XXIV.] FROM A PHYSICAL STANDPOINT. ISY 



when the light source under examination is subjected to the "action of 

 a strong magnetic field which, among other things, causes a proces- 

 sional movement of the orbits of the ions to which I have' already 

 referred. 



In order to consider the bearing of this, let us deal with the 

 spectrum of zinc which contains triplets. It has been shown that 

 denoting these in ascending order of refrangibility by AI, B b Ci, A 2 , 

 B_>, Co, &c., the lines AI, A 2 , &c., show the same magnetic effect in 

 character, and have the same value of 0/w. The lines BI, B-2, BS, &c., 

 and Ci, C-2, Cs, &c., form other series, and possess a common value for 

 the quantity e/m in each case. 



Dr. Preston, one of the most successful workers in this new field; 

 states : 



" The value of e/m for the A series differs from that possessed hy 

 the B series, or the C series, and this leads us to infer that the atom 

 of zinc is built up of ions which differ from each other in the value of 

 the quantity e/m, that each of these different ions is effective in pro- 

 ducing a certain series of lines in the spectrum, of the metal." 



But this is by no means all that is to be learned from Dr. Preston's 

 researches. He writes 



" When we examine the spectrum of cadmium or of magnesium 

 that is, when we examine the spectra of other metals of the same 

 chemical group we find that not only are the spectra homologous, 

 not only do the lines group themselves in similar groups, but we find 

 in addition that the corresponding lines of the different spectra are 

 similarly affected by the magnetic field. And further, not only is the 

 character of the magnetic effect the same for the corresponding lines 

 of the different metals of the same chemical group, but the actual 

 magnitude of the resolution, as measured by the quantity e/m, is the 

 same for the corresponding series of linos in the different spectra. 

 This is illustrated in the following table, and leads us to believe, or at 

 least to suspect, that the ion which produces the lines AI, A 2 , AS, &c., 

 in the spectrum of zinc is the same as that which produces the corre- 

 sponding series AI, A 2 , AS, &c., in cadmium, and the same for the 

 corresponding sets in the other metals of this chemical group. Iri 

 other words, we are led to suspect that, not only is the atom a com- 

 plex composed of an association of different ions, but that the atoms of 

 those substances which lie in the same chemical group are perhaps 

 built up from the same kind of ions, or at least from ions which 

 possess the same e/m, and that the differences which exist in the 

 materials thus constituted arise more from the manner of association 

 of the ions in the atom than from differences in the fundamental cha- 

 racter of the ions which build up the atoms/' 



