To-day the safety and supply of the internal currency of the various states is provided for by a monometallic system or by note issue, while, conversely, trade in the precious metals has become free, and bullion flows automatically from land to land in accordance with the dictates of a now rightly-conceived theory of international trade. Just so far the monetary problem has changed--becoming a question of the evolution of a stable international exchange system. The theoretic pretensions of bimetallism have correspondingly widened, but on any ground, wide or narrow, the only material for the study, comprehension, and judgment of such pretensions lies in the actual experience of Europe during the past five centuries. A few words of more particular explanation are necessary. 1. To the student of money and monetary standards the perpetually recurring phenomena of reductions of the unit and standard weights and contents of coins will present no difficulty. Three causes underlay the process--(1) the practice of alloying, (2) the competitive and dishonest action of governments, (3) the ideal nature of the unit itself, which permitted, literally, anything in the way of arbitrary manipulation (compare, e.g., the very different depreciations of the English shilling and the French sou, being both descendants of the solidus; or again, of the French livre and the Italian lire, being both descendants of the libra). 2. A second and much greater difficulty is presented by the confusion of nomenclature. It is often difficult to determine what particular piece is meant by a given name, or, if the identity of the piece can be fixed, its period may still be uncertain. In French numismatic history, for instance, the term florin d'or or denier d'or is used in documents quite generically for the more specific florins d'or à l'agnel, à l'écu, aux fleurs de lis, à la masse, moutons d'or, etc. This quite indeterminate use of the word "florin" (= denier = "piece," or generally, "coin") may possibly explain the crux to be found on pages 3, 9, 301, and 399 of the text (infra.), where florins d'or are mentioned in French history more than seventy years before the first authentic minting of the gold florin at Florence.