibrations of cylindrical and prismatic rods. For the latter, he again used the sand figure method. He deduced the velocity of sound in solids from the pitch that a long rod of a given material produces when made to vibrate longitudinally. He measured the velocity of sound in gases other than air in a similar way: he compared the pitch of a wind instrument filled with the gas being studied with the normal pitch of the instrument under standard atmospheric conditions.
The visible demonstration of surface vibration received much attention in the 1820’s and 1830’s. In Germany, Friedrich Strehlke continued experimental investigations; Wilhelm and Ernst Weber dedicated their treatise on wave motion to Chladni, since they believed that the acoustical figures had stimulated the contemporary interest in the subject; and in the middle of the century Gustav Kirchoff worked on the mathematical theory of vibration. Thomas Young in England had been interested in the experiments as early as 1800, and Charles Wheatstone later analyzed them by a geometrical superposition principle. Michael Faraday knew about the phenomenon and experimented with the figures, considering especially the surrounding air currents.
French scientists showed even more interest in Chladni’s work. Félix Savart, who was truly Chladni’s professional successor, carried on experimental investigations. Jean Baptiste Biot and Siméon Denis Poisson collaborated on a study of the sound vibrations of gases and gave much attention to Chladni’s relevant experiments. The most organized activity was in the study of the theory of the vibration of surfaces. Chladni had visited the Paris Academy in 1808 and had demonstrated the vibration patterns before an audience that included not only the leading French scientists but Napoleon himself. The physicists at the Academy responded by announcing a prize competition for the best mathematical study of elastic vibrations. They noted a similarity between Chladni’s demonstration of the nodal curves in vibrating surfaces and Joseph Sauveur’s demonstrations of the nodal points in vibrating strings a century earlier. Since Sauveur’s efforts had led to fruitful mathematical work, it was expected that the sand figures would have as beneficial an effect on theory. Sophie Germain was an early contributor to the large body of work on the mathematical theory of vibration, which, until the middle of the nineteenth century, is associated principally with Louis Navier, Poisson, and Augustin Cauchy.
BIBLIOGRAPHY
I. Oringinal Works. Chladni first described his early experiments using the sands figures in Entdeckungen über die Theorie des Klanges (Leipzig, 1781). They were presented with additional observations in Die Akustik (Leipzig, 1802), which is also a general acoustics text containing very complete historical material. This appeared in French translation in 1809 (Traité d’acoustique). There was a second edition, the Neue Beiträge zur Akustik (Leipzig, 1817). The work on the instruments was described in Beiträge zur praktischen Akustik and zur Lehre vom Instrumentbau (Leipzig, 1821). Chladni described his ideas about meteorites in Über den Ursprung der von Pallas gefundenen and anderen ähnlichen Eisenmassen, (Leipzig, 1794). For a complete listing of Chladni’s works, see Poggendorff.
II. Secondary Literature. Chladni gives an autobiographical summary in the introduction to his Traité d’acoustique. There are biographical essays by H. Schimanck, in Sudhoffs Archiv für Geschichte der Medizin and der Naturwissenschaften, 37 (1953) and by Kurt Loewenfeld, in Naturwissenschaftlicher Verein. Abhandlungen (Hamburg, 1929). There is also a biography by the acoustician F. Melde, Chladni’s, Leben and Wirken (Marburg, 1888). An interesting account of recent Chladni figure experiments, with comparisons to other nineteenth-century results and with photographs and analyses of them, will be found in Mary D. Waller, Chladni Figures: A Study in Symmetry(London, 1961).
Sigalia C. Dostrovsky