324 THE POPULAR SCIENCE MONTHLY. 



tion upou them is not altogether unprofitable. The time spent in con- 

 jectures and surmises is not wholly wasted ; for it is impossible to fol- 

 low up any of the lines of thought thus opened, without reaching some 

 valuable suggestions, which may pave the way to new discoveries. 

 New truth, in one direction or another, is sure to be reached in the 

 long-run. So, then, we may proceed to theorize in the most barefaced 

 manner, without entirely quitting the legitimate domain of science. 



It is plain that the nebular hypothesis would be doubled in impor- 

 tance, and our views of the universe greatly expanded, if it could be 

 shown that an evolution of complex from simple forms of matter ac- 

 companied the development of planets from the nebulae. Evolution 

 could look for no grander triumph. For the evidence to support such 

 a theory, we must depend mainly upon the spectroscope. Let us con- 

 tinue upon our task of finding the intermediate links between the two 

 extremes of planetary growth, and see whether, as we ascend in the 

 line of change, an increased chemical complexity can be observed. 

 Upon this theory, the planets should contain more elements than the 

 sun ; the sun more than some of the less advanced among the fixed 

 stars ; and these, in turn, should be more highly organized than the 

 nebula?. But we must not fail to remember that we are merely speculat- 

 ing, and that the spectroscope, in telling us of the presence of certain 

 substances, does not give us accurate information with regard to the 

 absence of others. In this investigation, we can look to the spectro- 

 scope only for hints, not certainties. Difficulties will abound in our 

 path, and, in a paper of this length, we cannot stop to scrutinize them 

 closely. We must bridge many chasms with guesses. 



The evidence concerning the constitution of the fixed stars has 

 been furnished chiefly by Secchi and Huggins. The former observer, 

 favored by Italian skies, has done, perhaps, the major portion of the 

 work, and has given us a classification of these bodies. According to 

 Secchi, the stars may be divided into four classes, as follows : 



In the first class, which is by far the largest, we find most of the 

 white stars, Sirius, Altair, Vega, Iiegulus, and Rigel, being especially 

 prominent. These give spectra characterized by the intense develop- 

 ment of the four hydrogen lines, which stand out with great distinct- 

 ness upon a background of the seven primary colors. Lines belonging 

 to some of the metals, particularly to sodium, magnesium, and iron, 

 are also visible, but are exceedingly faint in comparison with those of 

 hydrogen. The distinctness of this element, as compared with the 

 faintness of the metallic lines, is characteristic of the stars of this type. 

 The absence of bands, indicating an absorptive atmosphere, is also 

 noteworthy. 



In the second class of stars we find our sun, Arcturus, Aldebaran, 

 Capella, Pollux, Procyon, and many others. Here we have spectra in 

 which the lines of the metals are apparently more numerous, and cer- 

 tainly more distinct, the hydrogen being less conspicuous. In Aide- 



