61.9 These causal characters, which are the characters of apparent characters, are found to be expressible as certain scientific objects, molecules and electrons, and as certain characters of events which do not necessarily themselves exhibit any apparent characters. If we follow the route of the derivation of knowledge from the intellectual analysis of sensible experience, molecules and electrons are the last stage in a series of abstractions. But a fact in nature has nothing to do with the logical derivation of concepts. The concepts represent our abstract intellectual apprehension of certain permanent characters of events, just as our perception of sense-objects is our awareness of qualities of nature resulting from the shifting relations of these characters. Thus scientific objects are the concrete causal characters, though we arrive at them by a route of apprehension which is a process of abstraction. In the same way, what, in the form of a sense-object, is concrete for our awareness, is abstract in its character of a complex of relations between scientific objects. Thus what is concrete as causal is abstract in its derivation from the apparent, and what is concrete as apparent is abstract in its derivation from the causal. The ultimate scientific objects (at present, electrons and positive electric charges) are 'uniform' objects; and, in the limited sense of charges in the 'occupied' events, they are also 'material' objects. There does not appear to be any reason, other than the very natural desire for simplicity, for the assumption that ultimate scientific objects are uniform. Some of the atomic and 'quantum' properties of nature may find their explanation in the assumption of non-uniform ultimate scientific objects which would introduce the necessary discontinuities. 61.91 The causal character of the situation of a physical object is the fact that this situation contains a certain assemblage of ultimate scientific objects; namely, the fact that among the parts of this situation are various parts which are the occupied events of these scientific objects. The 'causal components' of a physical object are the scientific objects which occupy parts of the situation of the physical object, and whose total assemblage is what constitutes the qualities which are the apparent character which is the physical object apparent in the situation. 61.92 An adjustment, ordinarily negligible but often important, has to be made to allow for the belatedness of perception. Two situations are thus involved (even although in ordinary cases they are practically identical), namely the situation of the physical object from an assigned percipient event, and the situation of the assemblage of causal components which is the situation of the 'real' object. CHAPTER XVII FIGURES