“Neither has the wealth of a country any bearing on the valuation of its money. Nothing is more erroneous than the widespread habit of regarding the monetary standard as something in the nature of the shares of the State or the community.Such observers fail to recognize that the valuation of the rnonetary unit does not depend upon the wealth of the country, but upon the ratio between the quantity of money and the demand for it, so that even the richest country may have a bad currency and the poorest country a good one.”