For example, there is a living diplomatist who knows men and cities, and has, moreover, a fine sense of humour. "My Lord," said a famous Russian statesman to him, "you have all the qualities of a diplomatist, but you cannot control your smile." This gentleman, walking alone in a certain cloister at Cambridge, met a casual acquaintance, a well-known London clergyman, and was just about shaking hands with him, when the clergyman vanished. Nothing in particular happened to either of them; the clergyman was not in the seer's mind at the moment. This is a good example of a solitary hallucination in the experience of a very cool-headed observer. The _causes_ of such experiences are still a mystery to science. Even people who believe in "mental telegraphy," say when a distant person, at death or in any other crisis, impresses himself as present on the senses of a friend, cannot account for an experience like that of the diplomatist, an experience not very uncommon, and little noticed except when it happens to coincide with some remarkable event. {56b} Nor are such hallucinations of an origin easily detected, like those of delirium, insanity, intoxication, grief, anxiety, or remorse. We can only suppose that a past impression of the aspect of a friend is recalled by some association of ideas so vividly that (though we are not _consciously_ thinking of him) we conceive the friend to be actually present in the body when he is absent. These hallucinations are casual and unsought. But between these and the dreams of sleep there is a kind of waking hallucinations which some people can purposely evoke. Such are the visions of _crystal gazing_. Among the superstitions of almost all ages and countries is the belief that "spirits" will show themselves, usually after magical ceremonies, to certain persons, commonly children, who stare into a crystal ball, a cup, a mirror, a blob of ink (in Egypt and India), a drop of blood (among the Maoris of New Zealand), a bowl of water (Red Indian), a pond (Roman and African), water in a glass bowl (in Fez), or almost any polished surface. The magical ceremonies, which have probably nothing to do with the matter, have succeeded in making this old and nearly universal belief seem a mere fantastic superstition. But occasionally a person not superstitious has recorded this experience. Thus George Sand in her Histoire de ma Vie mentions that, as a little girl, she used to see wonderful moving landscapes in the polished back of a screen. These were so vivid that she thought they must be visible to others.