The America of the 1990s was fortunate in having not just one but two oracles. The course of events could be divined from the convoluted utterances of the inscrutable Alan Greenspan, chairman of the Federal Reserve. But it could also be observed in the daily fluctuations of the Dow Jones index. Since both indicators tended to say much the same thing - that all was for the best in the best of all possible worlds - the country was lucky indeed.

As stock prices have fallen, so has faith in both these oracles. But the idea that markets reflect the collective wisdom of millions of American investors and are an even more reliable measure of the democratic pulse than opinion polls remains influential.