.CHAP. XIV.] OBJECTIONS TO THE DISSOCIATION HYPOTHESIS. 121 



A possible vcra caum of such chemical differentiation wa$, I believe, 

 suggested by Dr. Wolf, who in 1866,* misled by Sir Wm. Huggins' 

 statements concerning the chemistry of the nebulae, endeavoured to 

 explain their spectra, and therefore their chemical constitution as 

 distinguished from that of stars, in a way that will be gathered from 

 the following extract : 



" If we admit the data of spectrum analysis as to the gaseous state 

 of these singular bodies (the nebulae), and the simplicity of their com- 

 position, one is led to see in them only the residuum of the primitive 

 matter after condensation into suns and into planets has extracted the 

 greater parts of the simple elements which we find on the earth, and 

 chemically in some of the stars." 



It will be seen that Wolf considers only the differentiation of 

 nebulae from suns by the "extraction of matter" by some previous 

 local action. The chemistry was general to begin with, then the resi- 

 duum was worked up. 



Dr. Schuster, however, has more recently gone further, still start- 

 ing however from a general chemistry : 



" We have no reason to believe that the nebulae of the present day 

 resemble our sun's ancestor. Some of the stars which are now in an 

 early stage of development, may be forming through the condensation 

 of matter which has been left over by others ; and it would not be 

 surprising if the youngest star did not agree in constitution with its 

 aged companions.''! 



Let us suppose then that the number of different chemical parishes 

 in space is : legion to begin with, and that by such actions as those 

 suggested by Drs. Wolf and Schuster more differences are established, 

 surely the stellar differences must be legion too. I would submit that 

 the more such causes as these be added to a hypothetic irregular dis 

 tribution of different kind of matter in space, the more differences in 

 the chemical, constitution of stars should be found. But this is not so 

 according to the facts. 



While the number of chemical elements known at the present tim e 

 is over seventy, the number of well-marked groups of stars is only ten, 

 if we take one side of the temperature curve ; that is, if we deal with 

 stars increasing or stars decreasing their temperature. We are justi- 

 fied in using one side only, because the spectra of stars on opposite 

 sides of the temperature curve indicate precisely the same elements, 

 though the percentage composition of effective absorbing regions is 

 different in the two cases. At the same temperature on opposite sides, 



* Hypotheses Cosmogoniques, p. 7. 

 f Proc. Roy. Soc., vol. 61, p. 209. 



