Since midnight on December 31, 1898, Philadelphia City Hall has known the time. That is when its four 26-foot diameter clocks began service, powered by compressed air. In 1947, this system was replaced by four synchronous electronic motors, a contraption that continues to power the clocks today. Housed in relatively small boxes, the motors move the clocks’ hands — the 11-foot minute hand and the nine-foot hour hand — via a long metal rod. In this photo, the rod is camouflaged amongst the perma-scaffolding inside City Hall’s tower, but if you look closely, you can see it running up the center. Right at 6 o’clock. For more on this story, visit Hidden City Daily, hiddencityphila.org.