Spectra of some of the Fixed Stars. 421 



from 1145 to 1170, and from 1280 to 1300. A similar shaded 

 band commences at 1420, and another at 1557*. 



The spectra obtained from sixteen elementary bodies were 

 observed simultaneously with the spectrum of aOrionis. In 

 five of these, viz. sodium, magnesium, calcium, iron, and bis- 

 muth, lines corresponding with certain stellar lines were found 

 to exist. 



(1) Sodium. — The lines coincident with D are fainter in this 

 star than in Aldebaran. 



(2) Magnesium. — Decided group of three stellar lines coinci- 

 dent with the group at b. 



(3) Calcium. — Four lines of this metal were on two different 

 occasions seen to be coincident with four lines in the spectrum 

 of the star. 



. (4) Iron. — The double line of this metal at E, and three other 

 more refrangible bright lines, coincide with lines in the star- 

 spectrum. 



(5) Bismuth. — In the spectrum of this metal also, four lines 

 were found to coincide with four in the stellar spectrum. 



Thallium. — The bright green line so characteristic of this 

 metal appears to coincide with one of the lines seen in the star- 

 spectrum ; but this line may be due to calcium, since the small 

 difference between the position of the thallium line and that of 

 one of the calcium lines very close to it would not be distinguish- 

 able with the dispersive power of the apparatus employed. 



In the spectra of the other elements which we compared with 

 that of the star, no coincidences occur. 



Hydrogen. — There is no line coincident with the red line C of 

 hydrogen ; but in the star are two strong lines, one on either 

 side of the position of C : there is also no line coincident with F. 

 It is strikingly confirmatory of this method of analysis, that in 

 all the stars hitherto examined by us in which a line correspond- 

 ing to C exists, that corresponding to F is also found. When 

 F is absent, C is also wanting. 



In nitrogen three strong double lines were compared. In tin 



* [oc Orionis has long been known as a variable star of great irregularity, 

 both of period and of extent of change of brightness. The authors found, 

 when they reobserved the spectrum of this star in February and March 1 866, 

 that the shading as of fine lines, terminated at its more refrangible end by 

 the strong line 1069*5, was not then to be seen. The absence of this group 

 is of great interest in connexion with the variability of the star's light, 

 especially as the time of the disappearance of this group coincides with the 

 epoch of the maximum brilliancy of the star. The variation in the colour 

 of the star's light observed by Mr. Baxendell is such as would be produced 

 by the absence or presence of this group. The authors have been engaged 

 with observations of other variable stars. (Monthly Notices of the Royal 

 Astronomical Society, vol. xxvi. p. 217.)] 



Phil. Mag. S. 4. Vol. 31. No. 211. June 1866. 2 F 



