This is why bank-notes—the circulation of which diminishes the quantity of money needed—have proved such a precious invention. What they do is to set free a certain quantity of gold and silver which may be sent abroad to pay for machinery and other instruments of production, and which will in turn increase the true revenue of the country. Smith’s parable in which he illustrates these advantages, has long since become classic: “The gold and silver money which circulates in any country may very properly be compared to a highway, which, while it circulates and carries to market all the grass and corn of the country, produces itself not a single pile of either. The judicious operations of banking, by providing, if I may be allowed so violent a metaphor, a sort of waggon-way through the air; enable the country to convert, as it were, a great part of its highways into good pastures and cornfields, and thereby to increase very considerably the annual produce of its land and labour.”[193] The conclusion is that every policy—the Mercantilist, for example—which aims at increasing the quantity of money within the country, whether by direct or indirect methods, is absurd, for money, far from being indispensable, is really an encumbrance. It is not only absurd, but also useless. Have we not seen already that money is a mere commodity designed to facilitate circulation and that the demand for it is entirely determined by that object? But the supply of any commodity usually adapts itself spontaneously to the demand for it. No one concerns himself with supplying the nation with wine or with crockery. Why trouble about money?[194] If the quantity of goods diminishes, exchange slackens and a part of the money becomes useless. But “the interest of whoever possesses it requires that it should be employed.”[195] Accordingly “it will, in spite of all laws and prohibitions, be sent abroad, and employed in purchasing consumable goods which may be of some use at home.”