619. For this purpose it would be convenient to dispense with external suggestion, and confine our attention to the mind of the percipient. There are already in ordinary life indications of some faculty of projecting supraliminally visual images apparently matured elsewhere; e.g. in dreams, memory-images, illusions hypnagogiques.

620. Crystal-vision affords a simple empirical method of finding the correlation between all these types of internal vision, by facilitating in the seers the externalisation of subliminal concepts or ideas. 620 A. Résumé of history of crystal-gazing.

621. Hypnotisation, which is sometimes induced by prolonged gazing, may occur in crystal-gazing and facilitate hallucination. And the visions are sometimes determined by points de repère.

622. But crystal-visions generally occur without hypnotisation, and develop in a way independent of points de repère.

623. Crystal-gazing is a harmless empirical method of developing internal vision. Experiments have been tried to test if the visions follow optical laws, independently of suggestion; - and should be tried again. 623 A. Discussion of optical effects in hallucinations.

624. A hypnotised person may be made to see visions on waking from the trance, and, as in the cases quoted in the Appendix, the seer, having forgotten the suggestion, may be unaware of the origin of the pictures and unable to explain what their subject or meaning is. 624 A. Post-hypnotic crystal visions recorded by the present writer.

625. These experiments illustrate the transition between post-hypnotic hallucinations and crystal-visions, and afford further evidence of the genuine occurrence of the latter. Crystal-visions of: 625 A. Mrs. Verrall; 625 B. Miss Goodrich-Freer; 625 C. "Miss. A."; 625 D. "Miss Angus".

626. These are really instances of the control of inward vision; although at first sight appearing lawless and arbitrary, - a random mixture of normal and supernormal knowledge with mere imagination.

627. Induced crystal-visions illustrate the various types of spontaneous sensory automatism; and these - to have any objective validity - must represent knowledge supernormally acquired, or direct communication between the subliminal strata of two minds, - that is, telepathy.

628. Telepathy must exist if any disembodied intelligences exist. On the principle of continuity, evolution from the lower carries with it a presumption of development into the higher. Conversely, the ancient belief in the possibility of telepathic communication with higher minds, as in prayer, might well have suggested that such communication was possible between minds on the same level. This notion has occurred from time to time to philosophic thinkers, but has only recently been systematised by actual experiment.

629. The operation of telepathy is probably constant and far-reaching, and intermingled with ordinary modes of acquiring knowledge. But since we know nothing of its method of action, we can only specifically postulate it when all other known causes are excluded. The best experimental evidence is where the ideas to be transferred are trivial, and devoid of all association or emotion.

630. An account of the history and development of this form of experimentation, and the varied yet concordant results obtained, was given by Gurney in 1886 in Phantasms of the Living, and some part of this history is reproduced in our Appendices, with examples of the additional evidence received since as to experimental thought-transference in the normal state. 630 A. Note on "Number-habits." Experiments with agent and percipient in the same room by: 630 B. Mr. Guthrie; 630 C. Mr. Rawson. Experiments with agent and percipient at a distance from one another by: 630 D. Mr. Kirk; 630 E. Mr. Glardon; 630 P. Dr. and Mrs. S.; 630 G. Miss Dispard.

631. Thus telepathy may produce definitely sensory, or vague, or ideational impressions; it may sometimes be assisted by hypnotisation; and we find a continuous transition from experimental to spontaneous telepathy. The apparently favourable effect of proximity may be due to self-suggestion alone.

632. We cannot as yet command success in the experiments; - (a) the idea to be transferred may not reach the percipient's mind; or (b) if it does, it may be prevented from emerging into his ordinary consciousness. It has been suggested that telepathy is propagated by "brain-waves," that is, by ether waves passing from brain to brain.

633. But this suggestion rests on very superficial analogies, since the mental images of agent and percipient are generally dissimilar, the percipient greatly modifying the impression before externalising it.

634. Nor does it meet cases of collective percipience, or of varying time-relation, or of telepathy from discarnate spirits. We can at present say little more in the way of explanation than that Life has the power of manifesting itself to Life. Such manifestation may involve the lower animals also. 634 A. Case of animal apparition: Mrs. Bagot.

635. Hypothesis of a possible mode of psychical interaction: a "psychical invasion " by the agent, creating a "phantasmogenetic centre " in the place invaded; the spirit of the agent being actually transferred to the distant scene, which it perceives, but may or may not remember; while its presence may or may not be perceived by the persons materially present in the scene.

636. Mere telepathy may explain an apparition coinciding with the death of the person seen; but the hypothesis of "psychical invasion " seems to apply better to (1) collective cases; (2) telepathic clairvoyance; (3) reciprocal cases.

637. The increased evidence for communications from the dead must affect our view of telepathy; as may also the increasing evidence for precognition; and theorising must simply follow the evidence.

638. The present theory starts from the conception that different segments of the personality can operate independently of and unknown to each other, and sometimes apart from the organism; (this latter is implied in the assumption of telepathy, - still more in that of survival). Through hypnotism the first important step has been proved possible, namely, the independent operation of different segments, with separate streams of memory and consciousness, all working through the same organism.