1637 - René Descartes quantitatively derives the angles at which primary and secondary rainbows are seen with respect to the angle of the Sun's elevation,
1833 - Heinrich Lenz[?] states that an induced current in a closed conducting loop will appear in such a direction that it opposes the change that produced it (Lenz's law),
1845 - Michael Faraday discovers that light propagation in a material can be influenced by external magnetic fields,