494 Sir E. Rutherford on the 



and to be spherical in shape, it is clear that the sum of the 

 radii of the hydrogen and helium nuclei is not greater than 

 l'TxlO -13 cm. This is an exceedingly small quantity, even 

 smaller than the ordinarily accepted value of the diameter 

 of the electron, viz. 2 x 10 ~ 13 cm. It is obvious that the 

 method we have considered gives a maximum estimate of the 

 dimensions of the nuclei, and it is not improbable that the 

 hydrogen nucleus itself may have still smaller dimensions. 

 This raises the question whether the hydrogen nucleus is so 

 small that its mass may be accounted for in the same way as 

 the mass of the negative electron. 



It is well known from the experiments of Sir J. J. Thom- 

 son and others, that no positively charged carrier has been 

 observed of mass less than that of the hydrogen atom. The 

 exceedingly small dimensions found for the hydrogen nucleus 

 add weight to the suggestion that the hydrogen nucleus 

 is the positive electron, and that its mass is entirely electro- 

 magnetic in origin. According to the electromagnetic 

 theory, the electrical mass of a charged body, supposed 



2 e 2 

 spherical, is -, where e is the charge and a the radius. 



o 01 



The hydrogen nucleus consequently must have a radius about 

 1/1830 of the electron if its mass is to be explained in this 

 way. There is no experimental evidence at present contrary 

 to such an assumption. 



The helium nucleus has a mass nearly four times that of 

 hydrogen. If one supposes that the positive electron, i. e. 

 the hydrogen atom, is a unit of which all atoms are composed, 

 it is to be anticipated that the helium atom contains four 

 positive electrons and two negative. 



It is well known that a helium atom is expelled in many 

 cases in the transformation of radioactive matter, but no 

 evidence has so far been obtained of the expulsion of a 

 hydrogen atom. In conjunction with Mr. Robinson, I have 

 examined whether any other charged atoms are expelled 

 from radioactive matter except helium atoms, and the recoil 

 atoms vdiich accompany the expulsion of a particles. The 

 examination showed that if such particles are expelled, their 

 number is certainly less than 1 in 10,000 of the number of 

 helium atoms. It thus follows that the helium nucleus is a 

 very stable configuration which survives the intense disturb- 

 ances resulting in its expulsion with high velocity from the 

 radioactive atom, and is one of the units, of which possibly 

 the great majority of the atoms are composed. The radioactive 

 evidence indicates that the atomic weight of successive pro- 

 ducts decreases by four units consequent on the expulsion of 



