20 C. V. L. CHARLIER, 
The description of these subclasses is given by PrckERING and 
Miss Cannon in Vol. XXVIII of the Harvard Annals. I give here a 
summary of this description, referring moreover to the plate at the 
end of this volume, giving the spectrum of ¢ Orionis, a specimen of 
the spectrum of the subtype Bo which is here reproduced from the 
above mentioned volume. 
Summary of the description given by PICKERING (H. A. XXVIII P. 150 ff.) 
of the different subclasses of the spectral type B. 
Class Bo. 
Typical star: € Orionis (Compare spectrum reproduced on plate I). 
All lines dark. This spectrum is specially characterized by the great intensity of se- 
veral of the Orion lines, some of them being so well marked that the hydrogen series is 
not readily detected at the first glance, as may be done in all of the following classes of 
the B-stars. 
The most characteristic dark lines in this spectrum are at wave lengths 4089.2, 
4116.2 and 4649.2. These lines reach a maximum in spectra of this class, and are consi- 
derably fainter in spectra of Class Bi, 4649.2 is more intense than the helium line 4471.8; 
4089.2 is as intense as the helium line 4026.4; and 4116.2 is 2.0 as intense as line 41205, 
or 4144.0. The line 4096.9 is fainter than in spectra of Class Oe 5 B. The triplet, 4069.4, 
40720, and 4075.9, recently identified with oxygen, forms a conspicuous group near HÖ. 
The calcium line, K, is better defined than other faint lines. The calcium line, H, appears 
also to be present, although not distinetly separated from the adjacent hydrogen, He. Spectra: 
of faint stars whieh are photographed with one prism and do not show the less intense 
lines clearly, are recognized as belonging to this class by the presence of the well marked 
lines 4089.2, 4116.2, and 4649.2. 
Class Ba. 
Typical star, 8 Centauri. 
All lines are dark. The number of faint lines is greater than in spectra of Class 
Bo, but none of the Orion lines have as great intensity with respect to the hydrogen lines 
as in that class. By the diminished intensity of lines 4089.2 and 4116.2, the region of Hd 
has a slightly different aspect from the same region in spectra of Class Bo, 
The lines of helium are more intense than in spectra of Class Bo. 4471.8 now ex- 
ceeds 4649.2, and 4120.5 exceeds 4116.2, in intensity. 4120.5 and 4144.o are equally intense. 
The Helium line D,, wave length 5875.9, is present, with an intensity 0.5 as great as Hp. 
4089.2, 4116.2, and 4649.2 are muss less intense than in spectra of Class Bo. The cal- 
cium line, K, is faint. The calcium line, H, is not seen, and is perhaps concealed by the 
hydrogen line, He. 
eo: 
