Collisions of a Particles icith Hydrogen Nuclei. 939 



an H particle projected towards an a particle would 

 move under the ordinary electrostatic forces governed 

 by the inverse square law, until it reached a spheroidal 

 surface of the above dimensions. Here it would encounter 

 an extremely powerful field of force and recoil as from a 

 hard elastic body. The effect of this model of « particle 

 will be studied further, and an attempt will be made to 

 obtain its collision relation. 



It is not possible to say from these experiments whether 

 there is any actual discontinuity in the law of force between 

 the nuclei. The absence of a flat part in the p, 6 curves, 

 and the general shape of the p, (V /Vj 2 curves, would 

 suggest that these new forces merge gradually into the 

 inverse square law forces. 



As regards the structure of the a particle, it will be 

 apparent at once that no system of four H nuclei and two 

 electrons united by inverse square law forces could give 

 a field of force of such intensity over so large an extent. 

 We must conclude either that the a particle is not made up 

 of four H nuclei and two electrons, or that the law of force 

 is not the inverse square in the immediate neighbourhood 

 of an electric charge. It is simpler to choose the latter 

 alternative, particularly as other experimental, as well as 

 theoretical, considerations point in this direction. The 

 present experiments do not seem to throw any light on the 

 nature or the law of variation of the forces at the* seat of an 

 electric charge, but merely show that the forces are of very 

 great intensity. 



It is of interest to note that, assuming an a particle 

 composed of four H nuclei and two electrons, the present 

 experiments provide the only direct evidence we have as 

 to the size of the electron. These results show that 

 the radius of the electron cannot be greater than about 

 4xl0~ 13 cm. 



§ 9. Summary. 



In this paper, the relations which hold in the collisions 

 between ol particles and H nuclei have been investigated. 



(1) The angular distribution of the H particles projected 

 by a particles of mean range G M 6 cm. has been determined 

 up to an angle of 66°. The distribution for a-rays of mean 

 ranges 8'2, 4*3, and 2*9 cm. has been obtained over a smaller 

 range of angle. It is shown that the number of H particles 

 projected within tliese angles by a-rays of high velocity is 

 greatly in excess of that given by forces varying as the 



3 Q 2 



