Number 222 (Story #2), April 17, 1995 by Phillip F. Schewe and Ben Stein INTERGALACTIC MAGNETIC FIELDS are probably very weak but may well influence galaxy formation. These fields might be primordial or might arise from magnetized plasma expelled by galaxies. R. Plaga of the Max Planck Institute in Munich, Germany suggests that the fields between the galaxies can be detected through their influence on gamma ray bursts reaching the Earth. According to Plaga, fields as weak as 10**-24 gauss would delay the arrival of some gamma-ray photons by a measurable amount. He believes that it might be possible to extract such information from gamma-burst data of the type recorded by the Gamma Ray Observatory. (Nature, 30 March 1995.)