(j) It follows from the points already made, _that all permanent improvements in agriculture retard the operation of the law of diminishing returns_. The recent introduction of the silo, for example, upon the long-used and wearing-out farms of New England promises, if the public law would quit throwing in obstacles, to help restore the fertility of many of them. The discovery of new and more available fertilizers, the invention of better agricultural implements, the light thrown by chemistry upon agriculture, the consequent adoption of better methods of culture and rotation of crops, the more perfect adaptation to the various soils of the kinds of produce sought to be raised from them,--all these and similar improvements tend to increase the ratio of produce to the labor, and to disguise the law just established. The lands that are now under cultivation may be made, under more skilful modes of culture to yield indefinitely more than at present, and the vast still uncultivated lands of the world may come to render an incalculable quantity of food to the world's population; but yet, as improvements are naturally less continuous in this than in most other departments of production, as invention has much less play, as there is less opportunity for the division and co-operation of laborers, _as nothing can materially shorten the time during which the fruits of the earth must ripen_, it is certain that possible improvements will never override the law of diminishing returns; and, consequently, _that the value of agricultural produce tends constantly to rise relatively to manufactured products generally_.