Pythagoras, in the 6th century bc when in Greece philosophy and science were developing together, formulated a theory of light according to which rectilinear visual rays leave the eye and touch objects, so exciting visual sensation. Galileo Galilei asked in his Discorsi intorno a due nuove scienze if light propagates in an instantaneous way or with a finite speed, and devised an experiment which may be considered the forerunner of a later experiment in 1849 by A H L Fizeau. Rene Descartes’ particles are in continuous motion forming vortices, and light is simply the transmission of a pressure exerted on the eye from the motion of the vortices. In his work Dioptrique, scientist compared vision to the perception of an object detected by a blind man using his stick. Descartes went further, maintaining that physics, like Euclidean geometry, may be entirely derived from a priori principles, without any dependence on observation and experiment so supporting the doctrine of epistemological rationalism.