 In a second paper presented in May 1914 , Franck and Hertz reported on the light emission by the mercury atoms that had absorbed energy from collisions . They showed that the wavelength of this ultraviolet light corresponded exactly to the 4 @.@ 9 eV of energy that the flying electron had lost . The relationship of energy and wavelength had also been predicted by Bohr . Franck and Hertz completed their last paper together in December 1918 . In it , they reconciled the discrepancies between their results and Bohr 's theory , which they now acknowledged . In his Nobel lecture , Franck admitted that it was " completely incomprehensible that we had failed to recognise the fundamental significance of Bohr ’ s theory , so much so , that we never even mentioned it once " . On 10 December 1926 , Franck and Hertz were awarded the 1925 Nobel Prize in Physics " for their discovery of the laws governing the impact of an electron upon an atom . " . 
