On the Chemistry of the Hottest Stars. 



203 



The Orion Stars. 



Now if we consider another change higher lip in the scale of tem- 

 perature, taking as the lower level a Cygni, at which we have arrived, 

 we have independent evidence that the so-called Orion stars are 

 hotter than such a star as a Cygni. 



On proceeding to study the higher dissociating temperature at 

 work in the Orion stars, all the statements made with reference to 

 the changes likely to occur in the spectrum on the non-dissociation 

 hypothesis, strictly apply. We cannot expect any change in the 

 relative intensity of the lines, and the appearance of the spectrum 

 cannot be f andamentally altered. 



On the dissociation hypothesis, on the other hand, if we find certain 

 lines indicating certain substances disappearing, and other lines indi- 

 cating other substances making their appearance for the first time, 

 or if they were visible before, becoming much intensified, w 7 e shall 

 have an opportunity of studying the effects of the new dissociating* 

 forces at work. 



Now is there any change ? The facts are that this increase of 

 temperature we are now considering reduces the quantity of iron and 

 calcium present, increases the amount of hydrogen present, and the 

 lines of the cleveite gases now appear. 



Associating this with the former result, we get as distinct evidence 

 that an increase in the spectrum of the cleveite gases accompanies the 

 disappearance of the enhanced iron lines as that an increased develop- 

 ment of the enhanced iron lines accompanies the decrease of the iron 

 arc lines. 



To take iron as an example, for the sake of simplicity, it will be 

 seen then that the actual stellar phenomena might have been pre- 

 dicted up to a certain point, from a consideration of laboratory and 

 solar phenomena. But the stars carry us further than our predic- 

 tions ; we see the gradual increase of hydrogen and cleveite gases. 

 The facts demonstrate that as temperature increases hydrogen 

 increases, and, together with the cleveite gases not obvious before, 

 finally replaces iron which has disappeared. 



The Law of Continuity. 



I am bound to make this appeal to the law of continuity. The 

 verdict is that, as in all previous human experience, a higher tem- 

 perature brings about simplifications, and it is not strange that, as 

 our horizon is expanded by new work, we find the same laws in 

 operation. We have, I hold, in these phenomena the work of dis- 

 sociation carried on before our eyes in the hottest stars, to a point not 

 reached before, and the stars also tell us that this is beyond our 



