Discontinuity in the Phenomena of Radiation 77 



in all atoms, and this permanency is hard to reconcile with the 

 gradual loss of energy by the electron deduced by theory. True 

 the full force of the argument can be somewhat abated by pos- 

 tulating that there are a considerable number of electrons in any 

 one orbit following each other round in a stable ring ; for under 

 such circumstances it appears that the rate of radiation is greatly 

 reduced. 



Planck's hypothesis is this. He assumes that there are 

 electrons in the atom — " resonators " he calls them — which 

 oscillate without radiating in this continuous way. He also 

 assumes, to take his later views, that these resonators can absorb 

 energy in a continuous manner from the energy of the surround- 

 ing ether by reason of the electrical forces inherent in all radiant 

 energy according to the electro-magnetic theory of light. Such 

 absorption without emission could not go an for ever. Radiation 

 from the resonator must occur some time or other. Planck 

 postulates that this emission instead of being continuous is jerky 

 or spasmodic. He assumes that there are certain critical stages 

 in this loading up of energy when the resonator may suddenly 

 put out its whole content of energy in one rapid rush as it 

 were. These critical stages occur when the resonator possesses 

 exactly a definite multiple of a definite " quantum " of 

 energy. It is in the amount of this quantum that Planck's h 

 constant makes its appearance. The resonator will, of course, 

 have a definite frequency — n per second, let us say ; the 

 quantum of energy for this resonator is hn erg. Suppose 

 we conceive the resonator dcA^oid of energy^ it begins absorbing 

 from the surrounding ethereal energy : presently it is loaded 

 up with a value hyi, it may radiate then ; it cannot do so 

 before that moment (according to Planck) ; it may fail to radiate 

 at this moment ; it then keeps on absorbing until it attains an 

 energy 2 hn ; it cannot emit in the interval, but it may radiate 

 at this moment ; again if it fails to do so it keeps on absorbing 

 and cannot radiate until its energy reaches 3 hn, and so on. 

 Radiation can only occur at certain well-defined and discrete 



