To keep cool, sweltering Philadelphians — especially senior citizens — should go to public places such as malls, grocery stores, libraries and even subway stops. A leisurely grocery store visit or trip to the mall, even for only an hour or two, rejuvenates your body," said Steven Ridenour of Temple's College of Engineering. "And you'll be better able to cope with the heat long into the night." At night, Ridenour advised, open the windows to let cooler air in. In the morning, close everything up and keep it closed until it starts to feel uncomfortable. Then use an open window and a fan to pull the air through.