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.