The logic behind yesterday's effort to boost the supply of dollar liquidity on both sides of the Atlantic is simple: when globally integrated markets malfunction, they require international, not just national, repair.

For the Federal Reserve, the dilemma is particularly acute. It has, in effect, two roles - as the dollar funding authority for the world, and the national authority for the US financial system. It is difficult for the Fed to perform either role effectively in current conditions without the support of other central banks.