But it does give us a dim inkling of what the general nature of the causes at work may be, especially as regards the power of "internal vision" mentioned above and which I particularly wish to emphasise.
This is more than can be said of any alternative theory with which I am acquainted.
Future study will probably show that this class of phenomena is far from simple and is really capable of being resolved into a number of sub-classes, each requiring its own appropriate explanation.
It is interesting to note that Mr. C.W. Leadbeater, the well-known Theosophical writer and clairvoyant, definitely introduces the four-dimensional concept in his book on Clairvoyance and ascribes the power of long-range perception to the intervention of what he calls an "astral telescope"; but there would appear to be no evidence in support of this idea beyond the ipse dixit of the writer and even he is very vague on the point.
The third form of clairvoyance, namely, the perception of non-physical things, is readily explicable on the hypothesis which we are considering.
Just as the physical body has sense organs adapted for the perception of physical things, so the four-dimensional body or "vehicle" will presumably possess analogous organs adapted for the perception of four-dimensional things.
In ordinary persons, we must suppose either that these organs are almost completely undeveloped, or else that the mechanism, whereby the impressions received are conveyed to the consciousness and recorded as memories, is defective or inhibited.
In the clairvoyant on the contrary we may suppose that they are well developed and active and that he is able consciously to perceive by their aid.
In advancing this explanation of the third form of clairvoyance, I do not wish it to be thought that I attribute an objective origin to all visions of objects which have no obviously physical reality.
Hallucination is often a vera causa and indeed it is comparatively seldom that we can eliminate it with certainty.