206 THE NEW QUANTUM THEORY 



must be made equal to h ) or sometimes to an integral mul- 

 tiple of h. 



(2) The proviso often led to a self-contradictory use 

 of the classical theory. Thus in the Bohr atom the 

 acceleration of the electron in its orbit would be gov- 

 erned by classical electrodynamics whilst its radiation 

 would be governed by the h rule. But in classical elec- 

 trodynamics the acceleration and the radiation are indis- 

 solubly connected. 



(3) The proper sphere of classical laws was known. 

 They are a form taken by the more general laws in a 

 limiting case, viz. when the number of quanta concerned 

 is very large. Progress in the investigation of the com- 

 plete system of more general laws must not be ham- 

 pered by classical conceptions which contemplate only the 

 limiting case. 



(4) The present compromise involved the recognition 

 that light has both corpuscular and wave properties. 

 The same idea seems to have been successfully extended 

 to matter and confirmed by experiment. But this success 

 only renders the more urgent some less contradictory 

 way of conceiving these properties. 



(5) Although the above working rule had generally 

 been successful in its predictions, it was found to give 

 a distribution of electron orbits in the atom differing in 

 some essential respects from that deduced spectroscopi- 

 cally. Thus a reconstruction was required not only to 

 remove logical objections but to meet the urgent de- 

 mands of practical physics. 



Development of the New Quantum Theory. The "New 

 Quantum Theory" originated in a remarkable paper 

 by Heisenberg in the autumn of 1925. I am writing 

 the first draft of this lecture just twelve months after 



