Astronomy. — ''On the Parallax of some Stellar Clusters." (First 

 communication). By Mr. W. J. A. Schouten. (Communicated 

 by Prof. J. C. Kapteun). 



(Communicated in the meeting of January 26, 1918). 



Witli regard to most stellar clusters a direct measurement of the 

 parallax or a determination of their distance from the proper motions 

 of the stars is wholly excluded. We must therefore have recourse 

 to other means. Prof. Kapteyn has shown in Contrib. Mt. ^Wilson 

 Observ. N°. 82 how the parallax of stellar clusters can be ascertained 

 from the apparent magnitude, if the luminosity-curve is known and 

 is the same every whei'e in space. _ 



If we determine the mean apparent magnitude m of all those 

 individual stars of a group of stars, practically at equal distances from 

 the sun, which are brighter than m„, 'we shall have — sup- 

 posing jhe luminosity-curve to have the form: (p {M) diM = 



= — L= e -hHM-K)^ dM - 

 1/3.41 



X 



7/1 g-A^CwJ+S— A'-|-5/o7 7r)ï cl,m 



i 



^, _/,2r,„4-5-A'+5 % tt)» dm 



or, simplified : 



m = A — 5 — b log jr = 



az 



%J 00 



in which P ^= h (m^ — K -\- b -\- 5 log jt). 



If h and K are known jt can be determined at once. 



It is our intention to investigate how far this method of determi- 

 ning distances is practicable and what results are obtained with 

 some of the best-known stellar clusters. In order to facilitate its 

 practical application we have used in our investigation the method 

 in a somewhat altered form. 



In the article of Prof. Kapteyn which we quoted, a preliminary 

 value for the parallax of the Small Magellanic Cloud was determined 

 by way of example and the prospect of a more accurate determi- 

 nation of it by means of a photo, to be found in the Astronomical 



