The rainbow is truly an apparition; you cannot approach it; you cannot grasp it, or find its end. I has no end, and no beginning. It is also born of the spray of cataracts, but sways not as the spray sways. It is one of the oldest and most striking phenomena in nature, and one of the most subtle and elusive.

The Heart of Burroughs's Journals, July 15, 1911 (p. 263), Houghton Mifflin Co. 1928