soMF. co.VTFMPOR.iKy .iDcixcrs ix I'nysics ir 403 



sumption th.it tlu- nuclear oliarni-s of the first ami second elcmcni are 

 f and "if, resiH-etively. 



Meanwhile the rombinini; weights, without losing; their practical 

 utility, were slipping out o( the prominence into which they had 

 ln-en forced. It was (lisco\ered that they were not always to he 

 identified with the atomic weiRhts; that an element miijht have 

 several kinds of atoms; that even the masses of these atoms were not 

 absolute characteristics of the elements, as two very ilifTercnt elements 

 mit;ht have atoms of apparently identical mass. In Remy cle Gour- 

 mont's phrase, there occurred a dissociation of ideas; the idea of 

 atomic weiijht was dis-associatcd from the idea of clement, and the 

 idea of atomic numlxT supplanted it. The eighty-sc%en (now the 

 eighty-eight) known elements formed themselves into a procession, 

 which is a procession of atoms iMjaring eighty-eight of the ninety-two 

 admissible nuclear charges between e and 92e, and possessing con- 

 secutively all except four of the possible electron-families ranging 

 in number from one to ninety-two. That at least eighty-eight out 

 of these ninety-two conceivable atoms should actually exist and ha\e 

 l)een disco\'ered, may seem strange; one might pxjrhaps have expected 

 that a stable nucleus with a net charge of ne could be built only for 

 an occasional value of m; but among the first eighty-two integers 

 there are certainly not more than two, perhaps none, which are not 

 represented by durable nuclei; and among the next ten at least eight 

 are represented by not-too-transient nuclei. We have also seen 

 that nuclei with certain values of charge, 54e or 90e for example, can 

 Ik.' constructed in several different ways. These problems of nuclear 

 structure are, however, problems for the future. What does seem 

 established at the present moment is, that if we could determine the 

 properties of the system formed by it electrons and a nucleus of 

 charge ne, we should know all the projierties of the elements except a 

 ver\- few having to do with intra-nuclear events. As the only case 

 thus far successfully dealt with is the case n = l, and we cannot even 

 explain what happens when two such atoms combine, this is not 

 meant as an augurv' of an early complete liquidation of the mysteries 

 of physics. Nevertheless, we have good reason to lM?lieve that, 

 though ours is doubtless not the generation w'hich will complete the 

 solution of the problem of the atom, it is the first to which the nature 

 of the problem has been revealed. 



REFERE.NCES 



F. \V. .Aston: Phil. Mag. 47, pp. 385-100 (1924); 4o, pp. 934-945 (1923) Isotopes 



(London, 1922). 

 P. .Auger and F. Perrin: Coniptcs Rcn<ius, 175, pp. 340-343 (1922t. 



