6 



compton: size and shape of electrons 



excess scattering on the emergent side, indicating that the 

 electrons act independently, while for hard 7-rays the excess 

 scattering is the same as for the heavier elements. 



The same difficulty is present if instead of considering the 

 electron as a point charge it is assumed to be a rigid spherical 

 shell incapable of rotation, as this assumption also makes the 

 scattered radiation symmetrical on the incident and the emergent 

 sides. If, however, the electron is a spherical shell of electricity 

 which can be rotated by a passing electromagnetic wave, it is 



Fig. 2. The intensity of the radiation scattered at an angle d with the incident 

 radiation, the electron being a perfectly flexible spherical shell. I, radius of 

 electron = 0; II, radius = 37rX/4. 



capable of producing excess scattering on the emergent side for 

 short 7-rays in much the same manner as groups of electrons 

 in the atom produce excess scattering in the case of the longer 

 X-rays. For purposes of calculation it is again simpler to con- 

 sider the nearly equivalent case of the electron which is a flexible 

 spherical shell. The intensity at any angle is then given by 

 equation (3). When a = 0, this expression becomes identical 

 with that calculated on Thomson's theory, and the correspond- 

 ing values are plotted in curve I of figure 2. In curve II, Ig/1 is 

 plotted for different values of d, using the value a = 3xX/4. 



