_Newton_, in 1687, had correctly explained the revolution of the moon around the earth, and of the planets around the sun, as the co-operation of gravitation and inertia, and thence concluded also the elliptic form of the orbits of planets previously discovered by _Kepler_. _Leibnitz_ rejected this theory, _Huygens_ called it absurd, and the Academy of Paris as late as 1730 still favoured the theory of revolution of _Descartes_; it was only about the year 1740 that it was generally accepted. _Huygens_, himself, had formed in 1690 his theory about light-waves. For a long time it was misunderstood. Only in 1800, or somewhat later, it received its merited acknowledgment, but noted physicists like _Biot_ and _Brewster_ rejected it still for some time and held to the theory of emission. “Even in the intellectual world the law of inertia holds good” (_Rosenberger_, Gesch. der Physik, III, 1887, 139). The great discoverer _Galvani_ complained of being attacked from two opposite sides, by the scientists and by the ignorant: “Both make fun of me. They call me the dancing master of frogs. Yet I know I have discovered one of the greatest forces of nature.” When _Benjamin Franklin_ explained the lightning-rod to the Royal Academy of Sciences, he was ridiculed as a dreamer. The same happened to _Young_ with his theory of the undulation of light. “The Edinburgh Review” proposed to the public to put _Thomas Grey_ in a strait-jacket when he presented his plan for railroads. Sir _Humphry Davy_ laughed at the idea of illuminating the city of London by gas. The French Academy of Sciences actually sneered at the physicist _Arago_ when he proposed a resolution to merely open a discussion of the idea of an electric telegraph (_Wallace_, Die wissensch. Ansicht des Uebernatuerlichen, 102 _seq._).