currently and scientifically, as the “collection of instruments” which aims, rightly or wrongly, at this Satisfaction. We take Satisfaction, then, as the boundary line of Economics—although a limit always suggests something on the further side. But what is Satisfaction? =Satisfaction.=—Satisfaction is found in men and animals alike, in the filling of physical wants and the forth-putting of activities. To these man adds infinite desires—less urgent, perhaps, but hungrier and more far-reaching than physical wants. Mark, however, that wants, desires, and activities merge into one another—human hunger, _e.g._, is appetite; the best life is one long purposed activity, subordinating, but necessitating, the satisfaction of wants and desires incidental to it. =Goods.=—This satisfaction gives us the meaning of Goods. The reason—and the sole reason—why we want goods is that by our constitution we cannot get satisfaction without them. Wealth, then, is the complex of goods on which satisfaction is presumed to be dependent. =Law of Satiable Wants.=—All wants and desires weaken with satisfaction, and, if satisfaction is carried far enough, they, for the moment, disappear. Generally, however, as our wants and desires are many and various, and as one satisfaction limits another, we leave off in the satisfaction of any want at a margin far short of satiation. This is purely a physiological and psychological phenomenon, not an economic law. =Law of Diminishing Utility.=—Satisfactions being dependent on Goods, we easily reflect the satisfaction on to the goods, and use the relative word Utility as if it were a quality of goods. Transferring, by the same process, the weakening satisfactions to goods successively presented to a want (or to similar goods in our possession), we get a statement of a fundamental tendency of human nature, the Law of Diminishing Utility; namely, that the additional utility which a person attaches to a given increase of his stock of anything diminishes as the stock increases. This is purely an Economic Law; for, physically considered, the goods themselves retain their material content unchanged, and are not in the abstract less capable of satisfying want, _if there be want_. Thus is explained Jevons’ “variation of Utility, depending on the quantity of commodity in our possession,” which, in developed exchange, gives us the law that Demand, _ceteris paribus_, decreases as Supply increases, and _vice versa_.