

KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 60. N:0 8. 11 



Comas Sola 41 considers that lie has found considerable proper motions in 

 Messier 11 at a measuring in the stereocomparator of plates with an epochal diffe- 

 rence of only 3 years, taken with an instrument of only 16 cm's aperture and a 

 focal length of 80 cm. Barnaed 16 låter has stated that he has not been able to 

 establish any proper motions at all in this group out of his micrometrical measurings 

 with the great Yerkes refractor extended över several years. As he has, besides, 

 examined two plates with an epochal difference of 22 years in the stereocomparator 

 without finding any proper motion of the stars in the cluster, it might be conside- 

 red as established, supposing that the background and the cluster have no common 

 motion, that the total displacement of this well-examined group must be very small. 



Summing up the preceeding resumé of the observations that may give informa- 

 tion regarding the value of the proper motions of the globular dusters, it may be 

 said that these certainly are considerably below the value 0",oi per year. As the 

 mean of the total radial velocities for 10 globular dusters is 150 km, we obtain, when 



[i m <0",oi 

 and consequently : 



T m <0",01 



according to (2): 



K m < 0",00032. 



According to Charlier the mean parallax for these globular dusters is 0",oio2, 

 from which follows: 



s'<0,03. 



Shapley's parallaxes give, as a mean value for the same dusters, ~ m = 0".oooo63. 



An acceptance of Charlier's parallaxes for globular dusters would give a z m 

 component of the proper motion to 0",3, from which follows 100 [t > 30", which dis- 

 agrees with the results that have been dealt with above regarding the value of the 

 total proper motion of the globular dusters. 



Another way of determining distances for globular dusters is given by the 

 method employed by Kapteyn to find with the aid of the luminosity-law the mean 

 parallax of a group of stars that can be supposed to be all at the same distance. 

 If the stars brighter than w? have the mean magnitude w, Kapteyn 100 finds the 

 relation : 



|rae -/ ' 2(m+5 



-gr+5io g .T)^ m • 



Jf 



7?2o 



e — A2 (ot+5 — K+b log n) 2 d m 



or: 



