Now in the ordinary way of reckoning the _real par_, the 100 Louis, 100 carolins, and 100 guineas, are all supposed to be of the same value, in the three markets; and the difference between this supposed value, and what is paid for it, is supposed to be a loss upon trade. In this light, the nation’s loss resembles the loss incurred by him, who, when he goes to the bank, and pays ten pounds sterling in coin, for a bank-note, says, that he has given ten pounds for a bit of paper, not worth one farthing; reckoning the value of the note, at the real par of the paper it is writ upon. The general rule, therefore, as I apprehend, is, to settle the real par of different coins, not according to the _bullion_ they contain, but according to the bullion they can buy with them in their own market at the time. If 1000 pounds weight of guineas can purchase at London 1000 pounds weight of standard bullion; and that 1000 pounds of the same weight of Louis can buy at Paris 1080 pounds weight of the same standard bullion; then the 1000 pounds weight of guineas is at the real par with 9256⁄1000 pounds weight of the Louis, and not worth 1000, as is commonly supposed. If the doctrine laid down in this chapter be found solid; if no essential circumstance has been overlooked, which ought to have entred into our combinations, (points left to the reader to determine) then we may conclude, _1mo_, That the course of exchange, in the way people take to calculate the real par, is no rule for judging of the balance of trade. _2do_, That the great duty laid upon the fabrication of the French coin, either deceives the English nation, and makes them conclude, from the course of exchange, that their commerce with France is extremely disadvantageous: or, if it be really disadvantageous, that it is the imposition of a duty on coinage in the French mint which occasions it. It is a question belonging to the theory of commerce, and not to that which we are now upon, to examine the nature of a disadvantageous trade, and to investigate the principles pointing out the commodities which every country ought to encourage for exportation, and those which are the most profitable to take in return. [Sidenote: Application of these principles to the English trade with France.]