(i.) Crystal-gazing is a world-wide method of divining, which is analogous to dreams, save that the vision is voluntarily initiated, though little, if at all, under the control of the scryer.
As a matter of fact such persons sometimes can and sometimes cannot see pictures in the way of crystal-gazing; while many who can see in the crystal have had no spontaneous hallucinations.
The experiments took this form: any person might ask the scryer (a lady who had never previously heard of crystal-gazing) "to see what he was thinking of."
There is a chapter on crystal-gazing in Les Nevroses et les idees fixes of Dr Janet (1898).
There is also a chapter on crystal-gazing in Myers' Human Personality.
Such hallucinations are commonly provoked by crystal-gazing, but auditory hallucinations may be caused by the use of a shell (shell-hearing), and the other senses are occasionally affected.
This fact was not observed (that is, the collections of examples were not made) till recently, when experiments in private non-spiritualist circles drew attention to crystal-gazing, a practice always popular among peasants, and known historically to have survived through classical and medieval times, and, as in the famous case of Dr Dee, after the Reformation.