Folklore has it that at the end of every rainbow sits an imp¹, hammering on a single shoe, who can, with persistence and guile, be forced to reveal to his discoverer the whereabouts of a crock of gold.

This is in fact no more than the truth.

Illusion?

According to Kermit the Frog rainbows are 'just an illusion'², but there is a lot more to a rainbow than there is to, say, a ghost.

For one thing rainbows are equally visible to all, available for photography, and rationally discussable in a way that many 'subjective' experiences are not. For three things, that is.

Furthermore, it is no explanation-away to say that a rainbow is (merely) the effect of sunlight on water vapour; the same can be said of the appearance of clouds, but no-one calls clouds illusory³.

Rainbows have an observable shape: circular (normally seen as an arc of a circle, or of two concentric circles). They also have a rationally discoverable shape in three dimensions; and this is where the insight begins.

There is an end to every rainbow

What is the rainbow? It is the sun⁴ you are seeing, reflected by myriad tiny water droplets. The droplets that contribute to the rainbow are those positioned at a critical angle relative to the sun and the viewer. The circular shape you see is not derived from the shape of the sun; rather it is the shape of the mirror. But it's not a two-dimensional circle. The shape of the reflecting droplet-group cannot be two-dimensional, like this page you are reading (or that screen it's on); it has some depth. The depth is not apparent because you are looking 'along its barrel'; working it out on paper shows that the rainbow's shape in three dimensions is:—conical. Part of a cone.

A cone is an open-ended shape with a single point. Mathematically a cone is complemented by its reverse cone, opening out from the same point to a second open end (circular, infinitely distant). The second cone makes no difference to the present discussion and can be retained in your mental image, or discarded, as you wish.

The Point

Where is the cone's point, when we are looking at a rainbow? Well, it would appear to be inside the eyeball, where the projected rainbow image is focussed for communication through the optic nerve into the brain. But this is where the insight really begins: what if we are looking at it with two eyes? Has the rainbow got two ends? or are we seeing two different rainbows?

Stiff-necked scientists may wish to leave the rest of us here and enter the 'two rainbows' lobby. Resist any temptation to join them, as such a decision is damningly short-sighted. If we really see two rainbows, we equally really see two of everything. It is true that two images are formed in normal two-eyed vision; but 'seeing double' is a pathological state, not the normal case. Another level to 'seeing' must be admitted, beyond eyeball-projection⁵.

Consciousness

In normal vision, the diverse images from left and right eyes are combined by the brain into the single image of which we become conscious⁶.

It is in our consciousness that every rainbow we see comes to a single and perfect end.

It is also in consciousness that all the values in the universe are situated.

For such boundless riches 'a crock of gold' is a poor enough metaphor.