JSatures of various Electric Radiations. 441 



pairs to have varying penetrating and ionizing powers ; a 

 pair of small moment being a good penetrater but a bad 

 ionizer. Such a pair would be incapable o£ deflexion by 

 magnetic or electric fields, and would show no refraction. It 

 is conceivable that it might show a one-sided or polarization 

 effect, for if it were ejected from a rotating atom it would 

 itself possess an axis of rotation. 



When X-rays were first investigated, and again when 

 7 rays were discovered, it was often suggested, in each 

 case, that the radiation might consist of material particles. 

 Rontgen himself proposed in the third of his memoirs a 

 theory of this nature. But it was always felt that the 

 difficulty of accounting for the great penetration of these 

 radiations was insuperable. It seems now that this difficulty 

 was quite exaggerated, and even imaginary. It does not 

 appear out of place, therefore, to reconsider the position in 

 the light of the more recent knowledge. 



Assuming, then, that the neutral pair has great penetrating, 

 but weak ionizing powers, is uninfluenced by magnetic or 

 electric fields, and shows no refraction, it does so far conform 

 to the properties of the 7 ray. And, further, if it has any 

 moment at all, and therefore any external field, it may at 

 last suffer some violent encounter which will resolve it into 

 a positive and a negative, an a and a /3 particle. Of these 

 the /5 particle would be the one possessed of much the greater 

 velocity, and would appear as a secondary ray. Thus, in 

 the neighbourhood of the point of impact, an ionization 

 would appear of much greater intensity than anything pro- 

 duced along the track of the pair itself. So Becquerel has 

 found the action of the 7 rays on a photographic plate to be 

 almost entirely due to the secondary rays which they produce. 

 On this view the appearance of the (3 secondary ray would be 

 really a scattering of the incident ray ; and this would make 

 the 7 ray fall into line with other radiations whose secondary 

 radiations are either scattered primary or h rays. 



If the gradual disappearance of a stream of 7 radiation 

 were caused by collision in this way, the number disappearing 

 in any unit of length of the course would be proportional to 

 the total number in the stream, so that an exponential law 

 would result. 



It appears, therefore, that all the known properties of the 

 7 rays are satisfied on the hypothesis that they consist of 

 neutral pairs. 



If the 7 ray is material and contains an a particle, this fact 

 must be considered in reckoning the number and magnitude 

 of the steps from the atomic weight of radium to that of lead. 



