332 Prof. W. D. Harkins on the 



bj using formulae for the nuclei of the most abundant 

 isotope of each element of even atomic number beginning 

 with carbon and up to iron. 



Table VII. expresses the remarkable fact that for 



THE SIX SUCCESSIVE ELEMENTS OF EVEN NUMBER, CARBON, 

 OXYGEN, NEON, MAGNESIUM, SILICON, AND SULPHUR, THE 

 MOST ABUNDANT ISOTOPE HAS BOTH A CHARGE AND A MASS 

 EQUAL TO A WHOLE NUMBER TIMES THE CHARGE AND MASS OF 



the alpha particle. With argon there is a slight irregu- 

 larity in that the less abundant isotope meets this condition, 

 while the adherence to the rule returns again in calcium. 

 The elements of higher atomic number titanium, chromium, 

 and iron (and presumably nickel 60 and zinc 64) show the 

 •same general relationship except that each nucleus contains 

 two negative (cementing) electrons in addition, so there is 

 also present in each case one alpha particle in excess of that 

 required to give the nuclear charge ; while the mass is still 

 expressed by that of a whole number of alpha particles. 

 This corresponds to the presence in these nuclei of a 

 quadruple neutron, which may be called a helio group, of 

 the formula p 4 <? 4 , where p represents a hydrogen nucleus or 

 proton, and e a negative electron. The two cementing 

 electrons correspond exactly in their function to the beta 

 electrons which are shot off in pairs, but not simultaneously, 

 in the radioactive disintegration series. Figure 7 (PL XII. j, 

 which is an enlarged section of figure 5, shows that 

 Ni 4 60 , Fe/ 6 , Cr/ 2 , Ti 4 48 , Ca 4 4t , A/ , K 2 40 , Ca ' i0 , A 36 , S 32 , 

 Si 28 , Mg 24 , Ne 20 , O 16 , and C 12 , show exactly the form of a 

 radioactive disintegration series, and while Ca 4 44 and K 2 40 

 have not been found as yet, there are indications that these 

 elements contain higher isotopes, both in the atomic weights 

 and in the fact that potassium seems to be radioactive, 

 which would hardlv be expected of K 39 . 



It is remarkable that these few atomic species make up 

 93 per cent, of the material of the meteorites, and nearly as 

 great a percentage of the surface of the earth, which fact ivhen 

 combined with the fact that the relations are exactly those of 

 the thorium disintegration series, seems to the writer to be 

 conclusive evidence that the alpha particle is the principal 

 group concerned in atom building, in the region of the light 

 atoms as well as in that of the heavy atoms. This is of 

 interest since Rutherford, from the results of extraordinary 

 experiments in which he has disintegrated the nuclei of 

 light atoms, has come to the conclusion that the group of 

 mass 3 is of more importance in the building of light atoms, 

 since he has obtained some evidence which seems to indicate 



