Presentation model of a 11 stage photomultiplier, mounted on a rectangular plastic base, made by the staff of 20th Century Electronics Ltd in 1956 and given to Mr G Tomes (the founder of the company). The operation of the photomultiplier was based upon the emission of electrons from matter by electromagnetic radiation of certain specified energies. Photomultipliers are often used in scintillation counters, which measure the activity of a radiation source.