We have measured the differential cross-section for electronelectron scattering at a total energy of 600 MeV in the center-of-mass system, by a colliding-beam technique using storage rings 1,2,3 . This letter reports the final analysis of the data. The parameters and operation of the storage rings have been described3'4,5. The Stanford Mark III linear accelerator supplied electrons of 300 MeV, which then circulated in the rings at the same energy, in a vacuum of 10 -a torr, with a mean storage

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... ime of 3O.minutes. A typical counting cycle consisted of 20 minutes of data-taking followed by 5 minutes for camera unloading, electron injection, and camera reloading. At the start of each cycle the electron beams were 30 to 60 ma. The detection apparatus is shown in Fig.