Seen and Unseen

Here's a letter to the New York Times:

I appreciate the sub-headline, appearing on your website, to a report on the BP oil spill: "The oil is clearing much faster than expected, but concern remains over the unseen effects" ("On the Surface, Gulf Oil Spill Is Vanishing Fast; Concerns Stay," July 28).*  Being an economist, I'm accustomed to looking beyond the visible effects of economic and political actions in order to take account also of unseen effects that often swamp that which is...