of consciousness follow step by step these waves of movement in the brain, and therefore when on two successive occasions the waves of movement pursue the same pathway in the brain, they are attended with a succession of the same ideas in the mind. Thus we see that the tendency of ideas to recur in the same order as that in which they have previously occurred, is merely an obverse expression of the fact that lines of wave-movement in the brain become more and more permeable by use. So it comes that a child can learn its lessons by frequently repeating them; so it is that all our knowledge is accumulated; and so it is that all our thinking is conducted.

A wholly new field of inquiry is thus opened up. By using our own consciousness as a physiological instrument of the greatest delicacy, we are able to learn a great deal about the dynamics of brain-action concerning which we should otherwise remain in total ignorance. But the field of inquiry thus opened up is too large for me to enter upon to-day. I will therefore merely observe, in general terms, that although we are still very far from understanding the operations of the brain in thought, there can be no longer any question that in these operations of the brain we have what I may term the objective machinery of thought. 'Not every thought to every thought succeeds indifferently,' said Hobbes. Starting from this fact, modern physiology has clearly shown why it is a fact; and looking to the astonishing rate at which the science of physiology is now advancing, I think we may fairly expect that within a time less remote than the two centuries which now separate us from Hobbes, the course of ideas in a given train of thought will admit of having its footsteps tracked in the corresponding pathways of the brain. Be this, however, as it may, even now we know enough to say that, whether or not these footsteps will ever admit of being thus tracked in detail, they are all certainly present in the cerebral structures of each one of us. What we know on the side of mind as logical sequence, is on the side of the nervous system nothing more than a passage of nervous energy through one series of cells and fibres rather than through another: what we recognize as truth is merely the fact of the brain vibrating in tune with Nature.

Such being the intimate relation between nerve-action and mind-action, it has become the scientifically orthodox teaching that the two stand to one another in the relation of cause to effect. One of the most distinguished of my predecessors in this place, the President of the Royal Society, has said in one of the most celebrated of his lectures:—'We have as much reason for regarding the mode of motion of the nervous system as the cause of the state of consciousness, as we have for regarding any event as the cause of another.' And, by way of perfectly logical deduction from this statement, Professor Huxley argues that thought and feeling have nothing whatever to do with determining action: they are merely the bye-products of cerebration, or, as he expresses it, the indices of changes which are going on in the brain. Under this view we are all what he terms conscious automata, or machines which happen, as it were by chance, to be conscious of some of their own movements. But the consciousness is altogether adventitious, and bears the same ineffectual relation to the activity of the brain as a steam-whistle bears to the activity of a locomotive, or the striking of a clock to the time-keeping adjustments of the clock-work. Here, again, we meet with an echo of Hobbes, who opens his work on the Commonwealth with these words:—

Now, this theory of conscious automatism is not merely a legitimate outcome of the theory that nervous changes are the causes of mental changes, but it is logically the only possible outcome. Nor do I see any way in which this theory can be fought on grounds of physiology. If we persist in regarding the association between brain and thought exclusively from a physiological point of view, we must of necessity be materialists. Further, so far as we are physiologists our materialism can do us no harm. On the contrary, it is to us of the utmost service, as at once the simplest physiological explanation of facts already known, and the best working hypothesis to guide us in our further researches. But it does not follow from this that the theory of materialism is true. The bells of St. Mary's over the way always ring for a quarter of an hour before the University sermon; yet the ringing of the bells is not the cause of the sermon, although, as long as the association remains constant, there would be no harm in assuming, for any practical purposes, that it is so. But just as we should be wrong in concluding, if we did not happen to know so much about the matter as we do, that the University sermon is produced by the vibration of bells in the tower of St. Mary's Church, so we may be similarly wrong if we were definitely to conclude that the sermon is produced by the vibration of a number of little nerve-cells in the brain of the preacher.

Now, if time permitted, and if I supposed that you would all care to go with me into matters of some abstruseness, I could certainly prove that whatever the connexion between body and mind may be, we have the best possible reasons for concluding that it is not a causal connexion. These reasons are, of course, extra-physiological; but they are not on this account less conclusive. Within the limits of a lecture, however, I can only undertake to give an outline sketch of what I take to be the overwhelming argument against materialism.

We have first the general fact that all our knowledge of motion, and so of matter, is merely a knowledge of the modifications of mind. That is to say, all our knowledge of the external world—including the knowledge of our own brains—is merely a knowledge of our own mental states. Let it be observed that we do not even require to go so far as the irrefutable position of Berkeley, that the existence of an external world without the medium of mind, or of being without knowing, is inconceivable. It is enough to take our stand on a lower level of abstraction, and to say that whether or not an external world can exist apart from mind in any absolute or inconceivable sense, at any rate it cannot do so for us. We cannot think any of the facts of external nature without presupposing the existence of a mind which thinks them; and therefore, so far at least as we are concerned, mind is necessarily prior to everything else. It is for us the only mode of existence which is real in its own right; and to it, as to a standard, all other modes of existence which may be inferred must be referred. Therefore, if we say that mind is a function of motion, we are only saying, in somewhat confused terminology, that mind is a function of itself.

Such, then, I take to be a general