A lot of hopes have been invested for decades now in the idea of a "Tobin tax." The idea, first formulated by Yale University economist James Tobin in 1972, is that a government can tax short-term, round trip transactions from one currency to another. That is, speculators might transfer their US dollars into UK pounds and, shortly thereafter, their pounds back into US dollars. That would be done, and is done, as a way of profiting off expected changes in the relative value of the currencies concerned: it is betting. Tobin's view was that such betting is destabilizing and it ought to be discouraged: thus the tax. Further, Tobin worked up this proposal soon after Nixon had destroyed the older Bretton Woods system. There was a great deal of concern over what would replace it, how the financial world was going to get along if every currency simply floats against any other, with no agreed up measuring/reference point. The idea seemed to die a quiet death. It was resur...