The structure of cosmic ray air showers at
sea-level has been studied by an investigation of the burst rate frequency and
the transition effect in lead, for cosmic ray bursts occurring simultaneously
in two high-pressure ionization chambers with varying separation.
Although extensive showers were
responsible for all the coincidences observed with the larger chamber
separations, they accounted for less than 3 per cent, of the bursts observed with a single chamber.
Of the remaining 97 per cent., somewhat more than one-half appear to be due to
nuclear disintegrations and the rest either to narrow showers of approximate
radius 30 cm. or to the core of an extensive shower of low density. The
extensive shower frequency was about 10 times that predicted by theory.
The bearing of these results on present
views of the origin and development of air showers is discussed.