Savart wheel

The Savart wheel is an acoustical device named after the French physicist Félix Savart (1791–1841), which was originally conceived and developed by the English scientist Robert Hooke (1635–1703).^[1]

A card held to the edge of a spinning toothed wheel will produce a tone whose pitch varies with the speed of the wheel. A mechanism of this sort, made using brass wheels, allowed Hooke to produce sound waves of a known frequency, and to demonstrate to the Royal Society in 1681 how pitch relates to frequency. For practical purposes Hooke's device was soon supplanted by the invention of the tuning fork.

About a century and a half after Hooke's work, the mechanism was taken up again by Savart for his investigations into the range of human hearing. In the 1830s Savart was able to construct large, finely-toothed brass wheels producing frequencies of up to 24 kHz that seem to have been the world's first artificial ultrasonic generators. In the later 19th century, Savart's wheels were also used in physiological and psychological investigations of time perception.

Nowadays, Savart wheels are commonly demonstrated in physics lectures, sometimes driven and sounded by an air hose (in place of the card mechanism).