GLOSSARY 287 



and carried out in 1923 by Arthur H. Compton, of the 

 University of Chicago, to test the hypothesis of 

 locahzed light-quanta. Since X-rays resemble Hght, 

 the scattering of X-rays is a phenomenon comparable 

 to the reflection of light. Compton proceeded on the 

 assumption that a collision between a "light-quant" 

 and a free electron should be governed by the general 

 law of the conservation of energy and Newton's law 

 of the conservation of momentum. The actual 

 shifting of lines, and the amount of the displacement 

 that resulted from the scattering of X-rays by free 

 electroms, were approximately those which Compton 

 predicted from these laws and the values belonging 

 to a light-quant (energy hv, velocity c, etc.) and a 

 "free" electron. The Compton experiments have 

 been repeated and confirmed by P. A. Ross, of Stan- 

 ford Universit}^ and others. (W. Duane, who re- 

 peated the experiments, failed to secure the Compton 

 effect, and secured an effect — now known as Duane's 

 effect — that is distinct from the Compton effect. 

 Duane therefore at first held that the Compton effect 

 did not exist. But both effects have since been 

 found on the same photographic plate.) The Comp- 

 ton effect demonstrates the existence of localized 

 "light-quanta," and thus is a directproof of Einstein's 

 theory. Sommerfeld holds that the Compton effect 

 promises to become the experhnentum crucis between 

 the wave-theory of light and the quantum theory. He 

 places the Compton effect "among the fundamental 

 experience facts," and says "it is perhaps the most 

 important discovery that in the present state of 

 physics could have been made." See Spectrometer, 

 Energy, Quantum, and X-rays. 



Coolidge Tube. A high-power cathode ray tube. 

 According to Dr. Coolidge, the tube is capable of 

 operation up to 900,000 volts. 



