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