334 Prof. W. D. Harkins on the 



atomic species whose atomic weights are divisible by 4 is 

 much greater than that of those divisible by 3, and the latter 

 seems to gain its relative importance only through the 

 inclusion of those weights which are common to the 

 column 4^. 



While the most abundant group seems to be the one with 

 a formula p±e 2 , the discovery of the p 3 e particle by Ruther- 

 ford, together with the fact that the general formula for 

 nuclei of isotopic number is (a/2) M , or {p 2 e) M , WDere M is 

 the atomic number, suggests the idea that electron groups 

 in which one negative electron alone is present may be even 

 more fundamental in a certain sense, especially since the 

 group p 2 e corresponds to the minimum value of N/P for a 

 nucleus stable both with respect to disintegration by 

 ordinary means, and moderately stable with regard to 

 aggregation. The hypothesis suggests itself that Ruther- 

 ford's p z e particle, in which N/P is less than the ordinary 

 minimum, will be found to be very stable with respect to 

 disintegration, but very unstable with respect to aggregation, 

 and that it will readily pick up and enter into nuclear com- 

 bination with possibly a neutron to form an alpha particle, 

 or an electron to form a p$e 2 group, or attach itself to some 

 other group. If p 2 e is the fundamental group, as the general 

 considerations suggest, then its low abundance may be 

 explained as due to the pairing of the negative electrons, 

 two p 2 e groups changing into one alpha particle ; or a p 2 e 

 group, especially one already in a nucleus, might pick up 

 either an electron and form a p 2 e 2 group ; or a neutron, 

 forming a p 3 e 2 group, thus accounting for the frequent 

 occurrence of an even number and the very low occurrence 

 of an odd number of negative electrons in nuclei. The 

 general formula of any atom may be written («/2). M (w') n ^' M , 

 where the prime indicates a planetary electron, n is the 

 isotopic number, n' indicates a neutron or a proton plus an 

 electron, and the 1/2 in a/2 suggests the rarity of atoms in 

 which M . aj'2 is not a whole number of alpha particles 

 (especially rare when n is zero), but it is hardly probable 

 that these general formulae represent the only groups 

 concerned in atom building. 



Classification of Isotopes into Series. 



Fig. 7 (PI. XII.) indicates that the known isotopes may 

 be classified into series which show all of the characteristics 

 of the radioactive series. These are the thorium-helium, 

 the uranium, the lithium, and the meta-chlorine (CI 17 3 37 ) 



