If the determinate function be that of simple addition [so that, being the quantities possessed respectively by and its two extensive components, ], then the kind of quantity will be called 'absolutely' extensive. When an extensive quantity is not absolutely extensive, it will be called 'semi-extensive.' 59.2 It is usual in philosophical discussions to con- fine the term 'extensive quantity' to what is here defined as 'absolutely extensive quantity,' and to ignore entirely the occurrence of semi-extensive quantities. But in physical science semi-extensive quantities are well known. For example, consider a sphere of radius uniformly charged with electricity throughout its volume. Divide the sphere into two parts, namely a concentric nucleus of radius and a shell of thickness . Then the electromagnetic mass of the whole sphere is not the sum of the electromagnetic masses of these two parts, but is to be calculated by a quadratic law from the charges. A material object expresses the spatial distribution of a quantity of 'material,' when the quantity is absolutely extensive. 59.3 The volume-density, at a time in the -space of a time-system , of the distribution of any absolutely extensive quantity possessed by a material object is calculated by the ordinary mathematical formula. Consider any event-particle occupying the -point at the -time . Let be the measure of a volume in the -space which contains ; and let ′ be the extensive component of located in , if there be such an extensive component. Let be the measure of the quantity possessed by ′. Then the limit of the ratio of to , as is indefinitely diminished, is the density at at the time of the material [i.e. of the absolutely extensive quantity]. 59.4 The above definitions contemplate quantities immediately possessed by the extensive objects as such, for example, charges of electricity and intensities of sense-objects. But there are also quantities which are only mediately possessed by the objects, but are immediately possessed by the events which are their situations. Such quantities may vary with the variation in the situation of the object mediately possessing them. A mediately possessed quantity may for a certain type of material objects satisfy the characteristic condition for an extensive quantity. In that case it is an extensive quantity mediately possessed by that type of material objects. All variable extensive quantities are of this mediate character. A quantity mediately possessed by a material object at a moment [i.e. at a time ] of a time-system is the limit of the quantity possessed by the successive converging situations of in the successive durations of an abstractive class (of durations in the time-system which converges to .