XVIII.] REPLIES TO SPECIAL OBJECTIONS. 14$. 



of hydrogen 1 This seems to me to be almost a crucial experiment. 

 Possibly, of course, we should get high temperature lines not hitherto 

 looked for, but present in the sun. If so, the objection would fall to 

 the ground, but if this is not the case, and if mercury at a high tem- 

 perature refuses to be dissociated into simpler elements, a most serious 

 objection to the theory would have to be answered." 



In reply to this I may state that in recent large dispersion photo- 

 graphs the differences pointed out by Dr. Schuster between the spectra 

 of the sun and Aldebaran do not exist. I quite agree that such experi- 

 ments as he describes should be made, and I have made many, but the 

 work which is necessary has been interrupted, since I have no longer 

 at my disposal the Spottiswoode coil, the superiority of which, over all 

 others, for such a general inquiry as this I have amply demonstrated. 

 I may say here, however, that so far as the observations have gone 

 there is apparently an agreement between the laboratory and stellar 

 results, but there are possible sources of error which require to be 

 studied, and also in a matter of such high importance the experiments 

 must be repeated many times before a final statement is made. 



Dr. Schuster next states : 



" While I think that we shall all admit that different stars are in 

 different stages of development, and that hydrogen stars will ulti- 

 mately approach more nearly to the state of our sun, it would be 

 unwise to push the argument of uniformity too far, and to say that 

 every star will pass exactly through the same stages. Ritter, who is 

 favourably inclined to the dissociation hypothesis,* gives good reason 

 to believe that the sun's surface was never much hotter than it is 

 now, and that the higher temperature of hydrogen stars is connected 

 with their greater masses. It is, in fact, impossible to admit that the 

 process of development should be quite independent of the total mass 

 of the star. It may be urged that Arcturus must have a mass much 

 larger than that of our sun, and its spectrum, according to Professor 

 Lockyer, is identical with that of the sun. But I suppose that that 

 statement only refers to the blue and violet region, for, according to 

 Dr. Huggins, to whose early stellar photographs we owe so much, the 

 spectrum of Arcturus in the ultra-violet approaches that of Sirius." 



Although the masses of very few white stars have been determined 

 with trustworthy results, one case in which a white star can be shown 

 to have a smaller mass than the sun will be sufficient to show a weak- 

 ness in Hitter's conclusions. For /3 Persei (Algol) Vogel states the 

 mass as four-ninths that of the sun; so that the sun, on Hitter's 

 theories, may be supposed to be of sufficient mass to reach a tempera- 

 ture as high as that of ft Persei a result which does not accord with 

 * Wied. Annalen, vol. xx, p. 152. 



