As regards its relation to ordinary physical science, we find nothing to conflict with it, but, on the contrary that there are a certain number of indications that four space is, as I suggest, more than a mere mathematical concept. It is possible that it may some day come to be recognised as having some significance in the theory of the nature of electrons and of ether, while recent views on "Relativity" strongly indicate that Physicists will soon regard the four-dimensionality of the Universe as a common place. * * * * * If the four-dimensional hypothesis is correct there should exist some sort of connecting link between the physical body and the four-dimensional vehicle. The function of this link would be to deflect sensory impressions out of three space into four space thus enabling them to reach the Consciousness resident in the latter. Such a link must therefore be, in some way, intermediate between ordinary matter and four-dimensional matter. That is to say, it must possess some degree of four-dimensional complexity. This may reasonably be supposed to endow it with peculiar properties. If such a connecting link be found to exist in practice, it would tend to confirm the hypothesis. The experiments of de Rochas, of Joire, of MacDougal, of Baraduc, of Kilner, and of Crawford seem to indicate that such a connecting link does, in fact, exist. This is confirmed by the testimony of clairvoyants, which, though not of a nature to be rated too highly or accepted lightly, should be allowed some weight. The attempt to formulate an hypothesis of this nature is not repugnant to Religion. Nor is there anything in this particular hypothesis which can be held to conflict with Religious doctrines. On the other hand, the acceptance of such an hypothesis would cut the ground from under the feet of those who seek to maintain that matter is the only reality and that therefore Spirit and the Spiritual life are mere illusions. * * * * * No writer can expect to bring all his readers to his way of thinking. Indeed it would be unfortunate if he were to do so, as the effect would be to eliminate that element of critical discussion which is so fruitful a source of progress. Consequently, I do not anticipate that every reader will agree with me. All I venture to hope is that I may have made good my contention that the four-dimensional concepts, in spite of the scorn poured on them as a result of the Zöllner fiasco, are worthy of very careful consideration as a tentative working hypothesis by those who are seeking to clear up the many obscure problems presented by Psychical Research. If this little book is thought worthy of criticism, I shall welcome it. Its purpose will have been amply served if it succeeds in arousing interest in what will prove, I believe, a very fruitful field of speculation and research. APPENDIX.