Number 25 (Story #2), March, 14 1991 by Phillip F. Schewe and Ben Stein FLUX LINES IN SUPERCONDUCTORS can now be imaged with electron holograms. One important application of superconductors is in magnets, where the movement of magnetic flux lines penetrating the superconductor can alter the critical current density. In an effort to study the lines' behavior, a method of imaging the lines was devised years ago in which ferromagnetic powder, sprinkled on the superconductor's surface, would line up in a characteristic pattern. Now a group of scientists at Hitachi in Japan (T. Matsuda et al., Phys. Rev. Lett., 28 Jan. 1991.) has succeeded in imaging the flux lines in a superconducting lead film by producing a holographic record on videotape at a rate of tens of frames per second; each hologram results from the interference between a reference electron wave and a wave whose phase has been altered, via the Aharonov-Bohm effect, by the flux lines. (Nature, 7 Mar. 1991.)