Reply #55: That is a huge wind chime (40 chimes representing those on 93)

[merh]

The "Tower of Voices," housing 40 wind chimes, marks the entry to and exit from the memorial site at Route 30. Set on a planted mound, the Tower of Voices is tall enough to be seen from the highway. "The continuing songs of chimes in the wind celebrate a living memory of those who are honored," say the architects. The curved tower, covered with white glass tile, will be illuminated at night, and stands in living memory to the voices of the forty heroes of Flight 93.

http://www.nps.gov/flni/parkmgmt/the-memorial-design.htm