eve] the constitution of the atom 



17 



for they occupy the same place in the periodic table. Thus the old 

 trouble of finding room in the periodic table for the thirty or forty 

 radiant elements has suddenly vanished. They may be superposed 

 even when their atomic weights differ, if their atomic numbers are 

 the same. The nuclear charges of isotopes must be identical but the 

 distribution of electrons may be different. Other examples of in- 

 separables are — 



Lead, radium B, Radium D, all 82. 



Thorium and radiothorium. 



Radium and mesothorium. 



If these views are distasteful to chemists let them discover 

 some method of separation of the known isotopes. 



It must be further noted that the results of radio-chemistry 

 appear to require the presence of negative electrons in the nucleus 

 itself. The expulsion of a p particle, or one negative electron, from 

 the nucleus is equivalent to the gain of one positive electron, and in- 

 volves a unit increase in the atomic number. 



(14). The last advance is the most important and far-reaching. 

 There has been long search for the positive electron and in vain, 

 yet it seems likely that it has been under our eyes all the time. Since 

 the hydrogen atom never loses more than a single electron, is it not 

 possible, suggests Rutherford, that the nucleus of the hydrogen atom 

 may be the positive electron ? 



The electro-magnetic mass of an electron is — — where e is the 



3 a 



charge and a the radius. If the mass of the hydrogen nucleus is 

 wholly electro-magnetic, then its radius must be smaller than that 

 of the electron (negative) as 1 : 1800, for that is the ratio of their masses 

 while their charges are equal and opposite. Hence we have- 

 Mass. Diameter. 



Atom 1 io- 8 cm. 



Negative electron 1/1800 10" 13 



, Positive electron 1 io~ 16 



Rutherford cautiously remarks that there is no experimental 

 evidence against such a supposition. 



Those who wish to follow the matter deeper must refer to many 

 articles in the Philosophical Magazine, several letters to Nature, 

 Soddy's "Chemistry of the Radio-elements, part II," and Perrin's 

 "Les Atomes." The chief writers have been Rutherford, W. H. Bragg, 

 W. L. Bragg, G. C. Darwin, Moseley, Brock, Bohr, Fajans, Soddy, 

 Russell, Hevesy, Nicholson and Marsden. 

 Sec. Ill, 1914—2 



