MASSliS OF VISUAL ]'.INARY STARS. 465 



There is no contrast of colour as seen in the telescope ; indeed, 

 the hue is so similar that it is often difficult to distinguish the 

 companion from pieces of the diffraction rings which surround 

 Sirius or from ghost images of Sirius formed hy reflexions 

 within the eyepiece. It may therefore fairly be assumed that the 

 companion has a similar type of spectrum. But, mass for mass, 

 it only shines as a star of the 9th magnitude against the Sun's 

 2.03 magnitude at etjual distance — a loss of no less than seven 

 magnitudes, or, in other words, its light emission is only 1/631 

 that of the Sun. One is forced to acce]>t the difficult conclusion 

 that the light of the com])anion of Sirius is in some way affected 

 by Siritis itself. Otherwise we should exj^ect to find some other 

 stars of about the 9th magnitude with similar gravitative ])ower, 

 but there are certainb none whatever known. 



Spectral class An. of wliicii Sirius is the typical member, has the 

 hydrogen lines at their niaximnni intensitx . Metallic or solar lines are 

 present, hut are very fainl. 



fM Hkrculks. — Triple Syslciii. Chief couiponeni . iiiac/iiifiide 

 3.48. Spectrum (^5. 

 Binary com-panioii, magnitude 9.C)8 ( 10 and 11 ). 

 The parallax of yu Hercules has been determined twice: — 



Russell ( photographs ) . . . o" . 038 i o" . 036 

 Chase ( heliometer) o". 122 -!- o".028 



To shine as a 3.48 magnitttde star the Sun must be removed to 

 4.97 radials (parallax = o".20). 



The spectral class G5 has weak hydrogen and very strong- metallic 

 lines. 



Strttve noted the colotir.s as yellow and blue. Yet the 

 binary companion is 6.2 magnitvtdes fainted than its primary. 



Gkavitativh P()Wi:r of the BiiNarv Compaxion of fx Hfrcules 



AT \^\riol'S Dtstan(.i-:s. 



Parallax. Gravitative 



Radial. " Power. 



5.0 o . 20 0.15 



6.0 0.17 0.25 



7.0 o. 14 0.40 



8.0 0.12 0.60 



lO.O O. 10 I . 18 



12.5 . 08 2 . 30 



20 . o 0.05 9-40 



25.0 0.04 18.35 



The magnitude of a solar type star at these distances and 

 powers would remain constant at 6.55. Thus, the companion, 

 in spite of its bluish tint, is three magnitudes fainter than a solar 

 type star of similar gravitative power would be. 



We may ask the question : Are there similar pairs to this 

 binary companion of the 9.68 magnitude with a semiaxis of 

 I ".30 and a period of 43.2 years? None are known, but few 



B 



