the only 30rt that M. Binet's theory allows. It seems probable on the whole, therefore, that centrally initiated hallucinations can exist. How often they do exist is another question. The existence of hallucinations which affect more than one sense is an argument for central initiation. For, grant that the thing seen may have its starting point in the outer world, the voice which it is heard to utter must be due to an influence from the visual region, i.e. must be of central origin.

Sporadic cases of hallucination, visiting people only once in a lifetime (which seem to be a quite frequent type), are on any theory hard to understand in detail. They are often extraordinarily complete; and the fact that many of them are reported as veridical, that is, as coinciding with real events, such as accidents, deaths, etc., of the persons seen, is an additional complication of the phenomenon. The first really scientific study of hallucination in all its possible bearings, on the basis of a large mass of empirical material, was begun by Mr. Edmund Gurney and is continued by other members of the Society for Psychical Research; and the Census' is now being applied to several countries under the auspices of the International Congress of Experimental Psychology. It is to be hoped that out of these combined labors something solid will eventually grow. The facts shade off into the phenomena of motor automatism, trance, etc.; and nothing but a wide comparative study can give really instructive results.*

* The writer of the present work is Agent of the Census for America, and will thankfully receive accounts of cases of hallucina tion of vision, hearing, etc., of which the reader may have knowledge

CHAPTER XXI.

THE PERCEPTION OF SPACE.

As adult thinkers we have a definite and apparently instantaneous knowledge of the sizes, shapes, and distances of the things amongst which we live and move; and we have moreover a practically definite notion of the whole great infinite continuum of real space in which the world swings and in which all these things are located. Nevertheless it seems obvious that the baby's world is vague and confused in all these respects. How does our definite knowledge of space grow up? This is one of the quarrelsome problems in psychology. This chapter must be so brief that there will be no room for the polemic and historic aspects of the subject, and I will state simply and dogmatically the conclusions which seem most plausible to.

me.

The quality of voluminousness exists in all sensations, just as intensity does. We call the reverberations of a thunder-storm more voluminous than the squeaking of a slate-pencil; the entrance into a warm bath gives our skin a more massive feeling than the prick of a pin; a little neuralgic pain, fine as a cobweb, in the face, seems less extensive than the heavy soreness of a boil or the vast discomfort of a colic or a lumbago; and a solitary star looks smaller than the noonday sky. Muscular sensations and semicircular-canal sensations have volume. Smells and tastes are not without it; and sensations from our inward organs have it in a marked degree.

Repletion and emptiness, suffocation, palpitation, headache, are examples of this, and certainly not less spatial is the consciousness we have of our general bodily condition

in nausea, fever, heavy drowsiness, and fatigue. Our entire cubic content seems then sensibly manifest to us as such, and feels much larger than any local pulsation, pressure, or discomfort. Skin and retina are, however, the organs in which the space-element plays the most active part. Not only does the maximal vastness yielded by the retina surpass that yielded by any other organ, but the intricacy with which our attention can subdivide this vastness and perceive it to be composed of lesser portions simultaneously coexisting alongside of each other is without a parallel elsewhere. The ear gives a greater vastness than the skin, but is considerably less able to subdivide it. The vastness, moreover, is as great in one direction as in another. Its dimensions are so vague that in it there is no question as yet of surface as opposed to depth; 'volume' being the best short name for the sensation in question.

Sensations of different orders are roughly comparable with each other as to their volumes. Persons born blind are said to be surprised at the largeness with which objects appear to them when their sight is restored. Franz says of his patient cured of cataract: "He saw everything much larger than he had supposed from the idea obtained by his sense of touch. Moving, and especially living, objects appeared very large." Loud sounds have a certain enormousness of feeling. Glowing' bodies as Hering says, give us a perception "which seems roomy (raumhaft) in comparison with that of strictly surface-color. A glowing iron looks luminous through and through, and so does a flame." The interior of one's mouth-cavity feels larger when explored by the tongue than when looked at. The crater of a newly-extracted tooth, and the movements of a loose tooth in its socket, feel quite monstrous. A midge buzzing against the drum of the ear will often seem as big as a butterfly. The pressure of the air in the tympanic cavity upon the membrane gives an astonishingly large sensation.

The voluminousness of the feeling seems to bear very little relation to the size of the organ that yields it. The ear and

eye are comparatively minute organs, yet they give us feelings of great volume. The same lack of exact proportion between size of feeling and size of organ affected obtains within the limits of particular sensory organs. An object appears smaller on the lateral portions of the retina than it does on the fovea, as may be easily verified by holding the two forefingers parallel and a couple of inches apart, and transferring the gaze of one eye from one to the other. Then the finger not directly looked at will appear to shrink. On the skin, if two points kept equidistant (blunted compass- or scissors-points, for example) be drawn along so as really to describe a pair of parallel lines, the lines will appear farther apart in some spots than in others. If, for example, we draw them across the face, the person experimented upon will feel as if they began to diverge near the mouth and to include it in a well-marked ellipse.

The dotted lines give the real course of the points, the continuous lines the course as felt.

NOW MY FIRST THESIS IS THAT THIS EXTENSITY, discernible in each and every sensation, though more developed in some than in others, IS THE ORIGINAL SENSATION OF SPACE, out of which all the exact knowledge about space that we afterwards come to have is woven by processes of discrimination, association, and selection.

The Construction of Real Space. To the babe who first opens his senses upon the world, though the experience is one of vastness or extensity, it is of an extensity within

which no definite divisions, directions, sizes, or distances are yet marked out. Potentially, the room in which the child is born is subdivisible into a multitude of parts, fixed or movable, which at any given moment of time have definite relations to each other and to his person. Poten tially, too, this room taken as a whole can be prolonged in various directions by the addition to it of those farther lying spaces which constitute the outer world. But actu ally the further spaces are unfelt, and the subdivisions ar undiscriminated, by the babe; the chief part of whose edu cation during his first year of life consists in his becoming acquainted with them and recognizing and identifying them in detail. This process may be called that of the con struction of real space, as a newly apprehended object, out of the original chaotic experiences of vastness. It consists of several subordinate processes:

First, the total object of vision or of feeling at any time must have smaller objects definitely discriminated within it;

Secondly, objects seen or tasted must be identified with objects felt, heard, etc., and vice versa, so that the same 'thing' may come to be recognized, although apprehended in such widely differing ways;

Third, the total extent felt at any time must be conceived as definitely located in the midst of the surrounding extents of which the world consists;

Fourth, these objects must appear arranged in definite order in the so-called three dimensions; and

Fifth, their relative sizes must be perceived-in other words, they must be measured.

Let us take these processes in regular order.

1) Subdivision or Discrimination. - Concerning this there is not much to be added to what was set forth in Chapter XV. Moving parts, sharp parts, brightly colored parts of the total field of perception catch the attention' and are then discerned as special objects surrounded by the remainder of the field of view or touch. That when