organ. The sensations of a particular group will then be those whose parallel bodily processes, in spite of difference of detail, have the same general effect within the organism. We may accordingly speak of eye sensations, muscle sensations, etc. Such a list, if completed, would be perfectly

accurate.

Finally, we may classify sensations by reference to the stimuli which arouse them. Sensations at large fall into two principal groups, according as their stimulus is external, originating outside the body, or internal, originating within the body. Light, the stimulus to vision, is an external stimulus; muscular contraction, the stimulus to muscular sensation, is an internal stimulus. We therefore distinguish between sensations of the special senses, which are stimulated from without, and organic sensations, whose stimulus consists in a changed state of the internal bodily organs from which they come.

Not all the sense qualities that are ordinarily grouped together fall into continuous series, like the series of colours and tones. We naturally think, for example, of the sensations of pressure and temperature as forming a group of qualities, although no transition is possible from one quality of the group to another. We naturally think, again, of the sensation of warmth as very closely related to the sensation of cold, although there are no qualities which join these two sensations, and although their sense organs are distinct. It might seem, then, that the sensations of pressure and temperature are bracketed together simply by reference to the skin as their common organ, and the sensations of warmth and cold simply by reference to their common stimulus. Nevertheless, there is a real introspective resemblance between them. Pressure is more like warmth and cold than it is like tone or colour; and we do not feel the jar, in passing from cold to warmth, that we should feel if the disappearing cold were followed by a low tone or a

faint odour. The kinship which introspection finds among these sensations is, in the last resort, a matter of conscious context: the sensations from part of consciousnesses of the same pattern, make the same sort of connections in consciousness, are more or less interchangeable in consciousness.

In making out a list of the various departments of sensation, we are at times compelled to speak in terms of sense-organ or of stimulus, for the simple reason that the sensations themselves have not received a name. There is, for instance, no name to designate the peculiar quality of the sensation aroused by contraction of striped muscle. Language has developed at the command, not of theoretical interest, but of practical convenience; and there has been no pressing reason for the naming of all the separate sensations. Even in the case of colours, we have terms like violet and orange, the names of flower and fruit, alongside of the much older terms blue, red, etc.; and to denote a particular tone we have to use such clumsy expressions as the c of the thrice accented octave.'

References for Further Reading

§§ 10, 11. E. B. Talbot, The Doctrine of Conscious Elements, Philosophical Review, iv., 1895, 154.

M. F. Washburn, Some Examples of the Use of Psychological Analysis in System-Making, Philosophical Review, xi., 1902, 445.

E. H. Hollands, Wundt's Doctrine of Psychical Analysis and the Psychical Elements, and Some Recent Criticism: 1. The Criteria of Elements and Attributes, American Journal of Psychology, xvi., 1905, 499.

O. Kuelpe, Outlines of Psychology, 1909, § 40 (elementary quality of will).

§ 12. M. W. Calkins, Attributes of Sensation, Psychological Review,

vi., 1899, 506.

M. F. Washburn, Notes on Duration as an Attribute of Sensations, ibid., X., 1903, 416.

M. Meyer, On the Attributes of the Sensations, ibid., xi., 1904, 83. E. B. Titchener, Lectures on the Elementary Psychology of Feeling and Attention, 1908, Lecture i.

It should be said that current works on psychology differ, not only as regards the nature and number of the elementary mental processes and their attributes, but also as regards the principles and aims of psychological analysis in general. The fact is not surprising, when we remember that the fundamental questions treated in the Introduction the questions of subject-matter, method and problem of psychologyare still in debate. The reader may compare with the discussion of the preceding paragraphs G. F. Stout, The Groundwork of Psychology, [1903] ch. iii.; C. H. Judd, Psychology: General Introduction, 1907, ch. iv. He should, nevertheless, look for underlying agreements rather than for superficial differences. Judd's preface, for instance, opens with the sentence: "There is very general agreement as to the main topics which must be treated in a text-book on psychology."

THE QUALITY OF SENSATION: VISION

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§ 14. The Visual Qualities. It needs but a casual glance at our surroundings, indoors or out, to assure us that the world of vision comprises a very large number of sense qualities. Besides all the wealth of colour, there is the whole scale of light, from the most brilliant white to the deepest black. Both alike are qualitative systems: black, white and grey, red, yellow, green and blue, and all are qualities of sensation, individual and elementary mental processes. To a certain extent, the sensations of light and of colour are independent of each other: a landscape or a coloured painting may be translated, by photography, into an arrangement of blacks, whites and greys. They are also, however, closely related. We speak of certain colours, without hesitation, as being darker or lighter, that is, nearer black or nearer white, than other colours; and we meet with colours of all grades or degrees, from the full quality, the deep red or rich green, to the merest tinge which is but a step from grey.

If we look, first, at the sensations of light, we find that they form a single linear series, extending from white through the lighter, neutral and darker greys to black. Language has very few words to denote the qualities of this series. We speak of black, for instance, as if it were a single quality. But glance, in succession, at black cardboard, black cloth, black velvet, and the black of a comparatively lightless space, say, the blackened interior of

a long pasteboard tube. You realise at once, not only that these four blacks are qualitatively different, but also that their differences are quite considerable, so that there must be several intermediate blacks between the successive terms of the series. The same thing holds of white. Lay upon the window-sill a sheet of white paper, and on this place a cover-glass, silvered on the under side, in such a position that the glass reflects a patch of uniformly bright sky. The reflected light is astonishingly white, and the white of the paper seems, by comparison, greyish. There are in all, if we count up the distinguishable whites, greys and blacks, between six and seven hundred qualities of light sensation.

The system of colour sensations is less simple; the colour qualities cannot be arranged upon a single straight line. Let us take, as the arrangement of colours with which we are most familiar, a chart or a projection of the solar spectrum, and let us work through it, from the left or long-wave to the right or short-wave end. On the extreme left we have the quality of red. As we travel to the right, the red takes on more and more of a yellowish tinge, until it passes through orange to a pure yellow. Here, then, we have a linear series of qualities, precisely similar · to the series of light sensations. Now, at yellow, we change our direction. The yellow gradually becomes tinged with a new quality, that of green; it passes through yellow-green to a pure green. Here is a second line of qualities. Again we change our direction; the green becomes more and more bluish, until it passes through blue-green to a pure blue. Here is a third line of qualities. Once more we change our direction. This time, however, the tinge that our initial quality takes on is not new; the blue becomes