002 Professor Sir Ernest Rutherford [June 4, 



uner«fj communicated to the latter should be liv. There is no doubt 

 that in many cases this simple relation holds very approximately, but 

 the measurements so far available are not sufficiently precise to settle 

 definitely whether a part of the energy may not appear in another form. 



Assuming that the transfer of the energy from an X-ray to an 

 electron is complete, we should expect to find groups of ft rays of 

 energy corresponding to hv where v is the frequency of the y rays 

 found experimentally. Such a relation is found to hold within the 

 limit of experimental error for three marked groups of low-velocity 

 /? rays emitted from radium B. On the other hand, it is found that 

 many of the high velocity groups of ^ rays both from radium B and 

 radium C have energies many times greater than correspond to any 

 observed frequency. Not the slightest evidence, however, has been 

 obtained that the corresponding high frequencies of vibration exist in 

 the radio-active atom ; in fact, all the evidence points to the fact 

 that these high-speed electrons arise from one or more of the observed 

 frequencies in the y-ray spectrum. 



In order to account for such results, it seems necessary to suppose 

 that the y rays of high frequency are not necessarily emitted as single 

 pulses, but consist of a train of pulses either produced simultaneously 

 or following one another at very short intervals. Each of these 

 pulses has an energy Itv corresponding to the frequency v, but the 

 total energy in the train of waves is ])hv where /> is a whole number, 

 which may have possible integral values 0, 1, 2, 3, . . . etc., 

 depending on the structure of the atom and the conditions of excita- 

 tion. The penetrating power of such a train of waves corresponds 

 to that of a single wave of frequency v, but on passing through 

 matter the energ^y of the whole train of p waves occasionally may 

 be transferred to an electron which consequently is expelled with an 

 energy phv. There is very strong evidence of the general correct- 

 ness of this point of view, for most of the stronger lines in the ^-ray 

 spectrum of radium C have energies which correspond to an integral 

 multiple of the energy corresponding to the strong lines actually 

 observed in the y-ray spectrum. It seems probable that under the 

 ordinary conditions of excitation by kathode rays in a vacuum tube, 

 the X-ray contains only one pulse or w^ave, but under the far more 

 powerful stimulus of the very swift y8 particle escaping from the atom, 

 a long train of waves, each of the same frequency, is produced. The 

 energy of the whole train of waves may under suitable conditions be 

 given to an electron, which consequently has a speed very much 

 greater than that impre-sed upon it by a single wave of the same 

 frequency. 



Limit to the Frequency of Vibration of the Atom. 



There is one question of fundamental importance which arises in 

 considering the modes of vibration of the atom, viz. whether there 



