It has not been found possible to determine, before experiment, whether any given man or woman will prove capable of the hallucinatory experiences.
The evidence, of course, is necessarily only that of the scryers themselves, but repeated experiments by persons of probity, and unfamiliar with the topic, combined with the world-wide existence of the practice, prove that hallucinatory pictures are really induced.
Pseudopremonitions, due to hallucinatory memory, are not unknown; there is also some ground for holding that crystal-gazers are able to perceive incidents which are happening at a distance from them.
But hallucinatory figures, both in dreams and waking life, are not necessarily those of the living; from the reappearance of dead friends or enemies primitive man was inevitably led to the belief that there existed an incorporeal part of man which survived the dissolution of the body.
Some persons do not even find a clear deep necessary, and are content to gaze at the palm of the hand, for example, when hallucinatory pictures, as they declare, emerge.