This specific array of precision tuning forks are highly-specialized experimental forks that relate directly to Koenig’s long-standing disagreement with Helmholtz on the nature of combination tones. Some of them date back to Koenig's display at the 1876 Philadelphia exposition.
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 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.