The circulation of money implies the circulation of commodities; money circulates commodities which have prices, i. e., which are beforehand ideally equated to certain quantities of gold. In the determination of the prices of commodities, the value of the quantity of gold which serves as a unit of measure, or the value of gold, is assumed to be given. Under that assumption the quantity of gold necessary for circulation is determined first of all by the sum total of the prices of commodities that are to be realized. But this sum is itself determined: 1. By the level of prices, the relatively high or low exchange value of commodities estimated in gold; and 2. By the mass of commodities circulating at fixed prices, i. e. by the number of purchases and sales at given prices.[73] If one quarter of wheat is worth 60 shillings, then twice as much gold is required to circulate it or to realize its price as would be the case if it were worth only 30 shillings. To circulate 500 quarters of wheat at 60 shillings, twice as much gold is necessary as for the circulation of 250 quarters at the same price. Finally, to circulate 10 quarters at 100 shillings only half as much money is necessary as when circulating 40 quarters at 50 shillings. It follows that the quantity of gold required for circulation may fall in spite of a rise in price, if the mass of commodities in circulation declines in a greater ratio than the rise of the combined sum of prices; and, inversely, the quantity of the circulating medium may rise in spite of a decline of the mass of commodities in circulation, if the sum total of prices rises in a greater ratio. Thorough and minute English investigations have demonstrated e. g. that in the early stages of a dearth of grain in England the quantity of money in circulation increases, because the total price of the diminished supply of grain is greater than the former total price of a larger supply of grain, while the circulation of the other commodities continues undisturbed for some time at their old prices. At a later stage of the dearth of grain, there is a decline in the quantity of circulating money, either because less goods are sold at old prices besides grain, or the same quantity of those goods is sold at lower prices.