are 



Al 



142 Mr. M. Ishino on the Scattering and 



§ 5» Conclusions. 



(1) We can clearly see from Table VII. that the mass 

 scattering for each element is of roughly the same order of 

 magnitude. This is in a fairly good agreement with the expe- 

 riments of Florance. The values of <r//o, however, were in 

 addition compared with the ratios of Moseley's * " atomic 

 number" of the element divided by the atomic weight of 



the element. The ratios of ~ J l~) and ^/(x) 



given in the 4th and 5th columns in Table VII. respec- 

 tively. It is very interesting to see that the two ratios 

 for each element are very nearly equal. Moseley's atomic 

 number of the element probably represents the number of 

 electrons exterior to the central nucleus,, according to the 

 atomic structure suggested by Sir E. Rutherford f. Taking 

 this to be the case, we can conclude that the scattering of 

 the o-amma rays per atom is approximately proportional 

 to the number of the electrons exterior to the nucleus in the 

 atom. Sir J. J. Thomson { showed, on theoretical grounds, 

 that the scattering of X rays should be proportional to the 

 number of electrons which were influenced by the primary 

 rays. According to the atomic structure suggested by 

 Sir E. Rutherford, it would be expected that the scattering 

 electrons should be those exterior to the nucleus, and 

 therefore should be equal in number to the atomic number 

 of the element. From Barkla's measurements of scattering 

 of X rays of ordinary frequencies, it is clearly seen that the 

 scattering coefficient is approximately proportional to the 

 atomic number for the elements of atomic weight not 

 greater than 32, including hydrogen. For the elements 

 heavier than sulphur, Barkla's results led to a different 

 conclusion. J. J. Thomson's simple theory of scattering 

 assumes that the scattering electrons are independent of 

 each other when they are influenced by primary rays. This 

 condition would be satisfied only in the case where the 

 displacement of the electrons influenced by the primary rays 

 is very small compared with their mutual distance apart, so 

 that the mutual action is negligible. The deviation from 

 the simple theory of scattering in the heavier elements, 



* Moseley, Phil. Mag. xxvi. p. 1026 (1913) ; xxvii. p. 703 (1014). 

 t Sir E. Rutherford, Phil. Mag. xxi. p. 669 (1911). 

 X Sir J. J. Thomson's theory of scattering was given in the first 

 edition of ' Conduction of Electricity through Gases.' 



