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. Suppose the following articles
 to be sold or partially metamorphosed simultaneously in different localities:
 say, one quarter of wheat, 20 yards of linen, one Bible, and 4 gallons
 of brandy. If the price of each article be £2, and the sum of the
 prices to be realised be consequently £8, it follows that £8
 in money must go into circulation. If, on the other hand, these same articles
 are links in the following chain of
 metamorphoses: 1 quarter of wheat — £2 — 20 yards of linen — £2
 — 1 Bible — £2 — 4 gallons of brandy — £2, a chain that
 is already well known to us, in that case the £2 cause the different
 commodities to circulate one after the other, and after realising their
 prices successively, and therefore the sum of those prices, £8, they
 come to rest at last in the pocket of the distiller. The £2 thus
 make four moves. This repeated change of place of the same pieces of money
 corresponds to the double change in form of the commodities, to their motion
 in opposite directions through two stages of circulation. and to the interlacing
 of the metamorphoses of different commodities. [29]
 These antithetic and complementary phases, of which the process
 of metamorphosis consists, are gone through, not simultaneously, but successively.
 Time is therefore required for the completion of the series. Hence the
 velocity of the currency of money is measured by the number of moves made
 by a given piece of money in a given time. Suppose the circulation of the
 4 articles takes a day. The sum of the prices to be realised in the day
 is £8, the number of moves of the two pieces of money is four, and
 the quantity of money circulating is £2. Hence, for a given interval
 of time during the process of circulation, we have the following relation:
 the quantity of money functioning as the circulating medium is equal to
 the sum of the prices of the commodities divided by the number of moves
 made by coins of the same denomination. This law holds generally.