When each country produced both commodities for itself, 10 yards of broad cloth exchanged for 15 yards of linen in England, and for 20 in Germany. They will now exchange for the same number of yards of linen in both. For what number? If for 15 yards, England will be just as she was, and Germany will gain all. If for 20 yards, Germany will be as before, and England will derive the whole of the benefit. If for any number intermediate between 15 and 20, the advantage will be shared between the two countries. If, for example, 10 yards of cloth exchange for 18 of linen, England will gain an advantage of 3 yards on every 15, Germany will save 2 out of every 20. The problem is, what are the causes which determine the proportion in which the cloth of England and the linen of Germany will exchange for each other? This, therefore, is a question concerning exchangeable value. There must be something which determines how much of one commodity another commodity will purchase; and there is no reason to suppose that the law of exchangeable value is more difficult of ascertainment in this case than in other cases. The law, however, cannot be precisely the same as in the common cases. When two articles are produced in the immediate vicinity of one another, so that, without expatriating himself, or moving to a distance, a capitalist has the choice of producing one or the other, the quantities of the two articles which will exchange for each other will be, on the average, those which are produced by equal quantities of labour. But this cannot be applied to the case where the two articles are produced in two different countries; because men do not usually leave their country, or even send their capital abroad, for the sake of those small differences of profit which are sufficient to determine their choice of a business, or of an investment, in their own country and neighbourhood. The principle, that value is proportional to cost of production, being consequently inapplicable, we must revert to a principle anterior to that of cost of production, and from which this last flows as a consequence,--namely, the principle of demand and supply. In order to apply this principle, with any advantage, to the solution of the question which now occupies us, the principle itself, and the idea attached to the term demand, must be conceived with a precision, which the loose manner in which the words are used generally prevents. It is well known that the quantity of any commodity which can be disposed of, varies with the price. The higher the price, the fewer will be the purchasers, and the smaller the quantity sold. The lower the price, the greater will in general be the number of purchasers, and the greater the quantity disposed of. This is true of almost all commodities whatever: though of some commodities, to diminish the consumption in any given degree would require a much greater rise of price than of others.