the natural value be necessary to make the demand equal to the supply, the market value will deviate from the natural value; but only for a time; for the permanent tendency of supply is to conform itself to the demand which is found by experience to exist for the commodity when selling at its natural value. If the supply is either more or less than this, it is so accidentally, and affords either more or less than the ordinary rate of profit; which, under free and active competition, cannot long continue to be the case.
To recapitulate: demand and supply govern the value of all things which cannot be indefinitely increased; except that even for them, when produced by industry, there is a minimum value, determined by the cost of production. But in all things which admit of indefinite multiplication, demand and supply only determine the perturbations of value, during a period which cannot exceed the length of time necessary for altering the supply. While thus ruling the oscillations of value, they themselves obey a superior force, which makes value gravitate towards Cost of Production, and which would settle it and keep it there, if fresh disturbing influences were not continually arising to make it again deviate. To pursue the same strain of metaphor, demand and supply always rush to an equilibrium, but the condition of stable equilibrium is when things exchange for each other according to their cost of production, or, in the expression we have used, when things are at their Natural Value.
