xiv.] HUGGINS' WORK. 187 



few substances a statement founded on the observation that 

 the lines in their spectra are matched by lines which we see in 

 the spectra of hydrogen, magnesium, and perhaps of sodium too, 

 but the faintness of the indication of these two latter substances 

 only intensifies the unmistakable development of the phenomena 

 by which the existence of the former is indicated. 



So much for the first class : now for the second. In this we 

 find our sun. In the spectra of stars of this class, the indica- 

 tions of hydrogen are distinctly enfeebled, and, accompanying 

 this change, we find all simplicity vanished from the spectrum. 

 The sodium and magnesium indications have increased, and a 

 spectrum in which the lines obviously visible may be counted 

 on the fingers is replaced by one of terrific complexity. 



The complexity which we meet with in passing from the first 

 class to the second is one brought about by the addition of the 

 lines produced by bodies of chemical substances of moderate 

 atomic weight. The additional complexity observed when we 

 pass from the second stage to the third is brought about by the 

 addition of lines due in the main to bodies of higher atomic 

 weight. And this is a point of the highest importance at 

 the third stage the hydrogen, which existed in such abundance in 

 stars of the first class, has now disappeared. 



Dr. Huggins' drawings of the spectra of Aldebaran and a 

 Orionis (Fig. 73) show how much care has been devoted to this 

 inquiry. Below the stellar spectra are mapped the lines of the 

 various elements with which they were compared, and from the 

 coincidence of some of these lines with those in the stellar 

 spectra the existence of the corresponding elements in the 

 atmospheres of these stars was inferred. 



It will be seen that in the spectrum of Aldebaran, the hydrogen 

 lines c and F are present, while they are absent from a Orionis. 

 No less than seventy lines have been observed in the spectra of 

 these two stars, and Mr. Huggins and Dr. Miller have detected 

 in Aldebaran the following elements: Hydrogen, sodium, 



