Bust of Berzelius in selenium. Berzelius discovered selenium in Sweden in 1817. From the International Exhibition of 1862

An oval medallion cast in selenium, showing a relief profile of the Swedish chemist Jons Jacob Berzelius who discovered selenium.This element is a semi-conductor whose electrical conductivity increases when light falls on it.Temperature measurement devices, which base their action on registering the amonnt of light emitted by a hot material, rely on selenium. Berzelius also discovered the elements thorium and cerium and was the first to isolate others. He introduced modern symbols, an electro-chemical theory and his accurate determination of atomic weights established the laws of combination and John Dalton's atomic theory. His great work was rewarded with the gold medal of the Royal Society.