Thus it was possible for a debtor to discharge his obligations with that one of the two metals that at the moment was the cheaper at the legal ratio.

Fluctuations in the prices of gold in terms of silver were at times such as to cause a large part of the full-weight coins of one or the other metal to leave circulation (in accordance with Gresham's law).

So from time to time the ratio was slightly changed by law in the various countries to permit the circulation or to bring back the kind of money that had been undervalued in terms of the other.

But it is a very remarkable fact that from the time of Xenophon until the discovery of America (a period of nearly 2000 years), the market ratio of silver to gold bullion in Europe remained pretty close to 10 to 1, being only temporarily altered by sudden and unusual occurrences.

From 1492 to 1660 the ratio changed to 15 to 1, where it remained with remarkable stability until about the year 1800.