compton: size and shape of electrons 7 



The circles are experimental values determined by D. G. H. 

 Florance^^ using the 7-rays from radium bromide scattered by a 

 plate of iron. Inasmuch as these rays are heterogeneous, and 

 as the softer rays are scattered relatively more strongly at larger 

 angles, the agreement of the experimental values with curve 1 1 

 is as good as can be expected. 



A better quantitative test of this explanation is afforded by 

 Ishino's observation^- that the radiation scattered on the inci- 

 dent side of a plate struck by hard 7-rays from radium-C is 

 about 15 per cent of that scattered on the emergent side. On 

 the hypothesis of the electron as a flexible sphere this ratio is 

 given by the relation 



^ = I I^sm edd \ Iq sin d dd 



/a Jv/'l i Jo 



(5) 



The values of this ratio for different values of a/X are plotted in 

 figure 3. This curve explains beautifully the observation of 

 Florance that the ''incident" scattered rays are softer than the 

 ''emergent" and the primary rays, since it shows that the rela- 

 tive amount of the rays scattered backward is much greater 

 for soft, or long wave-length, 7-rays than for hard rays. Ruth- 

 erford and Andrade^^ have found the hard 7-rays from radium-C 

 to consist of a strong line, X = 0.099 X 10~% and a weaker line, 

 X = 0.071 X 10-^ cm. Taking into account this selective effect, 

 we may take the effective wave-length to be 0.095 X 10~^ cm. 

 On this basis, and using a = 2.3 X 10"^" as determined above, 

 the calculated value of the ratio of the incident to the emergent 

 scattered radiation is 8 per cent. The agreement is hardly 

 within the probable experimental error, but the calculated value 

 is at least of the proper order of magnitude, which is a strong 

 verification of a flexible or a rotatable electron. 



According to electromagnetic theory it is obvious that the 

 mass of an electron cannot be accounted for on the basis of a 

 uniform distribution of electricity over the surface of a sphere 



"Florance. Phil. Mag. 20: 921. 1910. 



i^IsHiNO. Phil. Mag. 33: 129. 1917. 



'3 Rutherford and AxDRADE. Phil. Mag. 28: 263. 1914. 



