CLASSICAL AND QUANTUM LAWS 193 



ordinary scattering. Now gradually increase the energy 

 of the electrons; quite suddenly we find that the electrons 

 are leaving a great deal of their energy behind. That 

 means that the critical energy has been reached and 

 orbit jumps are being excited. Thus we have a means 

 of measuring the critical energy which is just that of the 

 jump — the difference of energy of the two states of the 

 atom. This method of measurement has the advantage 

 that it does not involve any knowledge of the constant h, 

 so that there is no fear of a vicious circle when we use 

 the measured energies to test the h rule.* Incidentally 

 this experiment provides another argument against the 

 collection-box theory. Small contributions of energy are 

 not thankfully received, and electrons which offer any- 

 thing less than the full contribution for a jump are not 

 allowed to make any payment at all. 



Relation of Classical Laws to Quantum Laws. To fol- 

 low up the verification and successful application of the 

 quantum laws would lead to a detailed survey of the 

 greater part of modern physics — specific heats, mag- 

 netism, X-rays, radioactivity, and so on. We must leave 

 this and return to a general consideration of the rela- 

 tion between classical laws and quantum laws. For at 

 least fifteen years we have used classical laws and quan- 

 tum laws alongside one another notwithstanding the 

 irreconcilability of their conceptions. In the model atom 

 the electrons are supposed to traverse their orbits under 

 the classical laws of electrodynamics; but they jump 

 from one orbit to another in a way entirely incon- 

 sistent with those laws. The energies of the orbits 



* Since the h rule is now well established the energies of different 

 states of the atoms are usually calculated by its aid; to use these to test 

 the rule would be a vicious circle. 



