[44] This theory, though often crudely formulated, has been accepted by Locke, Hume, Adam Smith, Ricardo Mill, Walker, Marshall, Hadley, Fetter, Kemmerer and most writers on the subject. The Roman Julius Paulus, about 200 A. D., stated his belief that the value of money depends on its quantity. See Zuckerkandl, _Theorie des Preises_: Kemmerer, _Money and Credit Instruments in their Relation to General Prices_, New York (Holt), 1909. It is true that many writers still oppose the quantity theory. See especially, Laughlin, _Principles of Money_, New York (Scribner). 1903. [45] See Scott, "It has been a most fruitful source of false doctrines regarding monetary matters, and is constantly and successfully employed in defense of harmful legislation and as a means of preventing needed monetary reforms." _Money and Banking._ New York, 1903, p. 68. [46] [For a method of determining the velocity of the circulation of money, see Appendix A.] [47] It is important to bear in mind that wherever _P_ is used in this chapter it represents the index number, or scale of prices, at which the trade, _T_, is conducted.--EDITOR. [48] An almost opposite view is that of Laughlin that normal credit cannot affect prices because it is not an offer of standard money and cannot affect the value of the standard which alone determines general prices. See the _Principles of Money_, New York (Scribner), 1903, p. 97. Both views are inconsistent with that upheld ... [here]. [49] This fact is apparently overlooked by Laughlin when he argues that there is not "any reason for limiting the amount of the deposit currency, or the assumption of an absolute scarcity of specie reserves." See _Principles of Money_, p. 127. [50] Interesting changes in the magnitudes of the equation of exchange between 1896 and 1914 are given in the appended diagram, which is taken from a reprint of Professor Fisher's article, _The Equation of Exchange for 1914, and the War_, the _American Economic Review_, Vol. V, No. 2, June, 1915.--EDITOR. [51] Adapted from Irving Fisher. _Recent Changes in Price Levels and Their Causes_, Bulletin of the American Economic Association. Fourth Series, No. 2, Papers and Discussions of the Twenty-third Annual Meeting, December, 1910, pp. 43-44. [52] Irving Fisher, _The Purchasing Power of Money_, pp. 74-88. [53] _Ibid._, pp. 149, 150. [54] _Causes of the Changes in Prices since 1896._ Bulletin of the American Economic Association, Fourth Series, No. 2, Papers and Discussions of the Twenty-third Annual Meeting, December, 1910, pp. 27-36. [55] There is a possible error here of perhaps $500,000,000. [56] The estimate for 1908 is $113,996,000. Cf. U. S. Report of Director of Mint, 1909, p. 80. [57] Bulletin, Am. Econ. Assoc., Fourth Series, No. 2, 1910, pp. 46-52. [58] _Ibid._, pp. 52-61. [59] _Money and Credit Instruments in their Relation to General Prices_, 2d edition, 1909. New York: Henry Holt & Company. [60] The passages referred to are omitted.--EDITOR.