January 25, 1900] 



NA TURE 



297 



test that if the purest specimens known (I have worked 

 on beads of Stas' silver which had never been touched) 

 were so impure, some of the decimals used to express 

 their atomic weight might be well spared. But it is not 

 a question of apparent impurities only. 



It is possible that some of the gases of lower atomic 

 weight which exist in the hottest stars may be repre- 

 sented by A in opposition to heavy metals represented 

 by Z, the existence of which is known in the cooler stars 

 only. 



The giving off of gases from metals when high tension 

 electricity is employed is well known. This has been 

 explained by assuming them to be "furnace gases," that 

 is, gases "occluded" by the metals during their reduc- 

 tion. But this does not seem to be a sufficient explan- 

 ation, for the same gases are given off by meteorites. 

 We now see why something like this may happen if 

 there is any foundation for the modern conception of the 

 structure of the "atom" ; and do not these facts explain 

 the chemistry of the hottest stars ? 



It is too early yet to attempt to discuss the effects of 

 the electric charge in this connection, but it must be 

 pointed out that so soon as the ions, however associated 

 their units may be, which are supposed always to have 

 an electric charge upon them, are subjected to the action 

 of a voltaic or induced current, the spectral phenomena 

 observed when they are heated are liable to great changes 

 in some cases, and especially when high atomic weights 

 are in question. Doubtless we have here a field of 

 research which will ultimately supply us with the most 

 precious knowledge. I have already shown that with 

 the gases, such as hydrogen and oxygen, heat alone gives 

 rise to no spectral phenomena, while in the case of such 

 metals as sodium heat is so effective in its dissociating 

 power that the subsequent application of electricity 

 produces no further change. 



We have, in fact, to consider that the effects produced 

 on different substances under the same conditions may 

 be different, and that the stars carry us further than our 

 laboratories ; that is there are stages of spectral change 

 within and beyond our experimental powers revealing a 

 shedding of ions at different temperatures. 



Dr. Prestotis Researches. 



Quite recently the study of magnetic perturbations of 

 spectral lines has brought a fresh array of evidence on 

 this question. 



It has now been proved that spectral phenomena are 

 different when the light source under examination is 

 subjected to the action of a strong magnetic field which, 

 among other things, causes a precessional 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 Aj, B„ Cj, A.,, B2, C2, &c., the lines 

 A,, A2, &c., show the same magnetic effect in character, 

 and have the same value of e,m. The lines Bj, B,, B3, 

 &c., and Cj, C.,, C3, &c., form other series, and possess a 

 common value for the quantity elm 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 pos- 

 sessed by 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 ^/w, 

 that each of these different ions is effective in producing 

 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 



NO. 1578, VOL. 61] 



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 oi 

 the resolution as measured by the quantity ejin is the 

 same for the corresponding series of lines 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.,, .A;,, &c., in the spectrum of 

 zinc is the same as that which produces the corresponding 

 series A,, Aj, A3, &c., in cadmium, and the same for the 

 corresponding sets in the other metals of this chemical 

 group. In other words, we are led to suspect that, not 

 only is the atom a complex 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 vi, and that the differences which 

 exist in the materials thus constituted arise more fronrv 

 the manner of association of the ions in the atom thark 

 from differences in the fundamental character of the ions 

 which build up the atoms.'' 



[This table shows the effect for the three lines which forms the first naturat 

 triplet in the spectrum of cadmium compared with the corresponding lines- 

 in the spectrum of zinc and magnesium. It will be .seen that the corre- 

 sponding lines in the different spectra suffer the same magnetic effect both 

 in character and magnitude. Thus the corresponding lines_ 4800, 4722, 

 5173 are each resolved into sextets, and the rate at which the ionic orbit is. 

 caused to precess is the same for each (denoted by ?/«/=87 in the table). 

 Similarly for the other corresponding lines.] 



This is a result of the first order of importance. I 

 previously discussed what might be expected to happen 

 if the complex system giving the spectrum of an element 

 were broken up., and showed that if less complex systems 

 of the same pattern — that is, consisting of centre of force 

 and ion with its electric charge — were thus produced^ 

 these systems would be just as capable of giving spectra, 

 as the one the breaking up of which produced them. 

 We should get new ions free to move and vibrate, and' 

 new spectra which may reveal the constituents, that is,, 

 the manner in which the complex system breaks up. 

 But Dr. Preston goes further than this. He shows that 

 the same ion associated with different centres of force 

 gives us lines at different wave-lengths. That a certain- 

 ion which in the spectrum of magnesium gives rise to ^is 

 also present in zinc and cadmium, though there is no trace 

 of b in their spectra. 



Now, if the views held by those who have worked along 

 any of these lines be confirmed, we shall be compelled 

 not only to give up polymerisation as the only cause of 

 greater complexity of the molecules of the elements, but 

 to acknowledge a great strengthening of the view that all 

 chemical atoms have a common basis, and build new 

 mental images on this basis. I now pass from the 

 spectroscopic evidence to work in a new field. 



Prof. J. J. Thomson^ s Researches. 

 I have before referred to the fact that science now 

 has to consider masses much smaller than the atom of 

 hydrogen. This we owe not only to a discussion of the 

 phenomena of series but also to some recent researches of 

 Prof. J. J. Thomson, made in connection with his work 

 on the kathode rays. 



