The Nature of Exchanges
The transportation of money comes at significant risk of robbery and requires a highly trustworthy porter, not to mention that money is very heavy stuff. The author considers at some length the weight of silver that is necessary for the merchants of Paris to obtain wines from the Chalons region - and find that quite some tonnage of silver would need to be transported from one to the other.
(EN: I'm cutting rather a long passage in which a great deal of detail is used to illustrate a simple concept: the merchants do not move all of the silver, but instead deposit in in a bank in Paris, and pay their rents and purchase goods with notes from that bank, and thereby save themselves the effort and risk of moving the money itself.)
It is common for banks in all trade cities to maintain a bank and provide notes thus. A note carries its full value in the city where it is written, and where it can be exchanged for money. In a more distant place it may be less valued for the difficulty of travelling to redeem it. Among the major trade cities of Europe, it is common for notes to he exchanged at 2% below their face value - such that a note for 100 ounces of silver in London may be exchanged for goods worth 98 ounces in Paris.
There is brief mention that a note may trade above par - such that a note for 100 ounces may be exchanged for goods that might normally sell for 102 ounces, but the author does not explain why that should be so. (EN: It can be deduced that the trader who receives it prefers a note to actual silver, for reasons of his own.)
There is some mention of the exchange of currencies among nations, which is done based on the weight of precious metal they represent. A coin that is worth half an ounce of silver will be traded for two that represent a quarter ounce. Coinage may also trade at a discount or premium in the same manner as notes, and a fee may also be deducted for the expenses and profit of the money-changer.
The use of specie facilitates trade among nations, but it also necessitates the transportation of specie. Consider a trade between England and France of wool for wine - the ships carrying these goods pass one another in the channel.
Some time later, 100,000 ounces of silver are returned to France from the sale of its wines, and the same quantity of silver (perhaps the same bars of specie) are sent back to England as the proceeds from the sale of its wool.
The exchange of goods is the point of trade, each must be moved from producers in one place to consumers in the other, but the exchange of silver is unnecessary: rather than move the same quantity from one place to another and back again: it could well have been deposited in a bank and the ownership transferred on paper without ever having to transport the silver itself.
The profit to the bankers, between discounting the par value of notes and collecting interest from borrowers, is not prohibitive so long as the amount is less than that which it would have cost to transfer the specie, plus some measure for reducing the risk of transportation.