Now what is the rationale of this kind of clairvoyance? As I have indicated above, it belongs usually to the "astral-current" type, and the crystal or other object simply acts as a focus for the will-power of the seer, and a convenient starting-point for his astral tube. There are some who can influence what they will see by their will, that is to say they have the power of pointing their telescope as they wish; but the great majority just form a fortuitous tube and see whatever happens to present itself at the end of it. Sometimes it may be a scene comparatively near at hand, as in the case just quoted; at other times it will be a far-away Oriental landscape; at others yet it may be a reflection of some fragment of an akashic record, and then the picture will contain figures in some antique dress, and the phenomenon belongs to our third large division of "clairvoyance in time." It is said that visions of the future are sometimes seen in crystals also--a further development to which we must refer later. I have seen a clairvoyant use instead of the ordinary shining surface a dead black one, produced by a handful of powdered charcoal in a saucer. Indeed it does not seem to matter much what is used as a focus, except that pure crystal has an undoubted advantage over other substances in that its peculiar arrangement of elemental essence renders it specially stimulating to the psychic faculties. It seems probable, however, that in cases where a tiny brilliant object is employed--such as a point of light, or the drop of blood used by the Maories--the instance is in reality merely one of self-hypnotization. Among non-European nations the experiment is very frequently preceded or accompanied by magical ceremonies and invocations, so that it is quite likely that such sight as is gained may sometimes be really that of some foreign entity, and so the phenomenon may in fact be merely a case of temporary possession, and not of clairvoyance at all. CHAPTER VI. CLAIRVOYANCE IN SPACE: UNINTENTIONAL. Under this heading we may group together all those cases in which visions of some event which is taking place at a distance are seen quite unexpectedly and without any kind of preparation. There are people who are subject to such visions, while there are many others to whom such a thing will happen only once in a life-time. The visions are of all kinds and of all degrees of completeness, and apparently may be produced by various causes. Sometimes the reason of the vision is obvious, and the subject matter of the gravest importance; at other times no reason at all is discoverable, and the events shown seem of the most trivial nature.