In these ultimates supreme reality is understood to lie; and on them at last, and indeed always, rests whatever reality truly exists in any object. All else is secondary--and, comparatively speaking, illusory,--unreal. Any phenomena that may be noted only affect the surface or show of these reals: the inner reality continues one and unchanged. Outside them, around them, is the void--emptiness, non-entity. Yet null and void as it may be, we may, in passing, reply,--this circumambient is the source of all that gives these masses of atoms any distinctive reality--any character of true being. Space may be empty enough,--a mere spectre-shell; and yet it is their differences in spatial circumstance that bring out and actualise what they implicitly are. These '_individua_' these units of reality, these atoms, are real and knowable only in their relations. So too Time may be contemptuously treated as a passive receptacle: yet it is only by its connexions in the past and the future that the present moment has any actuality it may claim. And time and space are potent agencies--in popular mode of utterance--whatever the mechanical philosophy may say. But all of these relations are in the realm of unreality. The atoms alone _are_: and yet the void, which ought _not_ to _be,_ in an unmistakable way _is_ also. To this mysterious vacuum which lies outside (and yet not outside) reality, to this not-being which _is,_ there can only be given a half-negative and baffling name. Let it be called Chance--or let it be called Necessity; let it be called inexplicable Law of co-existence and sequence,--the Force which is the beginning of motion. It is the ultimate key to the mystery--but it is at least a key which no human hand can use, or even lay hold of. It is enough for science if, leaving this ultimate inexplicability untouched, it trace in each separate instance the exact equation between the sum of the constituents and the total which they compose,--if it prove that the several items when put together exactly give the sum proposed. Identification--the establishment of quantitative equations--is the work of science. Identity is its canon, working on the presumption or axiom that there can be nothing in the result which was not in the antecedents or conditions. _Ex nihilo nihil fit._ The quantity of energy must always be the same, though its phases may vary, or temporarily avoid detection. Matter, i.e. the ultimate reality, is indestructible. In short, the method of analysis and synthesis, as that of addition and subtraction, is a calculus which takes the form of an equation.