  The photoelectric effect has been discovered by H. Hertz, and studied
experimentally by P. Lenard. First theoretical explanation has been done by A.
Einstein who suggested the corpuscular theory of light introducing the
"photons" which are particles of the light. In the framework of the
Schr\"odinger theory the effect has been described first by G. Wentzel who
calculated the angulardistribution of the photocurrent. The calculation relies
on the perturbation procedure applied to the coupled Maxwell-Schr\"odinger
equations.
