Van Helmont's account brings us face to face with a number of riddles. Certainly, there is nothing strange to us in his describing carbon dioxide gas as being 'finer than vapour and denser than air'; but why did he call this a 'paradox'? What prevented him from ranking it side by side with air? As to air itself, why should he describe it as belonging to the realm of the 'uncreated things'? What reason was there for giving 'vapour' the rank of a particular condition of matter? And last but not least, what was the ancient conception of Chaos which led van Helmont to choose this name as an archetype for the new word he needed? To appreciate van Helmont's astonishment and his further procedure, we must first call to mind the meaning which, in accordance with the prevailing tradition, he attached to the term Air. For van Helmont, Air was one of the four 'Elements', EARTH, WATER, AIR, and FIRE. Of these, the first two were held to constitute the realm of the 'created things', the other two that of the 'uncreated things'. A brief study of the old doctrine of the Four Elements is necessary at this point in order to understand the meaning of these concepts. * The first systematic teaching about the four elementary constituents of nature, as they were experienced by man of old, was given by Empedocles in the fifth century B.C. It was elaborated by Aristotle. In this form it was handed down and served to guide natural observation through more than a thousand years up to the time of van Helmont. From our earlier descriptions of the changes in man's consciousness it is clear that the four terms, 'earth', 'water', 'air', 'fire', must have meant something different in former times. So 'water' did not signify merely the physical substance which modern chemistry defines by the formula H2O; nor was 'air' the mixture of gases characteristic of the earth's atmosphere. Man in those days, on account of his particular relationship with nature, was impressed in the first place by the various dynamic conditions, four in number, which he found prevailing both in his natural surroundings and in his own organism. With his elementary concepts he tried to express, therefore, the four basic conditions which he thus experienced. He saw physical substances as being carried up and down between these conditions.