Music: Dancing Philadelphians

At Home-Philadelphians who stay home for the summer swelter. Those who like music go to the Philadelphia Orchestra concerts at Robin Hood Dell to console themselves. There last week 3,000 Philadelphians could almost imagine themselves out of the sticky, uncomfortable city when Mary Binney Montgomery and her troupe danced their own version of George Gershwin's An American in Paris. Miss Montgomery's choreography followed closely Gershwin's sparkling musical account of a tourist "adrift in the City of Light." The American (Harry Teplitz) elbowed his way bewilderedly through raucous vendors and squabbling shopkeepers, was...