§ 2. It was, of course, evident from the first that there was a certain duality of nature in hallucinations. In popular language, the mind and the sense were both plainly involved; the hallucinated person not only imagined such and such a thing, but imagined that he saw such and such a thing. But the attempts at analysing the ideational and the sensory elements have too often been of a very crude sort; the state of hallucination has been represented as one in which ideas and memories - while remaining ideas and memories and not sensations - owing to exceptional vividness took on the character of sensations. By the older writers, especially, it was not realised or remembered that sensations have no existence except as mental facts; and that, so far as a mental fact takes on the character of a sensation, it is a sensation. This was clearly stated, as a matter of personal experience, by Burdach and Muller; in the French discussions, the merit of bringing out the point with new force and emphasis belongs to Baillarger.1 He showed that when the hallucinated person says, " I see so and so," "I hear so and so," the words are literally true.

If the person goes on to say "You ought also to see or hear it," he is of course wrong; but when he says that he sees or hears it, his statement is to be taken without reserve. To him, the experience is not something like or related to the experience of perceiving a real external object: it is identical with that experience.1 To the psychology of our day this may seem a tolerably evident truth. Still it is easy to realise the difficulty that was long felt in admitting that any experience which was dissociated from the normal functions of the sense-organs could be completely sensory in character. Popular thought fails to see that the physical question which for practical purposes is all-important - whether the object is or is not really there - is psychically irrelevant; and a man who has been staring at the sun will, as a rule, think it less accurate to say that he sees a luminous disc wherever he looks than to say that he fancies it. The best corrective to such a prejudice is the following experiment of Fechner's. Two small slits are made in a shutter, and one of them is filled with a piece of red glass. The opposite wall is therefore lit by a mixture of white and red light.

A stick is now placed across the red slit; its shadow is of course cast on the wall; and the part of the wall occupied by the shadow, though illuminated only by white rays from the other slit, appears - owing to the optical law of contrast - a bright green. Let this shadow now be looked at through a narrow tube, which prevents any part of the wall external to the shadow from being seen. Nothing red is now in the spectator's view, so that there can be no effect of contrast: the red glass may even be removed; none but white rays are passing to his eye from the shadow; yet its colour remains green. And in this case the chances are that, unless previously warned, he will tell the exact truth; he will absolutely and flawlessly correct as a good musician's silent evocation of music, either by memory or by reading of the noted symbols; but even he is far from mis-furniture. It is worth noting that probably no recollected visual imago was ever so absolutely and flawlessly correct as a good musician's silent evocation of music, either by memory or by reading of the noted symbols; but even he is far from mistaking his vivid silent impression for actual sonority.

I may add that as long ago as 1832 the late Dr. Symonds, of Bristol, drew exactly the right distinction between images and hallucinations. (Lecture reprinted in Miscellanies, p. 241.) It is curious to find the same line drawn in the earliest really scientific attempt to deal with the subject that I have met with - the dissertation against Hobbes and Spinoza in Falck's De Doemonologia recentiorum Autorum (1692); but Falck still thinks that hallucinations are a mode in which daemons sometimes manifest their presence.

1 In the long and rather barren debates which took place in the Societe Medico-psychologique during 1855 and 1856, Baillarger, no doubt, insisted too strongly on an absolute gulf between percepts (true or false) and the ordinary images of fancy or memory. But his opponents made a far more serious mistake in so far identifying the two as not to perceive a difference of kind,at the point where the sensory element in the mental fact reaches such abnormal strength as to suggest the real presence of the object. Giesinger's statement(Die Pathologie und Therapieder Psychischen Krankheiten, p. 91), and Wundt's (Grundzuge der Physiologischen Psychologie, vol. ii., p. 353) seem too unguarded in the same respect. In a case which I have received, a child of four stopped in her play, looked intently at the wall, then " ran to it, crying out, 'My mother,' threw her little arms as if it were round a person, saying again, 'My mother,' and seemed wonderfully surprised at the fact that there was no substance to clasp." A child of four does not throw its arms round a memory. Nicolai's case is here very instructive.

Ho experimented on himself, and found that however vividly he pictured in his mind the persons of his acquaintance, he could never succeed in externalising them in such a way as to make them the least comparable to his phantoms; and his testimony on this point is the stronger in that his particular phantoms cannot have been of the most vivid sort, since he was always able to distinguish them from realities. Even more distinct mental images - the result of a rarer visualising power - may fall far short of hallucination. Raphael, who saw his "Transfiguration" in the air, Talma, who asserted that he worked himself into the necessary state of excitement on the stage by peopling the theatre with skeletons, are not recorded to have ever really localised their images as objects that concealed the walls and the furniture. It is worth noting that probably no recollected visual image was ever so admit, and even persist, that what he sees is green. He will scout the idea that the green is a mere memory of what he saw before he applied the tube; he will assert that it is presented to him as an immediate fact.

And such is assuredly the state of the case; but it is a state which, from the moment that he has put the tube to his eye, is kept up purely as a hallucination, and without regard to the facts of the external world. The delusion is of course instantly dispelled by the removal of the tube - when he perceives that the only light in the room is white, and that the shadow is grey; but for all that, he will probably never doubt again that a genuine hallucination of the senses is something more than "mere fancy".

1It may even be superior in distinctness to the percept of a real object; as when a shortsighted person who, during the hypnotic trance, had been impressed with a hallucination representing horsemen at some distance, saw them clearly, and remarked on this peculiarity. (Richet, L'Homme et l'Intelligence, p. 234.) A case of subjective hallucination experienced by the Rev. P. H. Newnham further illustrates the point. He distinctly saw in church the figure of a parishioner of marked appearance, who it turned out, had not been there and whose place had not been occupied by anyone else. "When I became convinced it was a hallucination, it then occurred to me that the clearness with which I had noted the eyes and the careworn look proved it; for my eyesight is now unable to distinguish such details of features at the distance of the pew in question." It is interesting in this connection to remark that Mr. Newnham, for the larger part of his life, enjoyed particularly good sight; while another correspondent, who occasionally sees subjective phantoms, and who has been short-sighted from birth, says, "I experience the same difficulty in discerning the unreal that I do when viewing real objects; unless the persons come near, I cannot clearly dis-tinguiah their features".

It is impossible to be too particular on this point; for high authorities, even in the present day, are found to contest it. When a person who habitually speaks the truth, and who is not colour-blind, looks at an object and says, "My sensation is green," they contradict him, and tell him that however much he sees green, his sensation is grey. Whether this be a mere misuse of language, or (as it seems to me) a misconception of facts, it at any rate renders impossible any agreement as to the theory of hallucinations. For it ignores the very point of Baillarger's contention - that images sufficiently vivid to be confounded with sensory percepts have become sensory percepts.

When once the truth of this contention is perceived, it is also perceived that the previous speculations had been largely directed to a wrong issue; and that the dual character of a false perception is after all no other than that of a true perception. A hallucination, like an ordinary percept, is composed of present sensations, and of images which are the relics of past sensations. If I see the figure of a man, then - alike if there be a man there and if there be no man there - my experience consists of certain visual sensations, compounded with a variety of muscular and tactile images, which represent to me properties of resistance, weight, and distance; and also with more remote and complex images, which enable me to refer the object to the class man, and to compare this specimen of the class with others whose appearance I can recall. If Baillarger did not carry out his view of hallucinations to this length, the whole development exists by implication in the term by which he described them - psycho-sensorial. The particular word was perhaps an unfortunate one; since it suggests (as M. Binet has recently pointed out1) that the psychical element is related to the sensorial somewhat as the soul to the body; and so, either that psychical events are independent of physical conditions, or that sensations are not psychical events.

I deo-sensational would avoid this difficulty; but the obverse term which M. Binet proposes - cerebro-sensorial - is on the whole to be preferred. For this brings us at once to the physical ground where alone the next part of the inquiry can be profitably pursued - the inquiry into origin. From the standpoint of to-day, one readily perceives how much more definite and tangible the problems were certain to become, as soon as they were translated into physiological terms. So far as the controversy had been conducted on a purely psychological basis, it had been singularly barren. In the vague unlocalised use, " the senses' and other ever-recurring terms become sources of dread to the reader. But as soon as it is asked, Where is the local seat of the abnormal occurrence? and on what particular physical conditions does it depend? - lines of experiment and observation at once suggest themselves, and the phenomena fall into distinct groups.

1 Revue Philosophique for April, 1884, p. 393.