Finally, as to the higher emotional element in music. Mr. Herbert Spencer has shown how the emotional expression of music is derived from the emotional expression of everyday life. But it is, so to speak, the ultimate outcome of that expression, pushed to the very highest pitch of delicate discrimination. Accordingly, we cannot expect that persons with less than average auditory endowments will be sensible to more than its broadest distinctions. And this is just the amount of appreciation exhibited by my subject. He can to some extent recognise the general tone of a piece-lively, gay, bright, subdued, tender, solemn, or majestic: but he cannot recognise those minor changes of feeling which are exhibited within the limits of a uniform composition. Of course his discrimination of the prevailing tone is largely due to time and degree of loudness; but it seems also to be influenced to some extent by the general pitch of the piece, and by the alternations of high and low notes. And it is noticeable that while he cares very little or not at all for purely musical pieces, where everything depends upon that delicate distribution of harmonies which is to him an absolute blank, he is slightly affected by bright popular tunes, in which the emotional element is pronounced, and in which rapid and striking variations keep alive the attention by the diversity of their arrangement. To put the matter simply, he understands in music only the part that is not strictly musical. And, as might be expected, he generally speaks in a rather monotonous voice, little modulated by emotional tones.

There are two other facts in connexion with this case worth notice for their wider psychological bearing. The first is this: my subject seems absolutely indifferent to the vast mass of musical sounds. If he is engaged in mental work, and a German brass-band or a barrel-organ is grinding discord under his very ears, he is quite unconscious of the fact until his attention is called to it. He suffers much from headache; but even in that morbid state of nerve, when noise is so intensely painful to most of us, he "would not perceive a drum-and-fife band just outside his window unless somebody happened to notice it in speaking to him". Music, in fact, under ordinary circumstances, quite escapes his observation. The second point is the converse aspect of the same peculiarity. Whenever circumstances compel his attendance at a concert, a choral service, or a musical party, where no other occupation is possible, he suffers from the most intense ennui, which "becomes after a time almost unsupportable". The music being an absolute matter of indifference to him, the effect is the same as if he "were made to sit quietly in an attitude of attention for two or three hours, while nothing whatsoever was taking place".

In conclusion, I should like to add that if any competent physicist or physiologist wishes to verify any of the above statements, or try any further experiments, I would endeavour to make arrangements with my subject for the purpose, on receiving a communication to that effect.

GRANT ALLEN.

II. THE QUESTION OF VISUAL PERCEPTION

IN GERMANY.

(II.)

In my first paper on this subject an attempt was made to give a rough sketch of the field of experimental research recently worked by the physiologists. The fruits of these labours have, as was there hinted, been turned to different accounts, since they have been taken up and embodied in quite dissimilar theories of the visual space-perception. In the present paper I purpose giving some account of these rival modes of interpretation, and indicating, as impartially as possible, what seems to be the relative value of these hypotheses.

It will be convenient to group these theories, after the example of Helmholtz, in two main divisions, the Innate or Intuitive and the Derivative theories; or, to adopt the German expressions the Nativistic and the Empiristic or Genetic theories. By the former are meant those modes of interpreting the phenomena which lay most emphasis on certain supposed instinctive dispositions and innate organic arrangements; by the latter those which accentuate the effects of experience, experience being of course conceived to be possible prior to the formation of the visual perception of space. The first class regard this perception more as something originally given, the latter conceive of it as a gradual process of growth or acquisition.

This division is necessarily a very rough one. The Nativists have always allowed that our visual knowledge of space owes something to experience, recollection, and inference. On the other hand the Empirist is now able, by means of the hypothesis of evolution and the law of heredity, to accept in a modified form some of the positions of the other side.

After reviewing the principal theories on the two sides, I will, in conclusion, touch on their relation to the space-problem as raised philosophically by Kant. With that problem the question between the Nativists and Empirists is, as we shall see, by no means identical.

I. The Nativists.

Beginning with the Nativists, we find a series of ingenious attempts to recast the innate hypothesis in accordance with the results of a progressive observation of the phenomena. We must content ourselves with considering some of the main developments of this theoretic movement.

*

The basis of the intuitive theory was laid by Johannes Müller, who sought to bring the physiology of the senses into agreement with Kant's peculiar conception of space as a subjective mental form. This he did in the case of visual perception by supposing that the retina has a direct knowledge of its own local arrangements. An impression on the retina—that is, a sensation of light-is regarded by Müller as a perception of the condition of a particular nervous fibre, and the excitation of any retinal element necessarily involves the consciousness of its local peculiarities. And this perception of the local order of the various parts of the retina is all that is immediately seen in visual perception. "The retina," he says, " sees in every field of vision only itself in its spacial extension in the condition of excitation (Affection)." It is sensible of itself when most at rest and perfectly closed, as "spacially dark".

This primitive subjective intuition gives immediately the relations of space in two dimensions, including relative position, distance, and apparent magnitude. Only since the retinal picture inverts the real object, this subjective form does not accurately teach the property of direction (right, left, &c.). The reference of this intuitive form to external objects is regarded by Müller as an act of inference depending on recollected experience. Thus the erect position of objects, their distance, and so their real magnitude, have to be learnt. Single vision, or the combination of the impressions of the two retinas in a perception of one object in one and the same space-position, is thus accounted for by Müller. The corresponding or identical elements of the retinas have from the first the same space-consciousness. This arises from the fact that in the chiasma (the point of intersection of the optic nerves) each fibre coming from the brain splits up into two threads running to identical points. Hence the two impressions coalesce in a single perception. This

* Zur vergleichenden Physiologie des Gesichtssinnes, p. 56; Handbuch der Physiologie, II., pp. 262, 350, 361.

This is asserted by thinkers as different as Helmholtz and Stumpf. On the other hand, W. Tobias thinks Kant stands to Müller in the relation of a midwife rather than of a father. (See Grenzen der Philosophie, pp. 106, 107.)

This is pointed out by Ueberhorst, Die Entstehung der Gesichtswahrnehmung, p. 129.

is the first form of the Theory of Identity, a hypothesis which has vigorously maintained its place in German physiological speculation.

Müller's way of regarding the visual intuition of space as subjective or retinal has been adopted by only a small number of his followers. Some of the physiologists who immediately succeeded him endeavoured by means of it to explain certain of the more intricate facts of vision. Thus, for example, Recklinghausen ingeniously argued that the discrepancy between the apparent and the real right angle arises from the fact that the surface of the retina and the axis of vision meet obliquely, and as a consequence of this the optical images of the lines containing a right angle in the retinal image could form an oblique angle. A curious development of Müller's theory of retinal perception appears in the doctrine of Ueberweg* that the magnitude which we attribute to our retina, after the analogy of the image of the retina of other persons, does not constitute its true circumference; that this latter rather coincides with our whole field of vision; and that, conversely, the apparent magnitude of an external object is in reality only that of its actual retinal image.† A survival (in a modified form) of this subjective theory will be found in the doctrine of monocular space-perception held by Hering and Kundt, of which I shall speak presently.

It may be supposed that this notion of a subjective or retinal form of space which has to be referred to external objects by help of experience, would not permanently satisfy the nativists themselves. It would seem more natural and consistent to extend the innate capacity of the retina by attributing to it an original perception of the space external to itself; and this was done by means of the Theory of Projection which was maintained in Germany by Tourtual, as also by Volkmann in one of his earlier works. According to this hypothesis the retina has an innate capability of projecting its impressions outwards in the divisions of certain straight lines, as the axes of the impinging pencils of rays.§ This theory was clearly an extension of

Zeitschrift für rationelle Medicin, Vol. V., PP. 268-282.

†This bold idea is criticised by Stumpf, Ueber den psychologischen Ursprung der Raumvorstellung, pp. 191, 192. Mr. Monck appears to put forward a doctrine of a perception of the retina not very different from that of Ueberweg, Space and Vision, p. 34 ff.

This is Wundt's name for the theory (Physiol. Psychologie, p. 632). Helmholtz uses the expression to denote the empirical doctrine that impres sions are referred to points of external space by help of certain mental processes, as distinguished from the hypothesis of identity (Physiol. Optik, p. 441).

§ Or the lines of vision (Visirlinien), i.e., the normals passing through the centre of curvature which nearly coincide with these axes.

the idea that space is originally seen, since it makes instinctive the perception of direction and of the erect position of objects which Müller had regarded as acquired. According to this hypothesis objects are seen single, not because their images fall on identical points, but because the rays impinging on the two retinas meet in the object which emits or reflects them.

A closer study of the phenomena of binocular vision showed that both the Theory of Identity and that of Projection in their earlier form were beset with insuperable difficulties. It is obvious that the latter fails to account for the presence of double images. If the retinal images are through an innate tendency projected in the direction of the rays or lines of vision, we ought (as Wundt observes) to see everything single under all circumstances (since the rays always intersect in the luminous point). This difficulty was felt by Nagel, who endeavoured to modify the theory. According to him the two retinas are projected independently on different spherical surfaces, having the points of intersection of the lines of vision-approximately the centres of the eyeballs as their centres. These surfaces intersect in the point of fixation; and in the case of vision with parallel axes, meet in a single plane. While the Projection-theory accounts for the coalescence of the retinal images but not for the facts of double vision, the Theory of Identity, though explaining in the main the facts of double vision, fails to clear up the phenomena of single vision in the case of disparate (non-identical) points. Brücket attempted to obviate this difficulty by saying that the coalescence of impressions in these cases may be effected by ocular movements which successively bring all points of the object on the identical centres of the yellow spots (points of fixation). This supposition was plainly disproved by the experiments of Dove with momentary electrical illumination.‡ (MIND NO. IX., p. 22.)§

A further modification of the Theory of Identity had therefore to be made before it could be accepted as an adequate interpretation of the facts. This has been attempted by one or two recent writers with very considerable ingenuity, and a fine appreciation of the complexity of the phenomena needing explanation. I refer more particularly to the hypotheses put forth by Panum and E. Hering, who not only seek to bring the

Nagel called this process of projection a "constructive" operation. He took a considerable step in the direction of the Empiristic hypothesis by affirming that this projection took place by help of the muscular feelings. See his work, Das Sehen mit zwei Augen, pp. 5, 99 ff.

+ Müller's Archiv, 1841, p. 459.

Berichte der Berliner Akademie, 1841, p. 252.

§ Further references to my previous article will be made under the form No. IX.