A nation may import to a greater value than it exports for half a century, perhaps, together; the gold and silver which comes into it during all this time, may be all immediately sent out of it; its circulating coin may gradually decay, different sorts of paper money being substituted in its place, and even the debts, too, which it contracts in the principal nations with whom it deals, may be gradually increasing; and yet its real wealth, the exchangeable value of the annual produce of its lands and labour, may, during the same period, have been increasing in a much greater proportion.