Harmonic analyzer

From Ccpi

In 1894, Olaus Henrici (1840-1918) devised a harmonic analyzer for finding the fundamental and harmonic components of complex sound waves. It consists of multiple glass spheres, called rolling-sphere integrators, connected to measuring dials. The image of a sound wave is placed under the device. The user moves a mechanical stylus along the curve's path, tracing out the wave form. As the stylus moves along the changing amplitude, the rolling-sphere integrators rotate, such that the first integrator rotates once over the entire length of the curve, representing the fundamental wavelength. Subsequent integrators rotate additional revolutions, with the fifth and final integrator turning fives times over the entire length of the curve. The end result is an instrument capable of computing the first ten Fourier coefficients of the curve.