elementary sensations. The resolution of the sensation is effected by the resolution of its most important condition, the ray of light. The prismatic spectrum comprehends a variety of distinct sensations which, previous to the analysis, must have been contained in the complex sensation of white light. A well-known optical toy, consisting of a disc of cardpaper with the spectral colours painted upon it, and made to revolve rapidly upon its axis, shows that the separate sensations may, by rapidity of succession, become blended together again and form one complex sensation more or less closely resembling the original one. The proper mixing of colours is an important part of the oil-painter's art, and in this there is a complex sensation produced by the mixing together in proper proportions of the oils, which, taken separately, would produce a simple, or at least a less complex, sensation. We thus see that in many cases the sensations of the two most noble senses may be shown to be composed of more simple elements, being, however, still sensations. A similar course of investigation, regarding the sensations of taste, smell, and of organic life, would probably show that in all these cases there are many complex sensations which are capable of resolution. But it is needless to continue the investigation farther, as we have already sufficiently established our conclusion, which may be thus stated:(1). There are in consciousness sensations of a complex character, which, as far as consciousness is concerned, appear to be simple. CHAP. II. SECT. II. Result of analysis. D CHAP. II. Analysis into unconscious but mental elements (2). The resolution of these complex states of consciousness cannot be effected by consciousness alone, but by applying the methods of physical science to the physical conditions of these states of consciousness. (3). Hence, we may conclude the possibility of there being other complex states of consciousness, which, by mere reflection, cannot be analysed into their component elements. § 17. We now consider the possibility and legitimacy of analysing sensations into elements which are not, and cannot be, brought within the sphere of considered. consciousness.* Suppose that the point of a needle has been made so small that when it is held in a clear light, directly before the eye, it is just visible, and no more. Upon the principle of the infinite divisibility of matter, this point may be divided into two halves, each of which is invisible. Or, suppose that in the wheel of Savart, referred to above, all the teeth except two have been broken off, and the concussion of two teeth upon the bar is necessary to produce an audible sound. If one of these teeth be broken, the vibration of the remaining one will be inaudible. In both of these cases, and in others which might be mentioned, a certain amount of physical antecedent is necessary as a condition of conscious sensation. And * The doctrine of latent mental modification, held by Sir W. Hamilton and others, asserts that underlying the sphere of our conscious activity there is a still more extensive sphere of mental activity, of which we are never conscious, but the results of which manifest themselves in consciousness. the question is, may that conscious sensation be resolved into mental elements of which we are not conscious? By some it is held that this resolution is not only possible, but necessary to explain the phenomenon. Against this view the following objections may be urged : CHAP. II. SECT. II. (1). The essential character of a sensation is that Objections. it is felt, and felt consciously. Therefore, to analyse sensations into elements of which we cannot be con scious is not legitimate. (2). There are other possible explanations of the difficulty. It may be that the object from which the light is reflected, or from which the vibration of the air proceeds, produces such a slight agitation of the intervening medium that it is spent or dispersed before it reaches the organ of sense. Or, suppose the agitation of the ether or air to reach the nerve of sense, it may be that the impression upon the nerve is so slight, that no vibration is propagated to the nerve centre in the brain, or that the vibration is so exceedingly slight as not to be a sufficient condition of sensation. And that either of these suppositions is the true one, appears to be supported by the fact that certain artificial appliances, such as the microscope, collect or intensify the physical conditions of sensation, so that what was before invisible or inaudible may be distinctly seen or heard. The rays of light falling from a point invisible to the naked eye, are collected and condensed by the microscope so as effectually to impress the optic nerve, from which we naturally conclude that, previous to the use CHAP. II. of the instrument, the vibrations of the ether nerve were so slight as not at all, or not sufficiently, to impress the nerve. It is possible, also, that there may be an excitement of nervous activity, either in the brain or the nervous fibres, but which is not a sufficient condition of sensation. We shall probably see reason afterwards to conclude that this is so. In the meantime, we may conclude that the most probable reason why, in certain cases, a conscious sensation does not take place, is that the physical conditions, whether here or there, whether nervous or extra-organic, are inadequate. Revived sensations described. SECTION III. REVIVAL AND ASSOCIATION OF SENSATIONS. § 18. The possibility of the revival of a sensation once experienced is a fact familiar to every one. But the sensation as revived is not the same as when actually experienced. It is idealised, it appears more refined, farther removed from sense than it was originally. Illustrations of this are numerous and familiar. If we have once seen a fine building which has made a great impression upon us by its architectural beauty, a very slight effort will serve to recall before our minds its colours and outlines. We imagine that we almost see it. So of sounds. We are familiar with the voice of a friend; in his absence it is quite easy to recall the tones and quality of his voice; we fancy that we hear him speaking. Other sensations of taste, smell, and touch, are capable of revival in a similar manner, some more vividly, more approaching the original, than others, but all to a greater or less extent. In all these cases the phenomenon, the revived sensation, is recognised as related to the original one-a repetition of it, but different from it. Moreover, the sensation revived appears always to be connected with the same organ as when originally experienced. § 19. The physical condition of the revival of sensations is probably some agitation of the same nerves as served for the physical condition of the original sensation. The researches of physiologists, however, appear to lead to the conclusion that a particular part of the brain, the cerebral lobes, is designed to prolong and repeat the action of the nerves of the senses. And many philosophers, assuming that they know the functions of the different parts of the nervous system, have given minute elaborate explanations of the nervous motions which take place in correlation with the revival and varied combination of our sensations. A distinguished writer, who has made great use of physiology in the explanation of psychical phenomena, has well expressed the indirectness and obscurity of our knowledge of the relation of nervous action to feeling, in the following sentences: "(1.) Each individual is absolutely incapable of knowing any feelings but his own. That there exist other sensations and emotions, is a conclusion CHAP. II. SECT. III. Physical of revival. conditions Correlation of nervous with psychical |