The fork-clock was first described by N. Niaudet in 1866. It is used to determine the frequency of a fork to high accuracy. The vibrating fork drives the clock in the same way as a pendulum in a pendulum clock–by way of an escapement mechanism. This Max Kohl clock uses a 100 Hz fork to drive a tiny escapement. Energy is provided by an enclosed wind-up spring. The three dials record the total number of vibrations. The absolute frequency of the fork can then be determined by comparison with an astronomical time standard.
Invented by John Shore in 1711, the tuning fork was initially used by musicians. After Chladni’s studies of its vibrations, however, it was also extensively employed by acousticians, who praised the purity of its sound. Hermann von Helmholtz, especially, based his experiments with beats, combination tones, and simple tones on tuning forks attached to resonators that enhanced their suitability for experimentation.
After coming to Paris in 1851, Rudolph Koenig trained with the violin maker Vuillaume until 1858, when he launched his own instrument-making business at Place Lycée Louis-le-Grand. Koenig’s workshop participated in Paris’s flourishing activities in scientific research and instrument-making from the 1830s to the 1880s. More specifically, it contributed to the development of acoustics as an independent field of research.
(The following description is from a “Description of Appunn’s Tonnemeters,” by Alexander J. Ellis, F.R.S., &c.; MS in the Western Galleries of the South Kensington Museum, 1880. With the tonometers. Science Museum technical file T/1876-466. The note was written by Alexander J.
Driesen, Otto. 1913. Das Grammophon Im Dienste Des Unterrichts Und Der Wissenschaft. Band I, Teil 1: Kindergarten, Volksschule, Mittelschule, Höhere Lehranstalten. Berlin: Deutsche Grammophon-Aktiengesellschaft.
Adjustable forks were used primarily as teaching instruments, although they may have had medical applications as well. These instruments seem to have been introduced in the 1890s and were common in 20th century high school laboratories. Adjustable forks could take the place of several individual forks and had the added advantages of being relatively inexpensive and quite durable. Moving the adjustable weight on each tine changes the tone by effectively changing the tines' length. Thus moving the weight down the tine raises the tone, and moving the weight up the tine lowers it.