When a commodity is not only made by labor and capital, but can be made by them in indefinite quantity, this Necessary Value, the minimum with which the producers will be content, is also, if competition is free and active, the maximum which they can expect. If the value of a commodity is such that it repays the cost of production not only with the customary but with a higher rate of profit, capital rushes to share in this extra gain, and, by increasing the supply of the article, reduces its value. This is not a mere supposition or surmise, but a fact familiar to those conversant with commercial operations. Whenever a new line of business presents itself, offering a hope of unusual profits, and whenever any established trade or manufacture is believed to be yielding a greater profit than customary, there is sure to be in a short time so large a production or importation of the commodity as not only destroys the extra profit, but generally goes beyond the mark, and sinks the value as much too low as it had before been raised too high, until the over-supply is corrected by a total or partial suspension of further production. As already intimated,(212) these variations in the quantity produced do not presuppose or require that any person should change his employment. Those whose business is thriving, increase their produce by availing themselves more largely of their credit, while those who are not making the ordinary profit, restrict their operations, and (in manufacturing phrase) work short time. In this mode is surely and speedily effected the equalization, not of profits, perhaps, but of the expectations of profit, in different occupations. As a general rule, then, things tend to exchange for one another at such values as will enable each producer to be repaid the cost of production with the ordinary profit; in other words, such as will give to all producers the same rate of profit on their outlay. But in order that the profit may be equal where the outlay, that is, the cost of production, is equal, things must on the average exchange for one another in the ratio of their cost of production; things of which the cost of production is the same, must be of the same value.