While passing Cape Frio, after coming out of Rio de Janeiro, Brazil, on the night of February 23, 1909, I observed a peculiarity of vision, or visibility, which seems to me worthy of note.
The night being dark (i. e., moonless), but clear and starlit, while looking directly at the cape, its outlines could be fairly well discerned. On accidently turning my gaze away about two points and looking out of "the 'tail of the eye," I noticed with surprise that the outlines of the headland were appreciably more distinct, and that the land itself was in darker contrast with its surroundings. Thinking that this effect might be due to the eyes becoming more accustomed to the darkness (I had recently come on deck), I tried the same thing several times, always with the same noticeable difference in distinctness. I then asked the officer of the deck to try the experiment; he immediately noted the difference.
Subsequently I experimented on vessels passing at night, with similar results.
Upon mentioning this peculiarity to Commander Ellicott the following day, he told me that he had known of it since his early days (nights) on Chesapeake Bay, and had always, more or less unconsciously, taken advantage of it while navigating along shore; but that he had never heard it mentioned in the course of Navy talk, neither seen it in print. It was certainly a new thing to me; it may also be to others.