Why is this a good idea? The Turner-Brown proposal is a modern version of an idea originally floated in 1972 by the late James Tobin, the Nobel-winning Yale economist. Tobin argued that currency speculation — money moving internationally to bet on fluctuations in exchange rates — was having a disruptive effect on the world economy. To reduce these disruptions, he called for a small tax on every exchange of currencies.

Such a tax would be a trivial expense for people engaged in foreign trade or long-term investment; but it would be a major disincentive for people trying to make a fast buck (or euro, or yen) by outguessing the markets over the course of a few days or weeks. It would, as Tobin said, “throw some sand in the well-greased wheels” of speculation.