Spectra of some of the Fixed Stars. 419 



atmosphere which the light would have to traverse would be 

 considerably lessened. With perhaps the exception of Mars, 

 telescopic observations are in favour of such a supposition. 



§ IV. Observations on the Fixed Stars. 



10. The number of fixed stars which we have, to a greater or 

 less extent, examined amounts to nearly 50. We have, however, 

 concentrated our efforts upon three or four of the brighter stars ; 

 and two only of these have been mapped with any degree of 

 completeness. These spectra are, indeed, as rich in lines as that 

 of the sun ; and even with these it may be advantageous to com- 

 pare the spectra of additional metals when the season is again 

 favourable. The few really fine nights that are available whilst 

 the star is well situated for such observations, in respect of alti- 

 tude and the time of sun-setting, necessarily make the complete 

 investigation even of a single star the work of some years. 



11. Aldebaran (aTauri) (Plate VI.). — The light of this star is 

 of a pale red. When viewed in the spectroscope, numerous strong 

 lines are at once evident, particularly in the orange, the green, 

 and the blue portions. The positions of about seventy of these 

 lines have been measured, and their places have been given in 

 the Table. Besides these, numerous other strong lines . are 

 visible, particularly in the blue ; but they have not been measured, 

 owing to the feebleness of the light ; we have therefore not in- 

 serted them in the Table or in the diagram. A similar remark 

 is applicable also to the results of our examination of a Orionis 

 and /S Pegasi. 



We have compared the spectra of sixteen of the terrestrial 

 elements by simultaneous observation with the spectrum of 

 Aldebaran, of course selecting those in which we had reason, 

 from the observations, to believe coincidence was most likely to 

 occur. Nine of these spectra exhibited lines coincident with 

 certain lines in the spectrum of the star. They are as follows : — 

 sodium, magnesium, hydrogen, calcium, iron, bismuth, tellurium, 

 antimony, and mercury. 



(1) Sodium. — The double line at D was coincident with a 

 double line in the stellar spectrum. 



(2) Magnesium. — The three components of the group at b, 

 from electrodes of the metal, were coincident with three lines in 

 the star-spectrum. 



(3) Hydrogen. — The line in the red corresponding to C, and 

 the line in the green corresponding to P in the solar spectrum, 

 were coincident with strong lines in the spectrum of Aldebaran. 



(4) Calcium. — Electrodes of the metal were used ; four lines 

 in its spectrum were observed to coincide with four of the stellar 

 lines. 



