The Wealth of Nations by Part 2 Chapter 3 Page 30

Their value, therefore, must diminish as the value of that produce diminishes, and along with it the quantity of money which can be employed in circulating them. But the money which by this annual diminution of produce is annually thrown out of domestic circulation will not be allowed to lie idle. The interest of whoever possesses it requires that it should be employed. But having no employment at home, 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. Its annual exportation will in this manner continue for some time to add something to the annual consumption of the country beyond the value of its own annual produce. What in the days of its prosperity had been saved from that annual produce, and employed in purchasing gold and silver, will contribute for some little