August Kundt

August Kundt was born on November 18, 1839, in Schwerin, Mecklenburg-Schwerin. He studied physics at the University of Berlin under Heinrich Gustav Magnus, where he developed a passion for experimental physics. After completing his doctorate in 1864, he became a professor at the University of Zurich in 1868, then moved to the University of Strasbourg in 1872, where he established a renowned laboratory. In 1888, he succeeded Hermann von Helmholtz as professor of experimental physics at the University of Berlin, a position he held until his death in 1894. His teaching and mentorship shaped many future physicists, including Wilhelm Röntgen and Franz Exner.

Kundt's most famous contribution is the invention of Kundt's tube in 1866, a simple yet powerful apparatus for measuring the speed of sound in gases. The tube contains a fine powder (such as lycopodium) that forms distinct striations when a standing wave is established, allowing precise measurement of the wavelength. This method enabled accurate determination of the speed of sound in various gases, and it was also used to measure the ratio of specific heats (γ) for gases. Kundt's tube remained a standard laboratory tool for decades and is still used in physics education today.

In optics, Kundt conducted groundbreaking experiments on the anomalous dispersion of light in absorbing media, such as fuchsine and other dyes. He demonstrated that the refractive index changes rapidly near absorption bands, a phenomenon later explained by electromagnetic theory. He also studied the rotation of the plane of polarization in magnetic fields (Faraday effect) and the optical properties of metals. His work on the dispersion of light in liquids and solids provided crucial data for the development of the electromagnetic theory of light by James Clerk Maxwell and others.

Beyond his famous tube, Kundt made several lesser-known contributions. He developed a method for measuring the refractive index of gases using an interferometric technique, and he studied the acoustical properties of solid rods and plates. He also investigated the absorption of sound in tubes, which had implications for architectural acoustics. Kundt was known for his exceptional skill in glassblowing, which allowed him to construct intricate experimental apparatus. His laboratory at Strasbourg attracted international students, and he was a founding member of the German Physical Society. Despite his early death at age 54, his experimental legacy persisted through his students and instruments.

Kundt's tube

A glass tube with a movable piston and a powder that forms striations to measure sound wavelength.

Anomalous dispersion

A rapid change in refractive index near absorption bands, opposite to normal dispersion.

Faraday effect

Rotation of the plane of polarization of light passing through a material in a magnetic field.