156 SPECTRA OF PERIODIC STARS. PARTI. 



Padre Secchi, the Eoman astronomer, divides the stars 

 into three types ; the first and most dominant type in- 

 cludes Sirius, a Lyrae, and other white stars, which 

 invariably contain hydrogen of high temperature, and 

 are denoted by a black line in their spectra, which 

 coincides with the solar line F ; and there is another 

 band also probably due to hydrogen in the violet half 

 of the stars visible to the naked eye belonging to this 

 group. A singular modification of this group, however, 

 occurs in the stars of the constellation Orion, which so 

 rarely show any deviation from one type, that, with the 

 exception of a Orionis or Betelgeux, they may be said 

 to form a family distinguished from all the other stars 

 in the sky ; their spectra are crossed by fine lines, faint 

 in the violet, with a band more or less visible in F. 

 7 Cassiopeise and fS Lyrse differ from the stars of the first 

 type in having a bright band near the solar line F, in- 

 stead of a black one. 4 



Padre Secchi's second type includes a Orionis, a 

 Tauri, Antares, ft Pegasi, &c., which have coloured 

 bands in the red and orange. According to M. Secchi, 

 the most remarkable star in this section is a Herculis. 

 It gives a spectrum which has the appearance of co- 

 lumns illuminated on one side ; ' the stereoscopic effect 

 of the convexity of these bands due to the shading 

 is so surprising, that it cannot be beheld without 

 astonishment.' The spectrum of the star S 2 Lyrse 

 has a similar appearance, only instead of convex it 

 has concave bands. 



The third type consists of stars whose spectra are 

 crossed by fine lines, as Arcturus, Capella and our 

 own sun. 



4 In 7 Cassiopeise, Mr. Huggins has detected a second bright line in the 

 red part of the spectrum. He has also found that these two bright lines 

 agree in position with the two brightest lines of the spectrum of hydrogen, 

 und may therefore be considered due to luminous hydrogen. 



