An interesting experiment is about to be conducted in London. A public-housing authority has constructed exact replicas of elegant early-Victorian townhouses on one side of Union Square in Islington, of the kind much coveted by bankers and lawyers in the nearby financial center, the famed (or ill-famed) City. The authority will rent these houses to relatively poor families at a steep discount. The scheme is revealing from at least three points of view: architectural, social, and politico-economic…