58 MASSES OF VISUAL i:iNAK\- STARS. 



according to Lewis, the relative motion is convex, so that the 

 gravitative force is more than negatived by some other force. 

 The spectral class Ml) has nunierons hands. 



^ 5{: :Jc ^ ;■; :|t 



Let tis arrange the stars of Table I in their spectral classes 

 A. F, G, and B, and compare the ntimber of each class with 

 expectancy. According to Prof. E. C. Pickering ( Harvard 

 Annals, Vol. 56, p. 19. Table \'I), the proportionate number of 

 stars all over the sky are : 



B A F G KM 



2 81 25 II 34 2 



As Table I just contains 25 stars of class F, we should 

 expect to find the other types in the same pro])ortion ; actually we 

 have : 



o 12 25 14 60 



or. in percentages of expectancy, 



14 TOO 128 16 ... percent. 



There are too lew B and M type stars to afford us any 

 information, but the low percentage of A and K type stars is 

 remarkable, and it appears that G type stars are somewhat over- 

 represented amongst the rapid binaries. The argument used in 

 the previous pages renders it now very certain that, in spite of 

 their great ntmiber, the A type is poorly represented amongst 

 binaries, because stars of that class have but little gravitative 

 power, for all their brilliancy. In the case of the K type, the 

 scarcity would appear to be solel}- due to the long periods of 

 such pairs — but long periods can only be due to absolutely large 

 mean distances. Classification b\' si)ectrum strengthens this 

 suggestion. 



Table \' is arranged accordingly, and in order of period. 



The stars in this table l)el(nv the broken lin.es have ])criods of 

 over a century. 



The third column in each class gives the mean distance in 

 terms of the Earth's mean distance from the Sttn, found by 

 multiplying the mean distance in seconds of arc by the number 

 whose logarithm is the star's magnitude divided by 5. 



When these columns of the four classes are considered, it 

 will be at once remarked that no binary stars with distances under 

 o".57 appear in classes G and K — nearly all the very close pairs 

 are found in classes A and F, but nearly all in F. Thus, of 

 systems under o".7o in any given class. 



Class A has 60 per cent. 

 Class F has 64 per cent. 

 Classes G and K have 20 ])er cent. 



There is no self-evident reason why there should not be close 

 and rapid binary pairs in the two last classes. The smallest semi- 

 axis major is that of 0^1400 = o".57, and why should there not 

 be many pairs at half that distance and of about one-third of the 



