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being taken up by an atom, as Rutherford has sugofested. 

 There is no reason to suppose the y ray or X-ray to possess any 

 great speed, so as to give it enough penetrating power. The 

 latter might depend rather on the limitation of the field of 

 the pair, and a sufficient range for the velocity can be found 

 between the minimum speed of the a particle and the mini- 

 mum speed n-ecessary for penetration, which appears to be 

 about 10^ for a charged particle, but may be less for one with- 

 out charge. A moderate speed would account for the reflection 

 or scattering of the X-ray, and would indeed be necessary for 

 this purpose. It is here that the neutral-pair hypothesis 

 clashes with the experiment of Marx, and, unless some way 

 out is found, must remain simply an interesting comparison. 

 In the case of the y ray the hypothesis seems to fit in very 

 well with the known facts. 



