( 138 ) 



magnitude 4.0; that is to say, we have imagined that every star 

 was replaced by one which in velocity and in brightness was perfectly 

 identical with the real one, but placed at such a distance that its 

 apparent magnitude was 4.0. If the ratio in which we then increase 

 the proper motion is 



p= 100-2 ('«-4) 



we have 



2 pv sin X S pt 



q4.o = ^ ■ , , and T4.0 = • 



^ sm / n 



In this computation we have used Maury's classes as a basis. We 

 have excluded 61 Cygni on account of its extraordinary great parallax, 

 while instead of the whole group of Ursa Major (/? y de S) we have taken 

 only one star (e). In the following table are combined the results 

 of the two computations. 



In both the series of results the phenomenon found by Monck and 

 Hertzsprung manifests itself clearly. I have not, however, used 

 these numbers T4.0 and ^40, but have modified them first, because it 

 was not until the computation was completed that I became ac- 

 quainted with Hertzsprung's remark that the above mentioned c stars 

 show a very special behaviour ; their proper motions and parallaxes 

 arc so much smaller than those of the a stars of the same classes 

 that they must be considered as quite a separate group of much 

 greater brilliancy and lying at a much larger distance ^). We have 



^ I In his list of parallaxes Hertzsprung puts the question whether perhaps the 

 bright southern star a Carinae (Canopus) belongs to the c stars ; but he finds no 

 indication for this except in its immeasurably small parallax and small proper 

 motion. In her study of the southern spectra Miss Gannon has paid no regard 



