??????????-??????????-????-??????-????????-???????-??????????René Descartes's sketch of how Major and secondary rainbows are shaped, Discours de la Méthode, 1637. Descartes' 1637 treatise, Discourse on System (Discours de la Méthode), further more Innovative this clarification. Being aware of that the measurement of raindrops did not seem to inf