In the 1970s the prices of most things Americans buy more than doubled. Such a general increase in prices is called inflation. Prices of selected goods may increase for reasons unrelated to inflation: the price of fresh lettuce may rise because unseasonably heavy rainfall in California has ruined the lettuce crop, or the price of gasoline may rise if the oil-producing countries set a higher price for oil. During inflation, however, all prices tend to rise. Over the last 400 years there have been many periods of inflation. In the 16th centur ....