No matter if you suspect they are a indicator of God's guarantee, or there's a pot of gold awaiting you at their finish, rainbows are among nature's most joyful-inducing displays.René Descartes's sketch of how Main and secondary rainbows are shaped, Discours de la Méthode, 1637. Descartes' 1637 treatise, Discourse on Method (Discours de la Métho