Those to whom a certain amount of clairvoyant power has come occasionally only, and without any reference to their own wish, have often been hysterical or highly nervous persons, with whom the faculty was to a large extent one of the symptoms of a disease. Its appearance showed that the physical vehicle was weakened to such a degree that it no longer presented any obstacle in the way of a certain modicum of etheric or astral vision. An extreme example of this class is the man who drinks himself into delirium tremens, and in the condition of absolute physical ruin and impure psychic excitation brought about by the ravages of that fell disease, is able to see for the time some of the loathsome elemental and other entities which he has drawn round himself by his long course of degraded and bestial indulgence. There are, however, other cases where the power of sight has appeared and disappeared without apparent reference to the state of the physical health; but it seems probable that even in those, if they could have been observed closely enough, some alteration in the condition of the etheric double would have been noticed. Those who have only one instance of clairvoyance to report in the whole of their lives are a difficult band to classify at all exhaustively, because of the great variety of the contributory circumstances. There are many among them to whom the experience has come at some supreme moment of their lives, when it is comprehensible that there might have been a temporary exaltation of faculty which would be sufficient to account for it. In the case of another subdivision of them the solitary case has been the seeing of an apparition, most commonly of some friend or relative at the point of death. Two possibilities are then offered for our choice, and in each of them the strong wish of the dying man is the impelling force. That force may have enabled him to materialize himself for a moment, in which case of course no clairvoyance was needed or more probably it may have acted mesmerically upon the percipient, and momentarily dulled his physical and stimulated his higher sensitiveness. In either case the vision is the product of the emergency, and is not repeated simply because the necessary conditions are not repeated. There remains, however, an irresolvable residuum of cases in which a solitary instance occurs of the exercise of undoubted clairvoyance, while yet the occasion seems to us wholly trivial and unimportant. About these we can only frame hypotheses; the governing conditions are evidently not on the physical plane, and a separate investigation of each case would be necessary before we could speak with any certainty as to its causes. In some such it has appeared that an astral entity was endeavouring to make some communication, and was able to impress only some unimportant detail on its subject--all the useful or significant part of what it had to say failing to get through into the subject's consciousness.