476 BELL SYSTEM TECHNICAL JOURNAL 



the laboratory; the truth about Hght was being wrung from Nature — 

 at times, and in this case, a most reluctant witness. 



In an extended examination carried on chiefly by Richardson and 

 K. T. Compton, Hughes, and Millikan, it was brought out that light 

 imparts energy to individual electrons in amounts proportional to its 

 frequency and finally that the factor of proportionality between energy 

 and frequency is just that previously deduced by Planck from the 

 black body spectrum. The idea of pressing the witness on the latter 

 point had come from Einstein who out-plancked Planck in not only 

 accepting quantization, but in conceiving of light quanta as actual 

 small packets or particles of energy transferable to single electrons 

 in toto. 



The case for a corpuscular aspect of light, now exceedingly strong, 

 became overwhelmingly so when in 1922 A. H. Compton showed that 

 in certain circumstances light quanta — photons as they were now 

 called — have elastic collisions with electrons in accordance with the 

 simple laws of particle dynamics. What appeared, and what still 

 appears to many of us as a contradiction in terms had been proved 

 true beyond the least possible doubt — light was at once a flight of 

 particles and a propagation of waves; for light persisted, unreasonably, 

 to exhibit the phenomenon of interference. 



Troubles, it is said, never come singly, and the trials of the physicist 

 in the early years of this century give grounds for credence in the 

 pessimistic saying. Not only had light, the perfect child of physics, 

 been changed into a gnome with two heads — there was trouble also 

 with electrons. In the open they behaved with admirable decorum, 

 observing without protest all the rules of etiquette set down in Lorentz's 

 manual, but in the privacy of the atom they indulged in strange and 

 unnatural practices; they oscillated in ways which no well-behaved 

 mechanical system would deem proper. What was to be said of 

 particles which were ignorant apparently of even the rudiments of 

 dynamics? Who could apologize for such perversity — rationalize the 

 data of spectroscopy? A genius was called for, and a genius appeared. 

 In 1913 Niels Bohr gave us his strange conception of "stationary" 

 orbits in which electrons rotated endlessly without radiating, of elec- 

 trons disappearing from one orbit and reappearing, after brief but 

 unexplained absences, in another. It was a weird picture — a picture 

 to delight a Surrealist — but one which fascinated the beholder, for in 

 it were portrayed with remarkable fidelity the most salient of the 

 orderly features which spectroscopic data were then known to possess ; 

 there was the Balmer series ! and there the Rydberg constant ! — correct 

 to the last significant digit! It was a masterpiece. It is important to 



