On Friday evening, 8 November 1895, Wilhelm Conrad Ro¨ntgen, a 50‐year‐old professor of physics and recently elected rector of the Julius Maximilian University of Wu¨rzburg, Germany, was unusually late for dinner. And when he did arrive at the family living quarters above his laboratory in the Physical Institute, he did not speak, ate little and then left abruptly to return to the experiments that had so disturbed him that afternoon.