Assuming the uniformity of nature, I carry forward and backward both the mental and the material series. A uniformity is observed in each, and a parallelism is observed between them, whenever observations can be made. But sometimes one series is known better, and sometimes the other; so that in telling a story we quite naturally speak sometimes of mental facts and sometimes of material facts. A feeling of chill made a man run; strictly speaking, the nervous disturbance which co-existed with that feeling of chill made him run, if we want to talk about material facts; or the feeling of chill produced the form of sub-consciousness which co-exists with the motion of legs, if we want to talk about mental facts. But we know nothing about the special nervous disturbance which co-exists with a feeling of chill, because it has not yet been localized in the brain; and we know nothing about the form of sub-consciousness which co-exists with the motion of legs; although there is very good reason for believing in the existence of both. So we talk about the feeling of chill and the running, because in one case we know the mental side, and in the other the material side. A man might show me a picture of the battle of Gravelotte, and say, 'You can't see the battle, because it's all over, but there is a picture of it.' And then he might put a chassepot into my hand, and say, 'We could not represent the whole construction of a chassepot in the picture, but you can examine this one, and find it out.' If I now insisted on mixing up the two modes of communication of knowledge, if I expected that the chassepots in the picture would go off, and said that the one in my hand was painted on heavy canvas, I should be acting exactly in the spirit of the new materialism. For the material facts are a representation or symbol of the mental facts, just as a picture is a representation or symbol of a battle. And my own mind is a reality from which I can judge by analogy of the realities represented by other men's brains, just as the chassepot in my hand is a reality from which I can judge by analogy of the chassepots represented in the picture. When, therefore, we ask, 'What is the physical link between the ingoing message from chilled skin and the outgoing message which moves the leg?' and the answer is, 'A man's Will,' we have as much right to be amused as if we had asked our friend with the picture what pigment was used in painting the cannon in the foreground, and received the answer, 'Wrought iron.' It will be found excellent practice in the mental operations required by this doctrine to imagine a train, the fore part of which is an engine and three carriages linked with iron couplings, and the hind part three other carriages linked with iron couplings; the bond between the two parts being made out of the sentiments of amity subsisting between the stoker and the guard.