246 On the Theory of Radiation. 



corpuscle. From the principle of resonance the alteration 

 in the angle will be far greater when the frequency of the 

 steady motion of the corpuscle coincides with that of the 

 incident electric wave than in any other case. A large alte- 

 ration in the angle will, however, result in the corpuscle 

 getting free from the doublet and going off with much the 

 same kinetic energy as it had in the steady motion ; this, 

 as we have seen, is equal to the frequency multiplied by 

 Planck's constant. On this view then a light-wave would 

 liberate corpuscles whose frequency when in a state of steady 

 motion is the same as that of the light, and the kinetic 

 energy of these corpuscles would be proportional to the 

 frequency. Thus the energy of the corpuscles ejected by 

 the light would on this view be proportional to the frequency 

 of the light, whether the energy of the light-wave was 

 made up of different units or not ; so that we cannot regard 

 Ladenburg's experiments as a proof of the unitary structure 

 of light. Again, the number of atoms in which there is 

 steady motion of the kind we are considering having a 

 frequency nearly equal to some particular value, is probably 

 a very small fraction of the whole number of molecules, so 

 that the number of particles emitted would on any view as 

 to the constitution of a light-wave be small compared with 

 the number of molecules passed over by the light. This 

 theory enables us to explain the electrical effects produced 

 by light, without assuming that light is made up of unalterable 

 units, each containing a definite and, on Planck's hypothesis, 

 a comparatively large amount of energy, a view which it is 

 exceedingly difficult to reconcile with well-known optical 

 phenomena. The existence of the doublets produces throughout 

 the body systems (the corpuscles in steady motion) which act 

 like resonators, having frequencies of all values, and pos- 

 sessing an amount of energy proportional to the frequency. 



The magnetic properties of bodies show, I think, that the 

 who'e number of these systems in steady motion for the 

 whole range of frequencies cannot be large compared with 

 the number of atoms. For the corpuscle moving round the 

 circle with radius r sin and velocity v is equivalent to a 

 magnet whose moment is ^evrsin 6. 



We see, however, from equations (3) that vr sin 6 is 

 constant for all the systems and equal to 



2 /We 



50 that . . A 1 e .— — 



3| m 

 = 5 x 10~ 21 5 approximately. 



