MASSES OF VISUAL HIXARY STARS. 459 



to that of the Sun ; but we can go much further, and show that 

 most of the double stars fall far short indeed. For this purpose 

 the data can be arranged differently. 



In comparing the gravitative power of the Sun with that 

 of a double star, we may consider the two extreme cases. In 

 the two-body motion, the total mass is Mi-|-AL,MjDeing the mass 

 of the primary. Mo of the second?fry. In the solar system M^ 

 would be the Sun, M^ the Earth ; in this case AL is so small, 

 compared to AI^ ( i 330.000), thai it becomes negligible. At the 

 other extreme M.^ may be equal to M^, as is the case with many 

 double stars. It is highly improbable that we could see the com- 

 panion in any double star system where the ratio of AL to M^ 

 is only i to 330,000. Sirius and Procyon have very faint com- 

 panions, btit their gravitative powers are not widely out of pro- 

 portion to those of their primaries ; thus, in the case of Sirius 

 we have M^ ^2.4 and Mo i.i. the unit of gravitative power 

 teing that of oin- .Sun. 



TABLE III. 



Magnituoes of Solar-Type P.mrs for DiKFi-RrxT Masses. 



m, Combined magnitude; lll■^. magnitude of cliief star; ///_,. mag- 

 nitude of companion star; .1/. mass or gra\'itati\e power of 

 system; M^, mass of chief star; M.^. mass of comjianion 

 star. 



;// Wi VI. ^ M M^ M.^ 



o . 00 o . 00 6 . 00 I . o 1 . 00 o . 000 



-o.oi 0.00 5.00 i.o 0.999 o.ooi 



-0.04 0.01 3.33 T.o 0.99 o.oi 



-o . 06 o . 02 2 . 83 1.0 o . 9(S o . 02 



-o.io 0.04 2.17 1.0 0.95 0.05 



-0.15 o . 08 1 . 67 1.0 0.9 0.1 



-0.20 0.16 1. 16 1.0 0.8 0.2 



-0.24 0.26 0.85 1.0 0.7 0.3 



-0.25 0.37 0.66 1.0 0.6 0.4 



-0.25 0.50 0.50 1.0 0.5 0.5 



m., - nil MJM.. 



0.0 1.0 



1.0 4.0 



2.0 15.8 



3-0 63.1 



4-0 251.2 



5.0 1000. o 



If. as stated earlier, the Sun was removed to a distance of 

 I radial (parallax i"). it would shine as a star of the 0.0 magni- 

 tude, and the Earth would revolve around it under a semiaxis 

 of i" in one year's time. If. however, the two bodies were equal 

 in size — which we may imagine would be got by creating two 



