It is easy to understand how clairvoyance of the first type arises. We know that light consists of very rapid vibrations in the ether which impinge upon the retina and cause the sensation of sight. We also know that if a beam of white light is passed through a triangular glass prism it is bent aside and split up into the seven colours of the rainbow, viz., Red, Orange, Yellow, Green, Blue, Indigo, and Violet. The resulting band of colour is called a Spectrum. If the Spectrum so obtained is thrown upon a screen and a number of people are asked to mark thereon the limits of what they can see it will be found that these limits vary considerably. We know, too, that there is a wide range of light-vibrations beyond the furthest of these visible limits, for although our eyes do not respond to them the photographic plate does. We also know that some of these vibrations will penetrate substances which are opaque to ordinary light although the opposite is the case for some substances. This is particularly the case with "ultra-violet" light which consists of vibrations more rapid even than those of violet light which are themselves the most rapid in all the visible spectrum. It seems reasonable therefore to suppose that certain people with abnormal retinæ or in an abnormal condition might be especially sensitive to these ultra-violet rays and that they might not only see things invisible to us but even see them _through_ obstacles which are opaque to the sort of light to which normal eyes respond. This explanation may serve for certain simple cases of clairvoyant vision but it soon breaks down because the visual image of any object seen in this way must be liable to confusion by the superimposed images of intervening objects. Suppose for instance that a clairvoyant wishes to see, by this method, what is written on page 100 of a closed book. We will suppose that the covers and paper of the book are transparent to some kind of ultra-violet light to which the eye of the clairvoyant responds, whereas the ink is opaque to the same light. On looking at the book the writing on page 100 would be visible all right, but so would that on the preceding 99 pages; it would, therefore, be practically impossible to read the 100th page. It will be seen, therefore, that clairvoyance of this type must be of very limited scope and cannot be held to account for cases of the second type where the clairvoyant perceives events happening at a considerable distance, amounting in some instances to a matter of hundreds of miles. I freely admit that at present I am not prepared to give an explanation of all cases where the distances involved are very large. But to cases where the incidents or objects perceived are reasonably near the percipient, the higher space hypothesis offers a simple and elegant solution. Consider the two dimensional analogue. [Illustration: _Fig. 7_]