1. In the first place let me refer to a doctrine which is generally considered to support the materialistic thesis. It is that of the development of mind, which may perhaps be held to be the great "discovery" of the modern psychologists. It is clear that just as there is a development of the physical frame and the nervous activities, from the ascidian up to man, so too is there a development of intelligence. In man's case, too, as he grows in body, so does he grow in mental power, and as he decays in body so, too, does his mental vigour decay. But this is only true when stated generally and if we look a little more closely, the facts hardly seem to warrant the conclusion which the Materialist urges that the development of the mind is the development of the nervous system. At certain epochs of life the evolution of the brain seems to stand far in advance of the mind; at others, the mind appears to have overtaken and passed by the stage reached by its physical substratum. During During a long period of life the growth of mental powers is constant and solid, while the growth of the physical basis has nearly ceased.

Take the case of a child. When it is born it has a far more complete and advanced nervous organism than the most fully equipped of other young animals. But judged by its sensations and its perceptions, it is much more stupid and insensate than the puppy or the kitten. The human infant has apparently a mental condition something like a dreamless sleep varied by unmeaning sensations, and yet it possesses a nervous mechanism complex and active enough to do anything. In a few years the mind has suddenly blossomed forth in a marvellous way, but there has been but little change in the so-called physical basis. No new organs have been formed within the cranium ; there is an increase of the brain substance, but it is a gradually diminishing increase which by no means corresponds with the enormous mental growth. Take again the case of maturity, the "middle life of man. During this time the nervous matter undergoes scarcely any discernible development. Nothing that the microscope or electro-meter can detect distinguishes the brain of the man of twenty-five from that of the man of fifty. A few grammes of weight have perhaps been added to it during the whole period. But is there not usually a considerable development of mind during this time? Has not the judgment widened and the mental powers expanded? Or again, old age presents us, it is true, with a steady decline of the physical vigour, but it is doubtful whether the decay of the mental powers in any sense keeps pace with it. On the contrary, while the old man is getting

physically feebler day by day, while he can daily do with less sleep and less exercise, less food and less excitement, as might be expected in one in whom the forces which make for life are already spent or fast waning, is it not the fact that his mental vigour remains comparatively unimpaired and that his judgment and his kindliness and his toleration are such that the younger gladly seek counsel from his maturer mind? It is then absurd to say that the evolution of the mind is the evolution of the nervous system, if it be meant that each mental phase, whether of increase or decrease, keeps time and pace with nervous growth or decay: for it is clear that the stages of the development of mind do not fully correspond with those of the development of the nervous mechanism any more than its gradual failure corresponds exactly with the failure of nervous energy. And thus the concave and convex theory, the subjective and objective aspect of one identical phenomenon or double-faced unity, does not appear to be exactly true to the facts.

II. There is, however, much greater and more significant evidence to prove that the mind has laws of its own, which are not those of the physical mechanism. It appears that there are certain elements which necessarily enter into what we mean by an intelligent consciousness which have nothing like them in the nervous material mechanism. According to Kant, knowledge can only arise if two elements are contributed to its growth: on the one side there is a material factor, on the other side there is a formal or mental factor. The mind has laws of its own, in accordance with which it works, and these laws are not the laws of that material element which it assimilates and on which it feeds. So in the same way we can assert that consciousness involves powers, faculties and elements which depend upon itself, and these cannot be accounted for by any enumeration of material mechanical processes. There are, for instance, certain mental products for which it would be difficult to find correspondent nervous processes. What nervous process could be held to correspond to the feeling of moral obligation or duty, or the sentiment of justice, or the love of truth, or the higher æsthetic feelings, or deliberate choice and acts of will in the higher sense? But there are humbler and more ordinary phenomena than these, which are exemplified in all our daily life, to which it is worth while to pay attention.

1. We will begin with a very elementary element in the acquisition of knowledge, viz., Attention. It is, of course, plain, that unless we pay attention to the phenomena that

come before us, they will come and go without leaving any trace, or communicating any data to our stock of mental acquisitions. But elementary though Attention may be, it is, notwithstanding, very difficult to explain its functions and its character. Psychologically, Attention seems due to a more or less conscious effort of mind which is directed to the more striking characteristics of the sensations which come before it. But again, there is nothing so capricious as Attention. Sometimes we by no means attend to the merely striking characteristics, but to any chance quality which for some reason or other engages us, to the exclusion of other qualities. Sometimes, again, Attention is apparently habitual or only semi-conscious; at other times, it appears impossible without a serious volitional effort. But, though we may labour to explain Attention psychologically, it is a far harder task for the physiologist. If all mental conditions were the material result or effect of molecular agitation within the nerves, it is very difficult to say why some forms of nervous agitation should produce "Attention," while other forms exactly similar, so far as their material character goes, should fail to get themselves registered within the brain. We are looking upon some scene or landscape, or, to talk a scientific language, various nerve messages are proceeding from the end-organs of sense, which have been excited by external stimuli: we attend to some features in this landscape; we notice a particular tree, or figure, or colour, not always because it is striking, but for some capricious fancy of ours. How can this be, if there be not a mind within us, with laws of its own, which has indeed a nervous mechanism, but is not the slave of the mechanism? Otherwise, one would think that all nerve-messages ought either to have equal values or to stimulate attention in equal proportion to their vividnessneither of which is the case. The only law, itself somewhat doubtful, is Weber's Law, which may be expressed as follows: Some ratio, although quantitatively different, is believed to exist for every sense. That is to say, it is true of every sense that not every change in objective stimulus occasions a change in subjective sensation, but that every change in stimulus must bear a certain definite ratio (varying in the different senses) to the already existing stimulus, before the intensity of the sensation, as a conscious state, changes. Differently stated, not absolute stimuli are felt, but only relative.

It is all very well to tell us that the seat of attention and concentration lies in the motor centres

in the brain, but this does not explain its activity. And if the answer of the physiologist be that there are certain associations set up between particular nerve-currents, and that when these run together they rouse all sorts of subsidiary commotions-just as in a telephone wire one might hear not only the voice of the speaker but the church bells of the spire near which it passes. then it must be said that nerve-associations however "dynamical" they may be declared to be, are yet not trains of thought. How absurd, in point of fact, is much of this quasi-scientific language when applied to the mind! We might, perhaps, understand how material nervous tracts are "associated" or "agglutinated," or subject to an "organic nexus:" but what on earth is the meaning of the "organic nexus" which binds one phase of consciousness to another? Is thought something which can be tied on to another thought so that the two can now hang together? Or is it not rather a complex idea, a unity of fused or transformed elements, which can only be due to the activity of a real and independent and immaterial mind?

2. We pass to another mental faculty, with which long habit has made us familiar, but the exact operation of which is hardly short of a mystery-I mean the faculty of memory. It is memory, of course, which renders possible any accumulation of knowledge. It is equally memory which renders possible any large exercise of constructive aud imaginative skill. In its two forms it lies at the foundation of what we understand by consciousness, its passive form being that which is called retentive or organic memory, and its active form, reproductive. It is by means of memory that those laws of mental association become possible which have been made of such use in explaining the train of our ideas and our processes of thought. Association works either through similarity of impressions or contiguity, whether in time or space. That is to say, we either associate together ideas or impressions which resemble one another, or which have come into our consciousness near each other, in neighbouring parts of space or successive moments of time. But only on the presupposition of memory can either form of association be realized.

Now can there be any physical explanation of memory? At first sight the answer seems certainly, yes. We are able to revive past impressions because of the existence of those nervous tracts or channels through which the ordinary impressions reached us. That there is a physical basis for memory

seems extremely probable. But that we can thus explain the whole operation of memory is a very different question. We must here distinguish the two forms of memory mentioned above, the passive or retentive function and the active or reproductive. With regard to the first of these the physical basis is obvious. For it is probable that every action of a stimulus or an end-organ of sense, and every transmission of energy through nervous fibres and cells, considerably, and perhaps permanently, affect the general nervous mechanism, just as in photography a plate of dry collodion, after a brief exposure to the sun's rays, retains for weeks in the darkness the effects of those delicate changes which it has undergone. We can get at this result by several commonplace experiments. We are jolted all day in a train, and for the next day and sometimes for succeeding days the same jolting motion continues in our consciousness, as a sort of abiding companion of all our other mental states. In the case of vision, there is, an after image impressed, as it were, on the retina which we can call up into consciousness for some time whenever we will. Or again, it is difficult to explain how certain actions become habitual without supposing some permanent alteration in our nervous energies. Thus knitting, or playing on the piano, which at first involve a series of acts of will, finally proceed with such regularity that we become unconscious of the accompanying nervous processes. There can be no doubt that there is every kind of interaction between the cells and fibres of our sensory and muscular system. Every activity leaves its mark or trace in an altered capacity or acquired tendency. And the many freaks of memory of which we have daily experience seem themselves to argue a physical and material explanation in the relative position of certain neural processes. That all this proves a physical basis for memory, so far as it is a retentive function, seems certain. Still it must be remarked that while such explanations show why we remember one thing rather than another, granted that we can remember at all, they hardly render clear and precise the possibility of memory itself. For the retentive function, so far as it is unconscious, is not what we mean

by inemory. Conscious memory doubtless presupposes all the range and sphere of retentive capacity. Still, unless it is conscious, it forms no more a part of what we include in our mental life than that vague phantasmagoria of dreams which we leave behind us when we rise from our beds.

What can we say, however, of active, reproductive memory? Can we give any physical explanation of this?