GLOSSARY 299 



an atom of metal in the photoelectric effect. This 

 value was purely theoretical. But in 1914, R. A. 

 Millikan, as the result of elaborate experiments on 

 the photoelectric emission of electrons, designed to 

 test Einstein's equation, obtained results that proved 

 Einstein's equation correct. Meanwhile Niels Bohr, 

 in developing his now generally accepted theory of 

 the atom, computed the value of the energy that is 

 lost when an electron in an atom jumps from one 

 state to another, in terms of hv. The results of cer- 

 tain experiments by W. Duane and his collaborators 

 corroborated this equation. A. Sommerfeld extended 

 the laws of the distribution of quanta in atomic 

 systems. (Of the formula which Sommerfeld worked 

 out, Planck holds that it "is an accomplishment in 

 every way comparable with the famous discovery of 

 the planet Neptune, whose existence and position 

 had been calculated by Le Verrier before it had been 

 seen by human eye.") Millikan and Bowen's work 

 on stripping valence electrons from atoms included 

 the furnishing of proof of Sommerfeld's formula. 

 With the aid of the quantum theory, and on the 

 basis of the Bohr theory of orbits, P. Epstein and 

 K. Schwarzschild were able to compute the value 

 of the energy changes caused in the orbital electrons 

 of atoms by a strong electrical field. (The so-called 

 "Stark effect," discovered by J. Stark in 1913.) 

 This brilliant theoretical work also was thoroughly 

 confirmed by the spectroscope. Other verification — 

 by J. Franck, G. Hertz, Paul D. Foote, K. T. Comp- 

 ton, R. W. Wood, and others — has come from the 

 field of optics, the experiments having to do with 

 the determination of the energy values in ionization 

 and radiation phenomena. In the X-ray field, too, 

 experiments by De Broglie and Ellis, and other 

 experiments by D. L. Webster supplied further 



