Prices were outrageously volatile. While traders attributed the sharp market movements to supply and demand, most politicians in Washington were sure that speculation was the culprit. The US public became incensed.

The year was 1958, the commodity in question onions. Congress held long and sometimes tumultuous hearings in which Everette Harris, then president of the Chicago Mercantile Exchange, tried to convince lawmakers that the futures market for onions was not the cause of the volatility. "We merely furnish the hall for trading . . . we are like a thermometer, which registers temperatures," Mr Harris told a hearing. "You would not want to pass a law against thermometers just because we had a short spell of zero weather." But such arguments were ignored and in August of that year the Onion Futures Act was passed, banning futures trading in the commodity.