Atomic Nucleus and the Law of Force. 745 



The values of /m 4 arc constant within the counting error 

 •of about 4 per cent. 



Taking the nuclear charge" of platinum as 78*% the distance 

 of approach of the high-velocity a. particles was about 

 7xl0 -12 cm. and of the low-velocity particles about 

 14x-10- u cm. 



We conclude, therefore, that in the region of 10 -11 cm. 

 from the platinum nucleus the force varies as ljr p , where 

 p lies between 1 # 97 and 203. 



§ 6. Summary. 



1. The charges of the nuclei of three atoms, viz. platinum, 

 silver, and copper, have been measured by a direct method 

 depending on the scattering of a particles. The values found 

 are 77*4, 46'3, and 293 respectively in fundamental units 

 of charge. The atomic numbers of these elements are 78, 

 47, and 29. 



2. The law of force around the platinum nucleus has been 

 tested by the dependence of scattering on the velocity of the 

 « particle. The results show that the inverse square law 

 holds accurately in the region concerned, viz. around 

 10" 11 cm. from the nucleus. 



§ 7. Discussion of Results. 



The good agreement between the measured values of the 

 nuclear charges and the atomic numbers of the elements 

 deduced from the X-ray spectra affords strong confirmation 

 of Moseley's generalization. Owing to the probability 

 fluctuations, it is hardly possible to attain sufficient accuracy 

 in the measurements to prove that the charge on the nucleus 

 is a whole number times the electronic charge. At present 

 this is only possible in one case — that of the helium nucleus 

 or a particle. There can, however, be little doubt that the 

 nuclear charge does really increase by unity as we pass from 

 one elem nt to the next, and that its net value is given by 

 the atomic number. 



The values of the nuclear charge combined with the 

 dependence of scattering on the velocity of the a particle 

 indicate that the inverse square law of force holds to a high 

 degree of accuracy in the region investigated, 10" n cm. 

 from the nucleus of a heavy atom like platinum. The 

 experiments of Geiger and Marsden on the angular dis- 

 tribution of « particles scattered by gold between 5° and 

 150° show that the same law must hold for distances 

 between 3*1 x 10~ 12 cm. and 36* X 10~ 12 cm. from the nucleus. 



Phil. Mag. S. 6. Vol. 40. No. 240. Dec. J 920. 3 



