Cible, porte-cible et chambres à étincelles

End-on view of two of the Argonne Group's early spark chambers during tests at CERN. Tracks caused by charged particles from a synchrotron target can be seen in the righthand chamber ; the left one was not connected. On either side of the chambers are scintillation counters for triggering. The numbers identifying the gaps are printed in reverse, since the photographs would normally be obtained, during experiments, with the aid of a mirror system