Particles that take photographs of themselves: the emergence of the triggered cloud chamber technique in early 1930s cosmic-ray physics

One of the major accomplishments of early elementary particle physics research was the development of an apparatus able to efficiently collect photographs of cosmic-ray particles. This accomplishment was achieved in 1932 at the Cavendish Laboratory in Cambridge by triggering a cloud chamber with two appropriately connected counters. A careful analysis of the literature reveals that the development of the Cavendish apparatus was preceded and, in some respect, influenced by hybrid counter-cloud chamber devices devised previously in two U.S. laboratories.