The vibration microscope is an electromagnetically-driven adaptation by Hermann von Helmholtz (1821-1894) of the earlier optical comparator by Jules Antoine Lissajous (1822-1880). The device allows one to determine the frequency of a tuning fork or other vibrating object with respect to a fork of known frequency, by way of Lissajous figure analysis.
Wooden sticks, when dropped on the floor, sound a variety of tones. While the bars of a xylophone are varied in tone by changing their length, these “tone bars” are all of the same length and width, but have different thicknesses and different densities and elastic properties.
A tonometer consists of a series of steel cylinders that resonate at specific frequencies upon being struck with a metal hammer. They are used as standards for high frequencies, in the same manner as tuning forks. The transverse vibrational frequencies (i.e. fundamental and harmonics) of a given cylinder depend on the length, elastic modulus, and linear density of the metal.
William Stern invented the tone variator in 1897 to study human sensitivity to changes in pitch, going beyond the traditional psychological research of studying the sensitivity to differences in discrete tones. The instrument consists of an adjustable brass resonator (see Helmholtz resonator for more information), which is supplied with a constant flow of air across an opening at the top.
