That the best method of determining exactly the true and intrinsic value of the metals, coin, or money, in which the balance due to or from a foreign nation is to be paid, is to compare the respective value of fine bullion with the respective denominations of the coin in the one and the other; and to state the difference as the price paid for the exchange[[20]].
[20]. There occurs another considerable difficulty to be removed, before the real par of exchange can be exactly determined from the price of bullion, to wit, the uncertainty of weights, and the multiplicity of them.
Every nation in Europe has a different weight, I might almost say every city. This has proceeded, in a great measure, from the inaccuracy with which they have been made formerly. I think it is highly probable, that many, at least, of the principal weights in Europe, have derived their origin from the same standard; although they are now considerably different. Those I am best acquainted with are the following, of which I shall here set down a short table, reduced to troy grains, according to the best calculation I have been able to make.
| One ounce troy contains | 480 troy grains. |
| One ounce Paris, or poids de marc, | 473 |
| One ounce Holland troes | 473.27 |
| One ounce Colonia | 449.33 |
These are the weights used in the mints of England, France, Holland, and Germany.
If therefore we should call the troy ounce 100, the proportion of the rest will be as follows:
| Troy | 100 |
| Paris | 98.541 |
| Holland | 98.597 |
| Colonia | 93.61 |
I have chosen to reduce to ounces; because it is the denomination in which the proportion of weights is best preserved.
These ounces I apprehend to have been originally taken from the old Roman pound, which was the weight adopted by the Emperor Charles the Great, who applied himself much to the establishing a general standard of weights in his dominions.
In the examples I have given, we see how the Colonia ounce deviates more than any other from the average on the whole.