Number 152 (Story #1), November 19, 1993 by Phillip F. Schewe and Ben Stein THE NATURE AND ORIGIN OF COSMIC RAYS seem to change above an energy of about 10**18.5 eV. The Fly's Eye collaboration---Utah, Illinois, Adelaide, Bartol---which operates in Dugway, Utah an array of photodetectors aimed at the sky, has measured the energy and composition of cosmic rays since 1981 (contact Pierre Sokolosky, 801-581-5398). The apparatus looks for the fluorescence of atmospheric nitrogen caused by airshowers set up by the incoming cosmic rays. The energy spectrum of the rays falls off steeply at a certain rate up to an energy of about 10**17.5 eV. Until that point, the flux is dominated by heavy nuclei. At higher energies, above about 10**18.5 eV, the spectrum, now dominated by protons, flattens, indicating a different sort of cosmic ray at these higher energies. (The data sample in this energy range consists of several thousand events.) Furthermore, no anisotropy in the directionality of the highest-energy events can be detected, suggesting to the Fly's Eye scientists that these particles do not originate in the galactic disk. (D.J. Bird et al., Physical Review Letters, 22 Nov. 1993.)