Were one to stand upon the apex of the Rock of Ages, or on the apex of any other high rock at the base of the Fall, at noon, when the sky was clear above, and the currents of air happened to surround the base of that rock on all sides with spray, as one turned completely around one would be in the center of a complete circular Rainbow—which would be below the level of the feet—and of which one would see but the half at any portion of the turn.
At Niagara, when one gazes on a complete circular bow, as seen against the perpendicular curtain of spray, the center of the circle will always be lower than the point where one is standing. This is necessarily so, from the very nature of things,—because the Sun, one's head, and the center of that circle must be in a line.
When the point of observation is high enough, and the spray-cloud spreads out extensively enough, it is possible to see two concentric, complete Rainbows at one time. In fact, one does often see a portion of the arc of such a second bow; but three complete concentric bows, or three arcs of bows, are never seen at Niagara, nor anywhere else.
George William Curtis, in "Lotus Eating," records,—
"There [at the Cave of the Winds], at sunset, and there only, you may see three circular rainbows, one within another,"—
He does not say, "complete circles"; he doubtless meant "arcs." He does not say he saw them; so in the absence of a more definite statement, it was certainly merely hearsay to which he referred.
John R. Barlow, who has been a guide at the Cave of the Winds for over thirty years, says that on numerous occasions during that period he has seen two complete circular Rainbows at one time, at that point. He observed it twice, and only twice, in 1905.
In 1872, Professor Tyndall, with Barlow as his guide, made an exhaustive study of the Goat Island ends of the American and Horse-Shoe Falls. As he was gazing at a complete Rainbow circle, Barlow told him that he had sometimes seen two complete concentric bows at one time. "That is possible," replied Tyndall.
"And I have heard people say they have seen three such bows; though I myself have never seen the third," said Barlow.
"Because it is an impossibility," answered Tyndall. "The second bow is merely the reflexion of the first. A third bow would be a shadow of a shadow; and no one can see that."