Some 350 years ago, in his Discorsi e Dimostrationi Matematici Galilei], Galileo Galilei discussed whether or not light propagated with a finite though very high velocity, or with infinite speed, instantaneously. The ques tion was an open one then, with prominent proponents for either position. For example, Rene Descartes argued on philosophical grounds that light dispersed itself into all of space instantaneously, whereas Galileo was more inclined toward the idea of a finite velocity. In fact, he even reported about an early experiment, which, however, would have to be refined and per 1...