It is evident that generalised dynamics and thermodynamics have the great merit in common that they are essentially generalisations, and their application does not require any specialised information such as that involved in the molecular kinetic theory. What has been said therefore in Volume II. In regard to the advantage which this quality confers in the case of thermodynamics applies to much the same ex tent to generalised dynamics. The same disadvantage manifests itself of course, viz. That we do not get any clearer picture of the pheno menon in question in terms of the molecules taking part therein.