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the chief factors in determining the character of the hallucination, but as they acted through association it is not so clear to what its externalization is to be ascribed. Perhaps the hurlyburly of the storm outside had something to do with it; probably the drowsy, disordinated condition of the percipient favored the formation of the apparition, but of the details of the process one can not speak with confidence.

In the hallucinations of which the crystal vision is the type we have a form intermediate between the true hallucination and the illusion. Prolonged staring into a mirror, a glass of water, a crystal, a piece of glass, or even fixation of the gaze upon a point will induce in some persons brilliantly colored hallucinations. While they are certainly peripherally initiated by the prolonged staring, their special character is nearly always centrally determined—usually indeed, they simply reproduce old memories. Susceptibility to these hallucinations is by no means uncommon; I have tried about a hundred persons myself, and found that about one in four saw something. Similar hallucinations of hearing can be produced by listening to the "sound of waves" in a large shell, to the sound of water running from a spigot, etc. The stories of ghosts seen in mirrors probably all rest upon this principle. For example:[1]

"The first hallucination which I was in a position clearly to recognize as such occurred during the Indian mutiny. Several members of our family were in danger. One night on which we had all been talking late of them, after we had parted and gone upstairs to bed, I stood before my dressing table, plaiting my hair, when my attention was arrested by a faint spot in the center of the mirror; this, to my amazement, gradually enlarged (as a grease spot spreads with heat) till the whole surface was covered, and then, in the center of this veil, came through the face of one of the near relatives above mentioned, as plain as might have been his living reflection. I noted the day and hour, and ascertained, six weeks later, that the relative seen had incurred no sort of danger at that date." This misty discoloration of the glass is significant, for many of my subjects describe the glass as becoming milky or cloudy just before the hallucination appears. Occasionally it is possible by means of an indeterminate stimulus of this sort to raise a thought to sensory intensity. Thus Miss X—— saw in the polished surface of a piano a scene of which she was thinking,[2] I have met with one analogous experience, but it seems to be rare.

Many interesting questions arise as to the relation that exists

  1. Proceedings of the Society for Psychical Research, vol. x, p. 407.
  2. Ibid., vol. V, p. 512.