Lissajous, Jules Antoine (1822-1880)

French physicist who from 1855 developed Lissajous figures as a means of visually demonstrating the vibrations that produce sound waves. Lissajous was born in Versailles and educated at the Ecole Normale Supérieure. He became rector of the Academy of Chambéry in 1874, and then took up the same position at Besançon in 1875. Lissajous first reflected a light beam from a mirror attached to a vibrating object such as a tuning fork to another mirror that rotated. The light was then reflected onto a screen, where the spot traced out a curve whose shape depended on the amplitude and frequency of the vibration. He then refined this method by using two mirrors mounted on vibrating tuning forks at right angles, and produced a wider variety of figures. By making one of the forks a standard, the acoustic characteristics of the other fork could be determined by the shape of the Lissajous figure produced. Lissajous figures can now be demonstrated on the screen of an oscilloscope by applying alternating currents of different frequencies to the deflection plates. The curves produced depend on the ratio of the frequencies, enabling signals to be compared with each other.