ABSTRACT
In 1887, while receiving the electromagnetic waves in an induction
coil with a spark gap generator, Heinrich Hertz (1857-1894)
observed the reduction of maximum spark length when the
apparatus was put in a black box (Hertz, 1887). He noticed that the
spark occurred in the air gap between the two small metal spheres
of the transmitter when ultraviolet radiation was directed at one of
these spheres. The box absorbed such radiation, which helped the
electrons in jumping across the gap. Hertz reported the observations
but did not pursue the experiment further, and also did not make
any attempt to explain them, but others did. In 1897, J. J. Thomson
(1856-1940) showed that electrons are emitted when light falls
on a metal surface (Thomson, 1897). These are now referred to as
photoelectrons (the prefix “photo” refers to the incident light).
