1. _The supply of labor means here not the number of workers available in any one industry, but the number available in the whole field of industry._ The individual employer thinks of the supply of labor as consisting of the men seeking employment in his special industry. In this view it is the demand by the employers that apportions the workers among the various occupations. The social view of the supply of labor, however, looks at the whole field. The demand for labor is then seen to be represented not by human employers, but by resources and agents presenting opportunities and demanding labor to employ them. The rich acre, the tool, the machine, all material wealth needing the human touch to give it a higher utility, represent a demand for labor in this broad sense. The thought of a supply of labor is therefore relative to that of the demand embodied in resources. A million men are a great or a small supply of labor according as they occupy a little island or a large continent, according as they are equipped with a small or a large supply of agents. [Sidenote: Population in relation to resources] 2. _"Supply of labor," as an economic problem, presents a large and complex case of diminishing returns._ The population of different countries and of different sections of a country is seen to bear a general relation to their resources. An unintelligent race with little wealth and poor machinery is doomed to remain few in numbers. Mountains, districts poorly watered, the frozen regions of the North, are sparsely populated because natural resources are lacking. If food production alone is thought of there are apparent exceptions to this statement, but there are no absolute contradictions of it. A favored harbor may make possible a flourishing commerce on a rocky coast; an unfertile soil may support a large population when great deposits of coal or iron insure by exchange great food-supplies. Productivity must be measured under modern conditions by the purchasing power that is possible in the environment. The connection of wealth and resources with the extent of the population is in itself a recognition of diminishing returns, of an objective limit to the number of men that can occupy a certain area and employ a given stock of agents. [Sidenote: Equilibrium between numbers of animals of different species]