… is from pages 36 and 40 of Nicholas Barbon’s 1696 A discourse concerning coining the new money lighter, as quoted on page 12 of Jacob Viner‘s remarkable and indispensable 1937 volume, Studies in the Theory of International Trade (available without charge on-line here):
And yet there is nothing so difficult, as to find out the balance of trade in any nation; or to know whether there ever was, or can be such a thing as the making up the balance of trade betwixt one nation and another; or to prove, if it could be found out, that there is anything got or lost by the balance…. But if there could be an account taken of the balance of trade, I can’t see where the advantage of it could be. For the reason that’s given for it, that the overplus is paid in bullion, and the nation grows so much the richer, because the balance is made up in bullion, is altogether a mistake: for gold and silver are but commodities; and one sort of commodity is as good as another, so it be of the same value.