German physicist who won the Nobel Prize for Physics in 1919.
In 1902 he predicted, correctly, that high-velocity rays of positive
ions (canal rays) would demonstrate the Doppler effect, and in 1913
showed that a strong electric field can alter the wavelength of light
emitted by atoms (the Stark effect).
Stark modified in 1913 the photo-equivalence law proposed by Albert
Einstein in 1906. Now called the Stark-Einstein law, it states that
each molecule involved in a photochemical reaction absorbs only one
quantum of the radiation that causes the reaction.
Stark was born in Schickenhof, Bavaria, and studied at Munich.
He became professor 1906 at the Technische Hochschule in Hanover and
subsequently held other academic posts until 1922, when he attempted
to set up a porcelain factory. This scheme failed, largely because of
the depressed state of the German economy. Stark joined the Nazi party
1930 and three years later became president of the Reich Physical-Technical
Institute and also president of the German Research Association. But
his attempts to become an important influence in German physics brought
him into conflict with the authorities and he was forced to resign in
1939. After World War II, he was sentenced to four years' imprisonment
by a denazification court 1947.