The motion of the stars 



75 



According to Campbell ') we shall put 



,9 = 20 km/sec. 



But 



1 km/sec 



0.2118 astrouoDaical units per year 

 0.2118 X 10"-'' Siriometers per year. 



è^s = 2.3116 X 10-7 ± 0.0873 X 10-7. 



Which gives 



M i- \ = y-, = 0.05467 ± 0.00206. 



Using (34) we get: 



M(r)= 29.53 ± 1.11 Siriometers. 



where in the computation of the mean error no regard is paid to the mean error 

 in the adopted value of s. 



The corresponding value of the parallax is 



which hence represents the mean value of the parallax of the stars of the photo- 

 metric magnitude 5.5 (Harvard Scale). 



From a discussion of the BßADLEY-stars (A. N. 3487 (1898)) Kapteyn has 

 found 



a value considerably larger tlian that here found. The difference is partly due to 

 smaller value of the velocity of the sun, used by Kapteyn (,f = 16,7 km/sec); partly 

 it might be explained by the circumstance that the BBAOLEY-stars are com- 

 plete to the 6*^^ magnitude only for a part of the heaven, whereas the P. C. of 

 Boss, here used, embraces all stars down to the 6'^ magnitude (HS). 



15. Graphical determination of apex and vertex. Take a tangent-plane at a 

 point of the equator having the right ascension a^. The central projection of the 

 equator on this plane cuts out a straight line, which may be taken as the axis of 

 X in this plane, the origin being at the tangent-point. Consider any point of the 



*) Lick Bulletin N:o IS.'? (1911). This value is obtained from the radial velocities of Class B 

 stars. He suggests that the velocity of the solar system, with reference to the system of stars 

 brighter than 6"" is approximately 19 km per second. 



^) Mean of his results in tab. 4 for the stars of the magnitude 5* and 6'^. In Publications 

 N:o 8, Groningen 1901, Kapteyn arrives at the same value of M{Ti). From the parallaxes of 

 CoMSTOCK in Astr. Journal N:o 558 (1904) I derive the value ilfg .(tc) = 0".0138. 



TC) = 0".01126 ± 0". 00042, 



M[tz) = 0".0160, 2) 



