Abstract
Changes in the gain and resolution of photomultipliers of the DuMont type are examined with reference to changes in counting rate, axial magnetic fields and temperature. While the magnitudes of these variations are found to vary as between photomultipliers, graphs are given showing typical dependences. The effects of magnetic shielding are presented and the variation of resolution with γ-ray energy in scintillation counters equipped with large NaI crystals is discussed in the light of recent statistical considerations.