Jules Antoine Lissajous, date and photographer unknown.
Jules Antoine Lissajous (French pronunciation: [ʒyl ɑ̃twan lisaʒu]) (March 4, 1822, Versailles – June 24, 1880, Plombières-les-Bains) was a Frenchmathematician, after whom Lissajous figures are named. Among other innovations, Lissajous invented the Lissajous apparatus, a device that creates the figures that bear his name. In it, a beam of light is bounced off a mirror attached to a vibrating tuning fork, and then reflected off a second mirror attached to a perpendicularly oriented vibrating tuning fork (usually of a different pitch, creating a specific harmonic interval), onto a wall, resulting in a Lissajous figure. This led to the invention of other apparatus such as the harmonograph.