CELESTIAL CHEMISTRY. 421 



ena of dissociation are seen in a wonderful degree in the sun, the 

 fixed stars, and the nebulae. It is not necessary to recall to you the 

 marvelous field of celestial chemistry which the spectroscope, in the 

 hands of Kirchhoff and his followers, has made known to us, nor the 

 proofs that the solar atmosphere contains in a dissociated state very 

 many of the elements which in our own planet are met with in a free 

 state only in the laboratory of the chemist. It is instructive to com- 

 pare the spectra of the various fixed stars with each other, from white 

 stars like Sirius, to yellow stars like Aldebaran and our own sun, and 

 red stars like Alpha Orionis and Antares, and to note in these three 

 classes an increasing complexity of chemical composition. In the first, 

 with a predominance of hydrogen, we see only faint lines of magne- 

 sium, sodium, calcium, iron, and a few other metals, while in the sec- 

 ond, though free hydrogen still abounds, the number of metallic ele- 

 ments is greatly augmented, and finally in the red stars hydrogen is 

 seen only in combination, as aqueous vapor, the metals are wanting, 

 and the metalloids and their compounds appear. If, in accordance 

 with the nebular hypothesis, we look upon these different types of 

 stars as representing successive stages in the process of condensation 

 from nebula to planet, we may also see in them a gradual evolution 

 of the more complex from the simple forms of matter by a process of 

 celestial chemistry. Such was the view put forward by F. W. Clarke 

 in January, 1873, and some months later by Lockyer, who has reiter- 

 ated and enforced these suggestions, and, moreover, connected them 

 with the speculations of Dumas on the composite nature of the ele- 

 ments. The white stars are the hottest, and in the atmosphere of 

 these bodies the various metals, according to Lockyer, make their ap- 

 pearance in the oi'der of their vapor-densities. 



I ventured, in 1867, while speculating on the phenomena of dissocia- 

 tion, to remark that, although from the experiments of the laboratory 

 we can only conjecture the complex nature of the so-called elementary 

 substances, we may expect that their " further dissociation in stellar 

 or nebulous masses may give us evidence of matter still more ele- 

 mental." Now, while the nebulse, when scanned by the spectroscope, 

 show us only the lines of hydrogen and nitrogen, the two lightest 

 forms of gaseous matter known to chemistry, it is remarkable that the 

 recent studies of the solar chromosphere reveal to us the existence of 

 an unknown gaseous element which, from its extension beyond even 

 the layer of partially cooled hydrogen, must, according to the deduc- 

 tions of Mr. Johnson Stoney, be still lighter than this gas. The green 

 line by which this substance is distinguished is not as yet identified 

 with that of any terrestrial element. Is it not possible that we have 

 here that more elemental form of matter which, though not seen in 

 the nebula?, is liberated by the intense heat of the solar sphere, and 

 may possibly correspond to the primary matter conjectured by Dumas, 

 having an equivalent weight one-fourth that of hydrogen ? Mention 



