??????????-??????????-????-??????-????????-???????-??????????René Descartes's sketch of how Principal and secondary rainbows are fashioned, Discours de la Méthode, 1637. Descartes' 1637 treatise, Discourse on Technique (Discours de la Méthode), even further Sophisticated this clarification. Recognizing that the measurement of raindrops didn't su