[Footnote 23: The earliest detailed, though not typical, description of this phenomenon I have met with is by Dr. Simon Forman, the astrologer, in his entertaining _Autobiography_, written in 1600. He says that, as a child of six, 'So soon as he was always laid down to sleep he should see in visions always many mighty mountains and hills come rolling against him, as though they would overrun him and fall on him and bruise him, yet he got up always to the top of them and with much ado went over them. Then should he see many great waters like to drown him, boiling and raging against him as though they would swallow him up, yet he thought he did overpass them. And these dreams and visions he had every night continually for three or four years' space.' He believed they were sent him by God to signify the troubles of his later years. De Quincey accurately described the phenomenon in 1821, in his _Confessions of an English Opium-Eater:_ 'I know not whether my reader is aware, that many children, perhaps most, have a power of painting, as it were, upon the darkness, all sorts of phantoms: in some, that power is simply a mechanic affection of the eye; others have a voluntary or a semi-voluntary power to dismiss or to summon them, or, as a child once said to me when I questioned him on this matter, "I can tell them to go and they go; but sometimes they come, when I don't tell them to come."' E. H. Clarke (_Visions_, 1878, pp. 212-216) discussed the ability of children to see visions, and pointed out the element of will in this ability. It seems unusual for auditory impressions to intrude, though J. A. Symonds (biography by Horatio Brown, vol. i. p. 7), in describing his own night-terrors as a child, speaks of phantasmal voices which blended with the caterwauling of cats on the roof.] [Footnote 24: 'From being long and vehemently attent upon geometrical figures,' Hobbes says after referring to the after-images of the sun (_Leviathan_, part i., ch. 2), 'a man shall in the dark (though awake) have the images of lines and angles before his eyes: which kind of fancy hath no particular name; as being a thing that doth not commonly fall into men's discourse.'] [Footnote 25: Baillarger, 'De l'Influence de l'Etat Intermédiaire à la veille et au sommeil sur la Production et la Marche des Hallucinations,' _Annales Médico-Psychologiques_, vol. v., 1845.] [Footnote 26: Maury, _Le Sommeil et les Rêves_, 1861, pp. 50-77. Good descriptions of hypnagogic imagery are given by Greenwood, _Imagination and Dreams_, pp. 16-18, and Ladd, 'The Psychology of Visual Dreams,' _Mind_, 1892. See also Sante di Sanctis, _I Sogni_, pp. 337 _et seq._] [Footnote 27: This is the explanation offered by, for example, Delage (_Comptes-rendus de l'Académie des Sciences_, vol. cxxxvi., No. 12, pp. 731 _et seq._). It is accepted by Guyon and others. Delage insists on the retinal element since he finds that hypnagogic images follow the movements of the eye.]