It's sometimes said that great harbor cities don't appreciate their harbors, so the city of New York must be an exception. Look what happens every Fourth of July. For years without missing, regular as clockwork, Macy's fireworks display has locked-down the harbor with skies in eruption, which the masses trek shoreward to see. Around either side of that date, the fireworks season brings the burghers of Manhattan, the boaters and bathers of the Boroughs to their esplanades and beaches. Few of them know how those big black barges full of fireworks got there, but lo and behold, there they are.