First photographs of cosmic rays

Using a cloud chamber, Dimitry Skobelsyn took the first photographs of tracks left by cosmic rays. Skobeltsyn was the first to advance the idea of using the registration of recoil electrons (Compton electrons) in a gas-filled Wilson cloud chamber. In his 1927 experiments, Skobeltsyn worked out the momenta of charged particles passing through the chamber from their degree of deflection by a magnetic field.