The power of opium is somewhat similar, and, as DeQuincey long since pointed out, such power is simply a revival of a faculty usually possessed by children, although, judging from my own experiences with mescal, drugs exert it in a far more vivid and potent degree than that in which it usually occurs in the child. The psychologists of childhood have not often investigated this phenomenon,[22] but so far as my own inquiries go, all or nearly all persons have possessed, when children, the power of seeing visions in the dark on the curtain of the closed eyelids, perhaps the representation of fairy tales they had read, perhaps merely commonplace processions of individuals or events, a tendency sometimes appearing for the same figure to recur again and again. I think it is fairly certain that the so-called 'lies' of children, told in good faith, are in part due to the occasional eruption of this faculty into daylight life. People who deny that they ever possessed this power have, almost certainly, only forgotten. I should myself be inclined to deny that I had ever had any such visionary faculty if it were not that I can recall one occasion of its presence, at about the age of seven, when sleeping with a cousin of the same age; we amused ourselves by burying our heads in the pillows and watching a connected series of pictures which we were both alike able to see, each announcing any change in the picture as soon as it took place. This fact of community of vision served to impress on my mind the existence of a faculty of which otherwise I can recall no trace.[23] Of these various groups of allied phenomena, that which more especially concerns us in the investigation of dreams is the group of phenomena most strictly called hypnagogic, belonging, that is to say, to the ante-chamber of sleep, when the senses are in repose and waking consciousness is slipping away, or else when, as we leave the world of dreams, waking consciousness is flowing back again. This state has been known from very ancient times. Aristotle referred to it, and in the dawn of modern scientific thought Hobbes described allied phenomena.[24] The strictly psychological study of hypnagogic visions seems to have begun with Baillarger.[25] Then, some years later, Maury, who had a rich personal experience of such phenomena, devoted a chapter to the hypnagogic state, and gave it its recognised name.[26]