"In 1932 Millikan and Anderson were investigating cosmic rays, and they had built a large '... When subatomic particles passed through... they left ghostly vapor trails in the supersaturated air... They placed powerful magnets around it to blanket the interior... with a magnetic field. ...[[Cosmic ray|[C]osmic rays]] ...were bent by the field ...[T]he direction and thickness of the paths... revealed the mass of the particles—and their charge. Anderson... noticed that some of the trails were... like... electrons, but were curved by the magnetic field in the opposite direction. At this point Anderson was not aware of Dirac's prediction ...After nearly a year of effort ...he ...identified ...pair production of electrons and antielectrons from the impact of cosmic rays."