'The passage from the physics of the brain to the corresponding facts of consciousness is unthinkable. Granted that a definite thought and a definite molecular action in the brain occur simultaneously, we do not possess the intellectual organ, nor apparently any rudiment of the organ, which would enable us to pass, by a process of reasoning, from the one phenomenon to the other. They appear together but we do not know why. Were our minds and senses so expanded, strengthened, and illuminated, as to enable us to see and feel the very molecules of the brain; were we capable of following all their motions, all their groupings, all their electrical discharges, if such there be; and were we intimately acquainted with the corresponding states of thought and feeling, we should be as far as ever from the solution of the problem. How are these physical processes connected with the facts of consciousness? The chasm between the two classes of phenomena would still remain intellectually impassable[7].' Next, in all cases of recognized causation there is a perceived _equivalency_ between cause and effect, such equivalency belonging to the very essence of that in which we conceive causation to consist. But as between matter and motion on the one side, and feeling and thought on the other, there can be no such equivalency conceivable. That no such equivalency is conceivable may be rendered apparent on grounds of Materialism itself. For Materialism is bound to accept the fundamental doctrine of modern physics--that, viz. as to the conservation of energy--and therefore it becomes evident that unless we assimilate thought with energy, there is no possibility of a causal relation, or a relation of equivalency, as obtaining between the one and the other. For however little we may know about brain-dynamics, materialists, at least, must take it for granted that in every process of cerebration the matter and force concerned are indestructible quantities, and therefore that all their possible equations are fully satisfied, could we but follow them out. Howsoever complex we may suppose the flux and reflux of forces to be within the structure of a living brain, it is no more possible for any one of the forces concerned to escape from brain to mind, than it would be for such an escape to occur in a steam-engine or a watch; the doctrine of the conservation of energy forms an insuperable bar to the supposition that any equation in the region of physics can be left unsatisfied, in order to pass over and satisfy some other equation in the region of psychics.