1873.] Mr. J. N. Lockyer on Spectrum- Analysis. 513 



spectra of compounds are broken up — and that it is probable that no 

 compounds exist in the sun. The following facts, gathered from the 

 work already accomplished by Entherford and Secchi, are stated. 

 There are three classes of stars : — 



1. Those like Sirius, the brightest (and therefore hottest ?) star in the 

 northern sky, their spectra showing only hydrogen lines very thick, and 

 metallic lines exceedingly thin. 



2. A class of stars with a spectrum differing only in degree from those 

 of the class of Sirius ; and to this our sun belongs. 



3. A class of stars with columnar or banded spectra indicating the 

 formation of compounds. 



The question is asked whether all the above facts cannot be grouped 

 together in a working hypothesis, which assumes that in the reversing 

 layers of the sun and stars various degrees of " celestial dissociation " 

 are at work which prevents the coming together of the atoms which, at 

 the temperature of the earth, and at all artificial temperatures yet attained 

 here, form the metals, the metalloids, and compounds. 



In other words, the metalloids are regarded as quasi compound bodies 

 when in the state in which we know them ; and it is supposed that in the 

 sun the temperature is too great to permit them to exist in that state in 

 the reversing layer, though they may be found at the outer portions of 

 the chromosphere or in the corona. 



It is suggested that, if this hypothesis should gain strength from sub- 

 sequent work, stony meteorites will represent the third class of metal- 

 loidal or compound stars, and iron meteorites the other or metallic stars. 



The paper concludes as follows : — 



** An interesting physical speculation connected with this working 

 hypothesis is the effect on the period of duration of a star's heat which 

 would be brought about by assuming that the original atoms of which a 

 star is composed are possessed of the increased potential energy of 

 combination which this hypothesis endows them with. From the earliest 

 phase of a star's life the dissipation of energy would, as it were, bring 

 into play a new supply of heat, and so prolong the star's life. 



" May it not also be, if chemists take up this question, which has 

 arisen from the spectroscopic evidence of what I have before termed the 

 plasticity of the molecules of the metalloids taken as a whole, that much 

 of the power of variation which is at present accorded to metals may be 

 traced home to the metalloids ? I need only refer to the fact that, so far 

 as I can learn, all so-called changes of atomicity take place when metal- 

 loids are involved, and not when the metals alone are in question. 



"As instances of these, I may refer to the triatomic combinations 

 formed with chlorine, oxygen, sulphur, &c. in the case of tetrad or hexad 

 metals. May not this be explained by the plasticity of the metalloids 

 in question ? 



" May we not from these ideas be justified in defining a metal, provi- 



2 s 2 



