Cloud chamber photograph showing a shower" of three electrons & three positrons produced by a cosmic ray which has interacted in the wall of the cloud chamber. The electrons bend to the left in the chamber's magnetic field, the positrons to the right. Discovered in 1932 by American physicist Carl Anderson, the positron is the antimatter equivalent of the electron. This photo was taken by Anderson on top of Pike's Peak, Colorado; it was published in 1936."