The formula makes mathematically evident the time-binding capacity characteristic of the human class of life. Properly understood, _wealth_ consists of the fruits or products of this time-binding capacity of man. Animals do not produce wealth; it is produced by Man and only Man. The foregoing basic formulation should lead to further similar developments throwing much light upon the process of civilization and serving to eliminate "private opinion" from the conduct of human affairs. (In this writing it is not important to look deeper into these proposed series. The fact remains that _P_, as well as _R_, are peculiarly increasing series of a geometrical character—the precise form will be developed in another writing.) Human achievements and progress, because cumulative, are knocking out the barriers of time. This fact is the vital and dynamic difference between animal life and human life. As plants gather in and store up solar energy into sheaves for the use and growth of animal and man—so humans are gathering and binding the knowledge of past centuries into sheaves for the use and development of generations yet unborn. We have seen that the term wealth, rightly understood, means the fruit of the time-binding work of humanity. Wealth is of two kinds: one is material; the other is knowledge. Both kinds have use-value. The first kind perishes—the commodities composing it deteriorate and become useless. The other is permanent in character; it is imperishable; it may be lost or forgotten but it does not wear out. The one is limited in time; the other, unlimited in time; the former I call POTENTIAL USE-VALUE; the latter, KINETIC USE-VALUE. Analysis will justify the names. The energy of a body which is due to its position, is called potential energy. The energy of a body which is due to its motion, is called kinetic energy. Here the material use-value has value through its position, shape and so forth; it is immobile if not used, and has not the capacity to progress. Mental use-values are not static but permanently dynamic; one thought, one discovery, is the impulse to others; they follow the law of an increasing _potential_ function of time. (See app. II.) This is why these names correspond to the two names of the two mentioned classes of energy.