380 CELESTIAL CHEMISTRY. 



stars is sufificient to break up into simpler substances almost 

 every metal or element we know. We can accept the evidence 

 of the spectroscope for this. The spectrum of iron, for in- 

 stance, where that metal occurs in the cooler parts of our sun, 

 consists of considerably more than a thousand lines; in the 

 much hotter chromosphere of the sun those many lines dwindle 

 away to two. We cannot come to any other conclusion than 

 that the heat of the chromosphere is so great that what we 

 known as iron is broken up into a much simpler substance. 



Now applying this to the stars in general, we find by examin- 

 ing metals brought to a high temperature by the electric arc, 

 that they give exactly the same class of spectra that the cooler 

 or carbon stars give, and so we know that the temperature of 

 those stars is that of the electric arc, not hot enough to break 

 up the metals. We pass on to the hotter stars, of which 

 Sirius and Procyon are types, and there we find that the metals 

 calcium, magnesium, and iron do no longer exist, but have 

 broken up into simpler bodies. In still hotter stars, like Algol, 

 copper, manganese, and nickel have similarly broken up, and 

 helium — which we know to be produced by the breaking up 

 of radium — appears, together with another gas apparently 

 formed in a similar way, to which the name asterium has been 

 given, and which is as yet unknown on earth. It is probably an 

 inactive gas like helium and argon, and of light weight. Then 

 we come to the very hottest stars. Tike zeta Puppis and lambda 

 Cephei, where even hydrogen breaks up into a simpler form, 

 and another new gas makes its appearance. Only twelve years 

 have passed since this fact was first observed in the former of 

 these two stars : with regard to the latter the observation was 

 made by Professor Pickering as recently as four years ago, 

 thus tardily has changing and uncertain science arrived at the 

 conclusion expressed with authority many centuries ago "the 

 very elements shall melt with fervent heat," and an altogether 

 new light has been thrown upon those words. We know now 

 that the cooler a star is, the more and more complex chemically 

 does it become, and the more it is heated the simpler is its 

 chemical composition, until it is all iteduced to the bare 

 simplicity of helium and dissociated hydrogen. 



I cannot go into this subject more fully, but it is of interest 

 to note that thick hydrogen and thin metallic lines in a star's 

 spectrum show that that star is cooling; on the other hand, 

 when its temperature is increasing the lines of the metals are 

 thick and those of hydrogen thin. The spectrum of Sirius 

 affords an excellent illustration of a cooling star. In the 

 course of ages those cooling stars may become dark suns, but 

 those whose temperature is increasing finally arrive at the 

 condition of what we may call gaseous stars of the simple 

 chemical composition that I have already described. 



Even these are still spoken of as stars, although merely 

 whirling masses of flaming gas. There is an earlier stage in 

 the life of such a body, z'is. : before it has acquired any 

 semblance of form or coherence. Then it would not yet be a 

 star, but an irresolvable nebula. Many so-called nebulae, 

 when seen through a powerful telescope, can be resolved, i.e., 



