The Savart wheel is an acoustical device that was created by French physicist

Physicist

A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...

 Félix Savart

Félix Savart

Félix Savart became a professor at Collège de France in 1836 and was the co-originator of the Biot-Savart Law, along with Jean-Baptiste Biot. Together, they worked on the theory of magnetism and electrical currents. Their law was developed about 1820. The Biot-Savart Law relates magnetic fields to...

 (1791-1841), which he used for research on lower frequency limits of hearing.

The device consists of a mounted metal disk having a large number of teeth with uniform spacings on its circumference

Circumference

The circumference is the distance around a closed curve. Circumference is a special perimeter.-Circumference of a circle:The circumference of a circle is the length around it....

. When the toothed disk is spun in rapid revolution, and an edge of a playing card

Playing card

A playing card is a piece of specially prepared heavy paper, thin cardboard, plastic-coated paper, cotton-paper blend, or thin plastic, marked with distinguishing motifs and used as one of a set for playing card games...

 is held against the teeth, it produces a shrill tone. When the speed of the wheel slows down, the shrill tone correspondingly diminishes in pitch. Thus, the frequency in tone is directly proportional to the rotation rate of the disk.

A variation of the Savart wheel has a series of toothed wheels which can be used to produce the sound of a major chord

Major chord

In music theory, a major chord is a chord having a root, a major third, and a perfect fifth. When a chord has these three notes alone, it is called a major triad...

.