1. _The law of "diminishing returns" was first recognized and expressed with reference to the use of land in agriculture._ There are several evident reasons why this occurred. It is obvious to every farmer and gardener that he cannot indefinitely increase his crop, that two men cannot always produce twice as much as one man, and that in general the product does not always vary in proportion to the labor and materials applied. Moreover, the food supply is a fundamental factor in industry and in the welfare of states. The limit to the supply of food on a given area, cultivated by a given method, early appeared and became a serious practical problem. The circumstances in Europe in the eighteenth century drew attention to the subject. Population was increasing, and the pressure for food was strong. While all the forms of industry most common in cities were increasing, and the wealth of the cities was growing, poverty was increasing among the peasantry. Especially was this true in England during the Napoleonic wars, 1793-1815, owing to exceptional conditions. The food-supply from abroad was cut off, and when the English farmers, tempted by the high prices, took poorer land into cultivation, and sought to get larger crops from their older fields, a great object-lesson was presented on the principle of diminishing returns in agriculture. [Sidenote: This confused with historical diminishing returns] 2. _This truth of diminishing returns in agriculture was confused with the thought of historical diminishing returns._ Circumstances of the time led to the belief that because of lack of food misery must continue among the masses of men. It was thought inevitable that the population would continue to increase and food become more scarce. The idea of diminishing returns became thus a prophecy of what would happen, a social philosophy, that affected the thought of men on every practical social question. [Sidenote: The principle applies to land in all of its uses] 3. _The application of the principle of diminishing returns was soon broadened to include land in other than agricultural uses._ This was a natural and inevitable extension of the thought. It was evident that an unlimited use could not be made of a limited area of land, in any industry whatever. There is no explanation of rent of business sites, residences, lots, wharves, waterfalls, etc., unless account is taken of diminishing returns. If it were possible to do an unlimited amount of business upon a limited area of land, it would never get more scarce and could never rise in value. The idea of diminishing returns came properly, therefore, to be applied to land in all its uses. It is true, however, that the relatively large areas needed in agriculture make the phenomenon of diminishing returns much more striking in it than in most other industries. [Sidenote: And to all indirect agents]