A small cosmic-ray shower of positive and negative electrons (7900 gauss magnetic field). Image was part of Carl D. Anderson´s Nobel Lecture presented before the Swedish Royal Academy of Science at Stockholm, December 12, 1936. Courtesy of The Archives, California Institute of Technology.

One of s series of cloud chamber photographs taken in a very strong magnetic field by Carl Anderson, Robert Millikan, Seth Neddermeyer and William Pickering. This image shows an electron traversing a lead plate in the middle and transferring its energy to a positron. Courtesy of The Archives, California Institute of Technology.