This is known as the quantitative theory of money, and is recognized by Ricardo, Jevons, Macleod, John Locke, James Mill, John Stuart Mill, Senator John P. Jones, David Hume, William Huskisson, Sir James Graham, Prof. Torrens, Prof. Sidgwick, J. R. McCulloch, Mr. Gallatin, Prof. Fawcett, Prof. Perry, N. A. Nicholson, Earl Grey, Prof. Shield Nicholson, Lord Overstone, and, in fact, by all writers on political economy of any prominence since Adam Smith. Formerly it was supposed that the value of money depended upon the cost of production; that the reason why a dollar in gold or silver was worth 100 cents was because it took 100 cents' worth of labor to produce metal enough to make a dollar. This theory, however, has been abandoned by the best writers and speakers; in fact, by all economists of any standing, and it is now conceded that the cost of producing the metal has no influence on its money value, only as it may tend to increase or reduce the amount of money, and that it is the quantity of money, the number of units, available for use that determines and regulates its value; that is, if the quantity is increased its value will fall, and if the quantity is diminished its value will rise, and that it will fall or rise in value in a ratio exactly equivalent to the increase or diminution of the volume of money; and that if sufficiently reduced in volume, a dollar, whether stamped on gold, silver, or paper, would buy a plantation or pay a man for the labor of a lifetime. There can be no doubt as to the correctness of the quantitative theory of money. John Stuart Mill says: That an increase in the quantity of money raises prices, and a diminution lowers them, is the most elementary proposition in the theory of currency, and without it we have no key to any of the others. Prices, however, are not fixed by the total amount of money in existence; only that part of the money that is available for use can act on prices. Mr. Mill says: Whatever may be the quantity of money in the country, only that part of it will affect prices which goes into the market of commodities and is there actually exchanged for goods of some description. Whatever increases this portion of the money in the country tends to raise prices. Money kept in reserve by individuals to meet contingencies which do not occur, does not act on prices. Money in the coffers of banks, or retained as a reserve, does not act on prices until drawn out to be expended for commodities. It is also conceded that in fixing prices not only all the money actually available for use must be taken into consideration, but the rapidity of circulation must also be regarded; and due allowance must be made for the number of times commodities change hands before consumption.