Hume’s price-specie-flow mechanism will operate only if nations’ price levels differ enough to move exchange rates beyond the so-called “gold export” points, reflecting transport and other costs associated with importing goods from abroad. In practice, however, disequilibrium seldom developed to the point of triggering it under the classical gold standard. Instead, so long as gold convertibility commitments remained credible, speculators had reason to buy currencies as they depreciated in the foreign exchange market, and to sell them as they appreciated. Capital movements thus served to keep exchange rates from varying beyond the gold points, making actual gold transfers largely unnecessary.
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