ol-P articles with Hydrogen Nuclei. 487 



the a-particle is a plate of radius 3x 10" 13 cm. As long as 

 the a-particle does not approach within this distance of the 

 hydrogen nucleus, the ordinary law of repulsion holds, but 

 if it does a collision ensues, which sweeps the latter straight 

 forwards. His experiments were intended to be of a 

 preliminary nature, and so were not carried to any high 

 degree of accuracy. 



The object of the present paper was to submit these 

 experiments to a more rigorous analysis, so as to try and 

 discover more definite information about the structure of 

 the nucleus. But I have been recently informed through 

 the kindness of Sir E. Rutherford that more detailed 

 experiments are in progress in the Cavendish Laboratory to 

 redetermine the curves with greatly improved methods. 

 In particular, the number of hydrogen particles projected at 

 various angles to the primary beam of a-particles is under 

 determination by direct observation. The results so far 

 obtained indicate that some of his earlier curves require 

 modification. It thus appeared desirable to omit the more 

 speculative conclusions to which I had been led, until the 

 new more accurate experiments are finished, and the paper 

 only makes a study of the question of the reduction of the 

 earlier experiments to their simplest terms and an examina- 

 tion of what certain assumed patterns of nucleus would 

 give. 



We first discuss what is the complete information which 

 can be obtained from experiments of any kind whatever on 

 the subject, and show that these must lead to a certain 

 relation, which we call the collision relation. This relation 

 is then found for Rutherford's experiments, and it is seen 

 to be quite different from that for the collision of two point 

 charges. The complicated reduction was carried out in 

 considerable detail before it was realised that the new 

 methods were possible. In view of the extraordinary 

 difficulty of experimenting in the subject and the probability 

 that these new methods will not always be possible, it seems 

 desirable to retain this detail, as showing how quite com- 

 plicated experiments can be reduced to simple terms. The 

 rest of the paper is an attempt to make models of nuclei 

 which shall give the same collision relation as the ex- 

 perimental. These models must all obey the inverse square 

 law at great distances, and the attempt is of necessity 

 limited to cases where* the orbits are integrable, which 

 makes them rather artificial. In all of them one particle 

 is still taken as a point charge, and the complexity is 

 .attributed to the other. In view of the trend of modern 



2 K 2 



