An extension of the method renders possible the determination of the velocity of sound in different gases.[1] This experimental apparatus is called a Kundt's Tube. In 1876 at Strasbourg in collaboration with Emil Warburg, Kundt proved that mercury vapour is a monatomic gas.[2] In light, Kundt's name is widely known for his inquiries in anomalous dispersion, not only in liquids and vapours, but even in metals, which he obtained in very thin films by means of a laborious process of electrolytic deposition upon platinized glass. He also carried out many experiments in magneto-optics, and succeeded in showing what Faraday had failed to detect, the rotation under the influence of magnetic force of the plane of polarization in certain gases and vapours.[1]