SPECTRA OF STARS TO THE 3 MAGNITUDE. 129 



graphic spectra of the four stars, ft, 8, IT, and <r Scorpii, all near Antares, belong to 

 Division I. (a). They are in the area BB, and do not appear in the present series. 



BARNARD also photographed, with a six-hour exposure, an extended nebula 

 contiguous to Persei, a star of the 4th magnitude. The spectra of e and Persei, 

 on either side of it, appear in the photographs, and belong to Subdivision I. (a). 

 A photograph of the spectra of f Persei was recently obtained, and it also belongs 

 to the same division. 



Both these instances point to the same conclusion, that stars of this type are in the 

 first stage of stellar development from nebuke. 



The star Persei and also t Orionis give in their spectra three lines of the second 

 hydrogen series, recently identified by PICKERING in Puppis. One of the three 

 lines at wave-length 4027 corresponds to the characteristic helium line. The other 

 two at wave-length 4201 and wave-length 4544 do not appear in any other spectra 

 of Subivision I. (a) in the present photographs. These lines appear to belong to the 

 earliest stage of stellar development.] 



There is further evidence to the same effect in the similarity of the distribution of 

 this type of star, and of the gaseous and planetary nebulae. 



The gaseous nebuke, given in the Table in FROST'S edition of SCHEINER'S ' Spectro- 

 scopy,' have been distributed into the same equal areas as the stars. 



The following shows the relative distribution for the nebulae and for the stars : 



A. B. C. D. 



Gaseous nebulre .... 3 7 1G G 

 Stars of Division I. ... 3 G 17 3. 



Thus it appears that the helium stars of Division I. and the gaseous nebuke are 

 subject to a similar law of distribution in relation tq the galactic plane. 



All these facts afford grounds for accepting the conclusion that the helium stars of 

 Subdivision I. (a) are in the first stage of stellar development from the gaseous nebuke. 



Division I. has a second subdivision, viz., I. (b), which is also characterised by a few 

 special lines. These lines have been attributed to calcium, barium, and magnesium. 

 Since these special lines persist through the subsequent divisions, it may be concluded 

 with tolerable certainty, that in order of development Subdivision I. (b) follows after 

 Subdivision I. (). The K line of calcium, which first appears in this subdivision, 

 gradually increases in strength to such a marked extent in the subsequent divisions, 

 that it may be practically taken (as suggested by Dr. HUGGINS), as a criterion of the 

 type to which a spectrum belongs. Two bright line spectra have been treated as 

 belonging respectively to the divisions to which their absorption spectra belong. 



The spectrum given of y Cassiopeia, clearly places it in Subdivision I. (a). It is a 

 helium star. The bright hydrogen lines are weak, and are placed centrally in the 

 difiuse absorption lines. 



VOL. CXCT. A. s 



