[Footnote 12: The simile of the kaleidoscope for the most elementary process of dreaming has often suggested itself. Thus in an article on dreaming in the _Lancet_ (24th November 1877) we read: 'The combinations are new, but the materials are old, some recent, many remote and forgotten.... The turn of the kaleidoscope is instantaneous and any new idea thrown into the field, perhaps in the act of turning, becomes an integral part of the picture.'] [Footnote 13: Foucault, _Le Rêve_, p. 182.] [Footnote 14: This is in accordance with the view of Wundt, who attributes this multiplication of imagery to the retinal element.] [Footnote 15: Baron Charles Mourre, 'La Volonté dans le Rêve,' _Revue Philosophique_, May 1903.] [Footnote 16: Ribot, _Psychologie de l'Attention_, 1889, chs. i. and ii.] [Footnote 17: Maine de Biran, perhaps the earliest accurate introspective observer of dreaming, noted the absence of all voluntary active attention. Beaunis regards attention as possible in dreams, but fails to distinguish between different kinds of attention.] [Footnote 18: B. Leroy, 'Nature des Hallucinations,' _Revue Philosophique_, June 1907. As regards the importance of the absence of voluntary attention in the production of visual images, it may be remarked that even the after-image of a bright object in waking life is much more vivid when it occurs in a state of inattention and distraction. I noticed this phenomenon some years ago, especially when studying mescal, and in recent years it has been recorded by J. H. Hyslop (_Psychological Review_, May 1903).] [Footnote 19: We must be cautious in assuming that such imagery is purely retinal. Scripture ('Cerebral light,' _Studies from the Yale Psychological Laboratory_, vol. v., 1899) argues that even the so-called 'retinal light' or '_eigenlicht_' is cerebral, not retinal at all, since it is single and not double, and differs from after-images, which are displaced by pressure on eyeball. This view is perhaps too extreme in the opposite direction.] [Footnote 20: For a full and interesting study of these, see S. J. Franz, 'After-images' (Monograph Supplements to _Psychological Review_, vol. iii., No. 2, June 1899). He agrees with those who regard after-images as entirely retinal in origin.] [Footnote 21: See Havelock Ellis, 'A New Artificial Paradise,' _Contemporary Review_, January 1898; _ib._ 'Mescal: A Study of a Divine Plant,' _Popular Science Monthly_, May 1902.]