CELESTIAL CHEMISTRY. 225 



aid, nebuloe that had, up to his time, been unresolved, were sepa- 

 rated into stars ; and from this circumstance the argument was 

 advanced that all nebulee would yield to a sufficient increase of 

 power, and be demonstrated to consist of stars, which, while in 

 reality separated by immense distances, yet seem so closely 

 packed together that their light is blended into one mass. 



We have spoken of solar systems ; there are, according to 

 these statements, also stellar systems, where, instead of a sun and 

 planets, there are groups of suns. Our sun belongs to such a 

 grouj) of resolvable nebulas, the stars that we see individualized, 

 and those of the milky way, being his companions. 



Seen at a great enough distance, otu* nebular or stellar system 

 would present a flattened or lima-bean-like shape, somewhat ellip- 

 tical from one point of view, and like a naiTow band from another. 

 Is this group arrangement the only form in which luminous 

 matter is found in the universe? 



Here, again, the power of means apparently trivial, but rightly 

 applied, is shown. Once more the prism of glass solves a ques- 

 tion, which hundreds of thousands of dollars expended in tele- 

 scopes could not have settled. On appl5ing the spectroscope to 

 the investio:ation of the irresolvable nebulas, Huggins finds that 

 some of them px*esent the spectra characteristic of an ignited gas, 

 that is, of a flame. The Fraunhofer lines in that case are, as we 

 have said, bright instead of dark, as in the solar spectrum, and 

 the evidence is of a very tangible and unmistakable kind. 



There are, then, in space, masses of ignited gaseous matter of 

 prodigious extent, shining by their own light, containing no star, 

 and resembling the nebulas, which the nebular hj^pothesis declares 

 to have been the original state of our solar system. 



Now we can appreciate the assistance which the spectroscope 

 has lent in establishing that noble conception of Herschel and 

 Laplace. It has demonstrated the unity of the solar system by 

 establishing the existence throughout it of the same elements ; it 

 has shown 'the same unity in the materials of the universe ; and 

 lastly, it fortifies us in the belief that the theoi*etical conception is 

 . in process of realization before our eyes ; that we may see worlds 

 in the act of formation. The spectroscope has also a bearing on 

 a great geological hypothesis : the former heated state of our 

 globe. Geologists assert, from the presence in high latitudes of 

 fossil remains of tropical plants, that the earth was once in a 

 molten condition ; that it cooled gradually, and at one time 

 reached such a temperature that the internal heat sufficed to main- 

 tain a warm climate on every part. The polar regions were not 

 then dependent on the sun for their supply of heat, but needed 

 that luminar}' only for light. Vegetation was somewhat like that 

 of a hot-house in the north in winter, with plenty of heat, but 

 lacking light for part of the year. 



By this hypothesis, a great variety of facts, such as the forma- 

 tion of some mountain ranges, may be satisfactorily exijlained. 

 For example, when the heated mass of the earth was cooling it 

 was also shrinking, but as soon as an inflexible crust had formed 

 over the liquid ball, that exterior could no longer gradually 



