With the help of these qualitative concepts we are now in a position to determine more clearly still the difference between the older and the modern conceptions: in particular the difference between the aeriform condition of matter, as we conceive of it to-day, and the element Air. Contractedness manifests as material density, or the specific weight of a particular substance. We know that this characteristic of matter diminishes gradually with its transition from the solid to the liquid and aeriform states. We know also that this last state is characterized by a high degree of expansiveness, which is also the outstanding property of heat. Thus there is reason to describe also from the modern point of view the solid and liquid states as essentially 'cold', and the aeriform state as 'warm'. But aeriform matter still has density and weight, and this means that matter in this state combines the two opposing qualities. Contrary to this, Air, as the second highest element in the old sense, is characterized by the pure quality, warm. Thus, when man of old spoke of 'air', he had in mind something entirely free from material density and weight.3 By comparing in this way the older and newer conceptions of 'air', we come to realize that ancient man must have had a conception of gravity essentially different from ours. If we take gravity in the modern scientist's sense, as a 'descriptive law of behaviour', then this behaviour is designated in the older doctrine by the quality 'cold'. If, however, we look within the system of modern science for a law of behaviour that would correspond to the quality 'warm', we do so in vain. Polarity concepts are certainly not foreign to the scientific mind, as the physics of electricity and magnetism show. Yet there is no opposite pole to gravity, as there is negative opposite to positive electricity, etc.4 In the older conception, however, the gravitational behaviour 'cold' was seen to be counteracted by an autonomous anti-gravitational behaviour 'warm'. Experience still supported the conviction that as a polar opposite to the world subject to gravity, there was another world subject to levity. We refrain at this point from discussing how far a science which aspires to a spiritual understanding of nature, including material processes, needs a revival - in modern form - of the old conception of levity. In our present context it suffices to realize that we understand man's earlier view of nature, and with it the one still held by van Helmont, only by admitting levity equally with gravity into his world-picture. For the four elements, in particular, this meant that the two upper ones were regarded as representing Levity, the two lower ones Gravity. In close connexion with this polar conception of the two pairs of elements, there stands their differentiation into one realm of created, another of uncreated, things. To understand what these terms imply, we must turn to the ancient concept, Chaos, borrowed by van Helmont.