1917] on The Complexity of the Chemical Elements 139 



helium and electrons, nothing is known. Whilst as regards the 

 separate shells or rings of electrons which neutralise its charge and 

 are supposed to surround it, like the shells of an onion, we really 

 know nothing yet at all. The original explanation, in terms of the 

 electron, of the periodicity of properties displayed by the elements, 

 still remains all that has been attempted. We may suppose, as we 

 pass through the successive elements in the table, one more electron 

 is added to the outermost ring for each unit increase in the charge 

 on the nucleus, or atomic number, and that when a certain number, 

 8 in the early part of the table, IS later, a complete new stable 

 shell or ring forms, which no longer participates directly in the 

 chemical activities of the atom. Thanks, however, to Moseley's work, 

 this now is not sufficiently precise ; for we know the exact number of 

 the elements, and the various atomic numbers at which the remark- 

 able changes, in the nature of the periodicity displayed, occur. Any 

 real knowledge in this held will account not only for the two 

 short initial periods, but also for the curious double periodicity later 

 on, in which the abrupt changes of properties in the neighbourhood 

 of the zero family alternate with the gradual changes in the neigh- 

 bourhood of the Vlllth groups. The extraordinary exception to the 

 principle of the whole scheme presented by the rare-earth elements 

 remains a complete enigma, none the less impressive because, beyond 

 them again in the table, the normal course is resumed and continues 

 to the end. 



[F. S.] 



WEEKLY EVENIXa MEETING, 



Friday, May 25, 1917. 



Sir James Crichtox-Browne, J.P. M.D. LL.I). F.R.S. 



Treasurer and Vice-President, in the Chair. 



J. Barcroft, M.A. F.Pi.S. 

 Breath lessness. 



I No Abstract.] 



