EVOLUTION AND THE SPECTROSCOPE. 325 



baran, Mr. Huggins detected sodium, magnesium, calcium, iron, bis- 

 muth, antimony, tellurium, mercury, and hydrogen. 



The third class, in which are some stars of a red color, is compara- 

 tively small in numbers. Alpha Orionis or Betelgeux, Alpha Herculis, 

 Beta Pegasi, Mira beti, and Antares, are good examples of this type. 

 Their spectra, as a rule, resemble the spectrum of a solar spot, and 

 sometimes contain bright lines. Hydrogen is still present, but so diffi- 

 cult to detect that, at first, it was supposed to be wanting in the spec- 

 trum of Betelgeux. But, in a state of combination, as aqueous vapor, 

 it has been found in the stars of this order, and, most notably, in An- 

 tares. In the spectrum of Betelgeux, Mr. Huggins observed lines be- 

 longing to magnesium, sodium, iron, calcium, and bismuth. 



The stars of the fourth type are very inconspicuous, but give quite 

 peculiar spectra, consisting chiefly of three bright bands, separated by 

 dark spaces. Such a spectrum suggests that of carbon, but really tells 

 us nothing, as yet, of the constitution of these stars. We must, there- 

 fore, leave them out of account in our speculations. It would be easy 

 to theorize about them, only the theories would find no place in our 

 argument. 



Now, taking the spectra of stars of the first, second, and third 

 classes as a basis for our speculations, we have quite decent evidence 

 of a gradual increase in chemical complexity. And, if we bring the 

 nebula? into line, we can devise a very neat progressive series of devel- 

 opment up to the solid planet. Beginning with a nebula consisting 

 mainly of nitrogen and hydrogen at low temperature and pressure, we 

 can easily conceive of several ways by which it might gain great acces- 

 sions of heat, and give a bright, continuous spectrum. A collision 

 with meteoric or cometary matter would account for such an increase 

 of temperature. But, given a nebula which is sufficiently hot, and 

 from which a sun might be evolved by cooling, what shape will our 

 speculations assume ? This intensely-heated body undergoes a certain 

 condensation, rings are thrown off from it, and a nucleus appears, 

 which soon becomes a star or sun of the first type. Hydrogen still 

 predominates in its constitution, but metals begin to show themselves, 

 though very faintly. But the cooling continues, and gradually the 

 hydrogen lines become fainter, the metallic lines stronger, a larger 

 number of substances are detected, and we have a sun of the second 

 class. By another slow transition, chemical action, as we recognize it, 

 begins to set in. The hydrogen lines disappear ; aqueous vapor is 

 formed ; spots, like those of the sun, which are probably centres of 

 chemical activity, become more and more abundant, and the star enters 

 the third order. As the spots accumulate, the istar becomes more de- 

 cidedly a "variable," and, after violent and prolonged convulsions of 

 its surface, solidity is reached, the emission of light ceases, and a plan- 

 et is formed. Some volcanic heat, however, yet remains ; but this 

 slowly dies away, the volcanoes become extinct, and, at the end of the 



