92 BELL SYSTEM TECHNICAL JOURNAL 



of faith that a quantum must give all of its energy, or none — either 

 vanish altogether, or retain its frequency unchanged. 



Of course, till 1922 there was no compelling evidence that a corpuscle 

 of light may suffer a change of frequency in rebounding from a particle 

 of electricity or matter. However, it does not seem to have occurred 

 to anyone that the want of evidence was in any way surprising, or 

 that it should be possible to find quanta scattered with change of 

 energy. The reason for this satisfaction, I suspect, was perfectly 

 simple. It did not seem possible that a quantum should give up 

 part of its energy, for its energy was inseparably linked with its 

 frequency, and its frequency seemed to be its one indissoluble and 

 characteristic feature. As well say that an electron might lose part 

 of its charge and still be the same electron, or that an atom might 

 lose part of its mass and yet remain the same atom, as that a quantum 

 might give up part of its frequency without ceasing to be itself! 



Now this contention — if one may call it a contention— lost its force 

 through the discovery that electrons also are endowed with frequency 

 and wave-length, or in other words that negative electricity like light 

 possesses both qualities of corpuscles and qualities of waves. When- 

 ever a corpuscle of electricity parts with kinetic energy, whenever a 

 corpuscle of light parts with energy, the associated wave-length is 

 augmented. If we suppose that an electron retains its identity when 

 its wave-length changes, how can we deny like continuity of existence 

 to a quantum? If we admit that an electron may suffer change of 

 wave-length in rebounding from an atom, how may we be surprised 

 when a quantum does the like? It is true that the corpuscle of elec- 

 tricity has other features than wave-length : a charge which apparently 

 never changes, a mass which apparently never falls below a certain 

 minimum. The quantum does not have an immutable quality corre- 

 sponding to charge, and we do not know of any lower limit to its 

 mass short of complete disappearance. But for either sort of corpuscle 

 the wave-length is in principle variable. We say that all electrons 

 are of one kind, but may have any speed. Should we not also say 

 that all quanta are of a single kind, though they may have any 



frequency ? 



BIBLIOGRAPHY 



(The year is 1928, unless otherwise stated) 



S. K. Allison, W. Duane: Proc. Nat. Acad. Sci., 10, pp. 196-199 (1924). 



J. A. Becker: Proc. Nat. Acad. Sci., 10, pp. 342-345 (1924). 



C. E. Bleecker: Zs. f. Phys., 50, pp. 781-786. 



A. BoGROS, Y. Rocard: C. R., 186, pp. 1712-1713. 



M. Born: Naturwiss., 16, p. 673. 



F. G. Brickwedde, M. F. Peters: Bull. Amer. Phys. Soc, Nov. 15. 



M. de Broglie: C. R., 187, p. 697. 



J. Cabannes: C. R., 186, pp. 1201-1202, 1714-1715; 187, pp. 654-656. 



