After Joseph's studies at the "Atheneum", the lawyer Thirion, Joseph's uncle and guardian, forces him to enrol in the University of Liège in the Arts and Philosophy Faculty. On July 30th 1823 Joseph obtains the diploma of Candidate in Languages and on July 31 that of Candidate in Law. During these studies Joseph Plateau does a lot of things: he constitutes an herbal, collects minerals, and above all develops a passion for chemistry. He converts his rooms into a laboratory. He has health problems due to chlorine fumes. His curiosity makes him attend some classes in the chemistry department. He is so fascinated by what he sees that he makes a choice for science and obtains the diploma of Candidate in Science on 26 October 1824. At that time he thinks of a future in chemistry. Because of ill health, Thirion does not want to remain the guardian of the Plateau-children. In 1827 J. Plateau becomes a teacher of mathematics at the "Atheneum" school in Brussels. Though he is very busy he finds the possibility to publish his first paper in Quetelet's "Correspondance". He writes "Construire un angle équilatéral qui ait ses sommets sur trois circonférences données".

  Discs for the study of the mixing of colours
J.Plateau, Collection J.Plateau, Ghent

Two of the many discs used by Joseph Plateau to study the maximum of the colour-impression when colours are mixed due to the rotation of the discs.

"Sur les sensations produites dans l'oeil par les différentes couleurs" is his next paper. In it he proves that for each colour there exists a density between the lightest and the darkest, which leaves the maximum colour-impression in mixtures. This paper is the preamble to his fundamental studies of visual perception. His approach to experiment is very mathematical, as is demonstrated by his studies of the combination of two curves revolving around their axis. He is so fascinated by these constructions of locusses, that he draws several of them. Three are extant: the most beautiful one bears the mention "Coeur volant" in the handwriting of Plateau.


Construction drawing of the locus "Coeur volant" J.Plateau, Collection J.Plateau, Ghent.

Two parallel black surfaces, in which there are transparent mathematical curves, revolve in opposite sense at high speed. Their speeds are a multiple one of the other (1:2). When these discs are viewed against a luminous background then the varying intersections of the curves form a stationary curve about which Plateau says that it is a joy "de voir les courbes se dessiner dans l'air".

iiiiiiii i