I just now likened these intermediaries to relays of messengers. But messengers are expected to hand on their message in the form in which they have received it. The messengers change, but not the message. The metaphor, therefore, is far too complimentary to the train of physical causes which reveal the material thing to the perceiving consciousness. The neural changes which are in immediate causal contiguity with that psychical effect which we call “the experience of an external object” have no resemblance whatever either to the thing as it is perceived or to the thing as it really is. Nor have they any resemblance to the proximate cause which sets them going, namely, the ethereal vibrations; nor have these to the accelerated electrons which constitute the incandescent object which we “experience” as the sun. Nor has the sun, as experienced, the slightest resemblance to the sun as it really is. Hume, in his “Dialogues on Natural Religion,” urges the absurdity of arguing from an effect like the universe to a cause like God, since the argument from a particular effect to a particular cause, or from a particular cause to a particular effect, is only legitimate when we have had some previous experience of that particular class of causal sequence; and nobody, it is plain, has had the opportunity of observing Creation. Whatever be the value of this argument in the case of God and the world, it seems to me conclusive in the case of matter and man. We cannot argue from purely psychical effects, like perceptions and sensations, to external causes, like physiological processes or ethereal vibrations, _unless_ we can experience both sets of facts in causal relation. And this, if we accept the conclusions of science, we can never do—partly because the intermediate members of the causal series are unperceivable; partly because, if they were perceivable, perception has been reduced by science to a purely psychical effect—which obviously cannot include its material cause. This last must for ever remain outside the closed circle of sensible experiences.