BOOK III. THE DISSOCIATION HYPOTHESIS. 

 CHAPTER VIII. RECENT OPINION. 



WHEN stating in Chapter II some of the difficulties encountered by 

 the early workers in spectrum analysis who found it impossible to 

 reconcile the facts which the new method of work was accumulating 

 with the then received chemical view, I pointed out that as early as 

 1873 I had suggested that many of our difficulties would vanish if it 

 were conceded that the " atoms " of the chemist were broken up, or 

 dissociated, into finer forms by the high temperatures necessarily 

 employed in the new method of investigation. 



The year 1873 was 27 years ago ; I propose, therefore, to briefly 

 refer, as judicially as I can, to the recent state of opinion on this 

 subject, or rather on some of the main points of it. 



Only some of the views I had brought forward from time to time 

 have received general acceptance, those include the breaking up of the 

 solid metal giving (from whatever cause) a continuous spectrum into 

 smaller molecular groupings giving fluted and line spectra. 



My view as to the subsequent dissociation of molecules, when once 

 the line spectrum stage has been reached, was still rejected by many. 

 For myself, I am not surprised at this. In a question of such tran- 

 scendental importance, caution must be redoubled; an absence of 

 work and expression of opinion in such a line of inquiry with questions 

 of pure science only involved, is almost inherent to the nature of the 

 investigations. The chemist has little interest in an appeal to celestial 

 phenomena, and astronomers do not generally concern themselves with 

 chemistry. The region investigated by the chemist is a low tem- 

 perature region dominated by monatomic and polyatomic molecules. 

 The region I have chiefly investigated is a high temperature region, in 

 which mercury gives us the same phenomena as manganese. In 

 short, the changes with which spectrum analysis has to do take place 

 at a far higher temperature level than that employed in ordinary 

 chemical work, and hence probably it is that I can only refer to one 

 chemical experiment bearing on the subject. 



It is important, however, to point out that in cases where the two 

 regions overlap, vapour density determinations and other work have 

 been in harmony with the spectroscopic results, e.g., the changed 



