which his successors have not freed themselves; and the theory of natural processes which appears to have satisfied him, was that when two forces come into operation there is a partial or complete suspension of one by the other. In modern economics "fertility" has no very definite meaning. It may mean what is ordinarily understood by the word--climate, rainfall, railway rates or anything else except "indestructible powers of the soil." To speak of "additional labour and capital" without reference to the kind and quality of the labour and capital, and the manner in which they are employed, organized and directed, throws very little light on agriculture. Every improvement involves, from a quantitative point of view, more or less of capital or of labour, so that it is the "antagonizing" influences, which are nearly all qualitative, which appear to be really important. It is therefore extraordinarily difficult at present to know what happens, or rather what would happen if it were not prevented, when a country reaches "the stage of diminishing returns"; what precisely it is which comes into operation, for obviously the diminishing returns are the results, not the cause; or how commodities "obey" a law which is always "suspended." Possibly the present generation of English industrial history will furnish many illustrations of the law of diminishing returns. We can only say that it requires investigation and restatement. Closely related to the law of diminishing returns is the Theory of Rent. No economic doctrine so well illustrates the achievements and the defects of modern economic analysis. Ricardo's statement of the theory left upon the world an impression, not wholly just, of singular clearness. He employed the theory with wonderful success in unravelling the problems of his time. Its importance has not been seriously, or at any rate successfully, called in question. Treated at first as a doctrine peculiarly applicable to land, with a certain controverted relevance to other natural agents, it has been so extended that there is scarcely any subject of economic study in which we may not expect to find adaptations or analogies, so that Ricardo seemed to have discovered the key of economic knowledge. But it was discovered that there were no "indestructible powers of the soil"; that the fertility of land in a country like England is almost entirely the result of improvement at some time or other; that "advantage of situation" includes very much more than the words in their literal sense imply; that both "fertility" and "advantage of situation" include many kinds of differential advantage; that in some circumstances rent does not enter into the price of agricultural and other produce, and that in others it does. Moreover, the study of the theory of rent has had a very great influence on all branches of economics by destroying the notion that it is possible to draw sharp lines of distinction, or deal with economic conceptions as