The same would hold true in cases of possession and obsession; for if the bastion of the hand can thus be captured, so also may the citadel of the brain. Certain familiar forms of hypnotism are not different from obsession, the hypnotizer using the brain and body of his subject as though they were his own. All unconsciously to himself, he has called into play four-dimensional mechanics. Many cases of so-called dual personality are more easily explicable as possession by an alien will than on the less credible hypothesis that the character, habits, and language of a person can change utterly in a moment of time. CLAIRVOYANCE IN SPACE _Vision at a distance and the exercise of a superior power of sight_. Clairvoyance in space is of various kinds and degrees. Sometimes it consists in the perception of super-physical phenomena--the unfurling of a strange and wonderful land; and again it appears to be a higher power of ordinary vision, a kind of seeing to which the opacity of solids offers no impediment, or one involving spatial distances too great and too impeded for normal physical vision to be effective. That clairvoyance which consists in the ability to perceive not alone the superficies of things as ordinary vision perceives them, but their interiors as well, is analogous to the power given by the X-ray, by means of which, on a fluorescent screen, a man may behold the beating of his own heart. But, if the reports of trained clairvoyants are to be believed, there is this difference: everything appears to them without the distortions due to perspective, objects being seen as though they were inside and not outside of the perceiving organ, or as though the observer were in the object perceived; or in all places at the same time.