An anorthoscope is a device that demonstrates an optical illusion that turns an anamorphic picture on a disc into a normal image. This happens when the disc is spun fast enough and seen through the four radial slits of a counter-rotating black disc. It was invented in 1829 by Joseph Plateau before further studies on the same principle led to his invention of animation through the phénakisticope in 1832. Anorthoscopes with a black background have a translucent picture and need a luminous slit revolving behind the image disc. To make them translucent, the discs were impregnated with oil on the back and varnished on both sides.
History
As a university student, Plateau noticed in some early experiments that when looking from a small distance at two concentric cogwheels, which turned fast in opposite directions, an optical illusion of a motionless wheel appeared. He later read Peter Mark Roget's 1824 article Explanation of an optical deception in the appearance of the spokes of a wheel when seen through vertical apertures that addressed a similar illusion. Plateau decided to investigate the phenomenon further and later published his findings in Correspondance Mathématique et Physique in 1828 On 9 June 1829, Plateau presented his yet nameless anorthoscope as "une espèce toute nouvelle d'anamorphoses" in his doctoral thesisSur quelques propriétés des impressions produites par la lumière sur l'organe de la vue, at the University of Liège. It was later translated and published in the German scientific magazine Annalen der Physik und Chemie. A letter to Correspondance Mathématique et Physique dated 5 December 1829 included pictures of a disc and the resulting image as an illustration of these "new species of anamorphoses". Plateau revisited this concept several times in the Correspondance Mathématique et Physique and by January 1836 he finally decided to have the device itself published. He sent a box with the instrument to Michael Faraday on 8 January 1836 since they both studied these kind of phenomena. Faraday had previously inspired Plateau to use a mirror with revolving discs, which helped Plateau to develop his Fantascope a.k.a. Phénakisticope. Faraday thought the anorthoscope was a beautiful machine with an exceedingly curious and good effect, and mentioned: "It has wonderfully surprised many to whom I have showed it and they all refuse to believe their own eyes and cannot admit that the forms seen are the things looked at". The device was marketed starting in 1836 by publishers like Newton & Co in London, Susse in Paris and J. Duboscq in Paris. Plateau apparently first used the name "anorthoscope" in a letter to his mentor / publisher / friend Quetelet. He decided to send an example of the device to Miss Quetelet as a gift. Soon after, he presented it to the Royal Academy in Brussels in 1836. Joseph Plateau created a combination of his Fantascope and the Anorthoscope sometime between 1844 and 1849 resulting in a back-lit transparent disc with a sequence of figures that are animated when it is rotated behind a counter-rotating black disc with four illuminated slits, spinning four times as fast. Unlike the phénakisticope, several people could view the animation at the same time. This system has not been commercialized; the only known two handmade discs are in the Joseph Plateau Collection of the Ghent University. Belgian painterJean Baptiste Madou created the first images on these discs and Plateau painted the successive parts.
21st century
A scientific paper on the effects of the anorthoscope was published in 2007. A rare completed 1836 anorthoscope set by Susse with twelve discs was auctioned for in 2013. The other two known extant sets of this edition are in the Werner Nekes collection and in the Joseph Plateau Collection in the Science Museum of the Ghent University.
