130 



NA rURE 



[December 7, 1899 



So much, then, tor a possible reconciliation. The 

 tiext point to be considered is, is depolymerisation on 

 such a small scale sufificient ? 



To do this we have to see the basis of the atomic 

 ■weight of oxygen i6, and consider the series question in 

 relation to oxygen. This necessitates a digression. 



The simplest case presented in series phenomena is 

 that placed before us by sodium and other elements 

 which run through all their known spectral changes at a 

 1I0W temperature. Dealing with the line spectrum stage 

 we have three " series," one principal and two sub- 

 ordinate (first and second). The former contains the 

 orange line D, constantly seen at all temperatures, the 

 ifirst subordinate the red line, the second subordinate the 

 green line, representatives of two series of lines which 

 are best seen both in the flame and arc. 



The two subordinate series of sodium, like those of all 

 other elements so far examined, have the peculiarity that 

 !they end at nearly the same wave-length, while the end 

 of the principal series occurs at a different, sometimes 

 widely different, wave-length. This is a touchstone of 

 the highest importance, as we shall see ; it points to a 

 •solidarity of the two subordinate series, and to a difference 

 ^between them and the principal series. 



Although the original idea was that all three series 

 'were produced by the vibrations of the same molecule, 

 ■observations of the sodium phenomena alone are simply 

 and sufficiently explained by supposing that we have 

 ithree different masses vibrating, and that two of them, 

 producing the subordinate series, can be broken up by 

 heat, while that producing the principal series cannot. 

 The series represented by the red and green lines seen 

 Sbest at the lower temperatures have been seen alone, 

 and it is a matter of common experience that the orange 

 -line representing the principal series is generally seen 

 .alone : it is not abolished at high temperature as the 

 others are. Because the mass the vibrations of which 

 .give us the orange line is produced by the breaking up 

 ■of more complex forms at a low stage of heat, and it 

 •cannot be destroyed by the means at our command, it 

 fis the common representative of the element sodium. 

 Because the masses the vibrations of which produce the 

 •two subordinate series represented by the red and green 

 iines are easily destroyed by heat, they are more rarely 

 seen, scarcely ever at high temperatures when the quantity 

 is small, since, as I pointed out years ago, " the more 

 there is to dissociate, the more time is required to run 

 •through the series, and the better the first stages are 

 seen." 



This view is greatly strengthened by considering 

 another substance which, if we accept Pickering's and 

 Rydberg's results, has, like sodium, three series, one 

 .principal and two subordinates in quite orthodox fashion. 

 I refer to hydrogen. 



Till a short time ago we only knew of one " series " of 

 'hydrogen, and on this ground Rydberg assumed it to 

 ■represent the finest form of matter known, regarding the 

 other substances which give three normal series as more 

 •complex. This idea is in harmony with the view 

 •expressed above. 



Pickering in 1897 announced the discovery in the stars 

 of another series, and seeing that this ends in the same 

 part of the spectrum as the other, we can provisionally re- 

 gard the terrestrial and stellar hydrogen as representing 

 ithe first and second subordinate series. 



Rydberg in the same year gave reasons for supposing 

 that one line seen chiefly in the bright-line stars may 

 •represent still another series of hydrogen which we may 

 take as the principal series. The other lines in this series 

 he calculated to be out of range. 



If we accept all these conclusions we must regard 

 liydrogen as identical with sodium in its series conditions. 

 But there is this tremendous difference. In sodium we 

 NO. I 571, VOL. 61] 



easily at low temperatures — the bunsen is sufficient — 

 see all three series, while in the case of hydrogen even 

 the Spottiswoode coil can show us nothing more than 

 one of the subordinate series. At the same time, the 

 other subordinate and the principal series are visible 

 in stars which we have many reasons for believing to 

 be hotter than the spark produced by the Spottiswoode 

 coil. 



The argument for the existence of three different 

 masses producing the three different series derived from 

 the sodium observations is therefore greatly strengthened 

 by what we now know of hydrogen. 



I shall therefore assume it in what follows, and now 

 return from the digression. 



Oxygen, instead of having three series like metals or 

 low melting point such as sodium, and the gas hydrogen, 

 has six. These six have been divided by Runge and 

 Paschen into two normal sets of three, each set possess- 

 ing one principal and two subordinate series. 



There is evidently a new problem before us ; we 

 require to add the series of hydrogen to the series of 

 sodium to get a " series " result similar to that obtained 

 from oxygen. 



Before we go further it will be well to consider the 

 possible order of simplifications. Let us take the sim- 

 plest case represented by sodium and hydrogen in the 

 first instance. The facts are shown in the following 

 table :— 



High temperature. 



Hydrogen. 

 /"Principal \Celestial 

 Line.stagej Subordinate / gas. 

 (.Subordinates 



Line stage^ 



(Principal 

 Subordin ite 

 Subordinate 



Celestial 

 and ter- 

 restrial 

 vapour. 



Terres- 

 trial 



Flutings 

 Continuous 



and 

 liquid. 

 Lo7v temperature. 



Structure spectrum 

 Contir 



H Terres- 

 trial gas . 



We may now bring these results to bear upon oxygen. 

 We learned first from Egeroff that this gas at ordinary 

 temperature and pressure is so molecularly constituted 

 that it produces a fluted absorption in the red part of 

 the spectrum. On account of the constancy of the 

 results obtained by chemists we cannot be dealing with 

 a mixture of molecules, the fluting absorption therefore 

 must be produced by molecules of one complexity 

 having an "atomic weight" of 16. 



If we subject it to an induced current at low pressure 

 (at which the action of such a current is feeblest), it at 

 once breaks up into two normal sets of three series, that 

 is six series altogether ; it is almost impossible to con- 

 sider this state of things in the light of what happens in 

 the case of sodium and hydrogen without assuming on the 

 ordinary chemical view that the " molecule " with the fluted 

 spectrum is broken up into two, until finally we get — 



Line spectrum 



High Temperature. 



Set a. 

 ( Principal series 



- Subordinate 



i I 



N Subordinate 



\ 



Set B. 

 Principal series. 



I 

 Subordinate. 



I. 

 Subordinate. 



I 



Fluted spectrum. 

 Low temperature. 

 But if we accept this, we give up depolymerisation, 

 for the molecules of the subordinate series of sets A and 

 B thus produced cannot be identical because their spectra 

 j are not identical. 



! If we hold to depolymerisation we must arrange 

 i matters thus — : 



