1884 – 1954
Who was Pál Selényi?
He is also known as Paul Selenyi. Chester Carlson read one of Selenyi's papers in the 1930s and was very greatly impressed; subsequently, he invested in a big effort to develop xerography. That may be the reason why Selenyi was known as the "father of xerography" by some people.
From his early works, Selényi was engaged in studying the nature of light. One well-known result of this period is Selényi's wide-angle interference experiment whose foundations go back to the discovery of the photoeffect, by Albert Einstein, and Hertz's experiments on the reflection of radio waves.
Einstein's hypothesis was: elementary light sources emit electromagnetic waves along small solid angles, which had been supported by the fact that interference is simplest to achieve with lightwaves intersecting one another under small angles. The Young experiment is an example: light passing through a pair of neighboring holes results in the appearance of interference patterns on a screen behind the holes, but only if the angle covered by the incoming beams does not exceed a couple of degrees of angular width.