Abstract

René Descartes included a picture of his "mesolabium" twice in his "Géométrie". The functioning of this device is shown in an interactive simulation and it is further explained. The mesolabium was used by Descartes to compute multidimensional roots. It illustrated Descartes' classification of curves according to their grade of composition. Furthermore, it showed against the opinion of the ancients that composite curves were a legitmate part of geometry. Finally, by its means Descartes established continuous movement as a definitory criterion for geometric constructability.