I saw here the most brilliant rainbow that I ever imagined. It was just across the stream below the precipice, formed on the mist which this tremendous fall produced. And I stood on a level with the keystone of its arch. It was not a few faint prismatic colors merely, but a full semicircle only four or five rods in diameter, though as wide as usual, so intensely bright as to pain the eye, and apparently as substantial as an arch of stone. Henry David Thoreau, A Yankee in Canada.