_Ce n'est que le premier pas qui coûte._ If we have once got a man's _thought_ operating apart from his body--if my fixation of attention on the two of diamonds does somehow so modify another man's brain a few yards off that he seems to see the two of diamonds floating before him--there is no obvious halting-place on _his_ side till we come to "possession" by a departed spirit, and there is no obvious halting-place on _my_ side till we come to "travelling clairvoyance," with a corresponding visibility of my own phantasm to other persons in the scenes which I spiritually visit. No obvious halting-place, I say; for the point which at first seems abruptly transitional has been already shown to be only the critical point of a continuous curve. I mean, of course, the point where consciousness is duplicated--where each segment of the personality begins to possess a separate and definite, but contemporaneous stream of memory and perception. That these can exist concurrently in the same organism our study of hypnotism has already shown, and our study of motor automatisms will still further prove to us. _Dissociation of personality, combined with activity in the metetherial environment_; such, in the phraseology used in this book, will be the formula which will most easily cover those actually observed facts of veridical apparition on which we must now enter at considerable length. And after this preliminary explanation I shall ask leave to use for clearness in my argument such words as are simplest and shortest, however vague or disputable their connotation may be. I must needs, for instance, use the word "spirit," when I speak of that unknown fraction of a man's personality--not the supraliminal fraction--which we discern as operating before or after death in the metetherial environment. For this conception I can find no other term, but by the word _spirit_ I wish to imply nothing more definite than this. Of the spirit's relation to space, or (which is a part of the same problem) to its own spatial manifestation in definite form, something has already been said, and there will be more to say hereafter. And similarly those terms, _invader_ or _invaded_, from whose strangeness and barbarity our immediate discussion began, will depend for their meaning upon conceptions which the evidence itself must gradually supply. That evidence, as it now lies before us, is perplexingly various both in content and quality. For some of the canons needed in its analysis I have already referred the reader to extracts from Edmund Gurney's writings. Certain points must still be mentioned here before the narrative begins.