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.