3. _There being a limited number of indirect agents, their limited powers in a given period limit the supply of present goods._ The principle is familiar that value is always connected with relative scarcity. Now the desire for the present goods is indefinitely large. If the right kind and quality could be had at will, an enormously greater amount of present goods would be used. But the present goods are dependent on indirect agents. The psychic income of a civilized community is dependent on a favorable and extremely refined environment: houses, libraries, theaters, the agencies of travel, as well as the sources supplying the more material needs. These indirect agents, even in the richest community, are limited in variety, in quality, and in number. [Sidenote: The total of future uses in vastly greater] But if indirect agents could produce an indefinitely large product at any given moment, the supply of present goods could be indefinitely increased. The supply of utilities, therefore, is limited by "diminishing returns" in the use of agents, making their maximum yield depend upon the lapse of time. The uses any given material can yield in a limited period have an absolute limit: an acre of land with the most perfect cultivation cannot feed the world; but remove the limit of time, wait an eternity, and the acre would yield an infinite crop. The economic return of a given agent in a given period is reached much sooner than the technical return. If agents are forced to yield more bountifully, it is at the sacrifice of utilities in other agents, and a point of maximum net yield is found in any given period. Here also the lapse of time is the condition of the increase of the net utilities derivable from limited agents. [Sidenote: The choice open to the investor of money]