This being the case, the way to calculate the real par of exchange between nations, who have in common no determinate and invariable money, exclusive of coin, is to consider fine gold and silver as the next best standard. This is a merchandize which never varies in its quality. Fine gold is always the same in every mass; and weight for weight, there is no difference in its value or quality any where. This standard being once adopted, the calculation of the real par becomes an easy operation to those who know the course of the bullion market in the two places exchanging. If, by the exportation of all the heavy coin of London, bills must be paid in a worn out currency, the rise in the price of gold in their market, above mint price, will mark pretty nearly how far it is light. If, on the other hand, the wars of France, or an unfavourable balance upon her trade, shall oblige her to export her coin, that operation will _sink_ the value of it, or _raise_ the price of bullion, which ever way you choose to express it. It is not here a proper place to resume the question, which of the two expressions is the most proper: we are here considering the value of the bullion as what is fixed, because it answers the purpose. But whether we say that bullion _rises_ in the markets of Paris and London; or that the value of their currencies _sink_, though from very different causes, the calculation of the real par will proceed with equal accuracy. An example will illustrate this. When _fine_ gold is at the lowest price to which it can ever fall at Paris, that is to say, at the mint price, it is worth 740 livres 9 sols, or 740.45 livres _per_ mark, in decimals, for the ease of calculation. The mark contains eight ounces Paris weight. Were the ounces of Paris equal to those of troy weight, ⅛ of this sum, or 92.5562 livres, would be the value of that ounce by which gold is sold at London. But the Paris ounce is about 1½ _per cent._ lighter than the troy ounce; and the exact proportion between them is unknown, from the confusion of weights, and the want of a fixed standard in England. By the best calculation I have been able to make, a Paris ounce should contain 473 grains troy, which makes the proportion between the two ounces to be as 473 is to 480, which is the number of grains in the troy ounce. Gold bullion at Paris is regulated by the mark _fine_, at London by the ounce _standard_.