Ernst Chladni’s original illustrations of various patterns produced when sand placed on a plate is vibrated at a given frequency (“Chladni’s figures”) are available over at Monoskop (1,925 × 2,431 px). The plates are extracted from two books by Chladni: Die Akustik, 1802 (a French translation from 1809, Traité d’acoustique, is available at BNF’s Gallica and on Google Books as well) and Entdeckungen über die Theorie des Klanges, 1787 (Google Books, ETH-Bibliothek, ECHO). More reproduction (white sand on black plate) can be found in Charles Wheatstone’s 1833 Proceedings of the Royal Society of London “On the Figures Obtained by Strewing Sand on Vibrating Surfaces, Commonly Called Acoustic Figures”. Everything from those books is public domain. For another take on Chladni’s figures, see also “80 Mesh – La Forma del Suono” by the collective Marte.