Philipp Lenard
Albert Einstein explained this as a quantum effect.  This theory said that the plot of the cathode ray energy versus the frequency would be a straight line with a slope equal to Planck's constant, h. This was proved some years later. Einstein was awarded the Nobel Prize in Physics for this theory. Lenard did not like the attention given to Einstein. He did not believe in Einsteins theories, including relativity. However he did agree with Einstein's explanation of the photoelectric effect.