In a given country there take place every day at the same time, but in different localities, numerous one-sided metamorphoses of commodities, or, in other words, numerous sales and numerous purchases. The commodities are equated beforehand in imagination, by their prices, to definite quantities of money. And since, in the form of circulation now under consideration, money and commodities always come bodily face to face, one at the positive pole of purchase, the other at the negative pole of sale, it is clear that the amount of the means of circulation required, is determined beforehand by the sum of the prices of all these commodities. As a matter of fact, the money in reality represents the quantity or sum of gold ideally expressed beforehand by the sum of the prices of the commodities. The equality of these two sums is therefore self-evident. We know, however, that, the values of commodities remaining constant, their prices vary with the value of gold (the material of money), rising in proportion as it falls, and falling in proportion as it rises. Now if, in consequence of such a rise or fall in the value of gold, the sum of the prices of commodities fall or rise, the quantity of money in currency must fall or rise to the same extent. The change in the quantity of the circulating medium is, in this case, it is true, caused by the money itself, yet not in virtue of its function as a medium of circulation, but of its function as a measure of value. First, the price of the commodities varies inversely as the value of the money, and then the quantity of the medium of circulation varies directly as the price of the commodities. Exactly the same thing would happen if, for instance, instead of the value of gold falling, gold were replaced by silver as the measure of value, or if, instead of the value of silver rising, gold were to thrust silver out from being the measure of value. In the one case, more silver would be current than gold was before; in the other case, less gold would be current than silver was before. In each case the value of the material of money, i. e., the value of the commodity that serves as the measure of value, would have undergone a change, and therefore so, too, would the prices of commodities which express their values in money, and so, too, would the quantity of money current whose function it is to realise those prices. We have already seen, that the sphere of circulation has an opening through which gold (or the material of money generally) enters into it as a commodity with a given value. Hence, when money enters on its functions as a measure of value, when it expresses prices, its value is already determined. If now its value fall, this fact is first evidenced by a change in the prices of those commodities that are directly bartered for the precious metals at the sources of their production. The greater part of all other commodities, especially in the imperfectly developed stages of civil society, will continue for a long time to be estimated by the former antiquated and illusory value of the measure of value. Nevertheless, one commodity infects another through their common value-relation, so that their prices, expressed in gold or in silver, gradually settle down into the proportions determined by their comparative values, until finally the values of all commodities are estimated in terms of the new value of the metal that constitutes money. This process is accompanied by the continued increase in the quantity of the precious metals, an increase caused by their streaming in to replace the articles directly bartered for them at their sources of production. In proportion therefore as commodities in general acquire their true prices, in proportion as their values become estimated according to the fallen value of the precious metal, in the same proportion the quantity of that metal necessary for realising those new prices is provided beforehand. A one-sided observation of the results that followed upon the discovery of fresh supplies of gold and silver, led some economists in the 17th, and particularly in the 18th century, to the false conclusion, that the prices of commodities had gone up in consequence of the increased quantity of gold and silver serving as means of circulation. Henceforth we shall consider the value of gold to be given, as, in fact, it is momentarily whenever we estimate the price of a commodity.
On this supposition then, the quantity of the medium of circulation is determined by the sum of the prices that have to be realised. If now we further suppose the price of each commodity to be given, the sum of the prices clearly depends on the mass of commodities in circulation. It requires but little racking of brains to comprehend that if one quarter of wheat costs ?2, 100 quarters will cost ?200, 200 quarters ?400, and so on, that consequently the quantity of money that changes place with the wheat, when sold, must increase with the quantity of that wheat.
If the mass of commodities remain constant, the quantity of circulating money varies with the fluctuations in the prices of those commodities. It increases and diminishes because the sum of the prices increases or diminishes in consequence of the change of price. To produce this effect, it is by no means requisite that the prices of all commodities should rise or fall simultaneously. A rise or a fall in the prices of a number of leading articles, is sufficient in the one case to increase, in the other to diminish, the sum of the prices of all commodities, and, therefore, to put more or less money in circulation. Whether the change in the price correspond to an actual change of value in the commodities, or whether it be the result of mere fluctuations in market prices, the effect on the quantity of the medium of circulation remains the same.