Many undoubtedly know that a replica of the Civil War hot air balloon Intrepid is supposed to sail this summer. The story has been in the sesquicentennial news for some months now. Well, put the emphasis on the supposed to. An unforeseen helium shortage may ground the project before it takes off.

(image/inventor and aeronaut Thaddeus Lowe rises to witness the fighting at Seven Pines, June 1862; Matthew Brady studio)