"Higher space is a Physical reality and not a mere mathematical idea. In waking life the individual consciousness functions in a three-dimensional 'vehicle,' namely the physical body. But it may also possess at least one other vehicle--a four-dimensional one--and in this it may function after death and, possibly, during sleep, trance, anæsthesia and other forms of insensibility." This hypothesis is not my own and I am not prepared to defend it as being necessarily correct. But, as I hope to show, there are a number of considerations which tend to support it and I do think it is sufficiently plausible to make it worthy of serious consideration before it is finally rejected by those who are students of these matters. In this chapter I propose to deal with the different ways in which it is likely to prove of importance. First of all, then, it has strong claims to be adopted as a working hypothesis by those who are students of Psychical Research, especially by those who are convinced of the validity of the Spiritistic explanation of communications purporting to emanate from the deceased. Secondly, I believe that if accepted as valid it would do much to provide a common meeting ground for opposite schools of religious and scientific thought. Between these there was a most marked and unfortunate cleavage during last century and though there has been a very considerable rapprochement since the days when controversy was at its height there is still much to be done before we can hope for a complete community of thought and expression. It is hardly necessary to say that these two spheres of application are very closely allied, but it is none the less convenient to separate them for purposes of discussion. THE NEED OF A WORKING HYPOTHESIS IN PSYCHIC SCIENCE. The studies of Psychical Researchers must necessarily cover a very wide area which is bounded on the one hand by Physical science proper, on another by Philosophy, on a third by Psychology and on a fourth by Religion. With each of these subjects it has close relations and yet possesses features which serve to distinguish it from any of them. Sir William Barrett writes as follows of the scope of Psychical Research: