But this difficulty of conceiving a state of existence, at once real and non-physical, has induced scientists to prefer to seek an explanation of the observed facts in terms of Thought transference, Secondary personality and so forth.[1] But as soon as we introduce the concept of the Fourth Dimension this difficulty disappears. We have but to suppose that after physical death the Individual consciousness is embodied in a vehicle organised, not from physical matter, but from Four-dimensional matter, _i.e._, that which, in four space, corresponds to what we call "Matter" in three space. Such a vehicle fulfills the required conditions in every way. It is scientifically real--that is to say, it has its habitat in a region as subject to law and as susceptible to mathematical analysis as the three dimensional world in which we at present live. And yet it must be supposed to be, of its very nature, inapprehensible by our normal physical senses. We are thus enabled to understand how those who have left this physical world may, although discarnate, be none the less as truly _alive_ as ever, close to us and yet invisible, constantly in touch with us and yet beyond our normal ken. This is the first and supremely important application of the hypothesis and it is impossible to over-emphasise it. * * * * * Of the more specific phenomena suitable for discussion here, I will first deal with Clairvoyance. This is probably far from being a simple phenomenon of unvarying nature. There would appear to be at least four varieties and it is possible that as our knowledge of the subject increases we shall come to recognise still more. The four at present distinguishable may be denoted as follows:-- (1) So-called "Etheric Clairvoyance." This is apparently no more than a heightening of the ordinary powers of vision. (2) Perception of objects and contemporary events more or less removed in space from the percipient and invisible by ordinary means. (3) Perception of non-material objects or events; as when a clairvoyant describes the appearance of a deceased person alleged to be present in "spirit form." (4) Clairvoyance in time. That is to say the perception of future events--Prevision--or of past events--Postvision. Instances of each of these four forms are abundant and amply verified except, perhaps, in the case of class 3 where verification is scarcely possible.