[1] In the present volume I have given so much extension to the details of 'Sensation' that I have obeyed custom and put that subject first, although by no means persuaded that such order intrinsically is the best. I feel now (when it is too late for the change to be made) that the chapters on the Production of Motion, on Instinct, and on Emotion ought, for purposes of teaching, to follow immediately upon that on Habit, and that the chapter on Reasoning ought to come in very early, perhaps immediately after that upon the Self. I advise teachers to adopt this modified order, in spite of the fact that with the change of place of 'Reasoning' there ought properly to go a slight amount of re-writing.

[2] The subject may feel pain, however, in this experiment; and it must be admitted that nerve-fibres of every description, terminal organs as well, are to some degree excitable by mechanical violence and by the electric current.

[3] Thus the optic nerve-fibres are traced to the occipital lobes, the olfactory tracts go to the lower part of the temporal lobe (hippocampal convolution), the auditory nerve-fibres pass first to the cerebellum, and probably from thence to the upper part of the temporal lobe. These anatomical terms used in this chapter will be explained later. The cortex is the gray surface of the convolutions.

[4] Vorlesungen über Menschen u. Thierseele, Lecture VII.

[5] In other words, S standing for the sensation in general, and d for its noticeable increment, we have the equation dS = const. The increment of stimulus which produces dS (call it dR) meanwhile varies. Fechner calls it the 'differential threshold'; and as its relative value to R is always the same, we have the equation dR/R = const.

[6] Beiträge zur exp. Psychol., Heft 3, p. 4.

[7] I borrow it from Ziehen: Leitfaden d. Physiologischen Psychologie, 1891, p. 36, who quotes Hering's version of it.

[8] Successive ones also; but I consider simultaneous ones only, for simplicity's sake.

[9] The extreme case is where green light and red, e.g. light falling simultaneously on the retina, give a sensation of yellow. But I abstract from this because it is not certain that the incoming currents here affect different fibres of the optic nerve.

[10] The student can easily verify the coarser features of the eye's anatomy upon a bullock's eye, which any butcher will furnish. Clean it first from fat and muscles and study its shape, etc., and then (following Golding Bird's method) make an incision with a pointed scalpel into the sclerotic half an inch from the edge of the cornea, so that the black choroid membrane comes into view. Next with one blade of a pair of scissors inserted into this aperature, cut through sclerotic, choroid, and retina (avoid wounding the membrane of the vitreous body!) all round the eyeball parallel to the cornea's edge.

The eyeball is thus divided into two parts, the anterior one containing the iris, lens, vitreous body, etc., whilst the posterior one contains most of the retina. The two parts can be separated by immersing the eyeball in water, cornea downwards, and simply pulling off the portion to which the optic nerve is attached. Floating this detached posterior cap in water, the delicate retina will be seen spread out over the choroid (which is partly iridescent in the ox tribe); and by turning the cup inside out, and working under water with a camel's-hair brush, the vessels and nerves of the eyeball may be detected.

The anterior part of the eyeball can then be attacked. Seize with forceps on each side the edge of the sclerotic and choroid (not including the retina), raise the eye with the forceps thus applied and shake it gently till the vitreous body, lens, capsule, ligament, etc., drop out by their weight, and separate from the iris, ciliary processes, cornea, and sclerotic, which remains in the forceps. Examine these latter parts, and get a view of the ciliary muscle which appears as a white line, when with camel's-hair brush and scalpel the choroid membrane is detached from the sclerotic as far forward as it will go. Turning to the parts that cling to the vitreous body observe the clear ring around the lens, and radiating outside of it the marks made by the ciliary processes before they were torn away from its suspensory ligament. A fine capillary tube may now be used to insufflate the clear ring, just below the letter p in Fig. 3, and thus to reveal the suspensory ligament itself.

All these parts can be seen in section in a frozen eye or one hardened in alcohol.

[11] This vertical partition is introduced into stereoscopes, which otherwise would give us three pictures instead of one.

[12] The simplest form of stereoscope is two tin tubes about one and one-half inches calibre, dead black inside and (for normal eyes) ten inches long. Close each end with paper not too opaque, on which an inch-long thick black line is drawn. The tubes can be looked through, one by each eye, and held either parallel or with their farther ends converging. When properly rotated, their images will show every variety of fusion and non-fusion, and stereoscopic effect.

[13] Martin: The Human Body, p. 530.

[14] Ibid.

[15] The ordinary mixing of pigments is not an addition, but rather, as Helmholtz has shown, a subtraction, of lights. To add one color to another we must either by appropriate glasses throw differently colored beams upon the same reflecting surface; or we must let the eye look at one color through an inclined plate of glass beneath which it lies, whilst the upper surface of the glass reflects into the same eye another color placed alongside—the two lights then mix on the retina; or, finally, we must let the differently colored lights fall in succession upon the retina, so fast that the second is there before the impression made by the first has died away. This is best done by looking at a rapidly rotating disk whose sectors are of the several colors to be mixed.

[16] Martin: op. cit.

[17] Martin, pp. 525-8.

[18] In teaching the anatomy of the ear, great assistance will be yielded by the admirable model made by Dr. Auzoux, 56 Rue de Vaugirard, Paris, described in the catalogue of the firm as "No. 21—Oreille, temporal de 60 cm., nouvelle édition," etc.

[19] This description is abridged from Martin's 'Human Body'.

[20] Martin: op. cit.

[21] Martin: op. cit.

[22] Martin: op. cit.

[23] Martin: op. cit.

[24] Martin: op. cit.

[25] Martin: op. cit., with omissions.

[26] Martin: op. cit.

[27] Vierteljahrsch. für wiss. Philos., II. 377.

[28] This chapter will be understood as a mere sketch for beginners. Models will be found of assistance. The best is the 'Cerveau de Texture de Grande Dimension,' made by Auzoux, 56 Rue de Vaugirard, Paris. It is a wonderful work of art, and costs 300 francs. M. Jules Talrich of No. 97 Boulevard Saint-Germain, Paris, makes a series of five large plaster models, which I have found very useful for class-room purposes. They cost 350 francs, and are far better than any German models which I have seen.

[29] All the places in the brain at which the cavities come through are filled in during life by prolongations of the membrane called pia mater, carrying rich plexuses of blood-vessels in their folds.

[30] The Physiology of Mind, p. 155.

[31] J. Bahnsen: 'Beiträge zu Charakterologie' (1867), vol. I. p. 209.

[32] De l'Intelligence, 3^me édition (1878), vol. II. p. 461, note.

[33] Some of the evidence for this medium's supernormal powers is given in The Proceedings of the Society for Psychical Research, vol. VI. p. 436, and in the last Part of vol. VII. (1892).

[34] Mental Physiol., § 124. The oft-cited case of soldiers in battle not perceiving that they are wounded is of an analogous sort.

[35] Physiol. Optik, p. 741.

[36] I refer to a recency of a few hours. Mr. Galton found that experiences from boyhood and youth were more likely to be suggested by words seen at random than experiences of later years. See his highly interesting account of experiments in his Inquiries into Human Faculty, pp. 191-203.

[37] Miss M. W. Calkins (Philosophical Review, I. 389, 1892) points out that the persistent feature of the going thought, on which the association in cases of similarity hinges, is by no means always so slight as to warrant the term 'focalized.' "If the sight of the whole breakfast-room be followed by the visual image of yesterday's breakfast-table, with the same setting and in the same surroundings, the association is practically total," and yet the case is one of similarity. For Miss Calkins, accordingly, the more important distinction is that between what she calls desistent and persistent association. In 'desistent' association all parts of the going thought fade out and are replaced. In 'persistent' association some of them remain, and form a bond of similarity between the mind's successive objects; but only where this bond is extremely delicate (as in the case of an abstract relation or quality) is there need to call the persistent process 'focalized.' I must concede the justice of Miss Calkins's criticism, and think her new pair of terms a useful contribution. Wundt's division of associations into the two classes of external and internal is congruent with Miss Calkins's division. Things associated internally must have some element in common; and Miss Calkins's word 'persistent' suggests how this may cerebrally come to pass. 'Desistent,' on the other hand, suggests the process by which the successive ideas become external to each other or preserve no inner tie.

[38] A common figure-alphabet is this:

[39] In Mind, IX. 206, M. Binet points out the fact that what is fallaciously inferred is always an object of some other sense than the 'this.' 'Optical illusions' are generally errors of touch and muscular sensibility, and the fallaciously perceived object and the experiences which correct it are both tactile in these cases.

[40] Romanes, Mental Evolution in Animals, p. 324.

[41] M. Lazarus: Das Leben d. Seele (1857), II. p. 32. In the ordinary hearing of speech half the words we seem to hear are supplied out of our own head. A language with which we are familiar is understood even when spoken in low tones and far off. An unfamiliar language is unintelligible under these conditions. The 'ideas' for interpreting the sounds by not being ready-made in our minds, as they are in our familiar mother-tongue, do not start up at so faint a cue.

[42] Einleitung in die Psychologie u. Sprachwissenschaft (1881), p. 171.

[43] The great maxim in pedagogy is to knit every new piece of knowledge on to a preëxisting curiosity—i.e., to assimilate its matter in some way to what is already known. Hence the advantage of "comparing all that is far off and foreign to something that is near home, of making the unknown plain by the example of the known, and of connecting all the instruction with the personal experience of the pupil.... If the teacher is to explain the distance of the sun from the earth, let him ask ... 'If anyone there in the sun fired off a cannon straight at you, what should you do?' 'Get out of the way,' would be the answer. 'No need of that,' the teacher might reply. 'You may quietly go to sleep in your room, and get up again, you may wait till your confirmation-day, you may learn a trade, and grow as old as I am,—then only will the cannon-ball be getting near, then you may jump to one side! See, so great as that is the sun's distance!'" (K. Lange, Ueber Apperception, 1879, p. 76.)

[44] The writer of the present work is Agent of the Census for America, and will thankfully receive accounts of cases of hallucination of vision, hearing, etc., of which the reader may have knowledge.

[45] Cf. Raehlmann in Zeitschrift für Psychol. und Physiol. der Sinnesorgane, II. 79.

[46] Readers brought up on Popular Science may think that the molecular structure of things is their real essence in an absolute sense, and that water is H-O-H more deeply and truly than it is a solvent of sugar or a slaker of thirst. Not a whit! It is all of these things with equal reality, and the only reason why for the chemist it is H-O-H primarily, and only secondarily the other things, is that for his purpose of laboratory analysis and synthesis, and inclusion in the science which treats of compositions and decompositions, the H-O-H aspect of it is the more important one to bear in mind.

[47] Mental Evolution in Man, p. 74.

[48] Origin of the Emotions (N. Y. ed.), p. 292.

[49] Spalding, Macmillan's Magazine, Feb. 1873, p. 287.

[50] Ibid., p. 289.

[51] Psychologie de l'Enfant, p. 72.

[52] Der Menschliche Wille, p. 224.

[53] Deutsches Archiv f. Klin. Medicin, xxii. 321.

[54] Medicinische Psychologie, p. 293.

[55] This volitional effort pure and simple must be carefully distinguished from the muscular effort with which it is usually confounded. The latter consists of all those peripheral feelings to which a muscular 'exertion' may give rise. These feelings, whenever they are massive and the body is not 'fresh,' are rather disagreeable, especially when accompanied by stopped breath, congested head, bruised skin of fingers, toes, or shoulders, and strained joints. And it is only as thus disagreeable that the mind must make its volitional effort in stably representing their reality and consequently bringing it about. That they happen to be made real by muscular activity is a purely accidental circumstance. There are instances where the fiat demands great volitional effort though the muscular exertion be insignificant, e.g. the getting out of bed and bathing one's self on a cold morning. Again, a soldier standing still to be fired at expects disagreeable sensations from his muscular passivity. The action of his will, in sustaining the expectation, is identical with that required for a painful muscular effort. What is hard for both is facing an idea as real.