Lissajous’s figures, Wheatstone apparatus for compounding two orthogonal oscillations

This video demonstrates the principle of Lissajous's figures and the Wheatstone apparatus.

The Lissajous figures are produced through a combination of two orthogonal oscillations harmonics. They can be generated by means of two tuning forks whose tines are equipped with mirrors. One tuning fork is fixed vertically in a holder, the other horizontally. An arc lamp produces a light beam. This is reflected by the mirror of the first tuning fork on the mirror of the second. The beam is then focused by a converging lens onto a ground glass screen, where it appears as a bright spot. When the tuning fork is vibrated, vertical oscillations of the light spot produce a vertical line, the other tuning fork vibrations produce a horizontal line. When both tuning forks are vibrated, the Lissajous figures appear. By changing the position of the cursors on one of the tuning forks, different figures can be produced.

The Wheatstone apparatus for combining two orthogonal oscillations enables one to obtain a whole series of Lissajous figures. A rod bearing a polished steel sphere can move in all directions. The its lower end is connected to two arms which are moved by a handle back and forth. Thanks to a special mechanism of the oscillation frequency of one of the arms can be varied from zero to a maximum while a hand indicates the relationship between the two frequencies. A light beam is reflected from the steel sphere floating on the rod-mail that appears as a bright spot. Thanks to the persistence of vision on the retina this generates a series of Lissajous figures.