It is possible to see a complete circular Rainbow anywhere, on land or water, whenever one stands between the Sun and a sufficiently abundant mist (standing close to the latter), and the Sun is near the horizon.
It is possible to see it, at some point at Niagara, often,—that is on every bright day,—because that abundant curtain of mist is ever present; and the Gorge, by reason of its great width and depth, affords specially favorable opportunities.
This curious phenomenon is obtainable easily and regularly only in the Gorge at the Goat Island end of the American Fall, from the rocks in front of the Cave of the Winds (for the prevailing winds of the locality are from the southwest, which bring the spray cloud into the best relative position at this point), or from the deck of the steamboat, at certain parts of the trip,—and from both only in the afternoon.
It can sometimes be seen from Prospect Point, and from the Terrapin Rocks—in the early morning, when the spray-cloud rises towards the north.
It can also, sometimes (at the season when the Sun sets farthest to the northward), be seen from the rocks out in front of the American Fall, below Prospect Point.
This was the spot where the Aborigines would most easily have tested the efficacy of the Legend; for their descent into the Gorge was made at a point on the American shore, not so very far north from the end of that Fall.
When white men first settled near the Cataract, in the first decade of the 19th Century, the location of the "Indian Ladder" was amongst the present overflows from the mills of the Lower Milling district. That, by reason of the "debris slope" of the Gorge being highest at that point, had doubtless been its location for ages.
The fact that, even at the most accessible (and that by no means easily reached) end of the Fall in the Gorge, the entire conditions of the Legend could so rarely be fully complied with, would have been to the unscientific minds of the Savages only an additional incentive to a firmer belief in it.
It is also observable from the rocks beyond and below Terrapin Point, on the Goat Island side of the Horse-Shoe Fall; but the climb out to that point is both arduous and dangerous, and is very rarely attempted.
No such phenomenon can be seen from the Canadian shore, because there are no rocks out in front of that end of the Horse-Shoe Fall on which one can stand.