"Blackett had been working with a in Rutherford's group... a chamber that was ready for action every ten seconds or so, and took photos on ordinary film. ...[H]e accumulated ...pictures of trails made by s—a product of radioactive nuclear decays— ...bombarding nitrogen gas in the chamber. ...[I]n 1931 arrived ...His specialty was detecting nuclear radiation using s. ...Their big idea ...put one Geiger counter above a cloud chamber, and another... below. ...By connecting the Geiger counters to a ...a flash of light [and the cinematograph] captured the tracks of the cosmic rays on film. ...They noticed that ...a few tracks that appeared at first sight to be electrons, were ...curved the wrong way in the magnetic field. Blackett talked to Dirac about them... neither aware of the precious truth. ...It was only when they heard of Anderson's discovery that Blackett and Occhialini ...realized what they had."